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Hybridization and Speciation Among Cichlids: the Case of ‘Wesafu’, an Ecotype Cichlid

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Hybridization and Speciation Among Cichlids: the Case of ‘Wesafu’, an Ecotype Cichlid View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aquatic Commons FSN-FG 0004 HYBRIDIZATION AND SPECIATION AMONG CICHLIDS: THE CASE OF ‘WESAFU’, AN ECOTYPE CICHLID MEGBOWON I1*, H. A. BOMBATA-FASHINA2, T. O. MOJEKWU1, AND O. A. ADEJONWO1 1 Department of Fish Technology and Biotechnology, Nigerian Institute for Oceanography and Marine Research, Victoria Island ,Lagos.2 Department of Fisheries, Faculty of Science, Lagos State University, Ojo, Lagos Copyright 2010, Fisheries Society of Nigeria. components of subsistence fisheries for This paper was prepared for presentation at the 25th Annual International Conference and Exhibition in Administrative Staff College of Nigeria thousands of years but have gained (ASCON), Topo-Badagry, Lagos, Nigeria, 25th – 29th October, 2010. prominence in recent years in areas where This paper was selected for presentation by an FISON Program Committee following review of information contained in an abstract submitted by the they are not endemic (Modadugu and author(s). Contents of the paper, as presented, have not been reviewed by the Fisheries Society of Nigeria and are subject to correction by the author(s). Bellen, 2008). Fitzsimmons (2007) The material, as presented, does not necessarily reflect any position of the Fisheries Society of Nigeria, its officers, or members. Papers presented at reported that tilapia have become the FISON meetings are subject to publication review by Editorial Committees of the Fisheries Society of Nigeria. Electronic reproduction, distribution, or second most important fish produced in storage of any part of this paper for commercial purposes without the written consent of the Fisheries Society of Nigeria is prohibited. Permission to Aquaculture. This shows how significant reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous tilapia is to the world fisheries. acknowledgement of where and by whom the paper was presented. Write Librarian, Fisheries Society of Nigeria (FISON), P. O. Box 2607 Apapa, Essentially there are three genera in this Lagos. family, based on reproductive behaviour. They are; Oreochromis, Sarotherodon and ABSTRACT Tilapia. Oreochromis species are maternal Fishes of the family Cichlidae are known mouthbrooders, Sarotherodon species are for spectacular adaptive radiation and bi-parental mouthbrooder while Tilapia therefore serve as a model for species are substrate spawners (Christian, evolutionary and ecological studies. They et al, 2002). The Tilapia natural genetic are highly speciated due to hybridization resources are restricted to Africa but the that frequently occur in the wild. The culture industry is predominant in Asia. existence of an ecotype cichlid, ’wesafu’ in Compared to many other fish families that Epe lagoon, Lagos, Nigeria appears to be remained unchanged for millions of years, the result of such hybridization. This paper cichlids are highly speciated due to reviews the profile of wesafu and compare hybridization that frequently occurs in the the species with other cichlids, evaluate wild (Barlow, 2000). the probable causes of speciation which includes diversity in feeding morphology, Evolution of African Cichlid Fishes mate choice, adaptation to changes in The natural distribution patterns of tilapia habitat arising from water level dynamics , are the result of evolution (Kocher, 2005). eco-phenotypic variation, restricted Fishes of the family have long been known migration to predation and introgressive for their spectacular adaptive radiation and hybridization. The implication of such have therefore served as a model for speciation and hybridization were also evolutionary and ecological studies highlighted. (Barlow, 2000). Keywords: Speciation, Hybridization, In the lakes of East Africa (lakes Victoria, Cichlids, wesafu Malawi and Tanganyika), fishes of the family, cichlidae have undergone an INTRODUCTION extraordinary rapid and extensive radiation A cichlid is a fish in the family Cichlidae, (Kocher, 2004). At least 1500 species of a family of fishes of almost unbelievable fish have arisen from a common ancestor diversity. They differ greatly in size and in the last 10 million years (Kocher, 2005). taxonomic group (Olojo et al, 2003). The author maintained that within Lake Tilapias are members of this diverse fish Malawi over 700 species have arisen family and serve as important within just two million years. It becomes 320 Megbowon I, Bombata-Fashina H. A., Mojekwu T. O., & Adejonwo O. A. FISON EKO 2010 necessary to elucidate the forces which exchange or geographical variation in have caused this rapid speciation. A environmental