Increases in environmental temperature predicted to result from global warming have direct effects on performance of ectotherms. Moreover, cardiac function has been observed to limit the tolerance to high temperatures. Here we show that two wild populations of Atlantic salmon originating from northern and southern extremes of its European distribution have strikingly similar cardiac responses to acute warming when acclimated to common temperatures, despite different local environments. Although cardiac collapse starts at 21-23°C with a maximum heart rate of B150 beats per min (bpm) for 12°C-acclimated fish, acclimation to 20°C considerably raises this temperature (27.5°C) and maximum heart rate (B200 bpm). Only minor population differences exist and these are consistent with the warmer habitat of the southern population. We demonstrate that the considerable cardiac plasticity discovered for Atlantic salmon is largely independent of natural habitat, and we propose that observed cardiac plasticity may aid salmon to cope with global warming.

In a circumpolar wader, the dunlin (Calidris alpina), there are 11 named subspecies, but only five mitochondrial DNA (mtDNA) lineages have been found. In the present study, we investigated the genetic structure of dunlins in western Palearctic (from East Greenland to Taimyr peninsula) using DNA microsatellites and amplified fragment length polymorphism (AFLP) markers that may detect more recent differentiation than mtDNA. In this region, we consider four described subspecies; alpina, schinzii, arctica and centralis, together comprising two mtDNA lineages. We analyse seven polymorphic microsatellite loci and 91 AFLP markers in 287 and 152 unrelated individuals, respectively, originating from 17 populations. Neither microsatellites nor AFLPs reveal distinct groups that correspond to currently recognized subspecies. There is a clear pattern of isolation by distance in microsatellites. Our results do not contradict the former mtDNA results that there are two phylogenetic lineages (approximately corresponding to schinzii and centralis) that have met and formed a cline (alpina). We find no difference between schinzii and arctica (East Greenland). We conclude that, given the lack of distinct groups and the gradual changes in microsatellite allele frequencies, these markers provide little genetic support for the dunlin subspecies taxonomy in the western Palearctic.

Divergent sexual selection within allopatric populations may result in divergent sexual phenotypes, which can act as reproductive barriers between populations upon secondary contact. This hypothesis has been most tested on traits involved in precopulatory sexual selection, with less work focusing on traits that act after copulation and before fertilization (i.e., postcopulatory prezygotic traits), particularly in internally fertilizing vertebrates. However, postcopulatory sexual selection within species can also drive trait divergence, resulting in reduced performance of heterospecific sperm within the female reproductive tract. Such incompatibilities, arising as a by‐product of divergent postcopulatory sexual selection in allopatry, can represent reproductive barriers, analogous to species‐assortative mating preferences. Here, we tested for postcopulatory prezygotic reproductive barriers between three pairs of taxa with diverged sperm phenotypes and moderate‐to‐high opportunity for postcopulatory sexual selection (barn swallows Hirundo rustica versus sand martins Riparia riparia, two subspecies of bluethroats, Luscinia svecica svecica versus L. s. namnetum, and great tits Parus major versus blue tits Cyanistes caeruleus). We tested sperm swimming performance in fluid from the outer reproductive tract of females, because the greatest reduction in sperm number in birds occurs as sperm swim across the vagina. Contrary to our expectations, sperm swam equally well in fluid from conspecific and heterospecific females, suggesting that postcopulatory prezygotic barriers do not act between these taxon pairs, at this stage between copulation and fertilization. We therefore suggest that divergence in sperm phenotypes in allopatry is insufficient to cause widespread postcopulatory prezygotic barriers in the form of impaired sperm swimming performance in passerine birds.

Genetic studies have shown that extra-pair paternity is widespread among socially monogamous bird species. Yet, the role of males and females and their behavior leading to this mixed reproductive strategy is poorly understood. Here, we analyze paternity in relation to male age and mating behavior in the socially monogamous reed bunting (Emberiza schoeniclus). We report a positive relation between male extraterritorial forays and success in obtaining extra-pair fertilizations. Extraterritorial forays tended to increase in frequency with male age and older males sired a larger number of extra-pair offspring than young males. Identified extrapair sires were old in nine out of ten cases. The likelihood of being cuckolded was not affected by male age. Although based on correlative data, our results highlight age-dependent explorative male behavior as a key determinant for the understanding of extra-pair mating in the reed bunting. We do, however, emphasize the need for further studies to reveal the role of females in extrapair copulations and fertilizations.

The snowy owl (Bubo scandiacus) is a nomadic species with a circumpolar distribution. It has recently declined in the western Palearctic and may thus be worthy of special consideration for conservation. We investigated genetic structure in three well separated geographic regions within the snowy owls' breeding range. We sequenced two mitochondrial genes; the control region and cytochrome b, and two Z-chromosome introns; VLDLR-9 and BRM-15. We found no phylogeographic structure among the sampled regions, indicating high levels of gene flow in the recent past and possibly still today. Intra-population diversity did not vary between regions for the control region, but for Cyt b, North American birds had higher haplotype diversity than Scandinavian and eastern Siberian birds. Western Palearctic birds do not seem to be genetically deprived or inbred. Genetic diversity in the snowy owl was not lower than Scandinavian populations of three other owl species: tawny owls (Strix aluco), Tengmalm's owls (Aegolius funereus) and eagle owls (Bubo bubo).