Easy life of males? Indirect evidence that growth is easier than egg production in mangrove-dwelling monitor lizards ( Varanus indices )

Abstract

In male-larger species of animals, males typically continue to grow after the age of female sexual maturation has been reached. Consequently, a switch of energy allocation occurs as the female investment from growth is shifted into egg production. We focus on the transitional period when both sexes heavily invest into anabolic processes; males invest in the development of body tissues while females predominantly invest in egg production. In captive mangrove- dwelling monitor lizards, we found that relative food intakes as well as quantitative estimates of anabolic processes (relative growth and egg production rates) are fairly comparable between the sexes. In spite of this biochemical clini- cal values and body condition indices revealed sex differences suggesting costs of reproduction in females. These results clearly illustrate that growth and egg production still substantially differ in associated physiological costs. This may be attributed to qualitative requirements (nutrients, minerals, etc.) of these processes. Our results correspond well with the higher susceptibility and mortality rates of females than males in many lizard species in captivity.