1,721,026 research outputs found
The gills of Lake Victoria cichlids: theatre for parasite interspecific relationships¬ and niche segregation
No full textHosts often harbour multiple parasite species, that may interact and thus modify each other’s effects on host fitness. These interspecific interactions between parasites may result in parasites occupying different niches within hosts (niche segregation). The within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species.
We investigated the microhabitat distributions and species interactions of gill parasites infecting 14 sympatric Lake Victoria cichlid species. We found that the two most abundant parasite taxa (the monogenean Cichlidogyrus spp. and the copepod L. monodi) had non-random microhabitat distributions on gills, which also differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host-parasite interaction among host species.
Relationships among parasite of different genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and E. lamellifer tended to be positively correlated. In contrast, relationships among congeners (members of Cichlidogyrus belonging to different species) were antagonistic. Together with niche overlap, this suggests competition among species of Cichlidogyrus.
These findings may indicate host species-specificity in parasite niche selection and consequently in the host-parasite relationship. Microhabitat distribution of parasites over gills may represent an important axis of infection variation, therefore we suggest to include the location of parasites on the host in future studies, alongside with canonical measures of infection (i.e. parasite abundance).Swiss National Science Foundation (SNSF)
University of Bern,
FMNS Ubbo Emmius at University of Groninge
The gills of Lake Victoria cichlids: theatre for parasite interspecific relationships¬ and niche segregation
No full textHosts often harbour multiple parasite species, that may interact and thus modify each other’s effects on host fitness. These interspecific interactions between parasites may result in parasites occupying different niches within hosts (niche segregation). The within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species.
We investigated the microhabitat distributions and species interactions of gill parasites infecting 14 sympatric Lake Victoria cichlid species. We found that the two most abundant parasite taxa (the monogenean Cichlidogyrus spp. and the copepod L. monodi) had non-random microhabitat distributions on gills, which also differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host-parasite interaction among host species.
Relationships among parasite of different genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and E. lamellifer tended to be positively correlated. In contrast, relationships among congeners (members of Cichlidogyrus belonging to different species) were antagonistic. Together with niche overlap, this suggests competition among species of Cichlidogyrus.
These findings may indicate host species-specificity in parasite niche selection and consequently in the host-parasite relationship. Microhabitat distribution of parasites over gills may represent an important axis of infection variation, therefore we suggest to include the location of parasites on the host in future studies, alongside with canonical measures of infection (i.e. parasite abundance).Swiss National Science Foundation (SNSF)
University of Bern,
FMNS Ubbo Emmius at University of Groninge
Mechanisms of species divergence through visual adaptation and sexual selection: Perspectives from a cichlid model system
No full textThe theory of ecological speciation suggests that assortative mating evolves most easily when mating preferences are;directly linked to ecological traits that are subject to divergent selection. Sensory adaptation can play a major role in this process,;because selective mating is often mediated by sexual signals: bright colours, complex song, pheromone blends and so on. When;divergent sensory adaptation affects the perception of such signals, mating patterns may change as an immediate consequence.;Alternatively, mating preferences can diverge as a result of indirect effects: assortative mating may be promoted by selection;against intermediate phenotypes that are maladapted to their (sensory) environment. For Lake Victoria cichlids, the visual environment;constitutes an important selective force that is heterogeneous across geographical and water depth gradients. We investigate;the direct and indirect effects of this heterogeneity on the evolution of female preferences for alternative male nuptial colours;(red and blue) in the genus Pundamilia. Here, we review the current evidence for divergent sensory drive in this system, extract;general principles, and discuss future perspective
Variation in parasite infection between replicates of speciation in Lake Victoria cichlid fish
Full text linkBecause of potentially strong eco-evolutionary interactions with their hosts, parasites may initiate or enhance host diversification. The adaptive radiation of cichlid fish in Lake Victoria provides a good system to study the role of parasites at different stages of host speciation. We analysed the macroparasite infection of four replicates of sympatric blue and red Pundamilia species pairs that vary in their age and extent of differentiation. Sympatric host species differed in parasite community composition and in the infection levels of some of these parasite taxa. Most infection differences were consistent between sampling years, indicating temporal consistency in parasite-mediated divergent selection between species. Infection differentiation increased linearly with genetic differentiation. However, significant infection differences between sympatric species were only found in the oldest, most strongly differentiated Pundamilia species pair. This is inconsistent with parasite-driven speciation. Next, we identified five distinct species of Cichlidogyrus, a genus of highly specific gill parasites that has radiated elsewhere in Africa. Infection profiles of species of Cichlidogyrus differed between sympatric cichlid species only in the oldest and most differentiated pair, again inconsistent with parasite-mediated speciation. To conclude, parasites may contribute to host differentiation after speciation, but do not initiate host speciation
Microhabitat distributions and species interactions of ectoparasites on the gills of cichlid fish in Lake Victoria, Tanzania
Full text linkHeterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other's effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host-parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host-parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.sponsorship: This research was funded by the Swiss National Science Foundation and the University of Groningen, the Netherlands (Ubbo Emmius Programme). Infrastructure was provided by the Natural History Museum in Lugano, Switzerland and Hasselt University, Belgium (EMBRC Belgium -FWO project GOH3817N). We acknowledge Antoine Pariselle for help with identification of parasites belonging to Cichlidogyrus. (Swiss National Science Foundation, University of Groningen, the Netherlands (Ubbo Emmius Programme), Natural History Museum in Lugano, Switzerland, Hasselt University, Belgium (EMBRC Belgium - FWO project)|GOH3817N)status: Published onlin
The role of ecology and phenotypic plasticity in lake-stream divergence in an East African haplochromine cichlid fish
Full text linkUnderstanding the “origin of species” has been one of the major topics in biology ever since Charles Darwin’s famous publication (Darwin 1859). One and a half centuries later speciation still remains the “mystery of mysteries” (Pennisi 2005). While we have learned a lot from traditional laboratory model organisms, we now realize that many questions in speciation research can only be answered by studying how organisms adapt, behave and diversify in their natural environment (Nosil et al. 2017). Some of the main questions in speciation research at the moment are: “Which barriers contribute to reproductive isolation?”, “What are the genomic patterns of reproductive isolation?”, “What is the role of plasticity? ”, and “What is the role of changes in gene expression” (Butlin et al. 2012). With this thesis I aim to provide part of the answers to these questions by studying one of the best model systems for speciation research: the East African cichlid fishes (Kocher 2004).
