The importance of color in mate choice of the blue crab Callinectes sapidus

Abstract

SUMMARYVisual displays often play a large role in animal communication, particularly in sexual interactions. The blue crab Callinectes sapidus is both colorful and highly visually responsive, yet almost all studies of their courtship have focused on chemical cues. In the blue crabʼs underwater environment, however, visual cues may function more rapidly and over a longer distance than chemical cues. Given that blue crabs are aggressive and cannibalistic, visual cues may therefore allow blue crabs to quickly evaluate potential mates from safer distances. In the present study we show that courtship and mate choice behavior in C. sapidus can be stimulated by visual cues alone. Further, we show that males have a preference for females with red claw dactyls. In binary choice experiments, males displayed more often to photographs of females with red claws than to those with white claws or to those with black claws that were isoluminant to the red ones. This strongly suggests that male blue crabs made their choices based on the hue of the red claws, further suggesting that blue crabs are capable of color vision and use color in mate choice.

The male blue crab,Callinectes sapidus, uses both chromatic and achromatic cues during mate choice

“…Previous behavioral experiments have indicated that male blue crabs use chromatic cues when choosing a female mate by demonstrating male preference for red-clawed females over those with gray claws matched in relative luminance (Fig.6B) (Baldwin and Johnsen, 2009). It remained unclear, however, whether males would be capable of discriminating between female claw colors found in nature (Fig.1).…”

“…In addition, for easier comparison we normalized all crab-perceived luminance by the perceived luminance of the red test color used in the behavioral experiments described below, referring to this ratio as 'relative luminance'. To determine color as perceived by the blue crab eye, we assumed that color vision occurred via an opponency mechanism between the putative 440nm and a 508nm pigment in the blue crab eye (Martin and Mote, 1982;Baldwin and Johnsen, 2009). We used a simple model that assumes that the influence of the two pigments is balanced over the wavelength range of 400 to 700nm, i.e.…”

“…Most crabs made multiple stereotypic sexual displays that were unambiguously directed towards (and occurred within 5cm of) one of the two images. During these 5-30s displays, the crabs rose up on their walking legs, extended their claws, and waved their paddles while facing the photograph [see Baldwin and Johnsen (Baldwin and Johnsen, 2009) and number of displays, are given in supplementary material TableS1. We evaluated the statistical significance of choices for each variation of orange tested using two-tailed exact binomial tests.…”

“…However, these experiments did not control for the intensity of the colors used; thus, the responses may have been based on signal intensity rather than color. A more recent behavioral study demonstrated the blue crab's use of chromatic cues when males displayed a preference for images of red-clawed females over those of gray-clawed females that had the same luminance (as perceived by the blue crab eye) (Baldwin and Johnsen, 2009). Although males preferred red-clawed females to those with isoluminant gray claws, it was not determined how or whether male blue crabs can distinguish naturally occurring variations in the red and orange claw coloration of females.…”

Behavioral evidence illuminating the visual abilities of the terrestrial Caribbean hermit crab Coenobita clypeatus

“…Visual perception provides an important source of information for many animals to find food and mates, detect potential predators and threats, and notice changes in their surroundings (Baldwin and Johnsen, 2009;Kinoshita and Arikawa, 2014). Color and shape are two reliable and useful dimensions in visual signals.…”