Keeping it in the family: strong fine-scale genetic structure and inbreeding in <Emphasis Type="Italic">Lodoicea maldivica</Emphasis>, the largest-seeded plant in the world

The fine-scale spatial genetic structure (FSGS) of plant populations is strongly influenced by patterns of seed dispersal. An extreme case of limited dispersal is found in the charismatic yet endangered palm Lodoicea maldivica, which produces large fruits (up to 20 kg) dispersed only by gravity. To investigate patterns of seed dispersal and FSGS in natural populations we sampled 1252 individual adults and regenerating offspring across the species’ natural range in the Seychelles archipelago, and characterised their genotypes at 12 microsatellite loci. The average dispersal distance was 8.7?±?0.7 m. Topography had a significant effect on seed dispersal, with plants on steep slopes exhibiting the longest distances. FSGS was intense, especially in younger cohorts. Contrary to what might be expected in a dioecious species, we found high levels of inbreeding, with most neighbouring pairs of male and female trees (≤10 m) being closely related. Nonetheless, levels of genetic diversity were relatively high and similar in the various sampling areas, although these differed in disturbance and habitat fragmentation. We discuss potential trade-offs associated with maternal resource provisioning of progeny, seed dispersal and inbreeding, and consider the implications of our findings for managing this globally significant flagship species.     

Rapid evolution of dispersal‐related traits during range expansion of an invasive vine Mikania micrantha

Rapid range expansion of invasive plants provides a unique opportunity to explore evolutionary changes of dispersal‐related traits during the invasion process. Increasing evidence now suggests that a higher dispersal rate is favored at the invasion front. However, little is known about the role of genetic differentiation and phenotypic plasticity on patterns of dispersal ability during the invasion process. In this study, we combined a field survey and a common garden transplant experiment to test for evidence of genetically based dispersal ability in Mikania micrantha, a highly invasive vine, across its invaded range in southern China. Three dispersal‐related traits, plume loading, seed mass and pappus radius, were measured in both natural and common garden populations. We found that in natural conditions, plume loading and seed mass significantly decreased with expanding distance from the source population, but in controlled conditions, these two traits exhibited a significant humped trend against percent field cover, indicating that dispersal ability of M. micrantha was selected for during range expansion and that the related traits were likely to be under genetic control. Furthermore, rebounding dispersal ability was detected in highly competitive sites in the range core, which suggested that this evolutionary process was likely partially driven by intraspecific competition. Because more and more plant species are under spatial nonequilibirum due to climate change, this study can serve to provide hints at the fate of spatially fluctuant populations.     

Invasion ecology of wild pigs (<Emphasis Type="Italic">Sus scrofa</Emphasis>) in Florida,USA: the role of humans in the expansion and colonization of an invasive wild ungulate

Wild pigs (Sus scrofa) are the most widely distributed invasive wild ungulate in the United States, yet the factors that influence wild pig dispersal and colonization at the regional level are poorly understood. Our objective was to use a population genetic approach to describe patterns of dispersal and colonization among populations to gain a greater understanding of the invasion process contributing to the expansion of this species. We used 52 microsatellite loci to produce individual genotypes for 482 swine sampled at 39 locations between 2014 and 2016. Our data revealed the existence of genetically distinct subpopulations (F _ST  = 0.1170, p < 0.05). We found evidence of both fine-scale subdivision among the sampling locations, as well as evidence of long term genetic isolation. Several locations exhibited significant admixture (interbreeding) suggesting frequent mixing of individuals among locations; up to 14% of animals were immigrants from other populations. This pattern of admixture suggested successive rounds of human-assisted translocation and subsequent expansion across Florida. We also found evidence of genetically distinct populations that were isolated from nearby populations, suggesting recent introduction by humans. In addition, proximity to wild pig holding facilities was associated with higher migration rates and admixture, likely due to the escape or release of animals. Taken together, these results suggest that human-assisted movement plays a major role in the ecology and rapid population growth of wild pigs in Florida.     