Astatotilapia burtoni is a haplochromine cichlid that inhabits both Lake Tanganyika and affluent rivers. Lake and river populations of A. burtoni represent an emerging model system for studying early phases of adaptive divergence. In my thesis, I investigate the degree of reproductive isolation between different populations and the mechanisms that drive the lake-stream divergence. More specifically, I characterize the reproductive barriers contributing to reproductive isolation and investigate the roles of local adaptation, adaptive phenotypic plasticity, parasites, immune system response, and gene expression in lake-stream divergence.
The main body of work includes four chapters on East-African haplochromine cichlid fishes as a model for studying early phases of adaptive divergence.
In Chapter 1, I investigate the relative contributions of adaptive phenotypic plasticity versus local adaptation to fitness of A. burtoni populations from Lake Tanganyika and nearby rivers. Adaptive phenotypic plasticity has previously been proposed to play a key role in the impressive radiations of cichlids. However, mostly due to logistic difficulties, field-experiments are scarce in this system. By performing two transplant experiments in Lake Tanganyika, using both wild caught and common garden raised F1 individuals, I provide one of the first field-based experiments to assess direct fitness consequences of morphological and genetic divergence between lake and stream cichlids in nature.
In Chapter 2, I further investigate the correlation between genetic divergence between populations and the level of reproductive isolation between populations by performing a mesocosm mating experiment in a semi-natural setting at Lake Tanganyika. I assessed reproductive isolation in the presence of male-male competition by analysing survival and growth rates of introduced adults and their reproductive success from genetic parentage of surviving offspring. I provide one of the first field-based experiments to assess multiple environment dependent (extrinsic) components of reproductive isolation in cichlids.
In Chapter 3, I investigate the role of ecotype-specific parasites, the immune response of hosts, and gene expression in the lake-stream divergence. By performing parasitological screening, immune response measurements, and RNA-sequencing of immune-related organs of fish from natural habitats as well as a lake-like pond setup I reveal the mechanisms underlying phenotypic plasticity in this system.
In Chapter 4, three other haplochromine cichlid species that co-exist with A. burtoni in Lake Tanganyika and surrounding drainage systems were used to uncover commonalities and differences in adaptation to the river/lake habitat. We sequenced whole genomes of multiple lake- stream population pairs of A. burtoni and Ctenochromis horei, Haplochromis stappersi, and Pseudocrenilabrus philander. These natural replicates offered a unique possibility to test whether the same patterns and processes are involved in the adaptation to the lake-stream transition in four haplochromine species. I performed landmark-based geometric morphometric analysis on digital images of fishes of the four species to capture disparity in body shape and compare it with genomic disparity
Sexual conflict over breeding substrate causes female expulsion and offspring loss in a cichlid fish
Full text linkFemales of the Lake Tanganyika cichlid Lamprologus callipterus exclusively breed in empty snail shells that males collect in their territories. Male--male competition for shells is severe, leading to frequent shell stealing and territory takeover. As a consequence, males have breeding females in their shells that spawned with competitors. In this field study, we investigated both naturally occurring and experimentally induced encounters of territorial males with females that had spawned with other males. We found that the breeding success of females that were taken over by a different male was significantly reduced. Behavioral observations after experimental shell relocation further showed that males recognized females that they had not spawned with: males directed more exploration and manipulation behavior toward such shells compared with controls. Reoccupation rate of emptied experimental shells was significantly higher than that of unmanipulated empty shells. This indicates that shell stealing and nest takeover, followed by female expulsion, contribute to the reproductive success of L. callipterus males. We also found that female mate choice reduces expulsion risk: females preferred to mate with large males, and male size correlated with dominance. We conclude that the limited availability of breeding substrate is a key determinant of both intrasexual competition and intersexual conflict in this species. Copyright 2008, Oxford University Press.
Sexual dimorphism and directional sexual selection on aposematic signals in a poison frog
Full text linkIt is commonly assumed that natural selection imposed by predators is the prevailing force driving the evolution of aposematic traits. Here, we demonstrate that aposematic signals are shaped by sexual selection as well. We evaluated sexual selection for coloration brightness in populations of the poison frog Oophaga [Dendrobates] pumilio in Panama's Bocas del Toro archipelago. We assessed female preferences for brighter males by manipulating the perceived brightness of spectrally matched males in two-way choice experiments. We found strong female preferences for bright males in two island populations and weaker or ambiguous preferences in females from mainland populations. Spectral reflectance measurements, coupled with an O. pumilio-specific visual processing model, showed that O. pumilio coloration was significantly brighter in island than in mainland morphs. In one of the island populations (Isla Solarte), males were significantly more brightly colored than females. Taken together, these results provide evidence for directional sexual selection on aposematic coloration and document sexual dimorphism in vertebrate warning coloration. Although aposematic signals have long been upheld as exemplars of natural selection, our results show that sexual selection should not be ignored in studies of aposematic evolution
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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