Current geographical ranges of Malagasy dung beetles are not delimited by large rivers

Aim We investigated whether the largest river (Mangoro) on the east coast of Madagascar acts as a barrier to dispersal in dung beetles by comparing species composition and genetic differentiation of the most common species on the two banks of the river. Moreover, by analysing the current geographical ranges of all wet forest dung beetle species, possible long‐term effects of the largest rivers on the distribution of species were assessed. Location Madagascar. Methods Dung beetles were sampled with baited pitfall traps at a downstream and an upstream locality on the two banks of the Mangoro River. The most common species, Nanos binotatus (Canthonini), was sequenced for cytochrome c oxidase subunit I (COI; 804 bp) to characterize within‐population diversity and between‐population genetic differentiation. For the analysis of species geographical range boundaries in relation to the position of the largest rivers on the east coast, a database including all the records for 158 wet forest species was used. The congruence of species range boundaries with the positions of the rivers was tested with a randomization test. Results All common species were found on both sides of the Mangoro River. In Nanos binotatus, haplotype and nucleotide diversities ranged from 0.25 to 0.85 and 0.001 to 0.01, respectively. Population differentiation was high and significant in all comparisons (P < 0.01; average F_ST = 0.61). The differentiation was not significantly higher across than along the river, as would be expected by the riverine barrier hypothesis. There was no indication that the range boundaries of wet forest dung beetle species would generally coincide with the largest rivers in eastern Madagascar. Main conclusions The results provide little support for the riverine barrier hypothesis as an explanation for the current range boundaries of dung beetles in eastern Madagascar. However, extensive deforestation of the coastal regions in eastern Madagascar may have caused a great shrinkage of the ranges of many forest‐dwelling species. Thus the present‐day distributions may not reflect accurately the patterns of the past geographical ranges of the species.     

Comparative Genetic Structure of the Threatened Tenebrionid Beetle Oplocephala haemorrhoidalis and its Common Relative Bolitophagus reticulatus

We used RAPD and allozyme genetic markers to compare the genetic structures of a threatened saproxylic tenebrionid beetle, Oplocephala haemorrhoidalis, and its common relative (different subfamilies), Bolitophagus reticulatus, to evaluate the relative importance of habitat fragmentation on the occurrence of the two species. O. haemorrhoidalis showed significantly higher levels of genetic differentiation between sites than B. reticulatus for both types of genetic marker. Patterns of isolation by distance were consistent with (B. reticulatus) or close to (O. haemorrhoidalis) theoretical expectations for equilibrium between gene flow and genetic drift. For O. haemorrhoidalis, the RAPD-patterns also showed a steeper increase in isolation by distance where geographic distances were small than at larger distances. This suggests that gene flow between the populations of O. haemorrhoidalis has declined as an effect of recent habitat fragmentation and is probably relatively restricted at present. For B. reticulatus, levels of genetic differentiation were low, suggesting that B. reticulatus readily moves over large areas. Genetic variability was not low in either species. Genetic differentiation among and relatedness within fruiting bodies varied substantially within sites for both species. This variation was probably due to founder events: when levels of relatedness were close to zero, genetic differentiation was also low.     

Assessing the nucleotide diversity of three aphid species by RAPD

A method is presented for the estimation of nucleotide diversity and genetic structure of populations from RAPD (random amplified polymorphic DNA) data. It involves a modification of the technique developed by Lynch and Crease (1990) for the case of restriction sites as survey data. As new elements the method incorporates (i) dominance correction, (ii) values of asexual reproduction of the populations sampled, and (iii) an analytical variance of the number of nucleotide substitutions per site. Sampling was carried out at two geographic scales for three aphid species. At a macrogeographic scale, populations of Rhopalosiphum padi did not show statistical genetic differentiation. Aphis gossypii and Myzus persicae, which were sampled at a microgeographic scale, showed a higher genetic differentiation than R. padi, it being statistically significant in M. persicae. The major sources of sampling variance within- and between-populations were found to be nucleotide (i.e., the number of alleles used as a function of the number of primers used) and population (i.e., sample size) sampling. Extremely low estimates of nucleotide diversity were obtained for the species studied here. This result is consistent with previous reports on genetic diversity for the same or other aphid species which were based on allozyme polymorphism, mitochondrial DNA variation and qualitative analyses of RAPDs.     

