Lateral Transfer of a Lectin-Like Antifreeze Protein Gene in Fishes

Fishes living in icy seawater are usually protected from freezing by endogenous antifreeze proteins (AFPs) that bind to ice crystals and stop them from growing. The scattered distribution of five highly diverse AFP types across phylogenetically disparate fish species is puzzling. The appearance of radically different AFPs in closely related species has been attributed to the rapid, independent evolution of these proteins in response to natural selection caused by sea level glaciations within the last 20 million years. In at least one instance the same type of simple repetitive AFP has independently originated in two distant species by convergent evolution. But, the isolated occurrence of three very similar type II AFPs in three distantly related species (herring, smelt and sea raven) cannot be explained by this mechanism. These globular, lectin-like AFPs have a unique disulfide-bonding pattern, and share up to 85% identity in their amino acid sequences, with regions of even higher identity in their genes. A thorough search of current databases failed to find a homolog in any other species with greater than 40% amino acid sequence identity. Consistent with this result, genomic Southern blots showed the lectin-like AFP gene was absent from all other fish species tested. The remarkable conservation of both intron and exon sequences, the lack of correlation between evolutionary distance and mutation rate, and the pattern of silent vs non-silent codon changes make it unlikely that the gene for this AFP pre-existed but was lost from most branches of the teleost radiation. We propose instead that lateral gene transfer has resulted in the occurrence of the type II AFPs in herring, smelt and sea raven and allowed these species to survive in an otherwise lethal niche

Paleodistributions and Comparative Molecular Phylogeography of Leafcutter Ants (Atta spp.) Provide New Insight into the Origins of Amazonian Diversity

The evolutionary basis for high species diversity in tropical regions of the world remains unresolved. Much research has focused on the biogeography of speciation in the Amazon Basin, which harbors the greatest diversity of terrestrial life. The leading hypotheses on allopatric diversification of Amazonian taxa are the Pleistocene refugia, marine incursion, and riverine barrier hypotheses. Recent advances in the fields of phylogeography and species-distribution modeling permit a modern re-evaluation of these hypotheses. Our approach combines comparative, molecular phylogeographic analyses using mitochondrial DNA sequence data with paleodistribution modeling of species ranges at the last glacial maximum (LGM) to test these hypotheses for three co-distributed species of leafcutter ants (Atta spp.). The cumulative results of all tests reject every prediction of the riverine barrier hypothesis, but are unable to reject several predictions of the Pleistocene refugia and marine incursion hypotheses. Coalescent dating analyses suggest that population structure formed recently (Pleistocene-Pliocene), but are unable to reject the possibility that Miocene events may be responsible for structuring populations in two of the three species examined. The available data therefore suggest that either marine incursions in the Miocene or climate changes during the Pleistocene—or both—have shaped the population structure of the three species examined. Our results also reconceptualize the traditional Pleistocene refugia hypothesis, and offer a novel framework for future research into the area

Radiocarbon dating in estuarine environments

Radiocarbon (14C) is a radioactive cosmogenic isotope continuously produced in the upper atmosphere where it rapidly oxidises to 14CO2. As 14CO2, 14C enters the global carbon cycle and is incorporated into living organisms which can be radiocarbon dated following death. Radiocarbon is among the most common radiometric methods used to provide age estimates some 40–50,000 years back in time. Here, a review of the radiocarbon method covering commonly encountered problems in estuarine environments is given. Emphasis will be on methodological procedures concerning how to estimate the 14C reservoir age in these environments, including how reliably error estimates can be calculated. Subsequently, three case studies are presented, providing a short overview of investigations of 14C reservoir age variability in estuarine environments

New insights on polar bear (Ursus maritimus) diet from faeces based on Next Generation Sequencing technologies

Practical tools to quantify range-wide dietary choices on the polar bear have not been well developed impeding the monitoring of this species in a changing climate. Here we describe our steps toward non-invasive polar bear diet determination with the optimization of 454 pyrosequencing of a 136 (base pair: bp) mitochondrial cytochrome b (cytB) fragment amplified from the extracts of captive and wild polar bear faeces. We first determine the efficacy, reliability and accuracy of our method using polar bear faeces from captive polar bears fed known diets at the Cochrane Polar Bear Habitat (Canada, n = 5 faeces from 1 bear) and Metro Toronto Zoo (Canada, n =19 from 3 polar bears); and from wild (unfed) polar bears from a holding facility in Churchill (Canada; n=7 from 7 polar bears). We report 91% overall success in amplifying a 136 bp cytB amplicon from the faeces of polar bears. Our DNA analyses accurately recovered the vertebrate diet profiles of captive bears fed known diets. We then characterized multiyear vertebrate prey diet choices from free-ranging polar bears from the sea ice of the M’Clintock Channel (MC) polar bear Management Unit (Canada) (n =117 from an unknown number of bears). These data point to a diet unsurprisingly dominated by ringed seal (Phoca hispidia) while including evidence of bearded seal (Erignathus barbatus), harbor seal (Phoca vitulina), muskox (Ovibos spp.), Arctic foxes (Alopex lagopus), wolves (Canis lupus), herring gull (Larus argentatus) and willow ptarmigan (Lagopus lagopus). We found low levels pf contamination (<3% of sequences when present), suggesting specific process improvements to reduce contamination in range-wide studies. Together, these findings indicate that next generation sequencing-based diet assessments show great promise in monitoring free ranging polar bears in this time of climate chang

Genetic evidence for female-biased dispersal in the bullfrog, Rana catesbeiana (Ranidae)

Sex-biased dispersal is an important but unexplored area of amphibian ecology. We predicted female-biased dispersal in the bullfrog (Rana catesbeiana) based on aspects of their mating system and tested this prediction using data from seven polymorphic DNA microsatellite loci. Allelic (F-statistics) and genotypic [assignment index, (AIc)] frequencies from nine Ontario populations support our prediction, although significant sex differences in inbreeding and variance of AIc were not detected. The diversity of mating systems found in amphibians represents an important avenue for investigating the relationship between reproductive systems, dispersal and phylogeny.Support was provided by the National Sciences and Research Council of Canada (NSERC) operating grants to P.T.B. and S.C.L., the OMNR and by an NSERC Postgraduate Scholarship to J.D.A., and the OMNR. Additional funding for field work was provided by: The American Museum of Natural History, Theodore Roosevelt Memorial Fund; Sigmi Xi, Grants-in-Aid of Research; and the Mountain Equipment Co-op, Environment Fund.Peer reviewe