Spatial genetic structure in four understory Psychotria species and implications for tropical forest diversity

Premise of the study: Tropical forests are the most species-rich terrestrial communities on Earth, and understory trees and shrubs comprise a large fraction of their plant species diversity, especially at high rainfalls. The mechanisms responsible for generating such high levels of diversity remain unknown. One hypothesis is that fleshy-fruited understory species should have limited seed dispersal due to the sedentary nature of their avian dispersers, resulting in restricted gene flow, population differentiation at small spatial scales, and ultimately, high rates of allopatric speciation. Methods: We sampled four species of the hyperdiverse tropical shrub genus Psychotria (Rubiaceae) on Barro Colorado Island (BCI) and two nearby sites in Panama. We genotyped each species with AFLPs, assessed genetic differentiation among populations, and determined patterns of fine-scale spatial genetic structure in the BCI population. Measures of spatial autocorrelation and population density were used...

研究前提：热带森林是地球上物种最丰富的陆地群落，林下乔木和灌木构成了其植物物种多样性的很大一部分，尤其在高降雨量地区。产生如此高多样性水平的机制仍不明确。一种假说认为，肉质果林下物种的种子传播应受到限制——因其鸟类传播者的定居习性，导致基因流受限、小空间尺度上的种群分化，最终形成高频率的异域物种形成。方法：我们在巴罗科罗拉多岛（BCI）及巴拿马附近两个地点采集了高度多样化的热带灌木Psychotria属（茜草科）的四个物种样本。通过扩增片段长度多态性（AFLPs）对每个物种进行基因分型，评估种群间的遗传分化，并确定BCI种群的精细尺度空间遗传结构模式。此外，还使用了空间自相关和种群密度的测量方法……