Geometric morphometrics reveals surprising diversity in the Lake Malawi cichlid genus Labeotropheus

Abstract

The Lake Malawi cichlid genus Labeotropheus has been a source of confusion among biologists and taxonomists. Although unique populations of both L. fuelleborni and L. trewavasae exist throughout the lake, these populations have not been elevated to species, despite taxonomists doing so for populations within other Lake Malawi cichlids. One reason for this oversight is the supposed consistent differences in morphology between Labeotropheus species; since, where they co-occur, L. fuelleborni is always deeper-bodied than L. trewavasae, it is thought that all deep-bodied populations of Labeotropheus are L. fuelleborni, and the slender ones are L. trewavasae. Using geometric morphometrics, we analyze 18 populations of Labeotropheus and show that body shape varies among populations, and does not always fall into a deep-body/slender-body dichotomy. These differences in body shape are not related to geographical distance among populations, but are possibly related to the type of habitat in which the populations are found. Further, head shape is extremely variable among populations, and we find two locations where there is convergence in head shape between sympatric L. fuelleborni and L. trewavasae. Our results suggest that the morphological criteria applied to the Labeotropheus are not accurate, and hamper the recognition of Labeotropheus biodiversity.