Phylogeographical disjunction in abundant high‐dispersal littoral gastropods

Abstract

Phylogeographical disjunctions in high-dispersal marine taxa are variously ascribed to palaeogeographical conditions or contemporary ecological factors. Associated biogeographical studies, however, seldom incorporate the sampling design required to confidently discriminate among such competing hypotheses. In the current study, over 7800 gastropod specimens were examined for operculum colour, and 129 specimens genetically, to test ecological and historical biogeographical hypotheses relating to biogeographical disjunction in the Southern Hemisphere, and to southern Australia in particular. Mitochondrial DNA sequence analysis of the high-dispersal intertidal gastropod Nerita atramentosa in southern Australia (88 specimens; 18 localities) revealed an east-west phylogeographical split involving two highly divergent clades (26.0 +/- 1.9%) exhibiting minimal geographical overlap in the southeast. The eastern clade of Nerita atramentosa is also widespread in northern New Zealand (43 specimens, 10 localities), but no significant genetic differentiation is explained by the Tasman Sea, a 2000-km-wide oceanic barrier. Spatial genetic structure was not detected within either clade, consistent with the species' dispersive planktotrophic phase lasting for 5-6 months. Digital analysis of operculum colouration revealed substantial differences between eastern (tan) and western (black) specimens. Genetic analysis and visual inspection of 88 Australian specimens revealed a completely nonrandom association between mtDNA data and operculum colouration. Independent examination of a further 7822 specimens from 14 sites in southern Australia revealed both colour morphs at all localities, but reinforced the phylogeographical data by indicating a marked turnover in colour morph abundance associated with a palaeogeographical barrier: Wilsons Promontory. This sharp biogeographical disjunction is in marked contrast to the species' high dispersal abilities. The genetic similarity of Nerita morio (Easter Island) and the eastern Australian + New Zealand lineage (1.1 +/- 0.3%) provides further evidence of long-distance dispersal in southern Nerita. Phylogenetic relationships of nine species (four genera) of Neritidae, an almost exclusively tropical gastropod family, are consistent with the hypothesis that southern temperate black nerites comprise a monophyletic radiation.

Gall-forming protistan parasites infect southern bull kelp across the Southern Ocean, with prevalence increasing to the south

“…Although our sample sizes and sampling range were too limited in this study to allow detailed analysis of such fine-scale structure, a biogeographic break across Wilson's Promontory in southern Victoria would be consistent with patterns observed in a wide range of other taxa (O'Hara & Poore 2000, Waters 2008, including the host genus Durvillaea (Fraser et al 2009, Weber et al 2017. While this biogeographic pattern is broadly thought to be a historical outcome of vicariant processes related to the Bassian Isthmus land bridge during the Last Glacial Maximum (Fraser et al 2009), it is thought to have been maintained through modern oceanographic systems and through density-dependent ecological processes (Waters et al 2005.…”

Impacts of marine biogeographic boundaries on phylogeographic patterns of three South African estuarine crustaceans

“…Such patterns can usually be explained by present-day environmental conditions, but there are some notable exceptions in which past phylogeographic patterns are likely to have been retained, e.g. in west Pacific giant clams Tridacna maxima (Benzie & Williams 1997) and in the southern Australian gastropod Nerita atramentosa (Waters et al 2005). For example, the distributions of the eastern and western lineages of N. atramentosa are not defined by water temperature (both lineages occur in both warm and cool temperate waters), but by a geological feature that does not represent a barrier to gene-flow during the present interglacial phase.…”

Measures of taxonomic distinctness do not reliably assess anthropogenic impacts on intertidal mollusc communities

“…These sites covered ~570 km along a predominantly east -west coastline in southeastern Australia. Sites in eastern Victoria were not included, as this is a distinct region of faunal change (Knox 1963, King 1972, Waters et al 2005, Hidas et al 2007). Fifty-one reference sites were chosen haphazardly based on their geographical dispersion along the open coast.…”