South American Origins of Microctonus hyperodae Loan (Hymenoptera: Braconidae) Established in New Zealand as Defined by Morphometric Analysis

Eight South American geographic populations of the thelytokous parasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae) were released in New Zealand in 1991 to assist in the suppression of the pasture pest Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). With one exception, parasitoids from each South American geographic population were released in equal numbers at each New Zealand release site. It was postulated that the South American geographic population(s) best suited to the conditions encountered at each New Zealand release locality would eventually become prevalent there. A morphometric analysis of adult parasitoids of known South American origins, reported previously, allowed M. hyperodae derived from west of the Andes (i.e. two collection sites in Chile) to be distinguished from parasitoids derived from east of the Andes (i.e. three collection sites in Argentina and one each in Brazil and Uruguay). Parasitoids derived from a fourth site in Argentina (S. C. de Bariloche) could not be clearly discriminated from either the 'east of the Andes' or 'west of the Andes' categories. A morphometric analysis of M. hyperodae adults collected from five of the New Zealand release sites from 1992-1994 is presented in this contribution. The analysis indicated that parasitoids derived from east of the Andes were significantly more prevalent than expected. The possible reasons for the initial success in New Zealand of one or more east of the Andes populations include the greater fecundity of M. hyperodae collected in Uruguay and the likelihood that M. hyperodae from east of the Andes co-evolved more recently with the stock from which New Zealand's L. bonariensis was founded.     

A Morphometric Method to Assist in Defining the South American Origins of Microctonus hyperodae Loan (Hymenoptera: Braconidae) Established in New Zealand

In 1991, Microctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae), collected from eight diverse South American locations, was released in New Zealand as a biological control agent of the pasture pest Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). Equal numbers of each South American geographical population of this thelytokous endoparasitoid of adult hosts were released in New Zealand. A morphometric method described in this paper provided a means of classifying M. hyperodae adults as originating from either east or west of the Andes. Analysis revealed that, on average, specimens collected in Chile had significantly more antennal segments, narrower stigmas and longer radial cells than those collected in Brazil, Uruguay and Argentina. Significant differences between populations originating from each side of the Andes were also recorded in the dimensions of metasomal tergum one and basitarsus three. The morphometric method should, therefore, assist in defining the origins of M. hyperodae established in New Zealand. This information will be used in attempts to ascertain the importance of climate matching and host-parasitoid co-evolution to the outcome of the L. bonariensis biological control programme.     

Early impact of endoparasitoid Microctonus hyperodae (Hymenoptera: Braconidae) after its establishment in Listronotus bonariensis (Coleoptera: Curculionidae) populations of northern New Zealand pastures

The South American curculionid Listronotus bonariensis (Kuschel) is an important pest of pastures in New Zealand. Population census data were gathered for L. bonariensis in northern New Zealand pastures during 1980-1983 in the absence of parasitism and again in 1991-1996 after the introduction and establishment of the braconid parasitoid Microctonus hyperodae Loan as a biological control agent. M. hyperodae achieved high rates of parasitism, with 75-90% of overwintering L. bonariensis parasitized within 3 yr of the parasitoid establishing at a site. Multistratum analysis of variance (ANOVA), with allowance for variation in host plant resource (numbers of Neotyphodium-free grass tillers), indicated reduction in the abundance of L. bonariensis life stages in the early part of life cycle. Although providing evidence for suppression of L. bonariensis, these analyses indicated the regulatory role of M. hyperodae was weak because L. bonariensis populations continued to exhibit marked intergenerational variability in abundance. Analyses of life tables indicated larval + pupal survival contributed most to intergenerational changes in abundance, irrespective of presence or absence of M. hyperodae. However, the density dependence of the stage survivals was modified in the presence of the parasitoid, with loss of density-dependent mortality in overwintering adults and increased density dependence in population natality. Regression analyses indicated dual contribution of parasitism and host plant resource to regulation of population natality and population trend in L. bonariensis. We conclude that M. hyperodae is a useful adjunct to host plant resistance in reducing the economic status of L. bonariensis populations in northern New Zealand pastures.     

