Ecomorphological Decoupling and Integration in Structures to Detect, Capture, and Process Food in Damselfishes

Abstract

Some of the most extensively studied phenotypic adaptations in reef fish pertain to trophic diversification. Within the Pomacentridae family, a strong correlation between head morphology and diet has been identified. The relationship between structures involved in food detection (eyes) and capture (mouth) has been demonstrated, prompting the question of whether pharyngeal jaws vary in an integrated manner with the eyes and mouth to detect, capture, and process food according to different trophic guilds. In this study, morphometric analyses were applied to X-rays of the 24 damselfishes of the eastern Pacific. A comprehensive database of dietary items for all species was constructed. The species were grouped according to their diet in trophic groups, which were tested on the morphometric data to determine ecomorphological groups. Six ecomorphological groups were determined: three benthic feeders, one benthopelagic, and two pelagic. Phylogenetic (phy) and nonphylogenetic (n-phy) modulatory analyses were conducted on the entire sample, three broad ecomorphological categories (phy-benthic, pelagic, pelagic–benthopelagic; n-phy, benthic, benthopelagic, pelagic), and the six specific ecomorphological groups (n-phy). Four modularity hypotheses were tested: three modules, the eye (E), mouth (M), and pharyngeal jaws (PJ), and two modules, PJ&E versus M, M&PJ versus E, and M&E versus PJ. Across all groupings, the hypothesis of three distinct modules was most strongly supported, followed by PJ&E versus M, with M&E versus PJ being the least supported. These findings suggest that the eye and mouth are more functionally decoupled than the pharyngeal jaws. It was evident that these structures exhibit a greater decoupling in benthic species than in benthopelagic and pelagic species. Our results indicate that different trophic groups show different levels of decoupling and integration in structures to detect, capture, and process food, and that, despite operating within a relatively narrow range of ecomorphological variation, damselfishes display a remarkable array of ecomorphological combinations.