The variable colours of the fiddler crabUca vomerisand their relation to background and predation

Abstract

SUMMARY Colour changes in fiddler crabs have long been noted, but a functional interpretation is still lacking. Here we report that neighbouring populations of Uca vomeris in Australia exhibit different degrees of carapace colours, which range from dull mottled to brilliant blue and white. We determined the spectral characteristics of the mud substratum and of the carapace colours of U. vomeris and found that the mottled colours of crabs are cryptic against this background, while display colours provide strong colour contrast for both birds and crabs, but luminance contrast only for a crab visual system. We tested whether crab populations may become cryptic under the influence of bird predation by counting birds overflying or feeding on differently coloured colonies. Colonies with cryptically coloured crabs indeed experience a much higher level of bird presence, compared to colourful colonies. We show in addition that colourful crab individuals subjected to dummy bird predation do change their body colouration over a matter of days. The crabs thus appear to modify their social signalling system depending on their assessment of predation risk.

Color change and camouflage in juvenile shore crabs Carcinus maenas

“…The majority of work has concentrated on determining what changes to chromatophores and pigment dispersion occur when individuals are placed on different backgrounds, but rarely quantify the change in coloration that this causes (but see Hemmi et al, 2006). Much work has been undertaken on crabs in this regard (see discussion in Hemmi et al, 2006;Stevens et al, 2013), especially fiddler crabs (Uca spp.).…”

“…The majority of work has concentrated on determining what changes to chromatophores and pigment dispersion occur when individuals are placed on different backgrounds, but rarely quantify the change in coloration that this causes (but see Hemmi et al, 2006). Much work has been undertaken on crabs in this regard (see discussion in Hemmi et al, 2006;Stevens et al, 2013), especially fiddler crabs (Uca spp.). This has shown that color change can occur via day-night circadian rhythms (e.g., Atkins, 1926;Abramowitz, 1937;Brown and Sandeen, 1948;Fingerman, 1955;Fingerman and Yamamoto, 1967;Darnell, 2012), and that some species have the ability to change color with regards to the background (Brown and Sandeen, 1948;Rao et al, 1967).…”

“…This has shown that color change can occur via day-night circadian rhythms (e.g., Atkins, 1926;Abramowitz, 1937;Brown and Sandeen, 1948;Fingerman, 1955;Fingerman and Yamamoto, 1967;Darnell, 2012), and that some species have the ability to change color with regards to the background (Brown and Sandeen, 1948;Rao et al, 1967). Work by Hemmi et al (2006) has shown that fiddler crabs from populations with higher predation risk have lower levels of conspicuousness of their signaling patches (favoring greater concealment), and that simulating greater predation risk causes crabs to reduce their conspicuousness over a period of days.…”

The fiddler crabUca mjoebergiuses colour vision in mate choice

“…The walking legs, carapaces and chelae of ocypodid crabs, particularly the well-studied fiddler crabs (genus Uca), are often brilliantly coloured (Crane 1975). However, despite this array of colours and their likely role in social displays (Detto et al 2004(Detto et al , 2006Hemmi et al 2006), there is still some debate over whether ocypodid crabs are actually capable of colour vision and what role it might play. At least, two spectrally distinct classes of photoreceptor are required for colour vision (Goldsmith 1990) but the number possessed by fiddler crabs is still in question.…”

Relationship between colouration and body condition in a crab spider that lures pollinators

“…However, predator pressure can also directly affect prey colouration. For instance, the fiddler crab Uca vomeris can change its carapace from a bright to a dull colour over the course of a few minutes (Hemmi et al, 2006). Colonies of fiddler crabs that are highly exposed to bird predators have, on average, a duller colouration than less exposed colonies and there is evidence that individuals reduce their conspicuousness if the danger of predation is experimentally increased (Hemmi et al, 2006).…”