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715 results for “Cichlid”
The functional role of sibling aggression and "best of a bad job" strategies in cichlid juveniles
Siblings often compete for limited resources such as food provided by their parents. However, although several functions of non-lethal sibling (non-siblicidal) aggression have been proposed, there is currently little empirical evidence for these, apart from food monopolization. Here, we investigated the functions of non-lethal sibling aggression in the biparental-caring territorial herbivorous cichlid Varibilichromis moorii. We found that the juveniles of this species are highly aggressive and that larger juveniles are more aggressive toward their smaller siblings. Larger juveniles feed on algae more frequently than smaller siblings, thereby indicating a dominance hierarchy. Sibling aggression decreased when algae in the nest was experimentally removed. Furthermore, removal of smaller juveniles decreased sibling aggression among the remaining larger juveniles, whereas removal of larger juveniles increased aggression among smaller juveniles. The algal feeding rate of juveniles only increased when larger individuals were removed from the nest. Moreover, larger juveniles attained higher growth rates and remained in natal nests longer than smaller individuals. Our results indicate that sibling aggression may facilitate the monopolization of resources by larger juveniles and extend the parental care period. Interestingly, a small sub-set of juveniles were observed to migrate to other nests. These juveniles were larger than those of the host brood, and their growth rate increased within the new nests. We suggest that subordinate juveniles may disperse from natal nests and sneak into new nests to enhance their rank, which may represent a novel example of a "best of a bad job" strategy associated with sibling competition.
The genetic basis of coordinated plasticity across functional units in a Lake Malawi cichlid mapping population
Adaptive radiations are often stereotypical, as populations repeatedly specialize along conserved environmental axes. Phenotypic plasticity may be similarly stereotypical, as individuals respond to environmental cues. These parallel patterns of variation, which are often consistent across traits, have led researchers to propose that plasticity can facilitate predictable patterns of evolution along environmental gradients. This "flexible stem" model of evolution raises questions about the genetic nature of plasticity, including: How complex is the genetic basis for plasticity? Is plasticity across traits mediated by many distinct loci, or few "global" regulators? To address these questions, we reared a hybrid cichlid mapping population on alternate diet regimes mimicking an important environmental axis. We show that plasticity across an array of ecologically relevant traits is generally morphologically integrated, such that traits respond in a coordinated manner, especially those with overlapping function. Our genetic data are more ambiguous. While our mapping experiment provides little evidence for global genetic regulators of plasticity, these data do contain a genetic signal for the integration of plasticity across traits. Overall, our data suggest a compromise between genetic modularity, whereby plasticity may evolve independently across traits, and low-level but widespread genetic integration, establishing the potential for plasticity to experience coordinated evolution.
Prosocial and antisocial choices in a monogamous cichlid with biparental care
<p><span><span><span><span><span><span><span><span><span><span><span>Human society is cooperative and characterized by spontaneous prosociality. Comparative studies on endotherm vertebrates suggest that social interdependence causes the evolution of proactive prosociality. To test the generality of this hypothesis, we modified a prosocial choice task for application to the convict cichlid, <i>Amatitlania nigrofasciata,</i> a monogamous fish with biparental care and a strong pair bond. We show that subject males learned to favor prosocial choices when their mates were the recipients in neighboring tank. When the neighboring tank was empty, males chose at random. Furthermore, in the absence of their mates, males also behaved prosocially towards a stranger female. However, if the subjects' mate was also visible in a third tank, or if a male was the potential recipient, subjects made antisocial choices. In conclusion, fish may show both spontaneous prosocial and antisocial behaviors, according to their social relationships with conspecifics and the overall social context.</span></span></span></span></span></span></span></span></span></span></span></p>
Data from: Effect of craniofacial genotype on the relationship between morphology and feeding performance in cichlid fishes
The relationship between morphology and performance is complex, but important for understanding the adaptive nature of morphological variation. Recent studies have sought to better understand this system by illuminating the interconnectedness of different functional systems; however, the role of genetics is often overlooked. In this study, we attempt to gain insights into this relationship by examining the effect of genotypic variation at putative craniofacial loci on the relationship between morphology and feeding performance in cichlids. We studied two morphologically disparate species, as well as a morphologically intermediate hybrid population. We assessed feeding performance, jaw protrusion, and general facial morphology for each fish. We also genotyped hybrid animals at six previously identified craniofacial loci. Cichlid species were found to differ in facial geometry, kinematic morphology, and performance. Significant correlations were also noted between these variables; however, the explanatory power of facial geometry in predicting performance was relatively poor. Notably, when hybrids were grouped by genotype, the relationship between shape and performance improved. This relationship was especially robust in animals with the specialist allele at sox9b, a well-characterized regulator of craniofacial development. These data suggest a novel role for genotype in influencing complex relationships between form and function.
