Biology subjects

Cortesi, F.

Publications and source records attributed to Cortesi, F..

25 records · Page 2Linked to original sources

bioRxiv2020

Seeing Nemo: molecular evolution of ultraviolet visual opsins and spectral tuning of photoreceptors in anemonefishes (Amphiprioninae)

Many animals can see ultraviolet (UV) light (shorter than 400 nm) undetectable to human vision. UV vision may have functional importance in many taxa including for foraging and communication in birds, reptiles, insects and teleost fishes. Shallow coral reefs transmit a broad spectrum of light and are rich in UV; driving the evolution of diverse spectral sensitivities in teleost reef fishes, including UV-sensitivity. However, the identities and sites of the specific visual genes that underly vision in reef fishes remain elusive and are useful in determining how molecular evolution has tuned vision to meet the ecological demands of life on the reef. We investigated the visual systems of eleven anemonefish (Amphiprioninae) species, specifically probing for the molecular pathways that facilitate UV-sensitivity. Searching the genomes of anemonefishes, we identified a total of seven functional visual genes from all five vertebrate opsin gene subfamilies. We found rare instances of UV-sensitive SWS1 opsin gene duplications, that produced two functional paralogs (SWS1 and SWS1{beta}) and a pseudogene. We also found separate RH2A opsin gene duplicates not yet reported in the family Pomacentridae. Finally, we report on both qualitative and quantitative aspects of opsin gene expression found in the adult retina of the false clown anemonefish (Amphiprion ocellaris), and their photoreceptor spectral sensitivities measured using microspectrophotometry.

molecular biology↗

bioRxiv2020

Opsin gene expression in larval and adult deep-sea fishes supports a conserved cone-to-rod pathway in teleost visual development

Vertebrates use cone cells in the retina for colour vision and rod cells to see in dim light. Many deep-sea fishes have adapted to their environment to have only rod cells in the retina, while both rod and cone genes are still preserved in their genomes. As deep-sea fish larvae start their lives in the shallow, and only later submerge to the depth, they have to cope with diverse environmental conditions during ontogeny. Using a comparative transcriptomic approach in 20 deep-sea fish species from eight teleost orders, we report on a developmental cone-to-rod switch. While adults mostly rely on rod opsin (RH1) for vision in dim light, larvae almost exclusively express middle-wavelength-sensitive ("green") cone opsins (RH2) in their retinas. The phototransduction cascade genes follow a similar ontogenetic pattern of cone-followed by rod-specific gene expression in most species, except for the pearleye and sabretooth (Aulopiformes), in which the cone cascade remains dominant throughout development. By inspecting the whole genomes of five deep-sea species (four of them sequenced within this study: Idiacanthus fasciola, Chauliodus sloani; Stomiiformes; Coccorella atlantica, and Scopelarchus michaelsarsi; Aulopiformes), we found that deep-sea fish possess one or two copies of the rod RH1 opsin gene, and up to seven copies of the cone RH2 opsin genes in their genomes, while other cone opsin classes have been mostly lost. Our findings hence provide molecular evidence for a limited opsin gene repertoire and a conserved vertebrate pattern whereby cone photoreceptors develop first and rod photoreceptors are added only at later developmental stages.

evolutionary biology↗

bioRxiv2020

The visual ecology of Holocentridae, a nocturnal coral reef fish family with a deep-sea-like multibank retina

The visual systems of teleost fishes usually match their habitats and lifestyles. Since coral reefs are bright and colourful environments, the visual systems of their diurnal inhabitants have been more extensively studied than those of nocturnal species. In order to fill this knowledge gap, we conducted a detailed investigation of the visual systems of the coral reef fish family Holocentridae (squirrelfish and soldierfish). In addition to their nocturnality, this family is particularly interesting for dim-light vision studies due to its ecological and evolutionary connection to deeper habitats. Results showed that the visual system of holocentrids is well adapted to their nocturnal lifestyle with a rod-dominated retina. Surprisingly, rods in all species were arranged into 6-17 well-defined banks, a feature most commonly found in deep-sea fishes, that may increase the light sensitivity of the eye and/or allow colour discrimination in dim-light. Holocentrids also have the potential for dichromatic colour vision during the day with the presence of at least two spectrally different cone types: single cones expressing the blue-sensitive SWS2A gene, and double cones expressing one or two green-sensitive RH2 genes. Some differences were observed between the two subfamilies, with Holocentrinae having a slightly more developed photopic visual system than Myripristinae. Moreover, retinal topography of both ganglion cells and cone photoreceptors showed specific patterns for each cell type, likely highlighting different visual demands at different times of the day, such as feeding. Overall, their well-developed scotopic visual systems and the ease of catching and maintaining holocentrids in aquaria, make them ideal models to investigate teleost dim-light vision and more particularly shed light on the function of multibank retina and its potential for dim-light colour vision.

