Genetic diversity and structure of a Mediterranean endemic plant in Corsica (<Emphasis Type="Italic">Mercurialis corsica</Emphasis>, Euphorbiaceae)

The island of Corsica is a Mediterranean hotspot of plant biodiversity characterized by a high rate of plant endemism, but also by a lack of studies combining genetic diversity and conservation. In Corsica, the dioecious and Corso-Sardinian endemic Mercurialis corsica Cosson (Euphorbiaceae) occurs across a wide ecological gradient, but the number of populations have decreased considerably over the last century. The main aim of this study was to examine the patterns of genetic diversity occurring in the Corsican populations of M. corsica, depending on their location and demographic structure. The rDNA sequences did not show the existence of any polymorphism, whereas the cpDNA sequences revealed the divergence of the western Corsican populations. By contrast, when the AFLP markers were examined, although significant levels of differentiation were detected between populations, no distinct geographical patterns were observed except for the pronounced isolation of the Cap Corse genotypes. No significant correlations were found to exist between population size and the genetic diversity indexes used. The results of this study suggest that M. corsica has undergone a complex gene flow history involving past population admixtures, followed by fragmentation processes resulting in population differentiation but no geographical patterns of isolation. These results support the existence of three evolutive conservation units which have to be monitored in priority to determine whether the current pattern of demographic structure is still declining or has stabilized.     

Gene Geographic Variation and Genetic Differentiation in the Root Vole Microtus oeconomus Pallas 1776 (Cricetidae,Rodentia) from the Kuril Islands

Electrophoretic analysis of 12 enzyme systems and 3 nonenzyme proteins (in all, 24 interpretable loci) was carried out for Microtus oeconomus from ten Kuril Islands, Kamchatka Peninsula, and the vicinity of the city of Magadan. Gene geographic variation was examined and the coefficients of genetic variation and differentiation were estimated. The interpopulation allozyme differentiation was low (D _{Nei, 1972} not higher than 0.053) and caused by variation in the allele frequencies of polymorphic loci. The greatest genetic distances were found between the populations belonging to different subspecies. Allozyme differentiation of Far Eastern M. oeconomusand M. fortis are discussed in relation to the data on the age of the island isolation and paleontological records. Karyological analysis (G-, C-, and NOR-banding) demonstrated the absence of differences between M. oeconomus from Kamchatka and the vicinity of Magadan.     

Range‐wide genetic homogeneity in the California sea mussel (Mytilus californianus): a comparison of allozymes,nuclear DNA markers,and mitochondrial DNA sequences

We tested for genetic differentiation among six populations of California sea mussels (Mytilus californianus) sampled across 4000 km of its geographical range by comparing patterns of variation at four independent types of genetic markers: allozymes, single‐copy nuclear DNA markers, and DNA sequences from the male and female mitochondrial genomes. Despite our extensive sampling and genotyping efforts, we detected no significant differences among localities and no signal of isolation by distance suggesting that M. californianus is genetically homogeneous throughout its range. This concordance differs from similar studies on other mytilids, especially in the role of postsettlement selection generating differences between exposed coastal and estuarine habitats. To assess if this homogeneity was due to M. californianus not inhabiting estuarine environments, we reviewed studies comparing allozymes with other classes of nuclear DNA markers. Although both types of markers gave broadly consistent results, there was a bias favouring studies in which allozymes were more divergent than DNA markers (nine to three) and a disproportionate number of these cases involved marine taxa (seven). Furthermore, allozymes were significantly more heterogeneous than DNA markers in three of the four studies that sampled coastal and estuarine habitats. We conclude that the genetic uniformity exhibited by M. californianus may result from a combination of extensive gene flow and the lack of exposure to strong selective gradients across its range.     

Sexual Isolation Between Drosophila Melanogaster, D. Simulans and D. Mauritiana: Sex and Species Specific Discrimination

The sexual isolation among the related species Drosophila melanogaster, D. simulans and D. mauritiana is asymmetrical. While D. mauritiana males mate well with both D. melanogaster and D. simulans females, females of D. mauritiana discriminate strongly against males of these two species. Similarly, D. simulans males mate with D. melanogaster females but the reciprocal cross is difficult. Interspecific crosses between several populations of the three species were performed to determine if (i) males and females of the same species share a common sexual isolation genetic system, and (ii) males (or females) use the same genetic system to discriminate against females (or males) of the other two species. Results indicate that although differences in male and female isolation depend on the populations tested, the isolation behaviour between a pair of species is highly correlated despite the variations. However, the rank order of the isolation level along the populations was not correlated in both sexes, which suggests that different genes act in male and female sexual isolation. Neither for males nor for females, the isolation behaviour of one species was paralleled in the other two species, which indicates that the genetic systems involved in this trait are species-pair specific. The implications of these results are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic divergence of populations of the white char <Emphasis Type="Italic">Salvelinus Albus</Emphasis>, northern and southern forms of malma <Emphasis Type="Italic">S. malma</Emphasis> (Salmonidae), by microsatellite loci of DNA

