Temperature and senescence in frogs and toads
In a study published in PNAS in 2021 (https://doi.org/10.1073/pnas.2112235118), we have examined whether the average climatic conditions (temperatures and precipitation totals averaged over 30 years) experienced by populations influence the senescence rate in four species of anurans in North America (Anaxyrus boreas and Rana luteiventris) and Europe (Bufo bufo and Rana temporaria). We used long-term capture-recapture data from 20 populations comprising a total of 35,575 marked individuals. We generated age-dependent mortality curves from which senescence rates were estimated. The analyses showed that the rate of senescence increases with temperature in the four species of anurans (for Anaxyrus boreas and Rana luteiventris see Figure 1). Conversely, average precipitation has a marginal effect on the rate of senescence. In addition, temperature produced an inversion of the sex bias of the rate of senescence in Rana luteiventris. This study provides the first empirical evidence of the influence of temperature on senescence in natural populations.
Sex chromosome systems and senescence in amphibians
In paper recently published in Evolution (https://doi.org/10.1111/evo.14410), we examined the influence of the sex chromosome system on intersex differences in senescence rates. We used amphibians, a clade containing both XY and ZW sex chromosome systems, as biological models to test the hypothesis that heterogametic sex undergoes stronger senescence than homogametic sex. This phenomenon is potentially caused by the accumulation of deleterious variants in non-recombinant sex-linked genomic regions in XY males and ZW females. To address this question, we generated sex-specific mortality curves and senescence rates (see Figure 2) for 36 species from a global dataset comprising 56,207 marked individuals. Our results showed that in both XY and ZW systems, the heterogametic sex (XY male and ZW female) exhibits a higher rate of senescence on average. Although the mechanisms at work (Y-Toxic hypothesis or X-Unguarded hypothesis) still remain to be elucidated, this study provides the first empirical evidence of the influence of the sex chromosome system on sex differences in actuarial senescence.
Epigenetic variation and life history strategies in a marine fish
In a submitted manuscript, we examined associations between whole genome DNA methylation and environmentally-driven life history variation in two lineages of a marine fish, the capelin (Mallotus villosus), from North America and Europe. In both lineages, capelin harbour two contrasted life history strategies (demersal vs. beach-spawning strategies). Performing whole genome and methylome sequencing, we showed that life history strategies are more strongly associated with epigenetic changes than with variation in DNA sequence. Genetic differentiation between the capelin harbouring different life history strategies was negligible, but we found parallel genome-wide methylation changes across lineages. We identified 1,067 differentially methylated regions (DMRs) comprising 15,818 CpGs, with 22% of them located within 5-kb around genes comprising promotor regions. Strikingly, all DMRs were hypermethylated in demersal-spawning individuals. Our results suggest that environmental variation causes important parallel epigenetic changes that are associated with contrasted life history strategies in lineages with divergent genetic backgrounds. Our study emphasizes the potential role of genome-wide epigenetic variation in organisms’ adaptive responses to environmental variation.