Genetic variation in Plethodon cinereus and Plethodon hubrichti from in and around a contact zone

Climate change poses several challenges to biological communities including changes in the frequency of encounters between closely related congeners as a result of range shifts. When climate change leads to increased hybridization, hybrid dysfunction or genetic swamping may increase extinction risk—particularly in range‐restricted species with low vagility. The Peaks of Otter Salamander, Plethodon hubrichti, is a fully terrestrial woodland salamander that is restricted to ~18 km of ridgeline in the mountains of southwestern Virginia, and its range is surrounded by the abundant and widespread Eastern Red‐backed Salamander, Plethodon cinereus. In order to determine whether these two species are hybridizing and how their range limits may be shifting, we assessed variation at eight microsatellite loci and a 1,008 bp region of Cytochrome B in both species at allopatric reference sites and within a contact zone. Our results show that hybridization between P. hubrichti and P. cinereus either does not occur or is very rare. However, we find that diversity and differentiation are substantially higher in the mountaintop endemic P. hubrichti than in the widespread P. cinereus, despite similar movement ability for the two species as assessed by a homing experiment. Furthermore, estimation of divergence times between reference and contact zone populations via approximate Bayesian computation is consistent with the idea that P. cinereus has expanded into the range of P. hubrichti. Given the apparent recent colonization of the contact zone by P. cinereus, future monitoring of P. cinereus range limits should be a priority for the management of P. hubrichti populations.     

Comparative phylogeography and asymmetric hybridization between cryptic bat species

Cryptic speciation and hybridization are two key processes that affect the origin and maintenance of biodiversity and our ability to understand and estimate it. To determine how these two processes interact, we studied allopatric and sympatric colonies of two cryptic bat species (Eptesicus serotinus and Eptesicus isabellinus) with parapatric distribution in the Iberian Peninsula. These species are the main reservoir for the most commonly rabies virus found in bats in Europe: the European bat Lyssavirus type 1 (EBLV‐1). We used mtDNA and nuclear microsatellite markers to confirm the taxonomic status of both species and to show a more pronounced and geographically based genetic structure in E. isabellinus than in its sibling E. serotinus. Using approximate Bayesian computation (ABC), we inferred rapid range expansion in both species after the Last Glacial Maximum until reaching their present distributions. ABC analysis also supported interspecific differences in genetic diversity and structure, pointing to an earlier expansion of E. isabellinus northward. We found no evidence of mitochondrial introgression between species, but nuclear markers identified a male‐mediated ongoing asymmetric hybridization from E. isabellinus to E. serotinus (28% hybrids in E. serotinus and 5% in E. isabellinus) in the contact zone. Although none of the bats studied tested positive for Lyssavirus RNA, the asymmetric hybridization supports the potential for the recently suggested interspecific transmission of EBLV‐1 from E. isabellinus into E. serotinus.     

Geographic variation in hybridization across a reinforcement contact zone of chorus frogs (Pseudacris)

Reinforcement contact zones, which are secondary contact zones where species are diverging in reproductive behaviors due to selection against hybridization, represent natural laboratories for studying speciation‐in‐action. Here, we examined replicate localities across the entire reinforcement contact zone between North American chorus frogs Pseudacris feriarum and P. nigrita to investigate geographic variation in hybridization frequencies and to assess whether reinforcement may have contributed to increased genetic divergence within species. Previous work indicated these species have undergone reproductive character displacement (RCD) in male acoustic signals and female preferences due to reinforcement. We also examined acoustic signal variation across the contact zone to assess whether signal characteristics reliably predict hybrid index and to elucidate whether the degree of RCD predicts hybridization rate. Using microsatellites, mitochondrial sequences, and acoustic signal information from >1,000 individuals across >50 localities and ten sympatric focal regions, we demonstrate: (1) hybridization occurs and (2) varies substantially across the geographic range of the contact zone, (3) hybridization is asymmetric and in the direction predicted from observed patterns of asymmetric RCD, (4) in one species, genetic distance is higher between conspecific localities where one or both have been reinforced than between nonreinforced localities, after controlling for geographic distance, (5) acoustic signal characters strongly predict hybrid index, and (6) the degree of RCD does not strongly predict admixture levels. By showing that hybridization occurs in all sympatric localities, this study provides the fifth and final line of evidence that reproductive character displacement is due to reinforcement in the chorus frog contact zone. Furthermore, this work suggests that the dual action of cascade reinforcement and partial geographic isolation is promoting genetic diversification within one of the reinforced species.     

