Tanganyika Cichlid Research Articles

Sexually divergent selection, allometric constraints, and the evolution of sexual dimorphism in cichlids from Lake Tanganyika.

The evolution of sexual dimorphism is widely acknowledged as manifestation of sex-specific genetic architecture. Although empirical studies suggested that sexual dimorphism evolves as a joint consequence of constraints arising from the genetic architecture and sexually divergent selection, it remains unclear whether and how these established microevolutionary processes scale up to the macroevolutionary patterns of sexual dimorphism among taxa. Here, we studied how sexual selection and parental care drive sexual dimorphism in cichlid fishes from Lake Tanganyika. We found that male-male competition, female choice, and maternal mouthbrooding are associated with sexual dimorphism in body length, body color, and head length, respectively, despite strong allometric relationships between body length and head length. Within-species (static) allometry of head length on body length evolved as sex-specific responses to mouthbrooding where females evolved higher intercepts while males evolved steeper slopes. Thus, selection to increase mouth size in mouthbrooders may have broken down and reorganized the pattern of allometric constraints that are inherently strong and concordant between sexes. Furthermore, sex-specific responses to mouthbrooding left a remarkably clear signature on the macroevolutionary pattern, resulting in a decoupling of co-evolution in parameters of static allometries observed exclusively within maternal mouthbrooders. Our study provides multiple lines of evidence that are consistent with the idea that macroevolutionary patterns of sexual dimorphism in Lake Tanganyika cichlids result from sexually divergent selection. Our approach illustrates that an examination of within-population phenotypic variance in the phylogenetic comparative framework may facilitate nuanced understandings of how macroevolutionary patterns are generated by underlying microevolutionary processes.

Differences in inhibitory control in two species of Tanganyikan bower‐building cichlids contrasting in building flexibility

AbstractA central challenge in understanding the evolution of cognition is the ability to compare a set of species differing in a trait of interest while being ecologically and phylogenetically close. Here, we examine whether differences in bower‐building flexibility are related to differences in cognitive flexibility between two Tanganyikan cichlids. Cognitive flexibility enables animals to modify their decision rules when faced with new situations, and inhibitory control, the ability to inhibit a normally favoured response, is an essential component of this capacity. We tested male Aulonocranus dewindti and Cyathopharynx furcifer in a choice‐against‐preference paradigm. Both species clean their bowers of foreign objects and we found that both preferred to remove a snail shell over a stone. We tested their ability to modify this preference and learned to preferably select the stone instead of the shell. Although neither species showed clear learning of the new preference rule, both demonstrated inhibitory control through increased decision times and manipulations of the objects when selecting the stone. Specifically, A. dewindti, the species exhibiting greater behavioural flexibility in the construction of their bowers, selected the stone in fewer trials than C. furcifer, providing support for a link between behavioural flexibility in bower construction and cognitive flexibility.

The genetics of niche-specific behavioral tendencies in an adaptive radiation of cichlid fishes.

Behavior is critical for animal survival and reproduction, and possibly for diversification and evolutionary radiation. However, the genetics behind adaptive variation in behavior are poorly understood. In this work, we examined a fundamental and widespread behavioral trait, exploratory behavior, in one of the largest adaptive radiations on Earth, the cichlid fishes of Lake Tanganyika. By integrating quantitative behavioral data from 57 cichlid species (702 wild-caught individuals) with high-resolution ecomorphological and genomic information, we show that exploratory behavior is linked to macrohabitat niche adaptations in Tanganyikan cichlids. Furthermore, we uncovered a correlation between the genotypes at a single-nucleotide polymorphism upstream of the AMPA glutamate-receptor regulatory gene cacng5b and variation in exploratory tendency. We validated this association using behavioral predictions with a neural network approach and CRISPR-Cas9 genome editing.

Revision of the cichlid fish genus Gnathochromis (Teleostei: Cichlidae) from Lake Tanganyika with the description of a new genus Jabarichromis gen. nov.

