Meeting Abstract
Body elongation is one of the most prominent axes of morphological diversity in vertebrates, especially bony fishes. Elongation is known to occur by reducing the secondary body axis (depth or width), increasing the length of the precaudal or caudal vertebral regions, or increasing the relative length of the head. However, it is not known whether some body regions change more often than others or what suites of anatomical changes underlie major shifts in elongation. In this study, we quantify the contribution of four anatomical components to diversification of body shape in 23 species of labyrinth fishes (Anabantoidei), a clade of Old World freshwater teleosts that range from deep-bodied to torpedo-like forms. We found that two major subclades—Anabantidae and Osphronemidae—overlap broadly in overall body shape and that this variation is a consequence of similar anatomical changes, even though these clades have been largely geographically separated during their evolution. Phylogenetically controlled multiple regression revealed that in both clades head shape independently explains the most variation in elongation, while lengthening of the abdominal and caudal vertebral regions are secondarily important. Moreover, the torpedo-shaped bodies of Luciocephalus pulcher (pikehead) and Luciocephalus aura, which represent the most elongate forms in the clade by far, result from exaggerated changes in the same anatomical features that drive shape variability across all labyrinth fishes. Altogether our results reveal a common anatomical basis for body shape diversity that is taken to the extreme in Luciocephalus. Our study also showcases an approach for identifying general mechanisms underlying elongation when looking across other teleost clades.
