Intestinal coiling pattern in the epilithic algal-feeding cichlids (Pisces, Teleostei) of Lake Tanganyika, and its phylogenetic significance

This paper suggests that, on the basis of ontogenetic change in intestinal coiling pattern, four types and four subtypes could be recognized within 20 species of epilithic algal-feeding cichlids in Lake Tanganyika. The phylogenetically useful anatomical features characterizing each type are as follows. Petrochromis type: torsion of the intestinal tract generally occurs at Stage 5 Intersecting Point (IP), and the haplochromine loop and a two-loop coiling system are observable. Cyathopharynx type: the value of IP becomes 7 before torsion occurs, and the coiling system changes qualitatively from one-loop to two-loop types. Asprotilapia type: torsion occurs at Stage 5 IP, and a one-loop coiling system is retained throughout ontogeny. Telmatochromis type: no torsion occurs, and a one-loop coiling system is retained throughout ontogeny. Within the Petrochromis type, each of the four subtypes is characterized by the following features. Petrochromis subtype: the rostrally directed haplochromine loop has its rostral part situated to the right side of the stomach in the adult stage. Pseudosimochromis subtype: a circular haplochromine loop is present. Eretmodus subtype: the haplochromine loop tends to be prolonged and bends through 90 or 180 further counter-clockwise. Tropheus subtype: torsion occurs at Stage 7 IP.     

Tactic for bower acquisition by male cichlids,Cyathopharynx furcifer,in Lake Tanganyika

A tactic for bower acquisition by male cichlids,Cyathopharynx furcifer, was studied in Lake Tanganyika. Males held crater-shaped bowers of sand within their territories, which were located adjacent to each other. Females visited bowers to spawn eggs, subsequently brooding the eggs in their mouths. Some individuals held territories without bowers near those of males with bowers. Although only the males with bowers succeeded in reproduction, they were apparently exhausted by bower maintenance and reproduction, and often deserted their bowers. These were soon occupied by males which had held nearby territories without bowers, such males then engaging in reproductive activity. Although the construction of new bowers by males was observed, such was unsuccessful, probably because too much energy was required and/or the optimal space for bowers was limited. Direct aggression by males without bowers against bower-holding males to deprive the bowers was not observed, possibly due to the high costs of such competition. Therefore, waiting for bower desertion by other males may be the best bower acquisition tactic for males without bowers.     

Mating system and kin relationship between adults and young in the shell-brooding cichlid fish <Emphasis Type="Italic">Neolamprologus meeli</Emphasis> in Lake Tanganyika

Mating system and parental behavior of ten monogamous pairs and two polygynous groups of the Tanganyikan cichlid Neolamprologus meeli were observed in their natural habitat. The home ranges of males and females overlapped with each other. Most groups included one to six young. Paternal and maternal relationships were determined for 22 young from DNA microsatellite markers. Three types of kinship were found: (I) kinship to both the male and female; (II) kinship to females only; and (III) non-kinship to both sexes. In the groups with type II young, step-fathering or sneaking may have occurred. Type III young were larger than type I, suggesting that the former were of sufficient size to leave their birth nest and settle in the territories of foster parents. Both males and females drove out potential predators of young (including three species of Lepidiolamprologus) as a parental behavior. Adults with type III young attacked approaching predators with as much frequency as those with type I young only, indicating that they provided alloparental care. Adults and young swam together, but, a significant difference existed in the frequencies of interactions between adults versus kin young and adults versus non-kin young. The results suggest that both adults and young recognized kin. Electronic Publication     

Sperm size of African cichlids in relation to sperm competition

We compared pairs of closely related taxa of cichlid fishesfrom Lake Tanganyika to examine the relationship between spermsize and the presumed intensity of sperm competition. In contrastto previous reports of relatively short sperm in polygamousfishes across a variety of taxa, we found that polygamous cichlidshad significantly longer sperm than their closest monogamousrelatives. In addition, sperm length was significantly relatedto relative testis size (controlling for body size and phylogeny).The site of fertilization may also be correlated with spermlength, as species that fertilize in the female's buccal cavityhad significantly shorter sperm than those that fertilizedeggs on the substrate. Assuming that relatively large testesand polygamous mating are indicative of more intense sperm competition, these results indicate that sperm length is related to the intensityof sperm competition in this clade of cichlids, as has beenfound previously in insects, birds, and mammals.     

