Structural Evolution of the Glacier Ice Worm Fo ATP Synthase Complex.

The segmented annelid worm, Mesenchytraeus solifugus, is a permanent resident of temperate, maritime glaciers in the Pacific northwestern region of North America, displaying atypically high intracellular ATP levels which have been linked to its unusual ability to thrive in hydrated glacier ice. We have shown previously that ice worms contain a highly basic, carboxy terminal extension on their ATP6 regulatory subunit, likely acquired by horizontal gene transfer from a microbial dietary source. Here we examine the full complement of F1F0 ATP synthase structural subunits with attention to non-conservative, ice worm-specific structural modifications. Our genomics analyses and molecular models identify putative proton shuttling domains on either side of the F0 hemichannel, which predictably function to enhance proton flow across the mitochondrial membrane. Other components of the ice worm ATP synthase complex have remained largely unchanged in the context of Metazoan evolution.

Long-distance dispersal, ice sheet dynamics and mountaintop isolation underlie the genetic structure of glacier ice worms.

Disentangling the contemporary and historical factors underlying the spatial distributions of species is a central goal of biogeography. For species with broad distributions but little capacity to actively disperse, disconnected geographical distributions highlight the potential influence of passive, long-distance dispersal (LDD) on their evolutionary histories. However, dispersal alone cannot completely account for the biogeography of any species, and other factors-e.g. habitat suitability, life history-must also be considered. North American ice worms ( Mesenchytraeus solifugus) are ice-obligate annelids that inhabit coastal glaciers from Oregon to Alaska. Previous studies identified a complex biogeographic history for ice worms, with evidence for genetic isolation, unexpectedly close relationships among geographically disjunct lineages, and contemporary migration across large (e.g. greater than 1500 km) areas of unsuitable habitat. In this study, we analysed genome-scale sequence data for individuals from most of the known ice worm range. We found clear support for divergence between populations along the Pacific Coast and the inland flanks of the Coast Mountains (mean FST = 0.60), likely precipitated by episodic ice sheet expansion and contraction during the Pleistocene. We also found support for LDD of ice worms from Alaska to Vancouver Island, perhaps mediated by migrating birds. Our results highlight the power of genomic data for disentangling complex biogeographic patterns, including the presence of LDD.

Atypical Evolution of the F1Fo Adenosine Triphosphate Synthase Regulatory ATP6 subunit in Glacier Ice Worms (Annelida: Clitellata: Mesenchytraeus).

The glacier ice worm, Mesenchytraeus solifugus, is among a few animals that reside permanently in glacier ice. Their adaptation to cold temperature has been linked to relatively high intracellular adenosine triphosphate (ATP) levels, which compensate for reductions in molecular motion at low physiological temperatures. Here, we show that ATP6-the critical regulatory subunit of the F1Fo-ATP synthase and primary target of mitochondrial disease-acquired an unprecedented histidine-rich, 18-amino acid carboxy-terminal extension, which counters the strong evolutionary trend of mitochondrial genome compaction. Furthermore, sequence analysis suggests that this insertion is not of metazoan origin, but rather is a product of horizontal gene transfer from a microbial dietary source, and may act as a proton shuttle to accelerate the rate of ATP synthesis.

Phylogeny and cocoon production in the parasitic leech Myzobdella lugubris Leidy, 1851 (Hirudinidae, Piscicolidae).

Myzobdella lugubris is a commensal leech on crustaceans and a parasite to fishes, surviving predominantly in brackish waters throughout North America. Specimens in this study were collected within the tidal zone of the Delaware River basin (New Jersey and Pennsylvania). To compare regional M. lugubris specimens, defined characters were scored after dorsal and ventral dissections, and phylogenetic relationships were resolved using cytochrome c oxidase subunit 1 (CO1), 12S ribosomal RNA (rDNA) and 18S rDNA gene fragments. Variance between regional populations was low, suggesting recent dispersal events and/or strong evolutionary constraints. The reproductive biology of M. lugubris was explored by quantitative analysis of secreted cocoons. Specimens produced 32.67 ± 4.50 cocoons with fertilization ratios of 88.1% and hatching times of 48 ± 7 days at 17°C under laboratory conditions. At 22°C, 46 ± 28 cocoons were produced with fertilization ratios of 70.27% and hatching times of 28 ± 5 days. Surprisingly, each cocoon supported only one embryo, which is unusual among oligochaetes.

