Cichlids fish belong to the family Cichlidae. These fish inhabit a wide category of the environment which means that their adaptation is different. The different adaptations help this species of fish to fit within their specific niches. The diversity in these species means that they have divergent characteristics such as their temperament, quality of water in which they live and also their feeding habits. They live in different waters such as the fresh and also brackish waters. They are mainly categorized as secondary fishes. This is due to the fact that they originated from seawater to freshwater. This makes them have a high advantage in comparison to the fishes that are freshwater lakes. The advantage of these fish is in the fact that they can be able to colonize water bodies that have a high concentration of minerals dissolved. They are found in different geographical locations such as Asia, America and Africa. Over the years cichlid fish have undergone numerous evolutions. The aim of this paper is to discuss the evolution of cichlid fish in Lake Victoria and other African lakes.
The African cichlid originated from the seawater to the freshwater bodies. This made their adaptation to the new habitat to be different. Amongst the African lakes, Lake Victoria is considered to have the largest population of African cichlids. This is due to the fact that it has got four different genera and more than two hundred species (Fabrice et al 2008). This has been a subject of interest by the biologist considering the fact that lake Victoria does not provide isolation opportunities which is one of the reasons why evolution undertakes in a particular species.
One of the evolutionary processes that the cichlid underwent is with reference to the reproduction process. Their reproduction evolved in the same way in the three lakes that is Lake Victoria, Lake Malawi and Lake Tanganyika but they were independent of the habitat. In order to be able to adapt to the new habitat; there was a change in the brooding strategy amongst the cichlid fish. This enabled them to cope with the competition in these water bodies. The brooding strategy that was adopted is mouthbrooding. This means that the female cichlid fishes had to lay a small number of eggs and would take care of the fingerlings for a longer period of time (Darwin’s dream: the evolution of African cichlids 2009). The mouthbrooding strategy means that the mother does not have to find a breeding site. The mother can thus be able to provide protection to the offspring effectively. It also becomes possible for the offspring to adapt to the deep waters at an early age(Rosemary & George 2000). As these fishes continued to live in pelagic habitats leaving the rocky areas, their fecundity continued to greatly reduce. This was through a reduction in the number of eggs that these fish laid. This contributed to an increase in the size of the eggs that were laid by the females. It also resulted in an increase in the incubation period of the eyes. This means that the fry could reside in the mother’s mouth for a number of weeks until they were of 3cms in size. The females continue to offer protection to these fingerings even when they can swim on their own. This means that the fingerings can swim to the mother’s mouth in case of any perceived danger. The fact that the fecundity in the cichlid is low and the large size of the eggs indicates that there is a high level of investment by the parents in every offspring (Fabrice, Emanuel & Anthony 2008).
The cichlid fish are biparental; this means that both the male and the female take part in the process of protecting the offspring. By providing protection to the young ones, the survival of the cichlids was increased within the rocky and pelagic habitat which is mainly characterized by increased predation and scarcity of food.
Considering the fact that the cichlid offspring are hatched from eggs that are relatively large in size, the offspring are in a position to escape the predators and also find their own food. They are also in a position to adapt to a long period of time without food. This shows that the mouthbrooding strategy of breeding has enabled the African cichlids to continuously evolve over time.
The cichlids have evolved according to their geographical locations. The African cichlids have been considered to have undergone a rapid rate of evolution. This is mainly due to their geographical location. The African lakes especially those in the rift valley such as lake Victoria, Tanganyika and Malawi are considered to have a more stable climate compared to the temperate regions which are characterized by significant climatic fluctuations. This climatic stability has led to support of the specialization and also the speciation theory of evolution of the cichlid fish.
