When love is blind Vision constrained by molting during mating in the female blue crab

Meeting Abstract

89.5  Friday, Jan. 7  When love is blind: Vision constrained by molting during mating in the female blue crab BALDWIN FERGUS, J.L.*; JOHNSEN, S.; Duke University; Duke University jlb54@duke.edu

In the blue crab, Callinectes sapidus, mating is timed to the females’ pubertal molt. Mate attraction, courtship, and selection occur in the days prior to the females’ molt and use a combination of visual and chemical cues. Previously, we have shown that males can choose females based on color cues alone, preferring females with red claws. In similar laboratory experiments, females did not respond to visual cues. Considering the physiological stress of molting, we hypothesized that vision may be reduced in molting crabs. In the 7-10 days before molting, a new cuticle forms beneath the crab’s exoskeleton, gradually separating from the old exoskeleton. This occurs even in the eyes of the crab, where the chitin exoskeleton functions as a component of the lens of the eye. The separation of the existing exoskeleton and the newly forming cuticle may limit vision in a molting crab by disrupting the incoming light path. We investigated the possible changes in blue crab vision during the molting process, using behavioral and morphological assays. Visual acuity was estimated by using the optomotor response to moving stripes of varying widths. Four days prior to molting, visual acuity averaged 1.7º ±0.034 (mean ±SE) and decreased steadily to 21.4º ±3.6 in the final 24 hours before molting. Recovery after molting was similarly steady. Measurements taken within 24 hours of molting averaged 17.1º ±2.9 and increased to 1.83º ±0.14 by day 6 (close to pre-molt values). Noticeable changes in eye morphology were documented by sectioning fixed eyes at various molt stages and photographing them under a stereoscope. Overall, our results show a severe decrease in visual acuity during the molting period, which may preclude the use of visual cues during mating and explain the presence of multimodal cues in the female blue crab.

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