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<!-- EDIT BELOW THIS LINE -- How differential jaw evolution lead to the broad diversification of cichlid fishes, or maybe just slightly

1. Hulsey, C D, et al. MICRO- AND MACROEVOLUTIONARY DECOUPLING OF CICHLID JAWS: A TEST OF LIEM'S KEY INNOVATION HYPOTHESIS. Evolution 60.10 (2006): 2096-2109.

2. Hulsey, C D, et al. Co-evolution of the premaxilla and jaw protrusion in cichlid fishes (Heroine: Cichlidae). Biological Journal of the Linnean Society 100.3 (2010): 619-629.

3. Meyer, Axel. Adaptive phenotypic plasticity in the Midas cichlid fish pharyngeal jaw and its relevance in adaptive radiation. BMC Evolutionary Biology 11.1 (2011): 116.

4. Barluenga, M. The Midas cichlid species complex: incipient sympatric speciation in Nicaraguan cichlid fishes? Molecular Ecology 13.7 (2004): 2061-20176.

5. Gonzalez-Voyer, A. Rates of phenotypic evolution of ecological characters and sexual traits during the Tanganyikan cichlid adaptive radiation. Journal of Evolutionary Biology 24.11 (2011): 2378-2388.

Final Draft Below The Rapid Evolution of Cichlid Fishes and its Significance to Evolutionary Biology Cichlid fishes are one of the most species rich families of vertebrates in the entire world. More than 3,000 species of cichlids are distributed worldwide from Central and South America, across Africa to Madagascar, and also in southern India (Kocher, 2004). Their rapid evolution and speciation in the past one million years is one of the best examples in the natural world of adaptive radiation. These cichlids in their habitats give researchers a natural laboratory to study how different adaptations and speciation processes have contributed to the diversification of this family. Some of these diversification processes are morphological adaptation, sexual selection, and habitat divergence. Some populations may also help to further the case of sympatric speciation. With regard to the initial adaptive radiation of cichlids in places like Lake Victoria in Africa or crater lakes in Nicaragua, one of the main forces was the morphological adaptation, or evolution of a physical trait, associated with the feeding apparatus. Cichlids show a broad range of feeding apparatus that allow for many feeding strategies and behaviors including algae scraping, snail crushing, planktivores, piscivores, and insectivores (Albertson et al., 1998). The ability to adapt all these different feeding strategies is generally credited to the presence of the pharyngeal jaw apparatus. Pharyngeal jaws are a second set of jaws that are distinct from the oral jaws. They are modified gill arches and are contained in the throat of the fish. Cichlid pharyngeal jaws are highly efficient in prey processing and this frees the oral jaws to adapt independently for various methods of prey capture (Hulsey et al., 2006). The ability of the cichlid jaws to adapt to new feeding strategies and prey types may be in part to the phenotypic plasticity of cichlid jaws. Phenotypic plasticity refers to the ability of an organism to change its phenotype in response to changes in the environment. This phenotypic plasticity of the jaws allows for differentiated feeding habits in the presence of varied food sources. It also might occur in times when food sources are scarce. Cichlid fishes fed different diets from the same stock developed different jaw morphologies, papilliform versus molariform (Muschick et al., 2011). Individuals with papilliform jaw morphologies are more suited to feeding on soft foods, while individuals with molariform jaw morphologies are more suited to feeding on hard foods like snails. This is just one case of diversified morphologies in one species of cichlid, Amphilophus citrinellus. There exist a great number more possible sets of morphologies to allow for specialized feeding and therefore, speciation. Speciation might be achieved after morphological diversification as fish find themselves concentrating in certain areas where target prey can be found. The fish then find themselves alongside others of the same species that have undergone this plasticity of phenotypic traits and focused on feeding on snails as opposed to softer food forms (Muschick et al., 2011). This reinforces the morphology as these individuals have a very high chance of mating with each other and not other fish that have wound up feeding on another food source. These morphological adaptations allow for an initial adaptive radiation, but do not explain the rich diversification of species in places like Lake Tanganyika, Lake Malawi, or Lake Victoria, all of which are in Africa. A possible explanation for the diversification of cichlids fishes to the point it has reached now is sexual selection. Many sister species are very similar in morphology and feeding habits, but differ greatly in coloration. Convergent evolution could explain this, but the more plausible answer would be females exercising a choice in the color of males as directional sexual selection. Females have a preference for a particular sort of coloration, which is initially variable in the male population. The