Ian D. Hogg

Long-term isolation and recent range expansion from glacial refugia revealed for the endemic springtail Gomphiocephalus hodgsoni from Victoria Land, Antarctica

We examined the phylogeography of the endemic Antarctic collembolan Gomphiocephalus hodgsoni using allozymes and mitochondrial DNA (mtDNA; COI) to determine if potentially limited dispersal and long‐term habitat fragmentation have promoted regional genetic differentiation. Allozyme analyses showed that differentiation among 21 populations within the Ross Dependency was high (FST = 0.55) with two main groups each representing a distinct geographical region: (1) Ross Island and Beaufort Island; and (2) all continental sites. Ross Island populations showed low levels of differentiation (FST = 0.05) and no correlation with geographical distance, suggesting their derivation from a single glacial refuge. By contrast, continental regions revealed moderate levels of differentiation (FST = 0.27) and a strong correlation with geographical distance, indicating a much older history with several refugia likely. Two sympatric allozyme genotypes were found at three continental sites from Taylor Valley and were congruent with two mtDNA haplotypes, implying nonrandom breeding groups. Although haplotype sharing between one Ross Island site (Cape Bird) and one continental site (Granite Harbour) was identified, the clades showed mostly fragmented allopatric distributions. The extensive Pleistocene glaciations, in conjunction with limited dispersal opportunities, appear to have promoted isolation and divergence among the fragmented habitats. Furthermore, the McMurdo Sound appears to be an effective isolating barrier to dispersal. However, we suggest that the unaided dispersal capacity of G. hodgsoni is unlikely to account for the limited mixing of haplotypes across the McMurdo Sound and recent human‐ or bird‐mediated dispersal is highly probable.

Phylogeography of New Zealand's coastal benthos

Abstract During the past 30 years, 42 molecular studies have been undertaken in New Zealand to examine the phylogeography of coastal benthic invertebrates and plants. Here, we identify generalities and/or patterns that have emerged from this research and consider the processes implicated in generating genetic structure within populations. Studies have used various molecular markers and examined taxonomic groups with a range of life histories and dispersal strategies. Genetic disjunctions have been identified at multiple locations, with the most frequently observed division occurring between northern and southern populations at the top of the South Island. Although upwelling has been implicated as a cause of this disjunction, oceanographic evidence is lacking and alternative hypotheses exist. A significant negative correlation between larval duration and genetic differentiation (r2 = 0.39, P < 0.001, n = 29) across all studies suggests that larval duration might be used as a proxy for dispersal potential. However, among taxa with short larval durations (<10 days) there was greater variability in genetic differentiation than among taxa with longer pelagic periods. This variability implies that when larval duration is short, other factors may determine dispersal and connectivity among populations. Although there has been little congruence between the phylogeographic data and recognised biogeographic regions, recent research has resolved population subdivision at finer spatial scales corresponding more closely with existing biogeographic classifications. The use of fast‐evolving and ecologically significant molecular markers in hypothesis‐driven research could further improve our ability to detect population subdivision and identify the processes structuring marine ecosystems.

Expanded distributional records of Collembola and Acari in southern Victoria Land, Antarctica

Summary We provide new distributional records for the Collembola and Acari from south Victoria Land in the Ross Dependency, Antarctica, including the first extensive survey of Taylor Valley. We also describe the design of a modified device for the rapid sampling of Antarctic terrestrial arthropods. Sampling was carried out during the austral summers from 1998 to 2001. In several instances we found Gomphiocephalus hodgsoni, Neocryptopygus nivicolus and Stereotydeus mollis at sites where they were not reported in comprehensive surveys made some 40 years ago, which may imply recent range expansion (eg: local dispersal). By contrast, at McMurdo Station and at the former North Base (Marble Point) the distribution of G. hodgsoni and S. molliswas restricted, relative to previous records. We conclude that these latter changes may be the direct result of human activities.

Friends and strangers: a test of the Charnov-Finerty hypothesis

SummaryWe tested the hypothesis that populations composed of unrelated animals should perform worse than those composed of related animals by setting up two moderatedly dense field populations in adjacent enclosures: one was composed of related females and one of unrelated females; both had unrelated males. The survival and reproductive success of a number of litters located by spooling were determined. Final population size, pregnancy success, number of young recruited per pregnancy, and survival were similar in both populations. Thus, differences in relatedness produced no differences in demography. We conclude that the Charnov-Finerty Hypothesis in unlikely to be an explanation for microtine population fluctuations.

The consequences of global warming for stream invertebrates: A field simulation

Abstract 1. 1. We manipulated the thermal regime of a stream and analyzed the population genetics of constituent species to examine the effects of global warming on stream invertebrates. 2. 2. Increased temperature resulted in significantly lower total densities of invertebrates and altered growth patterns for two target species. 3. 3. Hyalella azteca showed the greatest change in growth and also exhibited high levels of genetic differentiation among populations. Nemoura trispinosa showed only small shifts in growth and phenology and exhibited little genetic differentiation among populations. 4. 4. The poteintial impacts of global warming may depend critically on the dispersal abilities and genetic structure of lotic populations.