The cichlid species flock from Lake Tanganyika is a well-studied system for evolutionary biology research because its species assemblage shows a high degree of endemism and is a product of adaptive radiation. While our understanding of the evolutionary history of Lake Tanganyika cichlids has advanced tremendously over the past decades, their taxonomy received considerably less attention, despite numerous taxonomic misplacements (e.g., polyphyletic genera and species) that have been revealed by phylogenetic studies. One prominent example of a polyphyletic genus is Gnathochromis, which includes two distantly related species, belonging to two different tribes. To resolve this issue, here we present a taxonomic revision based on an extensive morphological dataset obtained from a comprehensive taxon sampling including 587 specimens from 63 taxa. We introduce a new monotypic genus, Jabarichromis gen. nov. for Gnathochromis pfefferi, a member of the tribe Tropheini, thereby separating it from the type species of Gnathochromis, G. permaxillaris. As a result, the genus Gnathochromis, which belongs to the tribe Limnochromini, is rendered monophyletic. Further, we provide an additional character to distinguish the recently described genus Shuja, which also belongs to the Tropheini, from its former mostly riverine congeners.

Ancient standing genetic variation facilitated the adaptive radiation of Lake Victoria cichlids.

Cichlid fishes are textbook examples of explosive speciation and adaptive radiation, providing a great opportunity to understand how the genomic substrate yields extraordinary species diversity. Recently, we performed comparative genomic analyses of three Lake Victoria cichlids to reveal the genomic substrates underlying their rapid speciation and adaptation. We found that long divergent haplotypes derived from large-scale standing genetic variation, which originated before the adaptive radiation of Lake Victoria cichlids, may have contributed to their rapid diversification. In addition, the present study on genomic data from other East African cichlids suggested the reuse of alleles that may have originated in the ancestral lineages of Lake Tanganyika cichlids during cichlid evolution. Therefore, our results highlight that the primary factor that could drive repeated adaptive radiation across East African cichlids was allelic reuse from standing genetic variation to adapt to their own specific environment. In this report, we summarize the main results and discuss the evolutionary mechanisms of cichlids, based on our latest findings.

Species of Ergasilus von Nordmann, 1832 (Copepoda: Ergasilidae) from cichlid fishes in Lake Tanganyika.

Ergasilus (von Nordmann, 1832) (Ergasilidae) is a species-rich group of parasitic copepods with a wide distribution in freshwater, marine and brackish environments. Up to now, 9 species of Ergasilus are known from cichlid fishes in Africa. In this study, 5 species, including 3 new, were collected from the gills of 12 cichlid species (11 genera: Bathybates, Ctenochromis, Eretmodus, Gnathochromis, Lamprologus, Neolamprologus, Ophthalmotilapia, Perissodus, Simochromis, Spathodus and Tanganicodus) of the northeastern shore of Lake Tanganyika in Burundi, namely E. macrodactylus (Sars, 1909), E. megacheir (Sars, 1909), E. caparti n. sp., E. parasarsi n. sp. and E. parvus n. sp. All species found were identified and described on the basis of adult female specimens using an integrative taxonomy approach mixing morphological characterization and molecular analyses of 2 ribosomal DNA markers (partial 18S and 28S rDNA sequences). An identification key for Ergasilus species from Lake Tanganyika is included. This study provides the first molecular data for Ergasilus species in Africa. The phylogenetic analyses suggest that the Ergasilus species parasitizing Lake Tanganyikan cichlids form a well-supported clade within the Ergasilidae. However, their phylogenetic relationships with other congeners still remain unclear due to a lack of molecular data for this diverse genus.

Variable hybridization between two Lake Tanganyikan cichlid species in recent secondary contact.

Closely related taxa frequently exist in sympatry before the evolution of robust reproductive barriers, which can lead to substantial gene flow. Post-divergence gene flow can promote several disparate trajectories of divergence ranging from the erosion of distinctiveness and eventual collapse of the taxa to the strengthening of reproductive isolation. Among many relevant factors, understanding the demographic history of divergence (e.g. divergence time and extent of historical gene flow) can be particularly informative when examining contemporary gene flow between closely related taxa because this history can influence gene flow's prevalence and consequences. Here, we used genotyping-by-sequencing data to investigate speciation and contemporary hybridization in two closely related and sympatrically distributed Lake Tanganyikan cichlid species in the genus Petrochromis. Demographic modelling supported a speciation scenario involving divergence in isolation followed by secondary contact with bidirectional gene flow. Further investigation of this recent gene flow found evidence of ongoing hybridization between the species that varied in extent between different co-occurring populations. Relationships between abundance and the degree of admixture across populations suggest that the availability of conspecific mates may influence patterns of hybridization. These results, together with the observation that sets of recently diverged cichlid taxa are generally geographically separated in the lake, suggest that ongoing speciation in Lake Tanganyikan cichlids relies on initial spatial isolation. Additionally, the spatial heterogeneity of admixture between the Petrochromis species illustrates the complexities of hybridization when species are in recent secondary contact.

