Age cohort definition and evidence of sexual dimorphism in the Southern Hairy-nosed Wombat (Lasiorhinus latifrons), a large Australian marsupial.

Abstract

The ability to reliably differentiate age cohorts and detect and quantify sexual dimorphism in wildlife species is crucial before performing many ecological and biological analyses, including population demographics and commonly used body condition indices. In many wildlife species, however, these analyses are limited by a lack of detailed and reliable data. We used a long-term data set (>30 years and >2,600 individuals) to establish a method to reliably differentiate juvenile, subadult, and adult southern hairy-nosed wombats (Lasiorhinus latifrons) and provide evidence of sexual dimorphism in this species. Adult and subadult males were separated primarily through measurements of head width and head length, based on measurements from confirmed adult males (n = 160). We found adult males to have significantly longer (P-value = 4.374e^-16) and wider (P-value = 2.2e^-16) heads than adult females and a significantly longer pes length (P-value = < 2.2e^-16). This divergence appears to occur when subadult males are approaching adulthood. However, no difference in body weight or total body length was observed between the sexes. Using these data, we established approximate size ranges for wombats of all age cohorts to underpin future research on the impacts of rainfall and drought on body condition, breeding, recruitment, and survival in this semiarid dwelling species. This research also highlights the importance of separating the sexes for analyses involving body measurements even when the species does not display obvious dimorphism.