Sensitivity of amphibian embryos to timing and magnitude of present and future thermal extremes.

Ongoing climate change is increasing the frequency and intensity of extreme temperature events. Unlike the gradual increase on average environmental temperatures, these short-term and unpredictable temperature extremes impact population dynamics of ectotherms through their effect on individual survival. While previous research has predominantly focused on the survival rate of terrestrial embryos under acute heat stress, less attention has been dedicated to the nonlethal effects of ecologically realistic timing and magnitude of temperature extremes on aquatic embryos. In this study, we investigated the influence of the timing and magnitude of current and projected temperature extremes on embryonic life history traits and hatchling behavior in the alpine newt, Ichthyosaura alpestris. Using a factorial experiment under controlled laboratory conditions, we exposed 3- or 10-day-old embryos to different regimes of extreme temperatures for 3 days. Our results show that exposure to different extreme temperature regimes led to a shortened embryonic development time and an increase in hatchling length, while not significantly affecting embryonic survival. The duration of development was sensitive to the timing of temperature extremes, as early exposure accelerated embryo development. Exposure to temperature extremes during embryonic development heightened the exploratory activity of hatched larvae. We conclude that the timing and magnitude of ecologically realistic temperature extremes during embryogenesis have nonlethal effects on life history and behavioral traits. This suggests that species' vulnerability to climate change might be determined by other ecophysiological traits beyond embryonic thermal tolerance in temperate pond-breeding amphibians.

Underwater sound production varies within not between species in sympatric newts.

Sound production is a widespread phenomenon among animals. Effective sound use for mate or species recognition requires some acoustic differentiation at an individual or species level. Several species of caudate amphibians produce underwater sounds, but information about intra- and interspecific variation in their acoustic production is missing. We examined individual, sex, and species variation in underwater sound production in adults of two sympatric newt taxa, Ichthyosaura alpestris and Lissotriton vulgaris. Individual newts produced simple low- (peak frequency = 7-8 kHz) and mid-high frequency (14-17 kHz) clicks, which greatly overlap between sexes and species. Individual differences explained about 40-50% of total variation in sound parameters. These results provide foundations for further studies on the mechanisms and eco-evolutionary consequences of underwater acoustics in newts.

Genetic analysis of autosomal and X-linked markers across a mouse hybrid zone.

In this paper, we present results of the first comprehensive study of the introgression of both autosomal and sex-chromosome markers across the central European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and M. m. domesticus. More than 1800 individuals sampled from 105 sites were analyzed with a set of allozyme loci (hopefully representing neutral or nearly neutral markers) and X-linked loci (which are assumed to be under selection). The zone center is best modeled as a single straight line independent of fine-scale local geographic or climatic conditions, being maintained by a balance between dispersal and selection against hybrids. The width (w) of the multilocus autosomal cline was estimated as 9.6 km whereas the estimate for the compound X-chromosome cline was about 4.6 km only. As the former estimate is comparable to that of the Danish portion of the zone (assumed to be much younger than the central European one), zone width does not appear to be related to its age. The strength (B) of the central barrier was estimated as about 20 km; with dispersal (sigma) of about 1 km/gen(1/2), this means effective selection (s*) is approximately 0.06-0.09 for autosomal loci and about 0.25 for X-linked loci. The number of loci under selection was estimated as N= 56-99 for autosomes and about 380 for X-linked loci. Finally, we highlight some potential pitfalls in hybrid zone analyses and in comparisons of different transects. We suggest that conclusions about parts of the mouse genome involved in reproductive isolation and speciation should be drawn with caution and that analytical approaches always providing some estimates should not be used without due care regarding the support or confidence of such estimates, especially if conclusions are based on the difference between these estimates. Finally, we recommend that analysis in two-dimensional space, dense sampling, and rigorous treatment of data, including inspection of likelihood profiles, are essential for hybrid zone studies.