Biology subjects

Pierotti, M. E.

Publications and source records attributed to Pierotti, M. E..

4 recordsLinked to original sources

bioRxiv2026

Parallel phenotypes underpinned by different genes in the visual system of two trans-isthmian coral reef fish species pairs

Understanding the genetic basis of adaptation in natural populations to changing environmental conditions is challenging. The relatively simple genotype-to-phenotype relationship between opsin genes and visual pigments offers a particularly informative model to explore the molecular mechanisms underpinning adaptive phenotypic change in natural populations. Here we leveraged the natural experiment provided by the tectonic closure of the Central American seaway that created allopatric, sister taxa in multiple, independent lineages of marine organisms and exposed them to distinct underwater light environments: either the more turbid Tropical Eastern Pacific (TEP), or the spectrally broader Caribbean Sea. Using two species pairs of planktivorous teleosts, the Azurina multilineata/A. atrilobata damselfish and the Cephalopholis (Paranthias) furcifer/C. colonus groupers, we explore to what extent visual sensitivity converged to similar adaptations in response to similar foraging strategies and shared underwater light in each marine basin. We found that the compression of the underwater light field towards the central portion of the spectrum from Caribbean to TEP waters is reflected in similar shifts towards the centre of the light spectrum in overall single and double cone sensitivities in both families. Both TEP species have single (short-wavelength) cone sensitivities shifted to longer wavelengths and double (long-wavelength) cone sensitivities shifted to shorter wavelengths, compared to their Caribbean counterparts. These parallel shifts in visual sensitivities observed in response to shared underwater light environments are accomplished by different underlying opsin gene toolsets in the two lineages. Similarly, expression changes in pathways associated with the visual system revealed limited parallelism at the molecular level.

evolutionary biology↗

bioRxiv2021

Simultaneous expression of UV and violet SWS1 opsins expands the visual palette in a group of freshwater snakes.

Snakes are known to express a rod visual opsin and two cone opsins, only (SWS1, LWS), a reduced palette resulting from their supposedly fossorial origins. Dipsadid snakes in the genus Helicops are highly visual predators that successfully invaded freshwater habitats from ancestral terrestrial-only habitats. Here we report the first case of multiple SWS1 visual pigments in a vertebrate, simultaneously expressed in different photoreceptors and conferring both UV and violet sensitivity to Helicops snakes. Molecular analysis and in vitro expression confirmed the presence of two functional SWS1 opsins, likely the result of recent gene duplication. Evolutionary analyses indicate that each sws1 variant has undergone different evolutionary paths, with strong purifying selection acting on the UV-sensitive copy and dN/dS [~]1 on the violet-sensitive copy. Site-directed mutagenesis points to the functional role of a single amino acid substitution, Phe86Val, in the large spectral shift between UV and violet opsins. In addition, higher densities of photoreceptors and SWS1 cones in the ventral retina suggest improved acuity in the upper visual field possibly correlated with visually-guided behaviors. The expanded visual opsin repertoire and specialized retinal architecture are likely to improve photon uptake in underwater and terrestrial environments, and provide the neural substrate for a gain in chromatic discrimination, potentially conferring unique color vision in the UV-violet range. Our findings highlight the innovative solutions undertaken by a highly specialized lineage to tackle the challenges imposed by the invasion of novel photic environments and the extraordinary diversity of evolutionary trajectories taken by visual opsin-based perception in vertebrates.

evolutionary biology↗

bioRxiv2020

The visual ecology of a color polymorphic reef fish: the role of aggressive mimicry.

Since all forms of mimicry are based on perceptual deception, the sensory ecology of the intended receiver is of paramount importance to test the necessary precondition for mimicry to occur, i.e. model-mimic misidentification, and to gain insight in the origin and evolutionary trajectory of the signals. Here we test the potential for aggressive mimicry by a group of coral reef fishes, the color polymorphic Hypoplectrus hamlets, from the point of view of their most common prey, small epibenthic gobies and mysid shrimp. We build visual models based on the visual pigments and spatial resolution of the prey, the underwater light spectrum and color reflectances of putative models and their hamlet mimics. Our results are consistent with one mimic-model relationship between the butter hamlet H. unicolor and its model the butterflyfish Chaetodon capistratus but do not support a second proposed mimic-model pair between the black hamlet H. nigricans and the dusky damselfish Stegastes adustus. We discuss our results in the context of color morphs divergence in the Hypoplectrus species radiation and suggest that aggressive mimicry in H. unicolor might have originated in the context of protective (Batesian) mimicry by the hamlet from its fish predators.

evolutionary biology↗

bioRxiv2019

Lens Transmittance Shapes UV Sensitivity In The Eyes Of Frogs From Diverse Ecological And Phylogenetic Backgrounds

The amount of short wavelength (UV, violet and blue) light that reaches the retina depends on the transmittance properties of the ocular media, especially the lens, and varies greatly across species in all vertebrate groups studied previously. We measured the lens transmittance in 32 anuran amphibians with different habits, geographic distributions, and phylogenetic positions and used them together with eye size and pupil shape to evaluate the relationship with diel activity pattern, elevation and latitude. We found an unusually high lens UV transmittance in the most basal species, and a range that extends into the visible spectrum for the rest of the sample, with lenses even absorbing violet light in some diurnal species. However, other diurnal frogs had lenses that transmit UV light like the nocturnal species. This unclear pattern in the segregation of ocular media transmittance and diel activity is shared with other vertebrates and is consistent with the absence of significant correlations in our statistical analyses. Although we did not detect a significant phylogenetic effect, closely related species tend to have similar transmittances, irrespective of whether they share the same diel pattern or not, suggesting that ocular media transmittance properties might be related to phylogeny.

neuroscience↗