[Show abstract][Hide abstract] ABSTRACT: The Southern Ocean contains some of the most isolated islands on Earth, and fundamental questions remain regarding their colonization and the connectivity of their coastal biotas. Here, we conduct a genetic investigation into the Cellana strigilis (limpet) complex that was originally classified based on morphological characters into six subspecies, five of which are endemic to the New Zealand (NZ) subantarctic and Chatham islands (44-52°S). Previous genetic analyses of C. strigilis from six of the seven island groups revealed two lineages with little or no within-lineage variation. We analysed C. strigilis samples from all seven island groups using two mitochondrial (COI and 16S), one nuclear (ATPase β) and 58 loci from four randomly amplified polymorphic DNA markers (RAPDs) and confirmed the existence of two distinct lineages. The pronounced genetic structuring within each lineage and the presence of private haplotypes in individual islands are the result of little genetic connectivity and therefore very high self-recruitment. This study supports the significance of the subantarctic islands as refugia during the last glacial maximum and adds to the knowledge of contemporary population connectivity among coastal populations of remote islands in large oceans and the distance barrier to gene flow that exists in the sea (despite its continuous medium) for most taxa.
[Show abstract][Hide abstract] ABSTRACT: Eleven polymorphic microsatellite loci were isolated from the pulmonate limpet Siphonaria australis, an intertidal mollusc endemic to New Zealand. Genetic variation was characterized in 30 individuals from the Wellington
region. The number of alleles per locus ranged from 5 to 33, and observed heterozygosity ranged from 0.400 to 0.967. No significant
linkage disequilibrium was detected between locus pairs, and 10 loci showed no significant deviation from Hardy–Weinberg equilibrium.
These microsatellite markers are currently being used to study genetic connectivity among S. australis populations.
[Show abstract][Hide abstract] ABSTRACT: A set of 49 microsatellite loci isolated from the endemic New Zealand Greenshell™ mussel, Perna canaliculus, were evaluated for inclusion in a parentage assignment marker suite by assessing their ease of PCR amplification, allele scoring and conformity to Mendelian inheritance in hatchery-produced families. Ten polymorphic loci (mean He = 0.78 and polymorphic information content (PIC) = 0.72) were identified as being suitable for parentage assignment. These 10 microsatellite loci gave a combined non-exclusion probability of < 0.001 (probability that an unrelated parent pair will not be excluded from parentage of an arbitrary offspring), based on allele frequencies from 16 broodstock mussels. Simulations predicted an assignment success rate of 99.9% with all 10 loci and > 95% with the best 5 or more loci (mean PIC = 0.84). In actual parentage assignments, 124 offspring from 8 full-sib families were assigned to the correct parent pair with 4 or more loci. We found evidence for null alleles and extensive size homoplasy in many loci, highlighting the importance of thoroughly characterizing and evaluating microsatellite markers prior to parentage assignment and other applications.
[Show abstract][Hide abstract] ABSTRACT: A molecular phylogeny is presented for marine mussels of the genus Perna, based on nuclear (ITS1,ITS2) and mitochondrial (COI) DNA sequence data. The three generally recognised species (Perna viridis, Perna perna and Perna canaliculus) and one putative species (Perna picta) were each sampled from several locations within their known geographic distributions. A range of phylogenetic analyses was used to investigate the current taxonomic assignments, evolutionary relationships and the biogeographical history of the genus. The different analyses produced similar, well supported topologies and verified the monophyly of the genus with respect to five mytilid outgroup species. P. perna (Atlantic), P. viridis (Indo-West Pacific), and P. canaliculus (New Zealand) each formed distinct clades, confirming their specific status. Putative P. picta from North Africa clustered within the P. perna clade and is not regarded as a separate species. P. perna and P. canaliculus were the most closely related of the three species. Possible biogeographic explanations for the present species distributions are evaluated.
Molecular Phylogenetics and Evolution 09/2007; 44(2):685-98. · 4.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: the Kermadec Islands Marine reserve (KIMR), which is located at 30°S, is New Zealand's largest marine reserve at 748 000 ha, and its biota is composed of a mix of warm temperate, subtropical, and tropical species. A depth-stratified ecological survey was conducted of the abundance and percentage cover of macrobenthic species and of the water column at two sites (Meyer Island and west Chanter Island) 2 km apart. Significant differences in benthic community structure and in water column turbidity and chlorophyll concentrations were observed between the two sites despite their proximity and physical similarity. Compared with other "snapshot" surveys of benthic community structure at sites within the KIMr there was a high degree of similarity among the species observed, but often a low degree of similarity in species abundance or percentage cover as a function of depth. we suggest that despite its isolation and the degree of difficulty of working at this location, a full-scale ecological survey of the coastal marine biota of the KIMr is warranted to better understand new Zealand's subtropical marine biota and its affinities with other marine biotas of the South Pacific.
New Zealand Journal of Marine and Freshwater Research - N Z J MAR FRESHWATER RES. 01/2006; 40(1).
