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.     

Evolutionary history of the endemic Lake Tanganyika cichlid fish Tylochromis polylepis: a recent intruder to a mature adaptive radiation

With an age of 9–12 million years (Myr) Lake Tanganyika holds the oldest and most complex species flock of cichlid fishes. It is believed to be of polyphyletic origin and rooted in nine ancient African lineages, six of which underwent diversification, while three remained monotypic. Here, the evolutionary history, route and timing of colonization were analyzed, as well as intraspecific genetic diversity of Tylochromis polylepis , the single albeit endemic representative of the tribe Tylochromini in Lake Tanganyika. The role of Tylochromis in the radiation was uncertain and the species was suggested to be either an ancient colonizer or a recent addition to the fauna. With 2.8–4.2% sequence divergence to four congeners living in Lakes Bangweulu and Mweru (Upper Congo River) as well as from Luozi River and Lake Etsotso (Lower Congo River), the species appears to be a recent colonizer, which is likely to have diverged from its riverine allies less than 510 000 years ago. The ability to enter an adaptive radiation at a highly mature stage with its densely packed species community and fine-tuned niche segregation seems remarkable. So far it was assumed that all Tanganyikan endemics evolved within the lake ecosystem by intralacustrine speciation, and that complex competitive interactions among endemics tighten the system against intruders. The intruding species can be classified as a generalist living over muddy bottom in the lake and in river estuaries. Microgeographic substructuring is suggested, possibly because of geographic segregation of breeding sites. Concerning the route of colonization, a downstream movement via one of the inflowing rivers situated in the south of Lake Tanganyika is suggested.     

Recent speciation between sympatric Tanganyikan cichlid colour morphs

Lake Tanganyika, Africa's oldest lake, harbours an impressive diversity of cichlid fishes. Although diversification in its radiating groups is thought to have been initially rapid, cichlids from Lake Tanganyika show little evidence for ongoing speciation. In contrast, examples of recent divergence among sympatric colour morphs are well known in haplochromine cichlids from Lakes Malawi and Victoria. Here, we report genetic evidence for recent divergence between two sympatric Tanganyikan cichlid colour morphs. These Petrochromis morphs share mitochondrial haplotypes, yet microsatellite loci reveal that their sympatric populations form distinct genetic groups. Nuclear divergence between the two morphs is equivalent to that which arises geographically within one of the morphs over short distances and is substantially smaller than that among other sympatric species in this genus. These patterns suggest that these morphs diverged only recently, yet that barriers to gene flow exist which prevent extensive admixture despite their sympatric distribution. The morphs studied here provide an unusual example of active diversification in Lake Tanganyika's generally ancient cichlid fauna and enable comparisons of speciation processes between Lake Tanganyika and other African lakes.     

Modelling of essential fish habitat based on remote sensing,spatial analysis and GIS

Lake Tanganyika is not the most species-rich of the Great East African Lakes, but comprises the greatest diversity of cichlid fishes in terms of morphology, ecology, and breeding styles. The lake contains a polyphyletic assemblage of cichlid lineages, which evolved from several ancient species that colonized the emerging lake some 9–12 million years ago. Based on morphological characteristics, the Tanganyikan cichlids have been classified into 12, or, more recently, 16 tribes, which are largely supported by molecular data. The radiations of East African cichlids are believed to be driven by complex interactions between extrinsic factors, such as climatic changes and geological processes, and intrinsic biological characteristics of the involved organisms. Diversification within different lineages occurred simultaneously in response to drastic habitat changes such as the establishment of lacustrine deep-water conditions 5–6 MYA and subsequent major lake-level fluctuations. This seems particularly true for the mouthbrooding lineages whereas the substrate breeders underwent a more gradual process of diversification. This review presents an account of the taxonomy and phylogeny of the Lake Tanganyika cichlid species assemblage, its relationship to the African cichlid fauna, key factors leading to the astonishing diversity and discusses recently proposed alternative age estimates for the Lake Tanganyika cichlid species assemblage.     

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.     

