On the Cyprideis species flock (Crustacea, Ostracoda) in Lake Tanganyika, with the description of four new species

Four new species, belonging to three genera, of ostracods from Lake Tanganyika are described: Mesocyprideis nitida sp.nov., Romecytheridea belone sp.nov., R. plegma sp. nov. and Cyprideis loricata sp. nov. The Cyprideis species flock of Lake Tanganyika now consists of 17 formally described species (16 endemic) in 6 genera (4 endemic). The geographical and ecological distribution of the four species is briefly discussed and some supplementary remarks on the radiation of the Cyprideis species flock in Lake Tanganyika are offered.     

On the age and origin of the species flock of haplochromine cichlid fishes of Lake Victoria

Recent suggestions concerning the age and origin of the flock of haplochromine cichlid fishes in Lake Victoria (East Africa) are considered. These accept as proven the suggestion that Lake Victoria dried out completely in the Late Pleistocene, was dry for several thousand years, and refilled ca. 12400 years ago. Apart from the fact that other geophysical evidence contradicts this claim, its biological implications, which do likewise, have never been considered by those who have accepted it. Like those of all previous authors who have seized on the presence of the haplochromine flock of perhaps more than 600 species as evidence of extremely rapid evolution since the lake allegedly refilled, the account completely overlooks the fact that any such desiccation must have eliminated not only the haplochromine cichlids but the entire biota of the lake. Nevertheless, its present fauna not only includes the haplochromines but many other endemic organisms that would not be expected, and whose presence and history demand an explanation if the lake did indeed dry out. No such explanation has been offered, nor does such seem possible. The recent interpretation of events is questioned and rejected.     

A new diminutive genus and species of catfish from Lake Tanganyika (Siluriformes: Clariidae)

The examination of material representing one of Lake Tanganyika's six previously recognized endemic catfish lineages, has revealed the presence of an additional genus of clariid, described here as Pseudotanganikallabes new genus. This genus is represented by a single species, Pseudotanganikallabes prognatha sp. nov., which is distinguished from all other clariids by its lack of an infraorbital series, the presence of multiple osseous connections between the swim bladder capsules and elements of the neurocranium, the absence of an ethmoid notch, the presence of a very large, egg‐shaped occipital fontanelle and the extension of the lower lip beyond the margin of the upper jaw. A combination of additional external and molecular characters serves to further distinguish this taxon from all currently recognized clariid species. Phylogenetic analysis of mitochondrial (cytb) and nuclear (18S‐ITS1‐5.8S‐ITS2‐28S) sequence data supports the creation of a new genus for this species, as it appears to represent an independent, monophyletic lineage within the family Clariidae.     

Biparental mouthbrooding of the catfish Phyllonemus filinemus in Lake Tanganyika

This article reports biparental mouthbrooding of the bagrid catfish Phyllonemus filinemus in Lake Tanganyika, based on analysis of specimens collected during SCUBA diving. This catfish was nocturnally active, and in the daytime it was concealed singly or in pairs beneath rocks. Within a breeding pair, the male or female alone incubated all the brood in the mouth until the offspring attained 12 mm or so in total length, but thereafter joint mouthbrooding or guarding by both parents took place. Most females of nonbrooding pairs showed high values of gonadosomatic index (GSI), whereas all females of brooding pairs and most single females showed low GSI values. This fact indicated that a pair is formed at a time near the gonadal maturation of the female and separates after the brood is reared. No significant difference in body condition among parents of different reproductive states was observed, which suggested that their condition does not deteriorate markedly as the result of foraging by an off-duty parent. Received: September 16, 2000 / Revised: November 18, 2000 / Accepted: January 23, 2001     

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.     

