Mark I. Stevens

Antarctic terrestrial life – challenging the history of the frozen continent?

Antarctica is a continent locked in ice, with almost 99.7% of current terrain covered by permanent ice and snow, and clear evidence that, as recently as the Last Glacial Maximum (LGM), ice sheets were both thicker and much more extensive than they are now. Ice sheet modelling of both the LGM and estimated previous ice maxima across the continent give broad support to the concept that most if not all currently ice‐free ground would have been overridden during previous glaciations. This has given rise to a widely held perception that all Mesozoic (pre‐glacial) terrestrial life of Antarctica was wiped out by successive and deepening glacial events. The implicit conclusion of such destruction is that most, possibly all, contemporary terrestrial life has colonised the continent during subsequent periods of glacial retreat. However, several recently emerged and complementary strands of biological and geological research cannot be reconciled comfortably with the current reconstruction of Antarctic glacial history, and therefore provide a fundamental challenge to the existing paradigms. Here, we summarise and synthesise evidence across these lines of research. The emerging fundamental insights corroborate substantial elements of the contemporary Antarctic terrestrial biota being continuously isolated in situ on a multi‐million year, even pre‐Gondwana break‐up timescale. This new and complex terrestrial Antarctic biogeography parallels recent work suggesting greater regionalisation and evolutionary isolation than previously suspected in the circum‐Antarctic marine fauna. These findings both require the adoption of a new biological paradigm within Antarctica and challenge current understanding of Antarctic glacial history. This has major implications for our understanding of the key role of Antarctica in the Earth System.

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.

Haplotype Networks Can Be Misleading in the Presence of Missing Data

1Allan Wilson Centre for Molecular Ecology and Evolution, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand; E-mail: s.joly@massey.ac.nz (S.J.) 2School of Biological Sciences, Monash University, Clayton 3800, Victoria, Australia 3DST-NRF Centre of Excellence for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa

The diverse origins of New Zealand house mice

Molecular markers and morphological characters can help infer the colonization history of organisms. A combination of mitochondrial (mt) d-loop DNA sequences, nuclear DNA data, external measurements and skull characteristics shows that house mice (Mus musculus) in New Zealand and its outlying islands are descended from very diverse sources. The predominant genome is Mus musculus domesticus (from western Europe), but Mus musculus musculus (from central Europe) and Mus musculus castaneus (from southern Asia) are also represented genetically. These subspecies have hybridized to produce combinations of musculus and domesticus nuclear DNA coupled with domesticus mtDNA, and castaneus or musculus mtDNA with domesticus nuclear DNA. The majority of the mice with domesticus mtDNA that we sampled had d-loop sequences identical to two haplotypes common in Britain. This is consistent with long-term British–New Zealand cultural linkages. The origins of the castaneus mtDNA sequences widespread in New Zealand are less easy to identify.

House mouse colonization patterns on the sub-Antarctic Kerguelen Archipelago suggest singular primary invasions and resilience against re-invasion

BackgroundStarting from Western Europe, the house mouse (Mus musculus domesticus) has spread across the globe in historic times. However, most oceanic islands were colonized by mice only within the past 300 years. This makes them an excellent model for studying the evolutionary processes during early stages of new colonization. We have focused here on the Kerguelen Archipelago, located within the sub-Antarctic area and compare the patterns with samples from other Southern Ocean islands.ResultsWe have typed 18 autosomal and six Y-chromosomal microsatellite loci and obtained mitochondrial D-loop sequences for a total of 534 samples, mainly from the Kerguelen Archipelago, but also from the Falkland Islands, Marion Island, Amsterdam Island, Antipodes Island, Macquarie Island, Auckland Islands and one sample from South Georgia. We find that most of the mice on the Kerguelen Archipelago have the same mitochondrial haplotype and all share the same major Y-chromosomal haplotype. Two small islands (Cochons Island and Cimetière Island) within the archipelago show a different mitochondrial haplotype, are genetically distinct for autosomal loci, but share the major Y-chromosomal haplotype. In the mitochondrial D-loop sequences, we find several single step mutational derivatives of one of the major mitochondrial haplotypes, suggesting an unusually high mutation rate, or the occurrence of selective sweeps in mitochondria.ConclusionsAlthough there was heavy ship traffic for over a hundred years to the Kerguelen Archipelago, it appears that the mice that have arrived first have colonized the main island (Grande Terre) and most of the associated small islands. The second invasion that we see in our data has occurred on islands that are detached from Grande Terre and were likely to have had no resident mice prior to their arrival. The genetic data suggest that the mice of both primary invasions originated from related source populations. Our data suggest that an area colonized by mice is refractory to further introgression, possibly due to fast adaptations of the resident mice to local conditions.

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.

