A complex mode of aggressive mimicry in a scale-eating cichlid fish

Deceptive Seduction by Femme Fatale Fireflies and Its Avoidance by Males of a Synchronous Firefly Species (Coleoptera: Lampyridae)

Photuris female fireflies attract males of different firefly species by responding to their flashing signals; then, they try to capture and feed on them. This aggressive mimicry is considered a major selective pressure on the communication systems of the fireflies of the American continent. The intensity of this selective pressure is a function of its efficiency in prey capture. In this study, the rates of attraction and capture of males of the synchronous firefly Photinus palaciosi by the predatory females of Photuris lugubris are reported. Although the females attract numerous males, their hunting success is low. This result is consistent with the few previous measurements published. In agreement with the predicted coevolutionary race between predator and prey, behaviors consistent with predation avoidance in P. palaciosi and increasing prey encounters and prey deception by P. lugubris were observed.

Expression variations in ectodysplasin-A gene (eda) may contribute to morphological divergence of scales in haplochromine cichlids

BACKGROUND

Elasmoid scales are one of the most common dermal appendages and can be found in almost all species of bony fish differing greatly in their shape. Whilst the genetic underpinnings behind elasmoid scale development have been investigated, not much is known about the mechanisms involved in moulding of scales. To investigate the links between gene expression differences and morphological divergence, we inferred shape variation of scales from two different areas of the body (anterior and posterior) stemming from ten haplochromine cichlid species from different origins (Lake Tanganyika, Lake Malawi, Lake Victoria and riverine). Additionally, we investigated transcriptional differences of a set of genes known to be involved in scale development and morphogenesis in fish.

RESULTS

We found that scales from the anterior and posterior part of the body strongly differ in their overall shape, and a separate look on scales from each body part revealed similar trajectories of shape differences considering the lake origin of single investigated species. Above all, nine as well as 11 out of 16 target genes showed expression differences between the lakes for the anterior and posterior dataset, respectively. Whereas in posterior scales four genes (dlx5, eda, rankl and shh) revealed significant correlations between expression and morphological differentiation, in anterior scales only one gene (eda) showed such a correlation. Furthermore, eda displayed the most significant expression difference between species of Lake Tanganyika and species of the other two younger lakes. Finally, we found genetic differences in downstream regions of eda gene (e.g., in the eda-tnfsf13b inter-genic region) that are associated with observed expression differences. This is reminiscent of a genetic difference in the eda-tnfsf13b inter-genic region which leads to gain or loss of armour plates in stickleback.

CONCLUSION

These findings provide evidence for cross-species transcriptional differences of an important morphogenetic factor, eda, which is involved in formation of ectodermal appendages. These expression differences appeared to be associated with morphological differences observed in the scales of haplochromine cichlids indicating potential role of eda mediated signal in divergent scale morphogenesis in fish.

Hydrography rather than lip morphology better explains the evolutionary relationship between Gymnogeophagus labiatus and G. lacustris in Southern Brazil (Cichlidae: Geophagini)

ABSTRACT Gymnogeophagus labiatus and G. lacustris have been long recognized as sister species exhibiting different ecological requirements. Gymnogeophagus labiatus occurs in rock bottom rivers in the hydrographic basins of Patos Lagoon (HBP) and Tramandaí River (HBT), while G. lacustris is exclusive from sand bottom coastal lagoons of the HBT. In this study, we used molecular markers, morphological measurements and data from nuptial male coloration to investigate the evolutionary relationship between these species in each hydrographic basin. We found, for all data sets, a closer relationship between G. labiatus and G. lacustris from the HBT than between G. labiatus populations from HBT and HBP. In particular, lip area had a large intraspecific plasticity, being uninformative to diagnose G. lacustris from G. labiatus. Molecular clock-based estimates suggest a recent divergence between species in the HBT (17,000 years ago), but not between G. labiatus from HBP and HBT (3.6 millions of years ago). Finally, we also found a divergent G. labiatus genetic lineage from the Camaquã River, in the HBP. These results show that the current taxonomy of G. labiatus and G. lacustris does not properly represent evolutionary lineages in these species.