Foraging behaviour and functional morphology of two scale-eating cichlids from Lake Tanganyika

The foraging behaviours of two Tanganyikan scale-eating cichlids, Perissodus straeleni and Perissodus microlepis , were observed in laboratory. Video analyses of their feeding behaviours showed the distinct differences in scale-eating action between the two species. Perissodus straeleni presses and shifts its mouth laterally along the body of the prey as the prey attempts to break free. In contrast, P. microlepis quickly rotates its body, with both jaws pressed tightly against the flank of the prey. Scanning electron microscopy of tooth shapes confirmed that dental morphology clearly differs between the two species: the teeth of P. straeleni are laminar and leaf-shaped with sharp edges along the lateral sides, whereas P. microlepis has thick, broad-based teeth with spine-like points in the upper corners. In addition, inspection of tooth condition in wild-caught fishes showed that the ratio of wearing teeth was significantly higher in P. straeleni than in P. microlepis . These results indicate that the functional morphology of the teeth plays an important role in their scale-eating actions; in P. straeleni , the sharp edges of the teeth appear to function as blades for scraping while shifting the mouth laterally along the body of the prey, whereas the spine-like projections on the teeth of P. microlepis appear to effectively catch scales while pressing and rotating the mouth, simultaneously wrenching off scales. These results clearly demonstrate that the different scale-eating behaviours of the two species are closely associated with the functional diversification of their jaw teeth.     

Neolamprologus cancellatus, a new cichlid fish from Lake Tanganyika, Africa

Neolamprologus cancellatus, a new cichlid species, is described on the basis of eight specimens from the Zambian coast of Lake Tanganyika. The new species is characterized by a subtruncate caudal fin and a body that is slender (depth 22.3–25.2% in standard length) and easily distinguishable from its congeners by having 7–8 anal fin spines, 34–37 scales in longitudinal line, 33 total vertebrae, and a gridlike body pattern on a pale brownish body color. This species is only known to inhabit the shallow (2–7 m depth), rocky bottom of Wonzye Point in the southern part of the lake.     

Evolution of brain–body allometry in Lake Tanganyika cichlids

Brain size is strongly associated with body size in all vertebrates. This relationship has been hypothesized to be an important constraint on adaptive brain size evolution. The essential assumption behind this idea is that static (i.e., within species) brain–body allometry has low ability to evolve. However, recent studies have reported mixed support for this view. Here, we examine brain–body static allometry in Lake Tanganyika cichlids using a phylogenetic comparative framework. We found considerable variation in the static allometric intercept, which explained the majority of variation in absolute and relative brain size. In contrast, the slope of the brain–body static allometry had relatively low variation, which explained less variation in absolute and relative brain size compared to the intercept and body size. Further examination of the tempo and mode of evolution of static allometric parameters confirmed these observations. Moreover, the estimated evolutionary parameters indicate that the limited observed variation in the static allometric slope could be a result of strong stabilizing selection. Overall, our findings suggest that the brain–body static allometric slope may represent an evolutionary constraint in Lake Tanganyika cichlids.     

A new species and geographical variation in the Telmatochromis temporalis complex (Teleostei, Cichlidae) from Lake Tanganyika

Telmatochromis brachygnathus sp.n. is described from the southern and central parts of Lake Tanganyika. It can be distinguished from the similar T. temporalis mainly by its smaller mouth. Morphological distinct populations were found in both species.     

