Hallucal tarsometatarsal joint in Australopithecus afarensis

Hallucal tarsometatarsal joints from African pongids, modern humans, and Australopithecus afarensis are compared to investigate the anatomical and mechanical changes that accompanied the transition to terrestrial bipedality. Features analyzed include the articular orientation of the medial cuneiform, curvature of the distal articular surface of the medial cuneiform, and the articular configuration of the hallucal metatarsal proximal joint surface. Morphological characteristics of the hallucal tarsometatarsal joint unequivocally segregate quadrupedal pongids and bipedal hominids.     

Small Thaw Ponds: An Unaccounted Source of Methane in the Canadian High Arctic

Thawing permafrost in the Canadian Arctic tundra leads to peat erosion and slumping in narrow and shallow runnel ponds that surround more commonly studied polygonal ponds. Here we compared the methane production between runnel and polygonal ponds using stable isotope ratios, ¹⁴C signatures, and investigated potential methanogenic communities through high-throughput sequencing archaeal 16S rRNA genes. We found that runnel ponds had significantly higher methane and carbon dioxide emissions, produced from a slightly larger fraction of old carbon, compared to polygonal ponds. The methane stable isotopic signature indicated production through acetoclastic methanogenesis, but gene signatures from acetoclastic and hydrogenotrophic methanogenic Archaea were detected in both polygonal and runnel ponds. We conclude that runnel ponds represent a source of methane from potentially older C, and that they contain methanogenic communities able to use diverse sources of carbon, increasing the risk of augmented methane release under a warmer climate.     

Genetic structure of endangered lake chubsucker Erimyzon sucetta in Canada reveals a differentiated population in a precarious habitat

We used mitochondrial DNA to assess the genetic structure of endangered lake chubsucker Erimyzon sucetta across its Canadian range. We found unique mitochondrial haplotypes in Lyons Creek, a tributary of the Niagara River that faces a strong potential for habitat deterioration. Lyons Creek may therefore serve as a reservoir of unique genetic diversity. The sensitivity of Lyons Creek, combined with the genetic uniqueness of its E. sucetta population, call for further investigation into whether this population should be considered a separate designatable unit for conservation purposes.     

Membrane structure and the tenuously maintained resistance to staining with N epsilon-dansyl-L-lysine shown by many cells

The ability to resist staining by N epsilon-dansyl-L-lysine is tenuously maintained in the majority of live nucleated cells taken from tissues concerned with immune function. Resistance is lost under a variety of nonphysiological conditions known to, or likely to, cause protein denaturation or aggregation. In contrast to that of dansyl-gamma-aminobutyrate, the fluorescence intensity of N epsilon-dansyl-L-lysine is only weakly enhanced by native proteins. This is further reduced on denaturation or aggregation of the proteins. It is unlikely, therefore, that cellular uptake of, and staining by, N epsilon-dansyl-L-lysine is a direct consequence of membrane protein denaturation/aggregation but may result from a decrease in protein-phospholipid interactions leading to formation of phospholipid domains. Previous work has indicated that such features are stained by N epsilon-dansyl-L-lysine (Humphries, G.M.K., Lovejoy, J.P., 1983, Biophys. J. 42:307-310; Humphries, G.M.K., Lovejoy, J.R., 1983, Biochem. Biophys. Res. Commun. 111:768-774). Although it appears likely that passage through a dansyl-lysine-staining state is a common, if not universal, prelude to cell death (as monitored by uptake of trypan blue), not all cells that lose resistance to dansyl-lysine staining are moribund. Resistance to staining is also lost by macrophages on binding to solid substrates and multivalent ligands. The possible physiological significance of this is discussed.     

Vertical structure of archaeal communities and the distribution of ammonia monooxygenase A gene variants in two meromictic High Arctic lakes

The distribution of archaeal amoA and 16S rRNA genes was evaluated in two marine-derived, meromictic lakes in the Canadian High Arctic: Lake A and Lake C1 on the northern coast of Ellesmere Island. The amoA gene was recorded in both lakes, with highest copy numbers in the oxycline. Sequence analysis showed that amoA from the two lakes shared 94% similarity, indicating at least two phylogenetically distinct clusters. Clone libraries of archaeal 16S rRNA genes from Lake A revealed strong vertical differences in archaeal community diversity and composition down the water column. The oxic layer was dominated by one group of Euryarchaeota affiliated to the Lake Dagow Sediment (LDS) cluster. This group was absent from the oxycline, which had an extremely low archaeal diversity of two phylotypes. Both belonged to the Crenarchaeota Marine Group I (MGI), the marine group that has been linked to archaeal amoA ; however, there was a low ratio of amoA to MGI copy numbers, suggesting that many MGI Archaea did not carry the amoA gene. The anoxic zone contained representatives of the RC-V (Rice Cluster-V) and LDS clusters of Euryarchaeota. These results show the strong vertical differentiation of archaeal communities in polar meromictic lakes, and they suggest archaeal nitrification within the oxycline of these highly stratified waters.     

The evolutionary origins of diadromy inferred from a time-calibrated phylogeny for Clupeiformes (herring and allies)

One of the most remarkable types of migration found in animals is diadromy, a life-history behaviour in which individuals move between oceans and freshwater habitats for feeding and reproduction. Diadromous fishes include iconic species such as salmon, eels and shad, and have long fascinated biologists because they undergo extraordinary physiological and behavioural modifications to survive in very different habitats. However, the evolutionary origins of diadromy remain poorly understood. Here, we examine the widely accepted productivity hypothesis, which states that differences in productivity between marine and freshwater biomes determine the origins of the different modes of diadromy. Specifically, the productivity hypothesis predicts that anadromous lineages should evolve in temperate areas from freshwater ancestors and catadromous lineages should evolve in tropical areas from marine ancestors. To test this, we generated a time-calibrated phylogeny for Clupeiformes (herrings, anchovies, sardines and allies), an ecologically and economically important group that includes high diversity of diadromous species. Our results do not support the productivity hypothesis. Instead we find that the different modes of diadromy do not have predictable ancestry based on latitude, and that predation, competition and geological history may be at least as important as productivity in determining the origins of diadromy.