EVOLUTION OF THE PYGMY-FOREST EDAPHIC SUBSPECIES OF PINUS CONTORT A ACROSS AN ECOLOGICAL STAIRCASE

Patterns of allozyme variation within and between two of the subspecies of Pinus contorta were examined for the evolutionary relationship between them. In coastal northern California, these subspecies are parapatric. Pinus contorta ssp. contorta occurs on grassy coastal bluffs on the lowest and youngest of a sequence of five marine terraces; P. contorta ssp. bolanderi is endemic to a pygmy forest ecosystem that occurs on the increasingly older and harsher soils of the third, fourth, and fifth terraces. The soils of the upper three terraces are characterized by extreme podzolization, low pH, low nutrient availability, summer drought (with periodic fires), and winter surface flooding above the hardpan. Dune and cliff soils support a tall redwood and Douglas-fir forest between the terraces. Analyses of seeds collected from 11 pygmy-forest and 6 coastal populations showed ssp. bolanderi to have significantly less allozyme variation than spp. contorta. The two subspecies did not show the phylogenetic dichotomy in allozyme allelic constitutions expected for subspecific classification. Within ssp. bolanderi, the pattern of genetic distances correlated better with edaphic differences among sites than with geographic distance. It appears that ssp. bolanderi is a recently evolved derivative of ssp. contorta, and that the low degree of allozyme differentiation among the bolanderi populations may be due to colonization of the sites by small numbers of individuals, or to hitchhiking of allozyme loci linked to loci undergoing strong selection imposed by the severe edaphic conditions typical of bolanderi sites.     

Conservation of genetic diversity in old‐growth forest communities of the southeastern United States

Question: How do studies of the distribution of genetic diversity of species with different life forms contribute to the development of conservation strategies? Location: Old‐growth forests of the southeastern United States. Methods: Reviews of the plant allozyme literature are used to identify differences in genetic diversity and structure among species with different life forms, distributions and breeding systems. The general results are illustrated by case studies of four plant species characteristic of two widespread old‐growth forest communities of the southeastern United States: the Pinus palustris – Aristida stricta (Longleaf pine – wiregrass) savanna of the Coastal Plain and the Quercus – Carya – Pinus (Oak‐hickory‐pine) forest of the Piedmont. Genetic variation patterns of single‐gene and quantitative traits are also reviewed. Results: Dominant forest trees, represented by Pinus palustris(longleaf pine) and Quercus rubra (Northern red oak), maintain most of their genetic diversity within their populations whereas a higher proportion of the genetic diversity of herbaceous understorey species such as Sarracenia leucophylla and Trillium reliquum is distributed among their populations. The herbaceous species also tend to have more population‐to‐population variation in genetic diversity. Higher genetic differentiation among populations is seen for quantitative traits than for allozyme traits, indicating that interpopulation variation in quantitative traits is influenced by natural selection. Conclusion: Developing effective conservation strategies for one or a few species may not prove adequate for species with other combinations of traits. Given suitable empirical studies, it should be possible to design efficient conservation programs that maintain natural levels of genetic diversity within species of conservation interest.     

VOCAL DIALECTS AND THE STRUCTURE OF GEOGRAPHIC VARIATION IN MORPHOLOGICAL AND ALLOZYMIC CHARACTERS IN THE RUFOUS-COLLARED SPARROW,ZONOTRICHIA CAPENSIS