Geographic Variation in Egg Load of Microctonus hyperodae Loan (Hymenoptera: Braconidae) and its Implications for Biological Control Success

Eight South American geographic populations of the parthenogenic, proovigenic, koinobiont parasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae: Euphorinae) were introduced to New Zealand to assist management of the pasture pest Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). Geographic variation in fecundity has been suggested as a reason for the populations' differential successes in establishing in New Zealand. This study investigated whether geographic variation in fecundity was due to corresponding variation in pre-oviposition egg load (other possible sources of fecundity variation include searching efficiency, egg survival and female longevity). Variation in egg load accounted for that in fecundity, but also showed that the variation in fecundity was not as great as it had first appeared. Geographic variation in egg load did not explain the pattern of population establishment observed in New Zealand. Egg load was proportional to parasitoid size and this relationship was stronger in populations originating from west, rather than east, of the Andes. A new method for making parasitoid eggs visible is described.     

Microsatellites and 16S sequences corroborate phenotypic evidence of trans-Andean variation in the parasitoid Microctonus hyperodae (Hymenoptera: Braconidae)

Eight South American geographical populations of the parasitoid Microctonus hyperodae Loan were collected in South America (Argentina, Brazil, Chile and Uruguay) and released in New Zealand for biological control of the weevil Listronotus bonariensis (Kuschel), a pest of pasture grasses and cereals. DNA sequencing (16S, COI, 28S, ITS1, beta-tubulin), RAPD, AFLP, microsatellite, SSCP and RFLP analyses were used to seek markers for discriminating between the South American populations. All of the South American populations were more homogeneous than expected. However, variation in microsatellites and 16S gene sequences corroborated morphological, allozyme and other phenotypic evidence of trans-Andes variation between the populations. The Chilean populations were the most genetically variable, while the variation present on the eastern side of the Andes mountains was a subset of that observed in Chile.     

Genetic variation and differentiation at microsatellite loci in Drosophila simulans. Evidence for founder effects in new world populations.

Drosophila simulans isofemale lines from Africa, South America, and two locations in North America were surveyed for variation at 16 microsatellite loci on the X, second, and third chromosomes, and 18 microsatellites, which are unmapped. D. simulans is thought to have colonized New World habitats only relatively recently (within the last few hundred years). Consistent with a founder effect occurring as colonizers moved into these New World habitats, we find less microsatellite variability in North and South American D. simulans populations than for an African population. Population subdivision as measured at microsatellites is moderate when averaged across all loci (FST = 0.136), but contrasts sharply with previous studies of allozyme variation, which have showed significantly less differentiation in D. simulans than in D. melanogaster. There are substantially fewer private alleles observed in New World populations of D. simulans than seen in a similar survey of D. melanogaster. In addition to possible differences in population size during their evolutionary histories, varying colonization histories or other demographic events may be necessary to explain discrepancies in the patterns of variation observed at various genetic markers between these closely related species.     

Argentine stem weevil ( Listronotus bonariensis, Coleoptera: Curculionidae) population dynamics in Canterbury, New Zealand dryland pasture

The Argentine stem weevil (Listronotus bonariensis) was an economically important pest in New Zealand pastures until the release of the parasitoid Microctonus hyperodae. This contribution uses historical data to investigate the regulation of the pest populations prior to, and somewhat during, the establishment of this parasitoid in dryland Canterbury, New Zealand. Thus, a significant goal of this study is to provide an L. bonariensis population dynamics baseline for any future work that aims to analyse the full effects of M. hyperodae on the weevil, now that equilibrium with the weevil host has been reached.The population dynamics of L. bonariensis, based on a life-table approach, were investigated using data collected regularly for eight years from populations in Canterbury, New Zealand. The key factor affecting end-of-season L. bonariensis density was found to be variation in second generation fourth instar prepupal and pupal mortality. This may have been caused by arrested development and ongoing mortality resulting from the onset of cooler autumnal conditions.A compensatory response was found in recruitment to the second summer weevil generation, whereby the realised fecundity of the emergent first summer generation of weevils was found to be negatively related to the density of adult weevils per ryegrass tiller. This is the first time that this has been found via long-term population analysis of L. bonariensis, although indications of this have been found elsewhere in caging, pot and small plot experiments.In this study, the effect of the parasitoid biocontrol agent Microctonus hyperodae on L. bonariensis population dynamics was unclear, as the analysis covered a period when the parasitoid Microctonus hyperodae was introduced and still establishing. It does, however, raise important questions for future analysis in terms of the interaction between parasitism and unrealised fecundity.The results in this contribution also highlighted regional differences. Overwintering mortality of adult weevils in Canterbury was constant between years, whilst earlier studies in the North Island Waikato region indicated this mortality was density dependent. In addition, the availability of tillers in endophyte-free ryegrass pastures in Canterbury had no influence on egg and early-instar larval survival, which contrasts with the finding from endophytic Waikato pastures.     

