Comparative phylogeography can reveal processes and historical events that shape the biodiversity of species and communities. As part of a comparative research program, the phylogeography of a new, endemic Australian genus and species of log-dependent (saproxylic) collembola was investigated using mitochondrial sequences, allozymes and anonymous single-copy nuclear markers. We found the genetic structure of the species corresponds with five a priori microbiogeographical regions, with population subdivision at various depths owing to palaeoclimatic influences. Closely related mtDNA haplotypes are codistributed within a single region or occur in adjacent regions, nuclear allele frequencies are more similar among more proximate populations, and interpopulation migration is rare. Based on mtDNA divergence, a late Miocene-late Pliocene coalescence is likely. The present-day distribution of genetic diversity seems to have been impacted by three major climatic events: Pliocene cooling and drying (2.5-7 million years before present, Mybp), early Pleistocene wet-dry oscillations (c. 1.2 Mybp) and the more recent glacial-interglacial cycles that have characterized the latter part of the Quaternary (<0.4 Mybp).
Sea ice, including icebergs, has a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea-ice losses around West Antarctica's continental shelf generate longer phytoplankton blooms but also make it a hotspot for coastal iceberg disturbance. This matters because in polar regions ice scour limits blue carbon storage ecosystem services, which work as a powerful negative feedback on climate change (less sea ice increases phytoplankton blooms, benthic growth, seabed carbon and sequestration). This resets benthic biota succession (maintaining regional biodiversity) and also fertilizes the ocean with nutrients, generating phytoplankton blooms, which cascade carbon capture into seabed storage and burial by benthos. Small icebergs scour coastal shallows, whereas giant icebergs ground deeper, offshore. Significant benthic communities establish where ice shelves have disintegrated (giant icebergs calving), and rapidly grow to accumulate blue carbon storage. When 5000 km2 giant icebergs calve, we estimate that they generate approximately 106 tonnes of immobilized zoobenthic carbon per year (t C yr−1). However, their collisions with the seabed crush and recycle vast benthic communities, costing an estimated 4 × 104 t C yr−1. We calculate that giant iceberg formation (ice shelf disintegration) has a net potential of approximately 106 t C yr−1 sequestration benefits as well as more widely known negative impacts.This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.
Phylum Tardigrada consists of 1000 tiny, hardy metazoan species distributed throughout terrestrial, limno-terrestrial and oceanic habitats. Their phylogenetic status has been debated, with current evidence placing them in the Ecdysozoa. Although there have been efforts to explore tardigrade phylogeny using both morphological and molecular data, limitations such as their few morphological characters and low genomic DNA concentrations have resulted in restricted taxonomic coverage. Using a protocol that allows us to identify and extract DNA from individuals, we have sequenced 18S rDNA from 343 tardigrades from across the globe. Using maximum parsimony and Bayesian analyses we have found support for dividing Order Parachela into three superfamilies and further evidence that indicates the traditional taxonomic perspective of families in the class Eutardigrada are nonmonophyletic and require re-working. It appears that conserved morphology within Tardigrada has resulted in conservative taxonomy as we have found cases of several discrete lineages grouped into single genera. Although this work substantially adds to the understanding of the evolution and taxonomy of the phylum, we highlight that inferences gained from this work are likely to be refined with the inclusion of further taxa-specifically representatives of the nine families yet to be sampled.
We assessed the available morphological evidence to see if this corroborates the paraphyly in the Parachela (Tardigrada) as suggested by recent molecular data. We reconcile molecular phylogenetics with alpha morphology, focusing on claw and apophysis for the insertion of the stylet muscles (AISM). We combine molecular and morphological evidence to define six new taxa within the Parachela Schuster et al 1980. These include two new families of Isohypsibiidae fam. nov. and Ramazzottidae fam. nov. along with four new superfamilies of Eohypsibioidea superfam. nov., Hypsibioidea super- fam. nov., Isohypsibioidea superfam. nov., and Macrobiotoidea superfam. nov.
Comparative phylogeographic studies of animals with low mobility and/or high habitat specificity remain rare, yet such organisms may hold fine-grained palaeoecological signal. Comparisons of multiple, codistributed species can elucidate major historical events. As part of a multitaxon programme, mitochondrial cytochrome oxidase I (COI) variation was analysed in two species of terrestrial flatworm, Artioposthia lucasi and Caenoplana coerulea. We applied coalescent demographic estimators and nested clade analysis to examine responses to past, landscape-scale, cooling-drying events in a model system of montane forest (Tallaganda). Correspondence of haplotype groups in both species to previously proposed microbiogeographic regions indicates at least four refuges from cool, dry conditions. The region predicted to hold the highest quality refuges (the Eastern Slopes Region), is indicated to have been a long-term refuge in both species, but so are several other regions. Coalescent analyses suggest that populations of A. lucasi are declining, while C. coerulea is expanding, although stronger population substructure in the former could yield similar patterns in the data. The differences in spatial and temporal genetic variation in the two species could be explained by differences in ecological attributes: A. lucasi is predicted to have lower dispersal ability but may be better able to withstand cold conditions. Thus, different contemporary population dynamics may reflect different responses to recent (Holocene) climate warming. The two species show highly congruent patterns of catchment-based local genetic endemism with one another and with previously studied slime-mould grazing Collembola.
Phylogeography can reveal evolutionary processes driving natural genetic-geographical patterns in biota, providing an empirical framework for optimizing conservation strategies. The long-term population history of a rotting-log-adapted giant springtail (Collembola) from montane southeast Australia was inferred via joint analysis of mitochondrial and multiple nuclear gene genealogies. Contemporary populations were identified using multilocus nuclear genotype clustering. Very fine-scale sampling combined with nested clade and coalescent-based analyses of sequences from mitochondrial cytochrome oxidase I and three unlinked nuclear loci uncovered marked population structure, deep molecular divergences, and abrupt phylogeographical breaks over distances on the order of tens of kilometres or less. Despite adaptations that confer low mobility, rare long-distance gene flow was implicated: novel computer simulations that jointly modelled stochasticity inherent in coalescent processes and that of DNA sequence evolution showed that incomplete lineage sorting alone was unable to explain the observed spatial-genetic patterns. Impacts of Pleistocene or earlier climatic cycles were detected on multiple timescales, and at least three putative moist forest refuges were identified. Water catchment divisions predict phylogeographical patterning and present-day population structure with high precision, and may serve as an excellent surrogate for biodiversity indication in sedentary arthropods from topographically heterogeneous montane temperate forests.
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