UC San Diego

Studying evolutionary change with respect to the development of morphological traits in an organism can give insight on the evolutionary development and diversification of those traits, as well as valuable information about how these characteristics contribute to behavior. The Longjaw Mudsucker (Gillichthys mirabilis, Gobiidae) has been studied extensively for its ability to occupy low oxygen environments, yet few studies research the ontogeny of its elongate jaw as it relates to a unique gaping display behavior. Members of the Gillichthys genus exhibit this territorial defense behavior during mating months and G. mirabilis possess exceptionally long maxillae that are laterally flared during its gaping display. The elongate maxilla and associated buccopharyngeal membrane amplifies the aggressive gaping display of G. mirabilis and also increases surface area for gas exchange during aerial respiration. In this study, the maxillae of G. mirabilis, Gillichthys seta, and the outgroup species Eucyclogobius newberryi were examined and analyzed in an ontogenetic size series using digitized landmarks and caliper measurements. With these features, principal component analysis was used to study evolution in the maxilla of these three species under the heterochrony framework. Sexual dimorphism in the maxilla and body shape-space were also investigated to observe sexual trait selection and body shape correlation. The results show the maxilla of G. mirabilis evolved via acceleration (increased growth rate) and hypermorphosis (continued growth), two forms of peramorphosis. These results give us a start in understanding the evolutionary progression of the Longjaw Mudsucker and the potential connection of its elongated maxillae with its gaping display.