It is also evident that the African cichlid species are of different colors. This has been linked to genetic variations amongst the different species that reside on rocky shores. Geographical separation amongst different species of cichlids results in genetic variation. Genetic differences are evident amongst species that are separated by a distance of 700 meters. This is evident in lake Victoria where some cichlid populations are separated by rocky shores and small islands According to research, major fluctuations in the lake levels have an effect on the specialization and also the speciation process of the cichlid fish. In Lake Malawi, the evolution of the cichlid fish was contributed by the divergence in the peripheral habitat. According to a study of the fish species in Lake Chilingali which is approximately located eleven kilometers from lake Malawi, it forms a breeding ground for the Rhamphochromis, a cichlid species which was initially thought to be predatory. The two water bodies are connected but this species was restricted from accessing lake Malawi (Martin, Paul, Gary, Rosanna, Allan & George 2007).
The species in Lake Chilangali has a unique coloration from that in Lake Malawi and is smaller in size. When the male from Lake Chilangali is mated to a female from Lake Malawi, the female depicts a high tendency of mating assertively. This shows that the two cichlid species are incipient species. This study makes it evident that isolation amongst the cichlid species and their reconnection due to changes in the level of the lakes is one of the factors that have led to the increased diversity amongst the cichlid species in the African lakes (Martin et al 2007). The Rhamphochromis males from lake Malawi exhibit a small range of colors which mainly include orange, white, silver and black. The males that inhabit Lake Malawi are different in terms of coloration, especially the fins.
Lake Malawi is characterized by many islands. This makes some of the population of the cichlid species to be separated by either the rocky shores or the sandy bays. The cichlids which inhabit the rocky shores have got a high characteristic of specialization. They also do not move freely into the swampy areas or the open waters. This restriction makes them lack a dispersal phase within their lifecycle; for instance, migration. This means that they are completely isolated which plays a major role in the process of rapid diversification of the species.
The feeding practices of cichlids have also contributed to their evolution process into the current wide range of species. This is due to the fact that the cichlids have a very efficient feeding habit. This makes them be able to feed on a wide range of food products. In the Africa lakes, there is intense competition for food amongst the different fish species. The cichlid species have resulted in a wide range of specialization to enable them to survive. This enables them to feed to the wide array of food in the water bodies. Initially, the ancestral cichlid used to feed on the insects and the planktons. Currently, the different species of cichlid that have evolved over the years have different specializations in terms of feeding and on a lean food niche (Fabrice et al 2008). This is evident from the fact that some of the cichlid species feed on plankton algae, fish scales and insects. Considering the feeding specialization amongst the cichlid species has enabled this species to coexist in the African lakes. This shows that the process of trophic specialization which refers to feeding habits has contributed to the process of evolution of the cichlid fish in the African lakes. This has resulted in an increase in the diversity of the cichlid fish species. The fry cichlids are able to feed on the crustaceans and the zooplanktons in all the habitats compared to the other species of fish which only feed on the unicellular algae (Fabrice et al 2008). This increases the diversity of the cichlid species in terms of size. This is evident from the fact that their size range from 25 centimeters to one meter.
With regard to the feeding habit of the cichlid fish in the African lakes, they have also undergone morphological evolution resulting in the morphological specialization. This refers to form specialization which enables them to feed on their divergent diets effectively. The morphological specialization is evident in a wide range of their body forms; for instance, the teeth are of different shapes and also sizes. The mouths of the cichlid fish and their lips have also undergone morphological evolution. Their jaws also enable them to exploit the reduced food resources in the water bodies. They have got two jaws which help them to easily obtain food and process it; this concept of specialization is evident from the cichlid species in Lake Tanganyika. This lake was separated into three parts for a long time. In the southern part, the Lamprologus sexifasciatus depends on the small snail and the shells for food which it can effectively crush using its jaws. In the northern part of the lake, there is the Lamprologus tetrocephalaus which feed on both the small and the large snails. The nocturnal Lamprologus toae depends on the invertebrates. Despite the ancestor being Lamprologus sexifasciatus, the species in the northern part of the lake underwent evolution resulting in two different species. This evolution enabled these species to effectively exploit their niches. The species in the southern part of the lake did not undergo any form of specialization.
The evolution of the African cichlid fish species can also be explained in terms of their sexual selection. Sexual selection refers to the concept where different populations of a species have got divergent success in terms of reproduction. Within the African cichlid fish species, sexual selection arises from the number of females that the male is able to attract for mating. Sexual selection leads to an increased evolution of male characteristics in order to effectively attract females. The females also undergo evolution in terms of the preferences of the traits that are displayed by the males.
