Allozyme diversity in the federally threatened golden paintbrush, <Emphasis Type="Italic">Castilleja levisecta</Emphasis> (Scrophulariaceae)

Castilleja levisecta (Scrophulariaceae), the golden paintbrush, is an insect-pollinated herbaceaous perennial found in the Pacific Northwest. Currently restricted to two island populations off British Columbia and nine populations (eight on islands) in Washington, C. levisecta is a rare species threatened with extinction. Allozymes were used to describe genetic diversity and structure in these eleven populations. Despite its threatened status and small geographic range, exceptionally high levels of genetic diversity are maintained within C. levisecta. All sixteen of the loci resolved were polymorphic within the species (P_s=100%), while the mean percentage of loci polymorphic within populations (P_p) was 65.7%. The mean number of alleles per polymorphic locus (AP_s) was 2.94 within the species and averaged 2.38 within populations (AP_p). Genetic diversity (H_es) was 0.285 for the species, whereas mean population genetic diversity (H_ep) was 0.213. Smaller populations had, on average, fewer observed alleles and less genetic diversity. A significant negative correlation (r = –0.72) was found between genetic identity and geographic distance, indicating reduced gene flow between distant populations. The most geographically isolated population was one of the larger populations, one of the most genetically diverse and the most genetically divergent. A wide range of pairwise population genetic identities (I = 0.771 – 0.992) was found, indicating considerable genetic divergence between some populations. Overall, 19% of the total genetic diversity was distributed among populations. Results of this survey indicate that genetic augmentation of existing populations is unnecessary. The high allelic diversity found for the species and within its populations holds promise for conservation and restoration efforts to save this rare and threatened plant species.     

Population genetic structure of <Emphasis Type="Italic">Tamarix chinensis</Emphasis> in the Yellow River Delta,China

Tamarix chinensis, with its important ecological significance, is a vital dominant plant in the Yellow River Delta of China. To understand its genetic structure and population dynamics, five populations of T. chinensis, consisting of 140 individuals, were analyzed in this study using inter simple sequence repeat markers. Seventy-eight polymerase chain reaction fragments were scored, of which 62 were polymorphic. The mean percentage of polymorphic loci (P), the mean Nei’s gene diversity (h), and the mean Shannon’s information index (I) were 79.5%, 0.239, and 0.363, respectively. These indexes indicated that a moderate level of genetic diversity existed in T. chinensis populations of the Yellow River Delta. Both analysis of molecular variance (AMOVA) (Φ _st = 0.169) and Popgene (G _st = 0.159) analyses revealed the low level of genetic differences among the five populations of T. chinensis. The results implied that relatively frequent gene flow existed among populations. However, slightly uneven genetic diversity was also found among populations. Unweighted pair group method with arithmetic mean and principal component analysis showed that populations with similar soil salinity had a close relationship, rather than populations with closer geographical distance. A significant negative correlation between genetic diversity and soil salinity of the five populations (r = −0.958, p < 0.01) showed that soil salinity played an important role in shaping the population genetic structure of T. chinensis in the Yellow River Delta, China.     

Concordance between life history traits, invasion history, and allozyme diversity of the Everglades invader Melaleuca quinquenervia

During the century following its initial introduction in 1886, the Australian tree Melaleuca quinquenervia (Myrtaceae) dispersed from a few introduction points to occupy over 200,000 ha, primarily in historic Everglades wetlands of southern Florida. Cellulose acetate gel electrophoresis (CAGE) was used to investigate the allozyme diversity and population genetic structure of 208 individuals in a dozen populations resulting from this invasion. The analyses showed that these populations have a high (82%) rate of polymorphic loci and an average of 2 alleles/locus. There was substantial heterozygosity (mean H_e = 0.356), which concords well with recent studies reporting a greater number of introduction events and sources than generally recognized. The introduction history and distributional patterns within Florida have led to geographic structuring (G_ST = 0.419) in which the Gulf Coast metapopulation has a greater effective number of alleles and greater heterozygosity than the Atlantic Coast metapopulation. The gene diversity in M. quinquenervia was comparable to other tropical woody species. Its strong population divergence was reminiscent of pioneer species and consistent with its status as a plant invader in Florida.     