Genetic architecture of a key reproductive isolation trait differs between sympatric and non-sympatric sister species of Lake Victoria cichlids
One hallmark of the East African cichlid radiations is the rapid evolution of reproductive isolation that is robust to full sympatry of many closely related species. Theory predicts that species persistence and speciation in sympatry with gene flow are facilitated if loci of large effect or physical linkage (or pleiotropy) underlie traits involved in reproductive isolation. Here we investigate the genetic architecture of a key trait involved in behavioural isolation, male nuptial coloration, by crossing two sister species pairs of Lake Victoria cichlids of the genus <i>Pundamilia</i> and mapping nuptial coloration in the F2 hybrids. One is a young sympatric species pair, representative of an axis of colour motif differentiation, red-dorsum vs blue, that is highly recurrent in closely related sympatric species. The other is a species pair representative of colour motifs, red-chest vs blue, that are common in allopatric but uncommon in sympatric closely related species. We find significant QTLs with moderate to large effects (some overlapping) for red and yellow in the sympatric red-dorsum x blue cross, whereas we find no significant QTLs in the non-sympatric red-chest x blue cross. These findings are consistent with theory predicting that large effect loci or linkage/pleiotropy underlying mating trait differentiation could facilitate speciation and species persistence with gene flow in sympatry.
Decoupled jaws promote trophic diversity in Cichlid fishes
Functional decoupling of oral and pharyngeal jaws is widely considered to have expanded the ecological repertoire of cichlid fishes. But, the degree to which the evolution of these jaw systems is decoupled and whether decoupling has impacted trophic diversification remains unknown. Focusing on the large Neotropical radiation of cichlids, we ask whether oral and pharyngeal jaw evolution is correlated and how their evolutionary rates respond to feeding ecology. In support of decoupling, we find relaxed evolutionary integration between the two jaw systems, resulting in novel trait combinations that potentially facilitate feeding mode diversification. These outcomes are made possible by escaping the mechanical trade-off between force transmission and mobility, which characterizes a single jaw system that functions in isolation. In spite of the structural independence of the two jaw systems, results using a Bayesian, state-dependent, relaxed-clock model of multivariate Brownian motion indicate strongly aligned evolutionary responses to feeding ecology. So, while decoupling of prey capture and processing functions released constraints on jaw evolution and promoted trophic diversity in cichlids, the natural diversity of consumed prey has also induced a moderate degree of evolutionary integration between the jaw systems, reminiscent of the original mechanical trade-off between force and mobility.
Data from: Malagasy cichlids differentially limit impacts of body shape evolution on oral jaw functional morphology
Patterns of trait covariation, like integration and modularity, are vital factors that influence the evolution of vertebrate body plans. In functional systems, decoupling of morphological modules buffers functional change in one trait by reducing correlated variation with another. However, for complex morphologies with many-to-one mapping of form to function (MTOM), resistance to functional change may also be achieved by constraining morphological variation within a functionally stable region of morphospace. For this research, we used geometric morphometrics to evaluate the evolution of body shape and its relationship to jaw functional morphology in two independent radiations of endemic Malagasy cichlid (Teleostei: Cichlidae). Our results suggested that the two subfamilies used different strategies to mitigate impacts of body shape variation on a metric of jaw function, maxillary kinematic transmission (MKT): (1) modularity between cranial and postcranial morphologies, and (2) integration of body and jaw evolution, with jaw morphologies varying in a manner that limits change in MKT. This research shows that, unlike modularity, MTOM allows traits to retain strong evolutionary covariation while still reducing impacts on functionality. These results suggest that MTOM, and its influence on the evolution of correlated traits, is likely much more widespread than is currently understood.
