No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Hybriden und hybridogene Sippen ausOphrys bertolonii undO. atrata (Orchidaceae)
Abstract
Flower polymorphism in 15 ItalianOphrys populations (N = 282) was analysed in detail. Statistical and graphical evaluation of data demonstrates morphological relationships and amount of hybrid character coherence.O. bertolonii s. str. andO. atrata are stable parental taxa, but occasionally form hybrids and hybrid swarms. Much evidence suggests that it was through such homogamic hybridization, involving these and other species ofOphrys, that the stabilized taxaO. bertoloniiformis andO. promontorii (ecologically different, but sympatric with the parents on Gargano), andO. benacensis (geographically separated from the parents in the Insubric region) originated. These differentiation-hybridization cycles are linked to the break-down and new establishment of incomplete prezygotic crossing barriers (e.g. different flower biology, flowering time, habitat preference).
... Despite the documented close plant-pollinator relationship in this group, however, there is evidence that some of these species hybridize with each other, especially closely related or sympatric species. Despite the selective attraction of pollinators, nonlegitimate pollination does occur, and hybrids can sometimes be found ( Stebbins and Ferlan, 1956 ;Danesch and Danesch, 1972 ;Danesch et al., 1975 ;Ehrendorfer, 1980 ). Several hybrids have been described for Ophrys (see Pedersen and Faurholdt, 2007 ) and for several species, a hybridogenic origin has been proposed ( Paulus and Gack, 1990a ;Paulus and Gack, 1999 ;Devey et al., 2008 ) concurrently with the description of a great number of newly named species ( Delforge, 2001 ;Tyteca et al., 2003 ;Kreutz et al., 2007 ;Lowe, 2010 ;Lowe, 2011 ). Orchids off er a unique system for studying evolution, improving and integrating our knowledge of plant-pollinator interactions, and testing their eff ects upon diversifi cation. ...
Premise of the study:
Orchids in the genus Ophrys represent extraordinary cases of tight coevolution between plants and their pollinators, and as a result, they present opportunities for studying hybridization, or a lack thereof, during speciation. However, few studies assess the real effect of hybridization in diversification. The three most representative species of section Pseudophrys in the western Iberian Peninsula-O. dyris, O. fusca, and O. lutea-were chosen to study evolutionary relationships and examine speciation.
Methods:
Using eight specific nuclear microsatellite loci, 357 individuals from 28 locations were studied; 142 of these samples were also studied with four plastid microsatellite loci. Data were analyzed using Bayesian cluster analysis, a median-joint network, and multivariate analysis.
Key results:
Many O. dyris and O. fusca specimens had three or four alleles and were therefore treated as tetraploid. Ophrys dyris is poorly genetically separated from O. fusca, and pure populations are rare. Ophrys fusca and O. lutea are distinct, but hybrids/introgressed individuals were detected in most of the populations and supported by plastid haplotypes. Ophrys fusca is subdivided into three well-delimited genetic lineages with a strict geographic correspondence confirmed by plastid haplotypes.
Conclusions:
Because postzygotic barriers are weak, leakage in this highly specialized orchid-pollinator system contributes to hybridization and introgression. These leakages may have occurred during periods of past climate change, promoting homogenization and the potential for generations of new biodiversity via production of novel genotypes/phenotypes interacting with pollinators.
... However since the chromosome number is identical in nearly all species of the genus Ophrys, this method is not probable. The formation of new species by hybridization or introgression has been previously assumed to occur for the species of the genus Ophrys (STEBBINS & FERLAN 1956, EHRENDORFER 1984, DANESCH et al. 1975). This remains the most likely possibility, yet no verifying evidence so far has been brought forward. ...
... biscutella = ×salvatoris ± 0 für Italien Ophrys bombyliflora = ×cataldii ± 0 Ophrys fuciflora = ×valparmensis ± 0 für Italien Ophrys fusca s.l.= ×spuria ± 0 für Italien Den Autoren ist es nicht möglich, "magniflora" von "catalaunica" zu unterscheiden (vgl. Fig. 7 Auch die Areale unterscheiden sich deutlich wie schon Danesch et al. 1975 festgestellt haben. Sie unterscheiden "promontorii", "bertoloniiformis" und "benacensis", letztere von bauMann & KünKele (1986) in die Synonymie von "pseudobertolonii" gestellt. ...
... Speziell für die Ophrys bertoloniibertoloniiformis-Artengruppe wurde mehrfach versucht, eine Beweisführung im erstgenannten Sinn anzutreten. Sie lag einzig in einer differenzierten Maßanalyse, um eine Korrelation und Kohäsion der Merkmale der vermuteten Elternarten aufzuzeigen (STEBBINS & FERLAN 1956, O. DANESCH et al. 1975, VÖTH & EHRENDORFER 1976GÖLZ & REINHARD 1975, 1979 ...
... Artbildung über Hybridisierung bzw. Introgression wurde auch für Arten der Gattung Ophrys angenommen (STEBBINS & FERLAN 1956, EHRENDORFER 1959, DANESCH et al. 1975 Der leicht verständliche Weg der Artentstehung ist auch für Arten der Gattung Ophrys der über geographische Separationen (allopatrische Artbildung). Eine ganze Reihe von distinkten Arealen lässt am leichtesten diese Erklärung zu. ...
... Despite the selective attraction of pollinators, false pollination does occur and hybrids can be occasionally found (Stebbins and Ferlan 1956;Danesch et al. 1975;Ehrendorfer 1980). For several species, such as O. bertoloniformis, O. biancae, O. sitiaca or O. normanii, a hybridogenic origin has been proposed based in the floral intermediacy between putative parental species (Stebbins and Ferlan 1956;Paulus and Gack 1995;Delforge 2006). ...
Ophrys orchids mimic females of their pollinator species to attract male insects for pollination. Reproductive isolation is based on the specific attraction of males of usually a single pollinator species, mostly bees, by mimicking the female species-specific sex-pheromone. Sexually deceptive orchids are ideal candidates for studies of sympatric speciation, because key adaptive traits such as the pollinator-attracting scent are associated with their reproductive success and with premating isolation.
We have investigated processes of ecological speciation by using behavioural experiments and chemical, electrophysiological and population-genetic analyses. We show that minor changes in floral odour bouquets might be the driving force for pollinator shifts and speciation events. New pollinators act as an isolation barrier towards other sympatrically occurring species. Hybridisation occurs because of similar odour bouquets of species and the overlap of flowering periods. Hybrid speciation can also lead to the displacement of species by the hybrid population, if its reproductive success is higher than that in the parental species.
... However, the selective attraction works not always perfect because hybrids between Ophrys species are regularly found (Stebbins & Ferlan, 1956;Danesch & Danesch, 1972;Danesch et al., 1975). Furthermore, backcrosses do occur, resulting in gene flow between species. ...
