Disentangling the impact of demographic factors on population differentiation of an endangered freshwater crayfish (Austropotamobius pallipes) using population density and microsatellite data

Abstract

1. Habitat fragmentation of stream ecosystems often results in decreased connectivity between populations and lower population sizes. Hence, understanding how habitat fragmentation affects genetic erosion is important for the preservation of freshwater biodiversity, in particular, as small populations suffer from loss of genetic diversity through genetic drift and loss of fitness because of inbreeding, increasing the risk of extinction. 2. Here, we assess the impact of demographic factors on population differentiation in the endangered freshwater crayfish Austropotamobius pallipes by analysing population genetic structure, estimating effective population sizes and comparing levels of polymorphism at five microsatellite loci with density estimates of 10 populations within a small French catchment that has become progressively confined to headwaters over the last six decades. 3. Levels of expected heterozygosity and allelic richness per population were relatively low (0.214-0.396 and 1.6-2.6, respectively). We found strong genetic differentiation between these geographically close populations (F ST = 0.283), with weak statistical evidence for a pattern of isolation by distance. Estimates of effective population size were low (<150) in most populations, but potentially reached several thousands in three populations. 4. Population density and allelic richness were strongly positively correlated. A robust relationship between population density and heterozygosity values was also noted, but only after discarding two populations for which significant genetic signatures of a recent bottleneck were found; these two populations displayed high expected heterozygosity compared with a very low density. Populations with the highest densities of individuals had the highest effective population size estimates and vice versa. 5. Our results clearly show the importance of demographic factors and genetic drift on A. pallipes populations. Furthermore, analysis of genetic and population density data is a pragmatic and efficient approach to corroborate inferences from genetic data and can be

Critically low levels of genetic diversity in fragmented populations of the endangered Glenelg spiny freshwater crayfish Euastacus bispinosus

“…This is consistent with other freshwater crayfish (Fetzner & Crandall 2001, Baric et al 2006, Gouin et al 2011) and may be attributed to an inherent tendency to inbreed due to poor dispersal ability and small population size. Other factors such as male dominance hierarchies, commonly observed in freshwater crayfish and other crustacean groups (Moore & Bergman 2005), will also act to reduce effective population sizes (N e ) and exacerbate the severity of inbreeding.…”

“…Individuals are arranged into sites from which they were sampled following the order given in Table 1 (site codes are also derived from Table 1), and sites are pooled into regions (Victoria and South Australia) al. 2005, Baric et al 2006, Gouin et al 2011. The mitochondrial DN A analysis indicates that the high level of contemporary structuring is likely to be a relatively recent demographic feature, with 4 of the 5 Victorian sites sharing a single dominant haplotype due to historical gene flow and recent common ancestry.…”

Genetic analyses reveal limited dispersal and recovery potential in the large freshwater crayfish Euastacus armatus from the southern Murray–Darling Basin

“…Such genetic similarity -within and between catchments across river and tributaries separated by over 2000 km of waterways -is rarely observed in freshwater species, and is atypical of freshwater crayfish (Gouin et al 2006;Gross et al 2013) given inherent dispersal limitations, and the dendritic, and often fragmented, nature of freshwater environments. Large population sizes and sufficient gene flow among local populations has likely helped maintain high levels of genetic diversity and suppress the influence of genetic drift (Frankham et al 2010;Allendorf et al 2013), with the observed average allelic richness and heterozygosity (r ¼ 3.23 and H E ¼ 0.53) being uncharacteristically high for freshwater crayfish (Fetzner and Crandall 2002;Gouin et al 2011;Miller et al 2014). In fact, populations of E. armatus harbour similar, or in some cases higher, levels of genetic variation compared to widespread and more vagile freshwater fish species inhabiting the MDB; such as golden perch (Macquaria ambigua) (Faulks et al 2010), Murray cod (Maccullochella peelii) (Rourke et al 2011) and Australian smelt (Retropinna semoni) (Taylor et al 2010).…”

Modelling effects of invasive species and drought on crayfish extinction risk and population dynamics

“…In order to determine the median time to quasi‐extinction, the extinction threshold was based on estimates of effective population size from Gouin, Souty‐Grosset, Bórquez, Bertin, and Grandjean () for Austropotamobius pallipes (white‐clawed crayfish), an endangered European freshwater crayfish, as published data related to extinction thresholds of Faxonius species could not be obtained. For A. pallipes , estimates of effective population size were variable but ≤150 in most populations examined (Gouin et al, ), so the effective population size used in the models was 150. All models were run for 1000 iterations over 100 years.…”