The geographical patterns of variation shown at 20 allozyme and non-enzymatic protein-coding loci, in 8 external, and in 12 skeletal morphological characters in the rufous-collared sparrow, Zonotrichia capensis, were analyzed in order to test the local (genetic) adaptation hypothesis regarding the origin and maintenance of vocal dialects in birds. Approximately 20 males were collected from each of four sites within each of six different dialect zones. There was significant variability in both external and skeletal morphology among all 24 sites and among dialect groups. Average Wright's corrected fixation coefficient (F_ST) was 0.118, indicating significant genetic differentiation among all sites, regardless of dialect. Hierarchical F statistics indicated that only 50% of among site variability was due to a dialect effect. Puna dialect sites were highly differentiated from all other sites with respect to both morphology (external and skeletal measures) and allozyme frequencies. Heterogeneity at the PGM-1 locus among puna scrub sites was the major cause of the high average F_ST across all sites, and within the puna scrub dialect. Average genetic differentiation among non-puna sites (F_ST = 0.018) was similar to differentiation among sites within each of the five non-puna dialect groups (mean F_ST = 0.0132 ± 0.0069). Hierarchical F statistics indicated that none of the among-site differentiation in this subset of samples was due to a dialect effect. These observations are not consistent with the local adaptation hypothesis. All significant genetic heterogeneity occurred among sites in mountainous habitats, and we suggest that topography and patchiness of habitat may have been major factors involved in population differentiation, rather than vocal dialects.     

Wide but not impermeable: Testing the riverine barrier hypothesis for an Amazonian plant species

Wallace's riverine barrier hypothesis postulates that large rivers, such as the Amazon and its tributaries, reduce or prevent gene flow between populations on opposite banks, leading to allopatry and areas of species endemism occupying interfluvial regions. Several studies have shown that two major tributaries, Rio Branco and Rio Negro, are important barriers to gene flow for birds, amphibians and primates. No botanical studies have considered the potential role of the Rio Branco as a barrier, while a single botanical study has evaluated the Rio Negro as a barrier. We studied an Amazon shrub, Amphirrhox longifolia (A. St.‐Hil.) Spreng (Violaceae), as a model to test the riverine barrier hypothesis. Twenty‐six populations of A. longifolia were sampled on both banks of the Rio Branco and Rio Negro in the core Amazon Basin. Double‐digest RADseq was used to identify 8,010 unlinked SNP markers from the nuclear genome of 156 individuals. Data relating to population structure support the hypothesis that the Rio Negro acted as a significant genetic barrier for A. longifolia. On the other hand, no genetic differentiation was detected among populations spanning the narrower Rio Branco, which is a tributary of the Rio Negro. This study shows that the strength of riverine barriers for Amazon plants is dependent on the width of the river separating populations and species‐specific dispersal traits. Future studies of plants with contrasting life history traits will further improve our understanding of the landscape genetics and allopatric speciation history of Amazon plant diversity.     

Stratified analysis of the soil seed bank in the cedar glade endemic Astragalus bibullatus: evidence for historical changes in genetic structure

Persistent seed banks may provide information on historical changes in the genetic composition of populations. We used stratified sampling of the soil seed bank of Astragalus bibullatus (Pyne's ground plum) to assess levels of temporal variation in population genetic structure and to infer historical changes in the levels of inbreeding and relative gene flow. This species has an extremely limited distribution in the Central Basin of Tennessee, where it is found in open areas and along the edges of cedar glades. Protein electrophoresis was conducted on seedlings grown from seeds that had been recovered from three successive 1 cm thick layers of soil sampled from six sites. Analyses of seven polymorphic allozyme loci indicated that there were substantial levels of genetic differentiation among soil layers and sites. Higher levels of genetic diversity were found in seed than in vegetative populations that had been sampled in a previous study. Seed populations from the uppermost soil layer had higher heterozygote deficiencies, displayed higher levels of differentiation among sites, and had higher private allele frequencies than seed populations from the lower two layers. The change in heterozygosity and distribution of genetic variation among sites for the youngest soil layer is consistent with a pattern of increased selfing, sib mating, and decreased gene flow among populations. These changes in inbreeding and relative levels of gene flow are corroborated by information on historical land use practices in the region and support the hypothesis that loss of appropriate habitat has led to smaller population sizes and a more fragmented distribution of this cedar glade endemic.     