Ophrys orchids mimic the female sex pheromones of their pollinator species to attract males for pollination. Reproductive isolation in Ophrys is based on the selective attraction of only a single pollinator species. A change of floral odour can result in the attraction of a new pollinator species that acts as an isolation barrier towards other sympatrically occurring Ophrys species. Ophrys lupercalis, Ophrys bilunulata, and Ophrys fabrella grow sympatrically and bloom consecutively on Majorca and are pollinated by three species of Andrena. We investigated variation of phenotypic and genotypic flower traits, aiming to study the role of the floral odour for reproductive isolation and speciation. Using chemical and electrophysiology (gas chromatography coupled with an electroantennographic detector) methods, we show that the three Ophrys species use the same odour compounds for pollinator attraction, but in different proportions. A comparison of the floral odour bouquets in a multivariate analysis revealed a clear grouping of plants from the same species, although with an overlap between species. A comparison of the same plants using molecular markers gave a contrasting result. Although O. lupercalis and O. fabrella were genetically well separated, plants of O. bilunulata did not form a distinct group but were similar to either O. lupercalis or O. fabrella. Our data indicate gene flow and hybridization to occur between O. bilunulata and O. lupercalis as well as between O. bilunulata and O. fabrella. All plants of O. bilunulata, despite having different genotypes, showed a very similar floral odour. This reflects a strong selective pressure by the pollinating males. The overlap of genotypes of O. bilunulata and O. fabrella supports our hypothesis that O. fabrella diverged from O. bilunulata by scent variation and the attraction of a new pollinator species, Andrena fabrella.
... Ophrys hybrids are thought to arise through occasional false pollination and are regularly found (Danesch et al., 1975;Ehrendorfer, 1980;Stebbins and Ferlan, 1956). They can produce novel combinations of floral traits, particularly their floral odour and can in turn led to pollinator shift. ...
... Each species usually attracts only one pollinator species (Paulus and Gack 1990) and the specific Ophrys-pollinator relationship represents the main mechanism of reproductive isolation between the often interfertile Ophrys species (Ehrendorfer 1980;Scopece et al 2007), with the species-specific scent as main responsible factor for prezygotic isolation (Schiestl and Ayasse 2002). However, the attraction of a second pollinator species besides the main pollinator species has been shown to occur as the consequence of small differences in the relative amounts of certain compounds (Schiestl and Ayasse 2002) and thus hybrids, as result of interspecific pollination, have frequently been found (Stebbins and Ferlan 1956;Danesch et al. 1975;Ehrendorfer 1980;Stökl et al. 2008). Indeed, recent studies on gene flow at boundaries of sympatric Ophrys species have revealed that pollinator-mediated isolation is less specific than expected (Soliva and Widmer 2003;Mant et al. 2005;Stökl et al. 2008). ...
In the sexually deceptive orchid genus Ophrys, reproductive isolation is based on the specific attraction of males of a single pollinator species by mimicking the female species-specific sex pheromone. Changes in the odor composition can lead to hybridization and speciation by the attraction of a new pollinator that acts as an isolation barrier toward other sympatrically occurring Ophrys species. On Sardinia, we investigated the evolutionary origin of two sympatrically occurring endemic species, Ophrys chestermanii and O. normanii, which are both pollinated by males of the cuckoo bumblebee Bombus vestalis. Chemical and electrophysiological analyses of floral scent and genetic analyses with amplified fragment length polymorphisms and plastid-markers clearly showed that O. normanii is neither a hybrid nor a hybrid species. The two species evolved from different ancestors, viz. O. normanii from O. tenthredinifera and O. chestermanii from O. annae, and converged to the same pollinator attracted by the same bouquet of polar compounds. In spite of sympatry, pollinator sharing and overlapping blooming periods, no evidence has been obtained for gene flow between O. chestermanii and O. normanii indicating an unusual case among sexually deceptive orchids in which postmating rather than premating reproductive isolation mechanisms strongly prevent interspecific gene flow.
DELFORGE, P.-Ophrys arachnitiformis, Ophrys garganica or Ophrys caloptera ? The avatars of the Passion Ophrys, Ophrys passionis SENNEN 1926. In the south of France and Catalonia, the Ophrys sphegodes complex appeared for a long time to consist mainly of a single species, called O. aranifera and then, from 1950 onwards, O. sphegodes. This species was often subdivided into two or three subspecies. As this species was generally considered to have green sepals, taxa close to O. sphegodes but with mostly white or pink sepals gradually attracted attention and were described: O. arachnitiformis, an early flowering species from Provence, in 1859, and O. splendida, a fairly late flowering species also from Provence, in 1980. In addition, a fairly late flowering Italian species, O. garganica, whose description was validated in 1975, also appeared to be present in Catalonia and, occasionally, in the south of France. However, populations of Ophrys arachnitiformis with predominantly green sepals, frequent in the Rhône valley as far north as Lyon, as well as in Languedoc and Catalonia, appeared to be original. This taxon was described in 2002, unfortunately twice, first as O. exaltata subsp. marzuola (holotype from Hérault) and then as O. arachnitiformis subsp. occidentalis (holotype from Ardèche). The authors of both descriptions themselves suggested that they had described the same taxon. Doubts were soon expressed about the identity of the holotype of O. exaltata subsp. marzuola, which comes from an area where several tax-ons of the complex meet and hybridise. On the other hand, some specialists felt that the Rhodanian taxon and the Catalan-Languedocian taxon represented two different [sub-]species and that O. garganica was endemic to Italy. In 1926, SENNEN described Ophrys passionis from the area around Barcelona. That little-used name was considered at the time by A. CAMUS to be a synonym of O. arachniti-formis. For a long time, O. passionis was considered to be a nomen nudum, but SENNEN's description, based on distribution of herbarium parts, was recognised as valid in 1995. This species was then wrongly considered to be quite late flowering and placed in the synonymy of O. garganica by Catalan botanists following erroneous reasoning, in particular concerning the date of collection, 29 March 1926, indicated by SENNEN on his herbarium parts. It subsequently transpired that the epithet passionis had priority in the specific, subspecific and varietal ranks for naming the early Catalan-Languedocian taxon close to O. arachnitiformis. However, many botanists still mistakenly use the epithet passionis to name the fairly late flowering Catalan-French species close to O. garganica. This species must be named O. caloptera. The history of the taxonomy and nomenclature of the early flowering species of the Ophrys sphegodes complex in southern France and Catalonia is outlined. The diagnostic characters of the various taxa considered are recalled and a diagnosis is established for the (*) www.orchidelforge.eu Communication mise en lignele 17 janvier 2024.
The Author reports 15 taxa of Orchidaceae and two hybrids (Orchis ×colemanii and Neotinea ×dietrichiana) found in May 2018, during a first research stage around the top of Mount Cairo (1669 m a.s.l.).
