Geographical distribution of African freshwater fishes

Geographical distribution of African freshwater fishes is discussed with emphasis on the effects of major continental features, hydrographic history, and Pleistocene climatic fluctuations. Differences in the modes of dispersal and biological interactions among various categories of fishes, ecological as well as phyletic, have also had marked effects on distribution.
The African continent can be divided into ten ichthyofaunal provinces. The geography of these provinces and composition of their fish faunas is briefly described. The paper concludes with a consideration of the faunistic relationships of African lakes with endemic fishes.     

Phylogenetic relationships and evolutionary processes in East African cichlid fishes

Since their discovery almost one hundred years ago, the adaptive radiations of cichlid fishes in the largest East African lakes have fascinated biologists. They are a prime example of explosive speciation. Among vertebrates, these species assemblages are the most species rich and the most diverse, morphologically, ecologically and behaviorally. Recent phylogenetic analyses of molecular data and refined knowledge about the geological history of the East African lakes are throwing new light on the evolutionary history of these extraordinary fish faunas.     

Comparative aspects of adaptive radiation and speciation in Lake Baikal and the great rift lakes of Africa

Lakes Baikal, Tanganyika and Malawi have similar origins, are physiographically similar, and of similar size. The hydrological regime of Baikal is, however, very different from that which prevails in its African sisters. Apart from being much cooler, it differs fundamentally in being oxygenated to all depths while the two great African rift lakes possess only a relatively thin oxygenated surface layer and have vast oxygenless, and therefore azoic, abyssal regions. Nevertheless, like Baikal, they have rich endemic faunas.That these faunas originated largely by intralacustrine speciation and not by multiple invasion is now well established. They provide some of the world's most spectacular examples of species flocks, and some groups display what has been aptly described as explosive speciation. Certain features, and especially the adaptive radiation, of some of the groups involved, are noted. Comparisons between lakes are illuminating. Some species flocks, such as those of amphipods, sponges and turbellarians of Baikal and the atyid prawns and potamid crabs of Tanganyika, have no counterparts in the other lakes. Other groups, such as the prosobranch gastropods, ostracods and harpacticoid copepods of Baikal and Tanganyika, and the fishes of all three, involve representatives of the same major group, though often of different families or even higher taxonomic categories.That allopatric speciation has been involved is universally acknowledged but the problems posed by species multiplication in deep water in L. Baikal have led to suggestions that sympatric speciation could have played a part. Notwithstanding the difficulties, it is suggested that the process can be explained without invoking the assistance of the sympatric model.The faunas of these lakes provide immense fields for investigation and enormous intellectual challenges. While each is an entity in itself, comparative studies may be particularly enlightening.The substance of this paper was presented as a lecture at the First International Baikal Vereshchagin Conference held in Listvyanka, Irkutsk Region, U.S.S.R. in October 1989.     

Do coral-reef fish faunas have a distinctive taxonomic structure?

Do the highly diverse fish faunas that associate with coral reefs have distinguishing taxonomic and ecological characteristics, as proposed by Choat and Bellwood (1991) and Bellwood (1996)? Does a 50?my old (Eocene) fossil fish fauna from Italy represent a coral-reef fish assemblage that provides unique information about the evolution of such assemblages, as claimed by Bellwood (1996)? I compared the structure of the reef fish faunas of adjacent tropical regions rich and poor in coral reefs, in both America and Polynesia, and found that they exhibit no substantive differences in relative species richness among families of typical “coral-reef” fishes. While coral-rich regions have larger reef fish faunas, a variety of factors probably contribute to such differences. Thus coral-reef fish faunas may lack a distinctive taxonomic structure. A similar comparative approach would be useful for assessing whether assemblages of fishes on coral reefs have distinctive ecological characteristics. Based on patterns of habitat use by modern tropical shorefishes, the Italian Eocene fauna includes few definite reef fishes, and may well consist primarily of non-reef fishes preserved in a non-reef habitat. Until we know more about the environment in which those fossils were preserved, that fauna can contribute little to understanding how coral reef fish assemblages have evolved.     

