What has happened to the females? Population trends in the Aesculapian snake at its northern range limit

Evolution of parthenogenetic reproduction in Caucasian rock lizards: A review

Despite numerous works devoted to hybrid origin of parthenogenesis in reptiles, the causes of hybridization between different species, resulting in the origin of parthenogenetic forms, remain uncertain. Recent studies demonstrate that sexual species considered parental to parthenogenetic rock lizards (Darevskia spp) avoid interspecific mating in the secondary overlap areas. A specific combination of environmental factors during last glaciation period was critical for ectotherms, which led to a change in their distribution and sex ratio. Biased population structure (e.g., male bias) and limited available distributional range favoured the deviation of reproductive behaviour when species switched to interspecific mates. To date, at least seven diploid parthenogenetic species of rock lizards (Darevskia, Lacertidae) originated through interspecific hybridization in the past. The cytogenetic specifics of meiosis, in particular the weak checkpoints of prophase I, may have allowed the formation of hybrid karyotypes in rock lizards. Hybridization and polyploidization are two important evolutionary forces in the genus Darevskia. At present, throughout backcrossing between parthenogenetic and parental species, the triploid and tetraploid hybrid individuals appear annually, but no triploid species found among Darevskia spp on current stage of evolution. The speciation by hybridization with the long-term stage of diploid parthenogenetic species, non-distorted meiosis, together with the high ecological plasticity of Caucasian rock lizards provide us with a new model for considering the pathways and persistence of the evolution of parthenogenesis in vertebrates.

Decline in body size and female fraction in the grass snake (Natrix natrix, Linnaeus 1758) population after 40 years (Southern Poland)

Depletion of free-living populations is often associated with changes in fitness-related traits, e.g., body size. Ongoing decrease in body size has been reported in most vertebrates, but reptiles remain understudied. Moreover, sexual size dimorphism, commonly observed in reptiles, indicates that environmental pressures on body size may appear sex-specific. This can also result in shifts in sex ratio, an aspect even less studied. We investigated body size and sex ratio in population of grass snake (Natrix natrix) surveyed over 40 years ago in comparison with the current state. We found that both sexes express similar magnitude in body size decline. The current sex ratio does not deviate from 1:1, while in the past, females outnumbered males. The observed changes are likely an outcome of several non-mutually exclusive factors. In the studied area, an increase in road traffic and human presence and a drop in prey availability have been documented. Both factors may exert higher pressure on larger individuals, particularly females, due to their high costs of reproduction. It is recorded here that increase in ambient temperatures and summer duration may additionally enhance the mortality risk and resource requirements. Shifts in body size and sex ratio can catalyze further declines in abundance and reproductive potential of the population.