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Life-history trade-offs can mediate population declines following perturbations, and early reproduction should be favoured when adult survival is impacted more than juvenile survival. In Tasmanian devils (Sarcophilus harrisii), following the emergence of a transmissible cancer that caused steep population declines, females started to breed precocially (i.e. at age 1 instead of 2 years old). Here, using 18 years of mark–recapture data from a site where the disease was present (Freycinet Peninsula, Tasmania, Australia), we tested whether: (i) the probability of 1-yea-old females breeding continued to increase over time; (ii) there was a relationship between body size and breeding success for either 1-year-old or adult females; and (iii) there was inbreeding depression in breeding success for either age category. We show that the probability of 1-year-old females breeding did not increase between 2003 and 2021, and that the proportion of precocially breeding females remains at around 40%. We also show that there was no effect of skeletal body size on the probability of breeding, but heavier females were always more likely to breed. Finally, we found no evidence for inbreeding depression in breeding success. We discuss our results in the context of possible constraints by way of limitations to growth in the offspring of precocially breeding females. 

Abstract Resource competition among conspecifics is central to social evolution, as it serves as one of the primary selective pressures of group living. This is because the degree of competition for resources impacts the costs and benefits of social interactions. Despite this, how heterogeneity in resource competition drives variation in the type and quantity of long-term social relationships individuals foster has been overlooked. By measuring male mating competition and female foraging competition in a highly social, long-lived mammal, we demonstrate that individual variation in long-term intrasexual social relationships covaries with preferred habitat and experienced resource competition, and this effect differs based on the sex of the individual. Specifically, greater resource competition resulted in fewer social preferences, but the magnitude of the effect varied by both habitat and sex, whereas for social avoidances, both the directionality and magnitude of the effect of resource competition varied by habitat and sex. Together our work shows how fine-scale variation in individual socioecological niches (i.e., unique physical and social environments) can drive extensive variation in individual social behavior (here long-term relationships) within a population, thereby broadening current theories of social evolution. 

Abstract Emerging infectious diseases (EIDs) not only cause catastrophic declines in wildlife populations but also generate selective pressures that may result in rapid evolutionary responses. One such EID is devil facial tumour disease (DFTD) in the Tasmanian devil. DFTD is almost always fatal and has reduced the average lifespan of individuals by around 2 years, likely causing strong selection for traits that reduce susceptibility to the disease, but population decline has also left Tasmanian devils vulnerable to inbreeding depression. We analysed 22 years of data from an ongoing study of a population of Tasmanian devils on Freycinet Peninsula, Tasmania, to (1) identify whether DFTD may be causing selection on body size, by estimating phenotypic and genetic correlations between DFTD and size traits, (2) estimate the additive genetic variance of susceptibility to DFTD, and (3) investigate whether size traits or susceptibility to DFTD were under inbreeding depression. We found a positive phenotypic relationship between head width and susceptibility to DFTD, but this was not underpinned by a genetic correlation. Conversely, we found a negative phenotypic relationship between body weight and susceptibility to DFTD, and there was evidence for a negative genetic correlation between susceptibility to DFTD and body weight. There was additive genetic variance in susceptibility to DFTD, head width and body weight, but there was no evidence for inbreeding depression in any of these traits. These results suggest that Tasmanian devils have the potential to respond adaptively to DFTD, although the realised evolutionary response will critically further depend on the evolution of DFTD itself.