In Lake Malawi, the cichlid has experienced a rapid process of evolution radiation. This is due to the fact that the species have evolved into more than 400 different species within a period of 700,000 years (Patrick & Thomas 2009).
According to Patrick &Thomas, the evolution process of this species underwent three different phases of cladogenesis. Every clastogenic event was stimulated by a different force. The first phase culminated into two main divergences. These include the species that dwelled in the sandy waters while the others dwelled in the rocky habitat. This resulted in the respective species evolving differently according to the divergent benthic macro habitats (2009).
Considering the fact that the rocky habitat is characterized by a shortage of trophic resources, competition for food became intense. This resulted in more evolution of this species resulting in the second phase of cladogenesis. This evolution was mainly in terms of the species morphology. This enabled this species to adapt effectively to the scarce trophic resource.
The third phase of the evolution of this species was mainly with regard to nuptial coloration, especially amongst the male species. This was mainly with regard to the need to the increased divergence in terms of sexual selection amongst the females.
Lake Tanganyika is considered as one of the African lakes that have got the widest range of cichlid species. According to research (Fabrice et al 2008); the studies have shown that these species are endemic to this lake and that these species are not present in other lakes. This is due to the fact that this lake is closed which means that they evolved cichlid fish species cannot be able to access another aquatic environment. It also means that all the cichlid fish species in this lake have a single ancestor. This lake is considered to be very old since it was formed through tectonic forces approximately 20 million years ago. This means that the cichlid fish species in this lake had considerable time for the process of evolution to take place.
According to Fabrice and his counterparts (2008); the aquatic environment in Lake Tanganyika has been stable for millions of years. This makes the process of evolution of the cichlids undertake effectively without any form of interruption. This contrasts with the environment in Lake Victoria which has experienced a series of interruptions through drying out approximately 14,000 years ago. This is due to the large surface area of the water body and its limited depth. Lake Tanganyika is however narrow and deep giving it a small surface area which makes it not be greatly affected by changes in climate.
Over a long duration of time, the cichlid fish species in Lake Tanganyika have continued to branch into divergent myriad species and become more specialized differently. A particular species of the cichlid fish in Lake Tanganyika adapts to a limited environment. This means that it evolves in a different way according to the nature of the environment. This makes the different species have different coloration depending on the geographical habitat of the species.
In conclusion, it is evident that the African cichlid fish species have undergone a continuous process of evolution over the years. This has resulted in an increase in the number of species that result. There is a wide range of factors that have led to the rampant rate of evolution. The species in Lake Victoria are the ones that have undergone rapid evolution according to scientists. This is due to the fact that lake Victoria has experienced a series of drying out as a result of climatic changes compared to lake Tanganyika.
The evolution of the cichlid fish species has been explained to result from geographical isolation. This is in terms of the habitat that a particular species colonizes. These are either the rocky, swampy or sandy habitats. The geographical habitat results in the isolation of the species. This means that these species undergo independent evolution since the species do not access a wide range of aquatic environments.
The geographical isolation results in a particular cichlid species undergoing morphological evolution. This is in terms of the feeding habits; for instance with regard to the teeth and the jaws. The morphological evolution enables the divergent cichlid fish species to effectively exploit the scarce trophic resources. This results in the concept of specialization amongst the cichlid species.
The evolution is also enhanced by the fact that the cichlid fish have got a characteristic of sexual selection, especially amongst the female. This is mainly in terms of coloration. The females select a mating partner according to the particular coloration.
The African cichlid fish species have also continued to evolve over time with regard to their reproduction strategy. The African cichlid has incorporated the concept of mouthbrooding. Both males and females are involved in the process of protecting the offspring. This increases the chance of survival of the cichlids due to the fact that the offspring are given enough protection by the mother. The size of the eggs that the female lays are relatively larger in size which means that the offsprings are large in size which further increases their chance of survival in the deep waters where there are more predators.
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