Article

Effects of geographic distance, sea barriers and habitat on the genetic structure and diversity of all-hybrid water frog populations

April 2010
Heredity 106(1):25-36

DOI:10.1038/hdy.2010.37

Source
PubMed

Authors:

The history of population size and migration patterns leaves its mark in the genetics of populations. We investigate the genetic structure of the edible frog, Pelophylax esculentus in the Danish archipelago and adjacent countries. This frog is of particular interest because it is a hybrid that, in this area, forms all-hybrid populations of diploid (LR) and triploid (LLR and LRR) genomotypes with no (or very few) adults of the parental species (LL and RR). This study is the first to cover the entire geographic range of Danish, Swedish and German all-hybrid populations, documenting their extent and providing a broad picture of their diversity of neutral genetic markers and genomotype proportions. With 18 microsatellite markers, we found that genetic diversity declines northwards in agreement with the glacial refuge and central-marginal hypotheses; however, populations on small and mediumsized islands are no less diverse than those on large islands and continental peninsulas. Isolation by distance exists across the archipelago with limited influence of fragmentation by brackish seawater. The extremely low genetic diversity in all-hybrid populations, compared with adjacent populations, may be responsible for the maintenance of their special breeding system. We also show large variation among ponds in proportions of LLR, LR and LRR genomotypes, but little geographic pattern in their distribution. Instead, we found relationships between the genomotype proportions and some of 15 habitat parameters monitored. Body size differences among LLR, LR and LRR further suggest ecological differences.

Genetic and phenotypic traits in populations comprising diploid and polyploid hybrid water frogs (Anura, Pelophylax esculentus)

Article

Jan 2014

Alexandra Wild

Zusammenfassung Der Teichfrosch (Pelophylax esculentus, Genotypen LR, LLR oder LRR) ist ein natürlicher Hybrid zwischen dem Kleinen Wasserfrosch (P. lessonae, Genotyp LL) und dem Seefrosch (P. ridibundus, Genotyp RR). In der rein diploiden Form (LR) pflanzt sich der Hybrid via Hybridogenese fort, bei welcher ein Teil des elterlichen Genoms (entweder der L- oder der R-spezifische Teil) während der Gametogenese eliminiert und der verbleibende Teil klonal auf haploide Keimzellen übertragen wird. Rekombination zwischen dem L- und R-spezifischen Teil des Genoms ist in der Regel nicht möglich, weshalb es durch die wiederholte klonale Weitergabe innerhalb des Genoms zu einer Ansammlung schädlicher Mutationen kommt. Bei der Verpaarung zweiter Hybriden aus derselben Population sind deren Nachkommen durch die Kombination zweier klonaler Genome daher nicht überlebensfähig. Um lebensfähige Nachkommen zu zeugen, müssen sich die Hybriden mit der jeweiligen Elternart rückkreuzen, deren Teil des Hybridgenoms während der Gametogenese verloren ging. Aus dieser fortplanzungsbedingten Abhängigkeit heraus entwickelten sich verschiedene Formen eines gemischten Populationssystems aus Hybriden und Elternarten. In einigen Populationen produziert P. esculentus sowohl haploide (L oder R) als auch diploide Keimzellen (LR-Gameten, welche normalerweise nur von Individuen des Genotyps LR gebildet werden). Aus der Verschmelzung von diploiden und haploiden Keimzellen entstehen triploide Hybriden der Genotypen LLR und LRR, welche ihrerseits bei der Gametogenese jenen Genomteil ausschliessen, der nur in einzelner Ausführung vorliegt, und aus dem doppelt vorhandenen Genomteil haploide Gameten bilden (so produziert der Genotyp LLR haploide L-Gameten und der Genotyp LRR haploide R-Gameten). Dadurch entstehen über die Generationen hinweg abwechselnd diploide und triploide Hybride, welche sich unabhängig von der Anwesenheit der Elternarten erfolgreich miteinander fortpflanzen. Die reproduktive Unabhängigkeit dieser sogenannten gemischt-ploiden Systeme wird dadurch ermöglicht, dass die in den triploiden Fröschen doppelt vorhandenen Genomteile rekombiniert werden können, wodurch verhindert wird, dass sich in den Genomen zu viele schädliche Mutationen ansammeln. Sowohl die gemischten Systeme aus Hybriden und Elternarten als auch gemischt-ploide Systeme wurden in den letzten Jahrzehnten unter verschiedenen Aspekten und in unterschiedlichen geographischen Regionen untersucht. Jedoch fehlte bislang aufgrund der ungleichmässigen Verbreitung gemischt-ploider Populationssysteme in Europa ein umfassender und vergleichender populationsgenetischer Überblick im grösseren geographischen Masstab. Ferner sind die populationsgenetischen und phänotypischen Unterschiede zwischen Hybriden aus Elternarten-Populationen und gemischt-ploiden Populationen bisher noch weitgehend unbekannt, obwohl zwischen den unterschiedlichen Systemen, als auch zwischen geographischen Regionen, potentiell unterschiedliche Selektionsbedingungen herrschen. Die Zielsetzungen meiner Arbeit waren daher: a) gemischt-ploide Populationen aus unterschiedlichen Gegenden Europas genealogisch zu untersuchen und herauszufinden, ob deren ungleichmässige Verteilung auf eine unabhängige Entstehungsgeschichte zurückzuführen ist, b) zwei augenscheinlich unterschiedliche gemischt-ploide Fortpflanzungssysteme auf Unterschiede in der Keimzellenproduktion zu untersuchen, c) die bioakustischen Eigenschaften männlicher Paarungsrufe einer Anzahl gemischt-ploider Populationen unterschiedlicher geographischer Herkunft zu analysieren und mit den Eigenschaften der Paarungsrufe aus gemischten Hybrid-Elternarten-Populationen zu vergleichen, und d) die räumlichen Bewegungsmuster und das Distanzverhalten zwischen Männchen verschiedener Genotypen aus gemischt-ploiden und gemischten Hybrid- Elternart-Populationen zu untersuchen und potentielle Unterschiede auf Zusammenhänge mit phänotypischen Eigenschaften der Männchen sowie mit Eigenschaften der untersuchten Teiche zu testen. In Kapitel eins untersuchte ich durch Analysen von Mikrosatelliten-DNA und mitochondrialer DNA populationsgenetische Parameter für mehr als 2000 Gewebeproben, welche aus 72 Lokalitäten in Nord-, Mittel- und Osteuropa stammten. Die Ergebnisse dieser Studie zeigten, dass die auf der Mikrosatelliten- Analyse basierende genetische Diversität von der geographischen Lage, dem Vorhandensein der Elternarten P. lessonae und P. ridibundus sowie dem Populationstyp beeinflusst wird. Während sich die meisten gemischt-ploiden Populationen aus Mitteleuropa und dem östlichen Mitteleuropa genetisch nicht sehr unterscheiden, zeigen einige Populationen aus der Ukraine ein deutlich anderes genetisches Profil. Dieses Ergebnis wird durch den Fund ungewöhnlicher mitochondrialer DNA-Typen in Individuen jener Populationen bestätigt und legt die von den gemischt-ploiden Populationen Nord- und Mitteleuropas unabhängige Entstehung jener östlichen Populationen nahe. In der Diskussion interpretiere ich diese Ergebnisse mit Bezug auf nach- und zwischeneiszeitliche Kolonisationsszenarien in Europa. Kapitel zwei präsentiert eine Studie, welche in Zusammenarbeit mit Nicolas Pruvost durchgeführt wurde und in welcher wir Kreuzungsexperimente und Analysen von Mikrosatelliten-DNA benutzten, um fünf Populationen von unterschiedlicher Populationsstruktur zu vergleichen. Dafür untersuchten wir mit Hilfe von Indizes für Heterozygotie und genetische Differenzierung die Interaktionen zwischen verschiedenen Genotypen (LL, LLR, LR, LRR and RR). Die Ergebnisse dieser Studie erlaubten uns verschiedene Fortpflanzungssysteme zu definieren und zu unterscheiden, sowie ein evolutionäres Szenario für das Auftreten und die Aufrechterhaltung eines alternativen Systems gemischt-ploider Populationen in Mitteleuropa vorzuschlagen. In Kapitel drei befasste ich mich mit den bioakustischen Eigenschaften männlicher Paarungsrufe innerhalb und zwischen gemischt-ploider sowie gemischten Populationen aus Hybriden und den Elternarten P. lessonae und P. ridibundus. Aus der Analyse von Feldaufnahmen der Rufe leitete ich fünf Rufparameter ab, welche alle einen Dosiseffekt des jeweiligen Genoms L oder R zeigten, d.h. sie nahmen mit steigendem L:R-Verhältnis der Genotypen in der Reihenfolge LL-LLR-LR-LRR-RR entweder zu oder ab. Zwei der fünf Rufparameter unterschieden sich zudem zwischen Populationssystemen. Die Effektgrössen nahmen in der Reihenfolge Genotyp-Populationssystem –geographische Lage der Population ab. Die Rufe diploider Hybriden (LR) variierten zwischen den Populationssystemen in Abhängigkeit davon, ob die Hybriden zur erfolgreichen Fortpflanzung eine der beiden Elternarten benötigen, oder nicht. In Kapitel vier überprüfte ich innerhalb dreier Teiche (zwei mit gemischt- ploiden Populationen, einer mit einer Population aus LR-Hybriden und P. lessonae), ob sich das räumliche Mobilitätsmuster und Distanzverhalten der Männchen während der Paarungszeit zwischen Genotypen unterscheidet. Darüber hinaus testete ich die räumlichen Parameter auf Zusammenhänge mit der Körpergrösse und Kondition der Männchen, sowie mit der beobachteten Häufigkeit, in der die einzelnen Männchen im Amplexus mit Weibchen beobachtet wurden. Die Ergebnisse zeigten, dass weder Genotyp noch Kondition das räumliche Bewegungsmuster beeinflussen und deuteten darauf hin, dass vorhandene Unterschiede zwischen den Teichen wahrscheinlich auf Unterschiede in der Populationsdichte zurückzuführen sind. Die Verteilung der Genotypen der Männchen im Amplexus entsprach für gemischt-ploide Populationen der tatsächlichen Verteilung der Genotypen der Männchen im Teich. Bei den Amplexus-Männchen der gemischten Hybrid-P. lessonae-Population waren P. lessonae-Männchen leicht überproportional vertreten. In Kapitel fünf präsentiere ich eine kollaborative Studie mit Anke Stöhr über Ranavirus-Infektionen in wilden Wasserfrosch-Populationen. Die Studie kombiniert die Fallstudie eines Ranavirus-Ausbruchs unter in Gehegen gehaltenen Wasserfröschen mit der Beschreibung eines neuen Ranavirus und dessen phylogenetischer Klassifizierung. Die Kapitel eins bis vier meiner Dissertation ermöglichen ein tieferes Verständnis der Diversität, Verbreitung sowie der genetischen und phänotypischen Differenzierung von P. esculentus-Populationen. Als Schlussfolgerung daraus argumentiere ich, dass es keinen „Allerwelts“-Hybriden gibt, sondern dass Teichfrosch-Populationen in Europa so divers sind, dass sie als signifikante Evolutionseinheiten denselben Respekt und dieselbe Aufmerksamkeit verdienen wie „reine“ Arten. Summary The edible frog (Pelophylax esculentus, genotypes LR, LLR or LRR) is a natural hybrid between the pool frog (P. lessonae, genotype LL) and the marsh frog (P. ridibundus, genotype RR). Diploid hybrids (LR) reproduce by hybridogenesis, where one part of the hybrid’s parental genome (either the L or the R chromosome set) is excluded during gametogenesis and the other part is clonally transmitted into haploid gametes. Recombination between the L and R genome within the hybrid is usually not possible. Therefore, repeated clonal transmission of one part of the genome leads to the accumulation of deleterious mutations which normally renders offspring from inter-hybrid crossings within the same population unviable. In order to produce viable offspring, the hybrid is thus forced to mate with the parental species whose part of the genome was excluded. This reproductive dependence has led to several forms of mixed hybrid-parental population systems. In some populations, P. esculentus can produce both haploid (L or R) and diploid gametes, LR gametes usually coming only from LR individuals. The fusion of diploid with haploid gametes results in triploid hybrids of the genotypes LLR and LRR, which exclude the single copy genome and produce only haploid gametes of the other genome (LLR produce L, LRR produce R gametes). Thus, in a perpetuating way, diploid and triploid hybrids are generated and can successfully reproduce with each other, independent of the presence of the parental species. The reproductive independence of these so-called mixed-ploidy systems is due to the fact that triploids recombine the part of their genome which is present in a double copy and thus prevent the accumulation of deleterious alleles in the genetic pool of the population. Both the mixed hybrid-parental and the mixed-ploidy systems have been studied over the last decades in several aspects and geographic regions, but due to the patchy geographic distribution of mixed-ploidy systems in Europe, a comprehensive and comparative population genetic overview across a larger area has been lacking. Furthermore, population genetic and phenotypic differences between hybrid P. esculentus from mixed-parental and mixed-ploidy systems are vastly unknown, despite potentially different selection regimes between population types and geographic regions. The objectives of my thesis were thus: a) to compare mixed-ploidy populations from different European areas in a genealogical approach and to find out whether these patchily distributed populations are of independent origin, b) to examine the gamete production patterns between two supposedly different mixed-ploidy breeding systems, c) to study bioacoustic characteristics of male advertisement calls across a number of geographically distant mixed-ploidy populations and compare them with hybrids from mixed hybrid-parental systems, and d) to examine the spatial movement and spacing behavior of male frogs within and between mixed-ploidy and mixed hybrid-parental systems and relate potential differences to male genotype, male morphology and pond characteristics. In chapter one, I used microsatellite DNA and mitochondrial DNA analysis to obtain population genetic parameters for more than 2000 samples from 72 localities across Northern, Central and Eastern Europe. The results from this study showed that genetic diversity among populations based on microsatellites is structured by geographic latitude and longitude, the presence of parental genotypes (P. lessonae and P. ridibundus) and population type. Most mixed-ploidy populations from Central and East-Central Europe did not genetically differ substantially, but some populations from Ukraine showed a distinctively different genetic profile. This was confirmed by the novel finding of unusual types of mitochondrial DNA in specimens from there. My findings suggest an independent origin of polyploid water frogs from this area, which I discuss with reference to postglacial re-colonization scenarios in Europe. Chapter two presents a collaborative study with Nicolas Pruvost, where we used microsatellite DNA analyses and crossing experiments to compare five populations of different population structures. Indices of heterozygosity and genetic differentiation were used to depict the genetic interactions between the different genotypes (LL, LLR, LR, LRR and RR). The results from this study allowed us to define and differentiate between different breeding systems and propose an evolutionary scenario for the occurrence and maintenance of an alternative mixed- ploidy population type in Central Europe. In chapter three I studied the bioacoustic properties of male advertisement calls within and between mixed-ploidy and mixed hybrid-parental populations. From field recordings I derived five call parameters which all showed a genomic dosage effect, i.e. they either decreased or increased with the L/R ratio among genotypes in the order LL-LLR-LR-LRR-RR. Two of the five call parameters were also affected by the population system. Effect sizes decreased from genotype through population system to geographic location of the population. Calls of diploid (LR) hybrids varied between population systems, depending on whether they belonged to a system that required a sexual host for successful reproduction, or not. In chapter four I tested within three ponds whether male spatial movement and spacing behavior during the breeding season differs between genotypes. Furthermore, I related spatial parameters to male body size and condition, and to the observed frequency of amplexus by individual males. As a result, I found that neither genotype nor size nor condition affected spatial movement patterns and that differences are most likely to be explained by population density. The frequency of amplexus events among genotypes corresponded to the observed male genotype distribution in the two mixed-ploidy ponds, and slightly favored P. lessonae males in the mixed hybrid-parental population in the other pond. Chapter five represents a collaborative study with Anke Stöhr on ranavirus infection in wild populations of European water frogs. The study combines a case study of a ranavirus outbreak among captive water frogs with the description of a novel ranavirus and its phylogenetic classification. In conclusion, chapters one to four of my thesis allow a better understanding of the diversity, distribution and differentiation of P. esculentus populations in terms of genetic and phenotypic characteristics. I argue that there is no such thing as a “common” water frog hybrid, but rather that hybrid populations are so diverse that they represent evolutionary significant units which deserve the same respect and attention as other “true” anuran species.

