CICHLID FISH

Estimates of the number of modern cichlid species vary from 1400 to 1700 (and as a result, they compose about 8% of modern fish species). Does this group support the predictions of the evolutionary, creationism, or intelligent design models?

EVOLUTIONARY MODEL

If evolution is true, the various lineages of cichlid fish should form a nested hiearchy of relationships. They are only expected in the more recent epochs of the fossil record. Speciation in the group should occur through natural processes (such as allopatric speciation) and may result in significant differences within the group.

CREATIONISM MODEL

If the creationism model is correct, then the kind (s) of cichlid fish are equally unrelated to all other types of fish. They should be found since the first week of life on earth. Natural processes such as allopatric speciation should not be responsible for their diversity and variation within the kind is not expected to be significant.

INTELLIGENT DESIGN

If intelligent design is correct, then complex aspects of the natural world, such as speciation, cannot occur in graudal stages. Instead, supernatural influence acting in a specific instant should be evident through "irreducible complexity".

Anatomical and genetic studies indicate a nested hierarchy of relationships between the diverse lineages of cichlids. All cichlids form a monophyletic clade and within cichlids, there are a number of smaller clades which have been identified. The most primitive modern lineage is represented by the cichlids of Madagascar and Sri Lanka. All the New World cichlids form a Neotropical clade. Most cichlids form an endemic African clade. The speciation of cichlids correlates with the breakup of the former southern continent of Gondwana and the water systems created by tectonic activity on individual southern continents (Murray, 2001; Willis, 2007; Day, 2007; Sparks, 2004; Katongo, 2007).


Cichlid fish are classified in the order Perciformes. Relatives of perciforms are known in the Upper Cretaceous and perciform fish are definitely known by the Cenozoic (although there are possible perciform remains known from the Late Cretaceous (Sparks, 2004; Murray, 2001). Derived cichlids of the African lineage are known since the Eocene, indicating that ancestral lineages must predate the Eocene (Sparks, 2004).

Virtually all are freshwater, although some can survive in brackish waters (Sparks, 2004).
The most primitive modern cichlids are salt tolerant and can live in brackish and even marine environments. It is possible that cichlids originated in the marine environments which surrounded the southern continents during their breakup and that the freshwater adaptation of most modern lineages occurred secondarily (Murray, 2001; (Concheiro Perez, 2007). Before the division of the southern continent Gondwana, the land which composes modern Madagascar and the Indian subcontinent were in close proximity. The Madagascar and Indian/Sri Lankan lineages of cichlids are the most primitive cichlids alive today. From Africa, one lineage traveled to South America and was the source of the monophyletic Neotropical clade (Murray, 2001). Central American cichlids were colonized from South America and some South American cichlids belong to the clade which colonized Mesoamerica. One tribe (Heroini) diversified in Mesoamerica where they can compose a quarter of fish species(Concheiro Perez, 2007; Martin, 1998; Husley, 2004).


During the Miocene, tectonic uplift in East Africa changed water drainage patterns and created the great lakes which were the centers of cichlid diversity (Murray, 2001). Most African cihlids are thought to have arisen from the paleo-basin of Lake Tanganyika (including the extinct Lake palaeo-Makgadikgadi) and the greatest diversity of modern cichlids is endemic to East Africa (Katongo, 2007). More than a thousand species of cichlid fishes inhabit the three African Great Lakes, Tanganyika, Malawi and Victoria (Watanabe, 2007).


Lake Tanganyika is the oldest of the Great Lakes of East Africa and the anatomical, behavioral, and ecological diversity of its cichlids is greatest here. This species diversity seems to have resulted from nine original lineages which colonized the lake as it formed between 9 and 12 million years ago (Kobmuller, 2007). Different lineages of cichlid are dominant in different sites and many are endemic to a specific lake (Day, 2007). Lake Nabugabo is a Ugandan lake which was separated from Lake Victoria about five thousand years ago. Five species of endemic cichlids have evolved in the lake since its separation (Stager, 2005). African cichlids reached the Middle East and fossils of cichlids are known from brackish waters of Europe (Murray, 2001).


There is considerable variation among cichlids. Some species are behaviorally transitional between the substrate brooding and mouth brooding observed in other species. The tribe Perissodini contains basal species which feed on fish and zooplankton, species which feed on zooplankton and the scales of other fish, and species which specialize on scale-feeding (Kobmuller, 2007). Convergent evolution is known in the coloration and patterning of cichlids (Duftner, 2007). The kir7.1 affects body color patterning in fish, among other functions. A duplication of this gene occurred in ancestral cichlids, resulting in two copies in this group of fish. Modifications in the expression of this gene may have contributed to the diversification of cichlids (Watanabe, 2007).