Preliminary analysis of a hybrid zone between two subspecies of Zootermopsis nevadensis

For species largely allopatric in distribution, zones of contact provide an opportunity for hybridization, testing grounds for species boundaries, and may result in the formation of a new species. Thus, hybrid zones have the potential to provide important insights into speciation. In this study, we performed a preliminary analysis of a hybrid zone between two subspecies of the dampwood termite, Zootermopsis nevadensis (Z. n. nuttingi and Z. n. nevadensis) near Bartle, CA, using 12 microsatellite loci and a mitochondrial gene. Fifty-seven colonies collected in 36 locations were analyzed. The analysis of genetic markers revealed a large hybrid zone approximately 104 km in width. Although stepped clines best explained the data, we are unable to rule out the existence of a mosaic hybrid zone. We inferred weak selection (s* < 0.05%) against hybrids, but the data also suggested the existence of a barrier to gene flow from Z. n. nevadensis to Z. n. nuttingi, but not in the other direction. Given the large zone of contact, extensive sampling is needed to obtain a more complete characterization of the hybrid zone. However, the results of this study suggest that despite the accumulation of phenotypic and genetic differences and time since divergence (~2 million years), Z. n. nuttingi and Z. n. nevadensis are capable of extensive hybridization.     

Congruent population genetic structure but differing depths of divergence for three alpine stoneflies with similar ecology and geographic distributions

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Evolution,biogeography and systematics of the western Palaearctic Zamenis ratsnakes

The phylogenetic relationships between western Palaearctic Zamenis and Rhinechis ratsnakes have been troubled, with recent estimates based on the supermatrix approach questioning their monophyly and providing contradictory results. In this study, we generated a comprehensive molecular data set for Zamenis and closely related ratsnakes to assess their phylogenetic and systematic relationships and infer their spatial and temporal modes of diversification. We obtained a fully resolved and well‐supported phylogeny, which is consistent across markers, taxon‐sets and phylogenetic methods. The close phylogenetic relationship between Rhinechis and Zamenis is well‐established. However, the early branching pattern within this clade, and the position of R. scalaris and Z. hohenackeri, remains poorly supported. The Persian ratsnake Z. persicus is sister to the Mediterranean species Z. situla, Z. longissimus and Z. lineatus, of which Z. situla is sister to a clade containing the latter two species. These results are consistent with a recent phylogenomic study on ratsnakes based on hundreds of loci. Whereas, topological tests based on our data and evidence from such phylogenomic study strongly rejected previous phylogenetic estimates based on the supermatrix approach and demonstrate that these “mega‐phylogenies”, with hundreds of taxa and high levels of missing data, have recovered inconsistent relationships with spurious nodal support. Biogeographical and molecular dating analyses suggest an origin of the ancestor of Rhinechis and Zamenis in the Aegean region with early cladogenesis during the Late Miocene associated with the Aegean arch formation and support a scenario of east‐to‐west diversification. Finally, while we have little morphological and phylogenetic evidence for the distinctiveness between Rhinechis and Zamenis, a classification of them in a single genus, and the designation of Zamenis scalaris (Schinz, 1822), reflects better their evolutionary relationships.     