Composition and age structure of the Pelophylax esculentus complex (Anura; Ranidae) population in inland Croatia

Article

Full-text available

Feb 2018

Pelophylax esculentus is a vertebrate animal with hemiclonal heredity, attracting the interest of many reproductive and evolutionary biologists. It is a hybrid between P. ridibundus and P. lessonae. These three taxa form the so-called Pelophylax esculentus complex with a population structure usually comprising a hybrid taxa and one parental species. Data on population types at the southernmost distribution area of their sympatry are rare. Here we sampled five sites in inland Croatia in order to analyse the population structure, sex ratio and age structure. The individual genotypes of 93 randomly collected water frogs were verified with allozyme markers for three species-specific polymorphic loci. In order to estimate population age structure, the annual growth rate (skeletochronology) and growth index profiles were also investigated. The growth index profiles were analysed by an estimation of number of lines of arrested growth visible in the cross-section of femur bones. Our results revealed the presence of the R-E-L population with a dominance of P. esculentus. Pelophylax ridibundus was the least abundant taxon but with a relatively high age estimate of eight years on average. Its annual growth rate did not differ from the remaining two species. Gene introgression of mostly ridibundus alleles was also observed in hybrids. Most profiles of gonads in hybrids showed presence of both parental genomes with dominance of ridibundus alleles. The study area represents one of the southernmost distributions of the hybrid taxon in Europe, making it attractive to study gene flow and impact of P. esculentus on P. ridibundus, a typical water frog representative of the Balkan Peninsula. © 2018 Deutsche Gesellschaft für Herpetologie und Terrarienkunde e.V. (DGHT), Mannheim, Germany.

Volume 2, Issue 2, December 2024 Population Genetics of the Meat Ant (Iridomyrmex purpureus) (A Literature Review)

Article

Full-text available

Jan 2025

Mahboba Aldareh

A reassessment of the biogeographic range of northern clade pool frogs (Pelophylax lessonae) Herpetological Journal

Article

Full-text available

Apr 2018
HERPETOL J

Volume 28 (April 2018), 63-72 Published by the British Herpetological Society Distinguishing between native and introduced species can be difficult, particularly at range borders where patchily distributed populations may occur away from a species' natural core range. The case of native pool frog (Pelophylax lessonae) populations at their northern range limit in Europe is particularly interesting. These are morphologically and genetically distinct populations that are patchily distributed and have been reported from the UK, Sweden and Norway, but up until 2013 were thought to be absent from Finland. When pool frog populations were discovered in southwestern Finland they were morphologically classified as belonging to this northern clade. However, the origin of these populations has been unclear and it is possible that the Finnish populations originated through human aided introductions, established themselves recently through natural migration, or are indeed previously undiscovered relic populations. To establish the origin and relationship of these frogs to other populations across Europe we used phylogeographical analysis based on microsatellite and mitochondrial DNA markers. Our results indicate that the Finnish, Norwegian, Swedish, UK, as well as Estonian populations belong to the northern clade. The Finnish frogs are most closely related to Swedish northern pool frogs, but are genetically more diverse. This suggests that the Finnish pool frogs are most likely a relic from postglacial migration, though we could not entirely rule out the possibility of a recent natural or human aided colonisation from Sweden. This has implications for the conservation status of the pool frog in Finland, where it thus far has been considered an invasive alien species.

A simplified molecular method for distinguishing among species and ploidy levels in European water frogs (Pelophylax)

Article

Jan 2012
MOL ECOL RESOUR

Genomic effects on advertisement call structure in diploid and triploid hybrid waterfrogs (Anura, Pelophylax esculentus)

Article

Full-text available

Dec 2013
BMC Ecol

In anurans, differences in male mating calls have intensively been studied with respect to taxonomic classification, phylogeographic comparisons among different populations and sexual selection. Although overall successful, there is often much unexplained variation in these studies. Potential causes for such variation include differences among genotypes and breeding systems, as well as differences between populations. We investigated how these three factors affect call properties in male water frogs of Pelophylax lessonae (genotype LL), P. ridibundus (RR) and their interspecific hybrid P. esculentus which comes in diploid (LR) and triploid types (LLR, LRR). We investigated five call parameters that all showed a genomic dosage effect, i.e. they either decreased or increased with the L/R ratio in the order LL-LLR-LR-LRR-RR. Not all parameters differentiated equally well between the five genotypes, but combined they provided a good separation. Two of the five call parameters were also affected by the breeding system. Calls of diploid LR males varied, depending on whether these males mated with one or both of the parental species (diploid systems) or triploid hybrids (mixed ploidy systems). With the exception of the northernmost mixed-ploidy population, call differences were not related to the geographic location of the population and they were not correlated with genetic distances in the R and L genomes. We found an influence of all three tested factors on call parameters, with the effect size decreasing from genotype through breeding system to geographic location of the population. Overall, results were in line with predictions from a dosage effect in L/R ratios, but in three call parameters all three hybrid types were more similar to one or the other parental species. Also calls of diploid hybrids varied between breeding systems in agreement with the sexual host required for successful reproduction. The lack of hybrid call differences in a mixed-ploidy population at the northern edge of the water frog distribution is likely to be associated with genetic particularities, including a) low genetic variability and/or b) a local loss of genes coding for genotype-dependent call differentiation under conditions where female discrimination between diploid and triploid males is not beneficial.

A simplified molecular method for distinguishing among species and ploidy levels in European water frogs (Pelophylax)

Data

Dec 2012

Susanne Hauswaldt

Population Genetics and Stable Isotope Analysis of the Meat Ant (Iridomyrmex purpureus)

Thesis

Full-text available

Jan 2022

Ants‘ ability to use a great diversity of food sources contributes to their evolutionary and ecological success. However, this broad dietary niche along with their sociality makes this group of species notoriously difficult to examine with regard to nutritional ecology. To overcome this difficulty, stable isotopes have been used to assess the trophic position of ants in the food web. Stable isotope technology has greatly contributed to our understanding of the food web ecology of social insects, and can determine the dietary history of organisms. Furthermore, this method has been utilised successfully to study nutrient fluxes enriched with carbon and nitrogen isotopes. The aim of this study is to show if there is a relationship between δ13C and δ15N of meat ant nests and comparing the ration with soil adjacent to the ant nests. This study was carried out on 62 nests of meat ants (Iridomyrmex purpureus) and 62 samples of soil located adjacent to the nests in Armidale in New South Wales, Australia. The first ants nest was sampled at UNE, Armidale, and the following 61 nests were sampled in a northerly direction away from UNE on a wide road verge/ travelling stock route. There were no significant differences between the C and N stable isotopes collected from soil and ants nests and distance that nests were located away from one another ; and there were no significant differences between δ13C and δ15N and the size of the ants nest (based on the N-S nest length). Finally, the δ15N levels of meat ants were not correlated with their surrounding soil. Future study of measuring δ13C and δ15N levels to investigate particular interactions among ants and surrounding soil as well as with other resources that ants may feed on will be necessary to observe ants in a wide range of environments and that it will increase our understanding of ants‘ food webs.

Hybrid Form Pelophylax esculentus-ridibundus (Amphibia, Ranidae) from the Tisa River Drainage: Its Origin and Evolutionary Potential

Article

Full-text available

Nov 2021

Svyatoslav Morozov-Leonov

Chloroplast population genetics reveals low levels of genetic variation and conformation to the central–marginal hypothesis in Taxus wallichiana var. mairei, an endangered conifer endemic to China

Article

Full-text available

Sep 2019

The central–marginal hypothesis predicts that geographically peripheral populations should exhibit reduced genetic diversity and increased genetic differentiation than central populations due to smaller effective population size and stronger geographical isolation. We evaluated these predictions in the endangered conifer Taxus wallichiana var. mairei. Eight plastid simple sequence repeats (cpSSRs) were used to investigate plastid genetic variation in 22 populations of Taxus wallichiana var. mairei, encompassing nearly its entire distribution range. Low levels of plastid genetic variation and differentiation were detected in the populations, and the findings were attributed to low mutation rates, small population sizes, habitat fragmentation and isolation, and effective pollen or seed dispersal. Hunan and Hubei were identified as major refugia based on the number of private haplotypes and species distribution modeling. Trends in plastid genetic diversity and genetic differentiation from central to peripheral populations supported the predictions of the central–marginal hypothesis. In scenarios wherein the future climate becomes warmer, we predict that some peripheral populations will disappear and southern and southeastern regions will become significantly less habitable. Factors that include the levels of precipitation during the driest month, annual precipitation level, and annual temperature range will be decisive in shaping the future distribution of these populations. This study provides a theoretical basis for the conservation of T. wallichiana var. mairei. We detected low levels of chloroplast genetic variation and differentiation in the populations of Taxus wallichiana var. mairei. We identified Hunan and Hubei as major refugia. Our results supported the predictions of the central–marginal hypothesis. We clarified factors that will be decisive in shaping the future distribution of the populations.