From East Gondwana to Central America: historical biogeography of the Alstroemeriaceae

Aim The Alstroemeriaceae is among 28 angiosperm families shared between South America, New Zealand and/or Australia; here, we examine the biogeography of Alstroemeriaceae to better understand the climatic and geological settings for its diversification in the Neotropics. We also compare Alstroemeriaceae with the four other Southern Hemisphere families that expanded from Patagonia to the equator, to infer what factors may have permitted such expansions across biomes. Location South America, Central America, Australia and New Zealand. Methods Three chloroplast genes, one mitochondrial gene and one nuclear DNA region were sequenced for 153 accessions representing 125 of the 200 species of Alstroemeriaceae from throughout the distribution range; 25 outgroup taxa were included to securely infer evolutionary directions and be able to use both ingroup and outgroup fossil constraints. A relaxed‐clock model relied on up to three fossil calibrations, and ancestral ranges were inferred using statistical dispersal–vicariance analysis (S‐DIVA). Southern Hemisphere disjunctions in the flowering plants were reviewed for key biological traits, divergence times, migration directions and habitats occupied. Results The obtained chronogram and ancestral area reconstruction imply that the most recent common ancestor of Colchicaceae and Alstroemeriaceae lived in the Late Cretaceous in southern South America/Australasia, the ancestral region of Alstroemeriaceae may have been South America/Antarctica, and a single New Zealand species is due to recent dispersal from South America. Chilean Alstroemeria diversified with the uplift of the Patagonian Andes c. 18 Ma, and a hummingbird‐pollinated clade (Bomarea) reached the northern Andes at 11–13 Ma. The South American Arid Diagonal (SAAD), a belt of arid vegetation caused by the onset of the Andean rain shadow 14–15 Ma, isolated a Brazilian clade of Alstroemeria from a basal Chilean/Argentinean grade. Main conclusions Only Alstroemeriaceae, Calceolariaceae, Cunoniaceae, Escalloniaceae and Proteaceae have expanded and diversified from Patagonia far into tropical latitudes. All migrated northwards along the Andes, but also reached south‐eastern Brazil, in most cases after the origin of the SAAD. Our results from Alstroemeria now suggest that the SAAD may have been a major ecological barrier in southern South America.     

The biogeography of the austral, subalpine genus Ourisia (Plantaginaceae) based on molecular phylogenetic evidence: South American origin and dispersal to New Zealand and Tasmania

Molecular phylogenetic analyses of 26 of the 28 species of Ourisia , including eight of ten subspecies and two purported natural hybrids, are presented and used to examine the biogeography of the genus, which is distributed in subalpine to alpine habitats of South America, New Zealand and Tasmania. Gondwanan vicariance, often cited as the cause of this classic austral biogeographical pattern, was rejected by parametric bootstrapping of our combined dataset. Alternatively, various lines of evidence are presented in favour of a South American origin of Ourisia and subsequent dispersal to Australasia. Specifically, the genus likely arose in the Andes of central Chile and spread to southern Chile and Argentina, to the north-central Andes, and finally to Tasmania and New Zealand. The ancestor of the New Zealand species probably first arrived on the South Island, where the New Zealand species of Ourisia are most diverse, and migrated to the North and Stewart Islands. Because the Tasmanian and New Zealand species are sister to one another, the direction of dispersal between these two areas is equivocal. These results agree with other molecular phylogenetic studies that show that past dispersal between southern hemisphere continents has played an important role in the evolutionary history of many high-elevation austral plants. Our data also show that within South America, many of the geographical barriers (with the exception of the Atacama Desert) that have played a role in the evolution of other plant groups have not affected Ourisia species. Within New Zealand, the phylogeny and biogeography of species of Ourisia coincide with the geological history of the country and patterns of other alpine plants. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 479–513.     

