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Rapid Morphological Change in Channel Island Deer Mice
Abstract
Deer mice, Peromyscus maniculatus, collected over 90 years from three California Channel Islands, were examined for evidence of morphological change. Rapid morphological change has occurred in the endemic subspecies from Santa Barbara (P. m. elusus), Anacapa (P. m. anacapae), and Santa Cruz Island (P. m. santacruzae). Data were divided into two temporal classes, 1897-1941 and 1955-1988. Of the 16 morphological characters measured, between five and 10 measures changed significantly (P ≤ 0.05) with temporal class in each subspecies, and multivariate test statistics were significant (P ≤ 0.05) for all three subspecies. For each subspecies, depth of braincase, total length, tail length, and hind foot length became smaller over time, except depth of braincase, which became larger in P. m. elusus. The rates of change dramatically exceed those estimated from paleontological records and are even higher than those reported in some experimental selection studies. Temporal change in two characters exceeds differentiation between subspecies. Although changing, each subspecies remained well differentiated, and incorporation of temporal change allowed correct classification of most specimens. Unlike nearly all previous reports of rapid evolution, the changes in these populations were not associated with a founder events or recent introductions. This study demonstrates that rapid phenotypic change can occur in long-established natural populations and temporal stability of morphological characters in such populations, even over short evolutionary time periods, cannot be assumed.
... All three islets are rugged and steep. Although P. m. anacapae has been shown to be distinct in morphology (Gill 1980; Pergams & Ashley, 1999), allozyme variation (Gill 1976Gill , 1980), and mtDNA (Ashley & Wills 1987), it is not known whether deer mice from the different islets are genetically distinct. Further , the history and current status of East Anacapa deer mice are uncertain. ...
... -----------------= that significant morphological change in Channel Island deer mice had occurred over the last century (Pergams & Ashley, 1999), we used only mice collected since 1955. We examined specimens from the following locations: Anacapa ( P. m. anacapae ), Santa Barbara Island ( P. m. elusus ), Santa Cruz Island ( P. m. santacruzae ), and the California coastal mainland ( P. m. gambelii ). ...
... Twelve cranial measurements were taken (following the methods described by Hooper (1952), Fisler (1965), and Collins and George (1990) unless otherwise indicated): intermeatus width (IW), length of nasals (LN), length of palate plus incisor (LPI, measured as the greatest distance from the anterior edge of the alveoli of the incisors to the mesopterygoid fossa), breadth of rostrum (BR), alimentary toothrow (AL), length of incisive foramen (LIF), nasal width (NW, the narrowest width of the nasals and premaxilla dorsally and directly anterior to the infraorbital foramen), zygomatic breadth (ZB), interorbital breadth (IB), depth of braincase (DBC), breadth of braincase (BB), and breadth of zygomatic plate (BZP). All cranial measurements were taken with a digital caliper to the nearest 0.01 mm by O.R.W.P. Cranial measurement error was estimated and was found to be small, 2% of the variation between mice (Pergams & Ashley, 1999). The four standard external measurements were taken from museum tags: total length (TOT ), tail length (TAIL), hind foot length (HIND), and ear length (EAR). ...
We investigated the genetic and morphological status of an endemic subspecies of deer mice ( Peromyscus maniculatus anacapae) on Anacapa Island of California through mitochondrial DNA (mtDNA) analysis, morphometric discriminant function analysis, and population viability analysis. We sought to assist the development of a management plan that may include captive breeding, reintroduction, or translocation of mice following eradication of introduced rats. The genetic and morphological data were used to investigate whether the subspecies or populations on each of the three islets of Anacapa represent evolutionarily significant units for conservation. The status of the East Anacapa population was of particular concern because deer mice have recently been caught there following more than 15 years of no records of deer mice. Sequences of the mtDNA cytochrome oxidase c subunit II gene (COII ) indicated that the Anacapa subspecies had unique haplotypes not found on neighboring islands or the mainland and thus represents a distinct unit for conservation. Further, one of these haplotypes was shared among the islets, including most of the East Anacapa mice, suggesting that the East Anacapa population had either recovered from a severe bottleneck or had been recolonized by P. m. anacapae, but that it was not derived from other subspecies. Discriminant function analysis of morphological data also supported classification of the East Anacapa mice as P. m. anacapae. The mitochondrial mtDNA sequence data yielded estimates of two to seven migrants per generation among the Anacapa islets, suggesting a functioning metapopulation. Incorporating these data and information available on the life history and demographics of deer mice, we used a novel type of population viability analysis to develop a captive breeding and reintroduction plan for Anacapa deer mice should they be eradicated along with the rats. A sine wave was incorporated into the population viability analysis to simulate population size cyclicity. Our study provides baseline information needed for developing a comprehensive conservation and management plan for a threatened island endemic.
Resumen: Investigamos el estado genético y morfológico del ratón Peromyscus maniculatus anacapae de la isla Anacapa en California mediante un análisis del ADN mitocondrial, un análisis de función discriminante de los datos morfométricos y un análisis de viabilidad poblacional. Pretendimos colaborar con el desarrollo de un plan de manejo que podría incluir la reproducción en cautiverio, la reintroducción o el desplazamiento de ratones después de la erradicación de ratas introducidas. Los datos genéticos y morfológicos fueron utilizados para investigar si las subespecies o las poblaciones en cada una de las tres isletas de Anacapa representan unidades evolutivas significativas para la conservación. El estado de la población de Anacapa del Este fue de interés particular debido a la captura reciente de ratones, después de 15 años sin registros de esta especie. Las secuencias del gen citocromo oxidasa c subunidad II del ADNmt (COII ) indicaron que la subespecie de Anacapa tiene haplotipos únicos, que no se encuentran en las islas vecinas ni en tierra firme y, por lo tanto, representa una unidad única para la conservación. Más aún, uno de estos haplotipos fue compartido entre las isletas, incluyendo la mayoría de los ratones de Anacapa del Este, lo que sugiere que la isla ha sido recolonizada por P. m. anacapae o que la población de Anacapa del Este se ha recuperado de un cuello de botella severo pero que no ha derivado de otras subespecies. El análisis de función discriminante de los datos morfométricos también respalda la clasificación de los ratones de Anacapa del Este como P. m. Anacapae. Los datos de secuencias del ADNmt proveen estimaciones de 2 a 7 migrantes por generación entre las isletas Anacapa, lo que sugiere la presencia de una metapoblación en funcionamiento. Con la incorporación de estos datos y la información disponible sobre los antecedentes biológicos y la demografía del ratón, se utilizó un nuevo tipo de análisis de viabilidad poblacional para desarrollar un plan de reproducción en cautiverio y de reintroducción del ratón de Anacapa en caso de que los ratones sean exterminados junto con las ratas. Se incorporó una función seno al análisis de viabilidad poblacional para simular los ciclos del tamaño poblacional. Nuestro estudio provee la información básica necesaria para desarrollar un plan de conservación y de manejo integral para una especie endémica insular amenazada.
... Examples include studies of Peromyscus (Gill, 1980; Aquadro & Kilpatrick, 1981; Melton, 1982; Ashley & Wills, 1987; Allard & Greenbaum, 1988; Calhoun & Greenbaum, 1991; Pergams & Ashley, 1999), Clethrionomys (Corbet, 1964), Mus (Davis, 1983) & Rattus (Patton, Yang & Myers, 1975; Yom-Tov, Yom- Tov & Moller, 1999). We recently documented an example of rapid morphological evolution of island mice that differs from previous examples (Pergams & Ashley, 1999, 2000). We examined subspecies of deer mice, Peromyscus maniculatus, that occur on the California Channel islands. ...
... Patton, Yang and Myers (1975) measured both non-metrical cranial characters and mensural traits. Pergams and Ashley (1999) measured only mensural traits. Differences in incidences of binary, presence/absence characters such as skeletal variants are not directly comparable with changes in means of continuous characters such as mensural cranial or external measurements. ...
We perform a meta-analysis on morphological data from four island rodent populations exhibiting microevolution (>100 years). Data consisting of incidences of skeletal variants, cranial, and external measurements are from house mice (Mus musculus) on one Welsh and one Scottish island, black rats (Rattus rattus) on two Galapagos islands, and deer mice (Peromyscus maniculatus) on three California Channel islands. We report extremely high rates of microevolution for many traits; 60% of all mensural traits measured changed at a rate of 600 d or greater (max. 2682 d). The proportion of all mensural traits evolving at 600–800 d (23%) was idiosyncratic and departed from an expected negative exponential distribution. We argue that selection, rather than founder events, is largely responsible for the substantial shifts in morphology seen among insular rodents. Examining individual traits, there is a trend towards the nose becoming longer and wider, while the skull becomes shallower, shown by both rats and mice on five different islands. We found a significant correlation between island size and degree of skeletal variant evolution and between island distance from the mainland (or nearest island) and degree of cranial and external character evolution. Thus, microevolution of rodents is greater on smaller and more remote islands.
... In a classic study of Galapagos finches (Geospiza fortis), increases in body and beak size occurred in response to a single episode of selection brought on by drought conditions (Boag and Grant, 1981), a trend that was later reversed during an El Ninõ event (Gibbs and Grant, 1987; Grant and Grant, 1995). In the case of three subspecies of Channel Island deer mice (Peromyscus maniculatus), changes in external and cranial measurements as great as 10% were documented in museum specimens collected over less than 90 years (Pergams and Ashley, 1999). This case was an accidental discovery and the selective agent is not known; perhaps many cases of microevolution are never documented. ...
... Research on evolutionary mechanisms and effects should be incorporated into research programs in applied ecology and resource management. Museum collections can be used to characterize and quantify microevolution in species of interest (Pergams and Ashley, 1999 ). Conservation geneticists should measure quantitative genetic variation directly rather than relying on neutral molecular variation to assess a population's short-term evolutionary potential (Reed and Frankham, 2001). ...
