Pollen-mediated gene dispersal within continuous and fragmented populations of a forest understorey species, Trillium cuneatum

Pollen movement plays a critical role in the distribution of genetic variation within and among plant populations. Direct measures of pollen movement in the large, continuous populations that characterize many herbaceous plant species are often technically difficult and biologically unreliable. Here, we studied contemporary pollen movement in four large populations of Trillium cuneatum. Three populations, located in the Georgia Piedmont, are exposed to strong anthropogenic disturbances, while the fourth population, located in the Southern Appalachian Mountains, is relatively undisturbed. Using the recently developed TwoGener analysis, we extracted estimates of the effective number of pollen donors (N(ep)), effective mating neighbourhood size (A(ep)) and the average distance of pollen movement (delta) for each population. We extended the TwoGener method by developing inference on the paternal gametic contribution to the embryo in situations where offspring genotypes are inferred from seeds and elaiosomes of species with bisporic megagametogenesis. Our estimates indicate that maternal plants do not sample pollen randomly from a global pool; rather, pollen movement in all four populations is highly restricted. Although the effective number of pollen donors per maternal plant is low (1.22-1.66) and pollen movement is highly localized in all populations, N(ep) in the disturbed Piedmont populations is higher and there is more pollen movement than in the mountains. The distance pollen moves is greater in disturbed sites and fragmented populations, possibly due to edge effects in Trillium habitats.     

Evaluating the consequences of habitat fragmentation: a case study in the common forest herb Trillium camschatcense

The effects of habitat fragmentation on remnant plant populations have rarely been studied extensively using a single species. We have attempted to quantify the effects of forest fragmentation (primarily that of population size) on populations of Trillium camschatcense, a representative spring herb in the Tokachi plain of Hokkaido, Japan. In this region, intensive agricultural development over the past 100 years has divided once-large, continuous populations of this species into small, isolated fragments. Small populations generally produced fewer seeds than large populations, although this result differed between years. The level of seed production is unlikely to explain demographic structures based on life-history stages. Instead, the stage structure was better explained by population size, seedling recruitment being limited in smaller populations. This could be associated with edge effects because the stage structure in small populations corresponded well to that observed in forest edges, where altered microclimatic conditions strongly limit seedling recruitment. Small populations also experienced stochastic loss of rare alleles at allozyme loci as well as biparental inbreeding. Although one consequence of these changes is reduced fertility, the long-term effects on population growth can be controversial in long-lived forest herbs, since the negative effect on fertility may vary across years, and population growth rate may not be sensitive to changes in fertility. Further studies of long-term demography will reveal whether and how habitat fragmentation could limit population growth of remnant populations more than a century after fragmentation.     

Life History Studies on the Genus Trillium (Liliaceae) I. Reproductive Biology of Four Japanese Species

Abstract Four Japanese Trillium (Liliaceae) species which are representative perennial herbs of the temperate deciduous forests— Trillium kamtschaticum (2x), T. apetalon (4x), T. tschonoskii (4x) and T. smallii (6x)—were studied for their reproductive characteristics, e.g., patterns of reproductive resource allocation and reproductive output.
In spite of the differences in ploidy levels (from 2x to 6x), all four species showed very similar reproductive traits. It became evident that in response to the increase in reproductive allocation to total reproductive organs (RA), the number of seeds produced per plant (P_N) clearly increased. This trend is well in accord with the relationship found in four North American species and also several temperate woodland perennial herbs which occur in closed, stable and predictable environments, and possess typical xenogamous breeding systems. Although there is no conspicuous trend between ploidy levels and P_N, one of the significant differences noted in this study was in seed weight, which ranged from 2.93 mg in diploids, to 3.42–3.45 mg in tetraploids, and to 4.47 mg in hexaploids.     