Coloration Characteristic and Population Genetic Analysis of Wild-Captured Giant Tiger Shrimp (Penaeus monodon) from Aceh Timur

Article

Full-text available

Sep 2018

Giant tiger shrimp (Penaeus monodon) has become a prime commodity in Indonesia which was produced by aquaculture and capture fisheries activities. Aceh Province, in this case mostly represented by Aceh Timur District, was well-known as the center of wild-captured-adult giant tiger shrimp. Several previous investigations had proved for its high-quality shrimp spawner in producing good eggs in quality and quantity under artificial spawning condition. Two main interesting points of wild giant tiger shrimp from Aceh Timur came from their coloration and population clusters. This report was aimed to provide that information pre-preliminary and highlighted quantitative information of coloration characteristic through RGB (Red Green Blue) and CIE Lab color space data analysis, as well as, 16S rDNA-PCR-RFLP genetic comparison among four population clusters in Aceh Timur Waters. The color analysis resulted in significant differences between wild-captured and pond-cultured giant tiger shrimp which produced R value 0.1524±0.0091 and 0.1268±0.0004, respectively. Total pixel analysis through L* a* b* color space has distinguished detailed differentiation between wild-captured and pond-cultured giant tiger shrimp acquired images. It is known that most of the wild-captured image pixels were concentrated in quadrant I (+a, +b) while pond-cultured in quadrant II (-a, +b) and III (-a, -b).Genotyping of represented samples from 4 population clusters, i.e. Aceh Tamiang, Langsa, Peudawa, and Julok produce 2 haplotype composite, AAA and AAB. Among 4 clusters, it was found that Julok has become the only cluster which has a different haplotype composite ratio (1:1) (D 0.0348, V 0,9501) from the others (4:1)(V 0.9504).

Population structure of caribou in an ice‐bound archipelago

Article

Full-text available

Mar 2018

Aim Archipelagos provide ideal natural systems for testing the effects of isolation and fragmentation of habitats on the genetic makeup of populations—an important consideration, given that many insular species are of conservation concern. Two theories predominate: Island Biogeography Theory (IBT) posits that proximity to the mainland drives the potential for migrants and gene flow. The Central Marginal Hypothesis (CMH) predicts that island populations at the periphery of a species range may experience low gene flow, small population size and high rates of genetic drift. We investigated population genetic structure, genetic diversity and key drivers of diversity for Arctic island‐dwelling caribou (Rangifer tarandus). Our aim was to inform intraspecific units for conservation and decipher how IBT and CMH could act in an archipelago where isolation is highly variable due to sea ice and open water. Location Canadian Arctic Archipelago, Canada (Latitude, 55–82°N; Longitude, 61–123°W). Methods We genotyped 447 caribou at 16 microsatellite loci; these caribou represented two subspecies (R. t. groenlandicus, R. t. pearyi) and three designatable units. We used hierarchical Bayesian clustering and ordination to determine genetic groups. We evaluated the influence of ecological and geographic variables on genetic diversity using linear mixed‐effects models and compared diversity among mainland and island herds. Results Bayesian clustering revealed nine genetic clusters with differentiation among and within caribou subspecies. Genetic differentiation was explained predominantly by isolation‐by‐distance across all caribou, even at the scale of subspecies. Island caribou were less genetically diverse than mainland herds; individual heterozygosity was negatively correlated with distance‐to‐mainland and the extent of autumn ice‐free coastline and positively correlated with unglaciated island size. Main conclusions Our findings underscore the importance of hierarchical analysis when investigating genetic population structure. Genetic diversity and its key drivers lend support to both IBT and CMH and highlight the pending threat of climate change for Arctic island caribou.

Hemiclone diversity in the hybrid form Pelophylax esculentus-ridibundus (Amphibia, Ranidae) from the Tisa river drainage

Article

Full-text available

Nov 2017

Svyatoslav Morozov-Leonov

The hemiclonal structure of a hybrid form of Pelophylax esculentus-ridibundus (Amphibia, Ranidae) from the Tisa river drainage has been analyzed. The interpopulation differences of the inherited genome variation level have been demonstrated. The peculiarities of the waterfrogs reproduction system are discussed.

Human-modified habitats change patterns of population genetic structure and group relatedness in Peter's tent-roosting bats

Article

Full-text available

Aug 2016

Although coloniality is widespread among mammals, it is still not clear what factors influence composition of social groups. As animals need to adapt to multiple habitat and environmental conditions throughout their range, variation in group composition should be influenced by adaptive adjustment to different ecological factors. Relevant to anthropogenic disturbance, increased habitat modification by humans can alter species' presence, density, and population structure. Therefore, it is important to understand the consequences of changes to landscape composition, in particular how habitat modification affects social structure of group-forming organisms. Here, we combine information on roosting associations with genetic structure of Peter's tent-roosting bats, Uroderma bilobatum to address how different habitat characteristics at different scales affect structure of social groups. By dividing analyses by age and sex, we determined that genetic structure was greater for adult females than adult males or offspring. Habitat variables explained 80% of the variation in group related-ness (mainly influenced by female relatedness) with roost characteristics contributing the most explained variation. This suggests that females using roosts of specific characteristics exhibit higher relatedness and seem to be philopatric. These females mate with more males than do more labile female groups. Results describe ecological and microevolutionary processes, which affect relatedness and social structure; findings are highly relevant to species distributions in both natural and human-modified environments.

Parental and hybrid Daphnia from the D. longispina complex: Long-term dynamics in genetic structure and significance of overwintering modes

Article

Jan 2016
J EVOLUTION BIOL

In recent decades hybridization has become a focus of attention because of its role in evolutionary processes. However, little is known about changes in genetic structure within and between parental species and hybrids over time. Here, we studied processes of genetic change in parental species and hybrids from the Daphnia longispina complex (Crustacea, Cladocera) over a period of six years across ten habitats. These cyclical parthenogens respond to fluctuating environments by switching from asexual to sexual reproduction. Importantly, sexually produced diapausing eggs, which resist extreme conditions such as low temperatures and serve as dispersal stages, are produced to a lower extent by hybrids. Long-term microsatellite data revealed clear differences between hybrids and parental species. In hybrids, clonal diversity values were lower while heterozygosity and linkage disequilibrium values were higher compared to parental species. Clonal diversity of hybrids responded to the strength of the winter, with cold winters resulting in few genotypes in the following spring. In time windows when only asexual hybrid females survive, priority effects will favour the establishment of the hybrid offspring before hatchlings from parental diapause eggs can enter the community. The constant high levels of heterozygosity maintained by clonal reproduction in hybrids might lead to their successful establishment over time, when they are able to escape competition from both parental species. Although we found evidence that hybrids diversity depends on fluctuating environments, a direct link between hybrid abundance and the strength of winter was missing. Because of reduced adaptability in clonally reproducing hybrids, multiple factors must contribute to promoting their long-term success in fluctuating environments. This article is protected by copyright. All rights reserved.

Hoffmann ea 2015 Genetic diversity and distribution patterns

Data

Full-text available

Nov 2015

Polyploidization is a rare yet sometimes successful way for animals to rapidly create geno- and phenotypes that may colonize new habitats and quickly adapt to environmental changes. In this study, we use water frogs of the Pelophylax esculentus complex, comprising two species (Pelophylax lessonae, genotype LL; Pelophylax ridibundus, RR) and various diploid (LR) and triploid (LLR, LRR) hybrid forms, summarized as P. esculentus, as a model for studying recent hybridization and polyploidization in the context of speciation. Specifically, we compared the geographic distribution and genetic diversity of diploid and triploid hybrids across Europe to understand their origin, maintenance and potential role in hybrid speciation. We found that different hybrid and parental genotypes are not evenly distributed across Europe. Rather, their genetic diversity is structured by latitude and longitude and the presence/absence of parental species but not of triploids. Highest genetic diversity was observed in central and eastern Europe, the lowest in the northwestern parts of Europe. This gradient can be explained by the decrease in genetic diversity during postglacial expansion from southeastern glacial refuge areas. Genealogical relationships calculated on the basis of microsatellite data clearly indicate that hybrids are of multiple origin and include a huge variety of parental genomes. Water frogs in mixed-ploidy populations without any parental species (i.e. all-hybrid populations) can be viewed as evolutionary units that may be on their way towards hybrid speciation. Maintenance of such all-hybrid populations requires a continuous exchange of genomes between diploids and triploids, but scenarios for alternative evolutionary trajectories are discussed.

Extensive mitochondrial heteroplasmy in hybrid water frog ( Pelophylax spp.) populations from Southeast Europe

Article

Full-text available

Sep 2015

Water frogs of the genus Pelophylax (previous Rana) species have been much studied in Europe for their outstanding reproductive mechanism in which sympatric hybridization between genetically distinct parental species produces diverse genetic forms of viable hybrid animals. The most common hybrid is P. esculentus that carries the genomes of both parental species, P. ridibundus and P. lessonae, but usually transfers the whole genome of only one parent to its offsprings (hybridogenesis). The evolutionary cost of transfer of the intact genome and hence the hemiclonal reproduction is the depletion of heterozygosity in the hybrid populations. Pelophylax esculentus presents an excellent example of the long-term sustained hybridization and hemiclonal reproduction in which the effects of the low genetic diversity are balanced through the novel mutations and periodic recombinations. In this study, we analyzed the mitochondrial (mt) and microsatellites DNA variations in hybrid Pelophylax populations from southern parts of the Pannonian Basin and a north–south transect of the Balkan Peninsula, which are home for a variety of Pelophylax genetic lineages. The mtDNA haplotypes found in this study corresponded to P. ridibundus and P. epeiroticus of the Balkan – Anatolian lineage (ridibundus–bedriagae) and to P. lessonae and a divergent lessonae haplotype of the lessonae lineage. The mtDNA genomes showed considerable intraspecific variation and geographic differentiation. The Balkan wide distributed P. ridibundus was found in all studied populations and its nuclear genome, along with either the lessonae or the endemic epeiroticus genome, in all hybrids. An unexpected finding was that the hybrid populations were invariably heteroplasmic, that is, they contained the mtDNA of both parental species. We discussed the possibility that such extensive heteroplasmy is a result of hybridization and it comes from regular leakage of the paternal mtDNA from a sperm of one species that fertilizes eggs of another. In this case, the mechanisms that protect the egg from heterospecific fertilization and further from the presence of sperm mtDNA could become compromised due to their differences and divergence at both, mitochondrial and nuclear DNA. The heteroplasmy once retained in the fertilized egg could be transmitted by hybrid backcrossing to the progeny and maintained in a population over generations. The role of interspecies and heteroplasmic hybrid animals due to their genomic diversity and better fitness compare to the parental species might be of the special importance in adaptations to miscellaneous and isolated environments at the Balkan Peninsula.

Genetic diversity and distribution patterns of diploid and polyploid hybrid water frog populations (Pelophylax esculentus complex) across Europe

Article

Sep 2015
MOL ECOL

The Role of Deleterious Mutations in the Stability of Hybridogenetic Water Frog Complexes.

Article

Full-text available

May 2014
BMC EVOL BIOL

Background Some species of water frogs originated from hybridization between different species. Such hybrid populations have a particular reproduction system called hybridogenesis. In this paper we consider the two species Pelophylax ridibundus and Pelophylax lessonae, and their hybrids Pelophylax esculentus. P. lessonae and P. esculentus form stable complexes (L-E complexes) in which P. esculentus are hemiclonal. In L-E complexes all the transmitted genomes by P. esculentus carry deleterious mutations which are lethal in homozygosity. Results We analyze, by means of an individual based computational model, L-E complexes. The results of simulations based on the model show that, by eliminating deleterious mutations, L-E complexes collapse. In addition, simulations show that particular female preferences can contribute to the diffusion of deleterious mutations among all P. esculentus frogs. Finally, simulations show how L-E complexes react to the introduction of translocated P. ridibundus. Conclusions The conclusions are the following: (i) deleterious mutations (combined with sexual preferences) strongly contribute to the stability of L-E complexes; (ii) female sexual choice can contribute to the diffusion of deleterious mutations; and (iii) the introduction of P. ridibundus can destabilize L-E complexes.

Genotype-temperature interactions on larval performance shape population structure in hybridogenetic water frogs (Pelophylax esculentus complex)

Article

Apr 2013
FUNCT ECOL

The evolutionary potential and ecological importance of interspecific hybrids continues to be a controversial issue. Traditionally, hybridization – often associated with polyploidy and clonal reproduction – was considered an important mechanism for speciation in plants, but not in animals. More recently, investigations have shifted to the question: Under which genetic and ecological conditions do hybrid taxa and different ploidies arise and succeed, and when and where do they fail? Finding answers to this question is aggravated by the fact that suitable taxa for such studies are often far apart on the phylogenetic tree. Hence, results are influenced by many confounding variables. In this study, we reduce this problem by investigating the fitness within a complex of three closely related water frog taxa consisting of the two sexually reproducing parental species P elophylax lessonae (genotype LL ) and P . ridibundus ( RR ) plus their interspecific hybrid P . esculentus which comes in three ploidy types ( LR , LLR and LRR ), as well as with sexual and hemiclonal reproduction. Offspring of all five genotypes were produced by artificially crossing adults sampled from populations in Slovakia, Germany and Switzerland. This created genetic variation. They were then raised at two temperature levels: 18 and 24 °C. This created ecological variation. Larval performance under the two temperature regimes was analysed with respect to three fitness‐related parameters: survival rate, days to metamorphosis and weight at tail resorption. Survival rate was significantly higher for offspring of the three hybrid types ( LR , LLR and LRR ) compared with those of the parental species ( LL , RR ), at both rearing temperatures. For days to metamorphosis and weight at metamorphosis, we found an interaction between offspring type and temperature. In both cases, performance of hybrid and parental offspring did not differ at 24 °C, but at 18 °C hybrids metamorphosed faster and at a lower weight than parentals. We discuss these results in relation to those from other studies and conclude that under cold conditions hybrids (especially the two triploid types) have higher fitness than both parental species. This genotype × environment interaction could be one reason why all‐hybrid populations mainly occur at the cooler northern range of the water frog distribution.