neuroscience↗

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↗

bioRxiv2019

Neoteny in visual system development of the spotted unicornfish, Naso brevirostris (Acanthuridae)

Ontogenetic changes of the visual system are often correlated to shifts in habitat and feeding behaviour of animals. Coral reef fishes begin their lives in the pelagic zone and then migrate to the reef. This transition of habitat frequently involves a change in diet and light environment as well as major morphological modifications. The spotted unicornfish, Naso brevirostris, is known to shift diet from zooplankton to algae and back to zooplankton when transitioning from larval to juvenile and then to adult stages. Concurrently, N. brevirostris also moves from an open pelagic to a coral-associated habitat before migrating up in the water column when reaching adulthood. Using retinal mapping techniques, we discovered that the distribution and density of ganglion and photoreceptor cells in N. brevirostris do not change with the habitat or the feeding habits of each developmental stage. Instead, fishes showed a neotenic development with a slight change from larval to juvenile stages and not many modifications thereafter. Visual gene expression based on RNA sequencing mirrored this pattern; independent of stage, fishes mainly expressed three cone opsin genes (SWS2B, RH2B, RH2A), with a quantitative difference in the expression of the green opsin genes (RH2A and RH2B) when transitioning from larvae to juveniles. Hence, contrary to the ontogenetic changes found in many animals, the visual system is fixed early on in N. brevirostris development calling for a thorough analysis of visual system development of the reef fish community.

evolutionary biology↗

bioRxiv2018

Opsin gene evolution in amphibious and terrestrial combtooth blennies (Blenniidae)

Evolutionary adaptations to life on land include changes to the physiology, morphology and behaviour of an animal in response to physical differences between water and air. The visual systems of amphibious species show pronounced morphological adaptations; yet, whether molecular changes also occur remains largely unknown. Here, we investigated the molecular evolution of visual pigment genes (opsins) in amphibious and terrestrial fishes belonging to the Salariini division of blennies (Blenniidae). We hypothesized that when conquering land, blenny opsins adapt - in terms of sequence variation and/or gene expression - to match both higher light intensities as well as the broader light spectrum. Using retinal transcriptomes in six species ranging from fully aquatic to fully terrestrial, we found very little variation in opsin gene sequences or gene expression between species. All blennies expressed a single rod opsin gene as well as two cone opsin genes sensitive to longer-wavelengths of light: RH2A-1 (green-sensitive) and LWS (red-sensitive). They also expressed one or two short-wavelength-sensitive cone opsin genes (SWS2A, SWS2A{beta}; blue-sensitive) in a phylogenetically inert manner. However, based on amino acid predictions, both SWS2A proteins confer similar peak spectral sensitivities and differential expression is therefore unlikely to be ecologically significant. Red-sensitivity is likely beneficial for feeding on algae and detritus, the main food source of Salariini blennies, and could be co-adapted to perceive visual displays in terrestrial species, which often use red dorsal fins to signal during aggressive disputes and courtship. Our data suggests that on the molecular level, the visual systems that evolved in aquatic blennies have been retained in species that have transitioned onto land.

evolutionary biology↗

bioRxiv2018

Vision using multiple distinct rod opsins in deep-sea fishes

Vertebrate vision is accomplished through a set of light-sensitive photopigments, which are located in the photoreceptors of the retina and consist of a visual opsin protein bound to a chromophore. In dim-light, vertebrates generally rely upon a single rod opsin (RH1) for obtaining visual information. By inspecting 101 fish genomes, we found that three deep-sea teleost lineages have independently expanded their RH1 gene repertoires. Amongst these, the silver spinyfin (Diretmus argenteus Johnson 1863) stands out as having the highest number of visual opsins known for animals to date (2 cone and 38 rod opsins). Spinyfins simultaneously express up to 14 RH1s encoding for photopigments with different peak spectral sensitivities ({lambda}max=448-513 nm) that cover the range of the residual daylight, as well as the bioluminescence spectrum present in the deep-sea. Our findings present novel molecular and functional evidence for the recurrent evolution of multiple rod opsin-based vision in vertebrates.\n\nSHORT ABSTRACTContrary to the single rod opsin used by most vertebrates, some fishes use multiple rod opsins for vision in the dimly lit deep-sea.

evolutionary biology↗