Abstract
The riverine barrier hypothesis (RBH) posits that rivers comprise geographical barriers to gene flow for terrestrial organisms, thus promoting genetic differentiation between populations. Here, we explored the RBH on larviparous and pueriparous populations of the live-bearing fire salamander (Salamandra salamandra). While larviparous fire salamanders exhibit a semi-aquatic life cycle (females deposit pre-metamorphic larvae on water), pueriparous salamanders present a fully terrestrial life cycle (females deliver terrestrial juveniles) and, therefore, a greater independence from water for survival and reproduction. We performed a fine-scale sampling of opposite transects in 11 rivers (six and five for larviparous and pueriparous populations, respectively) to test the hypothesis that rivers are more effective barriers for pueriparous salamanders due to their terrestrial life cycle. We carried out individual- and population-based genetic analyses using 14 microsatellites and a mitochondrial marker to examine the extent to which rivers hinder short- and long-term gene flow. We found that rivers are semi-permeable obstacles for both larviparous and pueriparous salamanders, although they appear to be more effective barriers for the latter when rivers with similar attributes are compared. We also found that river width and possibly the presence of crossing structures may influence the genetic barrier effects of rivers in fire salamanders. This is one of the very few studies in amphibians showing how different reproductive strategies influence the barrier effects imposed by rivers.
Highlights
The riverine barrier hypothesis (RBH) posits that rivers can represent geographical barriers to dispersal for terrestrial organisms, leading to a reduction/restriction of gene flow between individuals at both sides of the river, and enhancing genetic differentiation and, allopatric speciation (Wallace, 1852)
We concluded that our 14 loci have high information content to discriminate individuals and, we considered none of the sampled individuals were recaptures and all were retained for downstream analyses
The following information is displayed for each river: sampled population (Pop), minimum number of allele mismatches (MA), mean number of alleles (NA), mean number of private alleles (PA), number of individuals with private alleles (NPA), observed heterozygosity (HO), expected heterozygosity (HE), allelic richness (AR), and mean inbreeding coefficient (F)
Summary
The riverine barrier hypothesis (RBH) posits that rivers can represent geographical barriers to dispersal for terrestrial organisms, leading to a reduction/restriction of gene flow between individuals at both sides of the river, and enhancing genetic differentiation and, allopatric speciation (Wallace, 1852). The barrier effects of rivers are expected to be lower in large-sized organisms that can swim and counteract water current, and in animals that exhibit great swimming/flight abilities (e.g. mammals, birds, some amphibians; Cushman et al, 2006; Pérez-Espona et al, 2008; Luqman et al, 2018; Kopuchian et al, 2020). Rivers generally comprise relatively impermeable barriers for small-sized and poor dispersers, such as small mammals, amphibians or reptiles (Funk et al, 2007; Nicolas et al, 2011; Fouquet et al, 2012; Pirani et al, 2019; Waraniak et al, 2019). One may hypothesize the extent to which rivers influence dispersal and gene flow may have changed in those species that underwent major lifehistory modifications involving the way they interact with aquatic systems, though this subject is still poorly explored
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