Molecular phylogeny and speciation patterns in host-specific monogeneans (Cichlidogyrus,Dactylogyridae) parasitizing cichlid fishes (Cichliformes,Cichlidae) in Lake Tanganyika

Cichlidogyrus (including Scutogyrus) is the most speciose dactylogyridean monogenean genus known from African and Levantine cichlid fishes (Cichlidae). While its taxonomy is well established, little is known about the phylogenetic relationships and evolutionary history of this ectoparasite, especially from hosts belonging to one of the most impressive vertebrate radiations, the cichlid fishes from the East African Great Lakes and surrounding hydrological systems. Phylogenetic inference based on DNA sequences of the nuclear 18S, internal transcribed spacer 1 and 28S rDNA genes revealed that Cichlidogyrus parasitizing mainly West African cichlid tribes is paraphyletic with respect to species parasitizing hosts belonging to the East African cichlid radiation, which constitute a well-supported monophylum. Members of Cichlidogyrus from tylochromine and oreochromine hosts that colonised Lake Tanganyika only recently, cluster with their non-Lake Tanganyika relatives, indicating that they colonised Lake Tanganyika with their current host species, and did not jump over from any of the many cichlid species already present in the lake. The diversification of Cichlidogyrus in Lake Tanganyika seems to be driven by failure to diverge in old lineages of cichlids, cospeciation in more recently evolved ones, and host switching followed by parasite duplication at the level of the various host tribes. Evaluation of host specificity and structural evolution of haptoral and reproductive organs in Lake Tanganyika Cichlidogyrus revealed that strict specialist species together with larval hook size represent the ancestral state of haptor configuration, suggesting that members of Cichlidogyrus in this system evolved from a very simple form to a more complex one similarly to their West African congeners. Generalist species among Cichlidogyrus with a sclerotized vagina parasitizing ancient Lake Tanganyika lineages seem to have developed a different hook configuration, most probably to ensure successful colonisation of new, phylogenetically unrelated hosts.     

Lake Tanganyika—A 'Melting Pot' of Ancient and Young Cichlid Lineages (Teleostei: Cichlidae)?

A long history of research focused on the East Africa cichlid radiations (EAR) revealed discrepancies between mtDNA and nuclear phylogenies, suggesting that interspecific hybridisation may have been significant during the radiation of these fishes. The approximately 250 cichlid species of Lake Tanganyika have their roots in a monophyletic African cichlid assemblage, but controversies remain about the precise phylogenetic origin and placement of different lineages and consequently about L. Tanganyika colonization scenarios. 3312 AFLP loci and the mitochondrial ND2 gene were genotyped for 91 species representing almost all major lacustrine and riverine haplotilapiine east African cichlid lineages with a focus on L. Tanganyika endemics. Explicitly testing for the possibility of ancient hybridisation events, a comprehensive phylogenetic network hypothesis is proposed for the origin and diversification of L. Tanganyika cichlids. Inference of discordant phylogenetic signal strongly suggests that the genomes of two endemic L. Tanganyika tribes, Eretmodini and Tropheini, are composed of an ancient mixture of riverine and lacustrine lineages. For the first time a strong monophyly signal of all non-haplochromine mouthbrooding species endemic to L. Tanganyika (“ancient mouthbrooders”) was detected. Further, in the genomes of early diverging L. Tanganyika endemics Trematocarini, Bathybatini, Hemibatini and Boulengerochromis genetic components of other lineages belonging to the East African Radiation appear to be present. In combination with recent palaeo-geological results showing that tectonic activity in the L. Tanganyika region resulted in highly dynamic and heterogeneous landscape evolution over the Neogene and Pleistocene, the novel phylogenetic data render a single lacustrine basin as the geographical cradle of the endemic L. Tanganyika cichlid lineages unlikely. Instead a scenario of a pre-rift origin of several independent L. Tanganyika precursor lineages which diversified in ancient rivers and precursor lakes and then amalgamated in the extant L. Tanganyika basin is put forward as an alternative: the ''melting pot Tanganyika'' hypothesis.     