Clonal and genetic diversity of Carex moorcroftii on the Qinghai-Tibet plateau

Carex moorcroftii Falc. ex Boott is a rhizomatous clonal sedge dominating vast alpine steppe and meadow vegetations in the hinterland of the Qinghai-Tibet plateau. To reveal the genetic and clonal structure of this species, nine populations were investigated using ten inter-simple sequence repeat (ISSR) markers. As compared to other rhizomatous Carex species, C. moorcroftii had lower genetic diversity (H_s = 0.10) at population level and higher genetic differentiation (G_st = 0.66) and lower gene flow (N_m = 0.26) between populations. Clonal diversity in C. moorcroftii in terms of Simpson index (D = 0.65) was comparable to that in other clonal species while lower than that in Carex species from the arctic and subarctic areas. The ratio of clonal diversity to genetic variation in C. moorcroftii was closely correlated with latitude, enabling a speculation about the northern migration of this species on this plateau.     

Genetic differentiation across eastern Pacific oceanographic barriers in the threatened seahorse <Emphasis Type="Italic">Hippocampus ingens</Emphasis>

Understanding the population structure and evolutionary history of the eastern Pacific seahorse Hippocampus ingens is critical for the effective management of this threatened species. Life history characteristics of H. ingens (site fidelity and brooding of young) may limit gene flow and lead to population differentiation. A recent study analyzing conserved fragments of the mitochondrial cyt b and control region found no population structure. We re-assess this conclusion with a phylogeographic analysis of relationships among 115 individuals of H. ingens over a broader geographic range (San Diego Bay in California, Gulf of California, Central America, Ecuador, and Peru) based on a more variable 428 base pair fragment of the control region. This expanded analysis affirms low overall nucleotide diversity relative to other seahorses (θ_π = 0.004), and shows evidence of a recent bottleneck and population expansion since the middle Pleistocene. AMOVA analysis shows moderate overall population structure (Φ_ST = 0.10, P val = 0.00), and pairwise Φ_ST estimates indicate structure between the Gulf of California and all Pacific coast localities. Knowledge of population structure in H. ingens may improve conservation efforts by identifying evolutionarily important management units, and could determine source regions in the continuing trade of seahorses for traditional Chinese medicine. The level of genetic divergence observed between the Gulf of California and all other localities sampled may distinguish the Gulf as a separate management unit. Additional phylogeographic research with more quickly evolving genetic markers and targeted sampling at the mouth of the Gulf of California is warranted to inform strategies for conservation of this threatened seahorse.     

Population genetic structure of island and mainland populations of the quokka, Setonix brachyurus (Macropodidae): a comparison of AFLP and microsatellite markers

Translocation and reintroduction are important tools for the conservation or recovery of species threatened with extinction in the wild. However, an understanding of the potential genetic consequences of mixing populations requires an understanding of the genetic variation within, and similarities among, donor and recipient populations. Genetic diversity was measured using two independent marker systems (microsatellites and AFLPs) for one island and four small remnant mainland populations of Setonix brachyurus, a threatened medium sized macropod restricted to fragmented habitat remnants and two off-shore islands in southwest Australia. Microsatellite diversity in the island population (R _s = 3.2, H _e = 71%) was similar to, or greater than, all mainland populations (R _s = 2.1–3.9, H _e = 34-71%). In contrast, AFLP diversity was significantly lower in the island population (PPL = 20.5; H _j = 0.118) compared to all mainland populations (mean PPL = 79.5–89.7; mean H _j = 0.23–0.29). Microsatellites differentiated all (mainland and island) populations from each other. However, AFLP only differentiated the island population from the mainland populations—all mainland populations were not significantly differentiated from each other for this marker. Given a known time since isolation of the island population from the mainland (6,000 years ago), and an overall more conservative rate of evolution of AFLP markers, our results are consistent with mainland populations fragmenting thousands of years ago (but <6,000 years), probably as a consequence of reduced rainfall and the constriction of the preferred mesic habitat of quokkas. Our results also support a recent history of severe population bottlenecks in mainland populations, and a long history of bottlenecks of the island population, but reflect a recent explosion in numbers since European occupation of the island. Our results indicate that translocation of island populations to supplement mainland populations would introduce genetically markedly differentiated, and possibly maladapted, individuals.     