Here we review growing evidence that microevolutionary changes may often be rapid and, in many cases, occur on time frames comparable to human disturbance and anthropogenic change. Contemporary evolutionary change has been documented in relatively pristine habitats, in disturbed populations, under captive management, and in association with both intentional and inadvertent introductions. We argue that evolutionary thinking is thus relevant to conservation biology and resource management but has received insufficient consideration. Ignoring evolution may have a variety of consequences, including unpredicted evolutionary responses to disturbance and naive or inappropriate management decisions. Philosophically, we must also grapple with the issue of whether the evolution of adaptations to disturbance and degraded habitats is sometimes beneficial or something to be rigorously avoided. We advocate promoting evolutionarily enlightened management [Lecture Notes in Biomathematics 99 (1994) 248], in which both the ecological and evolutionary consequences of resource management decisions are considered.
... Generation time in the study population has been estimated to be 263 days [14]. Species mean evolutionary rates of head and skull measurements in eight rodent species (and subspecies in the case of Peromyscus maniculatus) were used for comparison [28][29][30][31] (table 1). A onesample Wilcoxon's signed-rank test was used to compare the median evolutionary rates in darwins from the literature to that of the study population. ...
Similar phenotypic changes occur across many species as a result of domestication, e.g. in pigmentation and snout size. Experimental studies of domestication have concentrated on intense and directed selection regimes, while conditions that approximate the commensal and indirect interactions with humans have not been explored. We examine long-term data on a free-living population of wild house mice that have been indirectly selected for tameness by regular exposure to humans. In the course of a decade, this mouse population exhibited significantly increased occurrence of white patches of fur and decreased head length. These phenotypic changes fit to the predictions of the ‘domestication syndrome’.
... Therefore, rapid microevolutionary changes may be critical to the survival of species in an anthropogenic world. Rates of morphological adaptation of vertebrates, once thought to be incommensurate with ecological time scales, transpire quickly in some species under novel ecosystem pressures [1,2,3,4,5,6]. Surprisingly, few studies have examined morphological changes due to landscape change [7,8]. ...
Humans have altered the biotic and abiotic environmental conditions of most organisms. In some cases, such as intensive agriculture, an organism's entire ecosystem is converted to novel conditions. Thus, it is striking that some species continue to thrive under such conditions. The prairie deer mouse (Peromyscus maniculatus bairdii) is an example of such an organism, and so we sought to understand what role evolutionary adaptation played in the success of this species, with particular interest in adaptations to novel foods. In order to understand the evolutionary history of this species' masticatory structures, we examined the maxilla, zygomatic plate, and mandible of historic specimens collected prior to 1910 to specimens collected in 2012 and 2013. We found that mandibles, zygomatic plates, and maxilla have all changed significantly since 1910, and that morphological development has shifted significantly. We present compelling evidence that these differences are due to natural selection as a response to a novel and ubiquitous food source, waste grain (corn, Zea mays and soybean, Glycine max).
... Body size is a life history characteristic of a species that may be associated with multiple factors (BLACKBURN & GASTON, 1997;BOBACK, 2003); considering that one of our localities is an insular site, the island effect should be taken into account. One of the most notable changes in the morphometry of populations on islands is body size as has been recorded in several groups of animals, e.g., large mammals (ROTH, 1993), rodents (PERGAMS & ASHLEY, 1999), snakes (BOBACK, 2003), turtles (GIBBONS et al., 1979), birds (CLEGG et al., 2002 andmammals (ADLER & LEVINS, 1994). Island populations may exhibit a trend toward increase or decrease in body size depending on the environmental characteristics of the island or the particular characteristics of life history of the species (CASE, 1978;ROTH, 1993;BOBACK, 2003;LOMOLINO, 2005). ...
The Chocoan River Turtle, Rhinoclemmys nasuta (Geoemydidae), is a species of great importance due to its limited geographical distribution and threat status. In Colombia it is considered in the category data deficient (DD) and globally as a near-threatened species (NT). In this study we assessed the population density, variation in the demographic structure and population size, and morphometric variation in two localities. One island population has no human disturbance and the other, mainland locality is human-influenced. Population density was 6.3 times greater in the insular locality, which corresponds with the absence of some predators and human disturbance at this location. Additionally, there was no significant difference between localities in demographic structure and size classes, which may reflect that there is no removal of individuals for consumption or use as pets in the mainland population. On the other hand, body size was smaller on the island, a phenomenon that may be explained by a tendency of species to dwarfism in insular environments, or an effect of increased intraspecific competition. To clarify whether differences in population density and body size are attributable to island effects or to the difference in the degree of human disturbance between the two populations it will be necessary to sample at other locations on the mainland with different degrees of human disturbance. However, it is important to stress the importance of Isla Palma as a site for regional conservation of R. nasuta.
... This is comparable to the pygmy raccoon, which weighs 50% that of the average North American raccoon. The idea that island mammals may demonstrate dramatic morphological changes that appear accelerated on islands relative to the mainland is not new (Pergams & Ashley, 1999; Simberloff et al., 2000; Millien, 2006). The tendency for faster evolution on islands has been found to often hold over relatively short time scales, some over the span of decades (Millien, 2006, but see Meiri et al., 2009a ). ...
Insular dwarfism is common in mammals. Many theories have been put forward to explain it, including competitive release, predation release, resource limitation and limited dispersal abilities. However, recent analyses have challenged many of these assertions and indicate that size evolution is more complex with populations and species developing unique patterns of morphological variation. We explore the evolution of body size in a poorly studied island carnivore, the pygmy raccoon Procyon pygmaeus, and compare it with other mainland and island populations within its genus. We studied 36 males and 42 females of the endemic and endan-gered pygmy raccoon on Cozumel Island, Mexico, from 2001 to 2003. Insular P. pygmaeus are, on average, 17.5% smaller in linear dimensions than their closest mainland relative. Minimum linear rate of size change was 6.21% per 1000 years or 5.43 darwins. Size reduction is likely to have been an adaptation to fewer resources and predators. Our population genetic examination identified different patterns of divergence than the morphological examination, indicating that the rate of morphological evolution likely exceeds that represented in this genus' neutral genetic history. This case study highlights the importance of an auteco-logical approach toward examining insular dwarfism given that clear patterns are not visible across the Carnivora.
... This is comparable to the pygmy raccoon, which weighs 50% that of the average North American raccoon. The idea that island mammals may demonstrate dramatic morphological changes that appear accelerated on islands relative to the mainland is not new (Pergams & Ashley, 1999; Simberloff et al., 2000; Millien, 2006). The tendency for faster evolution on islands has been found to often hold over relatively short time scales, some over the span of decades (Millien, 2006, but see Meiri et al., 2009a ). ...
Insular dwarfism is common in mammals. Many theories have been put forward to explain it, including competitive release, predation release, resource limitation and limited dispersal abilities. However, recent analyses have challenged many of these assertions and indicate that size evolution is more complex with populations and species developing unique patterns of morphological variation. We explore the evolution of body size in a poorly studied island carnivore, the pygmy raccoon Procyon pygmaeus, and compare it with other mainland and island populations within its genus. We studied 36 males and 42 females of the endemic and endan-gered pygmy raccoon on Cozumel Island, Mexico, from 2001 to 2003. Insular P. pygmaeus are, on average, 17.5% smaller in linear dimensions than their closest mainland relative. Minimum linear rate of size change was 6.21% per 1000 years or 5.43 darwins. Size reduction is likely to have been an adaptation to fewer resources and predators. Our population genetic examination identified different patterns of divergence than the morphological examination, indicating that the rate of morphological evolution likely exceeds that represented in this genus' neutral genetic history. This case study highlights the importance of an auteco-logical approach toward examining insular dwarfism given that clear patterns are not visible across the Carnivora.
... For each squirrel captured I recorded sex, body mass in grams, posterior zygomatic breadth (PZB, measured as jaw width— Barnett 1977), and hind-foot length (HFL). HFL is a common index of animal size in several vertebrate species: it does not show acute fluctuations with reproductive status (Iason 1990), reflects skeletal size (i.e., the structural size of an animal, mass or fat deposits or both notwithstanding—Wirsing 2003), can indicate relatively acute changes in population body structure (e.g., Pergams and Ashley 1999), and is an easily acquired metric correlated to many less-measurable body morphologies (Cote et al. 1998; Suttie and Mitchell 1983; Suzuki et al. 2001). Body mass was recorded to the nearest 1 g using a Pesola spring scale (Pesola AG, Baar, Switzerland). ...
Red squirrels (Tamiasciurus) are hypothesized to be coevolving with pinecones (Pinus), whereby squirrel seed predation selects upon cone serotiny and seed number, which in turn select upon squirrel size and strength. I tested the hypothesis that cone morphology produces phenotypic size differentiation in red squirrels (T. hudsonicus). I measured body mass, hind-foot length, and jaw width of squirrels among spruce (smaller soft cones), lodgepole pine (larger serotinous cones), and mixed conifer (both cone types) habitats while controlling for variability in geographic isolation and latitude. I found identical average values among habitats for all body measurements: larger squirrels were not associated with larger tougher cones. Geographic isolation or a latitudinal gradient appear necessary to promote size differentiation in red squirrels, but how these factors interact with habitat (cone morphology) remains to be documented. As such, whether squirrels and pinecones actually are coevolving largely remains speculation.
... Therefore, most parks (or suburban woods) have been isolated for at least several decades. There is a good evidence that rodent populations are able to undergo morphological changes over just a few generations (Berry 1964; Pizzimenti 1981; Pergams and Ashley 1999). However, gene flow may outweigh the selective forces operating on a local scale. ...
