Testing Conjectures about Morphological Diversity in Cichlids of Lakes Malawi and Tanganyika
The morphological diversity of Malawi and Tanganyika cichlids has often been qualitatively described, but rarely have hypotheses based on these descriptions been tested empirically. Using landmark based geometric morphometrics, shapes are analyzed independent of other aspects of the body form (e.g., size). The estimation of shape disparity, the quantitative measure of the variance of these raw shapes, can then be applied in order to objectively test hypotheses about morphological diversity. The shape disparity within and between different groups is explored as well as how it is partitioned within the cichlid body. Tanganyika cichlids are found to have significantly greater shape disparity than Malawi cichlids. Ectodini is found to have significantly greater shape disparity than other Great Lake tribes. Piscivorous cichlids are significantly more disparate in shape than cichlids with other diets, and the shape disparity of the cranial region was significantly greater than that of the post-cranial region.Abstract
Landmarks (1) rostral tip of premaxilla (2) dorsal tip of premaxillary pedicel (3) anterior insertion of dorsal fin (4) posterior insertion of dorsal fin (5) dorsal insertion of caudal fin (6) caudal border of hypural plate aligned with lower lateral line (7) ventral insertion of caudal fin (8) posterior insertion of anal fin (9) anterior insertion of anal fin (10) dorsal base of pelvic fin (11) end of opercular membrane ventrally (12) inner aspect of dentary symphysis (13) caudal end of maxilla (14) dorsal end of preopercle ventral to pterotic (15) caudal end of opercule (16) pectoral fin origin (17) anterior margin of midline through eye (18) posterior margin of midline through eye. The base figure is redrawn from Nelson (1994)
Tribes shown in descending order of shape disparity. Star indicates a significant difference in shape disparity from all other groups. Numbers above bars indicate the number of species sampled and the number below each bar represents the percentage of species sampled from each clade, calculated using the total number of species found in each tribe as reported by Salzburger et al. (2002) and Takahashi (2003).
Cichlid diet classes shown in descending order of shape disparity. Malawi groups are represented by white bars and Tanganyika groups are indicated by black bars. A star indicates a significant difference in disparity from all other groups. The number above each bar is the number of species sampled in this analysis; the percent sampled from each diet class is given below each bar. A rough estimate of the number of species in each group was obtained from Konings (1998, 2001).
Contributor Notes
University of Michigan Museum of Zoology, Fish Division, 1109 Geddes Avenue, Ann Arbor, Michigan 48109-1079. pchakrab@umich.edu