Maternal effects and the evolution of aposematic signals

Abstract

Aposematic signals that warn predators of the noxious qualities of prey gain their greatest selective advantage when predators have already experienced similar signals. Existing theory explains how such signals can spread through selective advantage after they are present at some critical frequency, but is unclear about how warning signals can be selectively advantageous when the trait is initially rare (i.e., when it first arises through mutation) and predators are naive. When aposematism is controlled by a maternal effect gene, the difficulty of initial rarity may be overcome. Unlike a zygotically expressed gene, a maternally expressed aposematism gene will be hidden from selection because it is not phenotypically expressed in the first individual with the mutation. Furthermore, the first individual carrying the new mutation will produce an entire family of aposematic offspring, thereby providing an immediate fitness advantage to this gene.

Evolutionarily stable defence and signalling of that defence

“…However, many other authors assume that cryptic prey can in fact be highly defended (e.g. Harvey et al, 1982;Yachi & Higashi, 1998;Servedio, 2000;Speed, 2001;Brodie & Agrawal, 2001). In this work, we predict that in some cases (with high costs and/ or low predation risk) maximally cryptic prey will be undefended.…”

Aposematism: what should our starting point be?

“…Second, there is a better-known paradox of warning signals, which also emerges from commonly held assumptions about initial conditions. Ever since the seminal theoretical model of Harvey et al (1982), it is widely taken that aposematic mutants must emerge from defended cryptic species (Sillén-Tullberg & Bryant 1983;Sundberg 1987;Alatalo & Mappes 1996;Yachi & Higashi 1998;Lindström et al 1999;Servedio 2000;Brodie & Agrawal 2001;Speed 2001;Sherratt 2002;Sherratt & Beatty 2003;Thomas et al 2003;Franks & Noble 2004). When this is the case, new aposematic forms suffer combined and highly effective barriers to survival because of their rarity and their conspicuousness.…”

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

“…Since then, the functional role of warning colouration has been well demonstrated (Guilford 1990). However, the route by which aposematism evolved still poses an enigma (Lindström 1999;Mallet & Joron 1999;Brodie & Agrawal 2001;Sherratt 2002;Speed & Ruxton 2002;Santos et al 2003). The first brightly coloured individual in a population is likely to be detected by a predator and is therefore at greater risk than are its cryptic neighbours.…”