Genetic structure of the marsh frog (Pelophylax ridibundus) populations in urban landscape

Article

Oct 2012

Urbanization is a pervasive process causing habitat fragmentation, spatial isolation of populations, and reduction of biological diversity. In this study, we applied 11 microsatellite loci and Bayesian analyses to investigate genetic diversity and population structure in marsh frogs (Pelophylax ridibundus) living in two types of environment—highly fragmented urban landscapes, and landscapes characterized by the presence of a river and artificial canals. Our results show reduced genetic diversity, lower effective population sizes, and higher genetic differentiation for spatially isolated urban populations in comparison with populations outside intensely urbanized areas. Reduction of allelic diversity in urban localities isolated for 13–37 generations is more conspicuous than reduction of expected heterozygosity. Populations living close to the River Danube, its branches, and artificial canals are genetically more homogenous. Our results also suggest that the Danube in Bratislava is not a natural barrier to gene flow. In contrast, it acts as a natural corridor for water frog dispersal. Population structure of P. ridibundus also shows higher genetic connectivity within water paths than between them, suggesting limited overland dispersal, and reflects the historical landscape structure associated with the distribution of the lost river branches.

Carlquist revisited: History, success, and applicability of a natural history model

Article

Jul 2012

In 1966, island biogeographer Sherwin Carlquist published a list of 24 principles governing long-distance dispersal and evolution on islands. The 24 principles describe many aspects of island biology, from long-distance dispersal and establishment to community change and assemblage. Although this was an active period for island biogeography, other models and research garnered much more attention than did Carlquist’s. In this review, over 40 years of support for or against Carlquist’s principles is presented. Recent work has supported most of the 24 principles, and improved methodologies have generally substantiated his initial claims. However, Carlquist’s original work and ideas remain relatively under- represented in the biogeographic literature. Use of philosophical model domains provides one explanation as to why Carlquist’s work has received little attention. Carlquist’s principles are largely natural history tests, and don’t translate well into the theoretical, design of preserves, or the experimental domains—whereas other competing models do well in such domains.

Macro- and microgeographic genetic structure in an ant species with alternative reproductive tactics in sexuals

Article

Dec 2011
J EVOLUTION BIOL

The genetic structure of social insect populations is influenced by their social organization and dispersal modes. The ant Hypoponera opacior shows diverse reproductive behaviours with regular cycles of outbreeding via winged sexuals and inbreeding via within-nest mating wingless sexuals that reproduce by budding. This unusual life cycle should be reflected in the genetic population structure, and we studied this on different scales using microsatellites. On a macrogeographic scale, populations were considerably structured and migration rates within the Chiricahuas were higher than those in between mountain ranges. On a local scale, our analyses revealed population viscosity through dependent colony foundation and a high genetic diversity with a multicolonial structure. The latter was also evident from recognition trials revealing consistent aggression between non-nestmates. Within-nest matings led to high inbreeding coefficients. Finally, the observed seasonal changes in relatedness can be explained by variation in queen number and differential dispersal of the two reproductive morphs.

Ploidy composition in all-hybrid frog populations in relation to ecological conditions

Article

Jul 2010
EVOL ECOL RES

Question: What explains the differences in ratios of diploid (LR) and two types of triploid frogs (LLR, LRR) among all-hybrid frog populations? Hypothesis: Ecological conditions favouring one (LL) or the other (RR) parental species also favour those triploids that carry two copies of the respective genome (dosage effect), whereas diploids dominate under intermediate conditions. Organism: European water frog (Pelophylax esculentus). Field site: Thirty-four natural ponds in the province of Skåne, southern Sweden. Methods: We caught more than 3000 frogs, determined their genotypes with microsatellites, and related the ploidy composition to several uncorrelated ecological parameters, including pond morphology, vegetation, and physical and chemical water parameters. Conclusions: We found a shift from predominantly LLR in small isolated ponds to more LRR in large wetland ponds. This parallels the preferences of the parental species LL and RR for small and large bodies of water, respectively. The effects that pond vegetation and physico-chemical water parameters exert on the parental species were not found in all-hybrid populations. This suggests that environmental parameters affect the genotype composition of all-hybrid populations less than populations containing the parental species. Pond-to-pond differences in LR, LLR, and LRR proportions seem to be better explained by differences in gamete production and thus inheritance patterns.

Impact of gamete production on breeding systems and population structure of hybridogenetic frogs of the Pelophylax esculentus complex: The evolutionary potential of interspecific hybridization

Thesis

Full-text available

Jan 2013

Nicolas B. M. Pruvost

The European water frog Pelophylax esculentus (genome LR) is a natural hybrid between P. lessonae (LL) and P. ridibundus (RR). It presents a peculiar quasi-sexual reproductive mode known as hybridogenesis: the hybrid excludes one of the parental species’ genomes at a pre-meiotic stage of gametogenesis, thus producing gametes containing clonal copies of the other parental genome. By mating with the parental species whose genome has been excluded it re-establishes hybridity at each generation. Moreover, because of its hybrid nature and resulting problems of chromosome pairing at gametogenesis, P. esculentus also produces diploid gametes from time to time. These gametes often lead to the generation of triploid frogs which will allow, under certain ecological conditions, the establishment of all hybrid populations which are maintained without the genetic contribution of either parental species. Over the past decade, such populations have been well studied in the north-western part of Europe, but the presence of triploid water frogs has also been reported for various areas in Central Europe. However, for those localities details on the breeding system, i.e. the genetic contribution of the various frog types, are usually lacking. The major goals of this thesis were to (a) investigate the Central European populations more closely, (b) to compare the breeding systems there with that in all-hybrid populations from Northern Europe and (c) find out whether triploid water frogs in different areas are of mono- or polyphyletic origin. In chapter one I used microsatellite DNA analyses and crossing experiments to compare five populations (one in Poland, two in Germany and two in Slovakia) presenting different population structures. Indices of heterozygosity and of genetic differentiation allowed to depict the genetic interactions between the different type of frogs (LL, LLR, LR, LRR and RR). I was then able to define and differentiate the breeding systems occurring in each of them and to propose an evolutionary scenario for the appearance and maintenance of the all-hybrid populations. Chapter two presents a collaborative study with Alexandra Hoffmann. Here we enlarged our survey to populations distributed all over Europe and used microsatellite DNA and mitochondrial DNA (mtDNA) analyses to find patterns of genetic structure among different breeding system types. We found that genetic diversity among hybrid populations is influenced by geographic location (latitude, longitude) and by the proportions of parental genotypes in the hybrid population. Furthermore, we identified genetic clusters from both microsatellites and mtDNA, which indicate that there are at least two separate polyploid hybrid clades existing today: one in Northern and East-Central Europe and one in Eastern Europe (Eastern Ukraine). In chapter three I focused on eight Czech and Slovak populations. Using microsatellite DNA analyses, flow cytometry and crossing experiments I was able to enlighten and describe a new breeding system type of hybrid water frog populations, the “modified LE-system”. It is characterized by a triploid lineage consisting of males only. Chapter four takes a more ecological approach where I was looking for fitness differences in larval life history traits between the three hybrid types (diploid LR and two type of triploids LLR and LRR) and their parental species (LL and RR) when raised under two temperature regimes. Diploid and triploid hybrids performed better than their parental species under colder conditions. This finding helps to explain why all hybrid populations dominate in the colder northern part of the species distribution. Chapter five also presents a collaborative study with colleagues from Poland. A detailed microsatellite DNA analysis of 18 loci revealed the origin of an unexpected pentaploid froglet offspring obtained by artificial crosses. Using the dosage effect of seven microsatellite loci I was able to demonstrate that the pentaploid froglet was the result of the fusion of a haploid L sperm with a tetraploid egg containing two times the entire genome of the hybrid mother (LLRR egg). This study illustrates a practical application of the DNA microsatellite dosage effect which allows unraveling the ploidy level and the number of copies of the two specific genomes, P. lessonae and P. ridibundus, in the hybrids. In conclusion, this study (a) allows a better understanding of the diversity and complexity of water frog breeding systems containing triploid individuals, (b) demonstrates the multiple origins of triploids from different populations and (c) proposes an evolutionary scenario for the origin and maintenance of all hybrid populations. I argue that such populations represent significant evolutionary units which deserve attention of biologists but also the care of decision-makers in conservation policies.

Age and Size of Hybrid Water Frogs: The Role of Genotype and Ecology

Article

Dec 2012

Where fecundity, mortality, immigration, or emigration differ among species, genotypes, environments, sexes, or age and size classes, we must expect differences in the composition and dynamics of populations and communities. However, as shown in this study on all-hybrid populations of the hemiclonal waterfrog Pelophylax esculentus, the reverse conclusion is not necessarily true: Population differences in genotype composition were not paralleled by differences in genotype-specific age and size distributions. We investigated 12 ponds with different ratios of diploid (LR) and triploid (LLR and LRR) hybrids and tested whether the pond-to-pond ratio differences result from differential survival of the three genotypes under different ecological conditions (selection hypothesis). This should then be reflected in the age and size distribution of the frogs. Age (determined through skeletochronology) and size (measured as snout—vent length) were related to eight ecological variables that in previous studies had been found to affect genotype ratios: temperature, dissolved oxygen, pH, pond size, amounts of submerged and floating pond vegetation, and proportions of forest and wetland area within 20 m of the pond. Only two of these eight variables had a significant effect on growth and survival: frogs in larger ponds were, on average, older and larger than frogs in smaller ponds, and body size also increased with water temperature. Since these relationships did not differ between genotypes and sexes, we conclude that ecological conditions are unlikely to exert their influence on population structure via differential individual performance. The conclusion is supported by our finding that across the 12 study ponds there was no significant relationship between the proportion of a particular genotype × sex category and the average age and size of the individuals belonging to that category. An alternative to the selection hypothesis is offered by the recently proposed gamete pattern hypothesis. It states that pond-to-pond differences in genotype ratios arise from different gamete production patterns of LLR, LR, and LRR males and females. But, so far, support for this hypothesis is also weak.

Gamete production patterns, ploidy, and population genetics reveal evolutionary significant units in hybrid water frogs ( Pelophylax esculentus )

Article

Full-text available

Sep 2013

The European water frog Pelophylax esculentus is a natural hybrid between P. lessonae (genotype LL) and P. ridibundus (RR). It reproduces through hybridogenesis, eliminating one parental genome from its germline and producing gametes containing the genome of the other parental species. According to previous studies, this elimination and transmission pattern is very diverse. In mixed populations, where only diploid hybrids (LR) live in sympatry and mate with one or both parental species, the excluded genome varies among regions, and the remaining genome is transmitted clonally to haploid gametes. In all-hybrid populations consisting of diploid (LR) and triploid (LLR and/or LRR) frogs, diploid individuals also produce gametes clonally (1n in males, 2n in females), whereas triploids eliminate the genome they have in single copy and produce haploid gametes containing the recombined other genome. However, here, too, regional differences seem to exist, and some triploids have been reported to produce diploid gametes. In order to systematically study such regional and genotype differences in gamete production, their potential origin, and their consequences for the breeding system, we sampled frogs from five populations in three European countries, performed crossing experiments, and investigated the genetic variation through microsatellite analysis. For four populations, one in Poland, two in Germany, and one in Slovakia, our results confirmed the elimination and transmission pattern described above. In one Slovakian population, however, we found a totally different pattern. Here, triploid males (LLR) produce sperm with a clonally transmitted diploid LL genome, rather than a haploid recombined L genome, and LR females clonally produce haploid R eggs, rather than diploid LR eggs. These differences among the populations in gamete production go along with differences in genomotype composition, breeding system (i.e., the way triploids are produced), and genetic variation. These differences are strong evidence for a polyphyletic origin of triploids. Moreover, our findings shed light on the evolutionary potential inherent to the P. esculentus complex, where rare events due to untypical gametogenetic processes can lead to the raise, the perpetuation, and the dispersion of new evolutionary significant lineages which may also deserve special conservation measures.