Microsatellite diversity and genetic structure of fragmented populations of the rare,fire-dependent shrub Grevillea macleayana

Recent habitat loss and fragmentation superimposed upon ancient patterns of population subdivision are likely to have produced low levels of neutral genetic diversity and marked genetic structure in many plant species. The genetic effects of habitat fragmentation may be most pronounced in species that form small populations, are fully self-compatible and have limited seed dispersal. However, long-lived seed banks, mobile pollinators and long adult lifespans may prevent or delay the accumulation of genetic effects. We studied a rare Australian shrub species, Grevillea macleayana (Proteaceae), that occurs in many small populations, is self-compatible and has restricted seed dispersal. However, it has a relatively long adult lifespan (c. 30 years), a long-lived seed bank that germinates after fire and is pollinated by birds that are numerous and highly mobile. These latter characteristics raise the possibility that populations in the past may have been effectively large and genetically homogeneous. Using six microsatellites, we found that G. macleayana may have relatively low within-population diversity (3.2-4.2 alleles/locus; Hexp = 0.420-0.530), significant population differentiation and moderate genetic structure (FST = 0.218) showing isolation by distance, consistent with historically low gene flow. The frequency distribution of allele sizes suggest that this geographical differentiation is being driven by mutation. We found a lack mutation-drift equilibrium in some populations that is indicative of population bottlenecks. Combined with evidence for large spatiotemporal variation of selfing rates, this suggests that fluctuating population sizes characterize the demography in this species, promoting genetic drift. We argue that natural patterns of pollen and seed dispersal, coupled with the patchy, fire-shaped distribution, may have restricted long-distance gene flow in the past.     

Population genetic structure of orchid bees (Euglossini) in anthropogenically altered landscapes

Habitat degradation and fragmentation are widespread phenomena in tropical regions. Negative effects on the biota are numerous, ranging from interruption of gene flow among populations, to the loss of genetic diversity within populations, to a decline in species richness over time. Orchid bees (Hymenoptera: Apidae: Euglossini) are of major conservation interest due to their function as pollinators of numerous orchid species and other tropical plants. Here, we used microsatellite markers to investigate the effects of geographic distance and habitat fragmentation on gene flow among populations. Populations of Euglossa dilemma in three geographic regions??the Yucat??n peninsula (Mexico), Veracruz (Mexico), and Florida (USA)??were genetically structured predominantly across the regions, with the strength of differentiation among populations being positively correlated with geographic distance. Within geographic regions only little substructure was found, suggesting that dispersal is substantial in the absence of geographic or ecological barriers. In a second study, patterns of genetic differentiation among eight species of Euglossa were not related to habitat fragmentation following deforestation in southern Mexico (Veracruz). Specifically, most bee populations in the 9,800?ha forest remnant of Los Tuxtlas (Volcano San Martin) were neither differentiated from, nor had less genetic diversity than, populations in near-continuous forest separated from Los Tuxtlas by 130?km of agricultural land. Either occasional long distance dispersal across open areas has buffered the expected genetic effects of fragmentation, or the history of fragmentation in southern Mexico is too recent to have caused measurable shifts in allelic composition.     

Geographic range and structure of cryptic genetic diversity among Pacific North American populations of the non-native amphipod Grandidierella japonica

Reconstructing the invasion history of aquatic invasive species can enhance understanding of invasion risks by recognizing areas most susceptible to invasion and forecasting future spread based on past patterns of population expansion. Here we reconstruct the invasion history of the Japanese amphipod Grandidierella japonica Stephensen 1938 combining information from historical collection data with molecular genetic data to better understand post-invasion range expansion and anthropogenic connectivity across the Pacific coast of North America. Compilation of collection data from bays and estuaries of the Pacific North American coast show many new localities have been colonized in the last two decades, moving outward from harbors and bays with high commercial traffic into smaller coastal locations dominated by local recreational traffic. DNA barcode sequence data for G. japonica reveals two distinct clades: one found in San Francisco Bay and sites to the north, and one also found in San Francisco Bay and sites to the south. The two clades differ by an average 7.28 % genetic distance, large enough to consider these invasive amphipods two separate species. Both northern and southern clades exhibit low levels of genetic diversity, suggesting a single introduction event for each. The presence of cryptic diversity within this invasive amphipod highlights the need for more extensive study of the invasive and native populations of aquatic invasive invertebrates to address questions of taxonomy, diversity, and invasion history.     