The genetic diversity and spatial genetic structure of the Corso‐Sardinian endemic Ferula arrigonii Bocchieri (Apiaceae)

Corsica and Sardinia represent major hotspots of plant diversity in the Mediterranean area and are priority regions for conservation due to their high number of endemic plant species. However, information supporting human decision‐making on the conservation of these species is still scarce, especially at the genetic level. In this work, the first assessment is reported of the species‐wide spatial genetic structure and diversity of Ferula arrigonii Bocchieri, a Corso‐Sardinian endemic located in a few coastal sites and on small islands. Nine populations covering the entire natural range of the species were investigated by means of AFLP (amplified fragment length polymorphism) markers. Results indicate that this species is characterised by high levels of genetic polymorphism (92% polymorphic fragments) and of genetic diversity (H_w = 0.317) and by relatively low differentiation among populations (F_st = 0.057). PCoA, Bayesian analysis and neighbour‐joining clustering were also employed to investigate the genetic structure of this species. Three genetically distinct groups were detected, although with considerable overlap between populations.     

Genetic variation in some plants of Florida scrub

Genetic diversity in three genera of perennial plants found in the sand pine, oak scrub in peninsular Florida was examined by allozyme electrophoresis. These plants vary greatly in terms of geographic range, population size, pollination ecology, and seed dispersal mechanisms. Ceratiola ericoides (Empetraceae) is a shrub that occurs throughout scrub and other sandy habitats in Florida and neighboring states. In contrast, Eryngium cuneifolium (Apiaceae) is a Federally endangered herbaceous perennial, limited to the southern end of the Lake Wales Ridge, site of a proposed National Wildlife Refuge that would be the first designed primarily to protect plant diversity. Four species of endangered woody perennial Dicerandra (Labiatae) are part of a monophyletic group endemic to Florida sand pine scrubs; Dicerandra frutescens and D. christmanii are found on the southern end of the Lake Wales ridge, D. cornutissima is found in north-central Florida, and D. immaculata occurs in a small area along Florida's Atlantic coast. Allozyme electrophoresis of 17 loci for C. ericoides indicated that 64.7% of the loci were polymorphic (P_s), that there were 2.55 alleles per polymorphic locus (AP_s), and that the mean gene diversity (H_es) was 0.141. The proportion of genetic diversity among the four populations (G_ST) was 0.059. For the 31 loci analyzed in E. cuneifolium, P_s was 32.3%, AP_S was 2.1, and H_es was 0.104. G_ST was 0.106. The woody Dicerandra species complex (four species) was analyzed for 17 loci. P_s was 64.7%, AP_s was 3.1, and mean gene diversity was 0.219. The mean G_ST value across the species complex was 0.137. Taken together these results suggest that considerable genetic variation is still present in the relict populations of the rare scrub taxa (Eryngium and Dicerandra), but that to preserve current levels of genetic variation will require protecting areas in each of several different scrub regions along a 350-km stretch of peninsular Florida.     

Genetic diversity of natural populations of Larix principis-rupprechtii in Shanxi Province,China

