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Topic Choice: The role of sexual selection in African Cichlid speciation.

Annotated Bibliography

This article explores assortative mating preferences of female cichlids belonging to the Tropheus family. It was found that similarly colored fish of different species separated by about 40 km of shoreline showed no discrimination when mating. However, when species were different colors, the females sometimes showed assortative preferences indicating sexual isolation. In conclusion this article states that in the event of geological barriers being broken, diversity could be maintained by the assortative mate preference by restraining gene flow between populations.

This article looks at the effect of declining water transparency on sexual selection. It causes males to become duller in color and increases the hybridization between species. Females that live in the turbid water show less preference for male coloration than females from clear water. The differences in selection between these females gives further insight to how sexual selection affects speciation.

This article focuses on acoustic communication during reproduction in the fish Astatotilapia burtoni. Specifically they looked at differences in the sound production of males and hearing ability of females. The data shows that acoustic communication is important in female mate choice. This further contributes to the diversity of African Cichlids due to sexual selection.

This article looks at mate choice behavior in females of two different populations of Labeotropheus fuelleborni from lake Malawi. Both female populations preferred males that displayed more frequently, even when males from both populations were presented at the same time. When two males from the same population were presented males with higher color contrast and saturation were preferred. Speciation could be correlated to males preferentially courting same population females.

This article looks at the differences in nuptial hue (blue or red) of males of two species and assortative female mate choice between these two types of males. When the color of the males was visible females chose the male in their species. When the color was not visible females did not show discrimination in mate choice. The data showed that this one trait was enough produce reproductive isolation between the species.

Shuman.39 (talk) 03:03, 15 September 2014 (UTC)

Artical edited and commented on: https://en.wikipedia.org/wiki/Sympatric_speciation Shuman.39 (talk) 00:26, 1 October 2014 (UTC)

Final Draft Starts Here

Sympatric Speciation due to Sexual Selection in African Cichlids

African Cichlid speciation is of interest to an evolutionary biologist because of their large amount of diversity. Many of these species have arisen in the past million years which is a relatively short amount of time from an evolutionary standpoint. Cichlids are also interesting because this speciation is occurring sympatrically, meaning many of the species evolve within the same lakes. The major goal is to find out what drives reproductive isolation between species if it is not a geographical barrier. Sexual selection is one key argument giving reason for reproductive isolation between species. Recent studies focus on female choice with regards to male coloration, male-male competition, and acoustic reproductive communication as a means for sexual selection between cichlid species.

Female choice with regards to male coloration is one of the more studied modes of sexual selection in African Cichlids. Female choice is present in cichlids because the female does much of the work in raising the offspring, while the male has little energy input in the offspring. Therefore the female will choose a male based on one of four things; direct benefit to her (nuptial gifts, nest site, or protection), good genes, runaway sexual selection, or sensory bias. In this case sensory bias makes the most sense because there is selection based on color. It most likely does not provide any benefits to the fish. Maintaining sympatric speciation within the lakes requires reproductive isolation. Female choice provides reproductive isolation between species due to the different phenotypic colors.

In Lake Tanganyika, the species Tropheus moorii has many different color variants that are now geographically separated. This means they are now out of contact and allopatric populations. These now separate but closely related populations were bred together to find the degree of assortative mating that occured. It was found that more distinct color morphs maintained a separation, while similar color morphs did not (Egger et al. 2009). This study simply shows that speciation between distinct color morphs would be maintained without geographic barriers due to the sensory bias present in females. Choice is given to males that look like the females of the species.

Another study done on Lake Victoria cichlids agrees with these findings. Visual and chemical cues were manipulated to show that color is enough to produce a reproductive barrier (Selz 2014). When the color was visible between the fish, population separation was maintained while it wasn’t when the color was not visible or there was some sort of chemical barrier.

