Latitudinal cline of larval growth rate and its proximate mechanisms in a rhinoceros beetle

1. Juvenile growth rate is a key life-history trait with a major effect on various fitness components. Duration of the growing season changes with latitude, often resulting in latitudinal variations in growth rate. While many studies have shown a latitudinal cline of growth rate, most have used linear measurements of growth rate without considering the nonlinear nature of growth trajectories. Furthermore, elucidation of the proximate mechanisms causing increased growth rates would provide a fundamental understanding of the evolutionary process of the latitudinal cline of growth rates, which are largely unknown.

2. We used common garden experiments to examine the latitudinal variation of growth rate. We analysed the larval growth curve of 14 populations of the univoltine Japanese rhinoceros beetle Trypoxylus dichotomus (Coleoptera: Scarabaeidae) found along a 2000 km latitudinal gradient. In order to clarify the mechanisms responsible for the latitudinal cline of growth rate we compar...