Distribution of genetic diversity among disjunct populations of the rare forest understory herb, Trillium reliquum

We assessed genetic diversity and its distribution in the rare southeastern US forest understory species, Trillium reliquum. In all, 21 loci were polymorphic (PS=95.5%) and the mean number of alleles per polymorphic locus was 3.05. However, genetic diversity was relatively low (Hes=0.120) considering the level of polymorphism observed for this outcrossing species. A relatively high portion of the genetic diversity (29.7%) was distributed among populations. There was no relationship between population size and genetic diversity, and we did not detect significant inbreeding. These results are best explained by the apparent self-incompatibility of this species, its longevity and clonal reproduction. To address questions regarding the history of T. reliquum's rarity, we compared results for T. reliquum with that of its more common and partially sympatric congener, T. cuneatum. Despite shared life history traits and history of land use, we observed significant genetic differences between the two species. Although T. cuneatum contains slightly lower polymorphism (Ps=85%), we detected significantly higher genetic diversity (Hes=0.217); most of its genetic diversity is contained within its populations (GST=0.092). Our results suggest that not only is there little gene flow among extant T. reliquum populations, but that rarity and population isolation in this species is of ancient origins, rather than due to more recent anthropogenic fragmentation following European colonization. The Chattahoochee River was identified as a major barrier to gene exchange.     

Demographic population structure of black howler monkeys in fragmented and continuous forest in Chiapas,Mexico: Implications for conservation

For wild primates, demography studies are increasingly recognized as necessary for assessing the viability of vulnerable populations experiencing rapid environmental change. In particular, anthropogenic changes such as habitat loss and fragmentation can cause ecological and behavioral changes in small, isolated populations, which may, over time, alter population density and demographic structure (age/sex classes and group composition) in fragment populations relative to continuous forest populations. We compared our study population of Endangered black howler monkeys (Alouatta pigra) in 34 forest fragments around Palenque National Park (PNP), Mexico (62 groups, 407 individuals), to the adjacent population in PNP, protected primary forest (21 groups, 134 individuals), and to previous research on black howlers in fragments in our study area (18 groups, 115 individuals). We used χ² and Mann–Whitney U tests to address the questions: (a) what is the current black howler demographic population structure in unprotected forest fragments around PNP? (b) How does it compare to PNP's stable, continuous population? (c) How has it changed over time? Compared to the PNP population, the fragment populations showed higher density, a significantly lower proportion of multimale groups, and significantly fewer adult males per group. The population's age/sex structure in the fragmented landscape has been stable over the last 17 years, but differed in a higher proportion of multifemale groups, higher density, and higher patch occupancy in the present. In the context of conservation, some of our results may be positive as they indicate possible population growth over time. However, long-term scarcity of adult males in fragments and associated effects on population demographic structure might be cause for concern, in that it may affect gene flow and genetic diversity. The scarcity of adult males might stem from males experiencing increased mortality while dispersing in the fragmented landscape, whereas females might be becoming more philopatric in fragments.     

Life History Studies on the Genus Trillium (Liliaceae) III. Reproductive Biology of Six Sessile-flowered Species Occurring in the Southeastern United States with Special Reference to Vegetative Reproduction

Abstract Life history characteristics, e.g., stage class structures of natural populations and associated reproductive characteristics, were studied for six sessile-flowered, diploid Trillium (Liliaceae) species that are restricted to the Coastal Plain region of the southeastern United States.
These sessile-flowered species reproduce primarily by vegetative propagation. Leaf area measurements were used to categorize stage class distributions of natural populations. Populations propagating mainly by vegetative reproduction had non-sigmoidal, convex-shaped population structures with most plants being in the intermediate stage classes. Low numbers of individuals in smaller stage classes and an abundance of intermediate sized individuals are due to the fact that vegetative propagules are the primary method for maintenance of local populations.
Characteristics associated with sexual reproduction were also examined. Seed output averaged about 20 seeds per plant, except for T. lancifolium which produced 9.7 seeds on the average. Seed setting rates varied between 15.61–44.15% and mean seed weight varied from 4.89 to 10.75 mg. The dominance of vegetative versus sexual reproduction may be due to the fact that all six species occur in ecologically unstable flood plain habitats.     