POPULATION VARIATION,OUTCROSSING, AND COLONIZATION OF DISTURBED AREAS BY CALAMAGROSTIS CANADENSIS: EVIDENCE FROM ALLOZYME ANALYSIS

Calamagrostis canadensis (a rhizomatous grass) exists in temperate forest sites of different successional age. It can rapidly colonize disturbed sites to form dense swards. We examined allozyme variation in: four populations (mature forest, intermediate aged forest, forest cutblock, wetland); nine small plots (2 m × 4 m) within the cutblock; and progeny of several families from three populations; in order to assess the mode of colonization of disturbed areas and the effect of successional changes on population genetic structure. All four populations showed equal and extensive genetic variation (1.5 to 1.7 alleles per locus [K], 41.7% to 50% polymorphic loci [PPL], H_st = 0.155 to 0.208) and were not genetically differentiated (G_st = 0.0193, 1 = 0.986 to 0.997). The cutblock subpopulations also showed considerable genetic variation (K = 1.6 to 1.8, PPL = 50% to 58.3%, H_st = 0.151 to 0.278) and no microdifferentiation (G_st = 0.034, I = 0.967 to 0.997). We found 14 different genotypes among the 30 individuals sampled from the cutblock as a whole (based on five polymorphic loci). The cutblock subpopulations had from nine to 14 different genotypes each (same five loci, 18 individuals per subpopulation). Seed produced was primarily outcrossed (multilocus estimate 0.888 to 0.900). We concluded that disturbed sites are colonized primarily by sexually produced seedlings. Potential genetic drift and natural selection, which occur during subsequent successional changes, do not result in reduced genetic variation or population differentiation.     

Genetic structure,allozyme-habitat associations and reproductive fitness in Gypsophila fastigiata (Caryophyllaceae)

Relationships between allozyme differentiation, habitat variation and individual reproductive success were examined in local populations of a perennial herb, Gypsophila fastigiata, on the Baltic island of Öland (Sweden). Relatively little (c. 2%) of the total allozyme diversity in this largely outcrossing species is explained by differentiation between sites tens of kilometres apart. The low level of geographic differentiation suggests that gene flow between sites is, or has recently been, extensive. Yet the component of allozyme diversity due to differentiation between plots (only tens of meters apart) within sites is 3 times larger than the between-site component of diversity. Allozyme variation, especially at the Pgi-2 locus, is significantly associated with habitat variation within sites. Different allele x habitat combinations for the Pgi-2 locus are associated with differences in individual reproductive fitness. Differential selection in different local habitats may thus contribute to the fine-scale structuring of genetic diversity within sites.     

Low genetic diversity but local genetic differentiation in endemic Minasia (Asteraceae) species from Brazil

Espinhaço Range is a Brazilian chain of mountains, extremely rich in endemic species. Minasia has six species, all perennial herbs endemic to this range. Twenty-two populations were sampled from all Minasia species and assayed for allozyme variation. The species showed low genetic variation, compatible with the expectation for endemics. Genetic identities in Serra do Cipó and Diamantina were high, even between populations of different species. On the other hand M. cabralensis, from Serra do Cabral, was more differentiated from the other species. We also observed a marked genetic differentiation within M. cabralensis. Most strikingly, two close populations of this species showed very different allele frequencies. Our findings highlight the importance of local differentiation in campos rupestres. The observed genetic structure indicates that substantial portions of genetic diversity could be lost with the extinction of only one population, which is especially threatening considering the already low genetic diversity.     

GENETIC STRUCTURE OF POPULATIONS OF GEOGRAPHICALLY RESTRICTED AND WIDESPREAD SPECIES OF ASTRAGALUS (FABACEAE)

Evolutionary theory predicts that species with small ranges and few individuals will exhibit low levels of genetic polymorphism. We investigated the population genetic structure of two locally endemic and two geographically widespread species of Astragalus. To facilitate direct comparisons among these congeners, three populations of each species were sampled in a consistent manner and scored for allozyme polymorphisms at 12 loci. Genetic polymorphism was lower in restricted A. linifolius and A. osterhouti than in widespread A. pectinatus. However, the restricted species do exhibit a moderate level of isozyme variation, comparable to that of widespread A. pattersoni and higher than has been detected in several other rare plant taxa. As measured by Wright's F statistics, there were no consistent differences between the restricted and widespread taxa with respect to the organization of genetic variation. F_ST values were low in all taxa, indicating little heterogeneity among populations.     