Molecular evolution and depth-related adaptations of rhodopsin in the adaptive radiation of cichlid fishes in Lake Tanganyika.

The visual sensory system is essential for animals to perceive their environment and is thus under strong selection. In aquatic environments, light intensity and spectrum differ primarily along a depth gradient. Rhodopsin (RH1) is the only opsin responsible for dim‐light vision in vertebrates and has been shown to evolve in response to the respective light conditions, including along a water depth gradient in fishes. In this study, we examined the diversity and sequence evolution of RH1 in virtually the entire adaptive radiation of cichlid fishes in Lake Tanganyika, focusing on adaptations to the environmental light with respect to depth. We show that Tanganyikan cichlid genomes contain a single copy of RH1. The 76 variable amino acid sites detected in RH1 across the radiation were not uniformly distributed along the protein sequence, and 31 of these variable sites show signals of positive selection. Moreover, the amino acid substitutions at 15 positively selected sites appeared to be depth‐related, including three key tuning sites that directly mediate shifts in the peak spectral sensitivity, one site involved in protein stability and 11 sites that may be functionally important on the basis of their physicochemical properties. Among the strongest candidate sites for deep‐water adaptations are two known key tuning sites (positions 292 and 299) and three newly identified variable sites (37, 104 and 290). Our study, which is the first comprehensive analysis of RH1 evolution in a massive adaptive radiation of cichlid fishes, provides novel insights into the evolution of RH1 in a freshwater environment.

Dynamics of sex chromosome evolution in a rapid radiation of cichlid fishes

Sex is a fundamental trait determined by environmental and/or genetic factors, including sex chromosomes. Sex chromosomes are studied in species scattered across the tree of life, yet little is known about tempo and mode of sex chromosome evolution among closely related species. Here, we examine sex chromosome evolution in the adaptive radiation of cichlid fishes in Lake Tanganyika. Through the analysis of male and female genomes from 244 cichlid taxa (189 described species with 5 represented with two local variants/populations; 50 undescribed species) and of 396 multitissue transcriptomes from 66 taxa, we identify signatures of sex chromosomes in 79 taxa, involving 12 linkage groups. We find that Tanganyikan cichlids have the highest rates of sex chromosome turnover and heterogamety transitions known to date. We show that sex chromosome recruitment is not at random. Moreover convergently emerged sex chromosomes in cichlids support the “limited options” hypothesis of sex chromosome evolution.

Maternal Care-Providing Cichlid Neolamprologus furcifer Selectively Focuses on High-Threat Carnivorous Intruders, Limiting Attention to Other Threats

Animals adjust their behaviors based on information from multiple sources; however, the brain can effectively process limited amounts of information. Therefore, attention is restricted to a small portion of environmental stimuli. When animals process multiple information inputs, focusing on information that is deemed important improves detection probability. However, selective focus limits attention to other stimuli and associated behavioral responses. In this study, we examined how Tanganyikan cichlid, Neolamprologus furcifer, mothers selectively attack intruder fishes depending on the threat level and presence or absence of offspring. Species composition is complicated in Lake Tanganyika, and fish density is exceedingly high. Thus, parents must focus on high-threat-level intruders according to their parental care stage. Compared to females without offspring, mothers preferentially attacked carnivorous fishes farther from the nest over closer scale-eating fishes. Moreover, the percentage of females with injuries from scale-eating fish was significantly higher in those caring for offspring than those without offspring, demonstrating the cost of limited attention. Our results show that females focus on the early detection of carnivorous fishes because these predators dart in from long distances to forage eggs, fry, and juveniles, but this selective focus limits the attention placed on low-level threats. This study is the first to document the cost of limited attention in parents guarding offspring.

