Author: Thomas Madsen

Abstract

On several occasions during my many years of working with various snake species, I observed a significant positive relationship between body condition and head size (the former calculated from residual scores from a general linear regression of ln-transformed mass on ln-transformed snout-vent length). Based on results from my long-term study of water pythons (Liasis fuscus) this relationship is, however, most likely caused by a condition-dependent bias when recording snake snout-vent length (SVL). Water pythons in good condition were recorded as being "shorter" and hence having relatively larger head size, whereas snakes in poor condition were recorded as being "longer" with concomitant smaller head relative head size. Such a systematic bias may lead to spurious conclusions concerning the adaptive significance of the relationship between snake body condition and head size.

In: Amphibia-Reptilia
Authors: Jon Loman and Thomas Madsen

Abstract

A population of rainbow lizards (Agama agama) was studied in central Kenya. Rainbow lizards are able to rapidly change their colours. Dominant territorial males usually exhibited intensive bright colours. Dominant males were less intensively coloured when close to their territory border than in its center. Dominant males tolerated subordinate adult males in their territories. The colours of subordinate adult males were less intensive when these males were close to dominant males than when far from them. We interpret our findings in light of theories of sexual selection.

In: Amphibia-Reptilia
Authors: Thomas Madsen and Jon Loman

Abstract

Anuran sex ratio at breeding sites is typically male biased. Such sex ratios may be due to poor female survival, to females not breeding as frequently as males and/or to males becoming sexually mature earlier than females. In the present study, the first two factors are analyzed in a common toad (Bufo bufo) population in southern Sweden. Toads were captured, marked and recaptured at the breeding site during 5 years. Within season capture patterns were analyzed using the Jolly-Seber model and among-year captures using the Closed robust design model. Population estimates of males and females yielded an among year variation in breeding population sex ratio, ranging from 16% to 34% females. On average, 41% (proportion adult alive but not breeding) of the females skipped breeding seasons, whereas the corresponding estimate for males was less than 5%. Yearly survival averaged 42% for adult female and 63% for adult male toads. First year adult males and females had a lower survival rate than older toads. Our results demonstrate that both a female biased mortality rate and a higher proportion of skipped breeding in females contribute to the observed male biased sex ratio. However, a deterministic model suggests other factors may also be involved to obtain this degree of male biased sex ratio, the most likely being that females mature at a later age than male toads.

In: Amphibia-Reptilia

Abstract

The sequence diversity of the entire mitochondrial control region (CR) of three meadow viper (Vipera ursinii) populations was analysed and compared to previously documented nuclear genetic variability at the major histocompatibility complex (MHC) Class I loci. One of the populations, a small and inbred Hungarian population, exhibited no MHC polymorphism, whereas the two other, sampled from large viper populations in Ukraine, shoved very high MHC diversity. In spite of the great difference in population size and nuclear (MHC) diversity, all of the vipers from the three populations exhibited a CR haplotype diversity of zero. The dramatic discrepancy in nuclear vs. mitochondrial variability in the Ukrainian viper populations suggest that the lack of CR diversity was not caused by a population bottleneck, but rather by slow CR evolutionary rate, which has been documented in numerous other vertebrate taxa. Thus, due to the large taxonomic differences in CR rate of evolution, population genetic diversity estimates based on CR heterogeneity (and conservation management decisions that spring from those estimates) may depend as much upon the taxa being investigated, as upon the underlying pattern of genetic variation within the study population.

In: Amphibia-Reptilia