The species flocks of lacustrine gastropods: <Emphasis Type="Italic">Tylomelania</Emphasis> on Sulawesi as models in speciation and adaptive radiation

Endemic radiations provide splendid opportunities for studies in evolutionary biology. Species flocks in ancient lakes, such as in Tanganyika, Malawi or Baikal, have featured prominently in evolutionary biology, viewing these “evolutionary theatres” as hotspots of diversification. However, following a century of neglect, the endemic evolution of limnic cerithioidean gastropods in the two central lake systems on the Indonesian island of Sulawesi (i.e. Lake Poso and the lakes of the Malili system, e.g. Danau Matano, Mahalona and Towuti) also provide instructive model cases for the study of speciation mechanisms, adaptive radiation and annidation (i.e. niche exploitation). We here discuss the evolutionary and taxonomic implications of the lacustrine species flocks in Tylomelania from these lakes in Sulawesi as an exceptional endemic assemblage of morphologically distinct viviparous pachychilid gastropods. This first comprehensive compilation of data on both ancient lake systems, Poso and Malili, offers a new perspective on ecological differentiation in this radiation. Presented here within the framework of the theory of evolutionary ecology it provides a research program for acquiring a synthetical perspective that includes morphology, molecular genetics, ecology and biogeography. In this context, it will be possible to compare the species flocks of these truly “Darwinian snails” on Sulawesi with the long enigmatic, so-called thalassoid (i.e. marine-like) gastropod radiation in East African’s Lake Tanganyika.     

Lake level fluctuations synchronize genetic divergences of cichlid fishes in African lakes

Water level fluctuations are important modulators of speciation processes in tropical lakes, in that they temporarily form or break down barriers to gene flow among adjacent populations and/or incipient species. Time estimates of the most recent major lowstands of the three African Great Lakes are thus crucial to infer the relative timescales of explosive speciation events in cichlid species flocks. Our approach combines geological evidence with genetic divergence data of cichlid fishes from the three Great East African Lakes derived from the fastest-evolving mtDNA segment. Thereby, we show for each of the three lakes that individuals sampled from several populations which are currently isolated by long geographic distances and/or deep water form clusters of equally closely related haplotypes. The distribution of identical or equally closely related haplotypes in a lake basin allows delineation of the extent of lake level fluctuations. Our data suggest that the same climatic phenomenon synchronized the onset of genetic divergence of lineages in all three species flocks, such that their most recent evolutionary history seems to be linked to the same external modulators of adaptive radiation. A calibration of the molecular clock of the control region was elaborated by gauging the age of the Lake Malawi species flock through the divergence among the utaka-cichlid and the mbuna-cichlid lineages to minimally 570,000 years and maximally 1 Myr. This suggests that the low-lake-level period which established the observed patterns of genetic relatedness dates back less than 57,000 years, probably even to 17,000-12,400 years ago, when Lake Victoria dried up and Lakes Malawi and Tanganyika were also low. A rapid rise of all three lakes about 11,000 years ago established the large-scale population subdivisions observed today. Over that period of time, a multitude of species originated in Lakes Malawi and Victoria with an impressive degree of morphological and ecological differentiation, whereas the Tanganyikan taxa that were exposed to the same habitat changes hardly diverged ecologically and morphologically. Our findings also show that patterns of genetic divergences of stenotopic organisms provide valuable feedback on geological and sedimentological time estimates for lake level changes.     

Mitochondrial phylogeny of the Cyprichromini, a lineage of open-water cichlid fishes endemic to Lake Tanganyika, East Africa