Capturing Genetic Variation during Ecological Restorations: An Example from Kankakee Sands in Indiana

Genetic variation in populations, both natural and restored, is usually considered crucial for response to short‐term environmental stresses and for long‐term evolutionary change. To have the best chance of successful long‐term survival, restored populations should reflect the extant variation found in remnants, but restored sites may suffer from genetic bottlenecks as a result of founder effects. Kankakee Sands is a large‐scale restoration being conducted by The Nature Conservancy (TNC) in northwestern Indiana. Our goal was to test for loss of genetic variation in restored plant populations by comparing them with TNC’s seed source nursery and with local remnant populations that were the source of nursery seed and of the first few restored sites. Allozyme analysis of Baptisia leucantha, Asclepias incarnata, Coreopsis tripteris, and Zizia aurea showed low levels of allozyme diversity within all species and reductions in polymorphism, alleles per locus, and expected heterozygosity between remnants and restorations for all species except A. incarnata. Almost all lost alleles were rare; restored populations contained almost 90% of alleles at polymorphic loci that occurred in remnants at frequencies greater than 1%. Allele frequencies for most loci did not differ between remnants and restored sites. Most species showed significant allele frequency differentiation among remnant populations and among restored sites. Our results indicate that seed collection techniques used at Kankakee Sands captured the great majority of allozyme variation present in seed source remnant populations.     

Population structure and genetic diversity of trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) above and below natural and man-made barriers in the Russian River,California

The effects of landscape features on gene flow in threatened and endangered species play an important role in influencing the genetic structure of populations. We examined genetic variation of trout in the species Oncorhynchus mykiss at 22 microsatellite loci from 20 sites in the Russian River basin in central California. We assessed relative patterns of genetic structure and variation in fish from above and below both natural (waterfalls) and man-made (dams) barriers. Additionally, we compared sites sampled in the Russian River with sites from 16 other coastal watersheds in California. Genetic variation among the 20 sites sampled within the Russian River was significantly partitioned into six groups above natural barriers and one group consisting of all below barrier and above dam sites. Although the below-barrier sites showed moderate gene flow, we found some support for sub-population differentiation of individual tributaries in the watershed. Genetic variation at all below-barrier sites was high compared to above-barrier sites. Fish above dams were similar to those from below-barrier sites and had similar levels of genetic diversity, indicating they have not been isolated very long from below-barrier populations. Population samples from above natural barriers were highly divergent, with large F _st values, and had significantly lower genetic diversity, indicating relatively small population sizes. The origins of populations above natural barriers could not be ascertained by comparing microsatellite diversity to other California rivers. Finally, below-barrier sites farther inland were more genetically differentiated from other watersheds than below-barrier sites nearer the river’s mouth.     

DIFFERENT SPATIAL SCALES OF ADAPTATION IN THE CLIMBING BEHAVIOR OF PEROMYSCUS MANICULATUS: GEOGRAPHIC VARIATION,NATURAL SELECTION,AND GENE FLOW

