Meeting Abstract
The link between morphological variation and divergence in niche space partly depends on functional significance of the trait in question. Flatfishes (Order Pleuronectiformes) possess novel morphological variation in the form of whole body asymmetry not seen in other vertebrates. If and how this trait affects ecological diversity within the order is not well understood. Asymmetry direction varies among species and to date there is little known of how direction might impact the function, ecological niche, and adaptive landscape of these fishes. Only seven of >800 species of flatfishes are polymorphic for direction of body asymmetry. Two derived congenerics (Platichthys stellatus; P. flesus) exhibit geographically variable frequencies of left- and right-eyed morphs, and there is evidence of ecological segregation between them. Unlike the geographically variable and unequal frequencies of asymmetry morphs of these derived species, asymmetry morphs of Psettodes erumei, a member of the basal family Psettodidae, are reported to be equal in frequency and yet robust reports of this are rare in the literature. This raises the question: is asymmetry polymorphism being maintained by similar evolutionary mechanisms among flatfish species? Here I tested if, consistent with the derived Platichthys sp., sidedness is associated with niche divergence within the basal species P. erumei. Fish were collected from four localities in Taiwan, Thailand, and Malaysia. Photographs were analyzed for body shape variation, and trophic level was assessed with stomach contents and stable isotope analysis. The degree of divergence between morphs in the basal species P. erumei was compared to that within derived species, and insights into the evolutionary mechanisms responsible are discussed.