Endemism, speciation and adaptive radiation in great lakes

Synopsis Evolution in great lakes has often been both quantitative (many endemic species of distantly related taxa often being present) and qualitative (outstanding levels of adaptive radiation having sometimes been achieved). These situations pose many questions, such as why there are so many endemics and so many superspecialists (and at the same time often many sibling species), as well as presenting problems relating to such matters as convergent evolution in different lakes, the possible role of key innovations, the nature of isolating mechanisms, competition and co-existence in complex communities, the roles of diverse mutualistic associations, and many others. These rich faunas also provide particularly favourable opportunities for studying patterns of speciation, while attempts to elucidate phylogenies in groups such as African cichlid fishes, that have radiated in several lakes, can be pursued on both a broad scale and at the intralacustrine level using both recently developed techniques and time-honoured methods. Rates of evolution, which differ widely between ecologically equivalent taxa in different lakes, have sometimes been extremely rapid, as attested by both molecular data and evidence from field studies. Notwithstanding their evolutionary exuberance, these rich faunas are fragile as demonstrated dramatically by the appalling tragedy that has befallen the haplochromine cichlid flock of Lake Victoria.Paper from the Canadian Society of Zoologists symposium Great Lakes of the World, organized by David L.G. Noakes.     

Towards a cohesive strategy for the conservation of the United States’ diverse and highly endemic crayfish fauna

The fossil record of cichlids is sparse, and every new discovery can provide new insights into the evolutionary history of this speciose freshwater fish family. In this article, we describe †Rebekkachromis gen. nov. from the middle-to-late Miocene (c. 11 MYA) of the Central Kenya Rift within the East African Rift system. †Rebekkachromis is represented by two species that differ from all other fossil and extant African cichlids, except Etia, in possessing the unique character combination of two supraneural bones and a set of robust tricuspid oral teeth in the outer row of the dentition. Furthermore, †Rebekkachromis exhibits the only proposed morphological synapomorphy of the Haplotilapiini, namely the presence of tricuspid teeth in the inner row of the oral dentition. We show that †Rebekkachromis constitutes the oldest reliably identified fossil record of a haplotilapiine. The evolution of cichlid fishes possessing tricuspid teeth in the rivers and lakes of the Central Kenya Rift during the middle-to-late Miocene could have been facilitated by volcanic activity, as repeated ash falls may well have fostered the growth of algae and in particular diatoms. These fishes could thus have had a major advantage, because they could exploit the newly available, rich food resources.

     

Human-induced changes in the composition of fish communities in the African Great Lakes

Summary Large natural African lakes contain unique and diverse fish faunas which have evolved within each lake in a comparatively short period of time. members of the family Cichlidae are particularly diverse, although there is strong evidence to show that the haplochromines in Lake Victoria, and possibly Lake Malawi, are monophyletic. The unique faunas in Lakes Victoria and Kyoga have been subject to perturbations from the introduction of exotic fish, and the faunas in these and other lakes have been disturbed by fishing activities and other human endeavours.Factors governing the establishment of exotic species are not clearly understood. The exotic fish must be physiologically adapted to their new environment, able to compete successfully both for habitat and for food at each stage of their life history, able to avoid predation and must have a suitable reproductive potential. Although about 50 species of fish have been introduced into African inland waters, including reservoirs, only comparatively few, in particular Nile perch (Lates niloticus), various cichlids (especially tilapias) and clupeids (Limnothrissa miodon), have been successful in establishing themselves. Those that have become established have had obvious but unquantifiable impacts on the indigenous faunas.It is difficult to differentiate between the effects of fishing and of the presence of alien fish on the fish species composition of the lakes (Witte et al., 1992). Many of the lakes were overfished before introductions were made, with a resultant decline in some species, especially the larger ones, and the virtual disappearance of others. Some lake fish faunas, such as those of Lakes Kyoga and Victoria, which have been subjected to the perturbations described above, continue to change rapidly (Ogutu-Owayo, 1990b).There is a fundamental need to collect biological information on the fish communities of African lakes for effective management, resulting not only in the conservation of unique fish faunas but also the production of sustainable fish yields for the people relying on this source of protein. This information is required before any more introductions of exotic fish are made.     

