The Early Ontogeny of Feeding in Two Shark Species: Developmental Aspects of Morphology, Behavior, and Performance

Early ontogeny is a time of rapid anatomical and behavioral development in most organisms. The degree of synchrony between form and function during this period, and the concomitant performance consequences, can strongly impact individual survival. Understanding the development of feeding during early ontogeny is important because nutrient acquisition universally influences organismal biology. A one-year, longitudinal feeding study was conducted for two elasmobranch species that were selected for their disparate morphology, behavior, and habitat: the whitespotted bambooshark Chiloscyllium plagiosum and the leopard shark Triakis semifasciata. To quantify changes in cranial morphology, external attributes of the feeding apparatus were measured weekly. Additionally, specimens were dissected to examine trends in the growth of select muscles and the volume of the buccal cavity. To quantify feeding behavior, individuals were observed weekly using high-speed digital cameras as they consumed various food types. Suction performance was evaluated using particle image velocimetry and direct measurements of suction pressure. The cranial morphology of C. plagiosum exhibited primarily isometric growth while the cranial morphology of T. semifasciata was dominated by allometric growth. Allometric increases were noted in the cross-sectional area of every muscle examined in both species, though the primary hyoid depressor, the coracohyoideus, hypertrophied to a greater degree in C. plagiosum. Although intra-individual differences throughout ontogeny complicated comparison, modulation in response to food attributes was clearly evident in T. semifasciata but broadly absent in C. plagiosum. Over ontogeny C. plagiosum generated allometrically greater suction while T. semifasciata generated relatively less. The shape of the parcel of water ingested during feeding did not change over ontogeny in either species. The capacity to perform diverse feeding behaviors throughout ontogeny is not constrained in T. semifasciata but tends to be stereotyped and accompanied by enhanced performance in C. plagiosum. A functionally generalized feeding apparatus and repertoire may benefit T. semifasciata by allowing the use of diverse feeding behaviors in variable environments, such as estuaries, over ontogeny. Morphological and behavioral conservation of the feeding apparatus throughout ontogeny, however, may allow C. plagiosum to exploit taxonomically varied crevice-dwelling reef organisms using a single specialized behavior