Abstract
ABSTRACTDynamic changes in body color are commonly used as a means of intraspecific communication and for crypsis. It is well established that subordinate fish signal to dominant fish by darkening their body color. Similarly, salmonids can adapt their body color to match their environment. What is not known is whether social interactions or environment plays a larger role in driving dynamic changes in body color, as these factors rarely occur in isolation. Experiments conducted in artificial stream channels with wild brook trout tested for the potential of color matching by varying light and dark substrates and included treatments with individuals as well paired cohorts to test for the effect of social hierarchies. Fish displayed a broad ability to adapt their coloration to match a range of substrates, with a strong preference for dark substrate. In paired trials, dominant fish matched light substrate more effectively while subordinates displayed darker coloration, resulting in subordinates being poorly matched to their surroundings. Mismatching the environment in order to send appropriate social signals could have negative consequences that further reduce fitness in subordinate fish.
Highlights
Visual displays allow territorial salmonids to communicate information about social status and to minimize costs of dangerous fighting (e.g. Keenleyside and Yamamoto 1962; Grosenick et al 2007)
When paired over light substrate, dominant fish displayed more effective color matching and resulted in mismatched coloration for the subordinate fish that displayed a dark body near a light substrate (Figure 3)
Our observations indicated that dominant fish chased the subordinate until they retreated to the opposite end of the channel, where they remained darkened despite being out of direct contact
Summary
Visual displays allow territorial salmonids to communicate information about social status and to minimize costs of dangerous fighting (e.g. Keenleyside and Yamamoto 1962; Grosenick et al 2007). Losers of territorial disputes display submissive darkening to avoid conflict with familiar dominants (H€oglund et al 2000; O’Connor et al 2000) and allowing for stable groups to form social hierarchies through cooperative signaling (Hurd 1997). Juvenile salmonids can rapidly alter their body color in response to light conditions and become more mottled when holding position close to the streambed (Jenkins 1969). Their bodies lighten at night (Hafeez and Quay 1970), and preference has been found for positioning over low reflectance (Donnelly and Dill 1984) and dark surfaces (Gibson and Keenleyside 1966; Hafeez and Quay 1970), especially in brook trout
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