Gone with the wind: Negative genetic and progeny fitness consequences of habitat fragmentation in the wind pollinated dioecious tree Brosimum alicastrum

Habitat fragmentation negatively affects population size and mating patterns that directly impact progeny fitness and genetic diversity; however, little is known about the effects of habitat fragmentation on dioecious, wind pollinated trees. We assessed the effects of habitat fragmentation on population sex ratios, genetic diversity, gene flow, mating patterns and early progeny vigor in the tropical dioecious tree, <em>Brosimum alicastrum.</em> We conducted our study in three continuous and three fragmented forest sites in a Mexican tropical dry forest. We used eight microsatellite loci to characterize and compare the genetic diversity, gene flow via pollen distances and mean relatedness of progeny. We compared early progeny vigor parameters of seedlings growing under greenhouse conditions. Sex ratios did not deviate from 1:1 between habitat conditions, except for one population in a fragmented habitat, which was female biased. The genetic diversity of adult trees and their offspring was similar in both habitat conditions. Pollen gene flow distances were similar across habitat types; however, paternity correlations were greater in fragmented than in continuous habitats. Germination rates did not differ between habitat conditions; however, progeny from fragmented habitats produced fewer leaves and had a lower foliar area, total height, and total dry biomass than progeny from continuous habitats. Our results suggest that changes in mating patterns, as a consequence of habitat fragmentation, have negative effects on early progeny vigor. We conclude that negative habitat fragmentation effects on mating patterns and early progeny vigor may be a serious threat to the long-term persistence of tropical dioecious trees.

生境破碎化会对种群规模与交配模式产生负面影响，进而直接作用于子代适合度与遗传多样性；但目前学界对生境破碎化对雌雄异株、风媒传粉树木的影响仍知之甚少。本研究以热带雌雄异株树木Brosimum alicastrum为研究对象，评估了生境破碎化对其种群性比、遗传多样性、基因流、交配模式以及子代早期活力的影响。研究区域设于墨西哥热带干燥森林内，共选取3处连续森林样地与3处破碎化森林样地。我们采用8个微卫星位点，对子代的遗传多样性、花粉介导的基因流距离以及平均亲缘关系进行了表征与比对，同时对比了温室培养条件下实生苗的子代早期活力参数。结果显示，不同生境条件下的种群性比均未偏离1:1，仅一处破碎化生境中的种群表现出雌性偏倚。两种生境中成年植株及其子代的遗传多样性水平无显著差异。不同生境类型的花粉基因流距离无显著区别，但破碎化生境中的父本相关性显著高于连续森林生境。两种生境的种子萌发率并无显著差异，但破碎化生境来源的子代实生苗叶片数量更少，叶面积、总株高及总干生物量均显著低于连续森林来源的子代。本研究结果表明，生境破碎化引发的交配模式改变会对子代早期活力产生负面影响。综上，生境破碎化对交配模式及子代早期活力的负面影响，可能会对热带雌雄异株树木的长期存续构成严重威胁。