Active browsing by mouthbrooding females of Tropheus duboisi and Tropheus moorii (Cichlidae) to feed the young and/or themselves

Synopsis Fishes usually do not eat while brooding offspring in their mouths. In two epilithic algal eaters Tropheus duboisi and T. moorii in Lake Tanganyika, however, mouthbrooding females exhibited feeding actions. In T. duboisi, the feeding rate of mouthbrooding females was 80 percent of that of males and non brooding females irrespective of the developmental state of their offspring. In T. moori, females brooding early embryos rarely fed but their feeding rate increased with development of offspring. An examination of specimens revealed that such females took food for nourishment of themselves and the young in the former species but for nourishment of only the young in the latter.     

Intra- and interspecific social organization among three herbivorous cichlid fishes in Lake Tanganyika

Intra- and interspecific social organization among 3 coexisting herbivorous cichlids,Tropheus moorii, Petrochromis trewavasae andP. orthognathus, were studied at a rocky shore in Lake Tanganyika. Individuals of all species maintained discrete intra- and interspecific territories, exceptT. moorii andP. trewavasae whose feeding territories overlapped. Territory owners attacked smaller individuals but exhibited displays towards larger neighbours, irrespective of species. This observation suggests that both intra- and interspecifically, these cichlids interact in the context of size-dependent dominance hierarchies. Removal experiments showed that smallerT. moorii benefitted fromP. trewavasae in the maintenance of their territory borders against largerP. orthognathus. Interspecific dominance hierarchy and commensalism among these cichlids are not species specific, but change dynamically in relation to the difference in body size between component individuals. Mating territories of maleP. orthognathus andT. moorii are compared to their feeding territories, and territory forms are discussed. It is suggested that an approach incorporating the concept of an interspecific society may play an important role in the elucidation of guild structure and function.     

Grazing rates of crustacean zooplankton communities on intact phytoplankton communities in Canadian Subarctic lakes and ponds

Quantitative genetic studies in natural populations are of growing interest to speciation research since divergence is often believed to arise through micro-evolutionary change, caused by natural selection on functional morphological traits. The species flock of cichlid fishes in Africa’s oldest lake, Lake Tanganyika, offers a rare opportunity to study this process. Using the cichlid species Tropheus moorii, we assessed the potential for microevolution in a set of morphological traits by estimating their quantitative genetic basis of variation. Two approaches were employed: (1) estimation of trait heritabilities (h ²) in situ from a sample of wild caught fish, and (2) estimation of h ² from first generation offspring produced in a semi-natural breeding experiment. In both cases, microsatellite data were used to infer pedigree structure among the sampled individuals and estimates of h ² were made using an animal model approach. Although power was limited by the pedigree structures estimated (particularly in the wild caught sample), we nonetheless demonstrate the presence of significant additive genetic variance for aspects of morphology that, in the cichlid species Tropheus moorii, are expected to be functionally and ecologically important, and therefore likely targets of natural selection. We hypothesize that traits showing significant additive genetic variance, such as the mouth position have most likely played a key role in the adaptive evolution of the cichlid fish Tropheus moorii.     

The social and mating system of the maternal mouthbrooderTropheus moorii (Cichlidae) in Lake Tanganyika

Territorial behaviour, reproduction and migration of the epilithic algal eater,Tropheus moorii, were investigated in Lake Tanganyika, Africa. Adults of both sexes had individual feeding territories which adjointed each other. Males, who occupied higher rocks than females, usually stayed at the same sites for more than 5 months. Females left their territories to pair with males in the males’ territories. Paired females actively foraged under the protection of their mates for up to 3 weeks prior to spawning. After spawning, females usually settled in a site unoccupied by territory-holders to mouthbrood the offspring for a month. An examination of the ovaries and a removal experiment of dominant males suggest that females cannot attain fully mature ovaries in their own territories and choose males whose territories can provide enough food to satisfy their nutritive demand. The evolution of a number of local colour morphs in this fish is briefly discussed in relation to social selection.     

