Sex- and cohort-specific life-history strategies in Mongolian gerbils (Meriones unguiculatus)

- Information on life-history traits is crucial for understanding rodent evolution, ecology, and behavioral strategies.
- A seasonal cohort influence, instead of a sexual one, was found for five life history traits in wild Mongolian gerbils.
- This outcome is aligned with the sexual selective-monogamy system hypothesis and the adaptive switching of optimal decision.

Information on life-history traits is crucial for understanding rodent evolution, ecology, and behavioral strategies. Here, we report on the results from a 4-year study that collected data on the sexual and seasonal cohort (winter C1, spring C2, and summer C3) life-history traits of Mongolian gerbils (Meriones unguiculatus) maintained in a natural enclosure, using monthly live trapping, in Inner Mongolia (China). We found no sexual differences in the observed longevity, age of maturity, potential reproductive life span, or dispersal in the year of their birth, apart from a male-biased dispersal after gerbils overwintered as adults. Nevertheless, we did find cohort-specific life-history patterns in the above traits; for example, the C1 females matured at a significantly earlier age than did the C2 and C3 females, while the C3 gerbils commonly delayed their reproduction to the following year. Moreover, 21.7% of C1 and 6.1% of C2 females bred more than one litter, yet none of the C3 females did so during their birth-year breeding season. The average number of litters per female of C1 was greater than that of either C2 or C3 in their birth-year breeding season. Our results suggest that sex-specific life history traits may align with the predictions of sexual selection and the monogamy system hypothesis in Mongolian gerbils. In addition, the seasonal cohort-specific life-history traits revealed here lend support to the hypothesis of an adaptive switching behavior-from fast to slow development in the later-born gerbils-as opposed to the hypothesis of direct environmental limitation, although the slight inter-annual variation detected is consistent with the precipitation constraints.