We present a phylogeny of the Cyprichromini, a lineage of cichlid fishes from Lake Tanganyika, showing progressive adaptation towards pelagic life style. Our study is based upon three mitochondrial gene segments, 443 bp of the control region, 402 bp of the cytochrome b gene and the entire NADH dehydrogenase subunit 2 gene (1047 bp). The topologies obtained by different tree building methods subdivide the Cyprichromini into four distinct lineages: the Paracyprichromis-, the Cyprichromis zonatus-, the Cyprichromis microlepidotus-lineage, and a lineage comprising Cyprichromis pavo and Cyprichromis leptosoma. Our study thus corroborates the distinctness of C. zonatus which was recently described formally. Concerning ecology and mating behavior, a clear evolutionary trend towards progressive adaptation to the pelagic zone emerges during the evolution of the Cyprichromini. The linearized tree analysis further shows that the four lineages have split almost contemporaneously. The mean Kimura-2-parameter distance among the four lineages emerging from the primary radiation of the Cyprichromini amounts to 7.21% and is in close agreement to that previously found for the primary radiation of the tribe Tropheini (7.01%), a lineage of rock-dwelling cichlids endemic to Lake Tanganyika. To date, the influence of lake level fluctuations as promoters of diversification has been demonstrated only for rock-dwelling cichlids. Based on the agreement in temporary patterns of diversification, we suggest that Pleistocene lake level changes have left a similar genetic imprint in a group of cichlid fishes that progressively colonized the open water during their radiation.     

Marine incursion: the freshwater herring of Lake Tanganyika are the product of a marine invasion into west Africa

The spectacular marine-like diversity of the endemic fauna of Lake Tanganyika, the oldest of the African Great Lakes, led early researchers to suggest that the lake must have once been connected to the ocean. Recent geophysical reconstructions clearly indicate that Lake Tanganyika formed by rifting in the African subcontinent and was never directly linked to the sea. Although the Lake has a high proportion of specialized endemics, the absence of close relatives outside Tanganyika has complicated phylogeographic reconstructions of the timing of lake colonization and intralacustrine diversification. The freshwater herring of Lake Tanganyika are members of a large group of pellonuline herring found in western and southern Africa, offering one of the best opportunities to trace the evolutionary history of members of Tanganyika's biota. Molecular phylogenetic reconstructions indicate that herring colonized West Africa 25-50MYA, at the end of a major marine incursion in the region. Pellonuline herring subsequently experienced an evolutionary radiation in West Africa, spreading across the continent and reaching East Africa's Lake Tanganyika during its early formation. While Lake Tanganyika has never been directly connected with the sea, the endemic freshwater herring of the lake are the descendents of an ancient marine incursion, a scenario which may also explain the origin of other Tanganyikan endemics.     

Mastacembelid eels support Lake Tanganyika as an evolutionary hotspot of diversification

Background  

Lake Tanganyika (LT) is the oldest of the African Rift Lakes and is one of the richest freshwater ecosystems on Earth, with high levels of faunal diversity and endemism. The endemic species flocks that occur in this lake, such as cichlid fishes, gastropods, catfish and crabs, provide unique comparative systems for the study of patterns and processes of speciation. Mastacembelid eels (Teleostei: Mastacembelidae) are a predominately riverine family of freshwater fish, occurring across Africa and Asia, but which also form a small species flock in LT.     

Patterns in fish radiation are compatible with Pleistocene desiccation of Lake Victoria and 14,600 year history for its cichlid species flock

Geophysical data are currently being interpreted as evidence for a late Pleistocene desiccation of Lake Victoria and its refilling 14,600 years ago. This implies that between 500 and 1000 endemic cichlid fish species must have evolved in 14,600 years, the fastest large-scale species radiation known. A recent review concludes that biological evidence clearly rejects the postulated Pleistocene desiccation of the lake: a 14,600 year history would imply exceptionally high speciation rates across a range of unrelated fish taxa. To test this suggestion, I calculated speciation rates for all 41 phylogenetic lineages of fish in the lake. Except for one cichlid lineage, accepting a 14 600 year history does not require any speciation rates that fall outside the range observed in fishes in other young lakes around the world. The exceptional taxon is a lineage of haplochromine cichlids that is also known for its rapid speciation elsewhere. Moreover, since it is unknown how many founding species it has, it is not certain that its speciation rates are really outside the range observed in fishes in other young lakes. Fish speciation rates are generally faster in younger than in older lakes, and those in Lake Victoria, by far the largest of the young lakes of the world, are no exception. From the speciation rates and from biogeographical observations that Lake Victoria endemics, which lack close relatives within the lake basin, have such relatives in adjacent drainage systems that may have had Holocene connections to Lake Victoria, I conclude that the composition of the fish assemblage does not provide biological evidence against Pleistocene desiccation. It supports a hypothesis of recent colonization from outside the lake basin rather than survival of a diverse assemblage within the basin.     

