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It is postulated that melanism in ectotherms is adaptive by enhancing thermoregulation, subsequent resource acquisition, and growth. Such effects may differ between the sexes as a result of the differential costs of self-maintenance and reproduction, but empirical support for the sex-specific consequences of melanism remains inconsistent. We studied the effects of melanism on body size and sex ratio in a population of the European grass snake (Natrix natrix) in SE Poland and also carried out a systematic review of the literature on the consequences of melanism in terrestrial snakes. Melanistic grass snakes of both sexes appeared to be smaller than the typical phenotype, which indicates higher predation pressure and minimal thermal benefits for black individuals. A female-biased sex ratio was observed in the typical phenotype, but not in melanistic snakes, suggesting that the costs for females and/or benefits for males are higher in melanistic individuals. In conjunction with earlier studies, our data indicate that the consequences of melanism may be related to the reproductive mode of species. In viviparous species, melanism tends to improve growth and/or body size and is more frequent in females, whereas the opposite holds for oviparous snakes. Further studies on melanism should examine a wider array of species with different reproductive strategies and traits beyond the usual thermal benefits.

Infectious diseases are influenced by interactions between host and pathogens in variable environments and are rarely homogenous across the landscape. Areas with elevated pathogen burden and transmission may indicate a disruption to steady-state disease dynamics. However, isolating processes that result in increases in infection prevalence and intensity remains a challenge. Here we elucidate the contribution of host species, and pathogen clade in disease hotspots. We examined broad-scale patterns of infection of O. ophidiicola, the pathogen that causes snake fungal disease, in 21 species of snakes across 10 countries in Europe. Disease hotspots were evident across several regions in Europe, and our analyses revealed significant differences in infection based on host species and pathogen clade. Over 80% of positive detections were from host species in the Natrix genus, indicating potential higher susceptibility in this group. The presence of O. ophidiicola genotypes that have been associated with more severe disease in North America, also resulted in high rates of infection compared to genotypes only described from Europe. Elevated infection prevalence was best explained by an interaction between host and pathogen identity which was not uniform across all species. More broadly, these findings present important mechanisms underlying disease hotspots across a disease endemic region.

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The present study considers the genetic structure and phylogeography of the smooth snake (Coronella austriaca) in Central Europe, as analyzed on the basis of 14 microsatellite markers and a 284-bp fragment of cytochrome b. We found deep divergence between western and south-eastern Poland, suggesting at least two different colonization routes for Central Europe, originating in at least two different refugia. The west/south-east divide was reflected in the haplotype distribution and topology of phylogenetic trees as defined by mitochondrial DNA, and in population structuring seen in the admixture analysis of microsatellite data. The well supported western European clade suggests that another refugium might have existed. We also note the isolation-by-distance and moderate-topronounced structuring in the examined geographical demes. Our data fit the assumption of the recently suggested sex-biased dispersal, in that we found a strong divide in the maternal line, as well as evidence for a small but existent gene flow based on biparentally inherited microsatellite markers. All studied populations were very similar in respect of allelic richness, observed and expected heterozygosities, and inbreeding coefficients. However, some genetic characteristics were different from those expected compared to a similar fine-scale study of C. austriaca from Great Britain. In the present study, we observed heterozygosity deficit, high inbreeding, and low GarzaWilliamson indices, suggesting a reduction in population size.