Peer Review #1 of "Life history and past demography maintain genetic structure, outcrossing rate, contemporary pollen gene flow of an understory herb in a highly fragmented rainforest (v0.1)"

Abstract

Introduction. Forest fragmentation reduces population size and increases isolation among remnant populations in fragments, affecting genetic structure. The hummingbirdpollinated herb, Aphelandra aurantiaca, is a key element of regeneration in the understory of tropical rainforests. We examine the effects of rainforest fragmentation on genetic diversity, population structure, demographic history, outcrossing rate, and pollen dynamics. Methods. To study the genetic structure, we sampled forest fragments populations of different size at the Los Tuxtlas region, the northernmost limit of humid tropical rainforest in the Americas. We assessed population demographic change, genetic diversity, population structure, recent gene flow and connectivity among populations across the landscape by analyzing variation at microsatellite loci. We also estimated the mating system and pollen pool structure in four fragments. Results. Despite prevailing habitat fragmentation, populations of A. aurantiaca possess high genetic variation (H e = 0.61), weak genetic structure (R st = 0.037), and slight inbreeding in small fragments. In general, effective population size (N e) is large, but there is a tendency to decrease with fragment size. The highest rate of migrants and first-generation migrants derive mostly from large and medium size fragments. Although events of long distance gene dispersal were detected, most gene dispersal is restricted. Interestingly, populations within the largest fragment are not totally connected. Past demographic fluctuations may have affected the present population genetic structure. Bayesian coalescent analysis revealed the signature of past population expansion, possibly during warmer conditions after the last glacial maximum. Aphelandra aurantiaca shows a mixed mating system (t m = 0.81); outcrossing rate and pollen dynamics have not been affected by habitat fragmentation. A strong pollen pool structure was detected due to few effective pollen donors (N ep) and low distance pollen movement, pointing that most plants received pollen from close neighbors. Discussion. The predicted negative effects of rainforest fragmentation on genetic diversity and population structure of A. aurantiaca seem to have been buffered, as yet,