Male-biased sexual size dimorphism in a little-known echolocating mouse, Typhlomys daloushanensis

Much remains to be established about the socio-ecology and mating system of the soft-furred tree mouse, the Typhlomys species, only genus of rodents confirmed to have evolved echolocation. In this study, we examined sexual size dimorphism (SSD) in T. daloushanensis to gain insight into its as yet unknown mating system. Sexual selection has been generally theorized to drive male-biased SSD among mammals, linked to male competitiveness in polygynous mating systems. We live-trapped 212 adults from Xingshan County in Hubei Province from 2021 to 2023 and supplemented this dataset with 67 individuals measured during a previous study. Our findings revealed a significant male-biased sexual size dimorphism, with males exhibiting notably greater body length (+ 4.3%) and body mass (+ 16.7%) compared to females. This suggests that the larger size may provide an advantage to male T. daloushanensis in competition for access to females (i.e., the Darwin-Bateman-Trivers paradigm), implying the likelihood of a polygynous mating system, although monogamous and promiscuous mating strategies should also be considered in future research. Additionally, ANCOVA analyses revealed that males had significantly longer ears and forefeet than females, beyond allometric scaling. This may indicate a functional basis to specific trait sexual dimorphism linked to differences in agility and auditory perception in this echolocation species. Our first report of male-biased SSD in T. daloushanensis suggests directions for future research to expand understanding of this little-known, echolocating mice, and adds further data on SSD in the Muroidea.