Genetic structure of an introduced paper wasp,Polistes chinensis antennalis (Hymenoptera,Vespidae) in New Zealand

Several eusocial wasps are prominent invaders to remote islands. The paper wasp Polistes chinensis antennalis is native to East Asia, was introduced to New Zealand in 1979 and has expanded its distribution there. This provides an excellent opportunity to examine the impacts of an initial bottleneck and subsequent expansion on genetic structure. We analysed and compared the genetic population structures of the native (Japan and South Korea) and invasive New Zealand populations. Although 94% of individuals had shared haplotypes detected across both populations, the remaining 6% had private haplotypes identified in only one of the three countries. The genetic variation at microsatellite loci was lower in New Zealand than in native countries, and the genetic structure in New Zealand was clearly distinct from that in its native range. Higher frequencies of diploid‐male‐ and triploid‐female‐producing colonies were detected in New Zealand than in the native countries, showing the reduction in genetic variation via a genetic bottleneck. At least two independent introductions were suggested, and the putative source regions for New Zealand were assigned as Kanto (central island) and Kyushu (south island) in Japan. Serial founder events following the initial introduction were also indicated. The estimated dispersal distance between mother and daughter in New Zealand was twice that in Japan. Thus, the introduction history of P. chinensis antennalis in New Zealand is probably the result of at least two independent introductions, passing through a bottleneck during introduction, followed by population expansion from the point of introduction.     

High microsatellite diversity and differential structuring among populations of the introduced common brushtail possum, Trichosurus vulpecula, in New Zealand

An understanding of genetic variation and structure of pest populations has the potential to improve the efficiency of measures to control them. Genetic analysis was undertaken at five microsatellite loci in four native Australian and 14 introduced New Zealand populations of the common brushtail possum Trichosurus vulpecula in order to document these parameters. Genetic variation in New Zealand populations, and phylogenetic relationships among Australian and New Zealand populations, were largely predicted by the recorded introduction history. Populations on the two main islands of New Zealand had only slightly lower genetic diversity than did Australian populations, except that allelic richness on the South Is. was significantly lower. Diversity was higher in North Is. than in South Is. populations (although not significantly so) and mainland New Zealand populations as a group were significantly more diverse than offshore islands that represented secondary population size bottlenecks. In phylogenetic analyses South Is. and offshore island populations grouped with Tasmania, while North Is. populations grouped either with mainland Australia or were intermediate between the two Australian sources. This scheme was supported by admixture coefficients showing that North and South Is./offshore island populations were largely mainland Australian and Tasmanian in origin, respectively. Population structure differed markedly between the North and South Islands: populations were typically more genetically differentiated on the former than the latter, which also showed significant isolation-by-distance. Substantial linkage disequilibrium in most sampled New Zealand but no Australian population between microsatellite loci Tv16 and Tv27 suggests they may be physically linked.     

Neutral and functionally important genes shed light on phylogeography and the history of high‐altitude colonization in a widespread New World duck

Phylogeographic studies often infer historical demographic processes underlying species distributions based on patterns of neutral genetic variation, but spatial variation in functionally important genes can provide additional insights about biogeographic history allowing for inferences about the potential role of adaptation in geographic range evolution. Integrating data from neutral markers and genes involved in oxygen (O₂)‐transport physiology, we test historical hypotheses about colonization and gene flow across low‐ and high‐altitude regions in the Ruddy Duck (Oxyura jamaicensis), a widely distributed species in the New World. Using multilocus analyses that for the first time include populations from the Colombian Andes, we also examined the hypothesis that Ruddy Duck populations from northern South America are of hybrid origin. We found that neutral and functional genes appear to have moved into the Colombian Andes from both North America and southern South America, and that high‐altitude Colombian populations do not exhibit evidence of adaptation to hypoxia in hemoglobin genes. Therefore, the biogeographic history of Ruddy Ducks is likely more complex than previously inferred. Our new data raise questions about the hypothesis that adaptation via natural selection to high‐altitude conditions through amino acid replacements in the hemoglobin protein allowed Ruddy Ducks to disperse south along the high Andes into southern South America. The existence of shared genetic variation with populations from both North America and southern South America as well as private alleles suggests that the Colombian population of Ruddy Ducks may be of old hybrid origin. This study illustrates the breadth of inferences one can make by combining data from nuclear and functionally important loci in phylogeography, and underscores the importance of complete range‐wide sampling to study species history in complex landscapes.     

Genetic differentiation of starling (Sturnus vulgaris: Aves) populations in New Zealand and Great Britain

Several hundred starlings (Sturnus vulgaris) were introduced to New Zealand from Great Britain during1860–1880. Allozymic variation at 24 loci was analysed in winter populations sampled at six localities in each country. New Zealand samples had fewer alleles per locus but the same mean heterozygosity (3% per locus) and proportion of polymorphic loci as did British samples. Winter populations in Britain contain European migrants and were genetically homogeneous. Paradoxically, genetic distances among derived New Zealand populations, and between New Zealand and Great Britain were much greater, similar in magnitude to those observed among allopatric populations in other avian species. The geographical pattern of genetic variation in New Zealand suggests that reproductive isolation of populations and random drift have contributed to the development of population differentiation.     