The demonstration of speciation in fossil molluscs and living fishes

Contrary to a recent assertion, freshwater (and marine) prosobranch gastropods and freshwater bivalves are subject to considerable variability. This, and the lack of a detailed understanding of the taxonomy of the forms involved, makes it difficult to accept that the changes documented by Williamson (1981) in a fossil sequence from Lake Turkana (Africa) represent speciation events. That 10 lineages, involving gastropods and bivalves, should change simultaneously, and the deviant forms should then simultaneously become extinct, can, we believe, be more plausibly attributed to ecophenotypic responses to environmental changes than to speciation. In revealing the pattern and process of evolution, both fossil and living forms are helpful, but in demonstrating the fine-scale events during and after speciation in living animals one can utilize techniques and observations that cannot be applied to fossil material. African cichlid fishes are particularly informative in this respect. Their current explosive radiation can be interpreted as a punctuational event in evolution.     

Unique qualities and special problems of the African Great Lakes

Synopsis The African Great Lakes consist of large, deep rift valley lakes (e.g. Malawi & Tanganyika) and shallower lakes between the Eastern and Western Rifts (e.g. Victoria). They are a group comparable in size to the North American Great Lakes, but are old. Most are seasonally thermally stratified, and wind is the decisive factor that determines the annual cycle of cooling and mixing. Lakes Tanganyika, Malawi and Kivu are meromictic, with deep relict hypolimnia. Large magnitudes and time scales of periodic internal motion, where these have been measured, appear unique among lakes. These lakes harbour the world's richest lacustrine fish faunas, and the family Cichlidae provides the supreme example of geographically circumscribed vertebrate evolution. The lakes provide a unique comparative series of natural laboratories for evolutionary studies. Primary production is generally high, but in the deeper lakes standing stocks of plankton and of small fish species are low. These pelagic populations are characterised by very high P:B ratios. The fisheries are productive and of socio-economic importance. Large-scale mechanised fishing is not compatible with the survival of the diverse fish communities. Cichlids appear especially vulnerable to unselective fishing. Aquatic reserves might offer a means of survival for at least some communities. Various pollution threats exist. Because water retention times are long, extremely long for some deep lakes, and flushing rates are low, the lakes are vulnerable to pollution which would be long-lasting. Introductions of alien fishes have mostly had undesirable or disastrous results. While the faunas are one of the significant natural heritages of mankind, their conservation must realistically be linked to the legitimate development of the lakes for the well-being of the people who live there. Scientific value alone will not protect the lakes. Just as survival of African terrestrial wildlife in extensive reserves depends heavily upon tourism, so also might the cichlid flocks in underwater reserves. Greater interest from the international scientific community is needed to further rational development and conservation of these great lakes.Invited Editorial     

The bounty of minor lakes: the role of small satellite water bodies in evolution and conservation of fishes in the Lake Victoria Region,East Africa

The Lake Victoria Region (LVR) encompasses the large lakes Victoria, Kyoga, Edward, George and Kivu, as well as scores of small satellite lakes within the parent catchments. Taken as a whole, the LVR originally harbored a unique fish fauna that included in excess of 600 endemic species of cichlid fishes. As a result of human influence, including a commercial fishery and the introduction of several exotic species, nearly 200 cichlid species and several endemic genera have become extinct from lakes Victoria and Kyoga. Recently, we have discovered that some of the apparently extinct taxa survive as extant representatives in the satellite lakes. Here, we summarize the findings of our ecological survey of the fish species of the satellite lakes. We also discuss the results of some preliminary genetic analyses, and highlight major genetic and ecological changes in the fish fauna that have taken place in the regional fishery. Minor lakes now play a crucial role in conserving the endangered species of the entire region, and also as living museums of East African ecological history. Our findings allude to the historical importance of minor satellite lakes as natural refugia for the fishes of the Lake Victoria Region, a region characterized by a history of geological and climatic instability.     

The late Cenozoic Viviparidae (Mollusca, Gastropoda) of the Albertine Rift Valley (Uganda—Congo)