Phytoplankton pigments and community composition in Lake Tanganyika

1. A 2‐year (2002–2003) survey of chlorophyll and carotenoid pigments is reported for two off‐shore stations of Lake Tanganyika, Kigoma (Tanzania) and Mpulungu (Zambia), and from three cruises between those sites. Chlorophyll a concentrations were low (0.3–3.4 mg m^?3) and average chlorophyll a integrated through the 100 m water column were similar for both stations and years (36.4–41.3 mg m^?2). Most pigments were located in the 0–60 m layer and decreased sharply downward. Chlorophyll a degradation products (phaeophytins and phaeophorbides) were detected at 100 m depth, whereas carotenoids became undetectable. Temporal and seasonal variation of the vertical distribution of pigments was high. 2. The biomass of phytoplankton groups was calculated from marker pigment concentrations over the 0–100 m water column using the CHEMTAX software. On average for the study period, chlorophytes dominated in the northern station, followed by cyanobacteria T1 (type 1, or Synechococcus pigment type), whereas cyanobacteria T1 dominated in the south. Cyanobacteria T2 (type 2, containing echinenone), presumably corresponding to filamentous taxa, were detected in the rainy season. Diatoms (and chrysophytes) developed better in the dry season conditions, with a deep mixed layer and increased nutrient availability. Very large variation in the vertical distribution of algal groups was observed. 3. Our observations on phytoplankton composition are broadly consistent with those from previous studies. Our pigment data provide evidence for the lake‐wide importance of picocyanobacteria and high interannual variation and spatial heterogeneity of phytoplankton in Lake Tanganyika, which may render difficult assessment of long‐term changes in phytoplankton driven by climate change.     

Interspecific brood-mixing in Tanganyikan cichlids

Synopsis We collected schools of young, guarded by parents, of six common cichlid species to investigate the frequency and origin of interspecific brood-mixing. The main host species were a piscivore Lepidiolamprologus elongatus and a scale-eater Perissodus microlepis; more than half of their schools included heterospecific young, accounting for 20–40% of the total young. Most of the foreign young belonged to four biparental mouth-brooders whose parents have a habit of carrying their young in their mouths. Many of these young were smaller than the largest young brooded by their own parents. We concluded that adoption of young before independence results from farming-out, a behavior by which parents actively transfer their young to foster parents.     

An initial measurement of photosynthetic productivity in Lake Tanganyika

Measurements of ¹⁴C uptake and oxygen evolution by phytoplankton in Lake Tanganyika provide the first direct estimates of the lake's primary productivity. These measurements at the expected nadir of the annual range suggest that Lake Tanganyika is as productive as other large, deep tropical lakes.     

Microdontochromis rotundiventralis, a new cichlid fish (perciformes: Cichlidae) from Lake Tanganyika

Microdontochromis rotundiventralis, a new species of cichlid fish, is described on the basis of 13 specimens from Nkumbula Island, Lake Tanganyika (Zambia). It is distinct from its only congener,M. tenuidentatus, in having two (rarely one) rows of teeth on both jaws, a rounded distal margin on the pelvic fin, the outermost pelvic fin soft ray length 1.23–1.43 times the innermost ray, a deeper body (depth 26.8–29.1% standard length) and the anal fin with 9 (rarely 8 or 10) soft rays.     

Helping opportunities and space segregation in cooperatively breeding cichlids

Studies of cooperative breeding have largely ignored the roleof conflict among helpers and how it shapes group dynamics andhelping behavior. In the present study, performing laboratoryexperiments with cooperatively breeding cichlids from Lake Tanganyika,we show that secondary group members (potential helpers) occupyhome ranges within the group territory and may be aggressiveto one another. Experimental removal of secondary group membersallowed the individual next in rank to move closer to the removedindividual's home range. In the field, dominant secondary groupmembers stayed closer to the brood chamber than did subordinategroup members of similar size, and proximity to the brood chamberwas related to the length of time spent inside. We suggest thatspace segregation and competition among secondary group membersis common in these cichlids, and may limit the opportunitiesto provide help.     

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.     

Sedimentary diatom assemblages in the northern part of Lake Tanganyika

Surface sediment diatoms from the northern part of Lake Tanganyika were analysed with several ordination and classification techniques. Three sample groups characterized by four diatom assemblages were recognized. The first sample group occurs in a rather shallow area near the delta of the Rusizi River on a coarse-grained sand substrate. The second and most important sample group occurs on the silty bottom of an underwater depression situated off the delta of the Rusizi River in the north-eastern part of Lake Tanganyika; its diatom composition has a great affinity to the Rusizi River diatom population. The third sample group contains all the other samples and covers an area corresponding to the west-, east- and southward continuation of the area of the second group: its diatom composition is also related to the Rusizi River diatom population, but in a less pronounced manner.     