Microsatellite analysis of demographic genetic structure in fragmented populations of the tropical tree Symphonia globulifera

We developed genetic markers for three microsatellite loci in the tropical tree Symphonia globulifera and used them to examine the demographic genetic consequences of forest fragmentation. High levels of genetic variation were revealed in samples of adults, saplings, and seedlings. The more-variable loci exhibited less stability in allelic composition across sites and stages. The number of alleles per hectare (ha) of forest was similar when continuous forest plots were compared to plots from fragmented forest for all three stages. This pattern also held for the number of unique multilocus adult and sapling genotypes, but the number of unique seedling genotypes per ha of fragmented forest greatly exceeded expectations based on continuous forest data, probably due to the concentration of seeds into remnant forest patches by foraging bats. Significant inbreeding and genetic differentiation were most often associated with the fragmented forest and the seedlings. Finally, principal component analysis reaffirmed that a bottleneck, acting in concert with pre-existing genetic structure in the adults, had led to enhanced and rapid divergence in the seedlings following deforestation, a result that is of central interest for landscape management.     

Phylogeography of the Iberian populations of Mioscirtus wagneri (Orthoptera: Acrididae), a specialized grasshopper inhabiting highly fragmented hypersaline environments

Phylogeographic studies from western Palaearctic have generally focused on species able to disperse and track their emerging suitable habitats after the last ice age. However, data on species whose biogeographical histories differ from this bulk of Palaearctic fauna are scarce. This is clearly the case of some specialized organisms inhabiting inland hypersaline environments, which are likely to have had a wider distribution range during the late Tertiary and may have persisted through the Pleistocene to the present day only constituting relict populations. In this study, we use partial sequences from two mitochondrial genes [16S rRNA (16S) and cytochrome oxidase subunit II (COII)] to investigate the phylogeography of the Iberian populations of Mioscirtus wagneri (Orthoptera: Acrididae), a specialized grasshopper exclusively inhabiting hypersaline low grounds. Our results show that M. wagneri exhibits a marked phylogeographical structure, forming three main clades which correspond with populations located in north-east, central–south-east and south-west Iberia. These geographical areas did not share any haplotype, indicating that gene flow between them is absent. Nested clade analyses revealed that these lineages have probably evolved in allopatry and data on sequence divergence suggest population fragmentation from the Early Pleistocene. Overall, these results provide a broader perspective on the contribution of historical climate/geological events to biogeographical patterns of organisms currently forming relict populations of great conservation concern.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 623–633.     

Spatial population genetic structure in Trillium grandiflorum: the roles of dispersal, mating, history, and selection