Where Am I? Niche constraints due to morphological specialization in two Tanganyikan cichlid fish species

Food resource specialization within novel environments is considered a common axis of diversification in adaptive radiations. Feeding specializations are often coupled with striking morphological adaptations and exemplify the relation between morphology and diet (phenotype–environment correlations), as seen in, for example, Darwin finches, Hawaiian spiders, and the cichlid fish radiations in East African lakes. The cichlids' potential to rapidly exploit and occupy a variety of different habitats has previously been attributed to the variability and adaptability of their trophic structures including the pharyngeal jaw apparatus. Here we report a reciprocal transplant experiment designed to explore the adaptability of the trophic structures in highly specialized cichlid fish species. More specifically, we forced two common but ecologically distinct cichlid species from Lake Tanganyika, Tropheus moorii (rock‐dweller), and Xenotilapia boulengeri (sand‐dweller), to live on their preferred as well as on an unpreferred habitat (sand and rock, respectively). We measured their overall performance on the different habitat types and explored whether adaptive phenotypic plasticity is involved in adaptation. We found that, while habitat had no effect on the performance of X. boulengeri, T. moorii performed significantly better in its preferred habitat. Despite an experimental duration of several months, we did not find a shift in the morphology of the lower pharyngeal jaw bone that would be indicative of adaptive phenotypic plasticity in this trait.     

Species-Specific Population Structure in Rock-Specialized Sympatric Cichlid Species in Lake Tanganyika,East Africa

Species richness and geographical phenotypic variation in East African lacustrine cichlids are often correlated with ecological specializations and limited dispersal. This study compares mitochondrial and microsatellite genetic diversity and structure among three sympatric rock-dwelling cichlids of Lake Tanganyika, Eretmodus cyanostictus, Tropheus moorii, and Ophthalmotilapia ventralis. The species represent three endemic, phylogenetically distinct tribes (Eretmodini, Tropheini, and Ectodini), and display divergent ecomorphological and behavioral specialization. Sample locations span both continuous, rocky shoreline and a potential dispersal barrier in the form of a muddy bay. High genetic diversity and population differentiation were detected in T. moorii and E. cyanostictus, whereas much lower variation and structure were found in O. ventralis. In particular, while a 7-km-wide muddy bay curtails dispersal in all three species to a similar extent, gene flow along mostly continuous habitat appeared to be controlled by distance in E. cyanostictus, further restricted by site philopatry and/or minor habitat discontinuities in T. moorii, and unrestrained in O. ventralis. In contrast to the general pattern of high gene flow along continuous shorelines in rock-dwelling cichlids of Lake Malawi, our study identifies differences in population structure among stenotopic Lake Tanganyika species. The amount of genetic differentiation among populations was not related to the degree of geographical variation of body color, especially since more phenotypic variation is observed in O. ventralis than in the genetically highly structured E. cyanostictus. [Reviewing Editor: Dr. Rafael Zardoya]     

Intermediate number of major histocompatibility complex class IIB length variants relates to enlarged perivisceral fat deposits in the blunt‐head cichlid Tropheus moorii

Studying the genetic basis of host–parasite interactions represents an outstanding opportunity to observe eco‐evolutionary processes. Established candidates for such studies in vertebrates are immunogenes of the major histocompatibility complex (MHC). The MHC has been reported to reach high intra‐ and interindividual diversity, and a diverse MHC might be advantageous when facing infections from multiple parasites. However, other studies indicated that individuals with an intermediate number of MHC alleles are less infected with parasites or have other fitness advantages. In this study, we assessed the optimal number of MHC alleles in the blunt‐head cichlid Tropheus moorii from Lake Tanganyika. We investigated the influence of the interindividual variation in number of MHC length variants on parasite infection and body condition, measured by the amount of perivisceral fat reserves. Surprisingly, there was no correlation between parasite infection and number of MHC length variants or perivisceral fat deposits. However, the individual number of MHC length variants significantly correlated with the amount of perivisceral fat deposits in males, suggesting that male individuals with an intermediate number of alleles might be able to use their fat reserves more efficiently.     