Tracing species replacement in Iberian marbled newts

Secondary contact between closely related species can lead to the formation of hybrid zones, allowing for interspecific gene flow. Hybrid zone movement can take place if one of the species possesses a competitive advantage over the other, ultimately resulting in species replacement. Such hybrid zone displacement is predicted to leave a genomic footprint across the landscape in the form of asymmetric gene flow (or introgression) of selectively neutral alleles from the displaced to the advancing species. Hybrid zone movement has been suggested for marbled newts in the Iberian Peninsula, supported by asymmetric gene flow and a distribution relict (i.e., an enclave) of Triturus marmoratus in the range of T. pygmaeus. We developed a panel of nuclear and mitochondrial SNP markers to test for the presence of a T. marmoratus genomic footprint in the Lisbon peninsula, south of the enclave. We found no additional populations of T. marmoratus. Analysis with the software Structure showed no genetic traces of T. marmoratus in T. pygmaeus. A principal component analysis showed some variation within the local T. pygmaeus, but it is unclear if this represents introgression from T. marmoratus. The results may be explained by (a) species replacement without introgressive hybridization and (b) displacement with hybridization followed by the near‐complete erosion of the footprint by purifying selection. We predict that testing for a genomic footprint north of the reported enclave would confirm that species replacement in these marbled newts occurred with hybridization.     

Comparative phylogeographic study of Hosta sieboldiana and Hosta albomarginata (Asparagaceae) in Japan

We analyzed variations in chloroplast DNA (cpDNA) in the widespread herbaceous species Hosta sieboldiana and Hosta albomarginata across large portions of their geographic ranges in the Japanese archipelago. Our objective was to compare the phylogeographic histories and phylogeographic structures of the two congeneric species in the Japanese archipelago. The location of the study is Japanese archipelago. We sequenced 1380 bp of noncoding cpDNA from 45 populations of H. sieboldiana (n = 362) and 55 populations of H. albomarginata (n = 436) to assess genetic variations within and among populations across almost the entire distributions of the species in Japan. Extant patterns of geographic structure were analyzed using statistical parsimony networks and spatial analysis of molecular variance (SAMOVA). We also used Monmonier's algorithm to detect genetic barriers between regions. Relationships between the populations were examined using a neighbor‐joining (NJ) method. Four haplotypes were found for H. sieboldiana, whereas eight haplotypes were identified for H. albomarginata. Total genetic haplotype diversity (hT) and within‐population haplotype diversity (hS) for H. sieboldiana were 0.352 and 0.040, respectively, while the values for H. albomarginata were 0.529 and 0.085, respectively. The population differentiations (GST) for H. sieboldiana and H. albomarginata were 0.839 and 0.886, respectively. The SAMOVA analysis revealed two clusters in H. sieboldiana and four clusters in H. albomarginata. Differentiations between and among the clusters were supported by the BARRIER analysis and the NJ tree. We detected differences in the population genetic structure between the two species. We found that H. sieboldiana had lower haplotype diversity than H. albomarginata. These results may be partially explained by the difference in ecological habitats and geographic distributions between the species. Hosta albomarginata is more widely distributed than H. sieboldiana in East Asia including Russia, and this large distribution range would enable more chances to intraspecific gene flow.     

Thermal strategies and energetics in two sympatric colubrid snakes with contrasted exposure

The thermoregulatory strategy of reptiles should be optimal if ecological costs (predation risk and time devoted to thermoregulation) are minimized while physiological benefits (performance efficiency and energy gain) are maximized. However, depending on the exact shape of the cost and benefit curves, different thermoregulatory optima may exist, even between sympatric species. We studied thermoregulation in two coexisting colubrid snakes, the European whipsnake (Hierophis viridiflavus, Lacépède 1789) and the Aesculapian snake (Zamenis longissimus, Laurenti 1768) that diverge markedly in their exposure, but otherwise share major ecological and morphological traits. The exposed species (H. viridiflavus) selected higher body temperatures (~30°C) than the secretive species (Z. longissimus, ~25°C) both in a laboratory thermal gradient and in the field. Moreover, this difference in body temperature was maintained under thermophilic physiological states such as digestion and molting. Physiological and locomotory performances were optimized at higher temperatures in H. viridiflavus compared to Z. longissimus, as predicted by the thermal coadaptation hypothesis. Metabolic and energetic measurements indicated that energy requirements are at least twice higher in H. viridiflavus than in Z. longissimus. The contrasted sets of coadapted traits between H. viridiflavus and Z. longissimus appear to be adaptive correlates of their exposure strategies.     