The Lake Malawi cichlid species Labeotropheus fuelleborni were also studied with regards to color. Females were taken from two different populations and presented with two males either from their own population, two from the other population, or one from each population. The Katale females showed preference for males with higher levels of chroma, which correlates to the contrast of colors of the fish. No matter which populations the males came from this held true. The Chipoka females however only showed preference for males that displayed more often (Pauers and McKinnon 2012). The display is part of the ritualistic behavior that males use to court the females. The selection for contrast between colors has evolved in the Katale females while it has not in the Chipoka females. The sensory bias for contrast of colors provides a mode of sympatric speciation by creating a reproductive barrier between species. The result found for the Chipoka species showed no reproductive barrier, and there is only selection based on good genes. Males that display more often are more fit and therefore may provide a direct benefit to the offspring.

Phylogenies are a helpful tool in revealing the relationships between species. One study follows the speciation of Mbuna species using genetic loci. It was found that each main color trait was acquired and lost at several different origins (Allender et al. 2003). This implies that traits have been aquaired analogously in several different situations. Reasons for this similar selection could be due to the visual ecology of the fish eyes. Also, it shows that sensory bias is present in all females because certain colors have been selected for. What the females can see when selecting mates is important when considering their separation. There is a subset of possible colors selected for in males due to the spectra of light that is transmitted through the water. The spectra can be different at different geographical locations depending on the quality of the water.

Turbidity of the water is an important factor when considering the sensory bias in females. Females that come from turbid waters show less preference for male coloration than those from clear water. Also, males from turbid water show less coloration than males from clear water (Maan et al. 2009). This environmental factor plays a key role in the speciation of cichlids. The sensory bias is changing in response to the turbid water. Also, in areas where turbid and clear water are close together, viable hybrids may form new species because there is lower intersexual selection for color due to the decrease in female mating preferences for males with more vibrant coloration.

Male-male competition is a form of intrasexual selection and also has an effect on speciation in African Cichlids. Ritualistic fighting among males establishes which males are going to be more successful in mating. This is important in sympatric speciation because species with similar males may be competing for the same females. There may be a fitness advantage for one phenotype that could allow one species to invade another. Studies show this affect in species that are very genetically similar and interbreed, but show phenotypic color variation. Using this technique allows for identification of the dominant phenotype and may give insight to sympatric speciation.

In Lake Victoria, two sympatric species which have red and blue males defend their territories. Under white light both phenotypes can be seen and under green light it is harder to distinguish between red and blue. When contests were staged between the two different kinds of males, the red ones showed an advantage. The battles were quicker and red normally won. Under green light there was no advantage of red males and the competition lasted longer (Dijkstra 2004). It is apparent that the brightly colored red males intimidate blue males because of the short contests and high win rate of red males in white light. With this advantage it is possible for the red males to invade blue populations which promotes color diversification eventually leading to sympatric speciation. However, it is also important that the red males do not have a complete fitness advantage otherwise red would overtake the entire blue population. A possible factor to decrease the red males’ population size is more costly fights between red males. In a similar study, male-male competition is provided as a driving force behind speciation. Males with a rare color infer a fitness advantage because they win contests with a smaller amount of effort whereas males with a common color are having more intense contests with each other (Seehausen and Schulter 2004).

The last topic is acoustic reproductive communication. This is similar to mating frog calls. The male Cichlid quivers as a ritualistic display which produces a certain number of pulses and pulse period. Interspecific selection can happen between species based on the differences in these pulses. Sensory bias causes females to choose males that produce pulses specific to their species. Intraspecific selection also happens because males of the same species can be differentiated based on their fitness. Female choice for good genes and sensory bias is one of the deciding factors in this case, selecting for calls that are within the species and that give the best fitness advantage that will increase the survivability of the offspring (Maruska et al. 2012; Amorin et al. 2007).

When observing the evolution of the African Cichlids it is impossible to pin down one cause of their dramatic diversification. There are multiple reasons for their recent diversification which is being explored in great detail. With regards to sexual selection there are many possible causes of speciation. Female choice for color by sensory bias is one that helps to keep a reproductive barrier between species. However, if only female choice were the only reason, there would not have been an explosion in diversity in the population because the common ancestor would have had a smaller subset of color preferences. Male-male competition is another factor involved in sexual selection. A lot of cichlid species have color morphs that are at opposite ends of the spectrum but still very closely related. Males that show an advantage over their closely related counterparts give some insight into how speciation has occurred. Finally, unrelated to speciation by differences in color, acoustic reproductive communication can be a key factor. This is also known as reproductive character displacement. Female mate choice in this case is driven by the courtship call of the male. Her choice may be influenced by good genes for selection between males of her species or sensory bias for selection between species.