females then choose one of the variants and this creates a feedback loop that can eventually lead to two separate species. Evidence of this process was found in Pundamilia pundamilia, the ancestral population that is still extent, and Pundamilia nyererei, a sister species that exhibits a slightly different coloration (Maan et al., 2004). There still exists some debate about whether sexual selection or morphological adaptation is the main culprit behind the adaptive radiation shown in cichlid fishes. If sexual selection was the initial force behind the adaptive radiation, then you would expect to see sister taxa with differing morphological adaptations. If morphological adaption was the initial force behind the adaptive radiation, then you would expect to see sister taxa that are very similar morphologically, differing only in color patterns. Evidence suggests the latter of these two possibilities as the strongest and most likely situation (Albertson et al., 1998). Morphological adaption was the initial radiation into the different niches with sexual selection following behind it. Directional sexual selection further divided those species into more and more species and in a much faster amount of time. Sexual traits evolve at a much faster rate than do ecological characters (Gonzalez-Voyer et al., 2011). This seems contradictory to the findings that morphological traits were the first to arise, followed by sexual selection. However, it is still most likely that the initial adaptive radiation is due to morphological adaptation, and subsequent sexual selection accounts for the species richness. Cichlid speciation is one of the few cases that could prove sympatric speciation to be possible in nature with empirical data and not just theoretically possible. Sympatric speciation is the process by which a new species arises from a parent species without a geographical constraint. In Nicaragua, there are small crater lakes that have been populated by various cichlid species, most notably the Amphilophus citrinellus. A. citrinellus is the most common cichlid in Lake Nicaragua, the main body of water from where many of the colonizing fish originate. One of these crater lakes, Lake Apoyo, has some characteristics that make it a very strong candidate to provide evidence of sympatric speciation. Lake Apoyo is small, is of recent origin (<10,000 years), has a homogenous habitat, and is completely isolated, being in the caldera of a volcano (Baluenga et al., 2006). The second fish species that came from A. citrinellus is Amphilophus zaliosus and analysis of the two lends further support to sympatric speciation. Some of the characteristics of the fish themselves that lend to a model of sympatric speciation are strong assortative mating on the basis of color polymorphism and ecological differentiation based on morphological polymorphisms involving the feeding apparatus and body shape (Barluenga et al., 2004). A. zaliosus has taken advantage of an open water column habitat not typically inhabited by A. citrinellus, which stays in shallower water like those in its native Lake Nicaragua. However, the fish do overlap in their habitat and complete geographic isolation has not been achieved. This all suggests that the only way for A. zaliosus to have come into existence is through sympatric speciation. Sympatric speciation has been much harder to use a possible explanation for the rapid evolution seen in the lakes in Africa because allopatric speciation is just as, if not more, plausible then sympatric speciation. Allopatric speciation is the geographic separation of a species into two populations that eventually become two species. However, with this evidence, it is possible to suggest that sympatric speciation could play a larger role in the speciation seen in the African lakes like Lake Victoria or Lake Malawi. Cichlid fishes represent a very unique family of fishes in that they are capable of adapting to new environments in very small amounts of time. The possible differences in jaw morphology seen throughout the family helps cichlids adapt to new environments as well as new foods in times of scarcity. Coupled with the directional sexual selection seen demonstrated by female cichlids across many species, cichlids can quickly and successfully make use of and adapt to many new environments. They provide researchers with one of the most unique lines of speciation, as well one of the most challenging to resolve. As researchers continue to attempt to resolve cichlid phylogenies, they will most likely find new and important information to back up or discredit many competing theories on how evolution takes place. ~ Edited pages https://en.wikipedia.org/wiki/Talk:Cichlid I added a new talk section regarding my edit titled, Addition of information regarding cichlid speciation. Edit I made to page Pharyngeal jaw: Another notable example of animals possessing pharyngeal jaws are the fish from the family Cichlidae. Cichlid pharyngeal jaws have become very specialized in prey processing and may have helped cichlid fishes become one of the most diverse families of vertebrates.