Prince Rupprecht's Larch (Larix principis-rupprechtii Mayr.) is one of dominant components of middle and high elevation forests in North China. Shanxi Province is well known as “the Hometown of Prince Rupprecht's Larch” in China. In this study, six natural populations of this species across Shanxi were selected to investigate the genetic variation of the species using amplified fragment length polymorphism (AFLP) markers. Results showed that in comparison with some other species of Larix, higher genetic diversity was revealed at the species level for L. principis-rupprechtii (percentage of polymorphic loci PPL = 71.9%, Nei's gene diversity H_E = 0.225, Shannon information index I = 0.341). Most of genetic variation existed within populations (80.5%), while the genetic differentiation among populations was significant (p < 0.001) and higher (G_st = 0.194) than most other species of Larix. The differentiation can be attributed to the limited gene flow (N_m = 1.035) among populations, which could be due to the spatial isolation and habitat fragmentation. The six populations can be divided into three groups based on the Nei's genetic distances between populations (from 0.033 to 0.076). There was no significant correlation (r = 0.268, p > 0.05) between genetic distance and geographic distance among populations. The measures for in-situ or ex-situ conservation should be taken to preserve the genetic diversity of this species.     

Population genetic structure of the endemic rosewoods Dalbergia cochinchinensis and D. oliveri at a regional scale reflects the Indochinese landscape and life‐history traits

Indochina is a biodiversity hot spot and harbors a high number of endemic species, most of which are poorly studied. This study explores the genetic structure and reproductive system of the threatened endemic timber species Dalbergia cochinchinensis and Dalbergia oliveri using microsatellite data from populations across Indochina and relates it to landscape characteristics and life‐history traits. We found that the major water bodies in the region, Mekong and Tonle Sap, represented barriers to gene flow and that higher levels of genetic diversity were found in populations in the center of the distribution area, particularly in Cambodia. We suggest that this pattern is ancient, reflecting the demographic history of the species and possible location of refugia during earlier time periods with limited forest cover, which was supported by signs of old genetic bottlenecks. The D. oliveri populations had generally high levels of genetic diversity (mean H_e = 0.73), but also strong genetic differentiation among populations (global G_ST = 0.13), while D. cochinchinensis had a moderate level of genetic diversity (mean H_e = 0.55), and an even stronger level of differentiation (global G_ST = 0.25). These differences in genetic structure can be accounted for by a higher level of gene flow in D. oliveri due to a higher dispersal capacity, but also by the broader distribution area for D. oliveri, and the pioneer characteristics of D. cochinchinensis. This study represents the first detailed analysis of landscape genetics for tree species in Indochina, and the found patterns might be common for other species with similar ecology.     

Biochemical assessment of the taxonomic diversity of the operculate land snail, Cyclophorus fulguratus (Gastropoda: Cyclophoridae), from Thailand

Allozyme variation was examined in 223 samples of the operculate land snail Cyclophorus fulguratus from 13 localities across three regions of Thailand. Using horizontal starch gel electrophoresis, 13 allozyme presumed loci (12 polymorphic) were screened. Heterozygosity was moderate in C. fulguratus (H_exp = 0.008–0.127) with a high genetic heterogeneity among samples (F_st = 0.734). Populations showed a greater genetic differentiation in central Thailand (F_st = 0.380) than in northeastern Thailand (F_st = 0.108), suggesting frequent gene flow among populations in northeastern Thailand. C. fulguratus exhibits a strong pattern of isolation by distance over the entire tested species range in Thailand and may potentially have been involved in an extensive local fragmentation. Results of the distance analysis revealed that large genetic divergence has occurred among the central, northeastern and eastern Thailand groups [D = 0.361–0.701], strongly suggesting populations from these three geographical regions may actually represent or else be evolving into separate species.     

Population structure and conservation genetics of the Oregon spotted frog, <Emphasis Type="Italic">Rana pretiosa</Emphasis>

