Genetic diversity in the Gammarus pecos species complex: Implications for conservation and regional biogeography in the Chihuahuan Desert

Abstract

We used allozyme electrophoresis to quantify genetic variation in nine populations of the Gammarus pecos species complex endemic to spring systems of the northern Chihuahuan Desert. There was significant within-population and high among-population genetic variation. Two populations exhibited heterozygote deficiencies and high proportions of polymorphic loci, which suggests the presence of cryptic species. Genetic distances among populations were negatively correlated with previously published morphological similarities, which suggests congruence between allozyme and morphological phenotypes. Cluster analysis of genetic distances showed four major groups of populations within the G. pecos complex. Genetic identities and fixed allelic differences support the presence of at least four distinct species: Gammarus desperatus, G. pecos, Gammarus hyalleloides, and one or more undescribed species. Relatively large genetic distances between populations suggest long periods of isolation and allopatric speciation. Patterns of among-population genetic variation were similar between amphipods and several groups of endemic fishes and snails, which suggests a coherence to biogeographic patterns within this region. Thus, the understanding of the genetic structure and taxonomic status of the G. pecos species complex provides insight into the biogeography of other aquatic organisms in the northern Chihuahuan Desert. Given the alarming rate at which desert spring systems are being altered and the unique biotic assemblages present, protection of these habitats is imperative.In desert regions, springs have long been considered to be unlimited sources of water for a variety of human activities. The habitat destruction resulting from such activities is an especially severe problem when it affects regions of high endemism, where most endangered species are found (Dob-

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

“…These findings indicate limited dispersal and structuring of populations within and between catchments. This is consistent with previous findings of limited dispersal and small home ranges for Euastacus bispinosus and other freshwater crayfish species (Honan & Mitchell 1995a, Chaplin & Ayre 1997, Gervasio et al 2004, Verovnik et al 2004. Two-dimensional scatter plot showing the relationships among Euastacus bispinosus sample locales based on a factorial correspondence analysis of 11 microsatellite loci for 17 sites.…”

Confrontation of cryptic diversity and mate discrimination within Gammarus pulex and Gammarus fossarum species complexes

“…2) splits the highest divergence values (>20%) into two groups of haplotypes, Gp and Gf groups, identified as the well-recognised evolutionary units G. pulex and G. fossarum, respectively (Meyran, Monnerot & Taberlet, 1997;Hou et al, 2011). Such cryptic diversity has been identified in other gammarid species (Gervasio et al, 2004;Costa et al, 2009) and seems to be widespread in amphipods (Cristescu et al, 2004;Hogg et al, 2006;Cooper et al, 2007;Bradford et al, 2010;Baird, Miller & Stark, 2011;Havermans et al, 2011). Within both Gp and Gf groups, substantial divergence between haplotypes was also identified, ranging up to c. 18% in G. fossarum and up to c. 11% in G. pulex, confirming the existence of numerous morphologically cryptic MOTUs within these groups (Meyran et al, 1997;M€ uller, 1998, 2000Hou et al, 2011;Westram et al, 2011a;Weiss et al, 2014).…”

Genetic and community similarities are correlated in endemic‐rich springs of the northern Chihuahuan Desert

“…(2004) described the sampling sites, presented amphipod allozyme data (with a total of 50 alleles based on 11 polymorphic loci), and calculated Nei's (1978) unbiased genetic distances among pairs of populations. Although the amphipods are likely to consist of more than one species, allozyme (Gervasio et al ., 2004) and mtDNA sequence evidence (R. A. Seidel et al ., unpublished data) suggest that the Gammarus pecos species complex is a monophyletic group. We obtained Pecos gambusia ( Gambusia nobilis ) allozyme data (with a total of 19 alleles based on six polymorphic loci) and pairwise genetic distances from Echelle et al .…”

“…A single spring system is often the sole habitat for a variety of species, e.g. hydrobiid snails (Hershler et al ., 1999), pupfishes (Echelle & Echelle, 1992) and gammarid amphipods (Gervasio et al ., 2004). Human activities such as crop irrigation, resource extraction and recreation are, however, commonplace and compete with the biota for limited water resources (Shepard, 1993).…”

“…Genetic distances between pairs of populations of amphipods within the Gammarus pecos species complex (Cole) were strongly correlated with the corresponding Pecos gambusia ( Gambusia pecosensis , synonym G. nobilis Baird & Girard) populations from desert springs along the Pecos River in the northern Chihuahuan Desert (Gervasio et al ., 2004). Genetic distances among pupfish populations ( Cyprinodon spp.…”