condition (Christian et al, number of forces are at work which 2003). includes trophic specialization and sexual selection. We suspect that rapid evolution Speciation and Hybridization in Tilapia of male traits and female preference Although early experience influences the contributes to pre-mating isolating development of preferences in cichlid mate mechanism among local population, choice, the same species can be very facilitating speciation over small spatial ―tolerant‖ and spawn with members of scales (Kocher, 2004). It becomes other species appearing very different from necessary therefore to carry out gene conspecifics. The conditions under which mapping for phenotypic traits associated such inter-specific spawning occurs in with speciation, such as jaw morphology captivity are considered to exist in the and adult colour pattern. This will enable field. scientists to identify the genes responsible Bringing different tilapias together through for speciation of these fishes, and to study transfers has a consequences of undoing the geographic distribution of allelic the work of nature; selection over many variants among populations and species in thousands of years. From these we can the wild, (Kocher, 2005). infer that the conventional system nomenclature (genus, species, sub species) Speciation among Tilapias is fine for describing a natural situation but A species is never stable in nature. It may inadequate for an aquaculture situation in die out or spread to form another species which interbreeding occurs, as in tilapia (Ayinla and Williams, 2005). The author (Kocher, 2005). maintained that in taxonomy, species with Many cichlid fishes are genetically similar, a very restricted distribution are and inter-specific spawning often produces considered ―young‖ species, and those fertile hybrids. Professor H.M. Peters (in with wide distribution are considered Trewavas 1982) has artificially fertilized ―old‖. According to the author, once a eggs of Sarotherodon melanotheron with species has a very wide distribution it may sperm from Oreochromis niloticus. F1 fall apart. This happens frequently with hybrids of both sexes were obtained and fish species when water bodies become 12 of them, 4 males and 8 females of 82 – mutually isolated and the separated 98 mm standard length were examined. populations change through new mutations They resemble O. niloticus in most and genetic flux. The natural distribution contrasting proportion. The depth of the of pattern of tilapia suggests such a pre-orbital bone, which is S. melanotheron situation. Evolution of new strains of the of this size measure 22 - 25.5% length of cichlids is making identification difficult. head, in O. niloticus 15.0 - 19.0 in hybrids Morphological characters (Meyer et al, 17.0 - 20.0. In number of scales, vertebrae 1990) and molecular studies (Kocher et al, and dorsal fin rays they are intermediate 1993) were reported to have failed in the author reported. With O. mossanbicus resolving some relationship in the cichlid male and S. melanotheron female, the within the last two decades. hybrids were all female. With T. tholloni, Ecological factors play significant role in hybrids were obtained when the male speciation (Schuter, 2000). Other parent was S. melanotheron. The reverse possibilities are introgressive cross resulted in high mortality among the hybridization, eco-phenotypic variation or embryos (Trewavas, 1982). local adaptive differentiation in which case The target of inter-specific hybridization synoptic populations of two species should of two species in tilapia is to obtain be more similar due to local gene monosex populations (Beardmore et al, ISSN: 1117-3149 PROCEEDINGS OF FISHERIES SOCIETY OF NIGERIA (FISON) ASCON, BADAGRY 25th-29th OCTOBER 2010 FSN-FG 0004 321 Hybridization And Speciation Among Cichlids: The Case Of ‘Wesafu’, An Ecotype Cichlid FISON EKO 2010 2001). The author observed that the bulk observed weight range of 495 – 1500 g for of research on the genetic basis and wesafu is at variance with that of T. commercial potential of monosex hybrids guineensis (11 – 352 g). From the finding has been carried out on tilapia. Many of the above study it was observed mean Oreochromis hybrids are characterized by lateral line were the same (28). a majority of males, the occurrence of all Taming 1944 in Bombatta et al, 2004 male broods is relatively common and it is observed that there is a relationship where the major interest in hybridization between some meristic characteristics and lies. The first report of monosex hybrids the environmental condition to which eggs created significant interest with the and larvae are exposed. He further showed potential for mass production of all male that the number of rays in the pectoral and progeny to prevent the serious problem of the dorsal
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