Meeting Abstract

91.2  Monday, Jan. 6 13:45  Ontogenetic transitions from cleaning behavior are associated with shifts in cranial morphology in Thalassoma wrasses BALIGA, V.B.*; MEHTA, R.S.; Univ. of California, Santa Cruz; Univ. of California, Santa Cruz

In fishes, cleaning is a mutualistic behavior wherein a species will remove and consume ectoparasites or damaged tissues from other organisms. While over 120 species of teleost fishes exhibit cleaning behavior, more than two thirds of these species display it predominately as juveniles, and are referred to as “facultative juvenile cleaners”. Whether allometric changes in morphological traits are correlated with ontogenetic shifts from cleaning in the adult stage is unknown. Here, we tested the hypothesis that the transition from cleaning is associated with key allometric shifts in the feeding apparatus of facultative juvenile cleaners. We measured traits such as vertical gape distance, adductor mandibulae mass, and maxillary KT for ontogenetic series of specimens in a variety of Thalassoma wrasses (Labridae). As these fishes predominately capture prey via biting, we used MandibLever (v3.3) to create an ontogenetic trajectory of bite force for each species. Results indicate that facultative juvenile cleaners, when compared to closely-related non-cleaners, are relatively weak biters with small gapes, but shift to being stronger biters as adults. Shifts in maxillary KT towards an increase in forceful jaw movement also characterize these facultative species. Our results indicate that the functional basis for cleaning behavior in Thalassoma wrasses lies in slower-moving, relatively weaker-biting jaws in the juvenile condition. These traits ostensibly put these species at a competitive disadvantage with sympatric, non-cleaning congeners as juveniles, perhaps indicating cleaning behavior in Thalassoma wrasses is a result of competitive displacement. Through ontogeny, these facultative cleaner fishes develop the ability to compete with such congeners through an allometric increase in bite force, which possibly obviates the need to continue cleaning.