A very small but statistically significant genetic differentiation by allele frequencies (in the Kamchatka basin F _ST = 0.016 and in Kronotskoe Lake F _ST = 0.063) is revealed between sympatric populations of the northern malma Salvelinus malma malma and of the white char S. albus by analysis of nine microsatellite loci. Factor analysis and clusterization of individual multilocal genotypes in the sum sample of sympatric S. malma malma and S. albus also demonstrate their extremely weak genetic differentiation. Divergence between geographically isolated (allopatric) populations of each of these chars exceeds by two-three times the interspecies differentiation in the zones of sympatry. Samples from allopatric populations clusterize by the geographic principle but not by the taxonomic principle. Such a situation may be explained by the absence of reproductive isolation and presence of hybridization between sympatric S. malma malma and S. albus with the simultaneous existence of some limitations of genetic exchange related to the ecological specialization of these chars. Analysis of microsatellite loci revealed highly significant genetic differences between the northern and southern forms of malma S. malma krascheninnikovi by many times exceeding genetic differences between S. malma malma and S. albus. The obtained data do not confirm the independent species status of S. albus but support the opinion of the species level of differences between the northern and southern forms of malma.     

Comparative phylogeography of two co‐distributed but ecologically distinct rainbowfishes of far‐northern Australia

Aim

To test the influence of historical and contemporary environment in shaping the genetic diversity of freshwater fauna we contrast genetic structure in two co‐distributed, but ecologically distinct, rainbowfish; a habitat generalist (Melanotaenia splendida) and a habitat specialist (M. trifasciata).

Location

Fishes were sampled from far northern Australia (Queensland and Northern Territory).

Methods

We used sequence data from one mitochondrial gene and one nuclear gene to investigate patterns of genetic diversity in M. splendida and M. trifasciata to determine how differences in habitat preference and historical changes in drainage boundaries affected patterns of connectivity.

Results

Melanotaenia splendida showed high levels of genetic diversity and little population structure across its range. In contrast, M. trifasciata showed high levels of population structure. Whereas phylogeographic patterns differed, both species showed a strong relationship between geographical distance and genetic differentiation between populations. Melanotaenia splendida showed a shallower relationship with geographical distance, and genetic differentiation was best explained by stream length and a lower scaled ocean distance (11.98 times coast length). For M. trifasciata, genetic differentiation was best explained by overwater distance between catchments and ocean distance scaled at 1.16 × 10⁶ times coast length.

Main conclusions

Connectivity of freshwater populations inhabiting regions periodically interconnected during glacial periods appears to have been affected by ecological differences between species. Species‐specific differences are epitomized here by the contrast between co‐distributed congeners with different habitat requirements: for the habitat generalist, M. splendida, there was evidence for greater historical genetic connectivity with oceans as a weaker barrier to gene exchange in contrast with the habitat specialist, M. trifasciata.     

Patterns of isozyme variation in relation to population size,isolation, and phytogeographic history in royal catchfly (Silene regia; Caryophyllaceae)

The distribution of genetic variation within and among plant populations is influenced by both contemporary and historical factors. I used isozyme analysis of band phenotypes to examine genetic structure in the rare prairie forb Silene regia. Relationships between current-day population size, isolation, and phenotypic variation were assessed for 18 populations in two regions with differing postglacial history. Western populations from unglaciated southern Missouri and Arkansas were more genetically diverse based on the Shannon-Weaver index (H) and a polymorphic index than were more eastern populations. These differences may be due to loss of variation with repeated founding of new populations in previously glaciated sites in Indiana and Ohio. Within the western region, population size was not significantly correlated with genetic variation. In the east, size was correlated with Shannon-Weaver diversity. There was no relationship between variation and isolation in either region, but eastern populations were slightly more differentiated. Greater among-population differentiation and the demonstrated connection between population size and variation in the eastern sites may reflect lower levels of interpopulation gene flow in the fragmented remnant prairies of Indiana and Ohio.     