The roles of the various potential ecological and evolutionary causes of spatial population genetic structure (SPGS) cannot in general be inferred from the extant structure alone. However, a stage-specific analysis can provide clues as to the causes of SPGS. We conducted a stage-specific SPGS analysis of a mapped population of about 2000 Trillium grandiflorum (Liliaceae), a long-lived perennial herb. We compared SPGS for juvenile (J), nonreproductive (NR), and reproductive (R) stages. Fisher's exact test showed that genotypes had Hardy-Weinberg frequencies at all loci and stage classes. Allele frequencies did not differ between stages. Bootstrapped 99% confidence intervals (99%CI) indicate that F-statistic values are indistinguishable from zero, (except for a slightly negative FIT for the R stage). Spatial autocorrelation was used to calculate f the average kinship coefficient between individuals within distance intervals. Null hypothesis 99%CIs for f were constructed by repeatedly randomizing genotypic locations. Significant positive fine-scale genetic structure was detected in the R and NR stages, but not in the J stage. This structure was most pronounced in the R stage, and declined by about half in each remaining stage: near-neighbor f = 0.122, 0.065, 0.027, for R, NR, and J, respectively. For R and NR, the near-neighbor f lies outside the null hypothesis 99%CI, indicating kinship at approximately the level of half-sibs and first cousins, respectively. We also simulated the expected SPGS of juveniles post dispersal, based on measured R-stage SPGS, the mating system, and measured pollen and seed dispersal properties. This provides a null hypothesis expectation (as a 99%CI) for the J-stage correlogram, against which to test the likelihood that post-dispersal events have influenced J-stage SPGS. The actual J correlogram lies within the null hypothesis 99%CI for the shortest distance interval and nearly all other distance intervals indicating that the observed low recruitment, random mating and seed dispersal patterns are sufficient to account for the disappearance of SPSG between the R and the J stages. The observed increase in SPGS between J and R stages has two potential explanations: history and local selection. The observed low total allelic diversity is consistent with a past bottleneck: a possible historical explanation. Only a longitudinal stage-specific study of SPGS structure can distinguish between historical events and local selection as causes of increased structure with increasing life history stage.     

A field study of seed germination in the endangered Trillium reliquum Freeman (Trilliaceae)

Previous studies examining the seeds of most Trillium species have reported double dormancy, a type of seed dormancy where two cold periods and one warm period are needed for complete germination. In the present paper, we describe a field study examining the federally endangered Trillium reliquum Freeman (Trilliaceae) in which moderate to high numbers of seeds germinated after one winter following seed production. Sixteen baskets with seeds were placed in four T. reliquum populations (four baskets in each population) in Georgia, USA, in June 2005. In spring 2006, all seed baskets contained seedlings. Germination percentages ranged from 33.3 to 83.3% across sites with a mean of 56.9 ± 3.9%. Trillium reliquum had higher germination percentages compared with other field‐based germination studies with other Trillium species. Our findings will inform future demographic studies of T. reliquum and suggest that double dormancy in seeds may not be as widespread as previously reported within the genus Trillium.     

Genetic structure of fragmented November moth (Lepidoptera: Geometridae) populations in farmland

Habitats are now becoming increasingly fragmented throughout the world due to intense cultivation. As a consequence, populations of some animals with low mobility have become isolated, thus increasing the risk of inbreeding and local extinction. In Britain, weakly flying geometric moths of the genus Epirrita are a good model species with which to test the genetic effects of habitat fragmentation on insect populations. Genetic variation within and between populations of two Epirrita species captured using a network of light traps at two spatial scales (local and national) was assessed using allozyme electrophoresis, with particular reference to the local scale (the 330-ha arable farm estate at Rothamsted, Hertfordshire, in southern Britain). Populations sampled widely in England and Wales displayed low (but statistically significant) levels of genetic differentiation for both species ( F _st  = 0.0051–0.0114 and 0.0226 for E. dilutata and E. christyi , respectively). However, analysis of large samples of E. dilutata from four small woods at Rothamsted revealed low ( F _st  = 0.0046) but significant differentiation, indicating that gene flow was restricted, even at this very small scale. It was concluded that small intervening patches of farmland (often a few fields width) were enough to prevent genetic homogeneity. The close similarity between more distant Epirrita populations was considered to be a result of historical, rather than recurrent gene flow, as genetic equilibrium between drift and gene flow is unlikely over such scales.  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 467–477.     