Data from: Freshwater hydrozoan blooms alter activity and behaviour of territorial cichlids in Lake Tanganyika
Jellyfish blooms pose multiple threats to wild fish. Yet, we still know little about how blooms impact fitness-related behaviours of fish caught within their areas of effect, e.g. for littoral fish that are not able to relocate to avoid incoming blooms of stinging jellyfish. Here, we documented the behavioural impacts of freshwater jellyfish (Limnocnida tanganjicae) blooms on a territorial cichlid (Variabilichromis moorii) as well as on the wider community of cichlids in a shallow-water rocky habitat of Lake Tanganyika. Compared to non-bloom conditions, V. moorii individuals reduced their swimming and territory defence activities during jellyfish blooms (each by ~ 50%), but not their foraging or affiliative behaviours. Despite this reduction in activity, V. moorii could not entirely avoid being stung and preferred to remain closer to the rocky substrata as opposed to the more open demersal zone. Many other fishes similarly hid among the benthic substrata, changing the composition of the fish community in the demersal zone during bloom conditions. Reductions in activity could have multiple fitness-related implications for individual fish. Understanding these behavioural consequences is an important topic of research as blooms are predicted to increase in severity in the future especially along coastal habitats.
Evolutionary dynamics of structural variation at a key locus for color pattern diversification in cichlid fishes
<p>Color patterns in African cichlid fishes vary spectacularly. Although phylogenetic analysis showed already 30 years ago that many color patterns evolved repeatedly in these adaptive radiations, only recently have we begun to understand the genomic basis of color variation. Horizontal stripe patterns evolved and were lost several times independently across the adaptive radiations of Lake Victoria, Malawi, and Tanganyika and regulatory evolution of agouti-related peptide 2 (agrp2/asip2b) has been linked to this phenotypically labile trait. Here, we asked whether the agrp2 locus exhibits particular characteristics that facilitate divergence in color patterns. Based on comparative genomic analyses, we discovered several recent duplications, insertions, and deletions. Interestingly, one of these events resulted in a tandem duplication of the last exon of agrp2. The duplication likely precedes the East African radiations that started 8–12 Ma, is not fixed within any of the radiations, and is found to vary even within some species. Moreover, we also observed variation in copy number (two to five copies) and secondary loss of the duplication, illustrating a surprising dynamic at this locus that possibly promoted functional divergence of agrp2. Our work suggests that such instances of exon duplications are a neglected mechanism potentially involved in the repeated evolution and diversification that deserves more attention.</p>
Implementing large genomic SNP datasets in phylogenetic network reconstructions: a case study of particularly rapid radiations of cichlid fish
<p><span><span><span><span><span><span><span><span><span><span><span>The Midas cichlids of the <i>Amphilophus</i> <i>citrinellus </i>spp<i>.</i> species complex from Nicaragua, are an extraordinary adaptive rapid radiation (<24,000 years old; 13 described species). These cichlids are a very challenging group to infer its evolutionary history in phylogenetic analyses, due to the apparent prevalence of ILS, as well as past and current gene flow. Assuming solely a vertical transfer of genetic material from an ancestral lineage to new lineages is not appropriate in many cases of genes transferred horizontally in nature. Recently developed methods to infer phylogenetic networks under such circumstances might be able to circumvent these problems. These models accommodate not just incomplete lineage sorting, but also gene flow, under the multispecies network coalescent model (MSNC), processes that are at work in young, hybridizing, and/or rapidly diversifying lineages. There are currently only a few programs available that implement MSNC for estimating phylogenetic networks. Here, we present a novel way to incorporate single nucleotide polymorphism (SNP) data into the currently available PhyloNetworks program. Based on simulations, we demonstrate that SNPs can provide enough power to recover the true phylogenetic network. Moreover, our approach results in a faster algorithm compared to the original pipeline in PhyloNetworks, without losing power. We also applied our new approach to infer the phylogenetic network of Midas cichlid radiation. We implemented the most comprehensive genomic dataset to date (RADseq dataset of 679 individuals and >37K SNPs from 19 ingroup lineages) <span><span>and present estimated phylogenetic networks for this extremely young and fast-evolving radiation of cichlid fish. </span></span>We demonstrate that the MSNC is more appropriate than the multispecies coalescent alone for the analysis of this rapid radiation. </span></span></span></span></span></span></span></span></span></span></span></p>
FIGURE 1. Pelvicachromis rubrolabiatus, holotype. NMW 94835 in cichlid species (Teleostei, Perciformes) from Guinea, West Africa
FIGURE 1. Pelvicachromis rubrolabiatus, holotype. NMW 94835, male, 59.5 mm SL; Guinea: Badi River.
FIGURE 4 in cichlid species (Teleostei, Perciformes) from Guinea, West Africa
FIGURE 4. Geographical distribution of P. rubrolabiatus and P. signatus.
FIGURE 6 in cichlid species (Teleostei, Perciformes) from Guinea, West Africa
FIGURE 6. Pelvicachromis signatus, male, aquarium specimen, not preserved, Guinea: Kolente region.