Morphological versus genetic diversity of Viola reichenbachiana and V. riviniana (sect. Viola,Violaceae) from soils differing in heavy metal content

Morphological characters, AFLP markers and flow cytometry were used to investigate the morphological and genetic variability and differentiation of Viola reichenbachiana and V. riviniana in non‐metallicolous (NM) and metallicolous (M) populations. The aims were to clarify the taxonomic status of plants occurring in ore‐bearing areas, to determine any relationship in V. reichenbachiana and V. riviniana from sites not polluted with heavy metals, and to examine the genetic variability and differentiation of M and NM populations of both species. Multivariate analyses based on morphological characters showed significant differences between V. reichenbachiana and V. riviniana from non‐polluted sites, high levels of intra‐ and inter‐population variability, and the occurrence of inter‐specific hybrids. Plants from M populations showed hybrid characters but also fell within the range of V. riviniana or V. reichenbachiana. There were no significant differences in relative genome size between plants from polluted areas and V. riviniana from NM populations. Bayesian analysis of population genetic structure based on AFLP markers distinguished two main groups: V. reichenbachiana and V. riviniana together with the M populations. That analysis also revealed the occurrence of populations of inter‐specific hybrids from non‐polluted areas. Further Bayesian analysis of V. riviniana including NM and M populations separated all the studied M populations from NM populations. We conclude that plants forming the M populations are well adapted to a metal‐polluted environment, and could be considered as stabilised introgressive forms resulting from unidirectional (asymmetric) introgression toward V. riviniana.     

Males,but not females,contribute to sexual isolation between two sympatric species of <Emphasis Type="Italic">Gambusia</Emphasis>

Reproductive isolation restricts genetic exchange between species. Various pre- and post-mating barriers, such as behavior, physiology and gametic incompatibility, have been shown to evolve in sympatry. In certain scenarios, isolation can be asymmetrical, where species differentially prefer conspecifics. We examined sexual isolation via conspecific mate preference between Gambusia affinis and G. geiseri in both sexes. To investigate male contribution to sexual isolation, we compared the number of mating attempts (gonopodial thrusts) directed at either a conspecific or a heterospecific female, in both species. We also examined sperm priming and expenditure in males in the presence of conspecific or heterospecific females. We then measured female preference for either a conspecific or heterospecific male, in both species. We found that males of both species preferred to mate with conspecific females, but showed no difference in sperm production or expenditure between conspecific and heterospecific females. Females of both species did not prefer conspecific over heterospecific males. Our results suggest that sexual isolation might be mediated by male mate choice in this system and not female choice, suggesting that there is asymmetrical reproductive isolation between the sexes in G. affinis and G. geiseri, but symmetrical species isolation.     

THE RELEVANCE OF GENE FLOW IN METAPOPULATION DYNAMICS OF AN OCEANIC ISLAND ENDEMIC,OLEA EUROPAEA SUBSP. GUANCHICA

Theoretical and empirical studies suggest that geographical isolation and extinction–recolonization dynamics are two factors causing strong genetic structure in metapopulations, but their consequences in species with high dispersal abilities have not been tested at large scales. Here, we investigated the effect of population age structure and isolation by distance in the patterns of genetic diversity in a wind‐pollinated, zoochorous tree (Olea europaea subsp. guanchica) sporadically affected by volcanic events across the Canarian archipelago. Genetic variation was assessed at six nuclear microsatellites (nDNA) and six chloroplast fragments (cpDNA) in nine subpopulations sampled on four oceanic islands. Subpopulations occurring on more recent substrates were more differentiated than those on older substrates, but within‐subpopulation genetic diversity was not significantly different between age groups for any type of marker. Isolation‐by‐distance differentiation was observed for nDNA but not for cpDNA, in agreement with other metapopulation studies. Contrary to the general trend for island systems, between‐island differentiation was extremely low, and lower than differentiation between subpopulations on the same island. The pollen‐to‐seed ratio was close to one, two orders of magnitude lower than the average estimated for other wind‐pollinated, animal‐dispersed plants. Our results showed that population turnover and geographical isolation increased genetic differentiation relative to an island model at equilibrium, but overall genetic structure was unexpectedly weak for a species distributed among islands. This empirical study shows that extensive gene flow, particularly mediated by seeds, can ameliorate population subdivision resulting from extinction–recolonization dynamics and isolation by distance.     

