Diversity of reptile sex chromosome evolution revealed by cytogenetic and linked-read sequencing

Reptile sex determination is attracting much attention because the great diversity of sex-determination and dosage compensation mechanisms permits us to approach fundamental questions about mechanisms of sex chromosome turnover. Recent studies have made significant progress in better understanding diversity and conservation of reptile sex chromosomes, with however no reptile master sex determination genes identified. Here we describe an integrated genomics and cytogenetics pipeline,combining probes generated from the microdissected sex chromosomes with transcriptome and genome sequencing to explore the sex chromosome diversity in non-model Australian reptiles. We tested our pipeline on a turtle, two species of geckos, and a monitor lizard. Genes identified on sex chromosomes were compared to the chicken genome to identify homologous regions among the four species. We identified candidate sex determining genes within these regions, including conserved vertebrate sex-determining genes pdgfa,pdgfra amh and wt1, and demonstrated their testis or ovary-specific expression. All four species showed gene-by-gene rather than chromosome-wide dosage compensation. Our results imply that reptile sex chromosomes originated by independent acquisition of sex-determining genes on different autosomes,as well as translocations between different ancestral macro-and microchromosomes.We discuss the evolutionary drivers of the slow differentiation and turnover of reptile sex chromosomes.

Oxidative stress physiology in relation to life history traits of a free-living vertebrate:the spotted snow skink,Niveoscincus ocellatus

Recent research suggests that oxidative stress,via its links to metabolism and senescence,is a key mechanism linking life history traits such as fecundity and growth with survival;however,this has rarely been put under empirical scrutiny within free-living populations.Using a wild population of live-bearing skinks,we explored how plasma antioxidant activity(OXY),reactive oxidative metabolites(ROM),and the estimated oxidative stress index are associated with female and male life history.We found that male skinks have a significantly higher ROM and estimated oxidative stress index than female skinks,but this was not accompanied by a sex difference in mortality.Both sexes showed a non-linear association between OXY and age,indicating that the oldest and youngest individuals had the lowest OXY.Interestingly,female skinks with high OXY showed a decreased probability of survival to the following season.However,we found no significant associations between female reproductive investment(litter size or litter mass)or parturition date(i.e.metabolism)and oxidative status.Combined,our results offer mixed support for a role of oxidative stress in mediating life history traits and suggest that future studies need to explore oxidative stress during vitellogenesis in addition to using an intra-individual approach to understand the cost of reproduction and patterns of aging.

Multi-scale approach to understanding climate effects on offspring size at birth and date of birth in a reptile

Climate change is already impacting species around the world.Although most focus has been on the effect of temperature,changes in climatic variables other than temperature are also expected to drive biological change.Current models suggest that ectotherms,such as reptiles,will be strongly affected by climate change;however,data from natural populations are rare.Here,we use extensive data from 2 populations of a viviparous lizard(Niveoscincus ocellatus Gray,1845)at the climatic extreme of the species distribution.We examine the effects of climate at a local,a regional and a global scale(thus,integrating a suite of variables at different spatial and temporal scales)on 2 key life history traits:offspring date of birth and size at birth.Overall,our results show that across 9 years of study,local temperature had strong effects on the offspring date of birth but not on the size at birth.Therefore,a rapid increase in local temperature throughout the species range(as predicted under global warming scenarios)is likely to affect phenological processes with potential concomitant effects on offspring fitness and survival.