Active background choice facilitates crypsis in a tropical crab

Abstract

Animals can evade predators in multiple ways, one of the most effective of which is to avoid detection in the first place. We know much about the evolution of color patterns that match the visual background to avoid detection (i.e., crypsis), yet we know surprisingly less about the specific behaviors that have co‐evolved with these morphological traits to enhance or maintain crypsis. We here explore whether the match between body color and background in a seemingly well‐camouflaged tropical shore crab is a result of active background choice. Taking advantage of a coastal area in the Solomon Islands with variable sand color and a population of the pallid ghost crab Ocypode pallidula with varying carapace color, we experimentally tested whether individuals actively choose specific substrate that best matches their color patterns. We found that individuals taken from extreme sand colors chose substrate that maintained crypsis, with relatively darker crabs typically choosing dark sand and lighter crabs choosing light sand. Crabs of intermediate color pattern, in contrast, showed no clear preference for dark or light sand. Our results suggest that potential prey can actively choose specific backgrounds to enhance and maintain crypsis, providing insights into how behavior interacts with morphological traits to avoid predator detection.

Improved camouflage through ontogenetic colour change confers reduced detection risk in shore crabs

“…This is seemingly in contrast with the results here. However, there is growing evidence in many animal taxa including crabs that individuals of different appearance from within a species choose where to rest in order to improve camouflage in their respective habitats (Kang, Moon, Lee, & Jablonski, 2012;Kettlewell & Conn, 1977;Kjernsmo & Merilaita, 2012;Lovell, Ruxton, Langridge, & Spencer, 2013;Marshall, Philpot, & Stevens, 2016;Sargent, 1966;Uy et al, 2017; reviewed by Stevens & Ruxton, 2018). Otherwise, it is hard to explain very local level phenotype-substrate associations of crabs without the role of behavioural background selection (Nokelainen, Hubbard et al, 2017;Nokelainen, Stevens, & Caro, 2017;Todd et al, 2012 Note.…”

The Role of Life-History and Ecology in the Evolution of Color Patterns in Australian Chrysomeline Beetles

“…Together with our findings that red pattern does not differ with beetle length, this suggests that the less common adoption of a typical conspicuous color, red, by polyphagous species, could be to limit conspicuousness when they feed on diverse backgrounds. Recent studies of lizards (Marshall et al, 2016) and crabs (Uy et al, 2017) indicate that animals actively choose to match their background. As the spectral sensitivities of chrysomelids appear to be limited to UV, blue and green but not red (Sharkey et al, 2017), active background matching may not fully explain color pattern differences of beetles with their host plant.…”

The key role of behaviour in animal camouflage

“…Likewise, work on ghost crabs by Uy et al . () showed that darker and lighter crabs preferred darker and lighter backgrounds, respectively. However, these crabs were also much more likely to originate from darker and lighter sandy parts of the beach, respectively, meaning that they could have imprinted on their original background.…”

“…Recent work by Uy et al . () showed that lighter and darker individual pallid ghost crabs ( O. pallidula ) choose light and dark sand, respectively, in behavioural trials, whereas intermediate crabs show no preference.…”

“…can also adjust their coloration and brightness over hours to match the beach environment better (Stevens, Pei Rong & Todd, 2013). Recent work by Uy et al (2017) showed that lighter and darker individual pallid ghost crabs (O. pallidula) choose light and dark sand, respectively, in behavioural trials, whereas intermediate crabs show no preference.…”