Multiple introductions and no loss of genetic diversity: invasion history of Japanese Rose, Rosa rugosa, in Europe

The shrub Rosa rugosa (Japanese Rose), native to East Asia, is considered one of the most troublesome invasive plant species in natural or semi-natural habitats of northern Europe and has proven very difficult to control. We aimed at disentangling the species’ invasion history in Europe, including determining the number of introductions and their geographic origin, and at investigating whether populations in the introduced and native ranges differ in genetic diversity, structure and degree of differentiation. We found that introduced (n = 16) and native (n = 16) populations had similar levels of genetic diversity at seven nuclear SSR (microsatellite) loci. European populations lack isolation by distance and are less genetically differentiated than are populations in East Asia. Multiple and at least three independent colonization events, one of which was particularly successful, gave rise to current R. rugosa populations in Europe. The geographic distribution patterns of these three genetic clusters could not be explained by natural dispersal alone, indicating that human mediated secondary dispersal is driving the expansion in Europe. One cluster representing three of the European populations was most likely derived from NW Japan, whereas the origin of the remaining thirteen populations could not clearly be resolved. The introduction and expansion in Europe occurred with no significant loss of genetic diversity. We conclude that high propagule pressure at the primary establishment phase is the most parsimonious explanation for this pattern. A potential for long distance seed dispersal, coastal habitat connectivity and an outcrossing breeding system are factors likely to have enabled populations of R. rugosa to avoid detrimental effects of genetic bottlenecks and will further increase the species’ range size and abundance in Europe. We recommend that human-mediated dispersal should be prevented in order to halt the continued expansion.     

Genetic structure and seed-mediated dispersal rates of an endangered shrub in a fragmented landscape: a case study for Juniperus communis in northwestern Europe

Background

Population extinction risk in a fragmented landscape is related to the differential ability of the species to spread its genes across the landscape. The impact of landscape fragmentation on plant population dynamics will therefore vary across different spatial scales. We quantified successful seed-mediated dispersal of the dioecious shrub Juniperus communis in a fragmented landscape across northwestern Europe by using amplified fragment length polymorphism (AFLP) markers. Furthermore we investigated the genetic diversity and structure on two spatial scales: across northwestern Europe and across Flanders (northern Belgium). We also studied whether seed viability and populations size were correlated with genetic diversity.

Results

Unexpectedly, estimated seed-mediated dispersal rates were quite high and ranged between 3% and 14%. No population differentiation and no spatial genetic structure were detected on the local, Flemish scale. A significant low to moderate genetic differentiation between populations was detected at the regional, northwest European scale (PhiPT = 0.10). In general, geographically nearby populations were also genetically related. High levels of within-population genetic diversity were detected but no correlation was found between any genetic diversity parameter and population size or seed viability.

Conclusions

In northwestern Europe, landscape fragmentation has lead to a weak isolation-by-distance pattern but not to genetic impoverishment of common juniper. Substantial rates of successful migration by seed-mediated gene flow indicate a high dispersal ability which could enable Juniperus communis to naturally colonize suitable habitats. However, it is not clear whether the observed levels of migration will suffice to counterbalance the effects of genetic drift in small populations on the long run.     

