Meeting Abstract
Teleosts typically have a lower jaw comprised of three fused bones: the dentary, angular, and articular. However, several unrelated teleosts have an independently derived “extra” joint between the angular and dentary: the intramandibular joint (IMJ). This decoupling of bones allows the dentary to rotate about the angular, allowing for a wider gape. Little is known about the evolution of the IMJ or its ontogenetic construction, though the Meckel’s cartilage is the foundation of the joint. Poecilia spp. possess an IMJ, thus we studied the development of the jaw in Poecilia larvae to hypothesize the evolutionary construction of the IMJ. Specifically, we focused on the developmental changes to Meckel’s cartilage. If Meckel’s cartilage is the foundation for the IMJ, then ontogenetic changes in it could be an indicator of how the IMJ is constructed. Importantly, the cellular morphology of Meckel’s cartilage in Poecilia spp. is non-homogenous and we asked how this changes over ontogeny. We hypothesized that Meckel’s cartilage is non-homogenous throughout development; this can aid in the flexibility of the IMJ, allowing Poecilia spp. to have a wider gape. Specimens of black and balloon freshwater mollies (two variations of P. latipinna), as well as common mollies (P. sphenops), were cleared and stained to obtain an ontogenetic series. Histological sections for both species were generated to find patterns of ossification and allometric measurements of jaw elements. Histological sections stained with various methods were used to determine the composition of the Meckel’s cartilage, and were compared among the ontogenetic series as well as to adults. Understanding the ontogenetic formation of the IMJ in individuals will contribute to hypotheses on the evolution of this joint.