This is the main peak of a mountain massif in the province of Frosinone (South Latium), rather isolated from the main Apennine range. This habitat is classified as a Site of Community Interest (SCI) also for its wealth of orchids. The most interesting taxon found is Ophrys promontorii O. Danesch & E. Danesch, an endemic taxon of Central-South Italy, described in Apulia in 1971 and reported, in the following years, in other Adriatic regions (Molise, Abruzzo and Marche, the latter to be confirmed) and also in Thyrrenian regions (Latium and Campania). On Mount Cairo O. promontorii grows between 1400 and 1500 m
a.s.l., therefore beyond the extreme altimetric limit actually known for this species, due to a particularly favorable microclimate. Finally, the Author reports two more sites of O. promontorii in the Province of Frosinone, the first close to Settefrati, inside the Abruzzo Latium and Molise National Park, the other in the external protection zone of the Park itself, in the territory of Cardito.
Partendo dai dati bibliografici relativi alla flora del Monte Pisano, si è proceduto al riesame critico degli exsiccata conservati a Lucca presso l'Orto Botanico Comunale (Herb. Bicchi ed Herb. Puccinelli) e presso il Liceo Classico (Herb. Mezzetti), a Pisa presso l'Istituto Botanico Universitario (Herb. Generale, Herb. Arcangeli, Herb. Caruel, Herb. Cittadella, Herb. Giannini, Herb. Passerini, Herb. Pellegrini), a Firenze (Herb. Centrale Italico), a Siena presso l'Istituto Botanico Universitario e a Bologna presso l'Istituto Botanico Universitario (Herb. Bertoloni).
Sono poi state effettuate numerose ricognizioni di campagna per verificare l'attualità dei dati emersi e la consistenza, al momento presente, del contingente orchidologico del Monte Pisano.
Sono cosí risultate presenti nel territorio preso in esame 47 entità: precisamente 38 specie, 5 ibridi intragenerici e 4 ibridi intergenerici. La presenza della maggior parte di esse è ampiamente documentata da materiale d'erbario ed è stata confermata dalle nostre ricognizioni di campagna; per alcune entità, invece, i dati a nostra disposizione sono scarsi.
Oltre a quelle entità che risultano segnalate per la prima volta per il Monte Pisano, cioè: Ophrys tenthredinifera, Serapias parviflora, Serapias x godferyi, Serapias x meridionalis e Cephalanthera rubra, riteniamo opportuno sottolineare il ritrovamento delle seguenti che presentano qualche interesse dal punto di vista corologico o fitogeografico: Ophrys speculum che trova sul Monte Pisano la più settentrionale delle sue pochissime stazioni nella penisola; Ophrys sphegodes subsp. litigiosa che finora era nota in Italia solo per la Liguria occidentale; Ophrys sphegodes subsp. garganica che, già nota per la Maremma toscana, con i nostri reperti estende più a nord il suo areale; Ophrys sphegodes subsp. jeanpertii che risulta nuova per l'Italia, Ophrys x hoeppneri di cui il nostro reperto risulta essere il primo per la Toscana ed il terzo per l'Italia.
Riteniamo opportuno puntualizzare però che alcune entità sono testimoniate soltanto da reperti d'erbario scarsi e spesso di data remotissima, tra questi, oltre ad alcuni ibridi, possiamo citare: Ophrys tenthredinifera, Orchis palustris, Gymnadenia conopea, Spiranthes aestivalis, Neottia nidus avis, Cephalanthera rubra, Epipactis helleborine.
Può sorprendere il fatto che su di un territorio di superficie così limitata vivano tante entità di questa famiglia; a tale proposito dobbiamo considerare che il Monte Pisano ad una grande varietà di ambienti vegetali associa il fatto di raggiungere la quota di quasi 1000 m s.l.m., il che consente sia una certa distribuzione altitudinale delle varie entità, sia la presenza di specie appartenenti più propriamente all'ambiente montano oltre a quelle tipiche di ambiente mediterraneo o planiziale.
Non deve meravigliare, parimenti, la relativa frequenza degli ibridi; è anzi probabile che oltre a quelli da noi citati possano in futuro esserne reperiti altri.
In order to verify the bibliographical data known for the orchids of Monte Pisano (N-W Tuscany) the authors have critically examined all the exsiccata preserved in the herbaria of Lucca (Herb. Bicchi, Herb. Mezzetti and Herb. Puccinelli); Pisa (General Herbarium, Herb. Arcangeli, Herb. Caruel, Herb. Cittadella, Herb. Giannini, Herb. Passerini and Herb. Pellegrini); Florence (Herb. Centrale Italicum); Siena and Bologna. Most of the herbarium records have been also confirmed by personal country investigations.
At present, in the Monte Pisano territory 47 entities (38 of which are to be considered species, 5 intrageneric hybrids, 4 intergeneric hybrids) have been determined. Among them Ophrys tenthredinifera, Serapias parvifiora, Sera pias x godferyi, Serapias x meridionalis and Cephalanthera rubra are new for the investigated area. Furthermore Ophrys speculum appears to have on the Monte Pisano its northern record in the Italian peninsula; Ophrys sphegodes subsp. litigiosa till now known (in Italy) only for western Liguria extends eastwards its area; Ophrys sphegodes subsp. garganica already known for Tuscan Maremma extends northwards; Ophrys sphegodes subsp. jeanpertii is recorded for the first time in Italy; Ophrys x hoeppneri appears to be the second record in the world; our record of x Orchiaceras bergonii is the first one for Tuscany and the third one for Italy.
Nevertheless it is necessary to point out that some entities are testified only by scarce and/or very old herbarium specimens, as in the case of Ophrys tenthredinifera, Orchis palustris, Gymnadenia conopea, Spiranthes aestivalis, Neottia nidus-avis, Cephalanthera rubra and Epipactis helleborine.
It may be surprising that over a so limited area to many orchids species are present. But we must consider that Monte Pisano joints together both a large variety of environments and a remarkable altitude (about 1000 m on the sea level). These facts allow a certain zonation in height of the entities so that the presence of species belonging both to mountain and to mediterranean environment may be here well explained. At the same time the relative frequency of the hybrids is not surprising and other reports, besides the mentioned ones, could be possible.
RÉSUMÉ - Ophrys passionis Sennen a été effectivement décrit et devient le nom valide des Ophrys jusqu'alors dénommés O. garganica (E. Nelson) O. & E. Danesch, celui-ci n'étant d'ailleurs pas valide, au sens du Code International de la Nomencalture Botanique. MOTS CLÉS : Orchidaceae - Ophrys passionis - Ophrys garganica.
ABSTRACT - Ophrys passionis Sennen was effectively described and becomes the valid name of Ophrys until then called O. garganica (E. Nelson) O. & E. Danesch, moreover this one not being valid, in the sense of the International Code of Botanical Nomenclature. KEY WORDS : Orchidaceae - Ophrys passionis - Ophrys garganica.
A specimen of Orchis x dietrichiana, a natural hybrid between O. tridentata and O. ustulata (Orchidaceae) was collected at flowering time on the mountains E of Vallo di Diano (Salerno province, Italy) and characterised by using morphology and molecular characters. Randomly Amplified Polymorphic DNA (RAPD) and Restriction Fragment Length Polymorphism (RFLP) analysis of plastidial DNA (cpDNA) data were employed with the aim of gathering information on the hybrid nature of O. x dietrichiana and of verifying the hypothesis formulated for its parental lineage. RAPD showed that the plant is indeed a hybrid between the two above-mentioned species and the cpDNA pattern of the hybrid clearly demonstrated that O. tridentata provided the maternal lineage.