Fragmentation of Atlantic Forest has not affected gene flow of a widespread seed‐dispersing bat

Habitat loss and resultant fragmentation are major threats to biodiversity, particularly in tropical and subtropical ecosystems. It is increasingly urgent to understand fragmentation effects, which are often complex and vary across taxa, time and space. We determined whether recent fragmentation of Atlantic forest is causing population subdivision in a widespread and important Neotropical seed disperser: Artibeus lituratus (Chiroptera: Phyllostomidae). Genetic structure within highly fragmented forest in Paraguay was compared to that in mostly contiguous forest in neighbouring Misiones, Argentina. Further, observed genetic structure across the fragmented landscape was compared with expected levels of structure for similar time spans in realistic simulated landscapes under different degrees of reduction in gene flow. If fragmentation significantly reduced successful dispersal, greater population differentiation and stronger isolation by distance would be expected in the fragmented than in the continuous landscape, and genetic structure in the fragmented landscape should be similar to structure for simulated landscapes where dispersal had been substantially reduced. Instead, little genetic differentiation was observed, and no significant correlation was found between genetic and geographic distance in fragmented or continuous landscapes. Furthermore, comparison of empirical and simulated landscapes indicated empirical results were consistent with regular long‐distance dispersal and high migration rates. Our results suggest maintenance of high gene flow for this relatively mobile and generalist species, which could be preventing or significantly delaying reduction in population connectivity in fragmented habitat. Our conclusions apply to A. lituratus in Interior Atlantic Forest, and do not contradict broad evidence that habitat fragmentation is contributing to extinction of populations and species, and poses a threat to biodiversity worldwide.     

Going coastal: shared evolutionary history between coastal British Columbia and Southeast Alaska wolves (Canis lupus)

Background

Many coastal species occupying the temperate rainforests of the Pacific Northwest in North America comprise endemic populations genetically and ecologically distinct from interior continental conspecifics. Morphological variation previously identified among wolf populations resulted in recognition of multiple subspecies of wolves in the Pacific Northwest. Recently, separate genetic studies have identified diverged populations of wolves in coastal British Columbia and coastal Southeast Alaska, providing support for hypotheses of distinct coastal subspecies. These two regions are geographically and ecologically contiguous, however, there is no comprehensive analysis across all wolf populations in this coastal rainforest.

Methodology/Principal Findings

By combining mitochondrial DNA datasets from throughout the Pacific Northwest, we examined the genetic relationship between coastal British Columbia and Southeast Alaska wolf populations and compared them with adjacent continental populations. Phylogenetic analysis indicates complete overlap in the genetic diversity of coastal British Columbia and Southeast Alaska wolves, but these populations are distinct from interior continental wolves. Analyses of molecular variation support the separation of all coastal wolves in a group divergent from continental populations, as predicted based on hypothesized subspecies designations. Two novel haplotypes also were uncovered in a newly assayed continental population of interior Alaska wolves.

Conclusions/Significance

We found evidence that coastal wolves endemic to these temperate rainforests are diverged from neighbouring, interior continental wolves; a finding that necessitates new international strategies associated with the management of this species.     

Genetic Structure of Indian Valerian (Valeriana jatamansi) Populations in Western Himalaya Revealed by AFLP

Valeriana jatamansi Jones is a natural tetraploid species indigenous to the Indian Himalaya. To assess its genetic diversity and population structure, we analyzed six natural populations from the western Himalayan region using amplified fragment length polymorphism. An analysis of molecular variance found that 93% of the genetic variation of V. jatamansi was within populations and 7% among populations. The correlation between genetic and geographic distances (r = 0.14) was not significant. Though the populations are well separated, the lack of distinct genetic variation between populations may be due to either recent rapid fragmentation from a wide and continuous area resulting in genetically similar populations or wide dispersal of seed by wind, since the follicles are feathery. Polyploidy may be the reason for the lack of genetic impoverishment due to fragmentation.     

