Life history and past demography maintain genetic structure, outcrossing rate, contemporary pollen gene flow of an understory herb in a highly fragmented rainforest

Abstract

IntroductionTheory predicts that habitat fragmentation, by reducing population size and increasing isolation among remnant populations, can alter their genetic diversity and structure. A cascade of effects is expected: genetic drift and inbreeding after a population bottleneck, changes in biotic interactions that may affect, as in the case of plants, pollen dynamics, mating system, reproductive success. The detection of the effects of contemporary habitat fragmentation on the genetic structure of populations are conditioned by the magnitude of change, given the few number of generations since the onset of fragmentation, especially for long-lived organisms. However, the present-day genetic structure of populations may bear the signature of past demography events. Here, we examine the effects of rainforest fragmentation on the genetic diversity, population structure, mating system (outcrossing rate), indirect gene flow and contemporary pollen dynamics in the understory herb Aphelandra aurantiaca. Also, we assessed its present-day genetic structure under different past demographic scenarios.MethodsTwelve populations of A. aurantiaca were sampled in large (4), medium (3), and small (5) forest fragments in the lowland tropical rainforest at Los Tuxtlas region. Variation at 11 microsatellite loci was assessed in 28–30 reproductive plants per population. In two medium- and two large-size fragments we estimated the density of reproductive plants, and the mating system by analyzing the progeny of different mother plants per population.ResultsDespite prevailing habitat fragmentation, populations of A. aurantiaca possess high genetic variation (He = 0.61), weak genetic structure (Rst = 0.037), and slight inbreeding in small fragments. Effective population sizes (Ne) were large, but slightly lower in small fragments. Migrants derive mostly from large and medium size fragments. Gene dispersal is highly restricted but long distance gene dispersal events were detected. Aphelandra aurantiaca shows a mixed mating system (tm = 0.81) and the outcrossing rate have not been affected by habitat fragmentation. A strong pollen pool structure was detected due to few effective pollen donors (Nep) and low distance pollen movement, pointing that most plants received pollen from close neighbors. Past demographic fluctuations may have affected the present population genetic structure as Bayesian coalescent analysis revealed the signature of past population expansion, possibly during warmer conditions after the last glacial maximum.DiscussionHabitat fragmentation has not increased genetic differentiation or reduced genetic diversity of A. aurantiaca despite dozens of generations since the onset of fragmentation in the region of Los Tuxtlas. Instead, past population expansion is compatible with the lack of observed genetic structure. The predicted negative effects of rainforest fragmentation on genetic diversity and population structure of A. aurantiaca seem to have been buffered owing to its large effective populations and long-distance disper...

Bayesian quantification of ecological determinants of outcrossing in natural plant populations: Computer simulations and the case study of biparental inbreeding in English yew

“…We will address this point in a future study. It is worth noting that dummy variables can be also used to incorporate nominal explanatory variables, such as fragmented versus continuous populations (Suárez-Montes et al, 2016) or large versus small flower sizes (Dart, Samis, Austen, & Eckert, 2012).…”

Habitat fragmentation influences genetic diversity and differentiation: Fine‐scale population structure ofCercis canadensis(eastern redbud)

“…For example, roadways have transected forests and imposed long, linear artificial structure to forested patches that, in turn, may be invaded by a mix of ornamental plants, ornamental plant cultivars, and their wild‐type progeny (Hamberg, Lehvävirta, & Kotze, 2009; Hardiman & Culley, 2010; Kwak et al, 1998). Such fragmentation impacts the genetic diversity and population structure of a species in various ways depending on the ecology and biology of the species (Cuartas‐Hernández & Núñez‐Farfán, 2006; Suárez‐Montes, Chávez‐Pesqueira, & Núñez‐Farfán, 2016). In a constantly changing natural setting, the dynamics of a plant population and ecological succession of plant species are shaped by the following three major challenges: species dispersal, establishment, and persistence in a specific environment (Weiher et al, 1999).…”

“…Habitat fragmentation may affect these processes through a number of ecological and biological modifications imposed on the fragmented area (Haila, 1999; Kolb & Diekmann, 2005; Suárez‐Montes et al, 2016). For instance, pollination‐ and animal‐based seed dispersal mechanisms are negatively impacted by forest fragmentation, especially at local levels (Dickson, 1990; Santos, Tellería, & Virgós, 1999; Sato & Kudoh, 2014).…”

“…In geographically reduced or fragmented populations, genetic diversity level can be affected through genetic drift and inbreeding, which can additionally reduce the ability of the affected individuals to regenerate and respond to changes of selection pressures (Hadziabdic et al, 2010; Suárez‐Montes et al, 2016). Genetic drift and inbreeding in a plant species can erode the overall population fitness and the prospects for adaptive change, thus increasing the possibility of species decline, mortality, or extinction (Fischer & Matthies, 1998; Severns, 2003; Young, Boyle, & Brown, 1996).…”

Effect of habitat fragmentation on genetic structure of terrestrial orchid Cymbidium faberi in the Qinling Mountains

“…There have been efforts made to understand the impact of habitat fragmentation on genetic diversity of plant species, and genetic diversity of populations located in fragmented landscape was lower compared to those in continuous ones (Aguilar, Quesada, Ashworth, Herrerias-Diego, & Lobo, 2008;Dixo, Metzger, Morgante, & Zamudio, 2009), which can be explained by the increased genetic drift and inbreeding (Suárez-Montes, Chávez-Pesqueira, & Núñez-Farfán, 2016).…”