[Show abstract][Hide abstract] ABSTRACT: Mitochondria are responsible for the oxidative phosphorylation process. Accordingly, putatively adaptive changes in their genomic features have been variously associated with major eco-physiological shifts in animal evolution, including increased metabolic rates and heat adaptation. Antarctic pycnogonids offer an interesting system to test whether the selective pressure for heat production and increased aerobic metabolism may be driving genomic changes like: (a) unusual compositional biases at the nucleotide and amino acid level, possibly related to cold adaptation; (b) an accelerated rate of mutations/genomic rearrangements, possibly related to the mutagenic effects of oxygen intermediates. The complete mitochondrial genome (mtDNA) of the Antarctic sea spider Ammothea carolinensis Leach, 1814 (Arthropoda: Pycnogonida), the type species for the genus Ammothea, has been determined and is here compared to known genomes from Antarctic and temperate species. We describe a marked heterogeneity in base composition skewness parameters as well as a strong signature of purifying selection toward an increase in thymines at second codon positions, possibly associated with an increased stability of hydrophobic inter-membrane domains. We further observe a fairly high rate of genomic changes, including a possible hot spot of recombination at the level of tRNA-Q. Nevertheless, these features do not seem to be restricted to the two Antarctic pycnogonids analyzed, as to suggest a causal relationship between cold adaptation and genomic changes, and are better interpreted as basal features shared by the entire group. The relevance of the newly determined sequence for the phylogeny of pycnogonids, including its base composition and genomic rearrangements, is further discussed.
[Show abstract][Hide abstract] ABSTRACT: Gomphiocephalus hodgsoni Carpenter was only the second collembolon‡ to be described from the Antarctic continent. It was collected first in 1902 from Granite Harbour, southern Victoria Land, Eastern Antarctica, by the British National Antarctic Expedition (1901–1904). Since then several studies have investigated the distribution, ecology, ecophysiology and molecular composition of the species. Despite two morphological redescriptions and an absence of detailed evolutionary phylogenetic studies, the genus Gomphiocephalus was recently reduced to a subgenus of Schoettella Schäffer. Here, we redescribe the species in detail and use morphological and molecular (cytochrome c oxidase subunit I and 28S) data to indicate its generic relationships within Hypogastruridae. Characters of Gomphiocephalus do not conform with those of any extant genus in the family, including Schoettella. In addition, the only Schoettella species described from the southern hemisphere, Schoettella subcorta Salmon, is shown here to belong in the genus Xenylla. Furthermore, molecular data indicates the genus has no close relationship to any other in Poduromorpha, and in particular Hypogastruridae. Therefore, we restore Gomphiocephalus to generic status. Our results reinforce the already recognized high level of endemism in the Antarctic fauna at both species and generic levels, and emphasise the necessity of using both morphological and molecular data in determining the systematics and evolutionary relationships of the fauna.
Full-text · Article · Dec 2010 · Systematic Entomology
[Show abstract][Hide abstract] ABSTRACT: The mitochondrial COI gene of the Antarctic springtail, Gressittacantha terranova, was sequenced across a polar coastal landscape at Terra Nova Bay, northern Victoria Land. Samples from two altitudinal transects in the foothills directly south of Campbell Glacier were compared with samples from Springtail Valley (northern foothills) as an external reference population. We found that mtDNA haplotypes clustered into two lineages (clades) with a mean sequence divergence of 10% (uncorrected distance). However, there was no phylogeographic structure found at this spatial (landscape) scale with haplotypes from both divergent clades found sympatric across most populations. At the landscape scale, the considerable genetic divergence revealed within G. terranova is around five times greater than any other continental Antarctic springtail examined to date. These data indicate a Pliocene divergence event in G. terranova around 4–5 million years ago. The unusual distributional profile of haplotypes - occurrence of multiple haplotypes at single sites and genetic contiguity between sites that are not physically contiguous - suggests a subsequent ‘reshuffling’ of haplotypes in the Holocene that has an ecological basis.