We studied the wood mouse, Apodemus sylvaticus, inhabiting parks, cemeteries, suburban woods, and other green areas in the city of Prague. To assess the character displacement and (or) release hypothesis we compared seven samples from local populations occurring sympatrically with Apodemus flavicollis with 10 samples from those localities in which A. flavicollis has never been recorded. The analysis included 1410 specimens of A. sylvaticus collected during the years 1980-1990. Seventeen skull and body characters were measured. Then the data were age- or size-adjusted and treated by principal-component analyses. Factor scores were further subjected to statistical testing. Although the results revealed considerable variation among localities, they did not suggest character displacement and (or) release. Apodemus sylvaticus from populations sympatric with A. flavicollis were morphometrically similar to their conspecifics from other populations collected at the periphery of the city. However, slight but statistically highly significant differences were found between samples from localities in the city centre and those from the periphery. This phenomenon may be interpreted as the effect of urbanisation or isolation by built-up areas.
... Therefore, most parks (or suburban woods) have been isolated for at least several decades. There is a good evidence that rodent populations are able to undergo morphological changes over just a few generations (Berry 1964; Pizzimenti 1981; Pergams and Ashley 1999). However, gene flow may outweigh the selective forces operating on a local scale. ...
We studied the wood mouse, Apodemus sylvaticus, inhabiting parks, cemeteries, suburban woods, and other green areas in the city of Prague. To assess the character displacement and (or) release hypothesis we compared seven samples from local populations occurring sympatrically with Apodemus flavicollis with 10 samples from those localities in which A. flavicollis has never been recorded. The analysis included 1410 specimens of A. sylvaticus collected during the years 19801990. Seventeen skull and body characters were measured. Then the data were age- or size-adjusted and treated by principal-component analyses. Factor scores were further subjected to statistical testing. Although the results revealed considerable variation among localities, they did not suggest character displacement and (or) release. Apodemus sylvaticus from populations sympatric with A. flavicollis were morphometrically similar to their conspecifics from other populations collected at the periphery of the city. However, slight but statistically highly significant differences were found between samples from localities in the city centre and those from the periphery. This phenomenon may be interpreted as the effect of urbanisation or isolation by built-up areas.
... Further, the modest radiation of Peromyscus maniculatus into multiple genetically and morphologically distinct subspecies contributes much to the biodiversity of the islands and makes them an important subject for investigations of evolutionary history and adaptive radiations on the California Islands. It is therefore not surprising that California Island deer mice have been investigated by scientists for a century (Mearns 1897), and that these investigations continue today (Pergams and Ashley 1999; Pergams et al. 2000). The focus of this report will be recent genetic and morphological research on California Island deer mice, but we will begin with a brief review of earlier morphological and genetic investigations. ...
Deer mice, Peromyscus maniculatus, are found on all eight California Channel Islands and are classified as separate subspecies on each island. Distinct mitochondrial DNA haplotypes, identified by restriction enzyme analysis, were found in island deer mice, and on five of the eight islands deer mice have unique haplotypes, suggesting genetic isolation and independent evolution of several island subspecies. Founder effects on mtDNA diversity in island populations relative to mainland populations are evident. The connec-tivity of the deer mouse populations on East, Middle, and West Anacapa Islands (P. m. anacapae) was assessed using sequence data from the mitochondrial cytochrome c oxidase subunit II gene (COII). A common haplotype was found on all three Anacapa Islets, although Middle and East Anacapa each had an additional unique haplotype. This suggests that deer mice on Anacapa are functioning as a metapopulation, with some gene flow or extinction/recolonization occurring among the islets. Discriminant function analysis of cranial and external morphological characters for three island sub-species, P. m. anacapae, P. m. santacruzae, and P. m. elusus, produced a high rate of correct classification, indicating strong morphological as well as genetic differentiation. The specimens used for the morphometric study were museum specimens collected at different times during the past century. A surprising result of the morphological analysis was that each subspecies had exhibited extremely rapid change in several characters over this time period.
... Because island populations may differ morphologically from their mainland counterparts, these populations are frequently considered members of distinct subspecies or even species (e.g. Gonzalez et al., 1996; Pergams & Ashley, 1999; Furness et al., 2010). This assumption of differentiation is plausible given that water represents a barrier to gene flow for many terrestrial, non-volant organisms . ...
Aim
To evaluate whether population genetic structure reflects taxonomic recognition of the endangered Lower Keys marsh rabbit ( Sylvilagus palustris hefneri) and the two mainland subspecies.
Location
Southeastern United States.
Methods
We inferred phylogenetic relationships, population structure and genetic diversity within S. palustris using a mitochondrial gene (cytochrome b) and 10 microsatellite loci.
Results
The cytochrome b sequence data revealed taxonomy-phylogeography incongruence, and microsatellite data revealed moderate structure ( F ST = 0.22) with two genetic clusters recovered: one grouping the western Lower Keys, and the second grouping the eastern Lower Keys together with the mainland. Furthermore, island genetic diversity was not reduced relative to mainland populations (cyt b: π: t = −0.6952, P = 0.5651; h: t = −1.2053, P = 0.4305; microsatellite: H E: t = −4.1201, P = 0.1313; AR : t = −2.3113, P = 0.2441).
Main conclusions
The taxonomy-phylogeny disparity reveals unknown aspects of the evolutionary history including an absence of contemporary dispersal barriers between the mainland subspecies and a more recent Lower Keys isolation than originally thought. Moreover, diversity patterns indicate that undocumented man-mediated transfers may contribute to current genetic structure between eastern Lower Keys and the mainland. Although subspecies designations were not confirmed, these findings support recognition of western Lower Keys populations as a distinct population segment under the Endangered Species Act.
... Conserved specimens are used when live animals are difficult to obtain, or when data is required from large numbers of species or populations , e.g. for comparative analyses. As collections grow older and begin to span significant periods of time, they also offer the fascinating opportunity to observe temporal changes in mean body size and shape, thus allowing direct tests of morphological character plasticity and evolution (e.g. Pergams and Ashley, 1999; Yom-tov, 2003; Millien et al., 2006). One possible hazard of using morphological measurements of museum specimens is that fixation and preservation may deform bodies or body parts. ...
The millions of conserved biological specimens that are stored upon the shelves of Natural History Museums across the world constitute a capital of biological information that is becoming increasingly accessible to students of various disciplines. Most students have taken measures of body size and shape of preserved museum specimens to test various elements of ecological and evolutionary theory. One possible hazard of using morphological measurements of museum specimens is that fixation and preservation may deform bodies or body parts, but most researchers implicitely assume that the magnitude of conservation-induced distortions are insufficient to jeopardize their analyses. However, no study to our knowledge has clearly quantified those possible distortions. In this study, we have measured 17 morphological variables on a set of 65 green iguanas (Iguana iguana), starting shortly after their death and then repeatedly over a two month period, a period during which they were fixated and preserved. Our aims were (1) to quantify and compare the deformation in different morphometrics frequently used in evolutionary studies; (2) to determine the amount of temporal variation that can be attributed to reader variability; and (3) to build conversion equations that should improve the reliability of morphological comparisons of life and conserved specimens. Conserved lizards revealed major reduction in snout vent length and body weight. Changes in other measured traits are more subtle, but persistent. These facts disturb analyses when using relative measurements, especially when comparing (often small) intraspecific differences or even morphological differences within populations in a temporal frame. We urge caution in using museum specimens as direct proxies for living organisms in ecological and taxonomic studies.
... These Northern African metapopulations probably have undergone morphological and genetic differentiation from their Eastern Mediterranean counterparts as a result of long distance colonization patterns in Western Mediterranean, culminating in both founding and stochastic effects (Britton-Davidian, 1990, Bonhomme et al., in press). Several studies on insular populations of mice (Pergams & Ashley, 1999; Britton-Davidian et al., 2000; Pergams, Barnest & Nyberg, 2003) and rodents in general (Millien, 2006) have demonstrated that this diversification process can happen extremely rapidly and is followed by a morphological stasis (Millien, 2006). The similarities that we observe between the house mice of Alorda modern Tunisia, which are assumed to have maintained the phenotypic signature of their evolutionary history, contradict the diversification effect of long distance transfer that we mentioned using the insular model (Millien, 2006). ...
GRACPE), C/ Montalegre 6, E-08001, Barcelona, Spain 3 Muséum national d'Histoire Naturelle, UMR 7205 & Plate-forme Morphométrie UMS 2700, 45 rue Buffon F-75005, Paris, France 4 CNRS – Muséum national d'Histoire naturelle, Département Ecologie et Gestion de la Biodiversité, UMR 7209, Archéozoologie, archéobotanique: sociétés, pratiques et environnements, During the Iron Age, sea trade in the Mediterranean increased, particularly with the expansion of Phoenician and Greek colonies in the Western Mediterranean. A side effect of these human movements was the involuntary dispersion of commensal species, such as the house mouse (Mus musculus domesticus). One archaeological layer dated from the 4th Century BC, coming from an Iberian village located in the Mediterranean coast of Spain, contained a large and reliable accumulation of small mammals. The presence of the house mouse was highly suspected within this layer. To assess its abundance quantitatively, we used a geometric morphometrics approach of the first lower molar contour using elliptical Fourier analysis. We also increased the power of the discrimination between the Algerian mouse (Mus spretus) and the house mouse by combining a dimension reduction approach together with different validation procedures. The relative importance of age, sex, and geographical origin onto the shape and form of the lower molar contour was also investigated. The results obtained demonstrate the presence and the dominance of the house mouse in the landscape surrounding the Iberian village in the 1st Millennium BC, only a few centuries after its arrival in the Western Mediterranean Basin. A cross-validated linear discri-minant function considering different Mediterranean populations suggest Morocco and France as the most probable geographical origins for the Algerian mouse, and Tunisia for the origin of house mice in North-Eastern Spain.
... In addition, the morphological divergence exhibited by Mus cypriacus which involves both an increase in cranial size and shape changes suggests that it is not a simple case of macrodonty such as those mentioned above. Considering that morphological modifications of island mice and rats can occur in only a few centuries (Atchley, et al., 1982; Pergams & Ashley, 1999;, the extent of this differentiation can be attributed to the long period of isolation of Mus cypriacus on this island. ...