Spatial and host related genomic variation in partially sympatric cactophagous moth species

Surveys of patterns of genetic variation in natural sympatric and allopatric populations of recently diverged species are necessary to understand the processes driving intra- and interspecific diversification. The South American moths Cactoblastis cactorum, Cactoblastis doddi and Cactoblastis bucyrus are specialized in the use of cacti as host plants. These species have partially different geographic ranges and differ in patterns of host plant use. However, there are areas that overlap, particularly, in northwestern Argentina, where they are sympatric. Using a combination of genome-wide SNPs and mitochondrial data we assessed intra and interspecific genetic variation and investigated the relative roles of geography and host plants on genetic divergence. We also searched for genetic footprints of hybridization between species. We identified three well delimited species and detected signs of hybridization in the area of sympatry. Our results supported a hypothetical scenario of allopatric speciation in the generalist C. cactorum and genetic interchange during secondary geographic contact with the pair of specialists C. bucyrus and C. doddi that probably speciated sympatrically. In both cases, adaptation to new host plants probably played an important role in speciation. The results also suggested the interplay of geography and host plant use as drivers of divergence and limiting gene flow at intra and interspecific levels.     

Phylogeography,population genetics and distribution modelling reveal vulnerability of Scirpus longii (Cyperaceae) and the Atlantic Coastal Plain Flora to climate change

A proactive approach to conservation must be predictive, anticipating how habitats will change and which species are likely to decline or prosper. We use composite species distribution modelling to identify suitable habitats for 18 members of the North American Atlantic Coastal Plain Flora (ACPF) since the Last Glacial Maximum and project these into the future. We then use Scirpus longii (Cyperaceae), a globally imperiled ACPF sedge with many of the characteristics of extinction vulnerability, as a case study. We integrate phylogeographical and population genetic analyses and species distribution modelling to develop a broad view of its current condition and prognosis for conservation. We use genotyping‐by‐sequencing to characterize the genomes of 142 S. longii individuals from 20 populations distributed throughout its range (New Jersey to Nova Scotia). We measure the distribution of genetic diversity in the species and reconstruct its phylogeographical history using the snapp and rase models. Extant populations of S. longii originated from a single refugium south of the Laurentide ice sheet around 25 ka. The genetic diversity of S. longii is exceedingly low, populations exhibit little genetic structure and the species is slightly inbred. Projected climate scenarios indicate that nearly half of extant populations of S. longii will be exposed to unsuitable climate by 2070. Similar changes in suitable habitat will occur for many other northern ACPF species—centres of diversity will shift northward and Nova Scotia may become the last refuges for those species not extinguished.     

An ecological genetic delineation of local seed‐source provenance for ecological restoration

An increasingly important practical application of the analysis of spatial genetic structure within plant species is to help define the extent of local provenance seed collection zones that minimize negative impacts in ecological restoration programs. Here, we derive seed sourcing guidelines from a novel range‐wide assessment of spatial genetic structure of 24 populations of Banksia menziesii (Proteaceae), a widely distributed Western Australian tree of significance in local ecological restoration programs. An analysis of molecular variance (AMOVA) of 100 amplified fragment length polymorphism (AFLP) markers revealed significant genetic differentiation among populations (Φ_PT = 0.18). Pairwise population genetic dissimilarity was correlated with geographic distance, but not environmental distance derived from 15 climate variables, suggesting overall neutrality of these markers with regard to these climate variables. Nevertheless, Bayesian outlier analysis identified four markers potentially under selection, although these were not correlated with the climate variables. We calculated a global R‐statistic using analysis of similarities (ANOSIM) to test the statistical significance of population differentiation and to infer a threshold seed collection zone distance of ~60 km (all markers) and 100 km (outlier markers) when genetic distance was regressed against geographic distance. Population pairs separated by >60 km were, on average, twice as likely to be significantly genetically differentiated than population pairs separated by <60 km, suggesting that habitat‐matched sites within a 30‐km radius around a restoration site genetically defines a local provenance seed collection zone for B. menziesii. Our approach is a novel probability‐based practical solution for the delineation of a local seed collection zone to minimize negative genetic impacts in ecological restoration.     

