Habitat loss and fragmentation reduce effective gene flow by disrupting seed dispersal in a neotropical palm

Abstract

Habitat loss and fragmentation often reduce gene flow and genetic diversity in plants by disrupting the movement of pollen and seed. However, direct comparisons of the contributions of pollen vs. seed dispersal to genetic variation in fragmented landscapes are lacking. To address this knowledge gap, we partitioned the genetic diversity contributed by male gametes from pollen sources and female gametes from seed sources within established seedlings of the palm Oenocarpus bataua in forest fragments and continuous forest in northwest Ecuador. This approach allowed us to quantify the separate contributions of each of these two dispersal processes to genetic variation. Compared to continuous forest, fragments had stronger spatial genetic structure, especially among female gametes, and reduced effective population sizes. We found that within and among fragments, allelic diversity was lower and genetic structure higher for female gametes than for male gametes. Moreover, female gametic allelic diversity in fragments decreased with decreasing surrounding forest cover, while male gametic allelic diversity did not. These results indicate that limited seed dispersal within and among fragments restricts genetic diversity and strengthens genetic structure in this system. Although pollen movement may also be impacted by habitat loss and fragmentation, it nonetheless serves to promote gene flow and diversity within and among fragments. Pollen and seed dispersal play distinctive roles in determining patterns of genetic variation in fragmented landscapes, and maintaining the integrity of both dispersal processes will be critical to managing and conserving genetic variation in the face of continuing habitat loss and fragmentation in tropical landscapes.

The relative contributions of seed and pollen dispersal to gene flow and genetic diversity in seedlings of a tropical palm

“…This might also have important conservation implications, as some key frugivores (e.g., umbrellabirds) in the O. bataua system are directly threatened by hunting, habitat degradation and habitat loss whereas others (e.g., toucans) appear to be more resilient (Walter et al., ). For example, in a companion paper we show evidence for a stronger impact of forest loss and fragmentation on seed dispersal than pollen flow for O. bataua , consistent with shifts in the relative contribution of different foraging ecologies to the dispersal and genetic structure of O. bataua (Browne & Karubian, ). In closing, we suggest future studies would benefit from considering both dispersal distance and effective number of sources at deposition sites (as opposed to dispersal distance alone) when attempting to characterize how seed dispersal may impact genetic diversity and fine‐scale spatial genetic structure.…”

Recent Fragmentation May Not Alter Genetic Patterns in Endangered Long-Lived Species: Evidence From Taxus cuspidata

“…A lack of significant genetic structure at both cpDNA and mtDNA was confirmed by BAPS analysis applied to natural and transplanted population (Figure 2 ). These results suggest that extensive gene flow might compensate the barrier of genetic change in mountainous terrain ( Austerlitz et al, 2004 ; Hu et al, 2008 ; Browne and Karubian, 2018 ). However, retention of ancestral alleles is an alternative explanation as species with a long life span and a large effective population size tend to preserve these alleles.…”

Spatial genetic structure of an endangered orchid Cypripedium calceolus (Orchidaceae) at a regional scale: limited gene flow in a fragmented landscape

“…When genetic structure between genomic compartments was translated into a pollen/seed flow ratio (m p /m s = 2) it revealed that pollen flow is two times more efficient than seed dispersal. Although in orchids and other plants pollen flow may be a strong cohesive force (Pinheiro et al 2014;Browne and Karubian 2018), in C. calceolus, due to small (rarely longer than 600 m) foraging distance of its putative pollinators (Gathmann and Tscharntke 2002;Zurbuchen et al 2010), the homogenizing influence of pollen flow on populations' genetic diversity may be expected only over short distances. Effective seed dispersal distances were even lower in the studied species and did not exceed 5 m (Brzosko et al 2017b).…”