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

Scientific drilling projects in ancient lakes: integrating geological and biological histories

Sedimentary sequences in ancient or long-lived lakes can reach several thousands of meters in thickness and often provide an unrivalled perspective of the lake's regional climatic, environmental, and biological history. Over the last few years, deep drilling projects in ancient lakes became increasingly multi- and interdisciplinary, as, among others, seismological, sedimentological, biogeochemical, climatic, environmental, paleontological, and evolutionary information can be obtained from sediment cores. However, these multi- and interdisciplinary projects pose several challenges. The scientists involved typically approach problems from different scientific perspectives and backgrounds, and setting up the program requires clear communication and the alignment of interests. One of the most challenging tasks, besides the actual drilling operation, is to link diverse datasets with varying resolution, data quality, and age uncertainties to answer interdisciplinary questions synthetically and coherently. These problems are especially relevant when secondary data, i.e., datasets obtained independently of the drilling operation, are incorporated in analyses. Nonetheless, the inclusion of secondary information, such as isotopic data from fossils found in outcrops or genetic data from extant species, may help to achieve synthetic answers. Recent technological and methodological advances in paleolimnology are likely to increase the possibilities of integrating secondary information, e.g., through molecular dating of molecular phylogenies. Some of the new approaches have started to revolutionize scientific drilling in ancient lakes, but at the same time, they also add a new layer of complexity to the generation and analysis of sediment core data. The enhanced opportunities presented by new scientific approaches to study the paleolimnological history of these lakes, therefore, come at the expense of higher logistic, communication, and analytical efforts. Here we review types of data that can be obtained in ancient lake drilling projects and the analytical approaches that can be applied to empirically and statistically link diverse datasets for creating an integrative perspective on geological and biological data. In doing so, we highlight strengths and potential weaknesses of new methods and analyses, and provide recommendations for future interdisciplinary deep drilling projects

A qualitative assessment of the influence of bioturbation in Lake Baikal sediments

The impact of bioturbation in Lake Baikal sediments, particularly on rhythmic layering and mixing, was assessed by studying the actual vertical distribution of benthic animals in continuous accumulation zones selected by seismic survey (Vydrino, Shoulder, Posolskoe Bank, Continent Ridge). To assess the influence of the bioturbation, animals were extracted from short cores and identified at the relevant taxonomic level. The faunal distribution is examined in parallel with the bioturbation tracks observed in thin section. Oligochaeta, Nematoda, Ostracoda, Copepoda, Gammaridae, Chironomidae and Hydrachnidia were found inhabiting the sediment. Among them, only oligochaete worms were assumed to have a significant impact on sediment mixing because of their "conveyor belt" feeding. The other two most abundantly sampled groups, nematods and copepods, belong to the interstitial fauna that has no significant impact on the vertical displacement of sediment particles and do not ingest the sediment. The presence of a benthic fauna as deep as 15 cm in the sediment indicates that the possibility of sediment disturbance by invertebrate activity cannot be dismissed in Lake Baikal. The effect of biological mixing is more limited in the deepest stations because the number of potential bioturbators is reduced, qualitatively as well as quantitatively. Located in the abyssal zone, Continent and Vydrino (but outside turbidites) deep stations appear to be most promising sediment records for tracking climate signal at high resolution. (C) 2004 Elsevier B.V. All rights reserved.Continen

A faunistic review of the modern and fossil molluscan fauna from Lake Pamvotis, Ioannina, an ancient lake in NW Greece: implications for endemism in the Balkans

The Balkans are justifiably famous for being natural hotspots of floral and faunal biodiversity and endemism. Much of this biological diversity is witnessed in the ancient lakes that exist (or previously existed) in the region, which have provided stable, long-lived arenas within which evolutionary processes have been able to operate. One group that ably demonstrate such diversity are the gastropod molluscs. Their wide dispersal, morphological variability and relative ease of identification make them ideal candidates for addressing questions concerning patterns and processes of biodiversity and evolution over time (e.g. Michel, 1996). Furthermore, the fact that they are often well preserved in fossil sequences means that they can provide a temporal dimension to evolutionary investigation, something that is often difficult to resolve when using groups more traditionally associated with this kind of work, such as the cichlid fishes. The molluscan faunas of the Balkans (and Greece in particular) have been the subject of study for at least the last two centuries (e.g. Butot & Welter-Schultes 1994). Isolated ancient lakes from the region, and in particular Ohrid, have often been a focus for detailed investigation, because of their remarkable endemic faunas (e.g. Hadzisce, 1956; Hubendick & Radoman, 1959; Stankovic, 1960; Meier-Brook, 1983; Stankovic, 1985; Schtt, 1987; Sattmann & Reischtz, 1988; Dhora & Welter-Schultes, 1996). Despite this, the malacology of many other key localities from the area still remains poorly documented. In this paper we first briefly review the main controls thought to influence the radiation of gastropods in ancient lakes and then present the modern and fossil aquatic molluscan fauna from a typical but previously poorly known site: Lake Pamvotis, located in the Ioannina Basin in NW Greece. Comparisons are then drawn with the gastropod fauna derived from other extant and fossil ancient lakes from across the Balkan region (bivalves are considered by Korniushin elsewhere in this volume), before highlighting some common patterns and providing some thoughts on the implications for speciation in ancient Balkan lake systems