Hermit crabs (Pagurus bernhardus) use visual contrast in self-assessment of camouflage

Abstract

Animals can make use of camouflage to reduce the likelihood of visual detection or recognition and thus improve their chances of survival. Background matching, where body colouration is closely matched to the surrounding substrate, is one form of camouflage. Hermit crabs have the opportunity to choose their camouflage independently of body colouration as they inhabit empty gastropod shells, making them ideal to study their choice of camouflage. We used 3D-printed artificial shells of varying contrasts against a grey substrate to test whether hermit crabs prefer shells that they perceive as less conspicuous. Contrast-minimising shells were chosen for Weber contrasts stronger than -0.5. However, in looming experiments, animals responded to contrasts as weak as -0.2, indicating that while they can detect differences between shells and the background, they are only motivated to move into those shells when the alternatives contrast strongly. This suggests a trade-off between camouflage and vulnerability introduced by switching shells.

Polarization vision in terrestrial hermit crabs

“…The response of hermit crabs to visual stimuli was tested using an approach similar to previous studies on other crab species (How et al 2012(How et al , 2015Shragai et al 2017;Wilby et al 2018;Smithers et al 2019). Briefly, animals were tethered above a treadmill (for terrestrial species) or underwater over a slippery surface (for the marine species) so that they Fig.…”

“…To determine whether C. rugosus and C. brevimanus make use of the polarization of light, we determined their sensitivity to predator-like visual cues presented only in contrasts of polarization using an established playback assay (How et al 2012;Shragai et al 2017;Wilby et al 2018) and compared this to the polarization responses of a fully marine species, Pagurus bernhardus (Linnaeus 1758). To interpret our findings, we analysed the distribution of polarization cues in the visual habitats of the two terrestrial species by collecting footage with a polarization camera on the island of Mahé, Seychelles.…”

Enclosure Background Preferences Differ between Sexes and Color Morphs in the Gouldian Finch

“…The inability to camouflage with the background has been shown to cause stress and negative thigmotaxis in European cuttlefish ( Sepia officinalis ) [ 30 ] and stress, atypical behavior, and weight loss in African clawed frogs ( Xenopus laevis ) [ 31 ]. When given the choice, hermit crabs ( Pagurus bernhardus ) prefer shells that match the background [ 32 ], desert tortoises ( Gopherus agassizii ) preferentially rest next to rocks where they are more difficult to detect [ 10 ], and Gouldian finches ( Chloebia gouldiae ) prefer green over white backgrounds, which matches their color better [ 33 ]. Both 2D [ 30 , 33 ] and 3D backgrounds (e.g., [ 31 ]) are effective.…”

Polarization contrasts and their effect on the gaze stabilization of crustaceans

“…A common method for investigating objectbased motion vision is to expose animals to looming stimuli to elicit a startle response. By varying the parameters of computer-generated, two dimensional stimuli and tracking stereotypical defence and/or avoidance behaviours, thresholds of moving object detection can be determined, as shown in prior work on mammals (Maier et al, 2004;Yilmaz and Meister, 2013), fish (Pignatelli et al, 2011;Preuss et al, 2006), amphibians (Yamamoto et al, 2003), insects (Fotowat et al, 2009;Gabbiani et al, 1999;Rind and Simmons, 1992), cephalopods (Pignatelli et al, 2011;Temple et al, 2012) and crustaceans (Basnak et al, 2018;How et al, 2012Oliva et al, 2007;Wilby et al, 2018).…”