Mitochondrial DNA reveals multiple Northern Hemisphere introductions of Caprella mutica (Crustacea, Amphipoda)

Caprella mutica (Crustacea, Amphipoda) has been widely introduced to non‐native regions in the last 40 years. Its native habitat is sub‐boreal northeast Asia, but in the Northern Hemisphere, it is now found on both coasts of North America, and North Atlantic coastlines of Europe. Direct sequencing of mitochondrial DNA (cytochrome c oxidase subunit I gene) was used to compare genetic variation in native and non‐native populations of C. mutica. These data were used to investigate the invasion history of C. mutica and to test potential source populations in Japan. High diversity (31 haplotypes from 49 individuals), but no phylogeographical structure, was identified in four populations in the putative native range. In contrast, non‐native populations showed reduced genetic diversity (7 haplotypes from 249 individuals) and informative phylogeographical structure. Grouping of C. mutica populations into native, east Pacific, and Atlantic groups explained the most among‐region variation (59%). This indicates independent introduction pathways for C. mutica to the Pacific and Atlantic coasts of North America. Two dominant haplotypes were identified in eastern and western Atlantic coastal populations, indicating several dispersal routes within the Atlantic. The analysis indicated that several introductions from multiple sources were likely to be responsible for the observed global distribution of C. mutica, but the pathways were least well defined among the Atlantic populations. The four sampled populations of C. mutica in Japan could not be identified as the direct source of the non‐native populations examined in this study. The high diversity within the Japan populations indicates that the native range needs to be assessed at a far greater scale, both within and among populations, to accurately assess the source of the global spread of C. mutica.

Challenging species delimitation in Collembola: cryptic diversity among common springtails unveiled by DNA barcoding

Abstract. Collembola is one of the major functional groups in soil as well as a model taxon in numerous disciplines. Therefore the accurate identification of specimens is critical, but could be jeopardised by cases of cryptic diversity. Several populations of six well characterised species of springtails were sequenced using the COI barcode fragment as a contribution to the global Collembola barcoding campaign. Each species showed high intraspecific divergence, comparable to interspecific sequence divergence values observed in previous studies and in 10 congeneric species barcoded here as a reference. The nuclear marker, 28S, confirmed all the intraspecific lineages found with COI, supporting the potential specific status of these entities. The implications of this finding for taxonomy and for disciplines relying on species names, such as evolution and ecology, are discussed.

Abiotic factors influence microbial diversity in permanently cold soil horizons of a maritime-associated Antarctic Dry Valley

The McMurdo Dry Valleys collectively comprise the most extensive ice-free region in Antarctica and are considered one of the coldest arid environments on Earth. In low-altitude maritime-associated valleys, mineral soil profiles show distinct horizontal structuring, with a surface arid zone overlying a moist and biologically active zone generated by seasonally melted permafrost. In this study, long-term microenvironmental monitoring data show that temperature and soil humidity regimes vary in the soil horizons of north- and south-facing slopes within the Miers Valley, a maritime valley in the McMurdo Dry Valleys. We found that soil bacterial communities varied from the north to the south. The microbial assemblages at the surface and shallow subsurface depths displayed higher metabolic activity and diversity compared to the permafrost soil interface. Multivariate analysis indicated that K, C, Ca and moisture influenced the distribution and structure of microbial populations. Furthermore, because of the large % RH gradient between the frozen subsurface and the soil surface we propose that water transported to the surface as water vapour is available to microbial populations, either as a result of condensation processes or by direct adsorption from the vapour phase.

At limits of life: multidisciplinary insights reveal environmental constraints on biotic diversity in continental Antarctica.

Multitrophic communities that maintain the functionality of the extreme Antarctic terrestrial ecosystems, while the simplest of any natural community, are still challenging our knowledge about the limits to life on earth. In this study, we describe and interpret the linkage between the diversity of different trophic level communities to the geological morphology and soil geochemistry in the remote Transantarctic Mountains (Darwin Mountains, 80°S). We examined the distribution and diversity of biota (bacteria, cyanobacteria, lichens, algae, invertebrates) with respect to elevation, age of glacial drift sheets, and soil physicochemistry. Results showed an abiotic spatial gradient with respect to the diversity of the organisms across different trophic levels. More complex communities, in terms of trophic level diversity, were related to the weakly developed younger drifts (Hatherton and Britannia) with higher soil C/N ratio and lower total soluble salts content (thus lower conductivity). Our results indicate that an increase of ion concentration from younger to older drift regions drives a succession of complex to more simple communities, in terms of number of trophic levels and diversity within each group of organisms analysed. This study revealed that integrating diversity across multi-trophic levels of biotic communities with abiotic spatial heterogeneity and geological history is fundamental to understand environmental constraints influencing biological distribution in Antarctic soil ecosystems.