The cost of DNA sequencing continues to fall, which makes it feasible to develop genomic resources for new model species that are well suited for studying questions in evolutionary biology. The thousands of closely related cichlid fishes in the lakes of East Africa are an ideal model system for understanding the genetic basis of vertebrate speciation. Genomic techniques are helping to integrate empirical and theoretical studies by identifying the genes that underlie the phenotypic differences among species.

https://theantlife.com/wp-content/uploads/2014/03/Kocher-2004_Cichlid-fish-model-review-paper.pdf

Adaptive evolution and explosive speciation : the cichlid fish model

We present evidence of ecological character displacement among species of threespined sticklebacks that inhabit small lakes of coastal British Columbia. Geological data suggest that the populations resulted from multiple divergence and speciation events over the past 13,000 yr. In lakes with two species, one is invariably "limnetic" in morphology and habitat, and the other is "benthic." Other lakes contain a single form morphologically intermediate between sympatric species and exploiting both habitat's. Within solitary populations individuals exploit one habitat or the other according to their morphology, which underscores the divergent selection pressures operating on either side of the habitat boundary. Our results satisfy at least four of the six major criteria for demonstrating the occurrence of character displacement: (1) a statistical null model of no displacement is easily rejected; (2) variation between and within populations is genetically based; (3) differences in sympatry reflect evolutionary ...

Ecological character displacement and speciation in sticklebacks.

Lake Victoria, together with its satellite lakes, harbours roughly 200 endemic forms of cichlid fishes that are classified as 'haplochromines' and yet the lake system is less than a million years old. This 'flock' has attracted attention because of the possibility that it evolved within the lake from one ancestral species and that biologists are thus presented with a case of explosive evolution. Within the past decade, however, morphology has increasingly emphasized the view that the flock may be polyphyletic. We sequenced up to 803 base pairs of mitochondrial DNA from 14 representative Victorian species and 23 additional African species. The flock seems to be monophyletic, and is more akin to that from Lake Malawi than to species from Lake Tanganyika; in addition, it contains less genetic variation than does the human species, and there is virtually no sharing of mitochondrial DNA types among species. These results confirm that the founding event was recent.

/pdf/monophyletic-origin-of-lake-victoria-cichlid-fishes-3h7qvsrkpo.pdf

Monophyletic origin of Lake Victoria cichlid fishes suggested by mitochondrial DNA sequences.

The intense controversies that surrounded the youth of punctuated equilibrium have helped it mature to a useful extension of evolutionary theory. As a complement to phyletic gradualism, its most important implications remain the recognition of stasis as a meaningful and predominant pattern within the history of species, and in the recasting of macroevolution as the differential success of certain species (and their descendants) within clades.

/pdf/punctuated-equilibrium-comes-of-age-4aydc1k73a.pdf

Punctuated equilibrium comes of age

The tree of life of fishes is in a state of flux because we still lack a comprehensive phylogeny that includes all major groups. The situation is most critical for a large clade of spiny-finned fishes, traditionally referred to as percomorphs, whose uncertain relationships have plagued ichthyologists for over a century. Most of what we know about the higher-level relationships among fish lineages has been based on morphology, but rapid influx of molecular studies is changing many established systematic concepts. We report a comprehensive molecular phylogeny for bony fishes that includes representatives of all major lineages. DNA sequence data for 21 molecular markers (one mitochondrial and 20 nuclear genes) were collected for 1410 bony fish taxa, plus four tetrapod species and two chondrichthyan outgroups (total 1416 terminals). Bony fish diversity is represented by 1093 genera, 369 families, and all traditionally recognized orders. The maximum likelihood tree provides unprecedented resolution and high bootstrap support for most backbone nodes, defining for the first time a global phylogeny of fishes. The general structure of the tree is in agreement with expectations from previous morphological and molecular studies, but significant new clades arise. Most interestingly, the high degree of uncertainty among percomorphs is now resolved into nine well-supported supraordinal groups. The order Perciformes, considered by many a polyphyletic taxonomic waste basket, is defined for the first time as a monophyletic group in the global phylogeny. A new classification that reflects our phylogenetic hypothesis is proposed to facilitate communication about the newly found structure of the tree of life of fishes. Finally, the molecular phylogeny is calibrated using 60 fossil constraints to produce a comprehensive time tree. The new time-calibrated phylogeny will provide the basis for and stimulate new comparative studies to better understand the evolution of the amazing diversity of fishes.

The tree of life and a new classification of bony fishes.

Phyletic studies of teleostean fishes, with a provisional classification of living forms

The Cichlid Fishes of the Great Lakes of Africa. Their Biology and Evolution

The introduction of the Nile perch into Lake Victoria, East Africa, has had disastrous consequences Fisheries have been not merely damaged but destroyed Lake Malawi has the world's most species-rich fish fauna and the prospect of introduction of alien species could mean disaster

Destruction of fisheries in Africa's lakes

The Cichlid fishes of Lake Nabugabo, Uganda

Synopsis. Functional morphological analysis has revealed the existence of three functionally and morphologically different mechanisms underlying the tongue-parasphenoid and pharyngeal-parasphenoid bites in advanced teleost fishes. The bite is specialized differently in Pristolepis and the Anabantoidei, and in a primitive condition in both the Nandidae and Channiformes. These taxa belong to at least three unrelated lineages and do not share a common ancestry as was previously postulated. It has been possible to show how an originally primitive character can acquire a new biological and phylogenetic meaning by being integrated into a specialized functional complex. Based on functional data on the pharyngeal jaw apparatus, a new hypothesis is proposed stating that the Cichlidae, Embiotocidae, Labridae, Odacidae and Scaridae represent a monophyletic assemblage. This case study has demonstrated that reciprocal illumination of functional morphological and phylogenetic findings can lead to: (1) better tested and more precise phylogenetic hypotheses; (2) the construction of new hypotheses on the basis of specialized character complexes which were unrecognized by the use of a purely descriptive morphological approach.

P. H. Greenwood

Papers

Phyletic studies of teleostean fishes, with a provisional classification of living forms

The Cichlid Fishes of the Great Lakes of Africa. Their Biology and Evolution

Destruction of fisheries in Africa's lakes

The Cichlid fishes of Lake Nabugabo, Uganda

A Functional Approach to the Phylogeny of the Pharyngognath Teleosts