Biology subjects

Cheney, K.

Publications and source records attributed to Cheney, K..

5 recordsLinked to original sources

bioRxiv2024

Damsels in a hidden colour: development of ultraviolet sensitivity and colour patterns in damselfishes (Pomacentridae)

Damselfishes (Pomacentridae) are widespread and highly abundant on tropical coral reefs. They exhibit diverse body colouration within and between the [~]250 species and across ontogenetic stages. In addition to human visible colours (i.e., 400-700 nm), most adult damselfishes reflect ultraviolet (UV, 300-400 nm) colour patches. UV sensitivity and UV colour signals are essential for feeding and form the basis for a secret communication channel invisible to the many UV-blind predatory fish on the reef; however, how these traits develop across ontogenetic stages, and their distribution across the damselfish family is poorly characterised. Here, we used UV photography, phylogenetic reconstructions of opsin genes, differential gene expression analysis (DGE) of retinal samples, to investigate the development of UV vision and colour patterns in three ontogenetic stages (pre-settlement larval, juvenile, and adult) of eleven damselfish species. Using DGE, we found similar gene expression between juveniles and adults, which strongly differed from larvae. All species and all stages expressed at least one UV-sensitive sws1 opsin gene. However, UV body colour patterns only started to appear at the juvenile stage. Moreover, Pomacentrus species displayed highly complex UV body patterns that were correlated with the expression of two sws1 copies. This could mean that some damselfishes can discriminate colours that change only in their UV component. We demonstrate dramatic shifts in both UV sensitivity and UV colouration across the development stages of damselfish, while highlighting the importance of considering ontogeny when studying the coevolution of visual systems and colour signals.

ecology↗

bioRxiv2022

Highly defended nudibranchs do not 'escape' to visually diverse background habitats

The escape and radiate hypothesis predicts that once species have evolved aposematism, defended species can utilise more visually diverse visual backgrounds as they escape the need to be well camouflaged. This enables species to explore new ecological niches, resulting in increased diversification rates. To test this hypothesis escape component, we examined whether the background habitats of 12 nudibranch mollusc species differed among species depending on the presence and strength of chemical defences. We obtained a rich array of colour pattern statistics using Quantitative Colour Pattern Analysis (QCPA) to analyse backgrounds viewed through the eyes of a potential predator (triggerfish, Rhinecanthus aculeatus). Colour pattern analysis was done at viewing distances simulating an escalating predation sequence. We identified four latent factors comprising 17 non-correlated colour pattern parameters, which captured the among-species variability associated with differences in chemical defences. We found that chemically defended species, indeed, were found on visually distinct backgrounds with increased colour and luminance contrast, independent of viewing distance. However, we found no evidence for increased among-species background diversity coinciding with the presence and strength of chemical defences. Our results agree with the escape and radiate hypothesis, suggesting that potent chemical defences in Dorid nudibranchs coincide with spatiochromatic differences of visual background habitats perceived by potential predators. Lay SummaryAccording to the escape and radiate hypothesis, the ability to store potent chemical defences as protection from predators enables animals to be minimally dependent on matching visual backgrounds for camouflage. We found evidence supporting this hypothesis in 12 species of nudibranch molluscs. Aposematic species were found on visual backgrounds that differed consistently in appearance from the visual background of undefended cryptic species. However, we found no difference in the variability of visual backgrounds between species with or without chemical defences. This suggests that warning colouration in eastern Australian Dorid nudibranchs coincides with broadly generalisable spatiochromatic properties of visual backgrounds.

ecology↗

bioRxiv2022

Colour pattern edge contrast statistics can predict detection speed and success at ecologically relevant viewing distances in triggerfish (Rhinecanthus aculeatus)

