Human influence on the sexual behavior of African cichlids

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Human influence on the sexual behavior of African cichlids

By definition published by Charles Darwin (1958) in his manuscripts and described it in more detail in his later book (Darwin 1871), sexual selection is "a struggle between individuals of one sex, generally the males, for the possession of the other sex". In general, the female choose the most healthy-look male and by this way she can guarantee the best genetic match, transmitting to offspring such evolutionary advantage. The qualities that make it a more attractive partner compared with the competitor may be many, like feathers, colors, horns, physical strength, and are the comparisons between these features that will ensure the best female choice. This article will focus on sexual selection of cichlid fishes that inhabit great lakes, especially in Africa.

Belonging to the Perciformes order , Cichlidae is a family of freshwater fish which includes about 227 genus. Have a laterally compressed body, one nostril only side of the body, the divided line and lateral spines on the dorsal and anal fins. The group is characterized further by the presence of teeth in the two jaws and throat as well as the gut, which leaves the stomach the left side. The African continent, more precisely in the Rift Valley region (Lakes Victoria, Malawi and Tanganyika) stands out for its biodiversity of species of this family. At least three evolutionary forces may have contributed to the richness of cichlids: ecological selection, sexual selection and genetic conflict.

The haplochromines stand by the great variety of species in cichlids, many living in sympatry, as well as the mode of speciation, and are the group with the greatest diversity in the Great Lakes. In his study, Kocher (2004) suggests that Lake Malawi have been colonized by a single cichlid fish, which diverged two major benthic clades: Those who live in habitats with sandy soil (non - mbuna) and the habitat of rocky soil (mbuna ). The adaptation to the type of soil took several secondary morphological differentiation, such as trophic apparatus of mbuna. Their oral apparatus suffered two changes in morphology: One is the presence of a second jaw, located in the pharynx, used to break down food and macerating, allowing the speciation of the oral in the capture of food (Turner, 2007) the other one is the withdraw of certain elements in the upper jaw allowing a wider range of jaw movements. The buccal apparatus differentiation may represent a complete change in diet, behavior and ecological niche of the species. Such an idea has been widely documented, including by Charles Darwin and his experience with the beak of the finches in Galapagos.

Kocher (2004) also defends that sexual selection may also have an important role in the evolution of cichlids, and this would be the third stage of adaptation. Sexual dimorphism of mbuna occurs through variations of color pattern and the size difference between males and females . The parental care, as well as guarding of eggs and larvae is striking between individuals of this family, and this role played primarily by females. Males contribute only genes that are inherited. This discrepancy investment in parental care promotes sexual selection held by females.

The Cichlidae family is characteristic for presenting social interactions, much in dispute among males for territory, food, reproductive partner, as in male-female interactions (Baerends & Baerends van Roon, 1950).

Disputes among males may lead to the establishment of hierarchy dominance, in which the dominant animal defends a territory and has access preferred to females, obtaining higher reproductive success (Baerends & Baerends van Roon, 1950). This can occur due to two important mechanisms: the competition between males, called intra-sexual selection and female choice, called inter-sexual selection.

In the dispute between males several factors can affect the results the dominance hierarchy, as the size of the combatants, the previous experience and prior residence (Gonçalves-de-Freitas, 2002).Regardless of which factor is influencing the dominance hierarchy, the dominant male has a better competitive ability in relation to submissive, since that the most successful fish can reduce the access to some resources from the weaker fish (Candolin & Wong, 2005).

In general, females prefer to mate with dominant males which can both promote access to environmental resources as the material these potentially higher genetic males (Qvarnström, & Forsgren, 1998). This indicates that intra selection and sexual inter-sexual can operate mutually, reinforcing the same phenotypic and behavioral characteristics of males.

The three evolutionary factors responsible for the diversity of cichlids also collide in mating systems. With the differentiation of habitats and diet what occurred was the separation of environmental niche that each fish has occupied, in an sympatric speciation process. In sympatric speciation, populations diverge while still occupy the same area.

In the haplochromines case, another sexual selection mechanism is based on the recognition by fish coloration. Kocher (2004) studied the effect of light on that visual-based selection. His studies indicate that females prefer partners with the same color pattern but it is still possible to mate with different colored fish.

Water pollution - mainly due to human action - has made the water turbid, committing fish recognition engine which end up mating randomly and reversing the process of separation of the species (Seehausen, 1997). Morphological changes were also studied in benthic fish before and after the ecological changes. Because of the turbid water the diet of these fish has been changed and they became more carnivorous which caused a decrease in the size of their intestines (Lowe -McConnel, 2009).With this fact we can conclude that unfortunately human intervention results in changes in gene flow of these populations, which have interfered with the process of speciation. Speciation can be seen as the evolution of mechanisms of reproductive isolation between populations that previously performed genetic exchanges. These mechanisms must be maintained by barriers to gene flow for incipient species remain as separate entities.

References:

Baerends, G.P. & Baerends van Roon, J.M. (1950) An introduction to the study of the ethology of cichlid fishes. Behavior Supply, 1: 1-243.

Candolin, U. & Wong, B.B.M. (2005) How is female mate choice affected by male competition? Biological Reviews 80, 559-571.

Darwin, Charles. (1871) Descent of man, and selection in relation to sex. London : John Murray, Albemarle Street.

Gonçalves-de-Freitas, E. (2002) Confrontos assimétricos e hierarquia de dominância em ciclídeos. Anais do XX Encontro Anual de Etologia. Natal-RN. pp. 137-139.

Kocher, T.D. (2004) Adaptive evolution and explosive speciation: the cichlid fish model. Nature Reviews Genetics 5: 288-298.

Lowe-McConnell, R. (2009) Fisheries and cichlid evolution in the African Great Lakes: Progress and problems. Freshwater Reviews 2 (2): 131-151.

Qvarnström, A. and Forsgren, E. (1998) Should females prefer dominant males?Trends in Ecology and Evolution 13, 498-501.

Seehausen O., VanAlphen J.J.M., Witte F. (1997) Cichlid fish diversity threatened by eutrophication that curbs sexual selection. Science, 227, 1808–1811.

Turner, G.F. (2007) Adaptive radiation of cichlid fish. Current Biol 17(19):R827-31

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