Life history, life table, habitat, and conservation of Byasa impediens (Lepidoptera: Papilionidae)

This article investigates the biology of Byasa impediens, presenting its life-table data and analyzing its habitat requirements and the key factors threatening the survival of this species. This study also aims to detect specific protection methods to guarantee the long-term survival of Byasa impediens in Baishuijiang Reserve. Byasa impediens is bivoltine in Baishuijiang Reserve. The pupae overwinter on shrubs or on branches of trees. The eclosion of the first generation starts in mid-April. The adults of the first generation emerge in large numbers in mid-late May, and the second generation emerges from late June to mid-July. The two generations overlap. The adult males emerge 7–10 days earlier than the adult females. Their flight behavior is determined by factors such as perching along small rivers and gullies, and visiting flowers. The males are strong fliers. On the contrary, the flying ability of the females is weak; therefore, they just visit flowers, mate, and lay eggs near the natal area. The ratio of female to male is 1:4.1. The maximum lifespan of the males is 26 days, with an average of 6.9 days, whereas the maximum lifespan of the females is 21 days, with an average of 7.6 days. The pregnant eggs per female are 31.5 on average. The incubation period of the first generation is 12–14 days, whereas that of the second generation is 7–9 days. The larvae feed mainly on Aristolochia heterophylla. The larval period of the first generation lasts for 30 days with five instars and that of the second generation lasts for 30–40 days with five or six instars. The pupal period of the first generation begins in early June and lasts for 20–26 days whereas for the second generation, it begins between late July and late September. The adults prefer the following nectar plants: Albizzia julibrissin, Bauhinia glauca, Clerodendrum bungei, and Sambucus chinensis. The plant Aristolochia heterophylla is distributed at an altitude of 900–1680 m, and the most suitable range is 1200–1500 m. The host plants grow mainly along the paths and along the borders of forests where the canopy is rather open and shrubby undergrowth is found. The plant can hardly be found when the canopy density of the forest is greater than 80%. The elevation range most suitable for the larvae is 1200–1500 m. The ideal habitat of host plants also seems to be the ideal habitat of Byasa impediens. The key factors that adversely affect the population of Byasa impediens are loss and deterioration of habitats. The loss and deterioration of the habitats result in a decrease in the numbers of host plants and a more restricted distribution of the potential habitats. The habitat is easily influenced by anthropogenic activities, such as herding, cultivating, and using pesticides, which in turn influences the growth of the host plant Aristolochia heterophylla and the larvae of butterflies. Abnormal climatic conditions and natural enemies are the key factors affecting population density. The hot and dry weather in summer and the heavy rain in autumn considerably reduce the survival rate of eggs and larvae. The ichneumon parasitoids reduce the survival rate of the over-wintering pupae. The primary natural enemies of the larvae include spiders, earwigs, wasps, bugs, and ichneumon parasitoids. Other natural enemies of pupae and adults are birds. The most important conservation measures are preservation and reconstruction of the natural habitat, which includes rebuilding forests, enhancing management, enforcing existing laws, and developing eco-tourism. Creating a core-patch near all patches at a central area is also an important measure for conservation. In the most ideal habitat, appropriate shrub cutting can increase the growth of host plants, thereby promoting expansion of the Byasa impediens population.     

Reproductive traits of the freshwater oyster Etheria elliptica (Bivalvia: Etheriidae) in the Pendjari River,Benin: implications for conservation

The African freshwater oyster Etheria elliptica, which is of great economic importance throughout the continent, is facing overharvesting in many fisheries in West Africa. Its reproductive traits (sex ratio, size at sexual maturity, oocyte diameter and fecundity) were studied at four stations located along the Pendjari River, northern Benin, in April 2013. Histological techniques were implemented to identify sex and gonad development stages. Oocyte sizes were measured based on the histological images and mean oocyte diameter was 38 µm. Fecundity, estimated by counting the developing eggs, averaged 106 724 eggs and increased significantly with shell size. The average sex ratio was approximately 1:1. Hermaphrodites were rare. Males reached sexual maturity at 57.6 mm dorsoventral height, earlier than females at 64.7 mm. The majority of the oyster specimens were in ripe-spawning stages, indicating that reproductive activities partly took place towards the end of the dry season. Both mature and immature individuals were subjected to harvesting at all the investigated fishing sites. The mean size of exploited oysters was 60.6 mm, lower than the size of females at maturity. Management strategies must enforce the minimum size of 65 mm required for harvesting, particularly in open access sites where juveniles are mostly harvested.     