Natural Pathways towards Polyploidy in Animals: The Squalius alburnoides Fish Complex as a Model System to Study Genome Size and Genome Reorganization in Polyploids

Article

Jun 2013
CYTOGENET GENOME RES

When comparing the known picture of polyploidy in animals and in plants, it is possible to recognize some similarities, namely: (i) multiple and recurrent origins in several well-established taxonomic groups; (ii) a strong and regular association with hybridization events; (iii) the production of genotypic diversity; (iv) a rapid genomic reshuffling; (v) a very active role of transposable elements in allopolyploids; (vi) a comparatively privileged occurrence in harsher environments when compared with their diploid relatives, and (vii) gene silencing and divergence of duplicated genes without disruption of duplicated loci. Research on polyploidy was highly biased towards plants during the last century because polyploidy in animals was for long time considered rare, occasional and irrelevant from an evolutionary perspective. However, as empirically observed in plants, genome rediploidization starts in polyploid organisms immediately after the polyploid shock. Given the speed and dynamicity of this process, evidence of genome multiplication is completely erased over time, and hence, only the most recent events are likely to be acknowledged. Although varying in expression between and within taxonomic groups, polyploidy and hybridization are ubiquitous in animals and may be recurrent, fostering evolution. Since evolutionary allopolyploid genomes behave as biologically diploid, zoologists have to challenge the old paradigm of an irrelevant evolutionary role in animals using current genomic and cytogenomic tools. These methods are most likely to reveal the role of polyploid mechanisms in producing evolutionary novelties. Nonsexual complexes are the perfect models to bridge the gap between empirical and theoretical research, while the evolutionary process is in action. Such animal complexes represent a transient stage that, in general, moves towards a polyploid stage, where bisexuality might be recovered, ultimately giving rise to a new gonochoric species. These pathways are herein illustrated by the Iberian allopolyploid Squalius alburnoides. Some general aspects on this fish's complex are updated and reviewed, namely the reproductive modes of the distinct genomotypes, since variable ploidies and genomic combinations occur in natural populations. Most recent data on the mechanisms of gene expression regulation and the importance of the genomic context in driving allelic expression are also included. It was first demonstrated that a regulatory mechanism involving dosage compensation by gene-copy silencing exists in allotriploid females and that allelic expression patterns differed either between genomically equivalent individuals or within the same individual (between tissues and genes). Thus, instead of a whole haplome inactivation, a biased silencing towards repression of a specific allele was observed as well as a reduction of the transcript levels to the diploid state. See also sister article focusing on plants by Tayalé and Parisod in this themed issue.

Genetic and Cytogenetic Characteristics of Pentaploidy in Water Frogs

Article

Full-text available

Mar 2013

We describe a pentaploid froglet (LLLRR; three Pelophylax lessonaeand two Pelophylax ridibundusgenomes) that has never been reported before within the Water Frog Pelophylax esculentus)hybrid complexes. The pentaploid specimen was found among almost all triploid siblings obtained from a diploid femaleP. esculentus(LR) crossed with a diploid male P. lessonae(LL). We confirmed ploidy levels of the parents and the offspring by karyotyping, microsatellite analysis (18 loci), and measurements of DNA content and erythrocyte size. Microsatellite analysis indicated that the pentaploid originated from a tetraploid ovum (LLRR) fertilized by a haploid sperm (L). Surprisingly, the erythrocytes of the pentaploid were not proportionally larger than in triploids, despite a higher DNA content. Only 6.7% of the erythrocytes were distinctly large, whereas the others varied strongly in shape and size; besides typical ovoid mature erythrocytes there were small, tear-shaped, or enucleated ones. We discuss the possibility of loss of some cytoplasm by large erythrocytes as a result of mechanical damages during circulation through the narrow vessels; when the erythrocytes achieve a relatively higher surface-to-volume ratio, they may function more effectively in a proper gas exchange.

A simplified molecular method for distinguishing among species and ploidy levels in European water frogs (Pelophylax)

Article

Jun 2012
MOL ECOL RESOUR

Western Palearctic water frogs in the genus Pelophylax are a set of morphologically similar anuran species that form hybridogenetic complexes. Fully reliable identification of species and especially of hybrid ploidy depends on karyological and molecular methods. In central Europe, native water frog populations consist of the Pelophylax esculentus complex, that is, P. lessonae (LL), P. ridibundus (RR) and the hybrid form P. esculentus that can have different karyotypes (RL, LLR and RRL). We developed existing molecular methods further and propose a simple PCR method based on size-differences in the length of the serum albumin intron-1 and the RanaCR1, a non-LTR retrotransposon of the chicken repeat (CR) family. This PCR yields taxon-specific banding patterns that can easily be screened by standard agarose gel electrophoresis and correctly identify species in all of the 160 samples that had been identified to karyotype with other methods. To distinguish ploidy levels in LR, LLR and RRL specimens, we used the ratio of the peak heights of the larger (ridibundus specific) to the smaller (lessonae specific) bands of fluorescently labelled PCR products resolved on a capillary DNA sequencer and obtained a correct assignment of the karyotype in 93% of cases. Our new method will cut down time and expenses drastically for a reliable identification of water frogs of the P. esculentus complex and potentially for identification of other hybridogenetic complexes and/or taxa, and it even serves as a good indicator of the ploidy status of hybrid individuals.

Types of water frog populations (Rana esculenta complex) in Poland

Article

Full-text available

Jan 2001

Genetic structure of island populations of the anurans Rana temporaria and Bufo bufo

Article

Full-text available

Mar 1999

Amphibians have traditionally been considered to have low dispersal ability and they have become a model for studies on the effects of man-made habitat fragmentation on genetic variation and population differentiation. This study examined the genetic population structure in the common frog (Rana temporaria) and the common toad (Bufo bufo) in an archipelago of the northern Baltic Sea. Heterozygosity was not correlated with distance of the island from the mainland nor, in R. temporaria, with effective population size based on census estimates. Generally, no inbreeding was detected in island populations. The overall differentiation among islands was weak, but the F(ST) values were significantly larger in R. temporaria (F(ST) = 0.068) than in B. bufo (F(ST) = 0.019). Most of the differentiation was a result of differences among groups of islands, differentiation within them playing a minor role. Thus, assuming Wright's island model of migration, gene flow was rather high among closely located islands, but longer distances seemed to form a slight dispersal barrier for R. temporaria. Strong gene flow within the study area was confirmed by lack of isolation by distance. The estimated effective population sizes in R. temporaria were small, the average being 32 breeding females per island. The results indicate that gene flow between island populations across the matrix of open, brackish-water sea is extensive and suggest that the anurans are well able to disperse in this natural metapopulation system.

Inbreeding effects in wild populations

Article

Full-text available

Jan 2002
TRENDS ECOL EVOL

PAST: Paleontological Statistics Software Package for Education and Data Analysis

Article

Full-text available

May 2001

A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.

Die westpaläarktischen Wasserfrösche. Von Märtyrern der Wissenschaft zur biologischen Sensation

Book

Full-text available

Jan 2005

Jörg Plötner

Microsatellite analysis of the natterjack toad (Bufo calamita) in Denmark: Populations are islands in a fragmented landscape

Article

Full-text available

Feb 2009

The European natterjack toad (Bufo calamita) has declined rapidly in recent years, primarily due to loss of habitat, and in Denmark it is estimated that 50% of the isolated populations are lost each decade. To efficiently manage and conserve this species and its genetic diversity, knowledge of the genetic structure is crucial. Based on nine polymorphic microsatellite loci, the genetic diversity, genetic structure and gene flow were investigated at 12 sites representing 5–10% of the natterjack toad localities presently known in Denmark. The expected heterozygosity (H E) within each locality was generally low (range: 0.18–0.43). Further analyses failed to significantly correlate genetic diversity with population size, degree of isolation and increasing northern latitude, indicating a more complex combination of factors in determining the present genetic profile. Genetic differentiation was high (overall θ = 0.29) and analyses based on a Bayesian clustering method revealed that the dataset constituted 11 genetic clusters, defining nearly all sampling sites as distinct populations. Contemporary gene flow among populations was undetectable in nearly all cases, and the failure to detect a pattern of isolation by distance within major regions supported this apparent lack of a gene flow continuum. Indications of a genetic bottleneck were found in three populations. The analyses suggest that the remaining Bufo calamita populations in Denmark are genetically isolated, and represent independent units in a highly fragmented gene pool. Future conservation management of this species is discussed in light of these results.

Types of water populations (Rana esculenta complex) in Poland

Article

Full-text available

Apr 2001

Poland is inhabited by the two water frog species Rana ridibunda (genotype RR) and Rana lessonae (LL) and their hybrido-genetic hybrid Rana esculenta. Besides diploid (RL) hybrids two triploid (RRL, RLL) forms were found. In most populations the hybrid occurs syntopically with only one of the parental species. Concerning their genotypic structure water frog populations can be subdivided into three systems: the L-E (lessonae-esculenta) system, the R-E (ridibunda-esculenta) system and the E-E (esculenta-esculenta) system. The composition of water frog populations in Poland is highly differentiated. Among 27 population types described from central Europe 18 types were found in Poland. The highest diversity of population types was seen in the R-E system (8 types). In the L-E system three and in the E-E system four different types were found. Among 11170 investigated adult water frogs 690 (6%) presumptive triploid R. esculenta individuals occurred. In western Poland the proportion of triploid individuals and the diversity of population types was higher (7.7% triploid individuals, 13 population types) than in the eastern parts of the country (0.2% triploid individuals, six population types). The distribution picture of triploid individuals in western Poland is similar to that seen in eastern Germany (as a rule a high proportion of triploids occurs) while in eastern Poland the distribution pattern of triploid genotypes resembles the situation observed in the territory of the former Soviet Union (nearly no triploids appear).

Demography and evolution of pure hybridogenetic frog (Rana esculenta) populations

Article

Full-text available

Nov 2006
EVOL ECOL RES

Question: How can pure hybrid populations of the hemiclonal frog Rana esculenta persist over time? How can they maintain genetic diversity despite partial clonal inheritance? Mathematical methods: A deterministic model for identifying the composition of hybrid populations in relation to gamete production and primary fitness of its diploid and triploid members. Computer simulations for testing the effects of population composition on genetic diversity. Key model assumptions: Pure Rana esculenta populations consist of diploid males and females of the genotype LR and triploid males and females of the type LLR. Triploids of both sexes eliminate the R genome pre-meiotically (hybridogenesis) and produce haploid L gametes. Within the diploids, males produce R sperm and females either haploid R or diploid LR eggs. All individuals mate randomly and generations do not overlap. The overall hybrid population has a constant size with both sexes and ploidies affected equally by the limitation. Predictions: In pure Rana esculenta populations, the co-existence of diploid and triploid individuals is stable since each ploidy depends on the other for successful reproduction; hence, the mating system is balanced in itself. The genetic diversity and health in these hemiclonal populations resembles the diversity in similar sexual species due to a constant high amount of recombination in one of the parental genomes and a reduced mutation rate in the other. Thus diploid–triploid R. esculenta have become self-sustaining evolutionary units with a potential for new species formation.

Potential impact of genome exclusion by alien species in the hybridogenetic water frogs (Pelophylax esculentus complex)

Article

Full-text available

Jan 2009

Globalization and increasing human impact on natural aquatic systems have facilitated the movement of species and the establishment of nonindigenous species enhancing hybridisation opportunities between naturally allopatric species. In this review, we focus on a special case of natural hybrid speciation and the consequences of recent anthropogenic hybridisation in the water frog complex (Pelophylax esculentus complex), which consists of two parental species, Pelophylax lessonae and Pelophylax ridibundus and a hybrid taxon. The hybrid water frogs reproduce hybridogenetically and eliminate the genome of the syntopic water frog species. Although the actual cause triggering chromosome exclusion remains elusive, it has been proposed that chromosome elimination takes place prior to meiosis and may involve enzymatic degradation of the discarded genome. Translocations of water frogs in Western Europe have become frequent the last decade leading to rapid expansion of the range of the marsh frog P. ridibundus. Subsequent hybridisation of the exotic P. ridibundus may dramatically affect the viability and maintenance of hybrid water frog populations throughout Europe. Interestingly, the impact of this introduced species may differ depending on their geographic origin, which defines the ability to induce genome elimination. This may result in fertile or sterile hybrids, making global conservation guidelines challenging. We predict a severe genetic and ecological impact of nonindigenous P. ridibundus prompting for strict conservation measures to reduce species translocations and for studies on the geographic origin of exotic frog species.