Intraspecific morphological variation in Cichlidogyrus (Monogenea) parasitizing two cichlid hosts from Lake Tanganyika exhibiting different dispersal capacities

As parasites depend on their hosts and play a significant role in their ecology and evolution, we hypothesized an association between the host dispersal capacity and the intraspecific variability of their host-specific parasites. We investigated the morphological variability of the gill monogeneans Cichlidogyrus gistelincki and C. milangelnari parasitizing the Tanganyika cichlids ‘Ctenochromis’ horei and Cyprichromis microlepidotus, respectively. The profound ecological and behavioural differences between these host species allowed us to assume that the former is a good and the latter a poor disperser. Specimens of monogeneans were collected from cichlids inhabiting different locations at the northern end of Lake Tanganyika. Sequences of the 28S rDNA gene were used to confirm parasite conspecificity. Dorsal and ventral anchors of the attachment organ of parasite specimens were used to evaluate variability in shape. Geomorphometric analyses revealed that populations of C. milangelnari, which parasitize poorly dispersing cichlids, are more differentiated than populations of C. gistelincki infecting well-dispersing hosts. Both anchors showed significant shape variation between populations of C. milangelnari. In C. gistelincki, anchors were highly similar in comparisons of populations from nearby and from distant locations.

Reflections on the Predictability of Evolution: Toward a Conceptual Framework.

SummaryEvolution is generally considered to be unpredictable because genetic variations are known to occur randomly. However, remarkable patterns of repeated convergent evolution are observed, for instance, loss of pigments by organisms living in caves. Analogous phenotypes appear in similar environments, sometimes in response to similar constraints. Alongside randomness, a certain evolutionary determinism also exists, for instance, the selection of particular phenotypes subjected to particular environmental constraints in the “evolutionary funnel.” We pursue the idea that eco-evolutionary specialization is in some way determinist. The conceptual framework of phenotypic changes entailing specialization presented in this essay explains how evolution can be predicted. We also discuss how the predictability of evolution could be tested using the case of metabolic specialization through gene losses. We also put forward that microorganisms could be key models to test and possibly make headway evolutionary predictions and knowledge about evolution.

Wasteful carotenoid coloration and its effects on territorial behavior in a cichlid fish

The famously diverse body coloration of cichlid fish serves communicative functions in mating and social interactions including competition for resources. Here, we examined the effects of a color pattern trait—the width of a yellow bar on a black body—on territorial competition in males and females of a color variant (“Ikola”) of the Lake Tanganyika cichlid Tropheus. First, measuring integumentary carotenoid concentrations in the yellow and black body regions, we established that wider yellow bars require more carotenoids allocated to body coloration. However, we also detected high carotenoid concentrations in the black body regions (> 100 µg/g fresh skin), raising questions about the function of non-displayed integumentary carotenoids. Behavioral experiments showed that fish with wider bars were quicker to explore an unfamiliar area of the tank. In experiments including presentations of fish dummies, the bar width of ‘territorial’ dummies had no effect on the latency time which test fish took to intrude into the dummies’ territories. However, male test fish performed fewer aggressive acts against wide-barred than against narrow-barred dummy competitors. Our results suggest that intimidation by wide bars as well as correlations between bar width and explorative behavior may contribute to mediating success in territorial Tropheus “Ikola”.

Group-size preferences in a shoaling cichlid

Abstract Group size is an important criterion in social decisions. Accordingly, assessing quantities is common in many animals. In fishes, studies on numerical abilities focus on a limited range of species. Arguably, cichlids show the greatest variability of social patterns among vertebrates. Nevertheless, knowledge about their quantitative abilities is scarce. Here we use the Lake Tanganyika cichlid Lamprologus callipterus to scrutinize the quantitative abilities of fish in the context of shoaling. Females chose between different numbers of conspecifics, varying in absolute and relative number differences. In half of the trials both shoals were composed of familiar sisters, while all fish were unfamiliar non-kin in the other half. Test fish consistently preferred the larger of two shoals, irrespective of the ratios. Their activity differed significantly between familiarity/relatedness treatments, indicating recognition of this parameter. L. callipterus therefore has fine-tuned discrimination skills, adding to the evidence that quantitative abilities are widespread in fishes.