Rapid evolution of an ancient lake species flock: Freshwater limpets (Gastropoda: Ancylidae) in the Balkan Lake Ohrid

Ancient lakes have long been recognized as evolutionary theatres and hot spots of endemism; the evolution of their morphologically often highly diverse species flocks has received much attention. However, as each ancient lake has its own geological and evolutionary history, modes of speciation may differ from system to system. Ancient lakes can act as evolutionary reservoirs that assure the survival of relict species, but at the same time extant species may evolve through intralacustrine speciation. Other aspects of interest are the actual rates of immigration, diversification or extinction as well as the temporal framework of morphological change. Many of these questions have been addressed in the African (e.g. Lake Tanganyika) and Asian (e.g. Lake Baikal) ancient lakes. For an European ancient lakes (e.g. Lakes Ohrid and Prespa), such studies are largely missing. In the present paper, extraordinarily shaped endemic freshwater limpets of the genus Ancylus from the Balkan Lake Ohrid are used in a phylogeographic and phylogenetic context to test whether they represent an ancient lake species flock, to study the mode of speciation, and to assess the timing of morphological change. Based on DNA data from two mitochondrial genes (COI, LSU rDNA), it has been found that the Lake Ohrid Ancylus species form an endemic monophyletic group. In addition, the lake's feeder springs are inhabited by another, undescribed Ancylus species. All other studied waterbodies within the watershed do not support their own Ancylus lineages but are inhabited by a widespread Mediterranean taxon. The split between the species endemic to the lake and its sister taxon is dated to 1.4±0.6 million years ago. The study presents the first genetic confirmation for the existence of a species flock in a European ancient lake. Contrary to the prevailing opinion it shows that, concerning Ancylus, Lake Ohrid represents a site of intralacustrine speciation rather than an evolutionary reservoir. Moreover, it provides the first evidence for rapid morphological change in an European ancient lake species flock. See also Electronic Supplement at: http://www.senckenberg.de/odes/06-12.htm.     

African cichlid fish: a model system in adaptive radiation research

The African cichlid fish radiations are the most diverse extant animal radiations and provide a unique system to test predictions of speciation and adaptive radiation theory. The past few years have seen major advances in the phylogenetics, evolutionary biogeography and ecology of cichlid fish. Most of this work has concentrated on the most diverse radiations. Unfortunately, a large number of small radiations and 'non-radiations' have been overlooked, potentially limiting the contribution of the cichlid system to our understanding of speciation and adaptive radiation. I have reviewed the literature to identify 33 intralacustrine radiations and 76 failed radiations. For as many as possible I collected information on lake size, age and phylogenetic relationships. I use these data to address two questions: (i) whether the rate of speciation and the resulting species richness are related to temporal and spatial variation in ecological opportunity and (ii) whether the likelihood of undergoing adaptive radiation is similar for different African cichlid lineages. The former is a key prediction of the ecological theory of adaptive radiation that has been presumed true but remains untested for cichlid radiations. The second is based on the hypothesis that the propensity of cichlids to radiate is due to a key evolutionary innovation shared by all African cichlids. The evidence suggests that speciation rate declines through time as niches get filled up during adaptive radiation: young radiations and early stages of old radiations are characterized by high rates of speciation, whereas at least 0.5 Myr into a radiation speciation becomes a lot less frequent. The number of species in cichlid radiations increases with lake size, supporting the prediction that species diversity increases with habitat heterogeneity, but also with opportunity for isolation by distance. Finally, the data suggest that the propensity to radiate within lakes is a derived property that evolved during the evolutionary history of some African cichlids, and the appearance of which does not coincide with the appearance of proposed key innovations in morphology and life history.     