Nuclear markers reveal unexpected genetic variation and a Congolese-Nilotic origin of the Lake Victoria cichlid species flock

Phylogenetic analyses based on mitochondrial (mt) DNA have indicated that the cichlid species flock of the Lake Victoria region is derived from a single ancestral species found in East African rivers, closely related to the ancestor of the Lake Malawi cichlid species flock. The Lake Victoria flock contains ten times less mtDNA variation than the Lake Malawi radiation, consistent with current estimates of the ages of the lakes. We present results of a phylogenetic investigation using nuclear (amplified fragment length polymorphism) markers and a wider coverage of riverine haplochromines. We demonstrate that the Lake Victoria-Edward flock is derived from the morphologically and ecologically diverse cichlid genus Thoracochromis from the Congo and Nile, rather than from the phenotypically conservative East African Astatotilapia. This implies that the ability to express much of the morphological diversity found in the species flock may by far pre-date the origin of the flock. Our data indicate that the nuclear diversity of the Lake Victoria-Edward species flock is similar to that of the Lake Malawi flock, indicating that the genetic diversity is considerably older than the 15 000 years that have passed since the lake began to refill. Most of this variation is manifested in trans-species polymorphisms, indicating very recent cladogenesis from a genetically very diverse founder stock. Our data do not confirm strict monophyly of either of the species flocks, but raise the possibility that these flocks have arisen from hybrid swarms.     

Evolution in isolation: the Gyraulus species flock from Miocene Lake Steinheim revisited

The Miocene Steinheim Basin in SW Germany is an ancient (long-lived) palaeo-lake that has existed over some hundreds of thousands of years. It is an iconic fossil site, because the historically oldest phylogenetic tree of extinct organisms was based on specimens described from this locality. Today the basin contains 30–40 m thickness of lake sediments with planorbid snails of the genus Gyraulus occurring in rock-forming quantities. The shells are morphologically highly disparate with forms ranging from the tiny, planispiral founder species Gyraulus kleini, to fragile corkscrew-like uncoiled forms and to large trochiform morphs with thick shells. In total, this presumably monophyletic species flock contains 17 species distributed in time and space, all of which are endemic, except for the founder species. Up to nine of them occur in a single sedimentary level and are inferred to have lived together. Such an extreme rate of endemism makes fossil Lake Steinheim special among extant and fossil lakes. This review article summarises and discusses the species concept(s), indications for endemism, speciation processes, the phylogenetic concept(s) and factors controlling evolution. It also provides directions for future research.     

Haematology and habits in catfish of the genus Synodontis

African catfish of the genus Synodontis vary in their habits, from inverted plankton eaters to normally oriented benthos eaters. Haemoglobin concentrations and red cell counts vary between populations of one species, and between species of differing habits. Synodontis schall from the well-aerated White Nile had lower haemoglobin concentrations than members of the same species from Lake Kainji, Nigeria. Synodontis membranaceus , an inverted plankton eater, had lower haemoglobin concentrations than the bottom dwelling S. filamentosus and S. nigrita. Species with intermediate habits, such as S. batensoda and S. ocellifer had intermediate concentrations of haemoglobin.
It is suggested that these differences in haemoglobin concentration are a result of differing habits. Those species that enter poorly aerated water are stimulated to make more haemoglobin.     

A new species of Petrochromis (Perciformes: Cichlidae) from Lake Tanganyika

Based on morphological and molecular analyses of a Petrochromis fish (Cichlidae) from the southern end of Lake Tanganyika, this fish is considered a taxonomic species distinct from the six known congeners. A new scientific name is proposed for this fish. A key to the seven Petrochromis species is included.     

Ecological correlates of species differences in the Lake Tanganyika crab radiation

The endemic crabs of Lake Tanganyika include a phenotypically diverse clade that exhibits recent divergence and low phylogenetic species resolution. There are indications that ecological niche segregation has played a prominent role in the divergence of this clade. We used habitat surveys, gut content analyses and stable isotope analyses to test the extent to which morphological species are ecologically different. Our data show some interspecific segregation in depth, substrate type and mean stable isotope signatures. At the same time, a considerable level of ecological niche overlap is evident among species of Platythelphusa that coexist in rocky littoral habitats. We consider these results in the framework of adaptive radiation theory, and we discuss general ramifications for the maintenance of species diversity in Lake Tanganyika.     