Out of the forest: past and present range expansion of a parthenogenetic weevil pest,or how to colonize the world successfully

Previous research revealed complex diversification patterns in the parthenogenetic weevil Naupactus cervinus. To understand the origin of clonal diversity and successful spreading of this weevil, we investigated its geographic origin and possible dispersal routes and whether parthenogens can persist in habitats under unsuitable environmental conditions. This study is based on samples taken throughout a broad area of the species’ range. We used both mitochondrial and nuclear markers and applied phylogenetic and network analyses to infer possible relationships between haplotypes. Bayesian phylogeographic analyses and ecological niche modeling were used to investigate the processes that shaped genetic diversity and enabled the colonization of new geographic areas. Southeastern Brazil emerges as the original distribution area of N. cervinus. We detected two range expansions, one along natural corridors during the Pleistocene and the other in countries outside South America during recent times. Isolation due to climate shifts during the early Pleistocene led to diversification in two divergent clades, which probably survived in different refugia of the Paranaense Forest and the Paraná River delta. The origin of the clonal diversity was probably a complex process including mutational diversification, hybridization, and secondary colonization. The establishment of N. cervinus in areas outside its native range may indicate adaptation to drier and cooler conditions. Parthenogenesis would be advantageous for the colonization of new environments by preventing the breakup of successful gene combinations. As in other insect pests, the present distribution of N. cervinus results from both its evolutionary history and its recent history related to human activities.     

Disentangling the effects of geographic peripherality and habitat suitability on neutral and adaptive genetic variation in Swiss stone pine

It is generally accepted that the spatial distribution of neutral genetic diversity within a species’ native range mostly depends on effective population size, demographic history, and geographic position. However, it is unclear how genetic diversity at adaptive loci correlates with geographic peripherality or with habitat suitability within the ecological niche. Using exome‐wide genomic data and distribution maps of the Alpine range, we first tested whether geographic peripherality correlates with four measures of population genetic diversity at > 17,000 SNP loci in 24 Alpine populations (480 individuals) of Swiss stone pine (Pinus cembra) from Switzerland. To distinguish between neutral and adaptive SNP sets, we used four approaches (two gene diversity estimates, F_ST outlier test, and environmental association analysis) that search for signatures of selection. Second, we established ecological niche models for P. cembra in the study range and investigated how habitat suitability correlates with genetic diversity at neutral and adaptive loci. All estimates of neutral genetic diversity decreased with geographic peripherality, but were uncorrelated with habitat suitability. However, heterozygosity (H_e) at adaptive loci based on Tajima's D declined significantly with increasingly suitable conditions. No other diversity estimates at adaptive loci were correlated with habitat suitability. Our findings suggest that populations at the edge of a species' geographic distribution harbour limited neutral genetic diversity due to demographic properties. Moreover, we argue that populations from suitable habitats went through strong selection processes, are thus well adapted to local conditions, and therefore exhibit reduced genetic diversity at adaptive loci compared to populations at niche margins.     

Mito‐nuclear discordance across a recent contact zone for California voles

To examine the processes that maintain genetic diversity among closely related taxa, we investigated the dynamics of introgression across a contact zone between two lineages of California voles (Microtus californicus). We tested the prediction that introgression of nuclear loci would be greater than that for mitochondrial loci, assuming ongoing gene flow across the contact zone. We also predicted that genomic markers would show a mosaic pattern of differentiation across this zone, consistent with genomes that are semi‐permeable. Using mitochondrial cytochrome b sequences and genome‐wide loci developed via ddRAD‐seq, we analyzed genetic variation for 10 vole populations distributed along the central California coast; this transect included populations from within the distributions of both parental lineages as well as the putative contact zone. Our analyses revealed that (1) the two lineages examined are relatively young, having diverged ca. 8.5–54 kya, (2) voles from the contact zone in Santa Barbara County did not include F1 or early generation backcrossed individuals, and (3) there appeared to be little to no recurrent gene flow across the contact zone. Introgression patterns for mitochondrial and nuclear markers were not concordant; only mitochondrial markers revealed evidence of introgression, putatively due to historical hybridization. These differences in genetic signatures are intriguing given that the contact zone occurs in a region of continuous vole habitat, with no evidence of past or present physical barriers. Future studies that examine specific isolating mechanisms, such as microhabitat use and mate choice, will facilitate our understanding of how genetic boundaries are maintained in this system.     