During late Cenozoic pre-rift times the viviparid genus Bellamya was probably confined to eastern Africa while in the Congo Basin occurred the genera Neothauma and Kaya (a new genus described herein). During the Pliocene, Kaya became extinct and Neothauma became a relict in Lake Tanganyika. All African rift lakes formed during or after the Pliocene were colonised by populations of Bellamya, which evolved into lacustrine endemics. The changes in shell morphology in Bellamya, such as ornamentation functioning as protection against predators, are modest and repetitive in time and space. After the initial adaptations stasis followed, and there is no indication of an arms race between prey and predator in this genus. In the lakes of the western rift that were formed prior to the Pliocene, namely Lake Tanganyika and Palaeolake Obweruka, Neothauma instead of Bellamya was the coloniser. Initially morphological inertia also occurred in this genus both in Tanganyika and, during the first four million years of its existence, in Palaeolake Obweruka, although from the outset this lake contained abundant highly specialised molluscivorous fishes. About 4.5 Ma a major extinction event occurred in the Obweruka Basin which led to the extermination of 50% of the molluscan species but none of the molluscivores. Among the viviparids, only one of the Neothauma species survived, its populations isolated and highly reduced in numbers. Immediately after this crisis a conchological quantum change occurred, the surviving lineage changing into a strongly ornamented thalassoid form. The dramatic morphological change is deemed to have been due to focussed selection by the predators on isolated and small prey populations. A radiative event immediately followed, producing still more strongly ornamented forms. The morphological changes that occurred in the Obwerukan Neothauma, in comparison to the modest and repeated patterns of evolution that can be observed in viviparids from other lakes, provides an example of true or quantum evolutionary change and yields evidence as to how it may have occurred. The fossil record of the fresh water molluscs of the Albertine Basin, thanks to its duration (ca. 12 million years), its relatively fine resolution (0.5–1.0 million years) and its sound chronostratigraphic framework, is a unique resource for understanding the tempo and mode of macroevolution. This revised version was published online in July 2006 with corrections to the Cover Date.     

Explosive speciation in cichlid fishes of the African Great Lakes: a dynamic model of adaptive radiation

In the African cichlid species flocks several corresponding ecotypes and species communities have evolved independently in each of the lakes. These flocks can be viewed as reiterations of a process, induced by the same type of external event (the formation of a lake) and seeded by the same group of organisms, equipped with the same innovative potential. The East African lakes differ in their ages, so that different stages of adaptive radiation of a single group of fishes can be studied simultaneously. This review combines findings on various African cichlid species flocks and derives a generalized model of cichlid adaptive radiation. The model constitutes four stages, defined by the most influential habitat characteristics and interactions among members of the species community at each phase. It is an attempt to provide an explicit hypothesis for a dynamic evolutionary process, as a basis to future studies.     

The tropical history and future of the Mediterranean biota and the West African enigma

Aim Since the opening of the Suez Canal in 1869, many tropical taxa from the Indo‐West Pacific (IWP) realm have entered the Mediterranean Sea, which is experiencing rising temperatures. My aims are: (1) to compare biogeographically this tropical transformation of the Mediterranean biota with the tropical faunas of the Mediterranean and adjacent southern European and West African seas during the Late Oligocene to Pliocene interval; (2) to infer the relative contributions of the tropical eastern Atlantic and IWP to the tropical component of the marine biota in southern Europe; and (3) to understand why West Africa is not now a major source of warm‐water species. Location Southern Europe, including the Mediterranean Sea, and the coast of tropical West Africa. Methods I surveyed the literature on fossil and living shell‐bearing molluscs to infer the sources and fates of tropical subgenus‐level taxa living in southern Europe and West Africa during the Late Oligocene to Pliocene interval. Results Ninety‐four taxa disappeared from the tropical eastern Atlantic (including the Mediterranean) but persisted elsewhere in the tropics, mainly in the IWP (81 taxa, 86%) and to a lesser extent in tropical America (36 taxa, 38%). Nine taxa inferred to have arrived in the tropical eastern Atlantic from the west after the Pliocene did not enter the Mediterranean. The modern West African fauna is today isolated from that of other parts of the marine tropics. Main conclusions Taxa now entering the Mediterranean through the Suez Canal are re‐establishing a link with the IWP that last existed 16 million years ago. This IWP element, which evolved under oligotrophic conditions and under a regime of intense anti‐predatory selection, will continue to expand in the increasingly warm and increasingly oligotrophic Mediterranean. The IWP source fauna contrasts with the tropical West African biota, which evolved under productive conditions and in a regime of less anti‐predatory specialization. Until now, the post‐Pliocene West African source area has been isolated from the Mediterranean by cold upwelling. If further warming should reduce this barrier, as occurred during the productive and warm Early Pliocene, the Mediterranean could become a meeting place for two tropical faunas of contrasting source conditions.     

