Abstract
BackgroundDeveloping a greater understanding of population genetic structure in lowland tropical plant species is highly relevant to our knowledge of increasingly fragmented forests and to the conservation of threatened species. Specific studies are particularly needed for taxa whose population dynamics are further impacted by human harvesting practices. One such case is the fishtail or xaté palm (Chamaedorea ernesti-augusti) of Central America, whose wild-collected leaves are becoming progressively more important to the global ornamental industry. We use microsatellite markers to describe the population genetics of this species in Belize and test the effects of climate change and deforestation on its recent and historical effective population size.ResultsWe found high levels of inbreeding coupled with moderate or high allelic diversity within populations. Overall high gene flow was observed, with a north and south gradient and ongoing differentiation at smaller spatial scales. Immigration rates among populations were more difficult to discern, with minimal evidence for isolation by distance. We infer a tenfold reduction in effective population size ca. 10,000 years ago, but fail to detect changes attributable to Mayan or contemporary deforestation.ConclusionPopulations of C. ernesti-augusti are genetically heterogeneous demes at a local spatial scale, but are widely connected at a regional level in Belize. We suggest that the inferred patterns in population genetic structure are the result of the colonization of this species into Belize following expansion of humid forests in combination with demographic and mating patterns. Within populations, we hypothesize that low aggregated population density over large areas, short distance pollen dispersal via thrips, low adult survival, and low fruiting combined with early flowering may contribute towards local inbreeding via genetic drift. Relatively high levels of regional connectivity are likely the result of animal-mediated long-distance seed dispersal. The greatest present threat to the species is the potential onset of inbreeding depression as the result of increased human harvesting activities. Future genetic studies in understory palms should focus on both fine-scale and landscape-level genetic structure.
Highlights
Developing a greater understanding of population genetic structure in lowland tropical plant species is highly relevant to our knowledge of increasingly fragmented forests and to the conservation of threatened species
We suggest that the inferred patterns in population genetic structure are the result of the colonization of this species into Belize following expansion of humid forests in combination with demographic and mating patterns
We suggest that species like C. ernesti-augusti have probably survived recurrent habitat changes by a combination of long-distance dispersal that maintains genetic connectivity, and reproductive and demographic patterns that maintain allele richness at a local spatial scale
Summary
Developing a greater understanding of population genetic structure in lowland tropical plant species is highly relevant to our knowledge of increasingly fragmented forests and to the conservation of threatened species. Hamrick [14] suggested that most trees have enough intrinsic genetic variation and mechanisms to maintain propagule movement in order to be resilient to habitat changes While this might be the case for most forest canopy species [15], evidence is less clear for understory taxa, which differ from canopy species in biological and demographic factors. Understory palms have small life forms, smaller seeds than canopy palms, striking phenotypic plasticity, generally narrow distributions along microenvironments, and most notably, variation in population densities across geographic areas [1621] They are sensitive to processes that occur at local spatial scales, such as changes in elevation or light within a single mountain slope [22,23,24,25]. It remains unclear whether theoretical expectations of genetic erosion occur after forest fragmentation in understory palms, or whether other factors, such as changes in demography due to overharvesting or localized ecological degradation, may be more important for the long-term survival of these important species [12]
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