[Show abstract][Hide abstract] ABSTRACT: Friesea grisea is the only springtail species currently described from both East (Victoria Land) and West Antarctica (Antarctic Peninsula), although levels of genetic divergence between the two regions suggest the possibility of cryptic species. Determining the genetic structure of populations in the two regions is necessary in order to compare the effects of the different environmental conditions in the two regions, the different evolutionary histories of their inhabitants, and for assessing any influence of latitude in each region on genetic diversity. We analysed sequences of the mitochondrial COX1 and ATP6 genes from a total of 111 individuals for 17 sites (nine on the Antarctic Peninsula and eight in Victoria Land), to assess levels of genetic diversity. Both regions have their own unique sets of haplotypes, differing by about 20% of their nucleotide sequences. A similar number of haplotypes was found in the two regions, and within each we found two groups of populations sharing no haplotypes. In the Antarctic Peninsula, two, presumably ancestral, haplotypes are dominant in frequency. In Victoria Land, the Cape Hallett population showed a distinct set of haplotypes, genetically different from the southernmost populations, suggesting differentiation on pre-Pleistocene timescales.
Full-text · Article · Nov 2010 · Antarctic Science
[Show abstract][Hide abstract] ABSTRACT: Collembola are one of the few hexapod groups adapted to live in the harsh environmental conditions of Antarctic terrestrial ecosystems. Diversity is limited to a few species that can be very abundant in coastal deglaciated sites. A remarkable lack of overlap in Collembola species composition is evident between Western and Eastern Antarctica, and Friesea grisea is currently the only species whose distribution is thought to span these two main regions of the continent. However, our analysis of the complete sequences of the mitochondrial genomes from specimens obtained from each of the two regions showed unexpected genetic divergence, well above the average levels observed between populations belonging to the same species, and so indicating that these are actually separate species, despite their lack of distinguishing morphology. Detailed analysis of the two genomes showed the presence of a non-coding region observed between trnS(uga) and nad1. Other features of these mitochondrial genomes, such as base compositional bias, secondary structure features of tRNAs and the presence of regulatory elements in the control region, are described and discussed from an evolutionary standpoint.
[Show abstract][Hide abstract] ABSTRACT: Aim: We examined the genetic structure among populations and regions for the springtails Cryptopygus antarcticus antarcticus and Gomphiocephalus hodgsoni (Collembola) to identify potential historical refugia and subsequent colonization routes, and to examine population growth/expansion and relative ages of population divergence. Location Antarctic Peninsula for C. a. antarcticus; Antarctic continent (southern Victoria Land) for G. hodgsoni. Methods: Samples were collected from 24 and 28 locations across the Antarctic Peninsula and southern Victoria Land regions for C. a. antarcticus and G. hodgsoni, respectively. We used population genetic, demographic and nested clade analyses based on mitochondrial DNA (cytochrome c oxidase subunit I and subunit II). Results: Both species were found to have population structures compatible with the presence of historical glacial refugia on Pleistocene (2 Ma–present) time-scales, followed by post-glacial expansion generating contemporary geographically isolated populations. However, G. hodgsoni populations were characterized by a fragmented pattern with several 'phylogroups' (likely ancestral haplotypes present in high frequency) retaining strong ancestral linkages among present-day populations. Conversely, C. a. antarcticus had an excess of rare haplotypes with a much reduced volume of ancestral lineages, possibly indicating historical founder/bottleneck events and widespread expansion. Main conclusions: We infer that these differences reflect distinct evolutionary histories in each locality despite the resident species having similar life-history characteristics. We suggest that this has predominantly been influenced by variation in the success of colonization events as a result of intrinsic historical glaciological differences between the Antarctic Peninsula and continental Antarctic environments.
Full-text · Article · Aug 2009 · Journal of Biogeography