Carapace shape of some trichodactylidae crabs: Analysis by geometric tools as a possible way of including females in taxonomic differentiation

GIRI FEDERICO; WILLINER VERONICA; COLLINS PABLO AGUSTIN

PALEONTOLOGIA I EVOLUCIÓ

Institut Catalá de Paleontologia

Año: 2009 vol. mem p. 69 - 70

0211-609X

Freshwater decapods of South America are grouped into seven families (Magalhães & Türkay, 1996, Morrone & Lopretto, 2001). One of them, the family trichodactilidae, characterizes the aquatic environments of the plain, being the Paraná River an important system in the continent. The taxonomic studies of this group were based on carapace ornamentations and male gonopod morphology but these systematic definitions, mainly the latter, only apply to male specimens. In studying the biodiversity of the group, females are not considered, and it is not possible to make specific identifications when only females are captured. The Thichodactylidae family have characteristic ornamentations of the carapace that are useful as distinctive points for fixation, corresponding to landmarks type 1 (Bookstein, 1991). The objective of this study was to explore an alternative way of taxonomic identification of the members of the Trichodactylidae family, including females. The study focused on the application of geometric-morphometric analysis to the carapace of representative species from the Middle Paraná River. Digital pictures of all specimens were taken using a Nikon EOS400 camera, placed at a fixed distance of 35 cm from the specimen. Twelve landmarks were recorded on the dorsal view of the cephalothorax through the tpsDig program (Rohlf, 2004), and two of them were analyzed as semilandmarks. Configurations were superimposed through the Generalized Procrustes Analysis (Rohlf and Slice, 1999) in the tpsRelw program (Rohlf, 2005). Shape variation between samples was first explored through Relative Warp Analysis (RW). There were no significant differences between genera in relation to RW 1, 2 and 3 (p>0.05). The MANCOVA revealed significant differences (P<0.05) among species. This occurred mainly in the position of the landmark, on the last spine of the carapace, causing variations in the RW1. Changes consisted in the migration of the last spine from an anterior to a posterior position. The second RW showed variations between balloon or angular shapes of the carapace. Furthermore, differences between males and females were not significant in all species studied. The methodology of geometric-morphometric analysis is useful in the differentiation of species of endemic freshwater crabs, members of the Trichodactylidae family. Moreover, when only female specimens are collected in sampling programs, the carapace shape and specially the position of the posterior spine can be used as systematic indicators.