Roads to isolation: Similar genomic history patterns in two species of freshwater crabs with contrasting environmental tolerances and range sizes

Abstract

Freshwater species often show high levels of endemism and risk of extinction owing to their limited dispersal abilities. This is exemplified by the stenotopic freshwater crab, Johora singaporensis which is one of the world's 100 most threatened species, and currently inhabits less than 0.01 km2 of five low order hill streams within the highly urbanized island city‐state of Singapore. We compared populations of J. singaporensis with that of the non‐threatened, widespread, abundant, and eurytopic freshwater crab, Parathelphusa maculata, and found surprisingly high congruence between their population genomic histories. Based on 2,617 and 2,470 genome‐wide SNPs mined via the double‐digest restriction‐associated DNA sequencing method for ~90 individuals of J. singaporensis and P. maculata, respectively, the populations are strongly isolated (FST = 0.146–0.371), have low genetic diversity for both species (also for COI), and show signatures of recent genetic bottlenecks. The most genetically isolated populations for both species are separated from other populations by one of the oldest roads in Singapore. These results suggest that anthropogenic developments may have impacted stream‐dependent species in a uniform manner, regardless of ubiquity, habitat preference, or dispersal modes of the species. While signs of inbreeding were not detected for the critically endangered species, the genetic distinctiveness and low diversity of the populations call for genetic rescue and connecting corridors between the remaining fragments of the natural habitat.

Phylogeographic structure and continued surveys of a Vulnerable South African freshwater crab (Potamonautidae, Potamonautes lividus): Implications for the IUCN Red Listing of the Afrotropical fauna

“…data). Our uncorrected ‘p’ sequence divergence value is within the range that has been reported intraspecifically for freshwater crabs, whereas the haplotypic and nucleotide diversity reported for P. lividus was moderately higher compared with that reported for COI in freshwater crabs (Tay et al, 2018).…”

“…Although mitochondrial DNA (mtDNA) markers, such as cytochrome c oxidase subunit I (COI) and 16S rRNA, have been used extensively in phylogeographical studies of invertebrates, including freshwater crabs (Daniels, 2011;Daniels et al, 2006;Daniels & Klaus, 2018;Daniels et al, 2002;Gouws et al, 2015;Phiri & Daniels, 2016;Tay et al, 2018), microsatellites, such as nuclear DNA (nDNA) markers, have not been used to examine the population structure of an Afrotropical freshwater crab species. Several studies have demonstrated that phylogeographical studies can often be complemented by ecological niche modelling to understand the relationships between lineage distribution and niche divergence (Hofmeyr et al, 2020).…”