The house mouse (Mus musculus domesticus) and the short-tailed mouse of the eastern Mediterranean
area (M. macedonicus) were thought to live sympatrically on Cyprus Island. Recently, a phylogenetic
survey has shown that the non-commensal mouse of Cyprus was an unknown sister
species of European wild mice. Here, we describe this new species of the genus Mus (Rodentia,
Mammalia), namely Mus cypriacus sp. n., based on 19 specimens trapped in the southern part of
Cyprus. These animals were first compared to Eurasian species of mice using both molecular genetics
(complete D-loop sequences and nuclear gene intron) and cytogenetics to state on its systematic
status. Then classical and geometric morphometric analyses on both cranial and dental characters have been performed to compare Mus cypriacus with circum-Mediterranean species and provide
diagnositic morphological characters. Genetic data strongly support a sister species relationship of
the new species to M. macedonicus, the closest mainland taxon. Morphometric analyses provide
satisfying criteria for diagnosis of this species relative to other Mediterranean species. The most
obvious phenotypic characteristics are its long tail and the allometric gigantism and shape robustness
of its cranial and dental characters compared to other Mediterranean mice. The molecular
clock and the history of the murine settlement on Cyprus are congruent and suggest that the common
ancestor of M. cypriacus and M. macedonicus arrived on Cyprus during the Middle Pleistocene
by a founder event on natural raft. The remoteness of Cyprus through time has prevented
introgression from the mainland gene pool, and favoured phenotypic adaptation to competition
release, leading to the allopatric speciation of M. cypriacus.
... Captive Peromyscus polionotus exhibit increased variance in response to cues of predators even over relatively short spans, suggesting the loss of anti-predator behavior can begin in 14?35 generations in congeneric rodents (McPhee 2003 ); although it is interesting to note that this response was to a visual, rather than olfactory cue. Moreover, rodents from the Channel Islands exhibit morphological evolution over 40-to 50-yr time spans (Pergams & Ashley 1999). As such, rapid evolution in this system is clearly possible, but anti-predator behavior of deer mice on San Miguel Island remains evident despite the short-term removal on historically fox-containing San Miguel Island. ...
Anti-predator behavior can alter the dynamics of prey populations, but little is known about the rate at which anti-predator behavior is lost from prey populations following predator removal. The Channel Islands differ in whether they have historically contained a top predator, the Island Fox (Urocyon littoralis), in evolutionary time (approximately 6200–10 000 yr). On a historically fox-containing island and two historically fox-free islands in 2007, I deployed live traps that contained olfactory cues of fox predators (fox feces), olfactory cues of an herbivore (horse feces) or a no-feces control. Due to a captive breeding program, foxes on the historically fox-containing island were effectively removed from 1998 to 2004. Rodents from one of the historically fox-free islands did not respond to fox cues, whereas rodents on the historically fox-containing island were more likely to be captured in a control trap and less likely to be captured in a fox-cue trap. Results from the other historically fox-free island that experienced a recent population bottleneck and period of captive rearing exhibited a preference for horse-scented traps. These results suggest that, on islands where foxes are the primary predators, anti-predator behavior in response to olfactory cues is not likely to be rapidly lost by short-term removals of foxes, although the nature of anti-predator behavior may depend upon founder events and recent population dynamics (e.g. population bottlenecks or several generations in captivity).
... The tempo of body size evolution on islands is not as well studied as the mode. Some authors reported cases of fast body size evolution on islands (Lister 1989; Chiba 1999; Pergams and Ashley 1999; Clegg et al. 2002; Millien 2006). For instance, Pergams and Ashley (1999) estimated that rate of morphological change in insular deer mice Peromyscus maniculatus in California Channel Islands: " dramatically exceed those estimated from paleontological records and are even higher than those reported in some experimental selection studies. ...
The tempo and mode of body size evolution on islands are believed to be well known. It is thought that body size evolves relatively quickly on islands toward the mammalian modal value, thus generating extreme cases of size evolution and the island rule. Here, we tested both theories in a phylogenetically explicit context, by using two different species-level mammalian phylogenetic hypotheses limited to sister clades dichotomizing into an exclusively insular and an exclusively mainland daughter nodes. Taken as a whole, mammals were found to show a largely punctuational mode of size evolution. We found that, accounting for this, and regardless of the phylogeny used, size evolution on islands is no faster than on the continents. We compared different selection regimes using a set of Ornstein-Uhlenbeck models to examine the effects of insularity of the mode of evolution. The models strongly supported clade-specific selection regimes. Under this regime, however, an evolutionary model allowing insular species to evolve differently from their mainland relatives performs worse than a model that ignores insularity as a factor. Thus, insular taxa do not experience statistically different selection from their mainland relatives.
... The difference in primary projection between mature forest species and open/ shrub species supports this idea, but the lack of temporal trends in culmen length in species found outside mature boreal forests is inconsistent with the idea that changes in foraging strategy are the main driving force behind temporal trends in wing shape. Museum specimens have been used previously to document rapid evolutionary change in birds (Smith et al. 1995) and mammals (Pergams and Ashley 1999). However, museum specimens remain a relatively untapped data source that could provide key information relevant to the fate of birds and other species in response to rapidly changing environments. ...
Major landscape changes caused by humans may create strong selection pressures and induce rapid evolution in natural populations. In the last 100 years, eastern North America has experienced extensive clear-cutting in boreal areas, while afforestation has occurred in most temperate areas. Based on museum specimens, I show that wings of several boreal forest songbirds and temperate songbirds of non-forest habitats have become more pointed over the last 100 years. In contrast, wings of most temperate forest and early-successional boreal forests species have become less pointed over the same period. In contrast to wing shape, the bill length of most species did not change significantly through time. These results are consistent with the "habitat isolation hypothesis", i.e., songbirds evolved in response to recent changes in the amount of available habitat and associated implications for mobility. Rapid morphological evolution may mitigate, without necessarily preventing, negative consequences of habitat loss caused by humans through direct exploitation or climate change.
... Furthermore, many factors are not mutually exclusive and evolutionary changes initially resulting from genetic drift within small founding populations may also provide the impetus for selection to drive phenotypic evolution towards a different adaptive peak[6]. The combination of both adaptive and nonadaptive forces acting concurrently may produce especially rapid rates of phenotypic evolution when compared to mainland source populations[7,8]. Although many extreme modifications to behavior and morphology among island populations seem unique and systemspecific, large-scale patterns are also evident and attest to common underlying evolutionary processes. ...
Background:
Speckled rattlesnakes (Crotalus mitchellii) inhabit multiple islands off the coast of Baja California, Mexico. Two of the 14 known insular populations have been recognized as subspecies based primarily on body size divergence from putative mainland ancestral populations; however, a survey of body size variation from other islands occupied by these snakes has not been previously reported. We examined body size variation between island and mainland speckled rattlesnakes, and the relationship between body size and various island physical variables among 12 island populations. We also examined relative head size among giant, dwarfed, and mainland speckled rattlesnakes to determine whether allometric differences conformed to predictions of gape size (and indirectly body size) evolving in response to shifts in prey size.
Methodology/principal findings:
Insular speckled rattlesnakes show considerable variation in body size when compared to mainland source subspecies. In addition to previously known instances of gigantism on Angel de la Guarda and dwarfism on El Muerto, various degrees of body size decrease have occurred frequently in this taxon, with dwarfed rattlesnakes occurring mostly on small, recently isolated, land-bridge islands. Regression models using the Akaike information criterion (AIC) showed that mean SVL of insular populations was most strongly correlated with island area, suggesting the influence of selection for different body size optima for islands of different size. Allometric differences in head size of giant and dwarf rattlesnakes revealed patterns consistent with shifts to larger and smaller prey, respectively.
Conclusions/significance:
Our data provide the first example of a clear relationship between body size and island area in a squamate reptile species; among vertebrates this pattern has been previously documented in few insular mammals. This finding suggests that selection for body size is influenced by changes in community dynamics that are related to graded differences in area over what are otherwise similar bioclimatic conditions. We hypothesize that in this system shifts to larger prey, episodic saturation and depression of primary prey density, and predator release may have led to insular gigantism, and that shifts to smaller prey and increased reproductive efficiency in the presence of intense intraspecific competition may have led to insular dwarfism.
... We should note that a preponderance of Cricetidae and Muridae exists in museum collections overall: for example 67.5% of all Rodentia specimens at the National Museum are Cricetidae and Muridae. Data from Channel Island deer mice [6], [27]–[28] and Chicago-area white-footed mice [11] were included. By continent, 13 cases were from North America (US, including Alaska), 11 from South America (Chile, Mexico, and Peru), three from Africa (Kenya), and one from Asia (Philippines). ...
In general, rapid morphological change in mammals has been infrequently documented. Examples that do exist are almost exclusively of rodents on islands. Such changes are usually attributed to selective release or founder events related to restricted gene flow in island settings. Here we document rapid morphological changes in rodents in 20 of 28 museum series collected on four continents, including 15 of 23 mainland sites. Approximately 17,000 measurements were taken of 1302 rodents. Trends included both increases and decreases in the 15 morphological traits measured, but slightly more trends were towards larger size. Generalized linear models indicated that changes in several of the individual morphological traits were associated with changes in human population density, current temperature gradients, and/or trends in temperature and precipitation. When we restricted these analyses to samples taken in the US (where data on human population trends were presumed to be more accurate), we found changes in two additional traits to be positively correlated with changes in human population density. Principle component analysis revealed general trends in cranial and external size, but these general trends were uncorrelated with climate or human population density. Our results indicate that over the last 100+ years, rapid morphological change in rodents has occurred quite frequently, and that these changes have taken place on the mainland as well as on islands. Our results also suggest that these changes may be driven, at least in part, by human population growth and climate change.
