Phylogeny of a rapidly evolving clade: The cichlid fishes of Lake Malawi, East Africa

Abstract

Lake Malawi contains a f lock of >500 species of cichlid fish that have evolved from a common ancestor within the last million years. The rapid diversification of this group has been attributed to morphological adaptation and to sexual selection, but the relative timing and importance of these mechanisms is not known. A phylogeny of the group would help identify the role each mechanism has played in the evolution of the f lock. Previous attempts to reconstruct the relationships among these taxa using molecular methods have been frustrated by the persistence of ancestral polymorphisms within species. Here we describe results from a DNA fingerprinting technique that overcomes this problem by examining thousands of polymorphisms distributed across the genome. The resulting dendrogram averages the evolutionary history of thousands of genes and should accurately ref lect the evolutionary history of these species. Our tree resolves relationships among closely related Lake Malawi cichlids and provides insights into the pattern of speciation in this group. We demonstrate that adaptive divergence in trophic morphology played an important role during the early history of the lake. Subsequent species diversity has arisen with little change in trophic morphology, which suggests that other forces are responsible for the continued speciation of these fishes.Lake Malawi and its fish fauna have attracted the attention of ecological, behavioral, and evolutionary biologists for over a century (1). Lake Malawi cichlids exhibit spectacular diversity in trophic morphology, including specialist algal scrapers, planktivores, insectivores, piscivores, paedophages, snail crushers, and fin biters. As rich as they are in trophic diversity, these fishes are even more striking in their array of color patterns (2). Their complex mating behavior, polyandrous mating systems (3), and tendency to breed in leks also are intriguing to behaviorists.Both adaptive and nonadaptive processes likely have played a role in the explosive radiation of East African cichlids, but the importance of each mechanism has been the focus of considerable debate (4). On one hand, it has been suggested that morphological adaptation, particularly of the feeding apparatus, is a ''key innovation'' for rapid evolutionary change (5). An opposing hypothesis suggests that adaptive morphological change is not the primary cause of speciation but occurs after the establishment of genetic isolation by other means (6, 7). These authors argue that sexual selection is the force that creates reproductive isolation, allowing subsequent morphological differentiation. The competing hypotheses could be evaluated if a robust phylogeny of these taxa was available. If morphological adaptation is critical to speciation, then we expect that even closely related species will show significant divergence in trophic morphology. If sexual selection is responsible for speciation, then we expect that sister taxa will frequently differ in color pattern but not morphology.Most attempts to dete...

Phylogeny of bovine species based on AFLP fingerprinting

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Repeated trans-watershed hybridization among haplochromine cichlids (Cichlidae) was triggered by Neogene landscape evolution

“…Reconstructing robust phylogenetic relationships of haplochromine cichlids has proved to be difficult owing to limited taxon sampling and lack of phylogenetically informative characters. Until recently, phylogenetic analyses have delivered support for the monophyly of each of the major haplochromine species flocks, including the Lake Victoria superflock [3], southern African serrannochromines and Tropheini of Lake Tanganyika [1,[3][4][5]. The assumed monophyly of Lake Malawi haplochromines was recently falsified after inclusion of riverine haplochromines [6,7].…”

A Deterministic Genetic Model for Sympatric Speciation by Sexual Selection

“…In contrast, our models of sympatric speciation (this paper; Higashi et al 1999) focus on sexual selection as a driving force of speciation. Recent phylogenetic data has separated the roles of sexual selection and natural selection on the formation of cichlid species flock in Lake Malawi (Albertson et al 1999). The study suggests that ecological divergence of species occurred in the early stage of flock evolution, whereas the subsequent speciation, which involved little ecological change, must have resulted from other evolutionary forces such as sexual selection.…”