East African cichlid lineages (Teleostei: Cichlidae) might be older than their ancient host lakes: new divergence estimates for the east African cichlid radiation

BackgroundCichlids are a prime model system in evolutionary research and several of the most prominent examples of adaptive radiations are found in the East African Lakes Tanganyika, Malawi and Victoria, all part of the East African cichlid radiation (EAR). In the past, great effort has been invested in reconstructing the evolutionary and biogeographic history of cichlids (Teleostei: Cichlidae). In this study, we present new divergence age estimates for the major cichlid lineages with the main focus on the EAR based on a dataset encompassing representative taxa of almost all recognized cichlid tribes and ten mitochondrial protein genes. We have thoroughly re-evaluated both fossil and geological calibration points, and we included the recently described fossil †Tugenchromis pickfordi in the cichlid divergence age estimates.ResultsOur results estimate the origin of the EAR to Late Eocene/Early Oligocene (28.71 Ma; 95% HPD: 24.43–33.15 Ma). More importantly divergence ages of the most recent common ancestor (MRCA) of several Tanganyika cichlid tribes were estimated to be substantially older than the oldest estimated maximum age of the Lake Tanganyika: Trematocarini (16.13 Ma, 95% HPD: 11.89–20.46 Ma), Bathybatini (20.62 Ma, 95% HPD: 16.88–25.34 Ma), Lamprologini (15.27 Ma; 95% HPD: 12.23–18.49 Ma). The divergence age of the crown haplochromine H-lineage is estimated to 22.8 Ma (95% HPD: 14.40–26.32 Ma) and of the Lake Malawi radiation to 4.07 Ma (95% HDP: 2.93–5.26 Ma). In addition, we recovered a novel lineage within the Lamprologini tribe encompassing only Lamprologus of the lower and central Congo drainage with its divergence estimated to the Late Miocene or early Pliocene. Furthermore we recovered two novel mitochondrial haplotype lineages within the Haplochromini tribe: ‘Orthochromis’ indermauri and ‘Haplochormis’ vanheusdeni.ConclusionsDivergence time estimates of the MRCA of several Tanganyika cichlid tribes predate the age of the extant Lake Tanganyika basin, and hence are in line with the recently formulated “Melting-Pot Tanganyika” hypothesis. The radiation of the ‘Lower Congo Lamprologus clade’ might be linked with the Pliocene origin of the modern lower Congo rapids as has been shown for other Lower Congo cichlid assemblages. Finally, the age of origin of the Lake Malawi cichlid flock agrees well with the oldest age estimate for lacustrine conditions in Lake Malawi.

The effects of land use disturbance vary with trophic position in littoral cichlid fish communities from Lake Tanganyika

AbstractImpacts of anthropogenic disturbance are especially severe in freshwater ecosystems. In particular, land use disturbance can lead to increased levels of pollution, including elevated nutrient and sediment loads whose negative impacts range from the community to the individual level. However, few studies have investigated if these impacts are uniform across species represented by multiple trophic levels. To address this knowledge gap, we focused on Lake Tanganyika cichlid fishes, which comprise hundreds of species representing a wide range of feeding strategies. Cichlids are at their most diverse within the near‐shore environment; however, land use disturbance of this environment has led to decreasing diversity, particularly in herbivores. We therefore tested if there is a uniform effect of pollution across species and trophic groups within the hyper‐diverse rocky shore cichlid fish community.We selected three sites with differing levels of human impact along the Tanzanian coastline and 10 cichlid species, comprising varying taxonomic and trophic groups, common to these sites. Nitrogen and carbon stable isotope values for 528 samples were generated and analysed using generalised linear mixed models. We also estimated stomach contents including sediment proportions.Our study highlights that multiple sources of pollution are having differing effects across species within a diverse fish community. We found that nitrogen stable isotope values were significantly higher at the most disturbed (urbanised) site for benthic feeding species, whereas there was no difference in these isotopes between sites for the water column feeding trophic group. Stomach contents revealed that the elevated δ15N values were unlikely to have been caused by differences in diet between sites. However, at the most disturbed site, higher proportions of sediment were present in most herbivores, irrespective of foraging behaviour.It is likely that anthropogenic nitrogen loading is the cause of higher nitrogen stable isotope values since there was no evidence of species shifting trophic levels between sites. Results support our previous study showing herbivore species to be most affected by human disturbance and make the link to pollution much more explicit. As lower diversity of consumers can negatively affect ecosystem processes such as stability, alleviating environmental impact through sewage treatment and afforestation programmes should continue to be a global priority for the conservation of aquatic ecosystems, as well as human health.