... Multivariate discrimination between morphotypes using a specific set of characters is widely used, for example in the identification of Colorado fish species (Douglas et al . 1998) and in the separation of Californian Channel Island deer mouse populations (Pergams & Ashley 1999); a study that also demonstrates how the optimal set of selected characters can change over small evolutionary time. Hence, in this study we sought to use a selective approach with AFLP data in order to isolate a suite of characters (genetic markers) from the total character set that contain the clearest population signal. ...
Fine-level taxon discrimination is important in biodiversity assessment and ecogeographical research. Genomic markers are often required for studies on closely related taxa, however, most existing mitochondrial and nuclear markers require prior knowledge of the genome and are impractical for use in small conservation projects. This study describes the application of amplified fragment length polymorphism (AFLP) to discriminate at four progressively finer evolutionary levels of Caribbean Anolis lizards from the central Lesser Antilles. AFLP is shown to be a rapid and effective method for discriminating between species. Separation increases with primer pair number and choice of primer combination appears to be noncritical. Initial population-level results show markedly less discriminatory power. A screening technique for the identification of population informative markers combining principal component and principal coordinate analyses is presented and assessed. Subsequent results show selected conspecific AFLP data to be remarkably congruent with those of mitochondrial DNA, microsatellite and morphological markers. The use of AFLP as a low-cost nuclear marker in species-level taxon discrimination is supported, whereas population level application demands further consideration.
... Resource limitation may also explain body size changes in some island species. In addition, morphological changes in some island mammals have been shown to occur rapidly1112131415. The fossil record suggests that island species adapt to their new environment rapidly following isolation, through conspicuous changes in size and morphology [5,16]. ...
Dramatic evolutionary changes occur in species isolated on islands, but it is not known if the rate of evolution is accelerated on islands relative to the mainland. Based on an extensive review of the literature, I used the fossil record combined with data from living species to test the hypothesis of an accelerated morphological evolution among island mammals. I demonstrate that rates of morphological evolution are significantly greater--up to a factor of 3.1--for islands than for mainland mammal populations. The tendency for faster evolution on islands holds over relatively short time scales--from a few decades up to several thousands of years--but not over larger ones--up to 12 million y. These analyses form the first empirical test of the long held supposition of accelerated evolution among island mammals. Moreover, this result shows that mammal species have the intrinsic capacity to evolve faster when confronted with a rapid change in their environment. This finding is relevant to our understanding of species' responses to isolation and destruction of natural habitats within the current context of rapid climate warming.
Mammals are predicted to vary in body size following Bergmann’s rule, with individuals found at higher latitudes in colder temperatures being larger in size compared to conspecifics occurring at lower latitudes in warmer temperatures. Body size is similarly expected to vary temporally, with a decrease in size through time due to recent climate warming. While Bergmann’s rule is well-supported in mammals, there is increasing evidence of exceptions to the rule. Here, we present patterns of size variation in 17 North American mammal species using five morphological traits (condylobasal skull length, skull width, maxillary toothrow length, body weight, and head-and-body length) to determine if size varies predictably for each species in space and time. We found little support for a widespread Bergmannian pattern for these species at a broad spatial scale (across North America) and a contemporary temporal scale (the past 120 years). The effects of latitude or year on each trait were highly variable with three types of responses: an increase, a decrease, or no change in size across space or through time. Spatial size trends were detected more often than temporal size trends, as the temperature range was significantly larger in space than through time. Body weight (the most variable trait) and head-and-body length were more likely to conform to Bergmann’s rule than craniodental measurements. We did not detect any changes in size variability with latitude, and our study species either increased or decreased in size variability over time. Our findings demonstrate that size variation in mammals is highly context-dependent. As such, caution is needed when using rules of body size variation to predict the future response of species to climate warning while valid in theory, it is likely too simplistic of an approach.
We report photo documentation of a newly discovered fur variation on the face of American Deer Mice, Peromyscus maniculatus, in populations across northern Nevada. American Deer Mice usually have all-brown facial fur with dark-colored ears, whereas these novel records show white fur patches at the base of the ears, sometimes with bicolored ears and white fur extending behind, and more rarely with a white strip of fur down the middle of the face. Across all field sites, we captured 1685 Deer Mice; of these, 216 had some variation of the white facial fur patterns. These facial patterns are most prominent in northeastern Nevada, comprising 13 to 16% of all Deer Mice captured.
The white-footed deer mouse (Peromyscus leucopus) and the North American deer mouse (P. maniculatus) are widely distributed throughout North America, often with overlapping distributions. These species are believed to be sympatric east of the Balcones fault zone in Texas, but records from natural history collections indicate that P. maniculatus is not common from this region. Given that these two species are notoriously difficult to differentiate morphologically, it is possible that specimens have been incorrectly identified and that P. maniculatus may be rare or not present in East Texas. This study aims to determine if P. leucopus and P. maniculatus can be differentiated morphologically east of the Balcones fault zone in Texas. Cranial and external characters from genetically identified specimens representing each species were analyzed using traditional and geometric morphometric methods. Morphological analyses revealed that genetically identified specimens of P. leucopus and P. maniculatus from east of the Balcones fault zone could be differentiated using a suite of morphological characters. Many of the specimens of P. leucopus used in this study were originally misidentified, suggesting that P. maniculatus is rare in East Texas.
Santa Cruz Island (SCI) is the largest, most topographically diverse, most speciose, least disturbed, and most intensively researched of the eight California Channel Islands. However, this natural laboratory has itself changed significantly in the recent past, and determining where limited research and management funds should be allocated is a significant issue that will determine the course of research and conservation on all of the Channel Islands.
Santa Cruz Island has undergone a significant transformation in the past two decades. Large introduced herbivores such as cattle, sheep and pigs that roamed the island for over a century have been completely removed. As such, the island is in a transition phase from one where vegetation communities and their associated fauna are controlled and limited by ungulate impacts to one where the vegetation is largely controlled by bottom- up processes such as edaphic controls, weather events, and interspecific competition. The fauna is likewise adapting to the removal of a significant terrestrial predator in feral pigs. The response of amphibians, reptiles, ground-nesting birds, and small mammals to the removal of pigs is likely to be significant, and in many cases surprising. While many decades of research have been conducted, the island is now significantly changed, and new questions and management issues will need to be addressed.
A wide diversity of literature has been produced from studies of the island over the past fifty years, including island biogeography (Diamond 1971, Jones and Diamond 1976), vegetation community evolution (Axelrod 1965), and even the biocontrol of native species (Goeden et al. 1967, Goeden and Ricker 1980). Klinger and Van Vuren (2000) reviewed and analyzed the articles published in the four symposia on California Islands that had been held. They provided a series of recommendations including 1) place research and management projects in an appropriate theoretical framework; 2) link genetic, demographic, and evolutionary studies across all of the islands; 3) continue basic life history studies of both plant and animal species; and 4) conduct ecosystem studies that integrate community and single species studies at multiple scales. The need for the fourth recommendation was recently demonstrated by the finding that restoration methods suitable at small scales had different results at larger scales (Ogden and Rejmanek 2005).
In our analysis and recommendations below, we are mindful of the importance of long-term research, and of the value of studies that provide datasets that have lasting utility. Therefore, while it is important to recognize the latest conceptual paradigms in a given field, we feel that scarce conservation-oriented funding for island projects are best spent answering specific questions that have practical conservation and management utility. We also feel that management dollars are best spent conducting long-term monitoring of species and communities, rather than short-term small-scale studies. One method for extending out the time frame of a study is by using historical papers and other data sets as comparisons for recently collected data. For instance, Yeaton (1974) provides abundance estimates for bird species in pine forest and chaparral habitats that could be compared with more recent values, and Bjorndalen (1978) provides vegetation community data that could be compared to more recent, post-ungulate samples.
A significant finding of this research effort was that a substantial amount of data exists in various institutions, but has yet to be analyzed due to lack of funding. For instance, many thousands of Channel Island plant specimens exist in some collections that have yet to be catalogued due to insufficient funding and staff time. Likewise, entomological collections at several institutions contain untold numbers of Santa Cruz Island specimens, yet these institutions have not electronically databased their collections. These collections are organized systematically, and retrieving the data for a given geographic area such as Santa Cruz Island entails examining all the specimens for each systematic group of organisms that may occur on the island. Providing financial support for efforts to make these data available to researchers—data that have already been collected during past field work—would provide a substantial contribution to our understanding of the ecology of the island, at relatively low cost.
Genetic studies have shown that New York City white-footed mouse (Peromyscus leucopus) populations exhibit substantial genetic structure and high levels of allelic diversity and heterozygos-ity. These studies have also identified mutations and genes involved in the divergence of urban and rural P. leucopus populations. To investigate whether morphological change mirrors the genetic differentiation observed in New York City P. leucopus populations, we conducted univariate and multivariate analyses on 4 external and 14 skull variables to compare urban, suburban and rural P. leucopus populations from in and around New York City. The only significant morphological differences among the three populations were in upper and lower toothrow lengths, both of which had high loadings in our principal components analyses. In general, rural individuals were found to have longer upper and lower toothrows than urban ones. This difference is likely due to the relationship between food quality and size of dental occlusal surfaces. Generally, lower-quality food requires more chewing and its consumption is facilitated by larger occlusal surfaces. Our results suggest that urban mice consume a higher-quality diet or food that requires less chewing than their rural counterparts by making use of the availability of natural food sources in rich, vegetative understories characteristic of urban forest fragments. Our cluster analysis of the skull variables revealed that urban and suburban populations are more similar to one another than to the rural population.
The gray-sided vole, Myodes rufocanus (= Clethrionomys rufocanus) is a widespread species in Hokkaido, Japan. We applied an integrative approach to determine adaptive and neutral genetic variation in the gray-sided vole populations to identify full or partial Evolutionarily Significant Units. We surveyed 38 mainland populations and six island populations. The mitochondrial DNA control region was analyzed for neutral genetic variation and cranial measurements were taken as a proxy for adaptive variation. Data on neutral genetic variation indicate that most island populations are differentiated from the mainland populations. The islands of Teuri and Yagishiri, Rishiri and, Kunashiri can be regarded as partial ESUs based on their unique haplotypes. Partial ESUs based on morphological features can be identified in the eastern part of mainland with populations from Akkeshi and Shibecha. A full ESU designation can be given to Daikoku Island based on its unique haplotype and unique morphological feature.