Contrasting Levels of Variation in Neutral and Quantitative Genetic Loci on Island Populations of Moor Frogs (Rana arvalis)

Article

Full-text available

Feb 2007

Reduced levels of genetic variability and a prominent differentiation in both neutral marker genes and phenotypic traits are typical for many island populations as compared to their mainland conspecifics. However, whether genetic diversity in neutral marker genes reflects genetic variability in quantitative traits, and thus, their evolutionary potential, remains typically unclear. Moreover, the phenotypic differentiation on islands could be attributable to phenotypic plasticity, selection or drift; something which seldom has been tested. Using eight polymorphic microsatellite loci and quantitative genetic breeding experiments we conducted a detailed comparison on genetic variability and differentiation between Nordic islands (viz. Gotland, Öland and Læsø) and neighbouring mainland populations of moor frogs (Rana arvalis). As expected, the neutral variation was generally lower in island than in mainland populations. But as opposed to this, higher levels of additive genetic variation (V A) in body size and tibia length were found on the island of Gotland as compared to the mainland population. When comparing the differentiation seen in neutral marker genes (F ST) with the differentiation in genes coding quantitative traits (Q ST) two different evolutionary scenarios were found: while selection might explain a smaller size of moor frogs on Gotland, the differentiation seen in tibia length could be explained by genetic drift. These results highlight the limited utility of microsatellite loci alone in inferring the causes behind an observed phenotypic differentiation, or in predicting the amount of genetic variation in ecologically important quantitative traits.

SPAGeDI: A versatile computer program to analyse spatial genetic structure at the individual or population levels

Article

Full-text available

Dec 2002

Abstract spagedi version 1.0 is a software primarily designed to characterize the spatial genetic structure of mapped individuals or populations using genotype data of codominant markers. It computes various statistics describing genetic relatedness or differentiation between individuals or populations by pairwise comparisons and tests their significance by appropriate numerical resampling. spagedi is useful for: (i) detecting isolation by distance within or among populations and estimating gene dispersal parameters; (ii) assessing genetic relatedness between individuals and its actual variance, a parameter of interest for marker based inferences of quantitative inheritance; (iii) assessing genetic differentiation among populations, including the case of haploids or autopolyploids.

The Amphibian Tree of Life

Article

Full-text available

Mar 2006

The evidentiary basis of the currently accepted classification of living amphibians is discussed and shown not to warrant the degree of authority conferred on it by use and tradition. A new taxonomy of living amphibians is proposed to correct the deficiencies of the old one. This new taxonomy is based on the largest phylogenetic analysis of living Amphibia so far accomplished. We combined the comparative anatomical character evidence of Haas (2003) with DNA sequences from the mitochondrial transcription unit HI (12S and 16S ribosomal RNA and tRNA(Valine) genes, 2,400 bp of mitochondrial sequences) and the nuclear genes histone H3, rhodopsin, tyrosinase, and seven in absentia, and the large ribosomal subunit 28S (approximate to 2,300 bp of nuclear sequences; ca. 1.8 million base pairs; x ($) over bar = 3.7 kb/terminal). The dataset includes 532 terminals sampled from 522 species representative of the global diversity of amphibians as well as seven of the closest living relatives of amphibians for outgroup comparisons.

Weir BS, Cockerham CC.. Estimating F-Statistics for the Analysis of Population-Structure. Evolution 38: 1358-1370

Article

Full-text available

Nov 1984

Formulae are given for estimators for the parameters F, θ, f (FIT, FST, FIS) of population structure. As with all such estimators, ratios are used so that their properties are not known exactly, but they have been found to perform satisfactorily in simulations. Unlike the estimators in general use, the formulae do not make assumptions concerning numbers of populations, sample sizes, or heterozygote frequencies. As such, they are suited to small data sets and will aid the comparisons of results of different investigators. A simple weighting procedure is suggested for combining information over alleles and loci, and sample variances may be estimated by a jackknife procedure.

Keller LF, Waller DM. 2002. Inbreeding effects in wild populations. Trends Eco Evol

Article

Full-text available

May 2002
TRENDS ECOL EVOL

Whether inbreeding affects the demography and persistence of natural populations has been questioned. However, new pedigree data from field populations and molecular and analytical tools for tracing patterns of relationship and inbreeding have now enhanced our ability to detect inbreeding depression within and among wild populations. This work reveals that levels of inbreeding depression vary across taxa, populations and environments, but are usually substantial enough to affect both individual and population performance. Data from bird and mammal populations suggest that inbreeding depression often significantly affects birth weight, survival, reproduction and resistance to disease, predation and environmental stress. Plant studies, based mostly on comparing populations that differ in size or levels of genetic variation, also reveal significant inbreeding effects on seed set, germination, survival and resistance to stress. Data from butterflies, birds and plants demonstrate that populations with reduced genetic diversity often experience reduced growth and increased extinction rates. Crosses between such populations often result in heterosis. Such a genetic rescue effect might reflect the masking of fixed deleterious mutations. Thus, it might be necessary to retain gene flow among increasingly fragmented habitat patches to sustain populations that are sensitive to inbreeding.

Gamete types, sex determination and stable equilibria of all-hybrid populations of diploid and triploid edible frogs (Pelophylax esculentus)

Article

Full-text available

Jul 2009
BMC EVOL BIOL

Ditte G Christiansen

Triploid individuals often play a key role in speciation by hybridization. An understanding of the gamete types (ploidy and genomic content) and stability of hybrid populations with triploid individuals is therefore of importance for exploring the role of hybridization in evolution. The all-hybrid populations of the edible frog, Pelophylax esculentus, are unique in their composition and genetic dynamics: Diploid (genotype LR) and triploid (LLR and LRR) hybrids depend on each other`s different gamete contributions for successful reproduction and maintenance of the populations, as the parental genotypes P. lessonae (LL) and P. ridibundus (RR) are absent among adults. This study provides data and interpretations on gamete types and sex determination that are essential for understanding the function, evolutionary potential and threats of this intriguing system.

A global assessment of endemism and species richness across island and mainland regions

Article

Full-text available

Jul 2009
P NATL ACAD SCI USA

Endemism and species richness are highly relevant to the global prioritization of conservation efforts in which oceanic islands have remained relatively neglected. When compared to mainland areas, oceanic islands in general are known for their high percentage of endemic species but only moderate levels of species richness, prompting the question of their relative conservation value. Here we quantify geographic patterns of endemism-scaled richness ("endemism richness") of vascular plants across 90 terrestrial biogeographic regions, including islands, worldwide and evaluate their congruence with terrestrial vertebrates. Endemism richness of plants and vertebrates is strongly related, and values on islands exceed those of mainland regions by a factor of 9.5 and 8.1 for plants and vertebrates, respectively. Comparisons of different measures of past and future human impact and land cover change further reveal marked differences between mainland and island regions. While island and mainland regions suffered equally from past habitat loss, we find the human impact index, a measure of current threat, to be significantly higher on islands. Projected land-cover changes for the year 2100 indicate that land-use-driven changes on islands might strongly increase in the future. Given their conservation risks, smaller land areas, and high levels of endemism richness, islands may offer particularly high returns for species conservation efforts and therefore warrant a high priority in global biodiversity conservation in this century.

Genetic consequences of habitat fragmentation in plant populations: Susceptible signals in plant traits and methodological approaches

Article

Full-text available

Jan 2009
MOL ECOL

Conservation of genetic diversity, one of the three main forms of biodiversity, is a fundamental concern in conservation biology as it provides the raw material for evolutionary change and thus the potential to adapt to changing environments. By means of meta-analyses, we tested the generality of the hypotheses that habitat fragmentation affects genetic diversity of plant populations and that certain life history and ecological traits of plants can determine differential susceptibility to genetic erosion in fragmented habitats. Additionally, we assessed whether certain methodological approaches used by authors influence the ability to detect fragmentation effects on plant genetic diversity. We found overall large and negative effects of fragmentation on genetic diversity and outcrossing rates but no effects on inbreeding coefficients. Significant increases in inbreeding coefficient in fragmented habitats were only observed in studies analyzing progenies. The mating system and the rarity status of plants explained the highest proportion of variation in the effect sizes among species. The age of the fragment was also decisive in explaining variability among effect sizes: the larger the number of generations elapsed in fragmentation conditions, the larger the negative magnitude of effect sizes on heterozygosity. Our results also suggest that fragmentation is shifting mating patterns towards increased selfing. We conclude that current conservation efforts in fragmented habitats should be focused on common or recently rare species and mainly outcrossing species and outline important issues that need to be addressed in future research on this area.

Genetic structure of island populations of the anurans Rana temporaria and Bufo bufo

Article

Full-text available

May 1999

Amphibians have traditionally been considered to have low dispersal ability and they have become a model for studies on the effects of man-made habitat fragmentation on genetic variation and population differentiation. This study examined the genetic population structure in the common frog (Rana temporaria) and the common toad (Bufo bufo) in an archipelago of the northern Baltic Sea. Heterozygosity was not correlated with distance of the island from the mainland nor, in R. temporaria, with effective population size based on census estimates. Generally, no inbreeding was detected in island populations. The overall differentiation among islands was weak, but the FST values were significantly larger in R. temporaria (FST = 0.068) than in B. bufo (FST = 0.019). Most of the differentiation was a result of differences among groups of islands, differentiation within them playing a minor role. Thus, assuming Wright's island model of migration, gene flow was rather high among closely located islands, but longer distances seemed to form a slight dispersal barrier for R. temporaria. Strong gene flow within the study area was confirmed by lack of isolation by distance. The estimated effective population sizes in R. temporaria were small, the average being 32 breeding females per island. The results indicate that gene flow between island populations across the matrix of open, brackish-water sea is extensive and suggest that the anurans are well able to disperse in this natural metapopulation system.

Determination of biogeographical range: An application of molecular phylogeography to the European pool frog Rana lessonae

Article

Full-text available

Jun 2001

Understanding how species are constrained within their biogeographical ranges is a central problem in evolutionary ecology. Essential prerequisites for addressing this question include accurate determinations of range borders and of the genetic structures of component populations. Human translocation of organisms to sites outside their natural range is one factor that increasingly complicates this issue. In areas not far beyond presumed natural range margins it can be particularly difficult to determine whether a species is native or has been introduced. The pool frog (Rana lessonae) in Britain is a specific example of this dilemma . We used variation at six polymorphic microsatellite loci for investigating the phylogeography of R. lessonae and establishing the affinities of specimens from British populations. The existence and distribution of a distinct northern clade of this species in Norway, Sweden and England infer that it is probably a long-standing native of Britain, which should therefore be included within its natural range. This conclusion was further supported by posterior probability estimates using Bayesian clustering. The phylogeographical analysis revealed unexpected patterns of genetic differentiation across the range of R. lessonae that highlighted the importance of historical colonization events in range structuring.

Andersen LW, Fog K, Damgaard C. Habitat fragmentation causes bottlenecks and inbreeding in the European tree frog (Hyla arborea). Proc R Soc Ser B 271: 1293-1302

Article

Full-text available

Jul 2004

A genetic study of the European tree frog, Hyla arborea, in Denmark was undertaken to examine the population structure on mainland Jutland and the island of Lolland after a period of reduction in suitable habitat and population sizes. The two regions have experienced the same rate of habitat loss but fragmentation has been more severe on Lolland. Genetic variation based on 12 polymorphic DNA microsatellites was analysed in 494 tree frogs sampled from two ponds in Jutland and 10 ponds on Lolland. A significant overall deviation from Hardy-Weinberg expectations could be attributed to three ponds, all on Lolland. This was most probably caused by an inbreeding effect reducing fitness, which was supported by the observed significant negative correlation between larva survival and mean F(IS) value and mean individual inbreeding coefficient. A significant reduction in genetic variation (bottleneck) was detected in most of the ponds on Lolland. Population-structure analysis suggested the existence of at least 11 genetically different populations, corresponding to most of the sampled population units. The results indicated that the populations were unique genetic units and could be used to illustrate the migration pattern between newly established ponds arisen either by natural colonization of tree frogs or by artificial introduction. A high degree of pond fidelity in the tree frogs was suggested. A severe fragmentation process reducing population size and fitness within some of the populations probably caused the significant reduction in genetic variation of tree frog populations on Lolland.

Estimation of Average Heterozygosity and Genetic Distance from A Small Number of Individuals

Article

Full-text available

Aug 1978

Masatoshi Nei

The magnitudes of the systematic biases involved in sample heterozygosity and sample genetic distances are evaluated, and formulae for obtaining unbiased estimates of average heterozygosity and genetic distance are developed. It is also shown that the number of individuals to be used for estimating average heterozygosity can be very small if a large number of loci are studied and the average heterozygosity is low. The number of individuals to be used for estimating genetic distance can also be very small if the genetic distance is large and the average heterozygosity of the two species compared is low.