Patterns of geographic variation in tree-climbing ability of Peromyscus maniculatus were used to examine the influence of spatial variation in natural selection and gene flow on the genetic divergence of climbing behavior among populations. Offspring of adults of two subspecies sampled from 10 localities in montane conifer forest, conifer woodland, and desert scrub/grassland habitats were raised in the laboratory and tested to determine their tree-climbing ability (the maximum diameter artificial rod that a mouse could climb). Comparisons of mean rod-climbing scores revealed that individuals of P. m. rufinus sampled from montane conifer forest and conifer woodland in Arizona were better climbers than P. m. sonoriensis sampled from conifer woodland and desert habitats in Nevada. This result was consistent with the hypothesis that natural selection has produced large-scale adaptation in climbing behavior. However, the climbing ability of P. m. sonoriensis sampled from conifer woodland habitats on isolated mountaintops in Nevada has not evolved in response to natural selection to the degree expected. In addition, populations sampled from desert grassland habitat, adjacent to woodland P. m. rufinus in Arizona, have climbing abilities that are not significantly different from conifer woodland populations. These observations indicate that local adaptation was constrained. An estimate of the heritability of climbing ability (h² = 0.352 ± 0.077) indicates that lack of a response to selection was not due to the absence of additive genetic variation. In addition, regressions of interpopulation differences on the degree of geographic isolation between pairs of populations do not support the hypothesis that gene flow between habitats has constrained evolution. Instead, a combination of historical events and insufficient time to respond to selection appears to have influenced geographic variation and the spatial scale of adaptation in climbing ability.     

Contemporary habitat loss reduces genetic diversity in an ecologically specialized butterfly

Aim This study investigated the influence of contemporary habitat loss on the genetic diversity and structure of animal species using a common, but ecologically specialized, butterfly, Theclinesthes albocincta (Lepidoptera: Lycaenidae), as a model. Location South Australia. Methods We used amplified fragment length polymorphism (AFLP) and allozyme datasets to investigate the genetic structure and genetic diversity among populations of T. albocincta in a fragmented landscape and compared this diversity and structure with that of populations in two nearby landscapes that have more continuous distributions of butterflies and their habitat. Butterflies were sampled from 15 sites and genotyped, first using 363 informative AFLP bands and then using 17 polymorphic allozyme loci (n = 248 and 254, respectively). We complemented these analyses with phylogeographic information based on mitochondrial DNA (mtDNA) haplotype information derived from a previous study in the same landscapes. Results Both datasets indicated a relatively high level of genetic structuring across the sampling range (AFLP, F_ST = 0.34; allozyme, F_ST = 0.13): structure was greatest among populations in the fragmented landscape (AFLP, F_ST = 0.15; allozyme, F_ST = 0.13). Populations in the fragmented landscape also had significantly lower genetic diversity than populations in the other two landscapes: there were no detectable differences in genetic diversity between the two continuous landscapes. There was also evidence (r² = 0.33) of an isolation by distance effect across the sampled range of the species. Main conclusions The multiple lines of evidence, presented within a phylogeographic context, support the hypothesis that contemporary habitat fragmentation has been a major driver of genetic erosion and differentiation in this species. Theclinesthes albocincta populations in the fragmented landscape are thus likely to be at greater risk of extinction because of reduced genetic diversity, their isolation from conspecific subpopulations in other landscapes, and other extrinsic forces acting on their small population sizes. Our study provides compelling evidence that habitat loss and fragmentation have significant rapid impacts on the genetic diversity and structure of butterfly populations, especially specialist species with particular habitat preferences and poor dispersal abilities.     

Analysis of F ST outliers at allozyme loci in Pacific salmon: implications for natural selection

Natural selection has been invoked to explain the observed geographic distribution of allozyme allele frequencies for a number of teleost species. The effects of selection on allozyme loci in three species of Pacific salmon were tested. A simulation-based approach to estimate the null distribution of population differentiation (F _ST) and test for F _ST outliers was used. This approach showed that a majority of allozyme loci conform to neutral expectations predicted by the simulation model, with relatively few F _ST outliers found. No consistent F _ST outlier loci were found across species. Analysis of population sub-groups based on geography and genetic identity reduced the number of outlier loci for some species, indicating that large geographic groups may include genetically divergent populations and/or that there is geographic heterogeneity in selection pressure upon allozyme loci. Two outlier allozyme loci found in this analysis, lactate dehydrogenase-B and malic enzyme, have been shown to be influenced by selection in other teleost species. This approach is also useful in identifying allozyme loci (or other genetic markers) that meet assumptions for population genetic study.     

