The evolution of crypsis in replicating populations of web‐based prey

Abstract

To investigate the evolution of background matching (crypsis) when prey are viewed against uniform and heterogeneous (alternating) backgrounds, we conducted some web-based experiments. Visitors to our experimental web site were rewarded for finding artificial prey, thereby providing a measure of their detectability. We first compared the ''survivorship'' of a range of pixilated prey phenotypes presented against both light green and dark green pixilated backgrounds and found clear evidence for a concave tradeoff curve, indicating that specialism on one or the other background would maximise their overall survivorship. We then compared the survivorship of a range of spotted prey phenotypes presented against backgrounds with small spots and large spots and found evidence for a more linear tradeoff curve, indicating that both intermediates and specialists would have approximately equal survivorship. Replicated evolutionary experiments were then conducted in which the survivors in any given system automatically reproduced themselves (subject to occasional mutation) when their population size was depleted to a critical threshold. Here close background matching readily evolved when prey were presented against a single uniform pixilated environment and when prey were presented against a single uniform spotted environment. As expected, the background matching that evolved in alternating light and dark green environments involved specialism on one or other background, and no intermediate forms evolved. By contrast, a more polymorphic range of phenotypes evolved in the alternating small and large spotted environments. To our knowledge this is the first time that automatically regenerating populations of web based prey have been set up to address evolutionary questions. Our findings have clearly shown conditions under which jack-of-all-trades cryptic forms survive poorly, and, although more work is needed, it may also help explain why background matching frequently appears so specialized in natural systems.

Concealed by conspicuousness: distractive prey markings and backgrounds

“…by having a coloration adapted to one particular patch type or by having a compromised coloration adapted to several patch types Distractive markings conceal prey M. Dimitrova et al 1909(Merilaita et al 1999Houston et al 2007;Sherratt et al 2007). Our results can be interpreted from this point of view as well.…”

Animal camouflage: current issues and new perspectives

“…First, matching a random sample of the background does not necessarily minimize the risk of detection when an animal is found on several backgrounds (cf. 'compromise camouflage'; Merilaita et al 1999Merilaita et al , 2001Houston et al 2007;Sherratt et al 2007). Second, the risk of detection can be decreased by disruptive markings, where the emphasis is on specifically breaking up tell-tale features of the animal.…”

Empirical tests of the role of disruptive coloration in reducing detectability

“…Human predators have frequently been used by researchers in studies of crypsis (e.g. Tucker & Allen 1993;Knill & Allen 1995;Glanville & Allen 1997;Sherratt et al 2007) and good qualitative concordance has been found between the performances of birds and humans when conducting simple discriminative tasks (e.g. Dittrich et al 1993;Beatty et al 2005).…”