The Oregon spotted frog (Rana pretiosa) is one of the most threatened amphibians in the Pacific Northwest. Here we analyzed data from 13 microsatellite loci and 298 bp of mitochondrial DNA in frogs collected from 23 of the remaining R. pretiosa populations in order to (1) assess levels of genetic diversity within populations of R. pretiosa, (2) identify the major genetic groups in the species, (3) estimate levels of genetic differentiation and gene flow among populations within each major group, and (4) compare the pattern of differentiation among R. pretiosa populations with that among populations of R. cascadae, a non-endangered congener that also occurs in Oregon and Washington. There is a strong, hierarchical genetic structure in R. pretiosa. That structure includes six major genetic groups, one of which is represented by a single remaining population. R. pretiosa populations have low genetic diversity (average H _e = 0.31) compared to R. cascadae (average H _e = 0.54) and to other ranid frogs. Genetic subdivision among populations is much higher in R. pretiosa than in R. cascadae, particularly over the largest geographic distances (hundreds of kilometers). A joint analysis of migration rates among populations and of effective sizes within populations (using MIGRATE) suggests that both species have extremely low migration rates, and that R. pretiosa have slightly smaller effective sizes. However, the slight difference in effective sizes between species appears insufficient to explain the large difference in genetic diversity and in large-scale genetic structure. We therefore hypothesize that low connectivity among the more widely-spaced R. pretiosa populations (owing to their patchier habitat), is the main cause of their lower genetic diversity and higher among-population differentiation. Conservation recommendations for R. pretiosa include maintaining habitat connectivity to facilitate gene flow among populations that are still potentially connected, and either expanding habitat or founding additional ‘backup’ populations to maintain diversity in the isolated populations. We recommend that special consideration be given to conservation of the Camas Prairie population in Northern Oregon. It is the most geographically isolated population, has the lowest genetic diversity (H _e = 0.14) and appears to be the only remaining representative of a major genetic group that is now almost extinct. Finally, because the six major groups within R. pretiosa are strongly differentiated, occupy different habitat types, and are geographically separate, they should be recognized as evolutionarily significant units for purposes of conservation planning.     

Genetic differences between continuous and disjunct populations: some insights from sal (<Emphasis Type="Italic">Shorea robusta</Emphasis> Roxb.) in Nepal

Sal (Shorea robusta Gaertn., Dipterocarpaceae) is a wind-pollinated tropical tree species found in southern Asia. We investigated the genetic diversity and structure at four microsatellites of 15 populations comprising continuous-peripheral and disjunct-peripheral populations in Nepal. Estimates of genetic diversity (N _A = 8.98, H _O = 0.62, H _E = 0.69) were similar when compared with those of other tropical tree species. A higher level of genetic diversity was observed in continuous-peripheral populations (N _A = 9.61, H _O = 0.67, H _E = 0.72) as compared to disjunct-peripheral (N _A = 8.04, H _O = 0.55, H _E = 0.64). Population differentiation was higher among disjunct-peripheral populations (F _ST = 0.043) than among continuous peripherals (F _ST = 0.012). There was a significant association between gene flow distances and genetic differentiation (r ² = 0.128, P ≤ 0.007). No spatial arrangement of populations according to their geographical locations was found. Based on observed genetic diversity protection of some populations in continuous-peripheral range are suggested for the sustainable conservation of genetic resources of the species while protection of some disjunct-peripheral populations are also recommended for conserving rare alleles.     

Molecular genetic relationships among east Palaerctic ground squirrels of the genus <Emphasis Type="Italic">Spermophilus</Emphasis> (Sciuridae,Rodentia)

Abstact  Genetic diversity in the four east Palearctic ground squirrel species of the genus Spermophilus—S. undulatus, S. parryi (subgenus Urocitellus), S. dauricus, and S. relictus (subgenus Citellus)—was investigated using RAPD PCR with ten random primers. Siberian chipmunk, Tamias sibiricus, was used as an out-group. Molecular markers for different taxonomic ranks were identified, including those for the genera Spermophilus and Tamias, subgenera Urocitellus and Citellus, as well as for each of the four species, S.undulatus, S. parryi, S. dauricus, and S. relictus. For the ground squirrel species and subgenera, genetic differentiation indices (H _t, H _s, D _st, G _st,Nm, and D) were calculated. In addition, for these groups the NJ phylogenetic reconstructions and UPGMA dendrograms of genetic similarity of the individuals and combined populations were constructed. Comparative molecular genetic analysis revealed a high genetic differentiation between S. undulatus, S. dauricus, S. relictus, and S. parryi (G _st= 0.58 to 0.82; D= 0.53 to 1.06), along with a low level of genetic differentiation of the subgenera Citellus and Urocitellus (G _st = 0.33; D= 0.27), distinguished in accordance with the existing taxonomic systems of the genus Spermophilus Original Russian Text ? M.V. Tsvirka, L.N. Spiridonova, V.P. Korablev, 2008, published in Genetika, 2008, Vol. 44, No. 8, pp. 1108–1116.     