Age of cichlids: new dates for ancient lake fish radiations

Timing divergence events allow us to infer the conditions under which biodiversity has evolved and gain important insights into the mechanisms driving evolution. Cichlid fishes are a model system for studying speciation and adaptive radiation, yet, we have lacked reliable timescales for their evolution. Phylogenetic reconstructions are consistent with cichlid origins prior to Gondwanan landmass fragmentation 121-165 MYA, considerably earlier than the first known fossil cichlids (Eocene). We examined the timing of cichlid evolution using a relaxed molecular clock calibrated with geological estimates for the ages of 1) Gondwanan fragmentation and 2) cichlid fossils. Timescales of cichlid evolution derived from fossil-dated phylogenies of other bony fishes most closely matched those suggested by Gondwanan breakup calibrations, suggesting the Eocene origins and marine dispersal implied by the cichlid fossil record may be due to its incompleteness. Using Gondwanan calibrations, we found accumulation of genetic diversity within the radiating lineages of the African Lakes Malawi, Victoria and Barombi Mbo, and Palaeolake Makgadikgadi began around or after the time of lake basin formation. These calibrations also suggest Lake Tanganyika was colonized independently by the major radiating cichlid tribes that then began to accumulate genetic diversity thereafter. These results contrast with the widely accepted theory that diversification into major lineages took place within the Tanganyika basin. Together, this evidence suggests that ancient lake habitats have played a key role in generating and maintaining diversity within radiating lineages and also that lakes may have captured preexisting cichlid diversity from multiple sources from which adaptive radiations have evolved.     

A review of the influence of biogeography,riverine linkages,and marine connectivity on fish assemblages in evolving lagoons and lakes of coastal southern Africa

The Holocene evolution of eight South African coastal lakes and lagoons is examined and related to changes in fish composition over that period. Historical and current connectivity with riverine and marine environments are the primary determinants of present‐day fish assemblages in these systems. A small and remarkably consistent group of relict estuarine species have persisted in these coastal lakes and lagoons. The loss or reduction of connectivity with the sea has impacted on the diversity of marine fishes in all eight study systems, with no marine fishes occurring in those water bodies where connectivity has been completely broken (e.g. Sibaya, Groenvlei). In systems that have retained tenuous linkages with the sea (e.g., Verlorenvlei, Wilderness lakes), elements of the marine fish assemblage have persisted, especially the presence of facultative catadromous species. Freshwater fish diversity in coastal lakes and lagoons is a function of historical and present biogeography and salinity. From a freshwater biogeography perspective, the inflowing rivers of the four temperate systems reviewed here contain three or fewer native freshwater fishes, while the subtropical lakes that are fed by river systems contain up to 40 freshwater fish species. Thus, the significantly higher fish species diversity in subtropical versus temperate coastal lakes and lagoons comes as no surprise. Fish species diversity has been increased further in some systems (e.g., Groenvlei) by alien fish introductions. However, the impacts of fish introductions and translocations have not been studied in the coastal lakes and lagoons of South Africa. In these closed systems, it is probable that predation impacts on small estuarine fishes are significant. The recent alien fish introductions is an example of the growing threats to these systems during the Anthropocene, a period when human activities have had significant negative impacts and show potential to match the changes recorded during the entire Holocene.     

Did shifting seawater sulfate concentrations drive the evolution of deep-sea methane-seep ecosystems?

The origin and evolution of the faunas inhabiting deep-sea hydrothermal vents and methane seeps have been debated for decades. These faunas rely on a local source of sulfide and other reduced chemicals for nutrition, which spawned the hypothesis that their evolutionary history is independent from that of photosynthesis-based food chains and instead driven by extinction events caused by deep-sea anoxia. Here I use the fossil record of seep molluscs to show that trends in body size, relative abundance and epifaunal/infaunal ratios track current estimates of seawater sulfate concentrations through the last 150 Myr. Furthermore, the two main faunal turnovers during this time interval coincide with major changes in seawater sulfate concentrations. Because sulfide at seeps originates mostly from seawater sulfate, variations in sulfate concentrations should directly affect the base of the food chain of this ecosystem and are thus the likely driver of the observed macroecologic and evolutionary patterns. The results imply that the methane-seep fauna evolved largely independently from developments and mass extinctions affecting the photosynthesis-based biosphere and add to the growing body of evidence that the chemical evolution of the oceans had a major impact on the evolution of marine life.     

