Form, function and phylogeny: comparative morphometrics of Lake Tanganyika's cichlid tribe Tropheini

Abstract

Lake Tanganyika's cichlid fishes represent one of the most diverse species assemblages of the world. In this study we focused on the tribe Tropheini which occupies several trophic niches, mostly in rocky habitats. We analysed morphological variation of seventeen closely related species by means of geometric morphometric methods and related these data to ecological characteristics and phylogeny of the study species. It turned out that morphology mostly correlated well with ecological parameters, but not always closely with the degree of the phylogenetic relatedness of the species. Overall, body shapes in the tribe Tropheini are of great evolutionary plasticity, but variation is restricted to particular body parts: the preorbital region once again emerged as a key factor that facilitated their impressive radiation.

Figure 1

Landmarks exemplarily shown on a specimen of Interochromis loocki. Number and position of landmarks: 1 – corner of the mouth, 2 – topmost point of the upper lip at the transition to the nasal region, 3 – most anterior and most ventral point of the upper lip, 4 – nostril, 5 – anterior extreme of the orbit along the anterioposterior body axis, 6 – posterior extreme of the orbit along the anterioposterior body axis (a connecting line between 5 and 6 would cross the centre of the orbit), 7 – anterior origin of the dorsal fin, 8 – posterior insertion of the dorsal fin, 9 – upper origin of the caudal fin, 10 – lower insertion of the caudal fin, 11 – posterior insertion of the anal fin, 12 – anterior origin of the anal fin, 13 – origin of the ventral fin, 14 – upper origin of the pectoral fin, 15 – ventral tip of cleithrum, 16 – dorsal end of the preopercular groove.

Figure 2

—A. PCA of all 396 specimens.—B. Pattern of shape change along PC1. —C. Pattern of shape change along PC2. —D. Pattern of shape change along PC3.

Figure 3

A. CVA of all 17 species. —B. Pattern of shape change along CV axis 1. —C. Pattern of shape change along CV axis 2. —D. Pattern of shape change along CV axis 3.

Figure 4

PCA (A) and CVA (B) of all 396 specimens grouped to carnivores, algae grazers, algae browsers and omnivores. Shape changes between omnivores and carnivores (C), carnivores and algae grazers (D), omnivores and algae grazers (E), omnivores and algae browsers (F), carnivores and algae browsers (G) and algae grazers and algae browsers (H), visualized through thin‐plate‐spline plots.

Figure 5

PCA (A) and CVA (B) of all 396 specimens grouped to lineages.