Unisexual salamanders (genus Ambystoma) present a new reproductive mode for eukaryotes. Genome 50: 119-136

Article

Full-text available

Mar 2007
GENOME

To persist, unisexual and asexual eukaryotes must have reproductive modes that circumvent normal bisexual reproduction. Parthenogenesis, gynogenesis, and hybridogenesis are the modes that have generally been ascribed to various unisexuals. Unisexual Ambystoma are abundant around the Great Lakes region of North America, and have variously been described as having all 3 reproductive modes. Diploid and polyploid unisexuals have nuclear genomes that combine the haploid genomes of 2 to 4 distinct sexual species, but the mtDNA is unlike any of those 4 species and is similar to another species, Ambystoma barbouri. To obtain better resolution of the reproductive mode used by unisexual Ambystoma and to explore the relationship of A. barbouri to the unisexuals, we sequenced the mitochondrial control and highly variable intergenic spacer region of 48 ambystomatids, which included 28 unisexuals, representatives of the 4 sexual species and A. barbouri. The unisexuals have similar sequences over most of their range, and form a close sister group to A. barbouri, with an estimated time of divergence of 2.4-3.9 million years ago. Individuals from the Lake Erie Islands (Kelleys, Pelee, North Bass) have a haplotype that demonstrates an isolation event. We examined highly variable microsatellite loci, and found that the genetic makeup of the unisexuals is highly variable and that unisexual individuals share microsatellite alleles with sexual individuals within populations. Although many progeny from the same female had the same genotype for 5 microsatellite DNA loci, there was no indication that any particular genome is consistently inherited in a clonal fashion in a population. The reproductive mode used by unisexual Ambystoma appears to be unique; we suggest kleptogenesis as a new unisexual reproductive mode that is used by these salamanders.

Zt: A Sofware Tool for Simple and Partial Mantel Tests

Article

Full-text available

Nov 2002
J STAT SOFTW

Different methods of data analysis (e.g. clustering and ordination) are based on distance matrices. In some cases, researchers may wish to compare several distance matrices with one another in order to test a hypothesis concerning a possible relationship between these matrices. However, this is not always self-evident. Usually, values in distance matrices are, in some way, correlated and therefore the usual assumption of independence between objects is violated in the classical tests approach. Furthermore, often, spurious correlations can be observed when comparing two distances matrices. A classic example is the comparison between genetic and environmental distances. Colonies that are in close proximity of each other tend to have similar environments and therefore there will be a positive correlation between environmental and geographical distances. Such colonies will also be more likely to exchange migrants so that genetic distances will be positively correlated with spatial distances. The consequence is that an observed positive association between genetic and environmental distances may be simply due to spatial effects. The most widely used method to account for distance correlations is a procedure known as the Mantel test (Mantel,'67; Mantel and Valand,'70 following the pioneering work of Daniels,'44 ; Daniels and Kendall'47). The simple Mantel test considers two matrices while an extension known as the partial Mantel test considers three matrices. These tools are widely used in different fields of research such as population genetics, ecology, anthropology, psychometrics and sociology.

Reproductive patterns and population genetics in pure hybridogenetic water frog populations of Rana esculenta

Article

Jan 2007

Martina Arioli

Structure and dynamics of pure hybridogenetic water frog populations of Rana esculenta in Southern Sweden

Article

Jan 2007

Christian Jakob

PERSPECTIVE: HIGHLY VARIABLE LOCI AND THEIR INTERPRETATION IN EVOLUTION AND CONSERVATION

Article

Apr 1999
EVOLUTION

P.W. Hedrick

Although highly variable loci, such as microsatellite loci, are revolutionizing both evolutionary and conservation biology, data from these loci need to be carefully evaluated. First, because these loci often have very high within-population heterozygosity, the magnitude of differentiation measures may be quite small. For example, maximum GST values for populations with no common alleles at highly variable loci may be small and are at maximum less than the average within-population homozygosity. As a result, measures that are variation independent are recommended for highly variable loci. Second, bottlenecks or a reduction in population size can generate large genetic distances in a short time for these loci. In this case, the genetic distance may be corrected for low variation in a population and tests to detect bottlenecks are advised. Third, statistically significant differences may not reflect biologically meaningful differences both because the patterns of adaptive loci may not be correlated with highly variable loci and statistical power with these markers is so high. As an example of this latter effect, the statistical power to detect a one-generation bottleneck of different sizes for different numbers of highly variable loci is discussed. All of these concerns need to be incorporated in the utilization and interpretation of patterns of highly variable loci for both evolutionary and conservation biology.

ESTIMATING F-STATISTICS FOR THE ANALYSIS OF POPULATION STRUCTURE

Article

Nov 1984
EVOLUTION

Perspective: Highly Variable Loci and Their Interpretation in Evolution and Conservation

Article

Apr 1999

P.W. Hedrick

Relationship of Genetic Variation to Population Size in Wildlife

Article

Jul 1995
CONSERV BIOL

Richard Frankham

Genetic diversity is one of three levels of biological diversity requiring conservation. Genetic theory predicts that levels of genetic variation should increase with effective population size. Soule (1976) compiled the first convincing evidence that levels of genetic variation in wildlife were related to population size, but this issue remains controversial. The hypothesis that genetic variation is related to population size leads to the following predictions: (1) genetic variation within species should be related to population size; (2) genetic variation within species should be related to island size; (3) genetic variation should be related to population size within taxonomic groups; (4) widespread species should have more genetic variation than restricted species; (5) genetic variation in animals should be negatively correlated with body size; (6) genetic variation should be negatively correlated with rate of chromosome evolution; (7) genetic variation across species should be related to population size; (8) vertebrates should have less genetic variation than invertebrates or plants; (9) island populations should have less genetic variation than mainland populations; and (10) endangered species should have less genetic variation than nonendangered species. Empirical observations support all these hypotheses. There can be no doubt that genetic variation is related to population size, as Soule proposed. Small population size reduces the evolutionary potential of wildlife species.

Reed DH, Frankham R. How closely correlated are molecular and quantitative measures of genetic variation? A meta-analysis. Evolution 55: 1095-1103

Article

Jun 2001
EVOLUTION

— The ability of populations to undergo adaptive evolution depends on the presence of quantitative genetic variation for ecologically important traits. Although molecular measures are widely used as surrogates for quantitative genetic variation, there is controversy about the strength of the relationship between the two. To resolve this issue, we carried out a meta-analysis based on 71 datasets. The mean correlation between molecular and quantitative measures of genetic variation was weak (r = 0.217). Furthermore, there was no significant relationship between the two measures for life-history traits (r =−0.11) or for the quantitative measure generally considered as the best indicator of adaptive potential, heritability (r =−0.08). Consequently, molecular measures of genetic diversity have only a very limited ability to predict quantitative genetic variability. When information about a population's short-term evolutionary potential or estimates of local adaptation and population divergence are required, quantitative genetic variation should be measured directly.

Fixation of deleterious mutations in clonal lineages: Evidence from hybridogenetic frogs

Article

Nov 2001
EVOLUTION

Christoph Vorburger

Abstract The hemiclonal waterfrog Rana esculenta (RL genotype), a bisexual hybrid between R. ridibunda (RR) and R. lessonae (LL), eliminates the L genome from its germline and clonally transmits the R genome (hybridogenesis). Matings between hybrids produce R. ridibunda offspring, but they generally die at an early larval stage. Mortality may be due to fixed recessive deleterious mutations in the clonally inherited R genomes that were either acquired through the advance of Muller's ratchet or else frozen in these genomes at hemiclone formation. From this hypothesis results a straightforward prediction: Matings between different hemiclones, that is, between R. esculenta possessing different R genomes of independent origin, should produce viable R. ridibunda offspring because it is unlikely that different clonal lineages have become fixed for the same mutations. I tested this prediction by comparing survival and larval performance of tadpoles from within- and between-population crossings using R. esculenta from Seseglio (Se) in southern, Alpnach (Al) in central, and Elliker Auen (El) in northern Switzerland, respectively. Se is isolated from the other populations by the Alps. Enzyme electrophoresis revealed that parents from Se belonged to a single hemiclone that was different from all hemiclones found north of the Alps. Parents from Al also belonged to one hemiclone, but parents from El belonged to three hemiclones, one of which was indistinguishable from the one in Al. Rana esculenta from Se produced inviable tadpoles when crossed with other hybrids of their own population, but when crossed with R. esculenta from Al and El, tadpoles successfully completed metamorphosis, supporting the hypothesis I tested. Within-population crosses from Al were also inviable, but some within-population crosses from El, where three hemiclones were present, produced viable offspring. Only part of the crosses between Al and El were viable, but there was no consistent relationship between hemiclone combination and tadpole survival. When backcrossed with the parental species R. ridibunda, hybrids from all source populations produced viable offspring. Performance of these tadpoles with a sexual and a clonal genome was comparable to that of normal, sexually produced R. ridibunda tadpoles. Thus, in the heterozygous state, the deleterious mutations on the clonal R genomes did not appear to reduce tadpole fitness.

The relative contribution of human cytochrome P450 isoforms to the four caffeine oxidation pathways: An in vitro comparative study with cDNA-expressed P450s including CYP2C isoforms

Article

Aug 2008

The aim of the present study was to estimate the relative contribution of cytochrome P450 isoforms (P450s), including P450s of the CYP2C subfamily, to the metabolism of caffeine in human liver. The experiments were carried out in vitro using cDNA-expressed P450s, liver microsomes and specific P450 inhibitors. The obtained results show that (1) apart from the 3-N-demethylation of caffeine – a CYP1A2 marker reaction and the main oxidation pathway of caffeine in man – 1-N-demethylation is also specifically catalyzed by CYP1A2 (not reported previously); (2) 7-N-demethylation is catalyzed non-specifically, mainly by CYP1A2 and, to a smaller extent, by CYP2C8/9 and CYP3A4 (and not by CYP2E1, as suggested previously); (3) C-8-hydroxylation preferentially involves CYP1A2 and CYP3A4 and, to a smaller degree, CYP2C8/9 and CYP2E1 (and not only CYP3A, as suggested previously) at a concentration of 100 μM corresponding to the maximum therapeutic concentration in humans. At a higher caffeine concentration, the contribution of CYP1A2 to this reaction decreases in favour of CYP2C8/9. The obtained data show for the first time the contribution of CYP2C isoforms to the metabolism of caffeine in human liver and suggest that apart from 3-N-demethylation, 1-N-demethylation may also be used for testing CYP1A2 activity. Moreover, they indicate that the C-8-hydroxylation is not exclusively catalyzed by CYP3A4.

Species and sex ratio differences in mixed populations of hybridogenetic water frogs: The influence of pond features

Article

Jan 2002

Among closely related species with overlapping fundamental niches usually one excludes the other(s), unless they differ in their realised niches. In some instances, however, niche overlap is inevitable. One example are European water frogs of the Rana lessonae / R. ridibunda / R. esculenta-complex, where the hybrid R. esculenta is reproductively dependent on one or the other of the two parental species. Hence, it has to live in close sympatry with them, but species and sex ratios in such mixed populations vary widely among ponds. In this paper we investigate the spatial and temporal distribution of the three species by comparing nine ponds with different ecological conditions and frog proportions. All three species occurred in all ponds, but in significantly different absolute and relative numbers. R. lessonae proportions are higher in smaller, more structured ponds with rich vegetation under water, while R. ridibunda dominates in larger, less structured ponds with little vegetation under water. The hybrid R. esculenta is intermediate in its distribution; it occurs in larger ponds than R. lessonae, but in more vegetated ones than R. ridibunda. The sex ratios of the three species differ also within the ponds. In R. esculenta, the proportion of females decreased with increasing fluctuation in water temperature. The observed spatial distribution of adults is best explained through 81 species differences in the habitat-related development and survival of their progeny, which is known from several experiments. Temporal changes in species proportions were not related to pond characteristics. This, however, is not surprising, as year-to21 year changes in pond features were small, and strong site fidelity, combined with high annual survival, creates substantial temporal autocorrelation between population compositions of successive years.

Non-hybrid offspring from mating between hemiclonal hybrid waterfrogs suggest occasional recombination between clonal genomes

Article

Nov 2001

Christoph Vorburger

The hemiclonal waterfrog Rana esculenta, a hybrid between R. ridibunda and R. lessonae, eliminates the lessonae genome from the germline and clonally transmits the ridibunda genome (hybridogenesis). Such genomes are prone to accumulate deleterious mutations, which may explain why offspring from matings between hybrids are typically inviable. Here I present field data from a population for which experimental crossings showed that some R. esculenta pairs produce viable R. ridibunda offspring. I demonstrate: (1) that R. ridibunda metamorphs are also produced and survive under natural conditions; (2) that their genotypes are consistent with combinations of clonal ridibunda genomes found in hybrids; and (3) that all R. ridibunda are female. These females possibly recombine the clonal genomes they inherited and, upon mating with syntopic R. lessonae, produce new hemiclones with novel combinations of alleles. Hence, occasional recombination between otherwise clonal ridibunda genomes seems plausible and may provide an escape from the evolutionary dead end they were proposed to be trapped in.