Evolution of body shape in sympatric versus non-sympatric Tropheus populations of Lake Tanganyika

Allopatric speciation often yields ecologically equivalent sister species, so that their secondary admixis enforces competition. The shores of Lake Tanganyika harbor about 120 distinct populations of the cichlid genus Tropheus, but only some are sympatric. When alone, Tropheus occupies a relatively broad depth zone, but in sympatry, fish segregate by depth. To assess the effects of competition, we studied the partial co-occurrence of Tropheus moorii ‘Kaiser'' and ‘Kirschfleck'' with Tropheus polli. A previous study demonstrated via standardized breeding experiments that some observed differences between Tropheus ‘Kaiser'' living alone and in sympatry with T. polli have a genetic basis despite large-scale phenotypic plasticity. Using geometric morphometrics and neutral genetic markers, we now investigated whether sympatric populations differ consistently in body shape from populations living alone and if the differences are adaptive. We found significant differences in mean shape between non-sympatric and sympatric populations, whereas all sympatric populations of both color morphs clustered together in shape space. Sympatric populations had a relatively smaller head, smaller eyes and a more anterior insertion of the pectoral fin than non-sympatric populations. Genetically, however, non-sympatric and sympatric ‘Kaiser'' populations clustered together to the exclusion of ‘Kirschfleck''. Genetic distances, but not morphological distances, were correlated with geographic distances. Within- and between-population covariance matrices for T. moorii populations deviated from proportionality. It is thus likely that natural selection acts on both phenotypic plasticity and heritable traits and that both factors contribute to the observed shape differences. The consistency of the pattern in five populations suggests ecological character displacement.     

Hidden species diversity in Marcusenius moorii (Teleostei: Mormyridae) from the Congo Basin

New collections from the Yangambi Biosphere Reserve (YBR) and Okapi Wildlife Reserve (OWR) revealed the presence of two groups of specimens similar to, but different from Marcusenius moorii. To study both these groups, an integrated morphological and genetic (mtDNA, cytb) approach was used. This study revealed that one of the two groups is conspecific with Marcusenius lambouri, a junior synonym of M. moorii, which is herein revalidated, with M. moorii longulus as its junior synonym. Marcusenius lambouri differs from M. moorii by a higher number of lateral line scales (44–46 vs. 40–43), a shorter pectoral-fin length (14.6–19.9 vs. 20.3–25.2% standard length; L_S) and a more elongated body due to a usually shallower middle body depth (19.8–26.5 vs. 26.3–35.9% L_S). The other group revealed to be a new species for science, Marcusenius verheyenorum, which can be distinguished from its congeners with eight circumpeduncular scales by the following unique combination of characters: a rounded head with a terminal mouth; a short and deep caudal peduncle (middle caudal-peduncle depth, 44.9–54.6% caudal-peduncle length; L_CP), a deep body (middle body depth, 27.7–34.2% L_S), 38–43 scales on the lateral line, 40–41 vertebrae, 20–21 dorsal-fin rays and 26 anal-fin rays. Some specimens previously attributed to M. moorii were examined and reassigned to M. lambouri or M. verheyenorum. As a result, M. moorii and M. lambouri occur in sympatry in the middle Congo Basin, with the distribution area of M. moorii still further extending into the lower Congo Basin. Instead, the distribution of M. verheyenorum is limited to some right bank tributaries of the upstream part of the middle Congo Basin. Two museum records from the Lilanda River (YBR), collected in the 1950s and previously identified as M. moorii, were re-identified as belonging to the new species, M. verheyenorum. However, the species now seems locally extinct in that region, which reflects the significant anthropogenic effects even within this reserve.     

A link between host dispersal and parasite diversity in two sympatric cichlids of Lake Tanganyika

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Group foraging by the herbivorous cichlid fish,Petrochromis fasciolatus,in Lake Tanganyika

Group foraging of the algae eating cichlid,Petrochromis fasciolatus, was studied along a rocky shore in Lake Tanganyika, in an area occupied by the feeding territories of several herbivorous cichlid species. SolitaryP. fasciolatus or schools comprising a few members only were nearly always repelled from such territories, although larger schools (40–250 individuals) ofP. fasciolatus were able to overwhelm the defenses of territory owners and enable subsequent foraging. The frequency and duration of individual foraging sessions on the algal mats were positively correlated with group size, probably owing to individuals in large schools suffering fewer attacks from territory owners. Almost all of the foraging sites ofP. fasciolatus were inside the territories of other herbivorous cichlids, especially those ofNeolamprologus moorii (more than 80% of total), in which the algal density was more than 10 times that in territories of the other species.N. moorii territories included only 4% rocky substrate, indicating that schools ofP. fasciolatus selectively chose territories containing rich resources.     

