Color as an Assessment Signal in the Balck-Winged Damselfly, Calopteryx maculata (Beauvois)
Rockwell, Sarah M.
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Many ethologists are interested in assessment signals and their role in providing cues for aggressive and reproductive behaviors. Signals may be used by rival males to assess each other's fighting potentials, or by females to assess the fitness of a potential mate. Calopteryx maculata, the black-winged damselfly, is an ideal organism for studying animal signalling systems. Previous studies have shown that fat reserves in C. maculata are a good predictor of fight outcomes (Marden & Waage 1990, Marden & Rollins 1994). However, the published data are divided on the question of whether or not damselflies are able to assess relative fighting abilities in a contest (Marden & Waage 1990, Marden & Rollins 1994, Mesterson-Gibbons et al 1996). Fitzstephens & Getty (2000) were the first to notice that abdomen color could be a possible mechanism for assessment. They found that younger males with high fat contents were significantly bluer in color. In this study, we attempted to clarify the correlations they found between male color and factors related to fitness: age, fat content, health and social status. We also tried to answer the question of whether damselflies actually use this color cue as an assessment signal in conflict resolution or in mate choice. By observing a tagged population of damselflies over time, we found that male damselflies become progressively greener as they age. We also discovered a weak positive correlation between greener color and intensity of infestation by gregarine gut parasites. We found that copulating males were greener than the average for the general population, contrary to expectations. Though abdomen color has a seemingly high potential as an assessment signal, more studies must be done to provide strong evidence for it.