Sul versante nordovest dell’Etna è nota da cica 20 anni una consistente popolazione di un’entità ascrivibile all’aggregato Ophrys sphegodes s.l., ma distinta dalla specie tipica per un labello da espanso tondeggiante a fortememnte convesso e una macula ampia e spesso riccamente ornata. Classificata dapprima come O. exaltata, differisce da quest’ultima per la minore altezza, il labello arrotondato ed i sepali esclusivamente verdi; si differenzia inoltre dall’affine O. exaltata subsp. panormitana per il lbello intero ed i sepali verdi, da O. rachnitiformis subsp. archipelaghi (incl. O. mateolana e O. cilentana) per i sepali verdi e da O. garganica per i petali più stretti, la macula più ornata e le callosità basali bruno-verdastre. Approfonditi esami morfologici hanno messo in evidenza la sua distinta posizione tassonomica e hanno permesso di identificarla come nuova sottospecie: Ophrys sphegodes subsp. grassoana. Si descrivono inolte due nuovi ibridi: Ophrys exaltata Ophrys garganica, confermato per il territorio di Niscemi (CL), e O. bertolonii subsp. explanata O. holosericea subsp. apulica, confermato per Favignana (isola dell’arcipelago delle Egadi, a circa 7 km dalla costa occidentale della Sicilia). Mentre i parentali del primo ibrido hanno un areale di distribuzione che si sovrappone per tutta la Calabria e Sicilia, l’areale comune dei parentali del secondo ibrido è molto ristretto, sovrapponendosi solo a livello delle Isole Egadi.
On the basis of symposium contributions onChlorella, Hibbertia, Eucalyptus, Ambrosia and on numerical approaches some fundamental problems of (bio)systematics, evolution, and taxonomic categories are discussed: Methods available for analysing “affinities”; conflicting evidence from phenetic, biochemical, cytogenetic and other analyses; further classification problems in cases of “intermediacy”, etc. While “sibs” of various levels and their “natural” hierarchy often can be objectively defined, this appears impossible for particular taxonomic levels itself (e. g. “species”). A single objective taxonomic system of organisms is unrealistic. Certain guiding lines for relative and practicable concepts of “species” and “genus” are proposed.
Statistical population analyses have been carried out on so-calledOphrys “arachnitiformis”, partly sympatricO. sphecodes s. l. as well as on other species ofOphrys (O. holosericea, O. exaltata, O. apulica, O. cornuta, O. biscutella, O. bertolonii, O. bertoloniiformis.). Altogether 63 populations with 521 individuals were studied in regard to 54 morphological parameters. — It can be shown thatO. arachnitiformis is an extremely heterogeneous assemblage which includes taxa of most diverse origin, different degrees of stability and nomenclatorial rank. Only common trait is their very diverse relationships withO. specodes s.l.—The basionymO. arachnitiformis
Gren. & Phil. refers to a colour variant ofO. sphecodes
Mill. subsp.sphecodes only, and is not applicable to other segments of the assemblage.
A late flowering, morphologically and biologically well isolated group of populations from southern France without any perceptible hybrid influence is established as a new species:Ophrys splendida
Gölz & Reinhard. Populations from north and central Italy with distinct characters but hybrid influences fromO. holosericea/O. exaltata are calledO. tyrrhena
Gölz & Reinhard.O. morisii, an endemic to Sardinia, represents an independent species of still obscure evolution. The hybrid interpretation ofO. catalaunica is statistically corroborated, but somewhat modified. For the remaining segments ofO. “arachnitiformis” investigated (from Castilia, Dalmatia, and the Monte Gargano) no formal taxonomic proposals are made, but some suggestions about their genesis are possible.
Population analyses, scatter diagrams and field observations demonstrate thatOphrys helenae is morphologically (and ecologically) well separated from the partly sympatricO. mammosa andO. ferrumequinum in N. Greece. Hybrids with the distantly relatedO. mammosa are very rare.
The RAPD methodology was utilized for analyzing the genetic material of four allopatric populations of the Ophrys bertoloniiformis type, as well as of two populations of O. bertolonii s.str., together with O. fuciflora as outgroup. Significant gene diversity was observed for all six ta-xa under examination, thus suggesting their separation at specific (or subspecific) level. Comparison with other methods (biostatistical analysis and pollination biology) is also reported.
Specimens of the orchid hybrid xOrchiaceras bergonii and of the two putative parental species Orchis simia and Aceras anthropophorum from Southern Italy were examined by using both morphology and molecular techniques. Hybrid morphological characters and protein profiles were intermediate between those of the two putative parental species. Chloroplast DNA restriction fragment polymorphism analysis showed differences between O. simia and A. anthropophorum. Hybrid restriction patterns were completely identical to the ones of O. simia. The data presented here confirm both the hybrid nature of xO. bergonii and that O. simia and A. anthropophorum are the parental species. Results also show that O. simia is the maternal lineage of the hybrid. The usefulness of a molecular approach in detecting maternal lineages in orchid hybrids as related to the understanding of the reproductive mechanism in parental species and to the direction of gene flow in hybrid formation are discussed.
Pollination by sexual deception in orchids is characterised by a high degree
of pollinator specificity, which may account for the rarity of natural hybrids
within the group. Only one such hybrid has been formally recognised in
Australia, Chiloglottis ×
pescottiana R.S.Rogers, which has intermediate floral
morphology between its putative parents, C. valida
D.L.Jones and C. trapeziformis Fitzg. In this paper,
genetic and morphometric analyses confirm the hybrid origin of this taxon.
Allozyme analysis of C. trapeziformis and
C. valida revealed fixed allelic differences at four
‘diagnostic’ loci and significant frequency differences at three
other loci. In all cases, C. ×
pescottiana exhibited fixed heterozygosity at the
diagnostic loci. Multidimensional scaling of both the genetic data and seven
morphometric traits revealed distinct clusters of
C. trapeziformis and C. valida
while C. × pescottiana
formed an intermediate cluster between the two parents. To test for genetic
compatibility between C. trapeziformis,
C. valida and C. ×
pescottiana, a series of reciprocal artificial crosses
were performed. In all cases, the percentage of capsules formed was at least
as great for between-species crosses as for within-species selfs and crosses
(range 75–100%). No significant differences in the percentage of
seed with normal embryos was detected between self- and cross-pollinations
within C. trapeziformis (range 77–81%),
C. valida (range 59–74%) and
C. × pescottiana (range
30–51%), but the percentage of normal embryos was notably lower
in C. × pescottiana. The
cross C. trapeziformis female by
C. valida male produced significantly more normal
embryos (90%) compared with the reverse cross (46%). Artificial
backcrosses of C. ×
pescottiana to C. valida and
C. trapeziformis had lower percentages of normal embryos
when C. × pescottiana was
the pollen donor (39–43%) rather than recipient
(62–68%), suggesting reduced pollen viability in the latter
taxon. The size of F2 embryos in C. ×
pescottiana seed capsules was smaller than the embryos
of both C. valida and
C. trapeziformis. Despite confirmation of hybridisation,
little evidence for backcrossing was found. Thus, while the specific
pollinator relationships may occasionally break down in these sexually
deceptive orchids, reduced viability of hybrid pollen and
F2 seed, and inefficient pollination of the hybrid, may
minimise introgression. It is concluded from the available evidence that
hybridisation has not been a major evolutionary factor in the diversification
of sexual deception worldwide.