Phylogeographic patterns and conservation implications of the endangered Chinese giant salamander

Understanding genetic diversity patterns of endangered species is an important premise for biodiversity conservation. The critically endangered salamander Andrias davidianus, endemic to central and southern mainland in China, has suffered from sharp range and population size declines over the past three decades. However, the levels and patterns of genetic diversity of A. davidianus populations in wild remain poorly understood. Herein, we explore the levels and phylogeographic patterns of genetic diversity of wild‐caught A. davidianus using larvae and adult collection with the aid of sequence variation in (a) the mitochondrial DNA (mtDNA) fragments (n = 320 individuals; 33 localities), (b) 19 whole mtDNA genomes, and (c) nuclear recombinase activating gene 2 (RAG2; n = 88 individuals; 19 localities). Phylogenetic analyses based on mtDNA datasets uncovered seven divergent mitochondrial clades (A–G), which likely originated in association with the uplifting of mountains during the Late Miocene, specific habitat requirements, barriers including mountains and drainages and lower dispersal ability. The distributions of clades were geographic partitioned and confined in neighboring regions. Furthermore, we discovered some mountains, rivers, and provinces harbored more than one clades. RAG2 analyses revealed no obvious geographic patterns among the five alleles detected. Our study depicts a relatively intact distribution map of A. davidianus clades in natural species range and provides important knowledge that can be used to improve monitoring programs and develop a conservation strategy for this critically endangered organism.     

Genomic replacement of native Cobitis lutheri with introduced C. tetralineata through a hybrid swarm following the artificial connection of river systems

River connections via artificial canals will bring about secondary contacts between previously isolated fish species. Here, we present a genetic consequence of such a secondary contact between Cobitis fish species, C. lutheri in the Dongjin River, and C. tetralineata in the Seomjin River in Korea. The construction of water canals about 80 years ago has unidirectionally introduced C. tetralineata into the native habitat of C. lutheri, and then these species have hybridized in the main stream section of the Dongjin River. According to the divergence population genetic analyses of DNA sequence data, the two species diverged about 3.3 million years ago, which is interestingly coincident with the unprecedented paleoceanographic change that caused isolations of the paleo‐river systems in northeast Asia due to sea‐level changes around the late Pliocene. Multilocus genotypic data of nine microsatellites and three nuclear loci revealed an extensively admixed structure in the hybrid zone with a high proportion of various post‐F1 hybrids. Surprisingly, pure native C. lutheri was absent in the hybrid zone in contrast to the 7% of pure C. tetralineata. Such a biased proportion must have resulted from the dominant influence of continually introducing C. tetralineata on the native C. lutheri which has no supply of natives from other tributaries to the hybrid zone due to numerous low‐head dams. In addition, mating experiments indicated that there is no discernible reproductive isolation between them. All the results suggest that the gene pool of native C. lutheri is being rapidly replaced by that of continually introducing C. tetralineata through a hybrid swarm for the last 80 years, which will ultimately lead to the genomic extinction of natives in this hybrid zone.     

Hybrid speciation in sparrows I: phenotypic intermediacy,genetic admixture and barriers to gene flow