Weak link between dispersal and parasite community differentiation or immunogenetic divergence in two sympatric cichlid fishes

Geographical isolation, habitat variation and trophic specialization have contributed to a large extent to the astonishing diversity of cichlid fishes in the Great East African lakes. Because parasite communities often vary across space and environments, parasites can accompany and potentially enhance cichlid species diversification. However, host dispersal may reduce opportunities for parasite‐driven evolution by homogenizing parasite communities and allele frequencies of immunity genes. To test for the relationships between parasite community variation, host dispersal and parasite‐induced host evolution, we studied two sympatric cichlid species with contrasting dispersal capacities along the shores of southern Lake Tanganyika. Whereas the philopatric Tropheus moorii evolved into several genetically differentiated colour morphs, Simochromis diagramma is phenotypically rather uniform across its distribution range and shows only weak population structure. Populations of both species were infected with divergent parasite communities and harbour differentiated variant pools of an important set of immune genes, the major histocompatibility complex (MHC). The overall extent of geographical variation of parasites and MHC genes was similar between host species. This indicates that immunogenetic divergence among populations of Lake Tanganyika cichlids can occur even in species that are strongly dispersing. However, because this also includes species that are phenotypically uniform, parasite‐induced evolution may not represent a key factor underlying species diversification in this system.     

Shifting barriers and phenotypic diversification by hybridisation

The establishment of hybrid taxa relies on reproductive isolation from the parental forms, typically achieved by ecological differentiation. Here, we present an alternative mechanism, in which shifts in the strength and location of dispersal barriers facilitate diversification by hybridisation. Our case study concerns the highly diverse, stenotopic rock‐dwelling cichlids of the African Great Lakes, many of which display geographic colour pattern variation. The littoral habitat of these fish has repeatedly been restructured in the course of ancient lake level fluctuations. Genetic data and an experimental cross support the hybrid origin of a distinct yellow‐coloured variant of Tropheus moorii from ancient admixture between two allopatric, red and bluish variants. Deficient assortative mating preferences imply that reproductive isolation continues to be contingent on geographic separation. Linking paleolimnological data with the establishment of the hybrid variant, we sketch a selectively neutral diversification process governed solely by rearrangements of dispersal barriers.     

Digestive enzyme activities and gastrointestinal fermentation in wood-eating catfishes

To determine what capabilities wood-eating and detritivorous catfishes have for the digestion of refractory polysaccharides with the aid of an endosymbiotic microbial community, the pH, redox potentials, concentrations of short-chain fatty acids (SCFAs), and the activity levels of 14 digestive enzymes were measured along the gastrointestinal (GI) tracts of three wood-eating taxa (Panaque cf. nigrolineatus “Marañon”, Panaque nocturnus, and Hypostomus pyrineusi) and one detritivorous species (Pterygoplichthys disjunctivus) from the family Loricariidae. Negative redox potentials (?600 mV) were observed in the intestinal fluids of the fish, suggesting that fermentative digestion was possible. However, SCFA concentrations were low (<3 mM in any intestinal region), indicating that little GI fermentation occurs in the fishes’ GI tracts. Cellulase and xylanase activities were low (<0.03 U g^?1), and generally decreased distally in the intestine, whereas amylolytic and laminarinase activities were five and two orders of magnitude greater, respectively, than cellulase and xylanase activities, suggesting that the fish more readily digest soluble polysaccharides. Furthermore, the Michaelis–Menten constants (K _m) of the fishes’ β-glucosidase and N-acetyl-β-d-glucosaminidase enzymes were significantly lower than the K _m values of microbial enzymes ingested with their food, further suggesting that the fish efficiently digest soluble components of their detrital diet rather than refractory polysaccharides. Coupled with rapid gut transit and poor cellulose digestibility, the wood-eating catfishes appear to be detritivores reliant on endogenous digestive mechanisms, as are other loricariid catfishes. This stands in contrast to truly “xylivorous” taxa (e.g., beavers, termites), which are reliant on an endosymbiotic community of microorganisms to digest refractory polysaccharides.     

