Three approaches commonly used to quantify diffusive gas exchange across aquatic surfaces were compared in a densely treed, low-wind environment Diffusive surface fluxes of carbon dioxide (CO2) and methane (CH4) from a small boreal reservoir were estimated using (i) surface water concentrations, the thin boundary layer (TBL) equation, and gas transfer velocities (k) calculated using sulfur hexafluoride (SF6); (ii) surface water concentrations, the TBL equation, and k estimated from wind speed; and (iii) static floating chambers (FCs). Comparisons were made during three different approximately 10-day intervals (August 2000, June and September 2001). CO2 and CH4 fluxes estimated from SF6-derived k were on average 1-3 times greater than those determined from wind-estimated k Overall agreement between FC CO2 and CH4 flux estimates and those based on SF6 and wind speed derived kvalues was much weaker, with FC CO2 and CH4 flux estimates ranging from -9 to 23 times those based on SF6 and wind-estimated k values. Chamber deployment likely enhanced gas transfer through disturbance of the surface boundary layer, and results of this study suggest that caution must be exercised concerning the use of FCs on very still water surfaces. Furthermore, findings of this study contradict the common belief that use of wind speed to approximate k is inappropriate for small bodies of water characterized by low winds and surface obstructions.

Reconstruction of the demographic and evolutionary history of populations assuming a consensus tree‐like relationship can mask more complex scenarios, which are prevalent in nature. An emerging genomic toolset, which has been most comprehensively harnessed in the reconstruction of human evolutionary history, enables molecular ecologists to elucidate complex population histories. Killer whales have limited extrinsic barriers to dispersal and have radiated globally, and are therefore a good candidate model for the application of such tools. Here, we analyse a global data set of killer whale genomes in a rare attempt to elucidate global population structure in a nonhuman species. We identify a pattern of genetic homogenisation at lower latitudes and the greatest differentiation at high latitudes, even between currently sympatric lineages. The processes underlying the major axis of structure include high drift at the edge of species' range, likely associated with founder effects and allelic surfing during postglacial range expansion. Divergence between Antarctic and non‐Antarctic lineages is further driven by ancestry segments with up to four‐fold older coalescence time than the genome‐wide average; relicts of a previous vicariance during an earlier glacial cycle. Our study further underpins that episodic gene flow is ubiquitous in natural populations, and can occur across great distances and after substantial periods of isolation between populations. Thus, understanding the evolutionary history of a species requires comprehensive geographic sampling and genome‐wide data to sample the variation in ancestry within individuals.

Eastern Canada-West Greenland (EC-WG) bowhead whales Balaena mysticetus migrate seasonally between northwestern Hudson Bay/Foxe Basin and Gulf of Boothia in summer and Hudson and Davis Straits in winter. Despite recent advances in knowledge of summer diet composition, determining seasonal variation in foraging behaviour of EC-WG bowhead whales remains a priority for understanding how annual metabolic requirements are met, as well as identifying factors driving seasonal habitat selection. We measured stable nitrogen, carbon, and sulfur isotope composition (δ 15 N, δ 13 C, and δ 34 S) along continuously growing baleen plates (n = 14) to assess alternative seasonal foraging hypotheses, namely winter fasting vs. year-round foraging. Synchronous δ 15 N and δ 13 C cycles, with periods of 15 N enrichment corresponding to foraging on the summer grounds, were inconsistent with standard fasting predictions, although δ 15 N cycles could reflect changes in diet-tissue δ 15 N discrimination between periods of intense foraging throughout the open-water season and supplemental protein intake during winter/spring. Correlations between δ 15 N and δ 34 S values, potentially meditated through amino acid metabolism, support this interpretation. Reasonable agreement between baleen isotope oscillations and regional baseline δ 15 N and δ 13 C variation also indicated foraging occurs within isotopically distinct food webs across the summer and winter ranges. We conclude that EC-WG bowhead whales forage throughout their distribution, and conservatively interpret δ 15 N and δ 34 S cycles to reflect reduced food consumption during winter. Foraging outside of periods of peak productivity likely contributes to annual metabolic requirements and winter habitat selection.