The behavioral origins of novelty: did increased aggression lead to scale-eating in pupfishes?

Behavioral changes in a new environment are often assumed to precede the origins of evolutionary novelties. Here, we examined whether an increase in aggression is associated with a novel scale-eating trophic niche within a recent radiation of Cyprinodon pupfishes endemic to San Salvador Island, Bahamas. We measured aggression using multiple behavioral assays and used transcriptomic analyses to identify differentially expressed genes in aggression and other behavioral pathways across 3 sympatric species in the San Salvador radiation (generalist, snail-eating specialist, and scale-eating specialist) and 2 generalist outgroups. Surprisingly, we found increased behavioral aggression and differential expression of aggression-related pathways in both the scale-eating and snail-eating specialists, despite their independent evolutionary origins. Increased behavioral aggression varied across both sex and stimulus context in both species. Our results indicate that aggression is not unique to scale-eating specialists. Instead, selection may increase aggression in other contexts such as niche specialization in general or mate competition. Alternatively, increased aggression may result from indirect selection on craniofacial traits, pigmentation, or metabolism-all traits which are highly divergent, exhibit signs of selective sweeps, and are affected by aggression-related genetic pathways which are differentially expressed in this system. In conclusion, the evolution of a novel predatory trophic niche within a recent adaptive radiation does not have clear-cut behavioral origins as previously assumed, highlighting the multivariate nature of adaptation and the complex integration of behavior with other phenotypic traits.

Crab Spider Lures Prey In Flowerless Neighborhoods

One fundamental question in prey luring systems is to understand how visual signals are interpreted by the receiver. Predators lure prey by falsely imitating the signal of a model, or may exploit sensory preferences of the receivers, which search for rewarding signals. Crab spiders reflect ultraviolet (UV) light, ambush pollinators on flowers, and manipulate flower UV signals altering the behavior and response of prey. Whereas crab spiders typically depend on flowers to forage, adult Epicadus heterogaster departs from this standard behavior by preying on pollinators upon green leaves, even in the absence of flowers nearby. This species has a conspicuous abdomen resembling the shape of a flower, which may reflect UV signals similar to that of flowers, and thus attract pollinators. Nevertheless, no empirical evidence is available that E. heterogaster foraging on leaves mimics flowers, nor how this crab spider interacts with its prey. Field and laboratory experiments demonstrated that UV reflection of adult E. heterogaster is the main signal responsible for the attraction of pollinators. This is the first study to demonstrate that a crab spider attracts pollinators regardless of flower UV signal, which may represent an evolutionary pathway beyond the dependence of flowers.

Community assembly in Lake Tanganyika cichlid fish: quantifying the contributions of both niche-based and neutral processes

The cichlid family features some of the most spectacular examples of adaptive radiation. Evolutionary studies have highlighted the importance of both trophic adaptation and sexual selection in cichlid speciation. However, it is poorly understood what processes drive the composition and diversity of local cichlid species assemblages on relatively short, ecological timescales. Here, we investigate the relative importance of niche-based and neutral processes in determining the composition and diversity of cichlid communities inhabiting various environmental conditions in the littoral zone of Lake Tanganyika, Zambia. We collected data on cichlid abundance, morphometrics, and local environments. We analyzed relationships between mean trait values, community composition, and environmental variation, and used a recently developed modeling technique (STEPCAM) to estimate the contributions of niche-based and neutral processes to community assembly. Contrary to our expectations, our results show that stochastic processes, and not niche-based processes, were responsible for the majority of cichlid community assembly. We also found that the relative importance of niche-based and neutral processes was constant across environments. However, we found significant relationships between environmental variation, community trait means, and community composition. These relationships were caused by niche-based processes, as they disappeared in simulated, purely neutrally assembled communities. Importantly, these results can potentially reconcile seemingly contrasting findings in the literature about the importance of either niche-based or neutral-based processes in community assembly, as we show that significant trait relationships can already be found in nearly (but not completely) neutrally assembled communities; that is, even a small deviation from neutrality can have major effects on community patterns.

