An empirical study of the evolutionary significance of cannibalism in tree-hole mosquitoes (Diptera : Culicidae) from ecological and biological perspectives

Abstract

To be adaptive, optimality theory suggests that behavioural traits should maximise the fitness of the carrier by spread of genotypes through a population. Expression of these traits are expected to vary with biological and ecological factors modifying fitness consequences. This study investigates the consequences of such factors to the dynamics of cannibalism in aquatic larvae of three tropical tree-hole mosquitoes, Aedes aegypti, Trichoprosopon digitatum and Toxorhynchites moctezuma and examines the adaptive nature of cannibalism in the context of these findings.1. Expression and rate of cannibalism varied with food and density levels in A. aegypti. When food limits development, a greater percentage cannibalise and at a higher rate. At high larval density, a higher proportion cannibalise, but at a comparatively lower rate, probably due to physical interference of feeding. No nutritional benefits of cannibalism were reflected in adult fitness parameters of size and development time. 2. No fitness consequences, in terms of adult size and development time, were detected at intermediate food levels, between T. digitatum larvae allowed and larvae prevented from cannibalising, despite recurrent cannibalism. 3. Comparison among clutches of T. digitatum revealed a significant variation in propensity to cannibalise. 4. Inter-species comparison of cannibalism in kin and non-kin situations revealed no evidence kin selection, despite disparity in expected benefits amongst species and seemingly obvious fitness advantage to T. moctezuma. 5. The adaptive significance of cannibalism is considered in the light of these discoveries. Anomalies can be explained by viewing cannibalism as a strategy, representing a trade-off between relative costs and benefits in particular ecological and biological conditions, and conflict with other behavioural strategies such as oviposition and predator avoidance, which maximises reproductive success. Focused empirical studies provide a powerful tool for identifying anomalies and generating refutable trade-off hypotheses. 6. Population and community level consequences of cannibalism are examined together with their probable epidemiological implications.