Surviving the change to warning colouration: density-dependent polyphenism suggests a route for the evolution of aposematism

Authored by E Despland, SJ Simpson

Date Published: 2005

DOI: 10.1007/s00049-005-0296-6

Sponsors: National Science and Engineering Research Council of Canada (NSERC) Royal Society

Platforms: No platforms listed

Model Documentation: Other Narrative

Model Code URLs: Model code not found

Abstract

How warning colouration first appeared remains a disputed question in evolutionary biology. A density-dependent transition from crypsis to aposematism that occurs during phase change in the desert locust (Schistocerca gregaria) provides insight into the conditions under which acquiring warning colouration is adaptive. When crowded for only a few hours, solitarious locusts cease avoiding each other and actively aggregate. This occurs well before they acquire warning colouration. We show that accompanying this early behavioural gregarisation is a remarkable shift in feeding behaviour, in which solitarious insects switch from being deter-red by a toxic plant alkaloid to feeding avidly upon foods containing it. A computer simulation shows how crypsis ceases to be effective as an anti-predator strategy when solitarious locusts are crowded, how chemical defence becomes essential as conspicuousness increases with local density, and how warning colouration becomes advantageous under these conditions. These findings provide empirical evidence for an adaptive route for the change from a cryptic edible phenotype to a brightly coloured toxic one.

Tags

insects Prey Desert locust Vegetation Phase-change Locust schistocerca-gregaria Initial evolution Gregariousness Signals Nymphs