Long-term individual marking of small freshwater fish: the utility of Visual Implant Elastomer tags

Tracking wild animals over long periods of time is a non-trivial challenge. This has caused a bias in the availability of individual-based long-term datasets with the majority including birds and mammals. Visual Implant Elastomer (VIE) tags are now a widely used technique that may facilitate the collection of such data for fish and amphibians. However, VIE tags might have important drawbacks. Overall, four potential issues with VIE tags have been proposed: tag loss or misidentification, limited number of individual identifiers, enhanced mortality risk, and effects on intra-specific interactions. Here, we present three experiments in which we investigated these potential problems with VIE tagging in small freshwater fish both in the laboratory and in the wild, using the cooperatively breeding Lake Tanganyika cichlid Neolamprologus pulcher. We find VIE tags to be generally suitable for work with these fish as they did not impair survival, were recognisable up to 2 years after injection, and did not generally disturb group formation. Nevertheless, we identify specific issues of VIE tagging, including colour- and position-dependent variation in tag identification rates, and indications that specific colours may influence social behaviour. Our results demonstrate the suitability of VIE tags for long-term studies on small freshwater fish, while also highlighting the need of validating this method carefully for any species and study.Significance statementInformation on the survival, dispersal, and reproductive success of wild individuals across their lifespan is among the most valuable data in Behavioural Ecology. Because tracking of free-ranging individuals over extended periods of time is challenging, there exists a bias in the taxonomic distribution of such long-term datasets. Here, we investigate the suitability of visible implant elastomers (VIE) as a tracking technique to allow for the collection of such data also in small tropical freshwater fish. We show that VIE tags neither alter social behaviour in our study species, nor do they reduce survival, but they enable the tracking of wild individuals across years. We also identify colours and tag positions that are less suitable. We conclude that VIE tags can help produce long-term datasets also for small fish, provided certain precautions are met.

Point-Combination Transect (PCT): Incorporation of small underwater cameras to study fish communities.

Available underwater visual census (UVC) methods such as line transects or point count observations are widely used to obtain community data of underwater species assemblages, despite their known pit‐falls. As interest in the community structure of aquatic life is growing, there is need for more standardized and replicable methods for acquiring underwater census data.Here, we propose a novel approach, Point‐Combination Transect (PCT), which makes use of automated image recording by small digital cameras to eliminate observer and identification biases associated with available UVC methods. We conducted a pilot study at Lake Tanganyika, demonstrating the applicability of PCT on a taxonomically and phenotypically highly diverse assemblage of fishes, the Tanganyikan cichlid species‐flock.We conducted 17 PCTs consisting of five GoPro cameras each and identified 22,867 individual cichlids belonging to 61 species on the recorded images. These data were then used to evaluate our method and to compare it to traditional line transect studies conducted in close proximity to our study site at Lake Tanganyika.We show that the analysis of the second hour of PCT image recordings (equivalent to 360 images per camera) leads to reliable estimates of the benthic cichlid community composition in Lake Tanganyika according to species accumulation curves, while minimizing the effect of disturbance of the fish through SCUBA divers. We further show that PCT is robust against observer biases and outperforms traditional line transect methods.

Comparative genomics reveals an outstanding sex chromosome diversity in cichlid fishes driven by genomic novelties and convergent evolution