Consequences of multiple mating‐system shifts for population and range‐wide genetic structure in a coastal dune plant

Evolutionary transitions from outcrossing to selfing can strongly affect the genetic diversity and structure of species at multiple spatial scales. We investigated the genetic consequences of mating‐system shifts in the North American, Pacific coast dune endemic plant Camissoniopsis cheiranthifolia (Onagraceae) by assaying variation at 13 nuclear (n) and six chloroplast (cp) microsatellite (SSR) loci for 38 populations across the species range. As predicted from the expected reduction in effective population size (N_e) caused by selfing, small‐flowered, predominantly selfing (SF) populations had much lower nSSR diversity (but not cpSSR) than large‐flowered, predominantly outcrossing (LF) populations. The reduction in nSSR diversity was greater than expected from the effects of selfing on N_e alone, but could not be accounted for by indirect effects of selfing on population density. Although selfing should reduce gene flow, SF populations were not more genetically differentiated than LF populations. We detected five clusters of nSSR genotypes and three groups of cpSSR haplotypes across the species range consisting of parapatric groups of populations that usually (but not always) differed in mating system, suggesting that selfing may often initiate ecogeographic isolation. However, lineage‐wide genetic variation was not lower for selfing clusters, failing to support the hypothesis that selection for reproductive assurance spurred the evolution of selfing in this species. Within three populations where LF and SF plants coexist, we detected genetic differentiation among diverged floral phenotypes suggesting that reproductive isolation (probably postzygotic) may help maintain the striking mating‐system differentiation observed across the range of this species.     

Relationships of eelpouts of the genus <Emphasis Type="Italic">Zoarces</Emphasis> (Zoarcidae,Pisces) inferred from molecular genetic and morphological data

Abstract-Molecular genetic and morphological analysis of eelpouts of the genus Zoarces was carried out. Based on the mitochondrial DNA sequence variation, haplotypes of notched-fin eelpout, Z. elogatus, more closely related Fedorov eelpout, Z. fedorovi, and common eelpout, Z. viviparus, as well as of Andriyashev eelpout, Z. andriashevi, were grouped in one macrocluster. Haplotypes of American eelpout, Z. americanus, and blotched eelpout, Z. gillii, clustered separately from other species. The genetic differences between Z. gillii and the other eelpout species were very high for within-genus comparisons, constituting 7.62%. Species divergence in terms of morphological characters was generally consistent with molecular genetic data and confirmed distinct isolation of American eelpout, and especially of blotched eelpout.     

THE GENETIC BASIS OF SEXUAL ISOLATION BETWEEN DROSOPHILA MELANOGASTER AND D. SIMULANS

The genetic analysis of sexual isolation between the closely-related species Drosophila melanogaster and Drosophila simulans involved two experiments with no-choice tests. The efficiency of sexual isolation was measured by the frequency of courtship initiation and interspecific mating. We first surveyed the variation in sexual isolation between D. melanogaster strains and D. simulans strains of different geographic origin. Then, to investigate variation in sexual isolation within strains, we made F₁ diallel sets of reciprocal crosses within strains of D. melanogaster and D. simulans. The F₁ diallel progeny of one sex were paired with the opposite sex of the other species. The first experiment showed significant differences in the frequency of interspecific mating between geographic strains. There were more matings between D. simulans females and D. melanogaster males than between D. melanogaster females and D. simulans males. The second experiment uncovered that the male genotypes in the D. melanogaster diallel significantly differed in interspecific mating frequency, but not in courtship initiation frequency. The female genotypes in the D. simulans diallel were not significantly different in courtship initiation and interspecific mating frequency. Genetic analysis reveals that in D. melanogaster males sexual isolation was not affected by either maternal cytoplasmic effects, sex-linked effects, or epistatic interaction. The main genetic components were directional dominance and overdominance. The F₁ males achieved more matings with D. simulans females than the inbred males. The genetic architecture of sexual isolation in D. melanogaster males argues for a history of weak or no selection for lower interspecific mating propensity. The behavioral causes of variation in sexual isolation between the two species are discussed.     