[Show abstract][Hide abstract] ABSTRACT: Overdominance for enzyme specific activity at the phosphoglucomutase-2 (PGM-2) locus has been demonstrated for wild, adult Pacific oysters (Crassostrea gigas) that are formed from heterozygous combinations of the allele at highest frequency and any other allele at this locus. Overdominant genotypes have been shown to have higher catalytic capacities than other genotypes, and consequently it was proposed that this effect might account for genotype-dependent weight differences among Pacific oysters. From an aquaculture perspective, it would be relatively easy for a selective breeding programme to exploit a genotype-dependent effect on production traits (growth rate, wet body weight) if this phenomenon could be demonstrated among hatchery-reared oysters. However, a previous test of this failed to detect either an overdominant effect or a genotype-dependent effect among wild juvenile oysters (9 months of age), among adults of this same batch 12 months later, or among juveniles (5 months of age) from 8 full-sib hatchery-reared families. In the present paper, we extend this work by examining the relationship between PGM-2 genotype and production traits in adult market-size Pacific oysters from five full-sib families specifically selected because they contain putatively overdominant and other genotypic combinations. Within-families, there were significant weight differences among genotypes, but there was no evidence of a consistent PGM-2 genotype-dependent effect, overdominant or otherwise, on wet tissue weight, dry shell weight or total weight (=wet tissue weight plus dry shell weight). Among families, tests of pooled data showed no significant difference between putative overdominant and other genotypes for wet tissue weight, dry shell weight or total weight. We conclude that there is no evidence on which to base a Pacific oyster-breeding programme using PGM-2 as a marker for increased production.
[Show abstract][Hide abstract] ABSTRACT: The mussels Mytilus edulis L. and Mytilus galloprovincialis Lamark hybridise naturally in the wild along the Atlantic coast of Europe producing a patchwork of mixed pure species and hybrid populations. Individuals of both species were spawned in the laboratory and were hybridised in a series of reciprocal crosses. After 72 h, the proportion of eggs which developed into larvae (%yield) and the proportion of those larvae which had a normal veliger morphology (%normality) were estimated and compared between pure species and hybrid families. There were no significant differences in %yield or %normality between pure species and hybrids, but significant differences were evident between the offspring from different parents irrespective of whether they were hybrids or pure species. Therefore confirmation of hybrid heterosis in laboratory studies should not be based on a single, or a few reciprocal crosses. Hybrid and pure species veliger larvae were grown for approximately 4 weeks at 10, 14 or 20 °C. In all trials, pure M. galloprovincialis larvae grew significantly faster at 20 °C than either reciprocal hybrid or pure M. edulis larvae. Irrespective of temperature, in general, hybrid larvae grew slower than larvae of either pure species. Increased exposure to planktonic predation due to slow growth can be interpreted as selection against hybrids and this may play a role in the structure and distribution of mixed pure species and hybrid populations.
Journal of Experimental Marine Biology and Ecology 01/2004; 302(2):177-188. · 2.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Blue mussels of the genus Mytilus have an unusual mode of mitochondrial DNA inheritance termed doubly uniparental inheritance (DUI). Females are homoplasmic for the F mitotype which is inherited maternally, whereas males are heteroplasmic for this and the paternally inherited M mitotype. In areas where species distributions overlap a varying degree of hybridization occurs; yet genetic differences between allopatric populations are maintained. Observations from natural populations and previous laboratory experiments suggest that DUI may be disrupted by hybridization, giving rise to heteroplasmic females and homoplasmic males. We carried out controlled laboratory crosses between Mytilus edulis and M. galloprovincialis to produce pure species and hybrid larvae of known parentage. DNA markers were used to follow the fate of the F and M mitotypes through larval development. Disruption of the mechanism which determines whether the M mitotype is retained or eliminated occurred in an estimated 38% of M. edulis x M. galloprovincialis hybrid larvae, a level double that previously observed in adult mussels from a natural M. edulis x M. galloprovincialis hybrid population. Furthermore, reciprocal hybrid crosses exhibited contrasting types of DUI disruption. The results indicate that disruption of DUI in hybrid mussels may be associated with increased mortality and hence could be a factor in the maintenance of genetic integrity for each species.
[Show abstract][Hide abstract] ABSTRACT: The advent of polymerase chain reaction (PCR)-based DNA markers, which claim to identify species diagnostically in the Mytilus edulis complex (M. edulis, M. galloprovincialis and M. trossulus) presents a possible method for simple, rapid species identification of Mytilus larvae. This study examines the inheritance of the Me 15/16 nuclear-DNA locus, which has previously been shown to produce three alleles diagnostic for M. edulis, M. galloprovincialis and M. trossulus. The Me 15/16 genotype was determined for pure species and hybrid larvae from 13 laboratory crosses between these three species and for adult mussels from five natural populations from which the parents of the crosses were selected. Genotype frequencies in the parent populations were generally as expected for M. edulis and M. galloprovincialis, but M. trossulus populations from eastern Canada and the Baltic Sea gave unexpected results. The marker was readily detected in individual larvae sampled 72 h and 2 weeks after fertilization, but amplification from 3 h old larvae was less reliable. Each cross produced larvae of all the expected genotypes and the results demonstrate that each of the three alleles can be inherited from either sex. The marker appears to be inherited in a Mendelian manner and should be of potential use in the future study of larvae in the M. edulis complex.
Journal of Molluscan Studies 01/2003; 69:61-66. · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A pronounced north–south multitaxon genetic discontinuity occurs in central New Zealand (NZ). Polymorphic microsatellite markers have been used to test the location and structure of this discontinuity in the endemic greenshell mussel, Perna canaliculus. Nine neutral loci revealed limited evidence of genetic structure, but one outlier locus (Pcan1-27) which may be under selection provided evidence of the discontinuity in central NZ. Whilst the limited multilocus evidence of structure is assumed to result from high levels of gene flow among populations of this continuously distributed species, assignment tests indicated high to very high mean levels of self-recruitment within the 14 populations and the north and south regions. The nine neutral loci were unable to provide further clarification as to the geographic location of the discontinuity, whereas the Pcan1-27 locus was particularly informative. These results highlight a tension between limited evidence of genetic structure and presumptive high gene flow among populations versus high levels of self-recruitment and pronounced structure depending on microsatellite loci and analyses in question. Evidence from all 10 loci indicates that the genetic discontinuity is maintained by high levels of self-recruitment, and evidence from Pcan1-27 suggests that selection may also be important in explaining the existence of the discontinuity.