Meeting Abstract
True eels (Anguilliformes) are characterized by a distinctive elongate morphology. Ichthyologists have informally, by utilizing the term “eel” in common names, identified a number of additional lineages with this morphology (e.g., “electric eels”, “swamp eel”). The apparent ubiquity of the “eel morphotype” has led researchers to search for common selective pressures towards elongation. However, a quantitative study of the degree to which this frequency requires adaptive explanations has never been conducted. Here we use a multi-dimensional database of body shape in teleost fishes to address the following questions: besides elongation, are there other distinctive morphological characteristics of true eels? Do other “eel-like” fishes occupy the same region of shape space as true eels? How many times have lineages invaded this region of shape space, and is this greater than expected without adaptive evolution? Besides being relatively long, true eels are also characterized by flat heads, narrow mouths, and tall caudal peduncles (relative to the rest of the fish). Few “eel-like” lineages occur within the region of shape space defined by true eels, but many are close to this region. Overall, 23 lineages have invaded the “true eel region” of shape space; this is not significantly greater than the number expected under a non-adaptive BM model. Thus the eel body plan, while distinctive, appears fairly easy to access. Although the various lineages which have adopted this form have probably done so for adaptive reasons, our results provide no evidence that a single explanation (e.g., evolution towards a single adaptive peak) is necessary to account for the diversity of “eel-like” teleosts.