Edge detection is important for object detection and recognition. However, we do not know whether edge statistics predict the detection of prey by non-human predators. Understanding the link between image statistics and animal behaviour is crucial and of increasing importance given the growing availability of image analyses and their application across non-human visual systems. Here, we investigated whether Boundary Strength Analysis (BSA), Local Edge Intensity Analysis (LEIA) and the Gabor Ratio (GabRat) could predict the speed and success with which triggerfish (Rhinecanthus aculeatus) detected patterned circular stimuli against a noisy visual background, in both chromatic and achromatic presentations. We found that individual pattern statistics could only explain up to 2% of the variation in detection time, whereas PCA regression analysis considering all edge statistics simultaneously explained up to 6% of the variation. This suggests that other factors explained more behavioural variation than individual edge statistics. Furthermore, different statistics significantly correlated with detection speed depending on treatment, viewing distance, and changes in fish response over time, while highlighting the importance of considering spatial acuity and relevant viewing distances in the study of visual signals. Our results demonstrate the need for broad and unbiased approaches for identifying task-specific predictive relationships between pattern statistics and animal behaviour using image statistics capturing different aspects of colour patterns. We require robust statistical approaches to investigate correlations between ecological effect and the ever-increasing dimensionality and size of datasets in the field of visual ecology, rather than pre-emptively narrowing down the choice of image statistics unless warranted by specific hypotheses. Summary statementCorrelations between edge detecting colour pattern statistics and animal behaviour are complex. Specifically, correlations are unlikely to be explained by single image statistics and depend upon observer distance.

animal behavior and cognition↗

bioRxiv2020

CRISPR/CAS9-mediated generation of biallelic G0 anemonefish (Amphiprion ocellaris) mutants

Genomic manipulation is a useful approach for elucidating the molecular pathways underlying aspects of development, physiology, and behaviour. However, a lack of gene-editing tools appropriated for use in reef fishes has meant the genetic underpinnings for many of their unique traits remain to be investigated. One iconic group of reef fishes ideal for applying this technique are anemonefishes (Amphiprioninae) as they are widely studied for their symbiosis with anemones, sequential hermaphroditism, complex social hierarchies, skin pattern development, and vision, and are raised relatively easily in aquaria. In this study, we developed a gene-editing protocol for applying the CRISPR/Cas9 system in the false clown anemonefish, Amphiprion ocellaris. Microinjection of eggs at the one-cell stage was used to demonstrate the successful use of our CRISPR/Cas9 approach at two separate target sites: the rhodopsin-like 2B opsin encoding gene (RH2B) involved in vision, and Tyrosinase-producing gene (tyr) involved in the production of melanin. Analysis of the sequenced target gene regions in A. ocellaris embryos showed that uptake was as high as 50% of injected eggs. Further analysis of the subcloned mutant gene sequences revealed that our approach had a 75% to 100% efficiency in producing biallelic mutations in G0 A. ocellaris embryos. Moreover, we clearly show a loss-of-function in tyr mutant embryos which exhibited typical hypomelanistic phenotypes. This protocol is intended as a useful resource for future experimental studies that aim to elucidate gene function in anemonefishes and reef fishes in general.

molecular biology↗

bioRxiv2019

Microhabitat partitioning correlates with opsin geneexpression in coral reef cardinalfishes (Apogonidae)

O_LIVertebrates exhibit diverse visual systems that vary in terms of morphology, number and distribution of spectrally distinct photoreceptor types, visual opsin genes and gene expression levels.\nC_LIO_LIIn fish, such adaptations are driven by two main factors: differences in the light environment and behavioural tasks, including foraging, predator avoidance and mate selection. Whether visual systems also adapt to small-scale spectral differences in light, between microhabitats, is less clear.\nC_LIO_LIWe suggest that differences in microhabitat use by cardinalfishes (Apogonidae) on coral reefs drive morphological and molecular adaptations in their visual systems. To test this, we investigated diurnal microhabitat use in 17 cardinalfish species and assessed whether this correlated with differences in visual opsin gene expression and eye morphology.\nC_LIO_LIWe found that cardinalfishes display six types of partitioning behaviours during the day, ranging from specialists found exclusively in the water column to species that are always hidden inside the reef matrix.\nC_LIO_LIUsing data on visual opsin gene expression previously characterized in this family, it was discovered that species in exposed habitats had increased expression of the short-wavelength sensitive violet opsin (SWS2B) and decreased expression of the dim-light active rod opsin (RH1). Species of intermediate exposure, on the other hand, expressed opsins that are mostly sensitive to the blue-green central part of the light spectrum (SWS2As and RH2s), while fishes entirely hidden in the reef substrate had an increased expression of the long-wavelength sensitive red opsin (LWS).\nC_LIO_LIWe found that eye size relative to body size significantly differed between cardinalfish species, and relative eye size decreased with an increase in habitat exposure.\nC_LIO_LIRetinal topography did not show co-adaptation with microhabitat use, but instead with feeding mode.\nC_LIO_LIWe suggest that, although most cardinalfishes are nocturnal foragers, their visual systems are also adapted to both the light intensity and the light spectrum of their preferred diurnal microhabitat.\nC_LI

ecology↗