Evidence for ancient genetic subdivision among recently fragmented populations of the endangered shrub Grevillea caleyi (Proteaceae)

The genetic effects of population fragmentation cannot be interpreted without understanding the underlying pattern of genetic variation resulting from historic population processes. We used AFLP markers to determine genetic structure and distribution of genetic diversity among populations of an endangered Australian shrub Grevillea caleyi (Proteaceae). Populations that occurred historically on four ridges have new been fragmented to varying degrees, producing some large, relatively pristine populations and very small populations consisting of fewer than 10 adult plants. We found marked population genetic structure (65.9% of genetic variation was among populations) and a significant relationship between genetic and geographic distance (rm=0.564, P=0.004). However, only 14% of overall genetic differentiation was attributable to variation among ridges, compared with 52% among populations within ridges. Moreover, genetic diversity within samples of plants did not vary with either population size or degree of isolation. Thus, the present genetic structure of populations is probably almost entirely the product of historical events. Fine-scale structuring within populations prior to fragmentation may have been caused by limited seed and pollen dispersal, despite a complex suite of (mostly avian) pollinators, and a mixed mating system that allows a large amount of selfing. The combined effects of adult longevity and a soil-stored seed bank may have buffered the recently fragmented populations against the effects of dramatic reductions in numbers of adult plants.     

Microsatellite analysis to estimate realized dispersal distance in <Emphasis Type="Italic">Phragmites</Emphasis><Emphasis Type="Italic">australis</Emphasis>

An understanding of the mean and maximum dispersal distances of target species and subsequent scaling of management efforts to dispersal distance can be key in slowing, containing, or eradicating invasive species. However, dispersal distance is often difficult to measure. Patterns of genetic relatedness can be interpreted to understand realized genetic dispersal distances, which can then be applied to management. We analyzed patterns of microsatellite relatedness using Mantel correlograms and used them to estimate realized dispersal distance for the invasive wetland grass, Phragmites australis. We found that genetic relatedness declined quickly with increasing distance, decreasing to the level of the mean subestuary genetic relatedness by 100 m and to nearly zero by 500 m. We interpret this to indicate that most dispersal is <100 m and very little dispersal extends beyond 500 m. This suggests that management of P. australis may need to consider dispersal from stands up to 500 m from an area that is being managed, perhaps at the scale of whole subestuaries. Results of this study demonstrate that analysis of dispersal patterns can be used to develop landscape-scale approaches to the management of invasive species.     

Shifting dispersal modes at an expanding species’ range margin

While it is generally recognized that noncontiguous (long‐distance) dispersal of small numbers of individuals is important for range expansion over large geographic areas, it is often assumed that colonization on more local scales proceeds by population expansion and diffusion dispersal (larger numbers of individuals colonizing adjacent sites). There are few empirical studies of dispersal modes at the front of expanding ranges, and very little information is available on dispersal dynamics at smaller geographic scales where we expect contiguous (diffusion) dispersal to be prevalent. We used highly polymorphic genetic markers to characterize dispersal modes at a local geographic scale for populations at the edge of the range of a newly invasive grass species (Brachypodium sylvaticum) that is undergoing rapid range expansion in the Pacific Northwest of North America. Comparisons of Bayesian clustering of populations, patterns of genetic diversity, and gametic disequilibrium indicate that new populations are colonized ahead of the invasion front by noncontiguous dispersal from source populations, with admixture occurring as populations age. This pattern of noncontiguous colonization was maintained even at a local scale. Absence of evidence for dispersal among adjacent pioneer sites at the edge of the expanding range of this species suggests that pioneer populations undergo an establishment phase during which they do not contribute emigrants for colonization of neighbouring sites. Our data indicate that dispersal modes change as the invasion matures: initial colonization processes appear to be dominated by noncontiguous dispersal from only a few sources, while contiguous dispersal may play a greater role once populations become established.     

High connectivity in a long-lived high-Arctic seabird,the ivory gull <Emphasis Type="Italic">Pagophila eburnea</Emphasis>

