Genetic monogamy in high density populations of a threatened Mediterranean rodent

Monogamous mammal species often exhibit flexible mating strategies in response to socio-ecological factors such as population density, though the extent of this flexibility remains unclear. In this study, we investigated the genetic mating system of the Cabrera vole (Microtus cabrerae) in high density habitat patches from Extremadura (Spain), assessing whether it aligns with or deviates from the genetic monogamy previously found in low-density populations (< 20 individual/ha). Using genetic non-invasive sampling of vole faeces combined with spatial capture-recapture modelling, we first obtained precise estimates of population density. We then evaluated whether Cabrera voles display alternative mating tactics in these high-density patches by means of space use and parentage analysis. Results indicated that, even under unusually high population densities (> 90 individuals/ha), Cabrera voles exhibit genetic monogamous mating system, contrasting with the density-dependent variations often observed in other socially monogamous species. This suggests that Cabrera voles may have limited flexibility in their reproductive behaviours, potentially influenced by life-history traits such as strong pair-bonds, paternal care, and low levels of sperm competition, which likely promote paternity assurance and reduce the chances of extra-pair mating. These traits probably evolved in response to the limiting conditions that semi-arid Mediterranean environments impose to herbivores, influencing the most optimal mating strategies to the successful rearing of offspring. Overall, our findings highlight that not all monogamous mammal species exhibit flexibility in their mating strategies in response to population density. In the case of the Cabrera vole, being a near-threatened Iberian endemism, the predominance of genetic monogamy may increase its vulnerability to land-use and climate changes, given this mating strategy is generally associated with lower effective population sizes and overall genetic diversity. Conservation efforts for Cabrera voles should thus focus on preserving large and stable habitat patches, while improving landscape connectivity to mitigate potential population and genetic bottlenecks, and enhance the long-term viability of extant populations.