The structure of morphometric and allozyme variation in relict populations of Gypsophila fastigiata (Caryophyllaceae) in Sweden

Patterns of variation and the structuring of diversity in seed phenotype and allozymes were investigated in Sweden Gypsophila fastigiata, a perennial herb with a disjunct ‘Late Glacial relict’ distribution in eastern and northern Europe. The overall patterns of variation in allozymes and seed morphology are congruent and are significantly correlated with geographic distance. However, most of the congruence between the distance matrices based on allozymes and seed morphology is attributable to regional differentiation between the isolated Öland and Dalarna metapopulations. On a local scale, within the two metapopulations, seed shape variation is partially correlated with geography whereas allozyme variation is unrelated to the geographic disposition of the sampling sites. Despite the fact that regional metapopulations can be discriminated on the basis of seed shape and allozyme frequencies, relatively little of the total diversity in seed morphology and allozymes is due to differentiation between regions. Partitioning of diversity into its within- and among-regional, site and individual components, showed that the majority of diversity (52% for seed shape and 91% for allozymes) is stored within sites. Seventy-three percent of the variation in allozymes is due to variation within individuals (i.e. heterozygosity) whereas phenotypic variation in seed shape within individuals is low (0.4% of the total diversity). The events that led to the large scale disjunction of the Late Glacial distribution of G. fastigiata may have shaped the pattern of differentiation observed among the regional isolates of the species. However, the species' history of local population disjunction during post-glacial and historic times has not had a substantial impact on the spatial organization of allozyme and morphometric diversity within regions. Extensive local gene flow may have allowed the regional metapopulations to have functioned as extended effective populations–on a time scale of tens or hundreds of years–and may have hindered the loss of within-site diversity.     

Extensive variation in the levels of genetic diversity and degree of relatedness among five species of Cypripedium (Orchidaceae)

An electrophoretic analysis of allozyme variation from 14 loci in Cypripedium calceolus, C. candidum, C. arietinum, C. acaule, and C. reginae was conducted to address evolutionary conclusions reached in prior studies on the Orchidaceae. The following specific questions were examined: 1) Do the allozyme data suggest that C. arietinum be transferred to the genus Criosanthes? 2) Do Cypripedium populations contain unusually low levels of genetic variation relative to other angiosperms with comparable life histories? and 3) Is the distribution of genetic variation among populations consistent with the idea that evolutionary processes produce higher levels of among-population differentiation in the Orchidaceae? Very low Nei's genetic identities (0.000–0.285) were found for most species comparisons; however, C. arietinum was not the most genetically distinct taxon and should be retained in the genus Cypripedium. Although most Cypripedium populations contain very low levels of expected heterozygosity, C. calceolus contains unusually high levels in all populations examined. Most species examined here have below average levels of variation distributed among populations. This result indicates that evolutionary processes produce relatively lower, not higher, levels of genetic differentiation among Cypripedium populations compared to other flowering plants. Historical events that could have influenced the observed genetic patterns are discussed.     

GENETIC STRUCTURE OF THE FROGS GEOCRINIA LUTEA AND GEOCRINIA ROSEA REFLECTS EXTREME POPULATION DIVERGENCE AND RANGE CHANGES,NOT DISPERSAL BARRIERS

I describe the genetic structure of two frog species, Geocrinia rosea and Geocrinia lutea, using allozyme electrophoresis to understand population structure and thereby possible mechanisms of divergence and speciation. The sampling regimes represented the entire range of both species and provided replicated tests of the impact of ridges, rivers, and dry forest on gene flow. Geocrinia rosea and G. lutea were highly genetically subdivided (F_ST = 0.69, 0.64, respectively). In the extreme, there were fixed allelic differences between populations that were only 4 km (G. rosea) or 1.25 km (G. lutea) apart. In addition to localized divergence, two-dimensional scaling of genetic distance allowed the recognition of broad-scale genetic groups, each consisting of several sample sites. Patterns of divergence were unrelated to the presence of ridges, rivers, or dry forest. I argue that range contraction and expansion, combined with extreme genetic divergence in single, isolated populations, best accounts for the genetic structure of these species.