Klassische and moderne Praktiken, Konzepte and Probleme der botanischen Systematik und Taxonomie im Hinblick auf die Species-Kategorie werden anhand von etwa 25 besser bekannten Gruppen von Samenpflanzen illustriert. Die grobe Mannigfaltigkeit an verschiedenen Artbildungsmustem und Evolutionsstrategien läbt sich auf mehrere Komponenten zurückführen: Variation (z. B. Modifikationen bzw. Gen-, Chromosomen- und Genommutationen, Rekombination und Hyridisierung), Reproduktion (z. B. Allogamie, Autogamie und/oder Apomixis, Genflub, Generationsdauer and Ausbreitung), genetische Kanalisation und Fixierung (z. B. verschiedene Arten and Intensitäten der Selektion, genetische Drift, Gröbe und Stabilität der Populationen), Separation und Isolation (z. B. exogene und/oder endogene Faktoren, Inkompatibilität, Hybridsterilität) und räumliche Aspekte (z. B. Alter, Struktur und Nischendifferenzierung der Standorte, allo-, peri-, para.-odersympatnsches Vorkommen verwandter Sippen). Aufgrund verschiedener Korrelationen zwischen diesen Parameters lassen sich gewisse Syndrome und Speciestypen erkennen; sie werden im breiteren Rahmen der Lebensformengruppen vieljähriger Holzpflanzen, mehrjähriger Stauden und einjähriger Krautpflanzen herausgestellt.
Population variability ofOphrys holosericea (Burm. f.)Greut. subsp.holosericea (=O. fuciflora
Crantz subsp.fuciflora) from near Vienna (Austria), and of subsp.maxima (Fleischm.)Greut. andO. cornuta
Steven with intermediates from the Dalmatian island Hvar (Yugoslavia) was analysed and illustrated by scatter diagrams. A hybrid origin of these intermediates is suggested. Aspects of hybridization betweenO. holosericea agg. andO. scolopax agg. are discussed.
Biosystematics is on the one hand an experimental science, and on the other essentially a theoretical and synthetic one. A good biosystematist knows how to embrace both. In a highly specialized scientific world abounding in data and hypotheses there is need for great minds capable of absorbing and working with this vast information. In both these respects, E EHRENDORFER'S merits are justly famous throughout the whole botanical world; he is a laudatory example for all of us. Professor EHRENDORFER represents the splendid synthesis of floristics and classical taxonomy (one of his teachers being KARL HEINZ RECH~CER), meticulous karyology (another important teacher was LOTHAR GEITL~R who pioneered chromosomal and cyanobacterial research) and evolutionary research (strongly stimulated and encouraged by the Californian school of new and experimental systematics comprising E. ANDERSON, J. CLAUSEN, D. D. KECK, W. M. HIESEY, and G. L. STEBBINS). FRIEDRICH EHRENDORFER was the most outstanding proponent in establishing the "New Systematics" in Central Europe. This was an essentially new approach which tried to link cytogenetics, evolutionary research, and phylogenetics. FRmDRICH EHRENDORFER succeeded in convincing his botany colleagues from the "physiological hemisphere" that taxonomy is not out-dated but an active, fascinating and indispensable component (or even central core) of plant science. His untiring advocacy for "experimental taxonomy" has proven fruitful for gaining new respect for this classical biological discipline. Thirty years later, he now shows us how to cope with the next and probably much further reaching revolutionary challenge in taxonomy - how to cope with macromolecular data in order to understand phylogeny and improving the classification of the angiosperms.
Ten species of orchid plants belonging to the generaOrchis (7),Dactylorhiza (2), andGymnadenia (1) were analyzed by enzyme electrophoresis. Each species can be identified by a combination of enzyme bands different from those of all other species examined. The electrophoretic data were used for the construction of phenetic and phylogenetic trees with the help of computer programs. The trees were almost identical regardless which method was used. Our results differ considerably from a classification based on morphological evidence. The electrophoretic data indicate that the genusOrchis is not a monophyletic group.
The diploid basic chromosome number forOphrys is 2n = 36. Tetraploidy has been found inO. fusca agg. only. Aneuploidy and aneusomaty are wide-spread; supernumerary chromosomes behave B-like, but do not differ by shape or structure from A-chromosomes. A new staining method reveals clearly differentiated bipartite meiotic kinetochores. Evolutionary aspects of homogamic hybridization, chromosome instability, and of the basic chromosome number x = 18 are discussed.
A putative natural hybrid betweenOrchis laxiflora andO. morio (Orchidaceae) from southern Italy, formerly known asO. alata, was characterized both on morphological and molecular grounds in order to confirm its hybrid status and to trace its maternal lineage. The morphological characters of the putative hybrid showed intermediacy between those of the parent species, and restriction fragment length polymorphism (RFLP) analysis of a region of the nuclear ribosomal DNA confirmed its hybrid origin. Chloroplast DNA RFLP analysis indicated thatO. morio provided the maternal genome.
The RAPD technique has been used for analyzing the genetic material of seven Italian populations of theOphrys bertolonii aggregate (Orchidaceae). For comparison the related speciesO. sphegodes andO. fuciflora have also been analyzed. A high genetic variability has been observed within the same populations, and on the whole onlyO. bertolonii can be safely differentiated from the other taxa of the aggregate, which are undistinguishable with this method.
According to the situation of recent biology it seems to be necessary to continue the theoretical foundation of this science, and especially a foundation beyond physics and metaphysics. The preconditions of such a project are given with the problems of causality, natural law and induction. The discussion of these subjects in modern philosophy of science did not bring useful results, for philosophy of science itself is orientated by physics. On the other hand even the history of these problems in biology shows that the acceptance of physical or philosophical viewpoints leads to invincible difficulties.
Therefore, in this paper, I have tried to demonstrate the necessity of analyzing these basic problems in a new way. The conditions and circumstances of a biological phenomenon have a special kind of multidimensional relationship, so that they cannot be reduced to simple linear systems of cause and effect. The fact that biological systems have a lot of retroactive effects makes the description of their causality much more complicated than it is in physics.
So the natural law in biology is characterized by its relativity concerning the parameters which create the special dependence of a biological phenomenon's constituent parts.
