Dissertation Research: Gene Flow, Reproductive Success and Inbreeding Depression in Fragmented Populations of Three Tropical Understory Trees

由于热带森林被砍伐用于农业，热带树木被限制在孤立的栖息地“岛屿”上。如果花粉和种子不能有效地在这些片段之间移动，就会发生局部交配，增加近亲繁殖和遗传多样性的侵蚀。近亲繁殖和遗传多样性的减少，反过来又会减少种子产量和幼苗活力，威胁种群的生存能力。本研究利用遗传标记研究了哥斯达黎加三种动物传粉的热带树种破碎化对花粉运动和近亲繁殖的影响。DNA指纹图谱将用于确定森林碎片中产生的种子的花粉来源，以及花粉运动如何影响近亲繁殖和遗传多样性的水平。比较碎片和附近连续森林之间的基因流动模式和幼苗活力，将有助于评估碎片造成的遗传威胁。地理分析将显示基因流动的模式如何受到片段大小和周围景观的影响。生物多样性的减少是一个深刻的全球威胁。这项研究将阐明栖息地的丧失和破碎化如何影响繁殖成功率、遗传多样性和近亲繁殖，所有这些都会降低种群的生存能力。因为它们明显依赖动物来授粉和传播种子，森林中的热带树木特别有灭绝的危险。由于植物是生物生产力和多样性的基础，这种损失可能导致级联灭绝。因此，需要这项研究的数据来确定对热带树木的最近威胁并指导长期管理。

As tropical forests are cleared for agriculture, tropical trees become restricted to isolated "islands" of habitat. If pollen and seeds do not move effectively among these fragments, local mating occurs, increasing inbreeding and the erosion of genetic diversity. Inbreeding and reduced genetic diversity, in turn, can diminish seed production and seedling vigor, threatening population viability. This study uses genetic markers to study how fragmentation affects pollen movement and inbreeding in three animal-pollinated tropical tree species in Costa Rica. DNA fingerprinting will be used to determine pollen sources for seeds produced in forest fragments and how levels of inbreeding and genetic diversity are affected by pollen movement. Comparing patterns of gene flow and seedling vigor between fragments and a nearby continuous forest will allow assessments of genetic threats posed by fragmentation. Geographic analyses will show how patterns of gene flow are affected by fragment size and surrounding landscapes. Declines in biological diversity represent a profound global threat. This study will illuminate how habitat loss and fragmentation are affecting reproductive success, genetic diversity and inbreeding, all of which can reduce population viability. Because they depend so obviously on animals for pollination and seed dispersal, tropical trees in forest patches are at particular risk of extinction. As plants represent the foundation for biological productivity and diversity, such losses can result in cascades of extinctions. The data from this study are thus needed to identify both proximal threats to tropical trees and to guide longer-term management.