The genus Cerradomys, comprising eight species, is distributed mainly in transitional, dry, open and inland South American biomes like Caatinga, Cerrado, and Chaco. However, Cerradomys goytaca is restricted to very harsh ecosystems along the Quaternary coast sandy plains (restingas) of the Rio de Janeiro and Espírito Santo states, in southeastern Brazil. Cytochrome b and IRBP DNA data were used for elucidating the phylogenetic relationships of Cerradomys and estimating the time of divergence of different evolutionary lineages, while morphometric analyses were carried out for analyzing the rate of phenotypic evolution. Our findings showed that the first speciation events occurred in the Pliocene and early Pleistocene, leading to the C. marinhus, C. maracajuensis, and C. scotti distributed in central and western Brazil while species from eastern Brazil (C. langguthi, C. vivoi, C. subflavus, and C. goytaca) originated in the middle to late Pleistocene. Cerradomys goytaca populations diverged from inland C. subflavus ca. 0.29 MYBP with an accelerated rate of phenotypic evolution resulting in unique craniometric attributes, likely due to the strong selective pressures imposed by harsh habitats.
Recently, there has been a growing interest for rapid evolution and its potential role in ecological processes. For example, it has been hypothesized that rapid adaptation is a factor favoring the establishment of invasive species in new environments. If this hypothesis is true, it could have implications in the management and prevention of biological invasions. In vertebrates, lots of studies report cases of rapid phenotypic changes in invasive species following their introduction in a novel environment. However, because of the difficulties of directly testing for adaptation, very few of them were able to prove that these phenotypic changes result from rapid adaptation. In this thesis, we were thus interested in assessing whether rapid adaptation can explain phenotypic changes observed in recently introduced populations. Instead of directly testing for adaptation, we tested for alternative hypotheses, which are easier to investigate. Indeed, a phenotypic difference observed between populations established in different environments can be caused by natural selection but also by phenotypic plasticity, by a different phylogenetic origin and by stochastic evolution (i.e. stochastic changes in allele frequencies in a population as the result of demographic processes such as founder effects and bottlenecks). Here, we studied two successful invasive bird species introduced in several kinds of environments. We described the morphology of individuals in these populations, and tested for the effects of historical factors (i.e. phylogenetic origin and recent demographic history) to explain morphological differences observed between populations. In both species, our results show that stochastic evolution resulting of recent demographic history is likely to be the cause of the morphological differences observed. This was true for all the cases we studied except one. In this last case, neither a difference in phylogenetic origin, nor stochastic evolution could explain de phenotypic differences observed between two environments. It is therefore possible that rapid adaptation occurred in this case but the hypothesis of phenotypic plasticity remains to be tested. In conclusion, with this work we highlighted that recent demographic processes can have an important role in causing morphological differentiation in invasive species. This role was probably underestimated in studies on rapid adaptation and should be taken into account in the future. We also showed that the comparative approach we used can allow identifying possible cases of rapid adaptation by first rejecting alternative hypotheses.
Rapid morphological change has been shown in rodent populations on islands, including endemic deer mice (Peromyscus maniculatus subspp.) on the California Channel Islands. Surprisingly, most of these changes were towards a smaller size. Black rats were introduced to Anacapa Island in the mid-1800s (probably in 1853) and eradicated in 2001–2002. To assess possible changes in these rats since their introduction, eleven cranial and four standard external measurements were taken from 59 Rattus rattus specimens collected from 1940–2000. All rat cranial traits changed 3.06–10.43% (724–2567 d, 0.06–0.42 h), and all became larger. When considered in haldanes, these changes are among the fastest on record in any organism, and far exceed changes found in other island rodents. These changes were confirmed by MANOVA (Wilk’s
λ < 0.0005, Fd.f.15 = 2974.386, P < 0.0005), and all 11 cranial traits significantly fit linear regressions. We speculate that concurrent changes in mice may have been due in part to competition with and/or predation by rats. Future research might evaluate whether the vector of mouse evolution on Anacapa is again changing after rat eradication.
Temporal variation in selection is typically evaluated by estimating and comparing selection coefficients in natural populations. Meta-analyses of these coefficients have yielded important insights, but selection coefficients are limited in several respects, including low statistical power, imperfect fitness surrogates, and uncertainty regarding consequences for trait change. A complementary approach without these limitations is to examine temporal variation in adaptive traits themselves, which is mechanistically easier and more directly relevant to evolutionary consequences. We illustrate this approach by analyzing the colour patterns of male guppies, Poecilia reticulata, from each of six sites in Trinidad in each of 6 years. This system is particularly appropriate for our study because key aspects of colour variation are genetically-based and responsive to selection. However, although spatial patterns of colour variation have been extensively considered in this system, no study has yet formally assessed annual temporal variation in non-manipulated populations. Matching previous conclusions for the guppy system, we find that guppies from different sites manifest different colour patterns in association with different predation regimes. We here add the new finding that, although some temporal variation is present, spatial patterns of colour variation are generally consistent across years. These results suggest that, when considering adaptive traits, spatial variation is more important than temporal variation, although our study system might be exceptional in this regard. Additional studies examining spatiotemporal variation in adaptive traits could help to improve our understanding of the role that spatiotemporal variation in selection plays in the evolutionary process. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, ●●, ●●–●●.
Aim We assessed the generality of the island rule in a database comprising 1593 populations of insular mammals (439 species, including 63 species of fossil mammals), and tested whether observed patterns differed among taxonomic and functional groups.
Location Islands world-wide.
Methods We measured museum specimens (fossil mammals) and reviewed the literature to compile a database of insular animal body size (Si = mean mass of individuals from an insular population divided by that of individuals from an ancestral or mainland population, M). We used linear regressions to
investigate the relationship between Si and M, and ANCOVA to compare trends among taxonomic and functional groups.
Results Si was significantly and negatively related to the mass of the ancestral or mainland population across all mammals and within all orders of extant mammals analysed, and across palaeo-insular (considered separately) mammals as well. Insular body size was significantly smaller for bats and insectivores than for the other orders studied here, but significantly larger for mammals
that utilized aquatic prey than for those restricted to terrestrial prey.
Main conclusions The island rule appears to be a pervasive pattern, exhibited by mammals from a broad range of orders, functional groups and time periods. There remains, however, much scatter about the general trend; this residual variation may be highly informative as it appears consistent with differences among species, islands and environmental characteristics hypothesized to influence body size evolution in general. The more pronounced gigantism and dwarfism of palaeo-insular mammals, in particular, is consistent with a hypothesis that emphasizes the importance of ecological interactions (time in
isolation from mammalian predators and competitors was 0.1 to > 1.0 Myr for palaeo-insular mammals, but < 0.01 Myr for extant populations of insular mammals). While ecological displacement may be a major force driving diversification in body size in high-diversity biotas, ecological release in species-poor biotas often results in the convergence of insular mammals on the size of intermediate but absent species.
Morphological variation was examined in large Japanese field mice, Apodemus speciosus, of five populations from the Izu Islands (from Oshima, Shikinejima, Niijima, Kozushima and Miyakejima), four from the Oki Islands (from Dogo, Nishinoshima, Nakanoshima and Chiburijima), and four from the Japanese mainland of Honshu. Univariate and multivariate (PCA) analyses were conducted on the basis of body-, mandible-, and molar-measurements. Overall, the insular mice had a tendency toward gigantism, and also showed marked morphological differentiation among the islands. The sizes of the mandible and molar were inversely correlated to island area and temperature, thus suggesting a selective effect. Although faunal diversity might be related to the morphological variation in size, there was no clear relationship between the morphological variation and biotic factors such as predation and competition. The populations from the Izu Islands underwent marked morphological divergence, suggesting founder effects. The Izu Island are oceanic and have probably never been connected with Honshu, hence mice were likely transported from Honshu. On the other hand, the Oki Islands had been connected with Honshu in the late Pleistocene. The founders of the insular mice related to the history of the islands could have likely affected the morphological variation.
Aim This paper examines body size variation in both recent and Quaternary populations of the Japanese field mouse Apodemus argenteus in order to assess the relative effects on body size of climate change, isolation and competitive interactions with its congeneric A. speciosus. Both temporal (since the Last Glacial Maximum, LGM) and spatial (over the Japanese archipelago) scales are considered.
Location The small field mouse is widespread in Japan, and the specimens examined were collected from 10 localities on islands of widely differing area (from 4 km2 to 230,510 km2) and at latitudes ranging from 30.3° N to 45.1° N.
Methods The effects of geographical factors such as latitude and island area on the size variation of A. argenteus were investigated, using the lower incisor size. In addition, the size of some specimens from two Quaternary localities was compared with the size of the extant specimens. Evolutionary rates of size change since the LGM were calculated in darwins. Hutchinson size ratios were used to examine the pattern of variation of the size segregation between the two Japanese field mice, A. argenteus and A. speciosus, in relation to time and space.
Results There was a negative relationship between size and latitude among living A. argenteus populations. In addition, there was no effect of island area on body size, especially at higher latitudes. At lower latitudes, A. argenteus were larger on smaller islands, although this trend was not statistically significant. Quaternary specimens of A. argenteus were smaller in size than their living representatives. The interspecific size ratio between the two Japanese Apodemus was larger on smaller islands and at higher latitudes, and there has been a decrease in the size ratio between the two Apodemus since the LGM. Lastly, in accordance with the theory of character displacement, the small A. argenteus was larger in allopatry than in sympatry, whereas the large A. speciosus was smaller in allopatry than in sympatry.
