Michael S. Roy

PHYLOGEOGRAPHIC ANALYSIS OF THE BROODING BRITTLE STAR AMPHIPHOLIS SQUAMATA (ECHINODERMATA) ALONG THE COAST OF NEW ZEALAND REVEALS HIGH CRYPTIC GENETIC VARIATION AND CRYPTIC DISPERSAL POTENTIAL

Abstract.— Direct development in benthic marine invertebrates is usually associated with narrow geographical range, low rates of colonization, and low levels of gene flow. Paradoxically, the small brittle star Amphipholis squamata broods its larvae to a crawl‐away juvenile stage, yet has a cosmopolitan distribution. Using sequence and restriction‐fragment‐length‐polymorphisms (RFLP) analyses of nuclear and mitochondrial DNA from 16 coastal populations throughout New Zealand, we tested whether the species is indeed a poor disperser, as may be expected from its brooding habit. We predicted that local and regional populations would be genetically structured according to isolation by distance. We also suspected that this ubiquitous “species” is composed of a variety of cryptic taxa in different geographic areas, as has been discovered in an increasing number of marine invertebrates. We found evidence of four genetically divergent and reproductively isolated lineages that can exist in syntopy. Lineages vary in abundance, haplotype diversity, and geographic distribution. The partitioning of genetic variation within the most common lineage, as well as the geographic distribution of the four lineages, suggest a north/south split. This pattern is consistent with known New Zealand marine biogeographic zones and appears to be linked to the regime of oceanic circulation, which is characterized by subtropical, southward‐moving water masses in the north, and sub‐Antarctic, northward‐moving water in the south. We conclude that the dispersal ability of A. squamata is regionally restricted but with sporadic long‐distance dispersal, which serves to increase local genetic variation. Our results support the idea that dispersal occurs through passive transport by drifting or rafting on macroalgae, which A. squamata commonly inhabits, and emphasize that poor dispersal ability is not necessarily a corollary of direct development.

Out of Africa: The Slow Train to Australasia

We used mitochondrial DNA (mtDNA) sequences to test biogeographic hypotheses for Patiriella exigua (Asterinidae), one of the worlds most widespread coastal sea stars. This small intertidal species has an entirely benthic life history and yet occurs in southern temperate waters of the Atlantic, Indian, and Pacific oceans. Despite its abundance around southern Africa, southeastern Australia, and several oceanic islands, P. exigua is absent from the shores of Western Australia, New Zealand, and South America. Phylogenetic analysis of mtDNA sequences (cytochrome oxidase I, control region) indicates that South Africa houses an assemblage of P. exigua that is not monophyletic (P = 0.04), whereas Australian and Lord Howe Island specimens form an interior monophyletic group. The placement of the root in Africa and small genetic divergences between eastern African and Australian haplotypes strongly suggest Pleistocene dispersal eastward across the Indian Ocean. Dispersal was probably achieved by rafting on wood or macroalgae, which was facilitated by the West Wind Drift. Genetic data also support Pleistocene colonization of oceanic islands (Lord Howe Island, Amsterdam Island, St. Helena). Although many biogeographers have speculated about the role of long-distance rafting, this study is one of the first to provide convincing evidence. The marked phylogeographic structure evident across small geographic scales in Australia and South Africa indicates that gene flow among populations may be generally insufficient to prevent the local evolution of monophyly. We suggest that P. exigua may rely on passive mechanisms of dispersal.

Phylogeography of a high-dispersal New Zealand sea-star: does upwelling block gene-flow?

New Zealands (NZ) geographical isolation, extensive coastline and well‐characterized oceanography offer a valuable system for marine biogeographical research. Here we use mtDNA control region sequences in the abundant endemic sea‐star Patiriella regularis to test the following literature‐based predictions: that coastal upwelling disrupts north–south gene flow and promotes population differentiation (hypothesis 1); and that an invasive Tasmanian population of the species was introduced anthropogenically from southern New Zealand (hypothesis 2). We sequenced 114 samples from 22 geographical locations, including nine sites from North Island, nine from South Island, one from Stewart Island and three from Tasmania. Our analysis of these sequences revealed an abundance of shallow phylogenetic lineages within P. regularis (68 haplotypes, mean divergence 0.9%). We detected significant genetic heterogeneity between pooled samples from northern vs. southern New Zealand (FST = 0.072; P = 0.0002), consistent with the hypothesis that upwelling disrupts gene flow between these regions (hypothesis 1). However, we are currently unable to rule out the alternative hypothesis that Cook Strait represents a barrier to dispersal (North Island vs. South Island; FST = 0.031; P = 0.0467). The detection of significant spatial structure in NZ samples is consistent with restricted gene flow, and the strong structure evident in northern NZ may be facilitated by distinct ocean current systems. Four shared haplotypes and nonsignificant differentiation (FST = 0.025; P = 0.2525) between southern New Zealand and Tasmanian samples is consistent with an anthropogenic origin for the latter population (hypothesis 2).

Effects of hydrographic barriers on population genetic structure of the sea star Coscinasterias muricata (Echinodermata, Asteroidea) in the New Zealand fiords

New Zealands 14 deep‐water fiords possess persistent salinity stratification and mean estuarine circulation that may serve to isolate populations of marine organisms that have a dispersal larval phase. In order to investigate this idea, we analysed the population structure of the sea star Coscinasterias muricata using a mitochondrial DNA marker. Genetic differentiation among populations of C. muricata was analysed using 366 base pairs of mtDNA D‐loop. We compared populations from the fiords with several others sampled from around New Zealand. At a macro‐geographical scale (> 1000 km), restricted gene flow between the North and South Islands was observed. At a meso‐geographical scale (10–200 km), significant population structure was found among fiords and between fiords and open coast. The pattern of population genetic structure among the fiords suggests a secondary contact between a northern population and a southern one, separated by a contact or mixing zone. These populations may have diverged by the effects of random genetic drift and population isolation as a consequence of the influence of estuarine circulation on dispersal. In northern Fiordland, genetic structure approximated an isolation by distance model. However, the pattern in genetic differences suggests that distance alone cannot explain the most divergent populations and that fiord hydrography may increase the effect of genetic drift within populations in the fiords. Finally, our study indicates that populations within the fiords underwent recent rapid expansion, followed most probably by genetic drift due to a lack of gene flow among the fiords.

Confirmation of low genetic diversity and multiple breeding females in a social group of Eurasian badgers from microsatellite and field data.

The Eurasian badger (Meles meles) is a facultatively social carnivore that shows only rudimentary co‐operative behaviour and a poorly defined social hierarchy. Behavioural evidence and limited genetic data have suggested that more than one female may breed in a social group. We combine pregnancy detection by ultrasound and microsatellite locus scores from a well‐studied badger population from Wytham Woods, Oxfordshire, UK, to demonstrate that multiple females reproduce within a social group. We found that at least three of seven potential mothers reproduced in a group that contained 11 reproductive age females and nine offspring. Twelve primers showed variability across the species range and only five of these were variable in Wytham. The microsatellites showed a reduced repeat number, a significantly higher number of nonperfect repeats, and moderate heterozygosity levels in Wytham. The high frequency of imperfect repeats and demographic phenomena might be responsible for the reduced levels of variability observed in the badger.