EFFECT OF SAMPLE LOCATION AND ONTOGENY ON DECAPOD CUTICLE, A CASE STUDY OF CALLINECTES SAPIDUS

To understand the variations in decapod cuticle microstructure as a result of ontogeny and sample location, parameters of cuticle microstructure were viewed in thin section and SEM in a population of the portunid crab Callinectes sapidus Rathbun, 1896. Density and size of nodes on the surface of the carapace varied with both sample location and carapace size. The size of nodes increased as the carapace size increased, and the density of the nodes decreased with growth. Crabs with carapaces more than 9 cm in width exhibit smaller nodes inserted between existing larger nodes. No thickness increase was observed in the epicuticle (outermost layer of the cuticle). The exocuticle (middle layer) and endocuticle (basal layer) did increase in thickness with carapace size. Prisms in the exocuticle, which are thought to be structures related to the geometry of cells producing the exocuticle, show no significant variation in size during growth. The fundamental structure of the cuticle did not vary with age or sample location. Results from this study are relevant to our ongoing research project that seeks to use characters of cuticle microstructure to elucidate phylogeny of the Decapoda. The model developed in Callinectes sapidus suggests that age and sample location on the dorsal carapace do not significantly alter characters used in our analysis of decapod cuticle; thus, cuticle can be used for phylogenetic studies with caution. Thickness of the cuticle, and surface feature size and density must be used with caution because they vary with ontogeny. Thickness of the cuticle and density and size of nodes can be used as proxies for age, which are relevant to understanding the population structure. Callinectes is an important part of commercial fisheries, and the age structure of their population is used to determine management practices of this resource. Approaches to the study of ontogeny of Callinectes with respect to cuticle microstructure will be applied to other crab populations, fossil and extant. This research is supported by NSF grant EF0531670 to Feldmann and Schweitzer.