Delayed mortality of males in Thylamys bruchi, a semelparous marsupial from the Monte Desert, Argentina

Abstract

Male-only obligate semelparity is a well-studied reproductive strategy in some Australian marsupials. This strategy has not been documented in South American species, although semelparity in both sexes occurs in some Neotropical didelphids. The fat-tailed mouse opossum, Thylamys bruchi, is an endemic species of the temperate Monte Desert, in Argentina. Seasonality and predictability of resources are two of the attributes associated with habitats where marsupial semelparity has evolved, and both are characteristic of the Monte Desert. We aimed to characterize the life-history strategy of T. bruchi to explore if it can be considered a semelparous species. We studied a fat-tailed mouse opossum population for 7 years with two different capture techniques (Sherman traps and nest boxes). Thylamys bruchi showed strong seasonality in abundance, with the highest captures during summer and autumn. Reproduction and weaning coincided with the most favorable period of the year with respect to climate and resource availability. Every year we observed a single cohort with little overlap until weaning of young. After breeding, all adults disappeared from the population; however, unlike any other didelphids, males showed delayed mortality and died, along with females, after weaning. We found no evidence of survival to a second breeding season for either sex. We therefore propose T. bruchi as a desert-dwelling marsupial with a semelparous reproductive strategy. Because the severity of winters may be acting as an important constraint on the energetic balance of adults in this population, we propose that challenging climatic conditions, coupled with the seasonality and high predictability of food resources, may have contributed to the evolution of the extreme reproductive strategy in this didelphid marsupial.

A TEST OF SEMELPARITY IN THE LONG-TERM POPULATION MONITORING OF THE MARSUPIAL Marmosops incanus (DIDELPHIMORPHIA, DIDELPHIDAE)

“…We found a decline in survival with the beginning of the reproductive activity, with small diff erences between sexes. The disappearance of both males and females had been observed in other didelphid species, such as M. paulensis (Leiner et al 2008), Monodelphis dimidiata (Pine et al 1985, Baladrón et al 2012, Gracilinanus agilis (Lopes & Leiner 2015), and Thylamys bruchi (Albanese et al 2021), although there is variation in this pattern. In a population of G. agilis, for example, a small proportion of males survived to a second breeding season, and they were considered partially semelparous (Martins et al 2006).…”

“…In a population of G. agilis, for example, a small proportion of males survived to a second breeding season, and they were considered partially semelparous (Martins et al 2006). In the case of T. bruchi, males showed delayed mortality and died after weaning, similar to females, but without any sign of second breeding due to severe winters (Albanese et al 2021).…”

“…Some studies claim the semelparous strategy and its variants (partial and facultative semelparity) for some species of the family Didelphidae (review in Zangrandi & Vieira 2022). The research on semelparity in didelphid marsupials suggests that both male and female individuals exhibit reduced survival following reproduction, although males may experience comparatively higher mortality than females (Lorini et al 1994, Martins et al 2006, Leiner et al 2008, Baladrón et al 2012, Barros et al 2015, Lopes and Leiner 2015, Albanese et al 2021.…”