The European orchidsOrchis mascula, O. pallens and their hybrids have been analysed by enzyme electrophoresis on starch gels. The two species differ in the electrophoretic mobilities of four out of eight enzymes tested. Three enzymes, phosphoglucomutase, phosphoglucoisomerase and malic enzyme exhibit typical heterozygote patterns in the hybrid plants demonstrating the presence of both differing parental alleles. Thus, species identification is easy by the electrophoretic analysis of a low number of enzyme loci, and hybrids are detectable even if morphological characters fail.
Micromorphology and distribution of trichomes in six taxa of theOphrys bertolonii aggregate (O. bertolonii, O. bertoloniiformis, O. benacensis, O. aurelia, O. drumana, O. catalaunica) are described. A fairly good homogeneity between all the taxa, with a moderate degree of variability even within the same taxon, has been observed. Comparison of these characters with those ofO. promontorii andO. garganica corroborates the inclusion of the former species into theO. sphegodes aggregate. Trichome analysis of a hybrid is exemplified byO. chiesesica (O. drumana O. fuciflora).
Results of chemical analyses of volatile compounds from flowers of 30 Ophrys taxa, from odour attracted insects, and the pollination biology of Ophrys orchids are reviewed. Chemical similarities were found between the volatiles released from Ophrys flowers and the insect glands in a number of pollination systems: (i) Ophrys taxa in the section Fusci-Luteae and bees of the genus Andrena s.l.; (ii) Ophrys taxa in the form complex Arachnitiformes-Araneiferae and bees of the genera Andrena s.l. and Colletes; (iii) Ophrys insectifera and its two digger wasps pollinators Argogorytes mystaceus and A. fargei and (iv) Ophrys scolopax heldreichii and the males of the bee Tetralonia cressa. Ethological field tests indicated chemical mimesis in certain pollinator systems. Aliphatic 1-alcohols and 2-alcohols and the terpenes geraniol, geranial, linalool, and E,E-farnesol are regarded as key attractive compounds, present especially in the Ophrys section Fusci-Luteae, the form complex Arachnitiformes-Araneiferae, and in a number of bee species in the genus Andrena s.l.
In the sexually deceptive orchid genus Ophrys, reproductive isolation is based on the specific attraction of males of a single pollinator species, mostly bees, by mimicking the female sex pheromone of this species. Changes in the floral odor can lead to hybridization, introgression, and possibly speciation. We investigated hybrid swarms of O. lupercalis and O. iricolor on Sardinia using behavioral, electrophysiological (GC-EAD), chemical, morphological, and genetic methods (AFLPs). In behavioral experiments, approximately 20% of the flowers from both species and hybrids were attractive to the "wrong" or both pollinator species. Analysis of the EAD-active hydrocarbons in the floral odor showed an overlap in the two species, whereby hybrid individuals could not be separated from O. iricolor. The genetic analysis confirmed the hybridization of the species. Plants of O. iricolor and hybrids are genetically indistinguishable and form an O. iricolor × lupercalis hybrid population. Remaining plants of O. lupercalis will possibly be displaced by the O. iricolor × lupercalis hybrid population in the future. Our study showed that in deceptive orchids, variation in the pollinator attracting cues, in this case, scent, can be the first step for speciation and at the same time cause the displacement of a species.
In the sexually deceptive orchid genus Ophrys, reproductive isolation is based on the specific attraction of males of a single pollinator species, mostly bees, by mimicking the female sex pheromone of this species. Changes in the floral odor can lead to hybridization, introgression, and possibly speciation. We investigated hybrid swarms of O. lupercalis and O. iricolor on Sardinia using behavioral, electrophysiological (GC-EAD), chemical, morphological, and genetic methods (AFLPs). In behavioral experiments, approximately 20% of the flowers from both species and hybrids were attractive to the "wrong" or both pollinator species. Analysis of the EAD-active hydrocarbons in the floral odor showed an overlap in the two species, whereby hybrid individuals could not be separated from O. iricolor. The genetic analysis confirmed the hybridization of the species. Plants of O. iricolor and hybrids are genetically indistinguishable and form an O. iricolor x lupercalis hybrid population. Remaining plants of O. lupercalis will possibly be displaced by the O. iricolor x lupercalis hybrid population in the future. Our study showed that in deceptive orchids, variation in the pollinator attracting cues, in this case, scent, can be the first step for speciation and at the same time cause the displacement of a species.
Scrub oak populations in the semidesert area of northeastern Arizona and southeastern Utah are ordinarily identified in regional manuals as Quercus undulata. They are very similar, both morphologically and ecologically, to Q. havardii of the Staked Plain of the Texas Panhandle and southeastern New Mexico. They differ, however, in a number of inconspicuous characters. Population sample analyses indicate that most of these differences are suggestive of Q. gambelii, and the deviant populations are thus interpreted as having been derived from ancestral Q. havardii through introgression by Q. gambelii. Two differences are not in accord with this interpretation; these are regarded as possible cases of transgressive segregation. Considering the evolution of these hybridized populations, it is speculated that the ancestral Q. havardii occurred to the south and west of the present range of this species during the Kansan period of the Pleistocene. During subsequent northward dispersal, it became split in two. The eastern portion ultimately came to occupy the present range of the species in the Staked Plain; the western portion—lying to the west of a north-south mountain barrier in central New Mexico—became introgressed by Q. gambelii (and locally by Q. turbinella), resulting in the present populations of Arizona and Utah.
The pattern of evolutionary phylogeny has been highly reticulate mainly on account of hybridization (crossing between individuals belonging to populations which have different adaptive norms) followed by stabilization and perpetuation of some of the hybrid derivatives. The significance of hybridization in obtaining a picture of evolutionary relationships is discussed. First the evolutionary advantages that might result from hybridization are considered, second the drawbacks; finally the ways and degrees to which such drawbacks may be overcome are discussed.
The modern biological species-concept, defined by genetic isolation, describes a phyletically independent system of populations. Most of the species-concepts in everyday use for the oaks (Quercus) exhibit genetic interchange with other so-called species. Nevertheless, these classical concepts remain in use and represent biologically meaningful populations. In addition, it is suggested that the classical species of Quercus may represent phyletic units in species-grade evolutionary advances. A comparison between the biological species-concept and the classical species-concept in Quercus suggests why the classical concepts have been retained. The biological species-concept appears to be a population system of extraordinary complexity and difficult to delimit in Quercus. This genetically isolated complex population system is not directly comparable to genetically discrete species in most other genera. The prime function of the species binomial is as a unit of communication. The biological species-concept must be used with greater flexibility as regards taxonomic rank if its designation by means of a binomial cannot provide a functional information retrieval system.
The interaction of divergent genomes as seen in the expression and stability of molecular, physiological and morphological characters may have a profound effect on the fitness of hybrids and bring forward new variations on which selection may act. The evolutionary implications of developmental interactions should prove to be a most rewarding area of inquiry for biosystematists.
