Cichlid Diversity, Speciation and Systematics: Examples from the Great African Lakes

Cichlid diversity, speciation and systematics: examples from the Great African Lakes Jos Snoeks, Africa Museum, Ichthyology- Cichlid Research Unit, Leuvensesteenweg 13, B-3080 Ter vuren,.Belgium. Tel: (32) 2 769 56 28, Fax: (32) 2 769 56 42(e-mail: [email protected]) ABSTRACT The cichlid faunas of the large East African lakes pro vide many fascina ting research tapies. They are unique because of the large number of species involved and the ir exceptional degree ofendemicity. In addition, certain taxa exhibit a substantial degree of intra~lacustrine endemism. These features al one make the Great African Lakes the largest centers of biodiversity in the vertebrate world. The numbers of cichlid species in these lakes are considered from different angles. A review is given of the data available on the tempo of their speciation, and sorne of the biological implications of its explosive character are discussed. The confusion in the definition of many genera is illustrated and the current methodology of phylogenetic research briefly commented upon. Theresults of the systematic research within the SADC/GEFLake Malawi/NyasaBiodiversity Conservation Project are discussed. It is argued that systematic research on the East African lake cichlids is entering an era of lesser chaos but increasing complexity. INTRODUCTION The main value of the cichlids of the Great African Grea ter awareness of the scientific and economi Lakes is their economie importance as a readily cal value of these fishes has led to the establishment accessible source of protein for the riparian people. In of varioüs recent research projects such as the three addition, these fishes are important to the specialized GEF (Global Environmental Facility) projects on the aquarium trade as one of the more exci ting fish groups larger lakes (Victoria, Tanganyika, Malawi/Nyasa). to be kept and bred by many hobbyists ali over the Though based on sorne common grounds and con world. cerns, these three projects each have different empha The economie importance of the cichlids by no ses and time schedules. Of these three, the largest way diminishes their enormous scientific value as emphasis on biodiversity research was placed on the ever-stimulating research subjects for systematists, SADC/GEF Lake Malawi/Nyasa Biodiversity Con evolutionary biologists, ecologists, ethologists, servation Project, the first core program of which geneticists, morphologists, fisheries biologists, etc. ended in July 1999. While many scientific studies are of direct relevance As senior systematist of this project, I often had to to the economie importance of these fishes and may deal with questions concerning the numbers of (de contribute to a better fisheries management, others scribed and undescribed) fish species in the lakes and are more focussed on purely scientific aspects oftheir the speed of their speciation. Also the poor knowledge fascina ting biology. of current cichlid systematics was repeatedly ques tioned, often with a certain amount of scepticism. It is indeed hard to explain to non-taxonomists how diffi JouRNAL OF AQUARICULTURE AND AQUATIC SciENCES ClcHLm REsEARcu: STATE OF THE ART cult it is to estimate the number of species present in VOLUME IX the lake and to produce simple descriptions and clas Page 150 sifications. It is equally difficult to explain that the y .!/~ ,y ,(/ ,,/ ,..( large, present day taxonomie confusion in the se fishes fish species than any other lake in the world. is not necessaril y the result of po or quali ty research in Taken in an African context, the described Afri the past (a truism easily forgotten). Many problems can cichlids constitute about a third of the total are simply due to the inherent difficulty of the re number of i ts fresh water fish fau na ( fig.l ). However, search subject or, in simple words, to the fact that given the large numbers of undescribed species, more these fishes look so similar. It is from a certain feeling so in cichlids than in other families, this ratio will of frustration when trying to answer these FAQ's increase considerably when a more detailed inven (Frequently Asked Questions) as weil as possible that tory of the lake cichlids becomes available. this manuscript originated. In aU large East African Lakes, except Albert and Turkana, the majority of fishes belong to the family A unique vertebrate fauna Cichlidae (fig. 2). Several hypotheses have been Systematics is essen ti ail y the study of the diversity of forwarded to explain the aberrantly low numbers in life, in this particular case; of the East African cichlids. Lakes Albert and Turkana, but probably the intrinsic Hence, it is a key discipline in understanding the morphological features (Bauplan) of the ancestors unique features of these fishes. were not the major determining feature in this process A first observation is that the speciose nature of (Snoeks, in press). The relative importance of other cichlids in the Great African Lakes is unmatched in intrinsic versus environmental factors (physical, the