Homoploid hybrid speciation is thought to require unusual circumstances to yield reproductive isolation from the parental species, and few examples are known from nature. Here, we present genetic evidence for this mode of speciation in birds. Using Bayesian assignment analyses of 751 individuals genotyped for 14 unlinked, nuclear microsatellite loci, we show that the phenotypically intermediate Italian sparrow (Passer italiae) does not form a cluster of its own, but instead exhibits clear admixture (over its entire breeding range) between its putative parental species, the house sparrow (P. domesticus) and the Spanish sparrow (P. hispaniolensis). Further, the Italian sparrow possesses mitochondrial (mt) DNA haplotypes identical to both putative parental species (although mostly of house sparrow type), indicating a recent hybrid origin. Today, the Italian sparrow has a largely allopatric distribution on the Italian peninsula and some Mediterranean islands separated from its suggested parental species by the Alps and the Mediterranean Sea, but co‐occurs with the Spanish sparrow on the Gargano peninsula in southeast Italy. No evidence of interbreeding was found in this sympatric population. However, the Italian sparrow hybridizes with the house sparrow in a sparsely populated contact zone in the Alps. Yet, the contact zone is characterized by steep clines in species‐specific male plumage traits, suggesting that partial reproductive isolation may also have developed between these two taxa. Thus, geographic and reproductive barriers restrict gene flow into the nascent hybrid species. We propose that an origin of hybrid species where the hybrid lineage gets geographically isolated from its parental species, as seems to have happened in this system, might be more common in nature than previously assumed.     

Genetic structure of two Prosopis species in Chaco areas: A lack of allelic diversity diagnosis and insights into the allelic conservation of the affected species

The Gran Chaco is the largest continuous region of the South American dry forest, spanning Argentina, Paraguay, Bolivia, and Brazil. Prosopis rubriflora and Prosopis ruscifolia are typical tree species of chaquenian area forests, which have been subjected to continuous fragmentation caused by cattle raising. This study evaluated P. rubriflora and P. ruscifolia in areas with varying levels of disturbance. We investigated the contemporary genetic diversities of both species in areas with distinct anthropogenic disturbances. Even with a lower heterozygote frequency, disturbed areas can provide important storage for alleles, allowing the maintenance of diversity. The genetic diversity of P. rubriflora was surprisingly similar to that of P. ruscifolia (H_e = 0.59 and H_e = 0.60, respectively) even with very different distribution ranges of both species. However, P. ruscifolia exhibited a higher intrapopulation fixation index than P. rubriflora. P. rubriflora showed evidence of bottlenecking in 64% of the sampled areas, while P. ruscifolia showed such evidence in 36% of the sampled areas. Additionally, P. rubriflora had two distinct populations due to its disjunctive geographic distribution, whereas P. ruscifolia had a single population that exhibited few signs of population structure in some areas, possibly due to the main pollinators presenting a short range of dispersion. Our results suggest that 42 Chaco areas should be conserved to retain the minimum of 500 individuals necessary to maintain genetic diversity for 100–1,000 generations. This study improves our understanding of these two Prosopis species and provides information for the conservation of their genetic diversities.     

Effect of Yangtze River on population genetic structure of the relict plant Parrotia subaequalis in eastern China

Parrotia subaequalis (Hamamelidaceae) is a Tertiary relic species endemic in eastern China. We used inter‐simple sequence repeat (ISSR) markers to access genetic diversity and population genetic structure in natural five populations of P. subaequalis. The levels of genetic diversity were higher at species level (H = 0.2031) but lower at population level (H = 0.1096). The higher genetic diversity at species levels might be attributed to the accumulation of distinctive genotypes which adapted to the different habitats after Quaternary glaciations. Meanwhile, founder effects on the early stage, and subsequent bottleneck of population regeneration due to its biological characteristics, environmental features, and human activities, seemed to explain the low population levels of genetic diversity. The hierarchical AMOVA revealed high levels (42.60%) of among‐population genetic differentiation, which was in congruence with the high levels of Nei's genetic differentiation index (G_ST = 0.4629) and limited gene flow (N_m = 0.5801) among the studied populations. Mantel test showed a significant isolation‐by‐distance, indicating that geographic isolation has a significant effect on genetic structure in this species. Unweighted pair‐group method with arithmetic average clustering, PCoA, and Bayesian analyses uniformly recovered groups that matched the geographical distribution of this species. In particular, our results suggest that Yangtze River has served as a natural barrier to gene flow between populations occurred on both riversides. Concerning the management of P. subaequalis, the high genetic differentiation among populations indicates that preserving all five natural populations in situ and collecting enough individuals from these populations for ex situ conservation are necessary.