A randomly mixed population consisting of Gossypium barbadense (variety Egyptian), G. hirsutum (variety Hopi), their F1, their F2, and the backcrosses to each species were grown at Raleigh, North Carolina, during the summer of 1964. The pedigree of each plant in the field was known. From these plants 25 plant families simulating short term intergradation (i.e., two generations of random mating) were fabricated. Each of these 25 plant, "multigeneration" families corresponded to different initial frequencies of the parental species. These ranged from five to 95 per cent. Measurements of eight taxonomically important traits were taken on each plant. The degree of mutual association or correlation between these taxonomic traits was measured by Kendall's coefficient of concordance and by two closely related measures of the width of Anderson's "linkage spindle." This was done for each of the "multigeneration" families and for each of the single generation families. The degree of morphological association was low in the segregating generations. However, the "multigeneration" families did have a high degree of multiple correlation. These results, when viewed in the light of the available literature on introgression, indicate that population structure is more likely to be responsible for the success of graphical analysis of introgressive hybridization than is linkage. It was concluded that the use of correlations between taxonomic characters to determine disputed parentage of hybrids in the genus Gossypium can be safely used only when interspecific hybridization is recent or when the history of selection is well known.
The annual species of the western North American genus Stephanomeria (Compositae) intergrade morphologically and have long been noted for their taxonomic complexity. The present study, involving morphological and cytological examination, analysis of breeding systems, and an extensive program of hybridization including cytogenetical study of F1 hybrid progenies, makes it possible for the first time to sort out the species. This paper presents evidence that the diploid, self-incompatible taxa are divided into three species. Both Stephanomeria exigua and S. virgata are polytypic species and differ in morphology, karyotype, and the structural arrangement of their chromosomes which results in strong reduction in the fertility of their hybrids. The differences between the two species are thought to represent a fundamental phylogenetic divergence within the annual Stephanomerias. The third species, Stephanomeria diegensis, combines the morphological features of both of them but is very sharply isolated reproductively from them. The available evidence suggests that S. diegensis as well as one of the subspecies of S. exigua are derived from independent interspecific hybridization between other subspecies of S. exigua and S. virgata followed by selection of adapted genotypes. This hypothesis, although necessarily speculative because it deals with events that happened in the past, provides a coherent view of the complex pattern of diversity of these plants.
A model is suggested in which, through hybridization and pollination by essentially flower-constant insects, sympatric speciation in angiosperms becomes a possible and plausible mechanism. There is evidence that despite frequent hybridizations there is no tendency for distinct species of Penstemon to be swamped. The hybrids between some species of Penstemon resemble other discrete species, all of which have their own normal range of selective pollinators. Such hybrids may form, or may have formed in the past, new species. The mechanism by which this operates appears to be true homogamy as defined essentially by Mayr (1947). It is thus possible that through homogamy new species may become established without either geographic or strong genetic isolation from their parents.
Delphinium gypsophilum is a well defined, wide spread species found at lower elevations in the foothills of the coastal and cross ranges that border the central valley of California. It is morphologically intermediate between two other widespread species and occupies a habitat that is geographically and ecologically intermediate. Evidence is discussed that suggests that D. gypsophilum had its origin by a rapid sequence of hybridizations and fixations of a limited number of hybrid genotypes, without change of chromosome number. Other evidence indicates that the process of reticulate anastomosing speciation represented by this example is a general attribute of Delphinium, because the barriers to interspecific gene exchanges are seldom absolute and are commonly moderate. Our criterion for speciation is the persistence for indefinite periods of well defined, recognizably stabilized taxa, even though they may frequently be in sufficient contact to exchange genes abundantly.
Hybridization between Purshia tridentata (Pursh) D. C. and Cowania stansburyana Torr. is common wherever these two species come together in nature. Subsequent introgression is so extensive that non-introgressed populations are rare or absent throughout Utah. The principal reproductive barrier between these two species appears to be disjunct flowering periods. On ridges providing contrasting exposures, the flowering periods are sometimes permitted to overlap and hybridization follows. Terrain having multidirectional exposures promotes abundant recombination that results in "hybrid swarm" types of populations. Where only two contrasting slopes are available, only direct introgression results. Purshia glandulosa Curran, growing at the southern limits of P. tridentata, appears to be a stabilized segregant from the hybrid between P. tridentata and Cowania. The unique combinations of Purshia and Cowania characters present in P. glandulosa is considered to represent a means for Purshia to extend its range southward. Purshia growing north of the range of Cowania also appears to be favored by introgression from Cowania. Immediately north of Cowania's current distribution, Purshia populations contain discontinuous associations of Cowania characters. Farther north in Idaho and Montana some of these characters have become stabilized and certain Cowania characters are in nearly every plant of many populations. Such widespread migration of Cowania characters into Purshia must have been promoted by some accompanying strong selective advantage. That this advantage may have been provided by increased unpalatability attending those Purshia plants which have been introgressed with Cowania characters, is suggested by the recent reports of unpalatable populations of Purshia throughout Idaho, Washington, and Montana.
The Hawaiian endemics, Scaevola gaudichaudiana and S. mollis, are diploids (n = 8) which comprise, with a broad range of intermediates, an interspecific complex with populations occurring on the islands of Molokai, Lanai, Oahu, and Kauai. Populations of S. mollis occur only on Oahu, but those of S. gaudichaudiana and of intermediates are found on all four islands. On Wiliwilinui Ridge, Oahu, the two species are sympatric, the plants of each species occurring within a few meters of each other, accompanied by a hybrid swarm. Some recombination types are comparable to those of isolated populations on Molokai and Kauai, as well as Oahu, suggesting that these and other similarly isolated populations originated through natural hybridization and subsequent dispersal, probably by birds, of the conspicuous drupaceous fruits. The evolutionary dynamics appear comparable to those operative in cyclic hybridization as proposed by Rattenbury for the New Zealand flora.
Measurements were made of certain floral characteristics in thirty plants each of Ophrys fusca and O. lutea, of two probable interspecific hybrids, and of seven plants of O. Murbeckii, all collected in the vicinity of Algiers. Similar measurements were made of several plants of O. Murbeckii from other parts of Algeria. From these measurements, certain ratios were computed, and various ones of these characters were combined according to the methods of the pictorialized scatter diagram and the hybrid index, as devised by Anderson. The two parental species are most easily separated on the basis of certain ratios of measurements of the labellum, and are clearly distinguished by the combination of characters used on the pictorialized scatter diagram. In respect to all of these character the supposed F1 hybrids are intermediate between their putative parents, but the plants of O. Murbeckii deviate from both parents in respect to certain characters, particularly the small size of the labellum. Neither the pictorialized scatter diagram nor the distribution of hybrid index values give any indication of introgression of genes from O. fusca into O. lutea or vice versa at the locality studied. Both the lack of sympatric introgression and the possible origin of O. Murbeckii as a hybrid derivative are explained on the basis of the peculiar and strong selective pressure exerted by the unusual mode of cross pollination effected by males of various species of Hymenoptera. There is good indication that interspecific hybridization has played a role in the evolution of forms of O phrys, but that this role has been greatly modified by the selective action of the insect vectors.
