UC Santa Cruz

Studies have shown that ontogenetic shifts in ecology often drive adaptive changes in the scaling of musculoskeletal systems, resulting in differential performance. These support the idea that allometric changes in morphology often co-occur with changes in feeding strategies, locomotor behavior or habitat use. Fewer studies, however, have compared the ontogenetic trajectories of functional traits across closely related species to better understand the extent to which such patterns of scaling may be specifically adaptive during a particular life history stage. A confound, however, is that phylogenetic information is inherently present in development; phenotypic evolution occurs via modification of ancestral development patterns. Thus, a phylogenetically-informed approach that makes comparisons among species’ ontogenetic scaling patterns can make important contributions to our understanding of morphological diversity among species. Presently, studies using such an approach are absent in the literature. I use the evolution of cleaning behavior as a model system to understand how ontogenetic scaling patterns contribute to macroevolutionary patterns of morphological and ecological diversity. I first identify general head and body characteristics that were associated with the evolution of cleaning: an elongate body paired with an elongate head, and a terminal mouth that allows jaws with low mobility to bite rapidly on individually-targeted prey items. My “phylo-allometric” analyses then enable me to show evidence that the repeated evolution of facultative and obligate cleaning (in which taxa continue to clean as adults) is associated with the maintenance of characters over ontogeny that are conducive to cleaning in the juvenile phase. On the other hand, taxa that transition away from cleaning during ontogeny do not maintain such characters, and exhibit phenotypic trajectories that are distinct from those of other wrasses. This indicates that the recurring evolution of juvenile cleaning behavior in the Labridae has involved similar effects on developmental scaling patterns. The repeated evolution of each of these patterns shows that labrid scaling trajectories are fundamentally labile and appear to evolve adaptively to changing ecological pressures over ontogeny.