Genetic effects of landscape,habitat preference and demography on three co‐occurring turtle species

Expanding the scope of landscape genetics beyond the level of single species can help to reveal how species traits influence responses to environmental change. Multispecies studies are particularly valuable in highly threatened taxa, such as turtles, in which the impacts of anthropogenic change are strongly influenced by interspecific differences in life history strategies, habitat preferences and mobility. We sampled approximately 1500 individuals of three co‐occurring turtle species across a gradient of habitat change (including varying loss of wetlands and agricultural conversion of upland habitats) in the Midwestern USA. We used genetic clustering and multiple regression methods to identify associations between genetic structure and permanent landscape features, past landscape composition and landscape change in each species. Two aquatic generalists (the painted turtle, Chrysemys picta, and the snapping turtle Chelydra serpentina) both exhibited population genetic structure consistent with isolation by distance, modulated by aquatic landscape features. Genetic divergence for the more terrestrial Blanding's turtle (Emydoidea blandingii), on the other hand, was not strongly associated with geographic distance or aquatic features, and Bayesian clustering analysis indicated that many Emydoidea populations were genetically isolated. Despite long generation times, all three species exhibited associations between genetic structure and postsettlement habitat change, indicating that long generation times may not be sufficient to delay genetic drift resulting from recent habitat fragmentation. The concordances in genetic structure observed between aquatic species, as well as isolation in the endangered, long‐lived Emydoidea, reinforce the need to consider both landscape composition and demographic factors in assessing differential responses to habitat change in co‐occurring species.     

Phylogeography of the red coral (<Emphasis Type="Italic">Corallium rubrum</Emphasis>): inferences on the evolutionary history of a temperate gorgonian

The red coral Corallium rubrum (Cnidaria, Octocorallia) is an exploited, long-lived sessile species from the Mediterranean Sea and the adjacent coastline in the Atlantic Ocean. Surveys of genetic variation using microsatellites have shown that populations of C. rubrum are characterized by strong differentiation at the local scale but a study of the phylogeography of this species was still lacking. Here, we used seven polymorphic microsatellite loci, together with sequence data from an intron of the elongation factor 1 (EF1) gene, to investigate the genetic structure of C. rubrum across its geographical range in the western Mediterranean Sea and in the Adriatic Sea. The EF1 sequences were also used to analyse the consequences of demographic fluctuations linked with past environmental change. Clustering analysis with microsatellite loci highlighted three to seven genetic groups with the distinction of North African and Adriatic populations; this distinction appeared significant with AMOVA and differentiation tests. Microsatellite and EF1 data extended the isolation by distance pattern previously observed for this species at the western Mediterranean scale. EF1 sequences confirmed the genetic differentiation observed between most samples with microsatellites. A statistical parsimony network of EF1 haplotypes provided no evidence of high sequence divergence among regions, suggesting no long-term isolation. Selective neutrality tests on microsatellites and EF1 were not significant but should be interpreted with caution in the case of EF1 because of the low sample sizes for this locus. Our results suggest that recent Quaternary environmental fluctuations had a limited impact on the genetic structure of C. rubrum.     

Synchronic east–west divergence in azure‐winged magpies (Cyanopica cyanus) and magpies (Pica pica)*

Morphometric and genetic analyses were performed to investigate the relationships between populations of the azure‐winged magpie (Cyanopica cyanus). In the morphometric analysis 193 specimens were included representing seven of the nine currently accepted subspecies. Among eight characters analysed, four showed significant differences between samples from Spain and Asia. In contrast, the Asian populations/subspecies are not differentiated morphologically except Cyanopica cyanus japonica. The genetic analysis was based on two mitochondrial sequences (control region, cytochromeb gene). The results are in accordance with the morphometric analysis, showing a clear distinction between birds from the western and eastern distribution ranges. The differentiation of C. c. japonica is not found at the sequence level. Both genetic and morphological data support species status of C. cyanus and Cyanopica cooki. The magpie (Pica pica) was included in the phylogenetic study for comparing intraspecific variation. As in C. cyanus, two clearly separated groups are found, one of them containing the far‐eastern populations (Pica pica jankowskii and Pica pica sericea) and the other the remaining subspecies studied. For both the azure‐winged magpie and the magpie the sequence data imply an east–west differentiation, probably caused by long lasting isolation that may have even started in the Pliocene or repeated expansions/restrictions of distribution ranges during the Pleistocene.     