Evolution of a cichlid fish in a Lake Malawi satellite lake

Allopatric divergence in peripheral habitats may lead to rapid evolution of populations with novel phenotypes. In this study we provide the first evidence that isolation in peripheral habitats may have played a critical role in generation of Lake Malawi's cichlid fish diversity. We show that Lake Chilingali, a satellite lake 11.5 km from the shore of Lake Malawi, contains a breeding population of Rhamphochromis, a predatory genus previously thought to be restricted to Lake Malawi and permanently connected water bodies. The Lake Chilingali population is the smallest known Rhamphochromis, has a unique male nuptial colour pattern and has significant differentiation in mitochondrial DNA from Lake Malawi species. In laboratory mate choice trials with a candidate sister population from Lake Malawi, females showed a strong tendency to mate assortatively indicating that they are incipient biological species. These data support the hypothesis that isolation and reconnection of peripheral habitats due to lake level changes have contributed to the generation of cichlid diversity within African lakes. Such cycles of habitat isolation and reconnection may also have been important in evolutionary diversification of numerous other abundant and wide-ranging aquatic organisms, such as marine fishes and invertebrates.     

Phylogeny of the Lake Tanganyika cichlid species flock and its relationship to the Central and East African haplochromine cichlid fish faunas

Lake Tanganyika, the oldest of the East African Great Lakes, harbors the ecologically, morphologically, and behaviorally most complex of all assemblages of cichlid fishes, consisting of about 200 described species. The evolutionary old age of the cichlid assemblage, its extreme degree of morphological differentiation, the lack of species with intermediate morphologies, and the rapidity of lineage formation have made evolutionary reconstruction difficult. The number and origin of seeding lineages, particularly the possible contribution of riverine haplochromine cichlids to endemic lacustrine lineages, remains unclear. Our phylogenetic analyses, based on mitochondrial DNA sequences of three gene segments of 49 species (25% of all described species, up to 2,400 bp each), yield robust phylogenies that provide new insights into the Lake Tanganyika adaptive radiation as well as into the origin of the Central- and East-African haplochromine faunas. Our data suggest that eight ancient African lineages may have seeded the Tanganyikan cichlid radiation. One of these seeding lineages, probably comprising substrate spawning Lamprologus-like species, diversified into six lineages that evolved mouthbrooding during the initial stage of the radiation. All analyzed haplochromines from surrounding rivers and lakes seem to have evolved within the radiating Tanganyikan lineages. Thus, our findings contradict the current hypothesis that ancestral riverine haplochromines colonized Lake Tanganyika to give rise to at least part of its spectacular endemic cichlid species assemblage. Instead, the early phases of the Tanganyikan radiation affected Central and East African rivers and lakes. The haplochromines may have evolved in the Tanganyikan basin before the lake became a hydrologically and ecologically closed system and then secondarily colonized surrounding rivers. Apparently, therefore, the current diversity of Central and East African haplochromines represents a relatively young and polyphyletic fauna that evolved from or in parallel to lineages now endemic to Lake Tanganyika.     

Role of ancient lakes in genetic and phenotypic diversification of freshwater snails

Endemic organisms of ancient lakes have been studied as models to understand processes of speciation and adaptive radiation. However, it remains unclear how ancient lakes play roles in genetic and phenotypic diversity of freshwater mollusks. In the present study, we focus on viviparid freshwater snails in the ancient lakes of East and Southeast Asia (Japan and China) to address this question. Using molecular phylogenetic analyses based on mitochondrial (COI, 16S) and nuclear genes (18S, 28S, H3), we show that patterns of species diversification in viviparid lineages. Colonization to ancient lakes occurred independently in China and Japan at least four times, with subsequent diversification into more than two species within each lake group. Morphological analyses of fossil related viviparids suggest parallel phenotypic evolution occurred in the different lakes and ages. Each lake contained a single lineage which was phenotypically diversified relative to those from other sites. Using genome‐wide SNPs obtained by MIG‐seq, we also examined the genetic structure of three Japanese viviparids, including two endemic species of ancient Lake Biwa. The results suggest that these two species diversified from the population of the third species living in wetlands surrounding the lake. These findings suggest that rapid diversification of lineages and phenotypic divergence can occur in ancient lakes compared to other habitats. Formation of large lakes probably promotes speciation and phenotypic divergence as a result of adaptation into different microhabitats. High numbers of ancient lakes could be a driver of species diversity in Asian viviparid snails.