Genetic tags in the New Zealand hoki Macruronus novaezelandiae1

Twelve enzymes and liver proteins were examined by starch and cellulose acetate electrophoresis in two samples of hoki Macruronus novaezelandiae from New Zealand. Two polymorphic enzymes, a-glycerophosphate dehydrogenase and sorbitol dehydrogenase, were found giving a mean heterozygosity of 0.027 over 12 enzyme loci or 0.016 over 15 protein loci. No differences in gene frequency were detected in nine regional samples collected from the New Zealand 200-mile exclusive economic zone. Together with existing biological information on spawning grounds these data suggest that hoki in the New Zealand fishery form one stock.     

Phylogeographic structure and cryptic speciation in the trans-Antarctic moss Pyrrhobryum mnioides

Abstract Many bryophyte species have distributions that span multiple continents. The hypotheses historically advanced to explain such distributions rely on either long-distance spore dispersal or slow rates of morphological evolution following ancient continental vicariance events. We use phylogenetic analyses of DNA sequence variation at three chloroplast loci ( atpB-rbcL spacer, rps4 gene, and trnL intron and 3'spacer) to examine these two hypotheses in the trans-Antarctic moss Pyrrhobryum mnioides. We find: (1) reciprocal monophyly of Australasian and South American populations, indicating a lack of intercontinental dispersal; (2) shared haplotypes between Australia and New Zealand, suggesting recent or ongoing migration across the Tasman Sea; and (3) reciprocal monophyly among Patagonian and neotropical populations, suggesting no recent migration along the Andes. These results corroborate experimental work suggesting that spore features may be critical determinants of species range. We use the mid-Miocene development of the Atacama Desert, 14 million years ago, to calibrate a molecular clock for the tree. The age of the trans-Antarctic disjunction is estimated to be 80 million years ago, consistent with Gondwanan vicariance, making it among the most ancient documented cases of cryptic speciation. These data are in accord with niche conservatism, but whether the morphological stasis is a product of stabilizing selection or phylogenetic constraint is unknown.     

Heritabilities and additive genetic variances of the activities of some enzymes in Drosophila melanogaster populations living in different habitats

Drosophila melanogaster samples were collected from a large population in two habitats: farmyards and distilleries. Samples were taken from two villages in each habitat. Three isofemale lines were established from all four samples and full-sib crosses were set in each isofemale line. Activities of four enzymes (ADH, alpha GPDH, IDH and 6PGDH) were measured in the offspring of each cross on starch gel after electrophoresis. Broad sense heritabilities and additive genetic variances were estimated in all four samples. Most of the activity variation was observed within the isofemale lines. The isofemale lines tended to be more different in the distilleries than in the farmyards. There was no significant difference in the average activities between the two habitats for any of the enzymes investigated. The additive genetic variance of the enzyme activities did not exhibit a consistent habitat pattern. In the farmyard habitat, we detected a higher activity variation in Tiszafüred than in the other village. Strong correlation was observed among the activities of the enzymes investigated. Correlation coefficients indicated higher level of correlation in the samples collected in Tiszafüred than in those originating from Tiszaszolos. The heritability values were rather high and they had a considerable variation both between the habitats and across the enzymes.     

Purging of inbreeding depression and fitness decline in bottlenecked populations of Drosophila melanogaster

Drastic reductions in population size, or bottlenecks, are thought to significantly erode genetic variability and reduce fitness. However, it has been suggested that a population can be purged of the genetic load responsible for reduced fitness when subjected to bottlenecks. To investigate this phenomenon, we put a number of Drosophila melanogaster isofemale lines known to differ in inbreeding depression through four ‘founder‐flush’ bottleneck cycles with flush sizes of 5 or 100 pairs and assayed for relative fitness (single‐pair productivity) after each cycle. Following the founder‐flush phase, the isofemale lines, with a large flush size and a history of inbreeding depression, recovered most of the fitness lost from early inbreeding, consistent with purging. The same isofemale lines, with a small flush size, did not regain fitness, consistent with the greater effect of genetic drift in these isofemale lines. On the other hand, the isofemale lines that did not show initial inbreeding depression declined in fitness after repeated bottlenecks, independent of the flush size. These results suggest that the nature of genetic variation in fitness may greatly influence the way in which populations respond to bottlenecks and that stochastic processes play an important role. Consequently, an attempt intentionally to purge a population of detrimental variation through inbreeding appears to be a risky strategy, particularly in the genetic management of endangered species.     