A comparison of genetic structuring of Yellowcheek Darters (Etheostoma moorei) using AFLPs and allozymes

The goals of this study were to characterize the genetic structure of 6 populations of Etheostoma moorei (Yellowcheek Darter), endemic to the Little Red River watershed of central Arkansas, to estimate the levels of gene flow within isolated streams, and to compare AFLP genetic diversity and distance data to our previously published allozyme data. The Yellowcheek Darter is a candidate species for listing under the Endangered Species Act. This darter is found in previously connected headwater streams presently isolated and partially inundated downstream by Greers Ferry Reservoir. AFLP data for the Yellowcheek Darter was concordant with previous work utilizing allozymes (r_s = 0.682; p < 0.01), yet genetic differences among populations were greater in magnitude. Genetic diversity (polymorphism = 92.7; heterozygosity = 0.496) is higher for the Yellowcheek Darter than would be expected for a species in decline, and greater for AFLP versus allozyme data. Genetic structuring among streams was also more evident using AFLP data. Gene flow levels are indicative of a metapopulation structure within streams (F_ST = 0.003 − 0.010), with genetic structuring indicating distinct populations among streams.     

Tandem repeat markers for population genetic studies of the protected California tiger salamander (<Emphasis Type="Italic">Ambystoma californiense</Emphasis>)

Habitat loss is the single greatest threat to persistence of the critically threatened California tiger salamander (Ambystoma californiense). To aid management plans that designate critical habitat for this species, I developed and characterized 21 tetranucleotide microsatellite markers using two native populations in Santa Barbara and Alameda Counties. Allelic variation and average heterozygosities were lower in the endangered Santa Barbara population (allele range 1–4, mean 2.4; H _O = 0.308 H _E = 0.288) compared with the threatened Alameda population (allele range 2–10, mean 6.7; H _O = 0.712, H _E = 0.722). In-depth population studies using these markers will provide vital information for plans to assign critical habitat that optimize gene flow among breeding populations, as well as for identifying non-native hybrid genotypes that threaten native A. californiense stocks. Beyond the conservation goals for A. californiense, the close phylogenetic relationships within the tiger salamander complex also suggest a broad utility for population studies using these markers.     

Genetic diversity in <Emphasis Type="Italic">Delphinium staphisagria</Emphasis> (Ranunculaceae), a rare Mediterranean dysploid larkspur with medicinal uses

Delphinium staphisagria is an endemic annual or biennial herb from the Mediterranean Basin, widely distributed in isolated populations of variable size. We evaluated the allozyme diversity of 31 populations along its distribution range via starch gel electrophoresis, assaying 12 enzyme systems and scoring 17 loci. The low levels of genetic variability detected (A = 11.8, A _p = 1.6, H _o = 0.026, H _e = 0.057), are discussed in relation to the life-history traits of the species, such as short life-span, selfing or gravity seed dispersion. Other factors influencing genetic diversity, such as evolutionary history and spreading are also considered. Due to its historical medicinal uses, this plant has probably become widespread in the Mediterranean area. Human-mediated distribution could have promoted few migrant genotypes, recent founder events and long distance dispersal. These events would explain the genetic homogeneity found within and among populations, as well as the absence of a clear biogeographic structure. The limited genetic variability, the high genetic similarity among populations and the dysploidy of this species make it worthy of conservation. Management strategies are proposed mainly to preserve its genetic pool.     