world of vertebrates (table 1). This is a direct chemical and biological) is still to be determined consequence ofthe explosive speciation within these (Fryer, 1965;Fryerandlles, 1972;Greenwood, 1994; lakes, the results of which complete! y overshadow the Snoeks, in press). classic textbook example of t~e Galapagos finches. While the highest numbers of cichlids are found in The underlying evolutionary processes that have the three larger lakes, the situation is somewhat differ resulted in this multitude of species are subject matter ent for the non-cichlids (fig. 3). In view oftheir large for many specialized publications and will not be size, the three largest lakes do not have a dispropor discussed here. tionately large non-cichlid component (fig. 3a). How A second feature of this unique fauna is that the ever, while the smaller lakes (Turkana, Albert, Ed majority of the species are endemie to a lake, i.e. they ward, and Kivu) harbour mo~ethan athird of the non iive only in one lake system and nowhere else (see cichlid fauna, they only comprise a smail fraction (6 below). %) of the cichlid fauna present in the East African The two main features (species richness and Lakes (fig. 3b). endem1sm) àlone make the Great African Lakes the The aberrant position ofLakes Turkana and Albert largest centres ofbiodiversity in the vertebrate world. also becomes apparent in a species 1area plot (fig. 4 ). While the data for the non-cichlids are situated rela- . The African cichlids: the view of the accountant tively close to the fitted linear flinction, the correla- Cichlids are reported to be the third im;gest f~mily of tion is less in the cichlids, which are iimch more fishes (marine, brackish and freshwater) in the world wi~ely scattered around the fitted line. Removing the (Nelson,J994). However, the figure given byNelson data of Lakes Turkana and Albert resulted in a much is without any doubt an underestimate .. Based on narrower dispersal ofthe cichlid numbers aromid the current estimates (Kullander, 1998;Snoeks, in press), regression line. Further exploration of these data the total number of cichlids might weil be around through speeies/vailable volume plots slightly changed 2,400 species, which would make it the large_st family the .relative position of severallakes, but the aberrant of fishes, and even of vertebrates. position of Lakes Albert and Turkana remained (re Although many species occur in South and Middle sults not shown). America [estimated at 550 (Kullander, 199&)1, itis in the East African Lakes that cichlids have speciated in greatest profusion. In fact, the cichlids of these lakes Jou~AL oF AQUARICULTURE AND AQUATIC SciENCES constitute more than 10 % of the extant freshwater CICHLID RESEARCH: STATE OF THE ART fishes of the world and each of the three larger lakes VoLUME IX (Victoria, Tanganyika, Malawi/Nyasa) harbours more Page 151 Others Mormyridae Cichlidae Cyprinidae Amphiliidae Mastaeembelidae Clariidae Gobüdae Moohokidae Cyprinodontidae Figure 1. Relative species richness of the fish families living in the Mrican fresh and brackish waters. Data from Cloffa 1, 2, 4 (Daget etal., 1984, 1986, -1990). Meanwhile the taxonomy of certain groups bas changed. Renee the Cloffa concept of Bagridae now encompasses Bagridae as well as Claroteidae and Austroglanididae. Cyprinodontidae are currently Poeciliidae and Aplocheilidae. ENDEMISM HOW MANY SPECIES? AgeneraltrademarkofthecichlidsintheEastMrican This is not an easy question to answer and in a way a region is their high degree ofendemisni (> 90 % in correct answer is not particularly relevant at the most lakes, fig. 5). Again:, outliers for this feature are moment. What needs to be made clear is that, contrary . Lakes Turkana and Albert; Non-tichlid endemism is to the situation in other vertebnite groups su ch as birds far less, but reaches a level of almost 60 % in Lake or large mammals, we arefar from a complete inven Tanganyika. This is most likely related t6 the great tory of the African species of fish. Particularly for the ·age of this lake which is èstimated at between 9 and 12 cichlids, estimates vary considerably, but the oum million years, with sorne parts of the present day lake bers put forward have to be interpreted in a historical significantly younger (Cohen et al., 1993). context. A summary of curient estimates is given in As if pure species richness and endemism is riot Table 1. Of the total, less than half are scientifically enough for this fauna to be unique, a high intra described. The least known are Lakes Victoria and lacustrine endemism (the restricted distribution of a Malawi of which one third and two fifths of the species within the lake itself) is also observed in cichlids are described respectively. certain groups within the three major lakes, Victoria Even near the beginning of the twenty-first cen (e.g. Seehausenetal., 1998), Tanganyika(e.g.Snoeks tury new species-rich cichlid assemblages are still et al., 1994 and literature discussedherein) and Malawi/ being discovered in the East African Lakes.

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