Comparative transcriptomics of anal fin pigmentation patterns in cichlid fishes

Background

Understanding the genetic basis of novel traits is a central topic in evolutionary biology. Two novel pigmentation phenotypes, egg-spots and blotches, emerged during the rapid diversification of East African cichlid fishes. Egg-spots are circular pigmentation markings on the anal fins of hundreds of derived haplochromine cichlids species, whereas blotches are patches of conspicuous anal fin pigmentation with ill-defined boundaries that occur in few species that belong to basal cichlid lineages. Both traits play an important role in the breeding behavior of this group of fishes. Knowledge about the origin, homology and underlying genetics of these pigmentation traits is sparse.

Results

Here, we present a comparative transcriptomic and differential gene expression analysis of egg-spots and blotches. We first conducted an RNA sequencing experiment where we compared egg-spot tissue with the remaining portion of egg-spot-free fin tissue using six individuals of Astatotilapia burtoni. We identified 1229 differentially expressed genes between the two tissue types. We then showed that rates of evolution of these genes are higher than average estimated on whole transcriptome data. Using quantitative real-time PCR, we found that 29 out of a subset of 46 differentially expressed genes showed an analogous expression pattern in another haplochromine species’ egg-spots, Cynotilapia pulpican, strongly suggesting that these genes are involved in the egg-spot phenotype. Among these are the previously identified egg-spot gene fhl2a, two known patterning genes (hoxC12a and bmp3) as well as other pigmentation related genes such as asip. Finally, we analyzed the expression patterns of the same gene subset in two species that feature blotches instead of egg-spots, one haplochromine species (Pseudocrenilabrus philander) and one ectodine species (Callochromis macrops), revealing that the expression patterns in blotches and egg-spots are rather distinct.

Conclusions

We identified several candidate genes that will serve as an important and useful resource for future research on the emergence and diversification of cichlid fishes’ egg-spots. Only a limited degree of conservation of gene expression patterns was detected between the egg-spots of the derived haplochromines and blotches from ancestral haplochromines, as well as between the two types of blotches, suggesting an independent origin of these traits.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3046-y) contains supplementary material, which is available to authorized users.

From crypsis to mimicry: changes in colour and the configuration of the visual system during ontogenetic habitat transitions in a coral reef fish

Animals often change their habitat throughout ontogeny; yet, the triggers for habitat transitions and how these correlate with developmental changes – e.g. physiological, morphological, and behavioural – remain largely unknown. Here, we investigated how ontogenetic changes in body colouration and of the visual system relate to habitat transitions in a coral-reef fish. Adult dusky dottybacks, Pseudochromis fuscus, are aggressive mimics that change colour to imitate various fishes in their surroundings; however, little is known about the early life stages of this fish. Using a developmental time-series in combination with the examination of wild caught specimens we uncover that dottybacks change colour twice during development: (i) nearly translucent cryptic pelagic larvae change to a grey camouflage colouration when settling on coral reefs; and (ii) juveniles change to mimic yellow or brown coloured fishes when reaching a size capable of consuming juvenile fish prey. Moreover, microspectrophotometric (MSP) and quantitative real time PCR (qRT-PCR) experiments show developmental changes of the dottyback visual system, including the use of a novel adult specific visual gene (RH2 opsin). This gene is likely to be coexpressed with other visual pigments to form broad spectral sensitivities that cover the medium-wavelength part of the visible spectrum. Surprisingly, the visual modifications precede changes in habitat and colour, possibly because dottybacks need to first acquire the appropriate visual performance before transitioning into novel life stages.