Postural control mechanisms in the upside-down catfish (Synodontis nigriventris)

The catfishSynodontis nigriventris normally swims upside-down but can assume any posture in response to a substrate it swims close to. Postural reflexes of the body and the eyes, labyrinthine anatomy and passively maintained posture were investigated to obtain indications for possible mechanisms controlling the peculiar postural behavior of this fish. Saccade-like resetting movements of the eyes during counter-roll to body tilt about the longitudinal axis, and maintained tilted swimming positions in blinded fish suggest that these animals reset their vestibular CNS circuits to zero when in tilted positions.Synodontis nigriventris is thus able to maintain any posture without interference from tilt-counteracting vestibular reflexes. The normal upside-down swimming apparently results from a central bias for this position and a supporting ventral light response.We conclude that if the reafference principle applies to the phenomena investigated, the efference copy may be fed through an integrator before reaching vestibular reflex circuits.     

Molecular analyses of ostracod flocks from Lake Baikal and Lake Tanganyika

Ancient lakes are excellent laboratories for evolutionary research, where species can be studied in the cradle where they originated. In this article, we investigate two endemic ostracod species flocks from the two oldest lakes in the world, Lake Baikal (LB) (ca. 28 myr) and Lake Tanganyika (LT) (ca. 12 myr), with DNA sequence data. Nuclear ITS1 failed to resolve the phylogeny of both flocks. Whilst most phylogenetic relationships of the Tanganyika flock are resolved with mitochondrial COI, the Baikalian tree contains multifurications of up to seven different clades. The Tanganyikan Cyprideis flock shows higher genetic variability, which matches its higher morphological variability. A significant deviation from a constant divergence rate through time indicates that the Cytherissa flock most likely experienced explosive speciation events during its earlier history. Comparative analyses of substitution rates furthermore revealed that they are not clock-wise for COI. Ancestral Cytherissa probably radiated in LB 5–8 myr ago, around the time when the cold, oxygenated abyss was formed in LB. The Tanganyikan Cyprideis flock is almost twice as old as the Baikalian Cytherissa flock, and possibly older than LT itself, ca. 15 myr. The Cyprideis flock has survived drastic lake level changes and resulting salinity crises during its entire history.     

Comparative study of otolith organs between two species of upside-down swimming catfish Synodontis nigriventris showing converse swimming postures

To clarify whether the unique postural control of the upside‐down swimming catfish (Synodontis nigriventris, family Mochokidae) is related to the histological characteristics of the otolith organs, we performed light microscopic observation of the utricle, the saccule and the lagena. The histological aspects of the otolith organs were compared between S. nigriventris and Synodontis multipunctatus, which belong to the same genus. S. multipunctatus usually shows upside‐up swimming posture except for feeding behaviour near water surface. As controls, we additionally used a miniature catfish, Corydoras paleatus and goldfish, Carassius auratus, which shows upside‐up swimming posture. We concluded that the structural aspects of the otolith organs did not cause the unique postural control of S. nigriventris. Light microscopic observation clarified the following aspects: (1) The utricle of S. nigriventris was located at the anterior region of the otocyst and under the semicircular canals, and the saccule and the lagena were located at the posteroventral region of the otocyst like those of S. multipunctatus and the other two fishes. (2) The hair cells of the utricle were arranged on the horizontal plane of the fishes with a variation in cell size at the ventral and ventrolateral sites in S. nigriventris, S. multipunctatus and the other two fishes. (3) The hair cells of the saccule and lagena of S. nigriventris, S. multipunctatus and C. auratus presented perpendicular to the horizontal plane of the fish. (4) Region‐specific differences in the size and shape of the hair cells of S. nigriventris were observed along the three‐dimensional axes of the otolith organs like those of S. multipunctatus and the other two fishes. It is unlikely that the unique postural control of upside‐down catfish is related to the localization of the utricle, the saccule and the lagena and the distribution of the different types of hair cell of the otolith organs. Furthermore, the distribution of the hair cells suggests that the otolith organs in S. nigriventris can detect three‐dimensional postural changes like the organs of other fishes showing generally observed upside‐up swimming posture.     