Data from: Functional trait plasticity diverges between sexes in African cichlids: a contribution toward ecological sexual dimorphism?
<p>Phenotypic plasticity enables development to produce multiple phenotypes in response to environmental conditions. Plasticity driven variation has been suggested to play a key role in adaptive divergence, and plasticity itself can evolve. However, the interaction of plasticity with the multiple levels involved with adaptive divergence is less understood. For example, sexual dimorphism can contribute to adaptive variation through ecological sexual dimorphism (ESD), but the contribution of plasticity to this phenomenon is unknown. Therefore, to determine the potential contribution of plasticity to ESD, we used the adaptive radiation of Malawi cichlids. Two mouthbrooding species (<em>Labeotropheus fuelleborni </em>and <em>Tropheops</em> "Red Cheek", hereafter LF and TRC respectively) with differences in foraging tactics underwent foraging experiments using benthic and limnetic treatments while accounting for sex. Plasticity in craniofacial shape and three functionally important traits were measured. Plasticity was shown, but without any sex-based differences in shape. However, for mechanical advantage traits of the mandible sex by diet interactions were found. This suggests that ESD, may be influenced by phenotypic plasticity that diverges between sexes. Given the involvement of the mandible in parental care in cichlids this may indicate that sexual divergence in plasticity may trade-off against maternal care tactics.</p>
Data from: Repeated divergence in opsin genes expression mirrors photic habitat changes in rapidly evolving crater lake cichlid fishes
<div> <div> <div class="msocomtxt"> <p class="MsoNormal"><span>Selection pressures differ along environmental gradients and organisms' phenotypes. Traits tightly linked to fitness (e.g., the visual system) are expected to closely track environmental variation along gradients. Within such gradients, adaptation to local conditions might be due to heritable and non-heritable, environmentally induced variation. Disentangling these sources of phenotypic variation requires studying, in nature and the laboratory, closely related populations experiencing different environments. The Nicaraguan great and crater lakes show an environmental gradient in photic conditions extending from clear crater lakes to very turbid great lakes. From two old, turbid great lakes, Midas cichlid fish (<em>Amphilophus </em>cf.<em> citrinellus</em>) independently colonized seven isolated crater lakes of varying light conditions, resulting in a small adaptive radiation. We estimated the variation in visual sensitivities along this photic gradient by measuring differential cone opsin gene expression among populations from different lakes. The visual sensitivities observed in all seven derived crater lake populations have not changed randomly but shifted predictably in direction and magnitude, repeatedly mirroring changes in photic conditions. Intrapopulation phenotypic variation decreases as environments become spectrally narrower suggesting different selective landscapes within the gradient. Comparing wild-caught and lab-reared fish revealed that 48% of this phenotypic variation is genetically determined and evolved rapidly. Our results demonstrate deterministic, rapid phenotypic evolution that fine-tunes visual sensitivity to fine-scale environmental variation.</span></p> <p class="MsoCommentText"><span> </span></p> </div> </div> </div>
Data from: Sympatry and parapatry among rocky reef cichlids of Lake Victoria explained by female mating preferences
<p><span>Work on the Lake Victoria cichlids <em>Pundamilia nyererei</em> (red dorsum males, deeper water), <em>Pundamilia pundamilia</em> (blue males, shallower water) and related species pairs has provided insights into processes of speciation. Here, we investigate female mating behaviour of five <em>Pundamilia </em>species and four of their F1-hybrids through mate choice trials and paternity testing. We discuss the results in the context of the geography of speciation and coexistence. Complete assortative mating was observed among all sympatric species. Parapatric species with similar depth habitat distributions interbred whereas other parapatric and allopatric species showed complete assortative mating. F1-hybrids mated exclusively with species accepted by females of the parental species. Although consistent with reinforcement in sympatry, a closer look at our results suggests otherwise and it is more likely that pre-existing female preferences influence which taxa can co-exist in sympatry. Regardless of the mechanism, mating preferences may influence species distribution in potentially hybridizing taxa, such as in the adaptive radiations of cichlid fish. We suggest that this at least partly explains why some species fail to establish breeding populations in locations where they are occasionally recorded. Our result support the notion that mating preferences of potentially cross-breeding species ought to be included in coexistence theory.</span></p>
Data from: An intronic transposon insertion associates with a trans-species color polymorphism in Midas cichlid fishes