Many other topics could be explored with regards to this speciation. One being ecological character displacement. Within each lake there are different niches that a species could occupy. For example, different diets and depth of the water could help to separate different species. Overall, there are many factors that drive sexual selection in African Cichlids, and many more that can help cause sympatric speciation of the growing family.

Literature Cited

Allender, C.J., O. Seehausen, M.E. Knight, G.F. Turner, and N. Macleen. 2003. Divergent selection during speciation of the Lake Malawi cichlid fishes inferred from parallel radiations in nuptial coloration. PNAS 100:14074-14079.

Amorim, M.C.P., J.M. Simóes, P.J. Fonseca, and G.F. Turners. 2008. Species differences in courtship acoustic signals among five Lake Malawi cichlid species (Pseudotropheus spp.). J. of Fish Biol. 72:1355-1368.

Dijkstra, P.D., O. Seehausen, and T.G.G. Groothuis. 2005. Direct male-male competition can facilitate invasion of new colour types in Lake Victoria cichlids. Behav. Ecol. Sociobiol. 58:136-143.

Egger, B., K. Mattersdorfer, and K.M. Sefc 2009. Variable discrimination and asymmetric preferences in laboratory tests of reproductive isolation between cichlid colour morphs. Evol. Biol. 23:433-439.

Maan, M.E., O. Seehausen, and J. Van Alphen. 2010. Female mating preferences and male coloration covary with water transparency in a Lake Victoria cichlid fish. Biological Journal of the Linnean Society 99:398-406.

Maruska, K.P., U.S. Ung, and R.D. Fernald. 2012. The African Cichlid Fish Astatotilapia burtoni Uses Acoustic Communication for Reproduction: Sound Production, Hearing, and Behavioral Significance. PLoS One 7:e37612.

Pauers, M.J., and J.S. McKinnon. 2012. Sexual selection on color and behavior within and between cichlid populations: Implications for speciation. Current Zoology 58:475-478.

Seehausen, O., and D. Schulter. 2004. Male-male competition and nuptial-colour displacement as a diversifying force in Lake Victoria cichlid fishes. Proc. R. Soc. Lond. 241:1345-1353.

Selz, O.M., M.E.R. Pierotti, M.E. Mann, C. Schmid, and O. Seehausen. 2014. Female preference for male color is necessary and sufficient for assortative mating in 2 cichlid sister species. Behavioral Ecology 25:612-626.

Shuman.39 (talk) 19:04, 16 November 2014 (UTC)

Edit to existing page: https://en.wikipedia.org/wiki/Sympatric_speciation

African cichlids also offer some evidence for sympatric speciation. They show a large amount of diversity in the Great Lakes of Africa. Many studies point to sexual selection as a way of maintaining reproductive isolation. Female choice with regards to male coloration is one of the more studied modes of sexual selection in African Cichlids. Female choice is present in cichlids because the female does much of the work in raising the offspring, while the male has little energy input in the offspring. She exerts sensory bias when picking males by choosing those that have colors similar to her or those that are the most colorful. This helps maintain sympatric speciation within the lakes. Cichlids also use acoustic reproductive communication. The male Cichlid quivers as a ritualistic display for the female which produces a certain number of pulses and pulse period. Female choice for good genes and sensory bias is one of the deciding factors in this case, selecting for calls that are within her species and that give the best fitness advantage to increase the survivability of the offspring. Male-male competition is a form of intrasexual selection and also has an effect on speciation in African Cichlids. Ritualistic fighting among males establishes which males are going to be more successful in mating. This is important in sympatric speciation because species with similar males may be competing for the same females. There may be a fitness advantage for one phenotype that could allow one species to invade another. Studies show this affect in species that are genetically similar, have the capability to interbreed, and show phenotypic color variation. Ecological character displacement is another means for sympatric speciation. Within each lake there are different niches that a species could occupy. For example, different diets and depth of the water could help to maintain isolation between species in the same lake. Shuman.39 (talk) 03:32, 17 November 2014 (UTC)