Differential response of phytoplankton to additions of nitrogen, phosphorus and iron in Lake Tanganyika

1. In order to evaluate limitation of different phytoplankton groups by inorganic nutrients, multiple nutrient enrichment bioassays using the addition of iron (Fe) and the combined addition of nitrogen and phosphorus (NP) were carried out in the north and the south of Lake Tanganyika during the rainy and dry seasons in 2003 and 2004. 2. Nutrient additions resulted in an increase in phytoplankton growth rate relative to control treatments in all experiments. HPLC pigment data and epifluorescence microscopy counts indicated differential stimulation of the dominant phytoplankton groups. Iron additions mainly stimulated prokaryotic picophytoplankton, while enrichments with nitrogen and phosphorus stimulated green algae and in some cases diatoms. Extended incubation (3 days) indicated co‐limitation of Fe and NP, in particular for picocyanobacteria.     

Alloparental care between catfishes in Lake Tanganyika

A bagrid catfish Auchenoglanis occidentalis cared for its brood, deposited within an accumulation of shells and gravel in the centre of a large saucer-like depression, for up to 2 weeks in Lake Tanganyika. Adults of another catfish Dinotopterus cunningtoni (Clariidae) persistently came to A. occidentalis nests near days of host spawning. Eggs of D. cunningtoni were found in the host nests on the day and within 2 days of host spawning. During and for a few days after the end of host brooding, associate species' young of much older ages than the host brood were often found in the nests together with those of a similar age to the host young. Associate young were rarely found in nests before spawning and in unused nests. These findings suggested that this brood-mixing has two origins: egg dumping by associate adults and voluntary intrusion of large associate young into host nests. Possible benefits to the associate species are to take advantage of nest preparation and parental behaviour of the host species and to feed on the host brood.     

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     

Seasonal patterns of sediment loading and benthic invertebrate community dynamics in Lake Tanganyika, Africa

1. This study investigated the spatiotemporal dynamics of benthic invertebrate communities located close to the mouths of the Kalambo and Lunzua Rivers, at the southern end of Lake Tanganyika, and subject to varying degrees of sediment load. 2. Metrics of exposure to riverine sediments were associated inversely with abundance and diversity of benthic organisms at sampling locations adjacent to both river mouths, indicating a major effect of riverine sediments on the structure of near‐shore benthic communities. 3. A lower abundance of benthos was found at the mouth of the Lunzua River, which exports significantly higher sediment loads than the Kalambo. 4. Seasonal cycles of abundance and diversity in the benthos varied with distance from river mouths. This has important implications for monitoring programmes investigating benthic communities close to the mouths of rivers. 5. Our findings suggest that recent increases in the sediment loading of Lake Tanganyika, owing to anthropogenic catchment disturbance, impact significantly on biological diversity throughout the lake littoral, which provides habitat for the majority of species in the lake.     

Paternal mouthbrooding bagrid catfishes in Lake Tanganyika

 This article gives the first information about paternal mouthbrooding in bagrid catfishes, based on analysis of specimens collected while SCUBA diving in Lake Tanganyika, Africa. Lophiobagrus aquilus and L. cyclurus, endemic to the lake, were nocturnally active, and in the daytime were found concealed singly or in pairs beneath rocks. Among 39 L. aquilus and 52 L. cyclurus collected, 8 and 1 solitary males, respectively, were incubating eggs or young in the buccal cavity. Paired males and females and solitary females never took care of the offspring. In both species, females of pairs showed much higher gonadosomatic index values and had larger oocytes in the ovaries than did solitary females. This fact suggests that pair formation takes place at a time near the gonadal maturation of the female and that the pair separate after spawning. We tentatively propose an evolutionary transition route of care patterns in bagrid catfishes. Received: January 25, 2002 / Revised: April 13, 2002 / Accepted: April 17, 2002