Phylogeographic structure suggests multiple glacial refugia in northern Victoria Land for the endemic Antarctic springtail Desoria klovstadi (Collembola, Isotomidae)

We carried out a phylogeographic study using mtDNA (COII) for the endemic springtail Desoria klovstadi (formerly Isotoma klovstadi) from northern Victoria Land, Antarctica. Low levels of sequence divergence (≤ 1.6%) across 26 unique haplotypes (from 69 individuals) were distributed according to geographic location. Cape Hallett and Daniell Peninsula contained the highest nucleotide (both > 0.004) and haplotype (both > 0.9) diversity with 10 (of 16) and 8 (of 12) unique haplotypes, respectively. All other populations (Football Saddle, Crater Cirque, Cape Jones) had lower diversity with 2–4 unique haplotypes. Across the 69 individuals from five populations there was only a single haplotype shared between two populations (Daniell Peninsula and Football Saddle). Furthermore, nested clade analyses revealed that some of the Daniell Peninsula haplotypes were more closely related to Football Saddle haplotypes than to any other population. Such discrete haplotype groupings suggest historical (rare) dispersal across the Pleistocene (1.8 mya−11 kya) and Holocene (11 kya–present), coupled with repeated extinction, range contraction and expansion events, and/or incomplete sampling across the species range. The nested clade analyses reveal that a common pattern of climatic and geological history over long‐term glacial habitat fragmentation has determined the geographic and haplotype distributions found for D. klovstadi.

Low genetic variability in small populations of New Zealand kokako Callaeas cinerea wilsoni.

The endangered kokako Callaeas cinerea wilsoni (Callaeidae), an endemic forest-dwelling passerine of New Zealand, has declined over the last century to a number of small isolated populations due to widespread habitat clearance and predation by introduced predators. To evaluate the genetic consequences of inbreeding and genetic drift, we examined genetic variability within and among 3 of the major remaining kokako populations using 4 polymorphic microsatellite loci. The largest remaining kokako population in the Te Ureweras was shown to have greater variability than the smaller Mapara and Rotoehu populations. Differentiation among the populations was low to moderate. We suggest there is no genetic barrier to translocations between the populations and that translocations of some individuals between the remaining kokako populations could enhance genetic variability of small populations to levels found in larger populations (e.g. Te Ureweras).

Fine scale distribution of mtDNA haplotypes for the springtail Gomphiocephalus hodgsoni (Collembola) corresponds to an ancient shoreline in Taylor Valley, continental Antarctica

We examined the fine scale distribution of the endemic Antarctic collembolan Gomphiocephalus hodgsoni in Taylor Valley, southern Victoria Land using the mitochondrial DNA cytochrome c oxidase I gene. We found an area of sympatry in the mid-region of the valley between two common haplotype groups (2.4% sequence divergence). The area of sympatry coincided with the extent of proglacial Lake Washburn (approx. 8,000 ya). This lake existed as a result of the damming of lower Taylor Valley by the grounding of the Ross Ice Sheet and may have acted as an isolating barrier to dispersal/gene flow. We suggest that the phylogenetic break occurring in the vicinity of the ancient shoreline may be the result of previous isolation of refugial allopatric populations, followed by recolonisation into a secondary contact zone during the Holocene.

Distribution and abundance of zooplankton in the Waikato River, New Zealand

Potamoplankton is often a well developed component in large lowland rivers, yet little is known about its structure in New Zealands longest river, the Waikato River. To redress this gap we sampled bimonthly at seven sites along the length of the river over 12 months. Rotifers were the dominant zooplankton in the Waikato River making up 85% of the total densities. Cladocerans represented 9% and copepods only 6%. Rotifers were also the most taxonomically rich group with 41 species in 20 genera identified throughout the study. Thirty rotifer species and nine genera represent new records for the river – two cladoceran species were also recorded for the first time. The highest densities of crustaceans and rotifers were found in the hydro lakes. Densities of crustaceans decreased with increasing distance downstream and densities of rotifers were on average 15 times greater than crustaceans in the lower river. The seasonality of Crustacea was similar to that in New Zealand lakes and rivers with high densities in summer and minimum densities over the winter period. Total rotifer densities showed a similar trend although there were marked seasonal differences between individual species.

The southernmost worm, Scottnema lindsayae (Nematoda): diversity, dispersal and ecological stability

The nematode worm Scottnema lindsayae (Cephalobidae) was found near the base of the Beardmore Glacier in the Transantarctic Mountains 83.48°S, over 5° further south than previously recorded. Identification was confirmed using morphological analyses of males, females and juvenile stages, and by DNA sequencing of the ITS1 region of the ribosomal RNA tandem repeat unit. These data revealed no discernable morphological or ITS rDNA sequence variation between the extreme southern population of S. lindsayae and disparate populations from the McMurdo Dry Valleys in south Victoria Land (77–78°S). Based on these results, we suggest that broadcast dispersal, with accompanying high rates of gene flow, establish the extreme southern distribution of the phylum Nematoda. High abundance, low rates of diversification and lack of an apparent biogeographic structure across latitudinal and environmental gradients implies that their presence in simple Antarctic soil ecosystems is stable, so long as physical and biological controls on their distributions remain within viable parameters. Recent evidence that S. lindsayae populations are in decline suggests that their high dispersal rates are insufficient to buffer current, unfavorable environmental changes and may foreshadow longer-term ecosystem disruption.