Deeply divergent lineages of the widespread New Zealand amphipod Paracalliope fluviatilis revealed using allozyme and mitochondrial DNA analyses

1. We evaluated the population genetic structure of the common New Zealand amphipod Paracalliope fluviatilis using eight allozyme loci, and the mitochondrial cytochrome oxidase c subunit I (COI) gene locus. Morphological analyses were also conducted to evaluate any phenotypic differences. Individuals belonging to P. fluviatilis were collected from a total of 14 freshwater fluvial habitats on the North and South Islands, New Zealand. 2. We found evidence for strong genetic differentiation among locations (Wright's F_ST > 0.25), and fixed differences (non‐shared alleles) at two of the eight allozyme loci indicating the possibility of previously unknown species. Analysis of a 545‐bp fragment of the COI locus was mostly congruent with the allozyme data and revealed the same deeply divergent lineages (sequence divergences up to 26%). 3. Clear genetic breaks were identified between North Island and South Island populations. North Island populations separated by <100 km also showed genetic differences between east and west draining watersheds (sequence divergence >12%). Accordingly, present‐day dispersal among hydrologically isolated habitats appears minimal for this taxon. 4. Although population differences were clearly shown by allozyme and mtDNA analyses, individuals were morphologically indistinguishable. This suggests that, as in North American and European taxa (e.g. Hyalella and Gammarus), morphological conservatism may be prevalent among New Zealand's freshwater amphipods. We conclude that molecular techniques, particularly the COI gene locus, may be powerful tools for resolving species that show no distinctive morphological differences.     

Large scale unicoloniality: the population and colony structure of the invasive Argentine ant (<Emphasis Type="Italic">Linepithema humile</Emphasis>) in New Zealand

The Argentine ant is native to South America and has spread widely across the globe. In this study, we use genetic analyses and behavioural assays to examine the colony structure of Argentine ants in New Zealand. Diet modification studies were also carried out in order to help identify what factors influence these behavioural assays. There was no aggression observed between any pairings tested across the North Island of New Zealand, though we found that diet manipulations in the laboratory could lead to low levels of aggression between previously amiable Argentine ant nests. The New Zealand population of Argentine ants was characterized by low levels of genetic variation in six microsatellite loci from their nuclear genome. Additionally, the population also lacked significant genetic structuring with no patterns of regional differentiation or isolation by distance. An analysis of molecular variation(AMOVA) found that themajority of genetic variation was present at a nest level (93% of total genetic variance), with little genetic differentiation observed within or between regions (3 – 4% of total genetic variance). No correlation between aggression and genetic relatedness was observed. This evidence suggests that Argentine ants in New Zealand effectively form a unicolonial population, which is likely the result of colonization from a single source population. As far as we know, this is the first country to have an entirely unicolonial population of Argentine ants. Received 21 February 2007; revised 20 May 2007; accepted 22 May 2007.     

Major Histocompatibility Complex (MHC) class II sequence polymorphism in long-finned pilot whale (Globicephala melas) from the North Atlantic

Determining how intra-specific genetic diversity is apportioned among natural populations is essential for detecting local adaptation and identifying populations with inherently low levels of extant diversity which may become a conservation concern. Sequence polymorphism at two adaptive loci (MHC DRA and DQB) was investigated in long-finned pilot whales (Globicephala melas) from four regions in the North Atlantic and compared with previous data from New Zealand (South Pacific). Three alleles were resolved at each locus, with trans-species allele sharing and higher levels of non-synonymous to synonymous substitution, especially in the DQB locus. Overall nucleotide diversities of 0.49?±?0.38% and 4.60?±?2.39% were identified for the DRA and DQB loci, respectively, which are relatively low for MHC loci in the North Atlantic, but comparable to levels previously described in New Zealand (South Pacific). There were significant differences in allele frequencies within the North Atlantic and between the North Atlantic and New Zealand. Patterns of diversity and divergence are consistent with the long-term effects of balancing selection operating on the MHC loci, potentially mediated through the effects of host-parasite coevolution. Differences in allele frequency may reflect variation in pathogen communities, coupled with the effects of differential drift and gene flow.