The distribution,diversity, and conservation status of Cycas in China

As ancient gymnosperm and woody plants, cycads have survived through dramatic tectonic activities, climate fluctuation, and environmental variations making them of great significance in studying the origin and evolution of flora biodiversity. However, they are among the most threatened plant groups in the world. The principal aim of this review is to outline the distribution, diversity, and conservation status of Cycas in China and provide suggestions for conservation practices. In this review, we describe the taxonomy, distribution, and conservation status of Cycas in China. By comparing Chinese Cycas species with its relatives worldwide, we then discuss the current genetic diversity, genetic differentiation of Cycas, and try to disentangle the potential effects of Quaternary climate changes and topographical events on Cycas. We review conservation practices from both researchers and practitioners for these rare and endangered species. High genetic diversity at the species level and strong genetic differentiation within Cycas have been observed. Most Cycas species in southwest China have experienced population retreats in contrast to the coastal Cycas's expansion during the Quaternary glaciation. Additionally, human activities and habitat fragmentation have pushed these endangered taxa to the brink of extinction. Although numerous efforts have been made to mitigate threats to Cycas survival, implementation and compliance monitoring in protection zones are currently inadequate. We outline six proposals to strengthen conservation measures for Cycas in China and anticipate that these measures will provide guidelines for further research on population genetics as well as conservation biology of not only cycads but also other endangered species worldwide.     

Sex, drugs and recombination: the wild life of Aspergillus

Throughout the eukaryotes, sexual reproduction is an almost universal phenomenon. However, within the Kingdom Fungi, this relationship is not so clear‐cut. Fungi exhibit a spectrum of reproductive modes and life‐cycles; amongst the better known species, sexual reproduction is often facultative, can be rare, and in over half of the known Ascomycota (the moulds) is unknown ( Taylor et al. 1999 ). However, over the last decade, it has become apparent that many of these asexual mitosporic taxa undergo cryptic recombination via unobserved mechanisms and that wholly asexual fungi are, in fact, a rarity ( Taylor et al. 1999, 2001 ; Heitman 2010 ). This revolution in our understanding of fungal sexuality has come about in two ways: Firstly, sexual reproduction leaves an imprint on fungal genomes by maintaining genes required for mating and by generating patterns of mutation and recombination restricted to meiotic processes. Secondly, scientists have become better at catching fungi in flagrante delicto. The genus Aspergillus is one such fungus where a combination of population genetics, genomics and taxonomy has been able to intuit the existence of sex, then to catch the fungus in the act and formally describe their sexual stages. So, why are sexy moulds exciting? One species in particular, Aspergillus flavus, is notorious for its ability to produce a diverse array of secondary metabolites, of which the polyketide aflatoxins (AF) are carcinogenic and others (such as cyclopiazonic acid) are toxigenic. Because of the predilection of A. flavus to grow on crops, such as peanuts, corn and cotton, biocontrol is widely used to mitigate infection by pre‐applying nonaflatoxigenic (AF?) strains to competitively exclude the wild‐type AF+ strains. However, the eventual fate in nature of these biocontrol strains is not known. In this issue of Molecular Ecology, Olarte et al. (2012) make an important contribution by using laboratory crosses of A. flavus to show that not only is AF highly heritable, but AF? strains can become AF+ via crossing over during meiosis. This observation has raised the spectre of cross‐breeding and non‐mendelian inheritance of AF between native and biocontrol strains of the fungus, leading to an increase in the natural diversity of the fungus with perhaps unanticipated consequences.     