Résumé
Les différentes espèces et sous-espèces constituant le genre Ophrys sont difficilement déterminables par suite du grand nombre de formes que l'on rencontre dans chacune d'elles. A l'aide d'un petit nombre d'individus et en appliquant les méthodes d'ANDERSON (1949) nous nous sommes efforcé de séparer certaines espèces les unes des autres. Cette étude sommaire ne constitue que le point de départ d'un travail plus important sur plusieurs espèces du genre Ophrys. Etant donné la forte densité de ces plantes sur une station près de Montpellier, des études statistiques plus poussées pourront être entreprises.
Hybrid plant types that morphologically closely approach the Peruvian diploid species Solanum raphanifolium are analyzed and described here for the first time. The results of these investigations suggest that S. raphanifolium is a stabilized hybrid derivative of S. megistacrolobum and S. canasense, two widely distributed diploid species whose ranges overlap in southern Peru. The importance of natural selection in the stabilization of hybrid genotypes is discussed.
The large number of Phlox taxa whose attributes are intermediate to or are a composite of those of other taxa suggests that hybridization may haveplayed a major role in the evolution of the genus. Of special interest in this regard are the origins of P. pilosa subsp, deamii and P. amoena subsp. ligbtbipei which bridge the morphological hiatis between P. pilosa subsp. pilosa and P. amoena subsp, amoana. The former pair occur as enclaves within the area of distribution of their allies, P. pilosa subsp, deamii in southern Indiana, western Kentucky, and western Tennessee and P. amoena subsp, ligbtbipei in the Coastal Plain of Georgia. These entities may be interpreted as representing steps in an evolutionary series, as representing stabilized hybrid derivatives, or a combination of these viewpoints. Evidence derived from a number of sources strongly suggests that P. pilosa subsp, deamii and P. amoena subsp, ligbtbipei are products of hybridization followed by the rapid fixation of certain recombinant types. T...
Analyses of populations ofRaphanus growing in the central part of California, from the Sierra Nevada foothills to the Pacific coast, show that pureR. raphanistrum can be found only in the Central Valley, while over the remainder of the area populations of the so-called “wild” (weedy)R. sativus occur. More detailed morphological studies of a number of populations in this area have revealed that the populations of “wild”R. sativus originated by hybridization of the cultivated forms of this species (the radish) with another introduced species, already a weed,R. raphanistrum. The composition of each hybrid population with respect to the proportion of characters of the one or the other species depends upon the habitat it occupies and its geographic location. Populations in inland areas display a high proportion ofR. raphanistrum characters, while in those near the coastR. sativus characters predominate.
Artificial hybrids betweenR. raphanistrum and a cultivated form ofR. sativus exhibited about 50% pollen fertility and were heterozygous for a reciprocal translocation. Examination of “wild” populations ofR. sativus revealed that plants heterozygous for a reciprocal translocation are present in varying proportions. Experimental evidence is produced to show that this translocation is identical with that separatingraphanistrum from cultivated forms ofsativus. Thus a cytological proof of the introgression is added to the morphological evidence. Introgression ofraphanistrum characters appears to have been a major factor in converting the erstwhile crop plant,R. sativus, into a highly successful weed in California.
The diploid basic chromosome number forOphrys is 2n = 36. Tetraploidy has been found inO. fusca agg. only. Aneuploidy and aneusomaty are wide-spread; supernumerary chromosomes behave B-like, but do not differ by shape or structure from A-chromosomes. A new staining method reveals clearly differentiated bipartite meiotic kinetochores. Evolutionary aspects of homogamic hybridization, chromosome instability, and of the basic chromosome number x = 18 are discussed.
Incluye bibliografía Publicado anteriormente por John Woley$Sons en 1949
Thesis (Ph. D.)--Univ. of California, Jan 1950. "Literature cited": p. 123-129.
Hybridization may influence evolution in a variety of ways. If hybrids are less fit, the geographical range of ecologically divergent populations may be limited, and prezygotic reproductive isolation may be reinforced. If some hybrid genotypes are fitter than one or both parents, at least in some environments, then hybridization could make a positive contribution. Single alleles that are at an advantage in the alternative environment and genetic background will introgress readily, although such introgression may be hard to detect. 'Hybrid speciation', in which fit combinations of alleles are established, is more problematic; its likelihood depends on how divergent populations meet, and on the structure of epistasis. These issues are illustrated using Fisher's model of stabilizing selection on multiple traits, under which reproductive isolation evolves as a side-effect of adaptation in allopatry. This confirms a priori arguments that while recombinant hybrids are less fit on average, some gene combinations may be fitter than the parents, even in the parental environment. Fisher's model does predict heterosis in diploid F1s, asymmetric incompatibility in reciprocal backcrosses, and (when dominance is included) Haldane's Rule. However, heterosis arises only when traits are additive, whereas the latter two patterns require dominance. Moreover, because adaptation is via substitutions of small effect, Fisher's model does not generate the strong effects of single chromosome regions often observed in species crosses.
Excerpt
The concept of differentiation-hybridization cycles was first elaborated in a group of diploid Galium species from the Eastern Mediterranean (Ehrendorfer 1958). In this group crossing barriers between the very distinct Galium graecum and G. canum remain practically intact on some Aegean Islands, e.g., Rhodes, where strong competition tolerates only a small amount of hybrid introgression in spite of extensive sympatric occurrence. On the Anatolian mainland, however, crossing barriers between G. graecum and G. canum have broken down under less rigorous competition and more possibilities for ecological and geographical expansion. Hybridization has led to the origin of the highly polymorphous G. dumosum, a hybrid complex which has widely replaced the parental species and is in full course of new differentiation, forming a center of variability. The data concerning this and other groups of Galium have been incorporated into a generalized diagram, conveying the concept of differentiation-hybridization in pictorial manner (fig. 1)...
Übersicht über die bisher bekannt gewordenenOphrys-Hybriden
- H R Reinhard
- O Indanesch
- E Unddanesch
1913: L'Ophrys Botteroni Chod. est-il une espèce en voie de formation?
- R Chodat
- R. Chodat
The genetic-physiologic structure of species complexes in relationship to environment
- W M Hiesey
Interspecific hybridization inLesquerella
- R C Rollins
- O T Andsolbrig
- R. C. Rollins
Iconographie des Orchidées d'Europe et du Bassin Méditerranéen
- E G Camus
- A Etcamus
- E. G. Camus
Über eineOphrys-Population aus Kreta
- Schmucker
- Th
Supplement to species and subspecics of the genus Ophrys The role of hybridization in evolution
- Hybriden
- Hybridogene Sippen
- G L Stebbins
- Jr
--1973: Supplement to species and subspecics of the genus Ophrys. Aeta Bot. Sci. Hung. 18, 379--384. Hybriden und hybridogene Sippen bei Ophrys STEBBINS, G. L., Jr., 1959: The role of hybridization in evolution. Proc. Amcr. Phih Soc. 103, 231--251.