Punctuated invasion of water, ice, snow and terrestrial ecozones by segmented worms (Oligochaeta: Enchytraeidae: Mesenchytraeus).

Segmented worms (Annelida) are among the most successful animal inhabitants of extreme environments worldwide. An unusual group of enchytraeid oligochaetes of genus Mesenchytraeus are abundant in the Pacific northwestern region of North America and occupy geographically proximal ecozones ranging from low elevation rainforests and waterways to high altitude glaciers. Along this altitudinal transect, Mesenchytraeus representatives from disparate habitat types were collected and subjected to deep mitochondrial and nuclear phylogenetic analyses. Our data identify significant topological discordance among gene trees, and near equivalent interspecific divergence levels indicative of a rapid radiation event. Collectively, our results identify a Mesenchytraeus 'explosion' coincident with mountain building in the Pacific northwestern region that gave rise to closely related aquatic, ice, snow and terrestrial worms.

Colonization of maritime glacier ice by bdelloid Rotifera.

Very few animal taxa are known to reside permanently in glacier ice/snow. Here we report the widespread colonization of Icelandic glaciers and ice fields by species of bdelloid Rotifera. Specimens were collected within the accumulation zones of Langjökull and Vatnajökull ice caps, among the largest European ice masses. Rotifers reached densities up to ∼100 individuals per liter-equivalent of glacier ice/snow, and were freeze-tolerant. Phylogenetic analyses indicate that glacier rotifers are polyphyletic, with independent ancestries occurring within the Pleistocene. Collectively, these data identify a previously undescribed environmental niche for bdelloid rotifers and suggest their presence in comparable habitats worldwide.

Historical biogeography of the North American glacier ice worm, Mesenchytraeus solifugus (Annelida: Oligochaeta: Enchytraeidae).

North American ice worms are the largest glacially-obligate metazoans, inhabiting coastal, temperate glaciers between southcentral Alaska and Oregon. We have collected ice worm specimens from 10 new populations, completing a broad survey throughout their geographic range. Phylogenetic analyses of 87 individuals using fragments of nuclear 18S rRNA, and mitochondrial 12S rRNA and cyctochrome c oxidase subunit 1 (CO1) identified 18 CO1 haplotypes with divergence values up to ~10%. Phylogeographic interpretations suggest a St. Elias Range, Alaskan ancestry from an aquatic mesenchytraeid oligochaete during the early-Pliocene. A gradual, northward expansion by active dispersal from the central St. Elias clade characterizes a northern clade that is confined to Alaska (with one exception on Vancouver Island, British Columbia), while a distinct southern clade representing worms from British Columbia, Washington and Oregon was likely founded by a passive dispersal event originating from a northern ancestor. The geographic boundary between central and southern clades coincides with an ice worm distribution gap located in southern Alaska, which appears to have restricted active gene flow throughout the species' evolutionary history.

A glutamine-rich factor affects stem cell genesis in leech.

Leech embryogenesis is a model for investigating cellular and molecular processes of development. Due to the unusually large size of embryonic stem cells (teloblasts; 50 - 300 µm) in the glossiphoniid leech, Theromyzon tessulatum, and the presence of identifiable stem cell precursors (proteloblasts), we previously isolated a group of genes up-regulated upon stem cell birth. In the current study, we show that one of these genes, designated Tpr (Theromyzon proliferation), is required for normal stem cell genesis; specifically, transient Tpr knockdown experiments conducted with antisense oligonucleotides and monitored by semi-quantitative RT-PCR, caused abnormal proteloblast proliferation leading to embryonic death, but did not overtly affect neuroectodermal or mesodermal stem cell development once these cells were born. Tpr encodes a large, glutamine-rich (~34%) domain that shares compositional similarity with strong transcriptional enhancers, many of which have been linked with trinucleotide repeat disorders (e.g., Huntingtons).