<p><span><span><span><span><span><span><span><span><span><span><span>Polymorphisms have fascinated biologists for a long time, but their genetic underpinnings often remained elusive. Here, we aimed to uncover the genetic basis of the gold/dark polymorphism that is eponymous of Midas cichlid fish (<i>Amphilophus </i>spp.) adaptive radiations in Nicaraguan crater lakes. While most Midas cichlids are of the melanic "dark morph", about 10% of individuals lose their melanic pigmentation during their ontogeny and transition into a conspicuous "gold morph". Using a new haplotype-resolved long-read assembly we discovered an 8.2kb, transposon-derived inverted repeat in an intron of an undescribed gene, which we term <i>goldentouch</i> in reference to the Greek myth of King Midas. The gene <i>goldentouch</i> is differentially expressed between morphs, likely due to structural implications of inverted repeats in both DNA and RNA (cruciform and hairpin formation). The near-perfect association with the phenotype across several independent populations suggests that this insertion likely underlies this trans-specific, stable polymorphism.</span></span></span></span></span></span></span></span></span></span></span></p>
Data from: Thyroid hormone tinkering elicits integrated phenotypic changes potentially explaining rapid adaptation of color vision in cichlid fish
Vision is critical for most vertebrates, including fish. One challenge that aquatic habitats pose is the high variability in spectral properties depending on depth, turbidity and composition of the water body. By altering opsin gene expression and chromophore usage, cichlid fish modulate visual sensitivities to maximize sensory input from the available light in their respective habitat. Thyroid hormone (TH) has been proposed to play a role in governing adaptive diversification in visual sensitivity in Nicaraguan Midas cichlids, which evolved in less than ~3,100 generations. As suggested by indirect measurements of TH levels (i.e., expression of deiodinases), populations adapted to short wavelength light in clear lakes have lower TH levels than ones inhabiting turbid lakes enriched in long-wavelength light. We experimentally manipulated TH levels by exposing two-week-old Midas cichlids to exogenous TH or a TH-inhibitor and measured opsin gene expression and chromophore usage (via cyp27c1 expression). Whereas exogenous TH induces long-wavelength sensitivity by changing opsin gene expression and chromophore usage in a concerted manner, TH-inhibited fish exhibit a visual phenotype with sensitivities shifted to shorter-wavelengths. Tinkering with TH levels in eyes results in concerted phenotypic changes that can provide a rapid mechanism of adaptation to novel light environments. --
Between a rock and a hard polytomy: phylogenomics of the rock-dwelling mbuna cichlids of Lake Malawi
<p>Whole genome sequences are beginning to revolutionise our understanding of phylogenetic relationships. Yet, even whole genome sequences can fail to resolve the evolutionary history of the most rapidly radiating lineages, where incomplete lineage sorting, standing genetic variation, introgression, and other factors obscure the phylogenetic history of the group. To overcome such challenges, one emerging strategy is to integrate results across different methods. Most such approaches have been implemented on reduced representation genomic datasets, but whole genomes should provide the maximum possible evidence approach. Here, we test the ability of SNPs extracted from whole genome resequencing data, implemented in an integrative genomic approach, to resolve key nodes in the phylogeny of the mbuna, rock-dwelling cichlid fishes of Lake Malaŵi, which epitomise the phylogenetic intractability that often accompanies explosive lineage diversification. This monophyletic radiation has diversified at an unparalleled rate into several hundred species in less than two million years. Using an array of phylogenomic methods, we consistently recovered four major clades of mbuna, but a large basal polytomy among them. Although introgression between clades apparently contributed to the challenge of phylogenetic reconstruction, reduction of the dataset to non-introgressed sites still did not help to resolve the basal polytomy. On the other hand, relationships among six congeneric species pairs were resolved without ambiguity, even in one case where existing data led us to predict that resolution would be difficult. We conclude that the bursts of diversification at the earliest stages of the mbuna radiation may be phylogenetically unresolvable, but other regions of the tree are phylogenetically clearly supported. Integration of multiple phylogenomic approaches will continue to increase confidence in relationships inferred from these and other whole-genome datasets.</p>
Molecular evolution and depth-related adaptations of rhodopsin in the adaptive radiation of cichlid fishes in Lake Tanganyika
<p><span>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 the virtually entire adaptive radiation of cichlid fishes in Lake Tanganyika, focusing on adaptations to the achromatic environment 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 </span><span>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 th first compralehensive analysis of RH1 evolution in a massive adaptive radiation of cichlid fishes, provides novel insights into the evolution of RH1 in a freshwater environment.</span></p>
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