The ontogeny of sexual dimorphism in cane toads ( <i>Rhinella marina</i> )

Abstract Determining an individual’s sex early in life may clarify fundamental issues such as progeny sex ratios and sex-based divergences in ecology and behaviour prior to maturity and be useful in captive breeding of endangered species or in developing methods to control invasive pests by skewing offspring sex ratios. We measured morphological traits in captive-raised cane toads (Rhinella marina) at intervals from metamorphosis to more than 2 years of age, at which time we could reliably score each individual’s sex and hence, quantify the ontogenetic development of sexually dimorphic traits during juvenile life. Discriminant function analysis of 11 morphological traits (involving body size and dimensions of limbs, feet and parotoid glands, but not including sexually dimorphic traits expressed only in adults) correctly predicted sexes of around 70% of toads in a cohort ranging from 161 to 400 days of age, increasing to 95% in the oldest cohort. Despite the scarcity of research on this topic, published data on anurans reveal interspecific diversity: males and females diverge morphologically during juvenile life in some species but not others.