Main conclusions These results indicate that A. argenteus does not conform to Bergmann's rule or to the island rule. The variation in size for the small Japanese field mouse at both spatial and temporal scales may be related to climate change, with an additional effect of competition with the large field mouse, especially on smaller islands. The size convergence between the two Japanese Apodemus observed over the last 21,000 years may be explained by the diminution of available food resources due to the reduction of land mass areas following the LGM. It may also be the result of an evolution towards an optimal body size; a hypothesis previously proposed to explain the evolution of body size in island mammals. Lastly, the evolutionary rates of body size calculated for A. argenteus since the LGM are typical of rates calculated for other Quaternary mainland mammals, thus suggesting that the evolution in this species was not particularly rapid, as is often thought for island mammals.
Artificially selected qualities can reduce fitness in a wild setting, thus feral domesticates should experience strong selective forces. Domestic sheep Ovis aries have frequently become feral on islands, which differ substantially from mainland environments. We examined changes in body mass and wool traits in feral sheep inhabiting Santa Cruz Island (SCI), California for ≥90 years. To elucidate the influence of nutrition, we compared the mass of feral island sheep with that of island sheep raised in farm conditions. We found that feral sheep on SCI were smaller than purported founder breeds, and that most documented populations of insular feral sheep worldwide have converged to similar body sizes (within 6 kg). SCI rams attained greater mass in farm conditions but ewes did not, suggesting phenotypic plasticity in ram body mass. Ewes exhibited self-shedding of wool at a greater frequency than rams, and sex differences and shedding patterns were consistent with thermoregulation and the risk of fly strike disease as benefits of wool loss. Pigmentation rates did not increase, further supporting the influence of heat stress on wool traits. These changes occurred in <25 generations and may have had a genetic basis, representing a potential example of rapid evolution in insular feral sheep.
Introduced species have the potential to outperform natives in two primary ways: via increased rates of predation and competition, and via the introduction of new parasites against which native species often lack effective immune defences. To assess the extent to which invasive species’ parasites spread to native hosts, we compared the composition of helminth parasites found in introduced black rat (Rattus rattus) and endemic deer mouse (Peromyscus maniculatus) populations on a subset of the California Channel Islands. Results suggest that the whipworm, Trichuris muris, may have spread from introduced black rats to endemic island deer mice and has continued to thrive in one island population where rats were recently eradicated. These results yield two important conservation messages: (1) although the parasites introduced with invasive species may be few, they should not be ignored as they can spread to native species, and (2) introduced parasites have the potential to remain in a system even after their founding host is extirpated. These findings underscore the importance of parasitological surveys in invasive species research and baseline data for ecosystems where exotic species are likely to invade.
We compiled a database of microevolution on contemporary time scales in nature (47 source articles; 30 animal species), comprising
2649 evolutionary rates in darwins (proportional change per million years) and 2151 evolutionary rates in haldanes (standard
deviations per generation). Here we demonstrate how quantitative rate measures can provide general insights into patterns
and processes of evolution. The frequency distribution of evolutionary rates was approximately log-normal, with many slow
rates and few fast rates. Net selection intensities estimated from haldanes were on average lower than selection intensities
commonly measured directly in natural populations. This difference suggests that natural selection could easily accomplish
observed microevolution but that the intensities of selection typically measured in nature are rarely maintained for long
(otherwise observed evolutionary rates would be higher). Traits closely associated with fitness (life history traits) appear
to evolve at least as fast as traits less closely tied to fitness (morphology). The magnitude of evolutionary difference increased
with the length of the time interval, particularly when maximum rates from a given study were considered. This pattern suggests
a general underlying tendency toward increasing evolutionary diversification with time. However, evolutionary rates also tended
to decrease with time, perhaps because longer time intervals average increasingly disparate rates over time, or because evolution
slows when populations approach new optima or as genetic variation is depleted. In combination, our results suggest that macroevolutionary
transitions may ultimately arise through microevolution occasionally ‘writ large’ but are perhaps temporally characterized
by microevolution ‘writ in fits and starts’.
Key wordscontemporary evolution–darwins–evolutionary rates–genetic variation–haldanes–microevolution–rapid evolution–selection
The island fox (Urocyon littoralis) is one of few reportedly endemic terrestrial mammals on California's Channel Islands. Questions remain about how and when foxes first colonized the islands, with researchers speculating on a natural, human-assisted, or combined dispersal during the late Pleistocene and/or Holocene. A natural dispersal of foxes to the northern Channel Islands has been supported by reports of a few fox bones from late Pleistocene paleontological localities. Direct AMS 14C dating of these “fossil” fox bones produced dates ranging from ∼ 6400 to 200 cal yr BP, however, postdating human colonization of the islands by several millennia. Although one of these specimens is the earliest securely dated fox from the islands, these new data support the hypothesis that Native Americans introduced foxes to all the Channel Islands in the early to middle Holocene. However, a natural dispersal for the original island colonization cannot be ruled out until further paleontological, archaeological, and genetic studies (especially aDNA [ancient DNA]) are conducted.
Island mammals often display remarkable evolutionary changes in size and morphology. Both theory and empirical data support the hypothesis that island mammals evolve at faster rates than their mainland congeners. It is also often assumed that the island effect is stronger and that evolution is faster on the smallest islands. I used a dataset assembled from the literature to test these assumptions for the first time. I show that mammals on smaller islands do indeed evolve more rapidly than mammals on larger islands, and also evolve by a greater amount. These results fit well the theory of an evolutionary burst due to the opening of new ecological opportunities on islands. This evolutionary burst is expected to be the strongest on the smallest islands where the contrast between the island and the mainland environments is the most dramatic.
Environmental variation over a species's range creates differing pressures to which organisms must adjust in order to survive. Taxa can respond to these pressures at population and individual levels, leading to localized phenotypic differentiation. Assessing the spatial distribution of phenotypic variation can illuminate how dramatically varying environmental factors shape phenotypes and may forecast a taxon's ability to adapt should conditions change. We characterized morphological variation along a transect sampled in the Grinnell Resurvey project to determine whether Gambel's white-footed mouse (Peromyscus maniculatus gambelii), a generalist taxon inhabiting the full elevational range of habitats in Yosemite National Park and surrounding areas, has responded morphologically to variation in its environment. We quantified variation in modern P. m. gambelii cranial shape using 2D generalized Procrustes analysis and Euclidean distance matrix-based geometric morphometrics. We performed multivariate regression of shape coordinates on elevation to test for environmental influences on shape within the principal geographic dimension of change along the transect. We observe a statistically significant correlation with shape on elevation for occlusal and lateral views of the cranium, explaining a small percentage of the overall variation in shape. Modern P. m. gambelii crania show a pattern of flexion in which the angle of the cranial base decreases at higher elevations. Results of EDMA parallel these findings, but highlight additional areas of the cranium that vary with elevation. Collectively, the patterns of variation detected suggest a biological response to the environment that warrants further study. This work lays the foundation for comparison with morphological data from historical specimens, which can address evolutionary scenarios generated from our findings, and for investigation of other taxa included in the resurvey project.
In 1912, Franz Boas published a study demonstrating the plastic nature of the human body in response to changes in the environment. The results of this study have been cited for the past 90 years as evidence of cranial plasticity. These findings, however, have never been critiqued thoroughly for their statistical and biological validity. This study presents a reassessment of Boas' data within a modern statistical and quantitative genetic framework. The data used here consist of head and face measurements on over 8,000 individuals of various European ethnic groups. By using pedigree information contained in Boas' data, narrow sense heritabilities are estimated by the method of maximum likelihood. In addition, a series of t tests and regression analyses are performed to determine the statistical validity of Boas' original findings on differentiation between American and European-born children and the prolonged effect of the environment on cranial form. Results indicate the relatively high genetic component of the head and face diameters despite the environmental differences during development. Results point to very small and insignificant differences between European- and American-born offspring, and no effect of exposure to the American environment on the cranial index in children. These results contradict Boas' original findings and demonstrate that they may no longer be used to support arguments of plasticity in cranial morphology.
As stated by the island rule, small mammals evolve toward gigantism on islands. In addition they are known to evolve faster than their mainland counterparts. Body size in island mammals may also be influenced by geographical climatic gradients or climatic change through time. We tested the relative effects of climate change and isolation on the size of the Japanese rodent Apodemus speciosus and calculated evolutionary rates of body size change since the last glacial maximum (LGM). Currently A. speciosus populations conform both to Bergmann's rule, with an increase in body size with latitude, and to the island rule, with larger body sizes on small islands. We also found that fossil representatives of A. speciosus are larger than their extant relatives. Our estimated evolutionary rates since the LGM show that body size evolution on the smaller islands has been less than half as rapid as on Honshu, the mainland-type large island of Japan. We conclude that island populations exhibit larger body sizes today not because they have evolved toward gigantism, but because their evolution toward a smaller size, due to climate warming since the LGM, has been decelerated by the island effect. These combined results suggest that evolution in Quaternary island small mammals may not have been as fast as expected by the island effect because of the counteracting effect of climate change during this period.
We report rapid change of morphology and mitochondrial genes in white-footed mice (Peromyscus leucopus) in the Chicago (Illinois, USA) region. We sequenced mitochondrial DNA COX2 from 55 museum skins of white-footed mice caught in the Chicago area since 1855 and from 44 mice recently trapped in the same locations. We found consistent directional genotype replacement at five separate collection locations. We later focused on a single one of these locations (Volo Bog State Natural Area) and sequenced mitochondrial D-loop control region from 58 museum skins of mice collected in 1903-1976 and 32 mice recently trapped there. We found complete and more recent replacement of D-loop haplotypes, apparently occurring between 1976 and 2001. We tested whether these genetic changes were mirrored by changes in morphology by comparing 15 external and cranial traits. We found no significant morphological differences between mice collected in 1903-1976; however, mice collected in 2001-2003 showed 9 of 15 measurements to be significantly changed relative to the earlier samples. Recent mice were longer in total length, with broader, longer noses, and longer but shallower skulls(1). Discriminant function analysis allowed for 100% correct classification using these traits. Principal components analysis shows variance over time is well distributed across both external and cranial measures. The sequential replacements of haplotypes and the rapid change of morphology can best be explained by replacement of the regional population with immigrants from genetically distinct neighbouring populations, likely facilitated by the large environmental changes occurring over the time period. Replacement with genotypes from external populations may be a common mechanism of evolution of newly adaptive local forms in an increasingly human-impacted world.