Species may cope with rapid habitat changes by distribution shifts or adaptation to new conditions. A common feature of these responses is that they depend on how the process of dispersal connects populations, both demographically and genetically. We analyzed the genetic structure of a near-threatened high-Arctic seabird, the ivory gull (Pagophila eburnea) in order to infer the connectivity among gull colonies. We analyzed 343 individuals sampled from 16 localities across the circumpolar breeding range of ivory gulls, from northern Russia to the Canadian Arctic. To explore the roles of natal and breeding dispersal, we developed a population genetic model to relate dispersal behavior to the observed genetic structure of worldwide ivory gull populations. Our key finding is the striking genetic homogeneity of ivory gulls across their entire distribution range. The lack of population genetic structure found among colonies, in tandem with independent evidence of movement among colonies, suggests that ongoing effective dispersal is occurring across the Arctic Region. Our results contradict the dispersal patterns generally observed in seabirds where species movement capabilities are often not indicative of dispersal patterns. Model predictions show how natal and breeding dispersal may combine to shape the genetic homogeneity among ivory gull colonies separated by up to 2800 km. Although field data will be key to determine the role of dispersal for the demography of local colonies and refine the respective impacts of natal versus breeding dispersal, conservation planning needs to consider ivory gulls as a genetically homogeneous, Arctic-wide metapopulation effectively connected through dispersal.     

Low plant density enhances gene dispersal in the Amazonian understory herb Heliconia acuminata

In theory, conservation genetics predicts that forest fragmentation will reduce gene dispersal, but in practice, genetic and ecological processes are also dependent on other population characteristics. We used Bayesian genetic analyses to characterize parentage and propagule dispersal in Heliconia acuminata L. C. Richard (Heliconiaceae), a common Amazonian understory plant that is pollinated and dispersed by birds. We studied these processes in two continuous forest sites and three 1‐ha fragments in Brazil's Biological Dynamics of Forest Fragments Project. These sites showed variation in the density of H. acuminata. Ten microsatellite markers were used to genotype flowering adults and seedling recruits and to quantify realized pollen and seed dispersal distances, immigration of propagules from outside populations, and reproductive dominance among parents. We tested whether gene dispersal is more dependent on fragmentation or density of reproductive plants. Low plant densities were associated with elevated immigration rates and greater propagule dispersal distances. Reproductive dominance among inside‐plot parents was higher for low‐density than for high‐density populations. Elevated local flower and fruit availability is probably leading to spatially more proximal bird foraging and propagule dispersal in areas with high density of reproductive plants. Nevertheless, genetic diversity, inbreeding coefficients and fine‐scale spatial genetic structure were similar across populations, despite differences in gene dispersal. This result may indicate that the opposing processes of longer dispersal events in low‐density populations vs. higher diversity of contributing parents in high‐density populations balance the resulting genetic outcomes and prevent genetic erosion in small populations and fragments.     

Diverse historical processes shape deep phylogeographical divergence in the pollinating seed parasite Greya politella

Understanding the historical framework in which species interactions have diversified across landscapes may help to partition the effects of vicariance and geographically variable selection in shaping the geographical mosaic of coevolving species. We used phylogeographical analyses of the pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae) to define the historical processes that may have structured interactions of this species with its host plants across major biogeographical breaks in western North America. Using 648 bp of cytochrome oxidase I and amplified fragment length polymorphisims, we identified deep genetic breaks among some populations consistent with some definitions of cryptic species. A combination of phylogenetic and population genetic approaches indicates that different historical processes may have structured G. politella genetic diversity in four regions: northern Pacific Northwest, southern Oregon, southern Sierra Nevada, and the remainder of California. The northern Pacific Northwest had high genetic diversity likely due to glacial refugia and subsequent spatial expansion, concordant with some other taxa. Populations in southern Oregon possessed unique, closely related haplotypes with restricted gene flow, possibly indicating a long-standing set of populations in this endemic-rich region. Analyses of California populations showed evidence of restricted gene flow and spatial expansion with many closely related haplotypes that occupy a broad geographical range. Southern Sierra Nevada populations were genetically distinct and highly diverse, possibly due to a localized glacial refugium. Together, these results suggest that vicariance and population expansion, possibly in combination with geographically variable selection, have shaped the diversification of G. politella and its interactions with its host plants.     

