Impaired mitochondrial function can lead to senescence and the ageing phenotype. Theory predicts degenerative ageing phenotypes and mitochondrial pathologies may occur more frequently in males due to the matrilineal inheritance pattern of mitochondrial DNA observed in most eukaryotes. Here, we estimated the sex-specific longevity for parental and reciprocal F1 hybrid crosses for inbred lines derived from two allopatric Tigriopus californicus populations with over 20% mitochondrial DNA divergence. T. californicus lacks sex chromosomes allowing for more direct testing of mitochondrial function in sex-specific ageing. To better understand the ageing mechanism, we estimated two age-related phenotypes (mtDNA content and 8-hydroxy-20-deoxyguanosine (8-OH-dG) DNA damage) at two time points in the lifespan. Sex differences in lifespan depended on the mitochondrial and nuclear backgrounds, including differences between reciprocal F1 crosses which have different mitochondrial haplotypes on a 50 : 50 nuclear background, with nuclear contributions coming from alternative parents. Young females showed the highest mtDNA content which decreased with age, while DNA damage in males increased with age and exceed that of females 56 days after hatching. The adult sex ratio was male-biased and was attributed to complex mitonuclear interactions. Results thus demonstrate that sex differences in ageing depend on mitonuclear interactions in the absence of sex chromosomes.

Background Patterns of gene expression can be dramatically different between males and females of the same species, in part due to genes on sex chromosomes. Here we test for sex differences in early transcriptomic response to oxidative stress in a species which lacks heteromorphic sex chromosomes, the copepod Tigriopus californicus. Results Male and female individuals were separately exposed to control conditions and pro-oxidant conditions (hydrogen peroxide and paraquat) for periods of 3 hours and 6 hours. Variance partitioning showed the greatest expression variance among individuals, highlighting the important information that can be obscured by the common practice of pooling individuals. Gene expression variance between sexes was greater than that among treatments, showing the profound effect of sex even when males and females share the same genome. Males exhibited a larger response to both pro-oxidants, differentially expressing more than four times as many genes, including up-regulation of more antioxidant genes, heat shock proteins and protease genes. While females differentially expressed fewer genes, the magnitudes of fold change were generally greater, indicating a more targeted response. Although females shared a smaller fraction of differentially expressed genes between stressors and time points, expression patterns of antioxidant and protease genes were more similar between stressors and more GO terms were shared between time points. Conclusions Early transcriptomic responses to the pro-oxidants H2O2 and paraquat in copepods revealed substantial variation among individuals and between sexes. The finding of such profound sex differences in oxidative stress response, even in the absence of sex chromosomes, highlights the importance of studying both sexes and the potential for developing sex-specific strategies to promote optimal health and aging in humans.

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A long-standing dogma in biology is that the ability to withstand stress is associated with longer life (Kirkwood & Austad, 2000). This is supported by overlap in the genetic bases for these two traits, including the roles of molecular chaperones, antioxidants, and genes involved in repair of oxidative damage (Landis et al., 2004;Vermeulen & Loeschcke, 2007). More direct evidence comes from artificial selection experiments, in which selection for longer life span increases resistance to stressors such as starvation, desiccation, ethanol, and high temperature (Scannapieco et al., 2009;Service et al., 1985), and selection for increased stress resistance (desiccation, starvation, and high temperature) also increases longevity (

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Understanding mechanisms of biological responses to environmental change is a central theme in comparative and evolutionary physiology. Here we analyzed variation in physiological responses to temperature, using 21 full-sibling larval families of the Pacific oyster, Crassostrea gigas. Pedigrees were confirmed with genetic markers for adult broodstock obtained from our breeding program. From these 21 larval families, 41 determinations of thermal sensitivity (Q10 values) were assayed for larvae of different sizes. For respiration, thermal sensitivity was consistent within a larval family during growth, but showed significant differences among families. Different Q10 values were evident among 21 larval families, with family accounting for 87% of variation. Specifically, four larval families maintained an increased thermal sensitivity for respiration (Q10 of 3). This physiology would confer resilience to rising temperature by matching the increased energy demand of protein synthesis (Q10 of 3 previously reported). For protein synthesis, differences in Q10 values were also observed. Notably, a family was identified that had a decreased thermal sensitivity for protein synthesis (Q10 of 1.7 cf. Q10 of 3 for other families), conferring an optimal energy allocation with rising temperature. Different thermal sensitivities across families for respiration (energy supply) and protein synthesis (energy demand) were integrated into models of energy allocation at the whole-organism level. The outcome of these analyses provides insights into the physiological bases of optimal energy allocation with rising temperature. These transgenerational (egg-to-egg) experiments highlight approaches to dissect components of phenotypic variance to address long-standing questions of genetic adaptation and physiological resilience to environmental change.