Diatoms from surface sediments of the northern part of Lake Tanganyika

227 Diatom taxa were observed in the surface sediments of the northern part of Lake Tanganyika, including 1 new to science: Amphora tanganyikae. The diatom community of these sediments is mainly composed of benthic organisms while planktonic diatoms are rather rare. Many brackish-water and a few marine organisms were observed. Cosmopolitan organisms (77.1%) dominate the diatom flora but tropical, tropical African and African taxa are also well represented (22.9%)Deceased.Deceased.     

Four new species of Gomphocythere (Crustacea, Ostracoda) from Lake Tanganyika, East Africa

Four new species of the ostracod genus Gomphocythere are described from Lake Tanganyika (East Africa): Gomphocythere downingi n. sp. G. coheni n. sp., G. wilsoni n. sp., and G. woutersi n. sp. All species are endemic to the lake and are found within a variety of substrates and depths. The addition of these four new species brings the total number of endemic Gomphocythere species in Lake Tanganyika to nine. Other Gomphocythere species are known from water bodies throughout East and South Africa and in the Levant. Brooding is an important, but not a unique, preadaptation for the persistence and taxic prolific speciation of this lineage in Lake Tanganyika.     

Retinofugal and retinopetal connections in the upside-down catfish (Synodontis nigriventris)

Summary The retinofugal and retinopetal connections in the upside-down catfish Synodontis nigriventris were studied by use of the horseradish-peroxidase (HRP) techniques, autoradiography, and degeneration-silver methods. An unusual retinal projection to the torus semicircularis as well as projections to the retina from three different sources in the brain are described. After intra-ocular injections of HRP, labeled cells were found in the optic tectum, the dorsomedial optic nucleus and one of the pretectal nuclei. These new findings support the basic hypothesis (i) that neuronal connections are more extensive in primitive brains, and (ii) that the evolutionary development of more complex brains involves the loss of some selected connections.     

Nuclear gene variation and molecular dating of the cichlid species flock of Lake Malawi

The cichlid fishes of Lake Malawi are famously diverse. However, evolutionary studies have been difficult because of their recent and uncertain phylogenetic history. Portions of 12 nuclear loci were sequenced in nine rock-dwelling species (mbuna) and three representatives of pelagic nonmbuna species. In contrast to the pattern of variation at mitochondrial genes, which do provide phylogenetic resolution at the level of mbuna versus nonmbuna, and among some genera, the nuclear loci were virtually devoid of phylogenetic signal. Only a small minority of variable positions were phylogenetically informative, and no phylogenetic branches are supported by more than one site. From the nuclear gene perspective the Malawian radiation appears to be a star phylogeny, as if the founding of the lake was accompanied by a partial bottleneck. The pattern is different from that found in Lake Victoria, in which nuclear loci share large amounts of ancestral variation. In the case of nuclear genes of Lake Malawi, the absence of phylogenetically informative variation suggests a relative absence of ancestral variation. Nuclear genes also differed from the mitochondria in having nearly twice the amount of divergence from Oreochromis (tilapia). An approximate splitting time between mbuna and nonmbuna lineages was estimated as 0.7 Myr. Oreochromis is estimated to have diverged from the cichlids in Lake Malawi and Lake Tanganyika about 18 MYA.     

Description of a new cichlid fish species of the genus Benthochromis (Perciformes: Cichlidae) from Lake Tanganyika

Benthochromis horii , a new cichlid species is described based on 19 type specimens from the deep waters of Lake Tanganyika. It differs from its congeners by having smaller eyes and longer snout (eye length usually shorter than snout length v. equal to or longer than snout length in Benthochromis tricoti and Benthochromis melanoides ), and more dorsal fin rays (total number of spines and soft rays in dorsal fin usually 30 or 31 v. usually 28 or 29 in B. tricoti and B. melanoides ). Large males of the new species differ from those of congeneric species in terms of their body colour pattern and long pelvic fins. This species has been confused with B. tricoti and has been traded as an aquarium fish.