Population dynamics of the Mexican cycad Dioon edule Lindl. (Zamiaceae): life history stages and management impact

The demographic dynamics of three populations of Dioon edule Lindl. (Zamiaceae) were studied in a fragmented landscape using projection matrix modelling. Compared with other plant species, D. edule behaves like a tree life-form species. Density and spatial distribution patterns varied among populations according to models for animal-dispersed tree species. In all scenarios, λ was most sensitive to changes in abundance of adult plants. The elasticity reproductive component (F) for the three populations was zero and stasis values (L) were higher, this being a function of the permanence of non-reproductive individuals. It was detected that disturbance influences the population dynamics of D. edule as a function of adult plant persistence. This observation suggests that the conservation of adult plants is critical for D. edule and perhaps for all cycads species. Adult plant decapitation should be halted at the 'Monte Oscuro' population, subjected to sustainable management since 1990, if higher seed production is needed in rural nurseries.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 381–391.     

A multiscale analysis of gene flow for the New England cottontail,an imperiled habitat specialist in a fragmented landscape

Landscape features of anthropogenic or natural origin can influence organisms' dispersal patterns and the connectivity of populations. Understanding these relationships is of broad interest in ecology and evolutionary biology and provides key insights for habitat conservation planning at the landscape scale. This knowledge is germane to restoration efforts for the New England cottontail (Sylvilagus transitionalis), an early successional habitat specialist of conservation concern. We evaluated local population structure and measures of genetic diversity of a geographically isolated population of cottontails in the northeastern United States. We also conducted a multiscale landscape genetic analysis, in which we assessed genetic discontinuities relative to the landscape and developed several resistance models to test hypotheses about landscape features that promote or inhibit cottontail dispersal within and across the local populations. Bayesian clustering identified four genetically distinct populations, with very little migration among them, and additional substructure within one of those populations. These populations had private alleles, low genetic diversity, critically low effective population sizes (3.2–36.7), and evidence of recent genetic bottlenecks. Major highways and a river were found to limit cottontail dispersal and to separate populations. The habitat along roadsides, railroad beds, and utility corridors, on the other hand, was found to facilitate cottontail movement among patches. The relative importance of dispersal barriers and facilitators on gene flow varied among populations in relation to landscape composition, demonstrating the complexity and context dependency of factors influencing gene flow and highlighting the importance of replication and scale in landscape genetic studies. Our findings provide information for the design of restoration landscapes for the New England cottontail and also highlight the dual influence of roads, as both barriers and facilitators of dispersal for an early successional habitat specialist in a fragmented landscape.     

Genetic structure and demographic history of the endangered tree species Dysoxylum malabaricum (Meliaceae) in Western Ghats,India: implications for conservation in a biodiversity hotspot

The impact of fragmentation by human activities on genetic diversity of forest trees is an important concern in forest conservation, especially in tropical forests. Dysoxylum malabaricum (white cedar) is an economically important tree species, endemic to the Western Ghats, India, one of the world's eight most important biodiversity hotspots. As D. malabaricum is under pressure of disturbance and fragmentation together with overharvesting, conservation efforts are required in this species. In this study, range‐wide genetic structure of twelve D. malabaricum populations was evaluated to assess the impact of human activities on genetic diversity and infer the species’ evolutionary history, using both nuclear and chloroplast (cp) DNA simple sequence repeats (SSR). As genetic diversity and population structure did not differ among seedling, juvenile and adult age classes, reproductive success among the old‐growth trees and long distance seed dispersal by hornbills were suggested to contribute to maintain genetic diversity. The fixation index (F_IS) was significantly correlated with latitude, with a higher level of inbreeding in the northern populations, possibly reflecting a more severe ecosystem disturbance in those populations. Both nuclear and cpSSRs revealed northern and southern genetic groups with some discordance of their distributions; however, they did not correlate with any of the two geographic gaps known as genetic barriers to animals. Approximate Bayesian computation‐based inference from nuclear SSRs suggested that population divergence occurred before the last glacial maximum. Finally we discussed the implications of these results, in particular the presence of a clear pattern of historical genetic subdivision, on conservation policies.