Double-check in Lizard Age Estimation:Use of Phalanx Bone and Keratin Claw Sheath Lamellas

Dear Editor,The problem of age estimation in amphibians and reptiles with annual fluctuations of growth pattern has been considered to be mostly solved since the skeletochronological method was introduced(Kleinenberg and Smirina,1969).This method is based on counting the number of lines of arrested growth(LAGs)—cyclical growth marks that are usually formed annually and characterized by different optical aspects within the tubular bones.

Do Larger and Older Individuals Occupy Better Areas in the Colony of Qinghai Toad-headed Agamas?

Group living reduces the chances of predation.This is also true for burrowing animals,which use burrows as refuges to escape predators.Living in the center of a colony is the safest because it offers access to the greatest number of burrows;however,it is stressful due to frequent aggressive interactions there.We predicted that larger and older animals should occupy areas of a colony with a higher density of burrows than smaller and younger ones.To test this prediction,we observed individually marked Qinghai toad-headed agamas(Phynocephalus vlangalii)from a single colony late in the breeding season when females were gravid.Density of burrows was the highest and distance between them the shortest in the center of the colony.Aggressive encounters were more frequent in the central part of the colony than on its periphery.We found a negative correlation between body size and distance to the center of the colony for females,but not for males.There was no such correlation between age of individuals and distance to the center of the colony.Females in this species likely compete with other females and males for central burrows in the colony even after mating season finishes.We suggest that gravid females likely compete for the dense burrows within the central part of the colony mainly due to their relatively lower sprint speed and higher probability of being caught by a predator if they are not refuged in a burrow.

Natural history of Valentin’s rock lizard(Darevskia valentini) in Armenia

Valentin's rock lizard (Darevskia valentini) is suggested to be the pare nt for several parthenoge netic species (e.g., D. armeniaca, D. bendimahiensis, D. sapphirina, and D. unisexualis) that evolved through hybridization. Complex evolutionary processes (ineluding reticulate evolution) are occurring within the areas where Valentin' s rock lizard coexists with these and other rock lizards. Hence, a detailed biological specification of this species is important for understanding how vertebrates evolve. Valentin's rock lizard is a longlived (up to 9 years), small diurnal lizard with larger females than males, which is unlike other species of the genus. Their relatively large eggs and early reproducti on period, which occurs just after emerge nee from winter shelters, are adaptatio ns for living in a high elevation climate (higher than 2 000 m a.s.l.). Their body temperatures (31 -32℃) are comparable to body temperatures of rock lizards living in milder climates, though female body temperature is more depe ndent on substrate temperature and basking due to their lower activity than that found in males. Population density fluctuates from several individuals to several hundred per hectare and is not affected by parthenogen coexistenee, although hybrids do occur in sexually biased populations where males are more common than females. The male home range is larger than that of females, though these home ranges broadly overlap. Prey is not limited in the mountain meadows and Valentin's rock lizards feed on a great variety of arthropods. Infan ticide occurs in high-de nsity populati ons.

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 favored the deviation of reproductive behavior when species switched to interspecific mates.To date,at least 7 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 l,may have allowed the formation of hybrid karyotypes in rock lizards.Hybridization and polyploidization are 2 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.