Meeting Abstract
East African cichlids exhibit one of the most impressive adaptive radiations, and pivotal to this are species-specific craniofacial structures that allow ecological specialization. In order to understand the developmental origins for this morphological variation, we examined the growth trajectory for three aspects of craniofacial shape from the onset of osteogenesis through juvenile stages using geometric morphometrics. Specifically, we assessed variation in lateral, ventral, and lower jaw shape in six species (n>350 individuals) of Lake Malawi cichlids that span a major ecomorphological axis that distinguishes species that forage from the water column (pelagic) and those that feed from the rocky substrate (benthic). We find that, despite drastic differences in adult craniofacial morphologies, there is striking conservation in the direction of craniofacial ontogeny, suggesting that natural selection is working within a conserved developmental program. However, we also note species-specific differences in the timing and/or duration of particular trajectories (e.g., paedomorphism). Previous work in cichlids and other systems suggests that species-specific differences in adult morphology are due to changes in molecular signaling pathways that regulate early craniofacial development. In support of this, we demonstrate that modulation of Wnt signaling at early stages has discrete effects over extended periods of development, and can shift a developmental trajectory into morphospace normally occupied by another species. However, craniofacial shape recovers by juvenile stages, which underscores the idea that craniofacial development is robust and that adult head shapes are the product of many molecular changes acting over extended periods of development.