Variable discrimination and asymmetric preferences in laboratory tests of reproductive isolation between cichlid colour morphs

Mating behaviour affects reproductive isolation and phenotypic differentiation. In Lake Tanganyika, the cichlid fish Tropheus moorii diversified into numerous, currently allopatric colour variants. Allopatric isolation is periodically interrupted by dispersal and secondary contact during lake level fluctuations, making long‐term differentiation partly dependent on assortative mating. Laboratory experiments with two moderately distinct morphs revealed assortative female preferences in one (Nakaku), but random mate choice in the other morph (Mbita). No discrimination was apparent between two subtly differentiated morphs (Chimba and Moliro). Tested against each other in a previous study, the highly distinct Moliro and Nakaku exhibited strong assortative preferences. The correlation between colour pattern similarity and mate discrimination suggests that allopatry and philopatric behaviour are less crucial for the maintenance of differentiation between highly distinct morphs than for more similar morphs. Interestingly, the asymmetric isolation in one pair of morphs is congruent with a pattern of unidirectional mitochondrial introgression between populations.     

Interspecific relationships of aufwuchs-eating fishes in Lake Tanganyika

Synopsis On a rocky shore of Lake Tanganyika aufwuchs-eating is practiced by 18 fish species: 17 cichlids and 1 cyprinid. The majority takes mostly either filamentous or unicellular algae.Tropheus moorei and its taxonomically related species most closely resemble one another in diet among the species taking mostly filamentous algae, and thePetrochromis species do so among the species taking mostly unicellular algae.Petrochromis polyodon andT. moorei severely interfere with the feeding activities of related species. These two dominant species share both intensive grazing sites and temporal grazing patterns, and there seems to be a symbiotic relationship between them. Symbiotic relationships are also seen in seven cases of associated feeding by carnivorous fishes. Differences in diet or feeding behavior are found between these symbionts. Small but clear differences are found betweenP. polyodon andT. moorei and between the associating and the carnivorous host fishes in the four cases of associated feeding. These small differences seem attributable to morphological differences and may have been effective for the evolution of symbiotic relationships.Contribution from the Laboratory of Animal Ecology, Kyoto University, No. 461.     

Seasonality in Dietary Shifts in Size-Structured Freshwater Fish Assemblages in Three Reservoirs of Sri Lanka

We studied seasonal changes in feeding habits of size-structured fish assemblages in three freshwater reservoirs in Sri Lanka. We obtained fish samples for diet analysis from three reservoirs during the months of rising water level (RIWL) and receding water level (REWL). During RIWL, peripheral areas with terrestrial/semi-terrestrial macrophytes get inundated, which resulted in increased food availability for macrophyte feeding fish. During REWL, detrital food sources increase due to decaying terrestrial plant material, which has inundated. Based on the dietary habits of individual species in the three reservoirs during RIWL and REWL, it is evident that detritivorous and phytoplanktivorous fish species, which belong to low trophic levels do not show significant variation in dietary habits between the two seasons (e.g. Oreochromis mossambicus, Oreochromis niloticus and Amblypharyngodon melettinus). Stenophagous species such as benthic invertebrate predators (Puntius chola and Puntius dorsalis), macrophytophagous species (Etroplus suratensis and Tilapia rendalli) and zooplanktivorous Hemirhamphus limbatus do not exhibit significant variation in dietary habits between seasons. Also their feeding habits do not vary with body size. Euryphagous species such as Puntius filamentosus on the other hand, exhibit variations in dietary habits between seasons as well as with body size. Stenophagous species, which feed on detritus and phytoplankton and euryphagous species, which exhibit temporal dietary plasticity, are therefore abundant in fish assemblages of these reservoirs.     