Colour-assortative mating among populations of Tropheus moorii, a cichlid fish from Lake Tanganyika, East Africa

The species flocks of cichlid fishes in the East African Lakes Tanganyika, Malawi and Victoria are prime examples of adaptive radiation and explosive speciation. Several hundreds of endemic species have evolved in each of the lakes over the past several thousands to a few millions years. Sexual selection via colour-assortative mating has often been proposed as a probable causal factor for initiating and maintaining reproductive isolation. Here, we report the consequences of human-mediated admixis among differentially coloured populations of the endemic cichlid fish Tropheus moorii from several localities that have accidentally been put in sympatry in a small harbour bay in the very south of Lake Tanganyika. We analysed the phenotypes (coloration) and genotypes (mitochondrial control region and five microsatellite loci) of almost 500 individuals, sampled over 3 consecutive years. Maximum-likelihood-based parenthood analyses and Bayesian inference of population structure revealed that significantly more juveniles are the product of within-colour-morph matings than could be expected under the assumption of random mating. Our results clearly indicate a marked degree of assortative mating with respect to the different colour morphs. Therefore, we postulate that sexual selection based on social interactions and female mate choice has played an important role in the formation and maintenance of the different colour morphs in Tropheus, and is probably common in other maternally mouthbrooding cichlids as well.     

Tempo and mode of diversification of lake Tanganyika cichlid fishes

Background

Understanding the causes of disparities in species diversity across taxonomic groups and regions is a fundamental aim in evolutionary biology. Addressing these questions is difficult because of the need for densely sampled phylogenies and suitable empirical systems.

Methodology/Principal Findings

Here we investigate the cichlid fish radiation of Lake Tanganyika and show that per lineage diversification rates have been more than six times slower than in the species flocks of Lakes Victoria and Malawi. The result holds even at peak periods of diversification in Lake Tanganyika, ruling out the age of the lake as an explanation for slow average rates, and is robust to uncertainties over the calibration of cichlid radiations in geological time. Moreover, Lake Tanganyika lineages, irrespective of different biological characteristics (e.g. sexually dichromatic versus sexually monochromatic clades), have diversified at similar rates, falling within typical estimates across a range of plant and animal clades. For example, the mostly sexually dichromatic haplochromines, which have speciated explosively in Lakes Victoria and Malawi, have displayed modest rates in Lake Tanganyika (where they are called Tropheini).

Conclusion/Significance

Our results show that either the Lake Tanganyika environment is less conducive for cichlid speciation or the remarkable diversifying abilities of the haplochromines were inhibited by the prior occupancy of older radiations. Although the results indicate a dominant role for the environment in shaping cichlid diversification, differences in the timing of diversification among the Tanganyikan tribes indicate that biological differences were still important for the dynamics of species build-up in the lake. While we cannot resolve the timing of the radiation relative to the origin of the lake, because of the lack of robust geological date calibrations for cichlids, our results are consistent with a scenario that the different clades reflect independent adaptive radiations into different broad niches in the lake.     

Oligochaeta and Aphanoneura in ancient lakes: a review

By their antiquity, history, rarity, great depth in many instances and the presence of highly diverse faunas with many endemics, ancient lakes constitute ecosystems of a special nature, clearly apart from the large majority of extant lakes. While the fauna of these lakes is becoming better and better known for various animals groups, the Oligochaeta are still poorly known. Tubificidae and Naididae are found in each ancient lake. On the other hand, some families are restricted to only one lake, such as Aeolosomatidae and Proppapidae in Lake Baikal or Eudrilidae and Ocnerodrilidae (megadriles) in Lake Tanganyika, but such a distribution is probably due to a lack of knowledge or sampling biases. All ancient lakes have an endemic oligochaete fauna except Lake Kinneret (Israël). The oldest, Lake Baikal (20–25 Ma), holds the most abundant and diverse oligochaete fauna, in which species flocks are even recognizable or suspected. In contrast, the oligochaete fauna of the slightly younger Lake Tanganyika is very scarce. This is partly due to an obvious lack of studies, as the oligochaete fauna of other great African lakes is virtually unknown, but this might be the result of an environment in these lakes less favourable to oligochaetes. Some factors likely to interact with speciation in oligochaetes are discussed but nothing can be concluded to date. A recent interest in African great lakes revealed a more diverse oligochaete fauna than previously assumed but a better study of this fauna is still badly needed.     