Survival and growth of parasitic <Emphasis Type="Italic">Maculinea alcon</Emphasis> caterpillars (Lepidoptera,Lycaenidae) in laboratory nests of three <Emphasis Type="Italic">Myrmica</Emphasis> ant species

The Alcon blue butterfly (Maculinea alcon) parasitizes the nests of several Myrmica ant species. In Denmark, it uses M. rubra and M. ruginodis, but never M. scabrinodis. To further examine the basis of this specificity and local co-adaptation between host and parasite, the pattern of growth and survival of newly-adopted caterpillars of M. alcon in Myrmica subcolonies was examined in the laboratory. M. alcon caterpillars were collected from three populations differing in their host use, and reared in laboratory nests of all three ant species collected from each M. alcon population. While there were differences in the pattern of growth of caterpillars from different populations during the first few months after adoption, which depended on host ant species and the site from which the ants were collected, there was no evidence of major differences in final size achieved. Survival was, however, much higher in nests of M. rubra than in nests of M. ruginodis and M. scabrinodis, even for caterpillars from a population that is never known to use M. rubra as a host in the field. The caterpillars of M. alcon thus do not show local adaptation in their pattern of growth and survival, but instead show a pattern that may reflect different nestmate recognition abilities of the host ants, related to their sociogenetic organisation. The pattern of observed host ant use in the field seems to result from a combination of differences in local host availability and locally adapted infectivity, modulated by smaller differences in survivorship in the nests of the different host ants.     

Genetic,phenotypic, and phytochemical polymorphism in Eastern European populations of <Emphasis Type="Italic">Mentha arvensis</Emphasis> L.

Variability of M. arvensis from five geographically distanced populations was examined using morphological traits and phytochemical composition of essential oil and with the help of DNA fingerprinting using ISSR markers. The population differentiation based on morphological traits was weak. Analysis of the essential oil composition provided the subdivision of the sample into three groups and, on the basis of the composition of ISSR amplicons, into four groups of specimens. A high degree of genetic polymorphism of M. arvensis and substantial, though incomplete, population differentiation were identified. It was demonstrated that the population of M. arvensis from the Komi Republic was the most genetically isolated, while the populations from Moscow and Penza provinces were weakly differentiated from each other. The population from the Republic of Belarus (near Grodno) was genetically and phytochemically considerably different from the other studied populations, although morphologically indistinguishable from them. We argue that the differentiation was caused not only by the isolation by distance but also owing to the formation of three different ecotypes adapted to different climatic conditions.     

Patterns of hybrid formation among cryptic species of bird‐nest fern,Asplenium nidus complex (Aspleniaceae), in West Malesia

In order to clarify patterns of hybrid formation in the Asplenium nidus complex, artificial crossing experiments were performed between individuals of genetically differentiated groups based on the sequence of the rbcL gene, including A. australasicum from New Caledonia, A. setoi from Japan and several cryptic species in the A. nidus complex. No hybrid plants were obtained in crosses between nine of the 16 pairs. Even for pairs that generated hybrids, the frequency of hybrid formation was lower than expected given random mating, or only one group was able to act as the maternal parent, when the genetic distance (Kimura's two parameter) between parental individuals was at least 0.006. Sterile hybrids were produced by three pairs that were distantly related but capable of forming hybrids. Considering the results of the crosses together with the genetic distance between the parental individuals, it seems that the frequency of hybrid formation decreases rapidly with increasing divergence. The frequency of hybrid formation has not been previously examined in homosporous ferns, but it seems that a low frequency of hybrid formation can function as an important mechanism of reproductive isolation between closely related pairs of species in the A. nidus complex in addition to hybrid sterility. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 42–63.     

Genetic Diversity and Structure in Fragmented Populations of the Tropical Orchid Myrmecophila christinae var christinae1

In recent years the coastal dune vegetation of the state of Yucatan, Mexico has become highly fragmented due to clearing for development. We evaluated patterns of genetic differentiation and genetic variability among orchid populations (Myrmecophila christinae var christinae) in eight habitat fragments along a west‐to‐east disturbance gradient in which sites located on the western end began experiencing fragmentation earlier than those in the east. Leaf samples from adult individuals and juvenile plants were collected from all eight populations, and analyzed using starch‐gel electrophoresis in a lithium buffer system. Per population estimates of genetic diversity, proportion of polymorphic loci at 95 percent, mean number of alleles per locus, allelic richness, and population structure were calculated, as well as estimate comparisons between generations. Genetic diversity at the loci analyzed did not show significant differences among the eight populations. Based on the results, the model of isolation by distance does not fit the M. christinae populations under study; in some cases, populations close to one another apparently experienced very little genetic exchange. Thus, we propose that so far, fragmentation has not led to significant genetic differences between populations subject to different historical backgrounds of disturbance (i.e., time since onset of disturbance), as well as between generations within each of the M. christinae study populations. Nevertheless, the genetic characteristics of some remnant populations might change over time due to a future decrease in the opportunities for genetic exchange with other populations.