Genomic analysis of the emergent aquatic plant Sparganium stoloniferum provides insights into its clonality,local adaptation and demographic history

Clonal propagation and extensive dispersal of seeds and asexual propagules are two important features of aquatic plants that help them adapt to aquatic environments. Accurate measurements of clonality and effective clonal dispersal are essential for understanding the evolution of aquatic plants. Here, we first assembled a high-quality chromosome-level genome of a widespread emergent aquatic plant Sparganium stoloniferum to provide a reference for its population genomic study. We then performed high-depth resequencing of 173 individuals from 20 populations covering different basins across its range in China. Population genomic analyses revealed three genetic lineages reflecting the northeast (NE), southwest (SW) and northwest (NW) of its geographical distribution. The NE lineage diverged in the middle Pleistocene while the SW and NW lineages diverged until about 2400 years ago. Clonal relationship analyses identified nine populations as monoclonal population. Dispersal of vegetative propagules was identified between five populations covering three basins in the NE lineage, and dispersal distance was up to 1041 km, indicating high dispersibility in emergent aquatic plant species. We also identified lineage-specific positively selected genes that are likely to be involved in adaptations to saline wetlands and high-altitude environments. Our findings accurately measure the clonality, determine the dispersal range and frequency of vegetative propagules, and detect genetic signatures of local adaptation in a widespread emergent aquatic plant species, providing new perspectives on the evolution of aquatic plants.     

Genetic effects of habitat fragmentation and population isolation on Etheostoma raneyi (Percidae)

The use of genetic methods to quantify the effects of anthropogenic habitat fragmentation on population structure has become increasingly common. However, in today’s highly fragmented habitats, researchers have sometimes concluded that populations are currently genetically isolated due to habitat fragmentation without testing the possibility that populations were genetically isolated before European settlement. Etheostoma raneyi is a benthic headwater fish restricted to river drainages in northern Mississippi, USA, that has a suite of adaptive traits that correlate with poor dispersal ability. Aquatic habitat within this area has been extensively modified, primarily by flood-control projects, and populations in headwater streams have possibly become genetically isolated from one another. We used microsatellite markers to quantify genetic structure as well as contemporary and historical gene flow across the range of the species. Results indicated that genetically distinct populations exist in each headwater stream analyzed, current gene flow rates are lower than historical rates, most genetic variation is partitioned among populations, and populations in the Yocona River drainage show lower levels of genetic diversity than populations in the Tallahatchie River drainage and other Etheostoma species. All populations have negative F_IS scores, of which roughly half are significant relative to Hardy–Weinberg expectations, perhaps due to small population sizes. We conclude that anthropogenic habitat alteration and fragmentation has had a profoundly negative impact on the species by isolating E. raneyi within headwater stream reaches. Further research is needed to inform conservation strategies, but populations in the Yocona River drainage are in dire need of management action. Carefully planned human-mediated dispersal and habitat restoration should be explored as management options across the range of the species.     

Spatial and Temporal Variation of Seed Rain in the Canopy and on the Ground of a Tropical Cloud Forest

Spatial and temporal patterns of seed rain impact plant fitness, genetic and demographic structure of plant populations, and species' interactions. Because plants are sessile, they rely on biotic and abiotic dispersal agents to move their seeds. The relative importance of these dispersal agents may shift throughout the year. In tropical forests, seed dispersal of epiphytes constitutes a major but hitherto unknown portion of seed rain ecology. For the first time, we report on patterns of seed rain for both epiphytic and terrestrial plants across an entire year in a Neotropical montane forest. To examine seed rain, we placed traps in the canopy and on the ground. We analyzed seed dispersal syndrome (bird, mammal, wind) and plant habit (epiphyte, liana, shrub, small tree, large tree) across all seasons of the year (dry, misty, wet). We found that the community of species collected in canopy traps was significantly different from the community in ground traps. Epiphytes were the most common plant habit found in canopy traps, while large trees were most common in ground traps. Species with bird‐dispersed seeds dominated all traps. Species richness was significantly higher during the dry season in ground traps, but did not vary across seasons in canopy traps. Our results highlight the distinct seed rain found in the canopy and on the ground and underscore the importance of frugivores for dispersing both arboreal and terrestrial plants in tropical ecosystems.