Zhifei Zeng ’23
Many animals have the ability to rapidly change color as a means to adjust to different environments, thermoregulate, and even communicate with other members of their species. This color adaptation is a complex subject, often related to environmental factors, animal behavior, visual perception, and cellular physiology. Specifically, for crustaceans living in intertidal systems where biological and environmental factors vary on multiple spatial and temporal scales, their color adaptation ability may be influenced by numerous environmental factors. A team of researchers from the University of Salford investigated the effects of spatial and temporal environmental diversity on the color-changing ability of the brown shrimp Crangon crangon.
The researchers began by calculating dark pigment cover (PiC), quantifying the percentage area of shrimp exterior covered by dark pigment. Then, they ran a series of three experiments. In one, the scientists tested if the presence of biorhythms and natural light effects coloration. Here, C. crangon were randomly divided between black and white beakers. The beakers were kept under natural light from 08:00 to 20:00 and moved to the dark from 20:00 to 08:00. The PiC results showed that the overall color of C. crangon was darker during the night and paler during the day, highlighting a clear rhythm. The researchers also conducted background matching experiments. They first estimated the initial PiC of shrimps, then varied both the color of the sediment and beaker sides. It was found that C. crangon coloration varied significantly with sediment color but not with beaker color, establishing a habitat limitation for adaptive shrimp coloration. In the final set of testing, one group of C. crangon was kept under black sediment and the other group alternated between white and black sediment every other day. After 3 weeks, shrimps exposed to dark backgrounds were darker and showed diminished color adaptation. On the contrary, shrimp that were exposed to daily switches between backgrounds maintained good background matching ability. This long-term adaptation result indicates that shrimp that use their color switching frequently have a competitive edge over the rest of the population.
In all, researchers concluded that temporal scales and habitat characteristics including light, sediment color, and sediment densities affect the coloration and background match of C. crangon. Adaptation to the correct color in a given environment is critical for survival, and determining the factors that influence animal color is a fundamental step in understanding the evolution of species.
 A. Siegenthaler, et al., Background matching in the brown shrimp Crangon crangon: adaptive camouflage and behavioural-plasticity. Sci Rep 8, 3292 (2018). doi.org/10.1038/s41598-018-21412-y
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