Geometric morphometric analyses provide evidence for the adaptive character of the Tanganyikan cichlid fish radiations

The cichlids of East Africa are renowned as one of the most spectacular examples of adaptive radiation. They provide a unique opportunity to investigate the relationships between ecology, morphological diversity, and phylogeny in producing such remarkable diversity. Nevertheless, the parameters of the adaptive radiations of these fish have not been satisfactorily quantified yet. Lake Tanganyika possesses all of the major lineages of East African cichlid fish, so by using geometric morphometrics and comparative analyses of ecology and morphology, in an explicitly phylogenetic context, we quantify the role of ecology in driving adaptive speciation. We used geometric morphometric methods to describe the body shape of over 1000 specimens of East African cichlid fish, with a focus on the Lake Tanganyika species assemblage, which is composed of more than 200 endemic species. The main differences in shape concern the length of the whole body and the relative sizes of the head and caudal peduncle. We investigated the influence of phylogeny on similarity of shape using both distance-based and variance partitioning methods, finding that phylogenetic inertia exerts little influence on overall body shape. Therefore, we quantified the relative effect of major ecological traits on shape using phylogenetic generalized least squares and disparity analyses. These analyses conclude that body shape is most strongly predicted by feeding preferences (i.e., trophic niches) and the water depths at which species occur. Furthermore, the morphological disparity within tribes indicates that even though the morphological diversification associated with explosive speciation has happened in only a few tribes of the Tanganyikan assemblage, the potential to evolve diverse morphologies exists in all tribes. Quantitative data support the existence of extensive parallelism in several independent adaptive radiations in Lake Tanganyika. Notably, Tanganyikan mouthbrooders belonging to the C-lineage and the substrate spawning Lamprologini have evolved a multitude of different shapes from elongated and Lamprologus-like hypothetical ancestors. Together, these data demonstrate strong support for the adaptive character of East African cichlid radiations.     

The endemic gastropod fauna of Lake Titicaca: correlation between molecular evolution and hydrographic history

Lake Titicaca, situated in the Altiplano high plateau, is the only ancient lake in South America. This 2- to 3-My-old (where My is million years) water body has had a complex history that included at least five major hydrological phases during the Pleistocene. It is generally assumed that these physical events helped shape the evolutionary history of the lake's biota. Herein, we study an endemic species assemblage in Lake Titicaca, composed of members of the microgastropod genus Heleobia, to determine whether the lake has functioned as a reservoir of relic species or the site of local diversification, to evaluate congruence of the regional paleohydrology and the evolutionary history of this assemblage, and to assess whether the geographic distributions of endemic lineages are hierarchical. Our phylogenetic analyses indicate that the Titicaca/Altiplano Heleobia fauna (together with few extralimital taxa) forms a species flock. A molecular clock analysis suggests that the most recent common ancestor (MRCAs) of the Altiplano taxa evolved 0.53 (0.28-0.80) My ago and the MRCAs of the Altiplano taxa and their extralimital sister group 0.92 (0.46-1.52) My ago. The endemic species of Lake Titicaca are younger than the lake itself, implying primarily intralacustrine speciation. Moreover, the timing of evolutionary branching events and the ages of two precursors of Lake Titicaca, lakes Cabana and Ballivián, is congruent. Although Lake Titicaca appears to have been the principal site of speciation for the regional Heleobia fauna, the contemporary spatial patterns of endemism have been masked by immigration and/or emigration events of local riverine taxa, which we attribute to the unstable hydrographic history of the Altiplano. Thus, a hierarchical distribution of endemism is not evident, but instead there is a single genetic break between two regional clades. We also discuss our findings in relation to studies of other regional biota and suggest that salinity tolerance was the most likely limiting factor in the evolution of Altiplano species flocks.