Morphological patterns of five fish species (four characiforms,one perciform) in relation to feeding habits in a tropical reservoir in south‐eastern Brazil

Described are the ecomorphological attributes of five abundant fish species and their relationships to the feeding ecology in a tropical reservoir in south‐eastern Brazil. A total of 140 individuals were used. All specimens were collected between October 2006 and September 2007. Nine ecomorphological indexes were used and patterns detected by principal components analysis. The carnivorous species (Oligosarcus hepsetus) showed higher relative height of mouth to the mouth width aspect. On the other hand, the herbivorous species (Metynnis maculatus) had a higher compression index to the relative height. Geophagus brasiliensis (perciform) exhibited a larger relative length of the head to the relative length of the caudal peduncle. The two Astyanax species (A. bimaculatus and A. parahybae), although with taxonomic and morphological proximities to each other, exhibited indications of morphological adjustments probably associated to adaptive divergence. Three well‐defined trophic groups were confirmed by the cluster analysis. The ecomorphology was effective in predicting feeding habits and aspects of locomotion, and the eventual consequences of the impoundment may be triggering a morphological divergence between closely related species. The authors hope that knowledge with regard to the effects of these man‐made ecosystems on ichthyofauna ecomorphology will be further elucidated in the coming years, perhaps providing advice for their implementation in future hydropower projects.     

Nitrogen,phenolic acids,and other feeding cues for salt marsh detritivores

Summary A number of feeding cues determine the palatability of detritus to detritivorous invertebrates. In salt marsh detritus the feeding cues include flavor provided by phenolics such as ferulic acid, pH, salinity, and nitrogen content. We examined the feeding responses to each cue by using experimental manipulations where we changed concentrations of these chemical cues. The palatability of detritus of the salt marsh grass Spartina alterniflora to the detritivorous snail Melampus bidentatus is reduced by increases in ferulic acid in the detritus. The acidity of the acid is partly responsible for inhibition of feeding, but other flavors of the ferulic acid are the major factor. Changes in salinity makes detritus more or less palatable to different species of detritivores. Available nitrogen confers greater palatability to detritus.In the field the feeding cues are all present simultaneously, and detritivores feed based on a hierarchy of cues. For M. bidentatus the presence of sufficient available nitrogen overwhelms the response to ferulic acid, the second most important cue. Salinity and pH, although used as discriminatory cues by themselves, are located lower in the hierarchy than nitrogen and ferulic acid.As detritus ages in the marsh, nitrogen content changes. Similarly, detritus from eutrophied environments shows enhanced nitrogen content. The differences in palatability of new and old detritus, and from eutrophic and non-eutrophic environments, suggests that detritivores respond not to total nitrogen but rather to the availabel nitrogen fractions. The increase in lignin found in old and eutrophic detritus may increase the binding of available nitrogen, and hence reduce the palatability of detritus.     

A review of the potential of surface flow constructed wetlands to enhance macroinvertebrate diversity in agricultural landscapes with particular reference to Integrated Constructed Wetlands (ICWs)

Discriminating female mate preferences enhance the variance in reproductive success among males of a population and create a potential for sexual selection, which can account for trait evolution and diversification. Fish color patterns are among the prime targets of mate choice-driven sexual selection. Populations of the cichlid Tropheus from Lake Tanganyika display remarkable geographic color pattern variation, but the role of female choice in their rapid and rich phenotypic diversification is unclear. Males and females establish a pair bond prior to spawning monogamously, but as brood care is strictly maternal, female investment in reproduction is high and the operational sex ratio is male-biased. Therefore, variance in male reproductive success can accrue if individual males succeed repeatedly in securing a mate. To test this prediction in the red colored Tropheus moorii “Chimba”, four pairs of males were presented to a series of females and female mate preferences were inferred from pairwise interactions. There was a significant difference in mating success between the males of each pair (P < 0.001 over all trials), as—with one exception—females shared preferences for the same males. Male courtship activity was strongly correlated with female choice. Our experiment suggests that female choice contributes to the variance in male reproductive success in the tested population.