From Clonal to Sexual Hybrids: Genetic Recombination Via Triploids in All-Hybrid Populations of Water Frogs

Article

Mar 2009
EVOLUTION

Speciation via interspecific hybrids is very rare in animals, as compared to plants. Whereas most plants overcome the problem of meiosis between different chromosome sets by tetraploidization, animal hybrids often escape hybrid sterility by clonal reproduction. This comes at the expense of genetic diversity and the ability to purge deleterious mutations. However, here we show that all-hybrid populations of diploid (LR) and triploid (LLR and LRR) water frogs (Pelophylax esculentus) have secondarily acquired sexual reproduction. First, in a crossing experiment analyzed with microsatellite markers, triploid hybrids of both sexes and genotypes (LLR and LRR) recombined their homospecific genomes. Second, the great majority of natural populations investigated had low multilocus linkage isequilibrium, indicating a high recombination rate. As predicted from mating system models, the L genome had constant, low levels of linkage disequilibrium, whereas linkage disequilibrium in th e R genome showed a significant reduction with increasing proportion of recombining triploids. This direct evidence of sexual reproduction in P. esculentus calls for a change of the conventional view of hybridogens as clonally reproducing diploids. Rather, hybridogens can be independent sexually reproducing units with an evolutionary potential.

Conservation of the introgressed European water frog complex using molecular tools

Article

Mar 2009
MOL ECOL

In Belgium, the Pelophylax esculentus complex has recently been subjected to multiple introductions of non-native water frogs, increasing the occurrence of hybridisation events. In the present study, we tested the reliability of morphometric and recently developed microsatellite tools to identify introgression and to determine the origin of exotic Belgian water frogs. By analysing 150 individuals of each taxon of the P. esculentus complex and an additional 60 specimens of the introduced P. cf. bedriagae, we show that neither of the currently available tools appears to have sufficient power to reliably distinguish all Belgian water frog species. We therefore aimed at increasing the discriminatory power of a microsatellite identification tool by developing a new marker panel with additional microsatellite loci. By adding only two new microsatellite loci (RlCA5 and RlCA1b20), all taxa of the P. esculentus complex could be distinguished from each other with high confidence. Three more loci (Res3, Res5 and Res17) provided a powerful discrimination of the exotic species.

The postglacial recolonization of Northern Europe by Rana arvalis as revealed by microsatellite and mitochondrial DNA analyses

Article

Nov 2008

The postglacial history of the moor frog (Rana arvalis) in Northern Europe was investigated with the aid of eight variable microsatellite loci and a 661 bp sequence of the mitochondrial cytochrome b gene. A division between eastern and western mitochondrial lineages was discovered, supporting two recolonization routes to Fennoscandia since the last glacial maximum. This result was corroborated by the microsatellite data, which revealed a contact zone between the two lineages in Northern Sweden. These findings add to the increasing evidence that an intraspecific genetic biodiversity founded on the existence of eastern and western clades is a common element in Fennoscandian fauna and flora.

Evolution in Mendelian Population

Article

Feb 1990

Wright SG

How closely correlated are molecular and quantitative measures of genetic variation? A meta-analysis

Article

Jul 2001

The ability of populations to undergo adaptive evolution depends on the presence of quantitative genetic variation for ecologically important traits. Although molecular measures are widely used as surrogates for quantitative genetic variation, there is controversy about the strength of the relationship between the two. To resolve this issue, we carried out a meta-analysis based on 71 datasets. The mean correlation between molecular and quantitative measures of genetic variation was weak (r = 0.217). Furthermore, there was no significant relationship between the two measures for life-history traits (r = -0.11) or for the quantitative measure generally considered as the best indicator of adaptive potential, heritability (r = -0.08). Consequently, molecular measures of genetic diversity have only a very limited ability to predict quantitative genetic variability. When information about a population's short-term evolutionary potential or estimates of local adaptation and population divergence are required, quantitative genetic variation should be measured directly.

Population genetics of a successful invader: The marsh frog Rana ridibunda in Britain

Article

Apr 2003

We investigated the genetic outcome of successful invasion by an alien species, the marsh frog Rana ridibunda, in Britain. Twelve adults translocated from Hungary into Kent (Romney) in 1935 resulted rapidly in a large localized population. A further successful translocation in 1973 from Romney to Sussex (Lewes), together with other range extensions, provided an opportunity to test bottleneck effects during colonization events. Romney and Lewes frogs had similar genetic diversities to those in Hungary at 14 random amplified polymorphic DNA marker (RAPD) and five microsatellite loci. The introduced populations were, however, differentiated genetically from each other and from a reference population in Hungary. Fitness assessments (larval growth and survival) revealed no differences between the Lewes and Romney populations. Despite starting with few founders, significant bottleneck effects on R. ridibunda in Britain were therefore undetectable, presumably because population expansions were rapid immediately after the translocations.

High degree of population subdivision in a widespread amphibian

Article

Oct 2004

In general, amphibians are known to exhibit a higher degree of population subdivision than any other major animal taxa, but large-scale population genetic surveys of widely distributed species are still scarce, especially in the Eurasian continent. Using microsatellite markers and mitochondrial DNA sequences, we investigated the large-scale population genetic structure of the common frog (Rana temporaria)--one of the most widespread amphibians of the Palearctic region. Analyses of cytochrome b sequences revealed evidence for two distinct lineages inhabiting western and eastern parts of Europe. The separation of these lineages c. 700,000 years ago may have been induced by the onset of the Middle Pleistocene continental glaciations. Analyses of the variability of microsatellite loci within each of the clades revealed evidence for evolution of a high degree of population subdivision (FST approximately 0.23) even in northern Fennoscandia, colonized less than 10,000 years ago. The high level of substructuring is puzzling in the face of an apparently high dispersal capacity, as evidenced by the rather rapid recolonization of northern Europe. This suggests that processes other than restricted dispersal capacity need to be explored as explanations for the high degree of population subdivision in amphibians. The colonization of northern Europe has been accompanied by loss of genetic variability as evidenced by decreasing levels of intrapopulational genetic variability in microsatellite loci from south to north across Europe.

Reproduction and hybrid load in all-hybrid populations of Rana esculenta water frog in Denmark

Article

Jul 2005

All-hybrid populations of the water frog, Rana esculenta, are exceptional in consisting of independently and to some extent sexually reproducing interspecific hybrids. In most of its range R. esculenta reproduces hemiclonally with one of the parental species, R. lessonae or R. ridibunda, but viable populations of diploid and triploid hybrids, in which no individuals of the parental species have been found, exist in the northern part of the range. We test the hypothesis that nonhybrids arise every year in these all-hybrid populations, but die during larval development. Microsatellite markers were used to determine the genotypes of adults and abnormal and healthy offspring in three all-hybrid populations of R. esculenta in Denmark. Of all eggs and larvae, 63% developed abnormally or died, with some being nonhybrid (genomes matching one of the parental species), many being aneuploid (with noninteger chromosome sets), a few being tetraploid, and many eggs possibly being unfertilized. The 37% surviving and apparently healthy froglets were all diploid or triploid hybrids. In all three populations, gametogenesis matched the pattern previously described for all-hybrid R. esculenta populations in which most triploid adults have two R. lessonae genomes. This pattern was surprising for the one population in which triploid adults had two R. ridibunda genomes, because here it leads to a deficiency of gametes with an R. lessonae genome and should compromise the stability of this population. We conclude that faulty gametogenesis and mating between frogs with incompatible gametes induce a significant hybrid load in all-hybrid populations of R. esculenta, and we discuss compensating advantages and potential evolutionary trajectories to reduce this hybrid load.

Conservation genetics of amphibians

Article

Jan 2006
HEREDITY

Trevor J. C. Beebee

Amphibians are good models for investigating the genetics of wild animal populations because they are: (1) widely distributed in most ecosystems; (2) easy to sample in breeding assemblages; (3) often philopatric to breeding sites, generating high levels of population genetic structure; (4) amenable to controlled crossings in the laboratory; and (5) of major conservation concern. Neutral genetic markers, mostly microsatellites, have been used successfully in studies of amphibian effective population sizes and structures, and in assessing the consequences of hybridisation. Phylogeography has provided important insights into population histories and the fates of introductions. Quantitative genetic methods have demonstrated adaptive variation in life history traits of importance to fitness and therefore to population viability.

Use of active consortia of constructed ternary bacterial cultures via mixture design for azo-dye decolorization enhancement

Article

Aug 2007
J HAZARD MATER

This first-attempt study used constructed bacterial consortia containing Escherichia coli DH5alpha (a weak decolorizer) and its UV-irradiated mutants (E. coli UVT1 and UV68; strong decolorizers) via equilateral triangle diagram and mixture experimental design to assess color removal during species evolution. The results showed that although strain DH5alpha was not an effective decolorizer, its presence might still played a significant role in affecting optimal color removal capabilities of mixed consortia (e.g., E. coli DH5alpha, UVT1 and UV68) for two model azo dyes; namely, reactive red 22 (RR22) and reactive black 5 (RB5). Contour analysis of ternary systems also clearly showed that decolorization of RR22 and RB5 by DH5alpha-containing active mixed consortia was more effective than mono-cultures of the stronger decolorizer alone (e.g., UVT1). The optimal composition of the mixed consortium (UV68, UVT1, DH5alpha) achieving the highest specific decolorization rate was (13%:58%:29%) and (0%:74%:26%) for decolorization of RR22 and RB5, respectively, with initial total cell density fixed at OD(600)=3.5+/-0.28.

Evolution in Mendelian Populations

Article

Apr 1931

Sewall Wright

The frequency of a given gene in a population may be modified by a number of conditions including recurrent mutation to and from it, migration, selection of various sorts and, far from least in importance, were chance variation

Non-gradual variation in colour morphs of the strawberry poison frog Dendrobates pumilio: Genetic and geographical isolation suggest a role for selection in maintaining polymorphism

Article

Nov 2007

The relative roles that geographical isolation and selection play in driving population divergence remain one of the central questions in evolutionary biology. We approached this question by investigating genetic and morphological variation among populations of the strawberry poison frog, Dendrobates pumilio, in the Bocas del Toro archipelago, Panama. We found significant population genetic structure and isolation by distance based on amplified fragment length polymorphism markers. Snout vent length (SVL), coloration and the extent and size of dorsal black spots showed large variation among the studied populations. Differences in SVL correlated with genetic distance, whereas black spot patterns and other coloration parameters did not. Indeed, the latter characters were observed to be dramatically different between contiguous populations located on the same island. These results imply that neutral divergence among populations may account for the genetic patterns based on amplified fragment length polymorphism markers and SVL. However, selective pressures need to be invoked in order to explain the extraordinary variation in spot size and coverage, and coloration. We discuss the possibility that the observed variation in colour morphs is a consequence of a combination of local variation in both natural selection on an aposematic signal towards visual predators and sexual selection generated by colour morph-specific mate preferences.

Genetic variation across species' geographical ranges: The central-marginal hypothesis and beyond

Article

Apr 2008
MOL ECOL

There is growing interest in quantifying genetic population structure across the geographical ranges of species to understand why species might exhibit stable range limits and to assess the conservation value of peripheral populations. However, many assertions regarding peripheral populations rest on the long-standing but poorly tested supposition that peripheral populations exhibit low genetic diversity and greater genetic differentiation as a consequence of smaller effective population size and greater geographical isolation relative to geographically central populations. We reviewed 134 studies representing 115 species that tested for declines in within-population genetic diversity and/or increases in among-population differentiation towards range margins using nuclear molecular genetic markers. On average, 64.2% of studies detected the expected decline in diversity, 70.2% of those that tested for it showed increased differentiation and there was a positive association between these trends. In most cases, however, the difference in genetic diversity between central and peripheral population was not large. Although these results were consistent across plants and animals, strong taxonomic and biogeographical biases in the available studies call for a cautious generalization of these results. Despite the large number of studies testing these simple predictions, very few attempted to test possible mechanisms causing reduced peripheral diversity or increased differentiation. Almost no study incorporated a phylogeographical framework to evaluate historical influences on contemporary genetic patterns. Finally, there has been little effort to test whether these geographical trends in putatively neutral variation at marker loci are reflected by quantitative genetic trait variation, which is likely to influence the adaptive potential of populations across the geographical range.

Evolutionary genetics of the Rana esculenta complex Evolution and Ecology of Unisexual Vertebrates

289-302

Jd Graf
Pelaz

Graf JD, Polls Pelaz M (1989). Evolutionary genetics of the Rana esculenta complex. In: Dawley RM, Bogart JP (eds). Evolution and Ecology of Unisexual Vertebrates. New York State Museum Bulletin pp 289–302

Nordens padder og krybdyr

Jan 1997

K Fog
A Schmedes
Rosenrn De Lasson

Fog K, Schmedes A, Rosenrn de Lasson D (1997). Nordens padder og krybdyr. Gad: Copenhagen, Denmark.

R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing

Jan 2009

R Development
Core Team

R Development Core Team (2009). R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing: Vienna, Austria, http://www.R-project.org.

Effects of geographic distance, sea barriers and habitat on the genetic structure and diversity of all-hybrid water frog populations

Abstract

No full-text available

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