A total of 383 Peromyscus was collected from southern Illinois to determine morphological characteristics useful in identifying individuals as either P. leucopus (Rafinesque, 1818) or P. maniculatus (Wagner, 1845). Polyacrylamide gel electrophoresis of salivary amylase was used to positively identify all specimens. No univariate morphological character accurately discriminated between the two species because of a high degree of intraspecific variation. Stepwise discriminant function analysis of external characters correctly classified 97.9% of subadults to species. The most important external character was the tail length/body length ratio. This ratio was also the most important factor in discrimination of adults; the function correctly classified 98.6% of individuals. Considering skull measurements of adults, 9 cranial characters were needed to differentiate between the two species, with a correct classification of 98.9%. For old adults, all specimens were classified correctly using 5 cranial characters. There was no fast, easy, accurate method to discriminate between these species 100% of the time in the field.
External features of the tail and pelage, and quantitative cranial characteristics were used to discriminate Peromyscus leucopus from P. maniculatus (n = 204) from northeastern North America. Species assignments were based on the phenotype of salivary amylase. Characteristics of the pelage and tail yielded correct identification of 55% of adult specimens. A previously published discriminant-function equation based on 11 cranial measurements correctly classified 66% of adults and 56% of specimens of all age classes. Two new discriminant equations were generated based on 12 and 11 skull measurements, respectively. The first equation correctly classified 100% of skulls in two separate datasets (n = 164; n = 50), and the second correctly classified 94% in a single dataset (n = 195).
Rates of morphological evolution documented in laboratory selection experiments, historical colonization events, and the fossil record are inversely related to the interval of time over which they are measured. This inverse relationship is an artifact of comparing a narrow range of morphological variation over a wide range of time intervals, and it is also a product of time averaging. Rates measured over different intervals of time must be scaled against interval length before they can be compared.
Survival of Darwin's finches through a drought on Daphne Major Island was nonrandom. Large birds, especially males with large beaks, survived best because they were able to crack the large and hard seeds that predominated in the drought. Selection intensities, calculated by O'Donald's method, are the highest yet recorded for a vertebrate population.
This chapter discusses how the discriminant function may be applied in systematic biology. Kendall and Stuart made clear the three classes of problems involved in differentiating between two or more populations on the grounds of multivariate measurements. Discrimination concerns the problem of alloting correctly an individual to the one of k populations from which it derives. This is distinct from classification, which is concerned with classifying a sample of individuals into groups that are to be as distinct as possible, and dissection, which involves the arbitrary construction of groups. The concept of classification, as expressed in these terms, is the most commonly occurring problem in numerical taxonomy. It is only recently that professional statisticians have begun to invade this virgin ground. Gower has made a noteworthy contribution to the theory of the subject, and Jardine and Sibson have recently written a book in which the first clear formalization of some of the ideas involved is given. The chapter reviews significant biological studies in the field, some recently reanalyzed by Blackith and Reyment.
Mitochondrial DNA (mtDNA) from 131 deer mice, Peromyscus maniculatus, collected on the eight California Channel Islands and from seven southern California mainland locations, was isolated and analyzed for restriction endonuclease fragment polymorphisms. A total of 26 mtDNA genotypes were distinguishable among the deer mice sampled. All of the island samples had mtDNA restriction-fragment patterns not found among the mainland samples. Distributions of specific restriction-fragment patterns provide evidence for at least four separate colonization events to the Channel Islands. The estimated percentage of sequence divergence between all mtDNA's in this study was less than 1%, suggesting that colonization of the islands occurred fairly recently, probably within the last 500,000 years. Levels of mtDNA heterogeneity were much lower within island populations than within mainland populations.
Chromosomes from 61 individuals representing 20 populations currently referable to Onychomys torridus were examined from Arizona, New Mexico, and Texas. Two distinct karyotypes were observed. In both chromosome forms the diploid number was 48. The principal differences reside in the morphology of biarmed chromosomes and number of acrocentric chromosomes. A contact zone between the two cytotypes was located in southwestern New Mexico. Based on karyotypes, no hybrid nor backcross individual was detected. These data indicate that two species have been included under the name O. torridus. The name arenicola is the oldest available name and is herein raised to specific rank.
A morphometric analysis using 12 cranial and six external measurements was carried out on a total of 363 specimens representing both cytotypes. Age, secondary sexual, and geographic variation were analyzed. A final discriminant analysis showed significant separation between the two species.
We report on eight years of data for a population of deer mice (Peromyscus maniculatus) on Santa Barbara Island, California which reaches exceptionally high densities and fluctuates markedly in an apparent three- to four-year cycle. The cyclic increase follows winters with high rainfall, and the decline may be similarly associated with low rainfall winters. The peak and early decline is marked by nearly complete cessation of breeding, along with heavy predation by barn owls (Tyto alba), whose numbers track those of the deer mice. This island population of Peromyscus differs from the well-established pattern for the species on the mainland, where populations occur in low to moderate numbers and are relatively stable from year to year. The pattern seen on the island is instead similar to that of cyclic microtines. We compare Microtus and the Santa Barbara Island deer mice and discuss parallels in the possible causes of the respective cycles.
There have been mice (Mus musculus) on the Welsh island of Skokholm for only about 70 years, yet they are very distinct from their mainland neighbors and relatives both in skeletal characters and overall size. Divergence of the same order was found between the mice on the similar Scottish island of the May and their nearest neighbors. There was no sign of convergence between the Skokholm and May populations. Skulls of the extinct M. m. muralis from St. Kilda showed less evidence of divergence from the pattern of skeletal variation that characterizes all mice classified from the British mainland (which populations are relatively uniform over a wide area). It is concluded that the peculiar features of these island races stem from the chance characteristics of their founder members.
Gene flow between morphologically differentiated populations of Thomomys bottae has led to detectable shifts in population morphology over a relatively short period of time (20-60 yr). Temporal samples from museum collections make it possible to document directed changes in the subspecies chrysonotus from the Ehrenberg area of Arizona in comparison with seemingly random temporal variation in other populations along the Colorado River. The most likely scenario involves pocket gophers from the California side of the river becoming established on the Arizona side S of Ehrenberg and serving as a source of gene flow into the Ehrenberg area. Electromorphic data support such a scenario.-from Authors
If colonizing populations are displaced into an environment that is
often very different from that of their source1, they are
particularly likely to diverge evolutionarily, the more so because they
are usually small and thus likely to change by genetic restructuring or
drift2,3. Despite its fundamental importance, the consequence
of colonization for traits of founding populations have primarily been
surmised from static present-day distributions1,2,4,5,
laboratory experiments6 and the outcomes of haphazard human
introductions7-9, rather than from replicated field
experiments. Here we report long-term results of just such an
experimental study. Populations of the lizard Anolis sagrei, introduced
onto small islands from a nearby source, differentiated from each other
rapidly over a 10-14-year period. The more different the recipient
island's vegetation from that of the source, the greater the magnitude
of differentiation. Further, the direction of differentiation followed
an expectation based on the evolutionary diversification of insular
Anolis over its entire geographic range. In addition to providing a
glimpse of adaptive dynamics in one of the most extensive generic
radiations on earth, the results lend support to the general argument
that environment determines the evolution of morphology.
Island populations are of interest for their differentiation as well as their species diversity; some of the earliest biological interest in islands was concerned with the number of ‘endemics’ thereon. There is dispute about the long-term evolutionary importance of island forms, but they are rich sources of data for studying the under-exploited interface of genetics, ecology and physiology. Differentiation of island populations may arise from genetic change after isolation, or from the chance collection of alleles carried by the colonizing group itself. The general reduction of genetic variance in island populations compared to continental forms of the same species suggests that founder events have played a major role in the formation of most island forms. However, there is ample evidence of adaptation in island populations despite this lower variation; this is relevant when using island biology as a base for the deriving of rules for genetic conservation.
Fluctuating asymmetry, or random deviations from bilateral symmetry, has been widely used as a measure of developmental stability. The relationship between fluctuating asymmetry (FA) and allozymic heterozygosity was evaluated using 18 natural populations of pocket gophers (Thomomys bottae). Heterozygosity in local populations of pocket gophers ranges over more than an order of magnitude (1.5—18.4%), making this burrowing rodent particularly apt for such studies. Two measures of FA in mensural skull characters were examined: absolute deviations between left and right sides and the variance of signed differences. After log transformations, levels of FA among individuals and populations were not related to size. Repeated-measures analyses of variance showed that FA was significant relative to measurement error, both across populations and within them. Asymmetries of different characters were uncorrelated, despite positive significant correlations among the characters themselves. FA levels varied only slightly among populations of gophers, and this variation was not significant for most characters. FA levels of populations were not correlated with allozymic heterozygosity, and analyses of variance in FA employing heterozygosity were not significant. Heterozygosity levels in these rodents appear more strongly related to aspects of population history (especially effective size and gene flow) than to developmental stability. Because so many genomic and environmental factors can affect morphological variation, caution is needed in interpreting correlations between genetic and phenetic variation.
http://deepblue.lib.umich.edu/bitstream/2027.42/56322/1/MP077.pdf
Conspicuous adaptive differentiation in color and size has occurred in the house sparrow (Passer domesticus) in North America
and the Hawaiian Islands since its introduction in the middle of the 19th century. Patterns of geographic variation in North
America parallel those shown by native polytypic species, in conformity with Gloger's and Bergmann's ecogeographic rules.
Racial differentiation of house sparrow populations may require no more than 50 years.