Event Abstract Back to Event Comparative genomics reveals an outstanding sex chromosome diversity in cichlid fishes driven by genomic novelties and convergent evolution Athimed El Taher1, Michael Matschiner2, 3, Fabrizia Ronco1, Walter Salzburger1 and Astrid Böhne1, 4* 1 University of Basel, Zoological Institute, Switzerland 2 Paleontological Institute and Museum, Faculty of Mathematics and Natural Sciences, University of Zurich, Switzerland 3 Centre for Ecological and Evolutionary Synthesis, Faculty of Mathematics and Natural Sciences, University of Oslo, Norway 4 Zoological Research Museum Alexander Koenig (LG), Center for Molecular Biodiversity Research (ZMB), Germany Sexual reproduction is ancient and almost universal in the eukaryotic kingdom. However, the mechanisms that actually determine male or female sex are highly divers encompassing a variety of extrinsic and intrinsic drivers. Intrinsic factors, commonly referred to as genetic sex determination, comprise systems as simple as a single base pair difference between the sexes to highly differentiated sex chromosomes. Why sex-determining systems change frequently in some taxa, whereas the same sex chromosome pair persists over long evolutionary time in others, remains an open question. With ~3000 species, cichlid fishes are one of the largest vertebrate families and an extraordinary example of adaptive radiations. If different sex-determining mechanisms contribute to the species richness of this fish lineage is largely unknown. The oldest and most diverse African cichlid assemblage is the one of Lake Tanganyika, which consists of 250 endemic species. Using whole genome sequencing, comparative genomics and expression data, we investigate the genetic basis of sex determination and the evolution of sex chromosomes in this radiation. We identified at least 28 sex chromosome transitions in cichlids with a transition rate of 0.19 per million years. To the best of our knowledge this is the highest transition rate so far described. We show that closely related species can have different sex chromosomal systems indicative of recent turnover events. On the other hand, it also seems that particular chromosomes evolved convergently as sex chromosomes in distantly related cichlid lineages. Chromosomal fusions likely played a role in cichlid sex chromosome evolution. Cichlids perfectly exemplify the diversity as well as the constraints of sex chromosome evolution and can reveal the forces driving the evolution of sex-determining systems. Acknowledgements Calculations were performed at sciCORE (http://scicore.unibas.ch/) scientific computing center at University of Basel, with support by the SIB - Swiss Institute of Bioinformatics. Keywords: Cichlid, sex chromosome, adaptive radiation, speciation, Lake Tanganyika cichlid fishes, Comparative genomics, Transcriptomics Conference: XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019. Presentation Type: Oral Topic: EVOLUTIONARY GENOMICS OF FISHES Citation: El Taher A, Matschiner M, Ronco F, Salzburger W and Böhne A (2019). Comparative genomics reveals an outstanding sex chromosome diversity in cichlid fishes driven by genomic novelties and convergent evolution. Front. Mar. Sci. Conference Abstract: XVI European Congress of Ichthyology. doi: 10.3389/conf.fmars.2019.07.00040 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 17 Jun 2019; Published Online: 14 Aug 2019. * Correspondence: Dr. Astrid Böhne, University of Basel, Zoological Institute, Basel, CH-4001, Switzerland, a.boehne@leibniz-zfmk.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Athimed El Taher Michael Matschiner Fabrizia Ronco Walter Salzburger Astrid Böhne Google Athimed El Taher Michael Matschiner Fabrizia Ronco Walter Salzburger Astrid Böhne Google Scholar Athimed El Taher Michael Matschiner Fabrizia Ronco Walter Salzburger Astrid Böhne PubMed Athimed El Taher Michael Matschiner Fabrizia Ronco Walter Salzburger Astrid Böhne Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

An exploration of the links between parasites, trophic ecology, morphology, and immunogenetics in the Lake Tanganyika cichlid radiation

Differences in habitat and diet between species are often associated with morphological differences. Habitat and trophic adaptation have therefore been proposed as important drivers of speciation and adaptive radiation. Importantly, habitat and diet shifts likely impose changes in exposure to different parasites and infection risk. As strong selective agents influencing survival and mate choice, parasites might play an important role in host diversification. We explore this possibility for the adaptive radiation of Lake Tanganyika (LT) cichlids. We first compare metazoan macroparasites infection levels between cichlid tribes. We then describe the cichlids’ genetic diversity at the major histocompatibility complex (MHC), which plays a key role in vertebrate immunity. Finally, we evaluate to what extent trophic ecology and morphology explain variation in infection levels and MHC, accounting for phylogenetic relationships. We show that different cichlid tribes in LT feature partially non-overlapping parasite communities and partially non-overlapping MHC diversity. While morphology explained 15% of the variation in mean parasite abundance, trophic ecology accounted for 16% and 22% of the MHC variation at the nucleotide and at the amino acid level, respectively. Parasitism and immunogenetic adaptation may thus add additional dimensions to the LT cichlid radiation.