Fine‐scale population structure of Collichtys lucidus populations inferred from microsatellite markers

The spinyhead croaker Collichthys lucidus (Richardson) is a small sciaenid species distributed along the inshore waters of northwestern Pacific Ocean, and now has been listed as Key Protected Commercial Sources of Aquatic Animals and Plants in China. To delineate stock boundaries and inform conservation policy for its management, samples were collected from eight locations across the Chinese coastal waters and analyzed at nine microsatellite loci. C. lucidus populations showed low genetic diversity (expected heterozygosity = 0.445–0.542; observed heterozygosity = 0.392–0.539; Polymorphism Information Content = 0.268–0.684). Strong genetic fdifferentiation (F_st = 0.065–0.510, all significant after Bonferroni correction) among all populations and high levels of self‐recruitment (89.2%–91.5%) were observed, which suggested limited genetic exchange for this species. Clustering results of discriminant analysis of principal components and STRUCTURE found strong support for obvious genetic clusters (populations FZ, XM and SZ vs. populations SH, YRE, ZS, WZ and ND). The results of the present study not only supported the phylogeographic pattern of north‐south differentiation, but also suggested that C. lucidus populations may be predominantly sustained by self‐replenishment rather than by recruitment from distant populations.     

Population genetics and fitness in fragmented populations of the dioecious and endangered <Emphasis Type="Italic">Silene otites</Emphasis> (Caryophyllaceae)

Population fragmentation is often correlated with loss of genetic diversity and reduced fitness. Obligate out-crossing (dioecy) is expected to enhance genetic diversity, reduce genetic differentiation, and avoid inbreeding depression through frequent gene flow. However, in highly fragmented populations dioecy has only diminishing effects upon genetic structure as pollination limitations (e.g. flight distance of pollinators) most often restrict inter-population gene flow in insect pollinated species. In fragmented dry grasslands in northeastern Germany, we analysed genetic structure, fitness, and habitat quality of the endangered dioecious Silene otites (Caryophyllaceae). Using AFLP markers, a high level of differentiation among ten populations was found (F _st = 0.36), while the intra-population genetic diversities (H _E = 0.165–0.240) were similar as compared to hermaphroditic species. There was neither a correlation between geographic and genetic distance nor between genetic diversity and population size, which indicates reduced gene flow among populations and random genetic drift. Plant size was positively correlated with genetic diversity. Seed set and number of juveniles were positively related to population size. Higher total coverage resulted in reduced plant fitness, and the number of juveniles was negatively correlated to cryptogam cover. Additionally, we found a sex ratio bias towards more male plants in larger populations. Overall, our results indicate that on a regional geographic scale dioecy does not necessarily prevent genetic erosion in the case of habitat fragmentation, especially in the absence of long distance seed and pollen dispersal capacity.     

Testing hypotheses driving genetic structure in the cooperatively breeding Brown‐headed Nuthatch Sitta pusilla

Habitat fragmentation has often been implicated in the decline of many species. For habitat specialists and/or sedentary species, loss of habitat can result in population isolation and lead to negative genetic effects. However, factors other than fragmentation can often be important and also need to be considered when assessing the genetic structure of a species. We genotyped individuals from 13 populations of the cooperatively breeding Brown‐headed Nuthatch Sitta pusilla in Florida to test three alternative hypotheses regarding the effects that habitat fragmentation might have on genetic structure. A map of potential habitat developed from recent satellite imagery suggested that Brown‐headed Nuthatch populations in southern Florida occupied smaller and more isolated habitat patches (i.e. were more fragmented) than populations in northern Florida. We also genotyped individuals from a small, isolated Brown‐headed Nuthatch population on Grand Bahama Island. We found that populations associated with more fragmented habitat in southern Florida had lower allelic richness than populations in northern Florida (P = 0.02), although there were no differences in heterozygosity. Although pairwise estimates of F_ST were low overall, values among southern populations were generally higher than northern populations. Population assignment tests identified K = 3 clusters corresponding to a northern cluster, a southern cluster and a unique population in southeast Florida; using sampling localities as prior information revealed K = 7 clusters, with greater structure only among southern Florida populations. The Bahamas population showed moderate to high differentiation compared with Florida populations. Overall, our results suggest that fragmentation could affect gene flow in Brown‐headed Nuthatch populations and is likely to become more pronounced over time.