Morphological distinctness despite large-scale phenotypic plasticity—analysis of wild and pond-bred juveniles of allopatric populations of Tropheus moorii

Abstract

Cichlids are an excellent model to study explosive speciation and adaptive radiation. Their evolutionary success has been attributed to their ability to undergo rapid morphological changes related to diet, and their particular breeding biology. Relatively minor changes in morphology allow for exploitation of novel food resources. The importance of phenotypic plasticity and genetically based differences for diversification was long recognized, but their relationship and relative magnitude remained unclear. We compared morphology of individuals of four wild populations of the Lake Tanganyika cichlid Tropheus moorii with their pond-raised F1 offspring. The magnitude of morphological change via phenotypic plasticity between wild and pond-bred F1 fish exceeds pairwise population differences by a factor of 2.4 (mean Mahalanobis distances). The genetic and environmental effects responsible for among population differentiation in the wild could still be recognized in the pond-bred F1 fish. All four pond populations showed the same trends in morphological change, mainly in mouth orientation, size and orientation of fins, and thickness of the caudal peduncle. As between population differentiation was lower in the wild than differentiation between pond-raised versus wild fish, we suggest the narrow ecological niche and intense interspecific competition in rock habitats is responsible for consistent shape similarity, even among long-term isolated populations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00114-010-0751-2) contains supplementary material, which is available to authorized users.

Incipient sympatric speciation in Midas cichlid fish from the youngest and one of the smallest crater lakes in Nicaragua due to differential use of the benthic and limnetic habitats?

“…This result stands in contrast to the fact that cichlids exhibit phenotypic plasticity in a number of different traits (Meyer ; Kerschbaumer et al. ; Machado‐Schiaffino et al. ).…”

Fast adaptive responses in the oral jaw of Lake Victoria cichlids

“…Phenotypic plasticity is described as the environmentally sensitive production of alternative phenotypes by given genotypes (DeWitt and Scheiner ). Plasticity is a common phenomenon in cichlids and laboratory experiments have confirmed the ability of many cichlid species to change the jaw apparatus in response to different diets (Witte ; Hoogerhoud ; Meyer ; Wimberger ; Huysseune ; Smits et al ; Bouton et al ; Stauffer and Van Snik Gray ; Kerschbaumer et al ; Muschick et al ; Gunter et al ), although different diets in the wild do not always lead to divergence in morphology in cichlids (see Odhiambo et al ). Some of these studies tested plasticity of the premaxilla and showed a shorter ascending arm and a larger angle β of the premaxilla as a phenotypic response to a feeding style involving manipulation of prey (especially biting, Witte ; Wimberger ; Bouton et al ).…”

“…In all four species, we found a shorter ascending arm and in P. degeni , the species with the most robust premaxilla, which indicates a biting‐like feeding style, a larger angle β. Recent plasticity experiments on Lake Tanganyika cichlids, three‐spined sticklebacks, and Trinidadian guppies have shown morphological responses resembling adaptive phenotypes evolved under natural conditions (Kerschbaumer et al ; Torres‐Dowdall et al ; Wund et al ). These studies all suggest that phenotypic plasticity might play an important role in the colonization of novel environments, which we think is likely to be the case for Lake Victoria cichlids.…”

Evolution of body shape in sympatric versus non-sympatric Tropheus populations of Lake Tanganyika

“…One alternative, reproductive character displacement, that is, the increase of isolation between taxa that are already good species (as opposed to reinforcement), seems less likely, given that all distinctive traits have a plausible ecological background. According to the six check-criteria for character displacement suggested by Grant (1972) and Arthur (1982) and considering the remarks of Schluter and McPhail (1992), the following evaluation can be made: Chance can be ruled out as an explanation of the pattern, given that other cases of sympatry also constitute the same depth segregation of the two entities.According to pond-breeding experiments (Kerschbaumer et al. , 2011; Koch et al , 2012), the phenotypic differences among populations in sympatry and allopatry have a genetic basis, on top of plasticity.…”