Biology subjects

Collin, S. P.

Publications and source records attributed to Collin, S. P..

6 recordsLinked to original sources

bioRxiv2026

Impact of heat and sex on embryonic brain growth in dragons with temperature induced sex-reversal (Pogona vitticeps, Lacertilia: Agamidae)

Climate warming can influence sex determination and embryonic growth in oviparous reptiles that rely on external temperatures during development. Warmer incubation temperatures can stimulate growth in ectotherms until oxygen supply can no longer keep pace with growth rate; at which point metabolically expensive organs like the brain suffer. We aimed to understand the impact of heat and sex on brain development in central bearded dragons, Pogona vitticeps (Agamidae), a uniquely thermosensitive species that exhibits sex-reversal at warm incubation temperatures. Three sexual phenotypes are possible in P. vitticeps: genetically driven ZW females and ZZ males, with the latter phenotype thermally overridden at incubation temperatures >32C to induce ZZ sex-reversed females. To visualise changes in brain anatomy, we used buffered Lugols iodine to perform contrast-enhanced micro computed tomography (microCT) and synchrotron propagation-based phase-contrast CT scanning. A total of 57 embryos were sampled across developmental stages and incubated at two temperature treatments: cool (28C, n = 26) and warm (36C, n = 21). Using high-resolution models of neuroanatomy, we found that the telencephalic region of the forebrain is significantly larger in individuals with ZZ genotypes (males and sex-reversed females) compared to concordant ZW females. Although incubation temperature significantly influenced growth rate and body size during development, overall brain size was not significantly different across temperature treatments. Our results indicate that the effects of genotypic sex on brain development are more important than thermal influences, and thus the brain may be somewhat buffered to the effects of warm incubation temperatures in this arid-adapted dragon.

neuroscience↗

bioRxiv2026

Optimising neural contrast and minimising tissue shrinkage in dragon lizard brains: buffered Lugol's iodine versus phosphotungstic acid for contrast-enhanced μCT

Contrast-enhanced micro-computed tomography (CT) has become a valuable tool for addressing neuroanatomical questions that previously required destructive histology. As a relatively new technique, it remains subject to ongoing technical refinement, and taxon- and tissue-specific protocol optimisation. We evaluated the performance of two common contrast-enhancing agents, buffered Lugol's iodine and phosphotungstic acid (PTA) in aqueous solution, for CT visualisation of the nervous system in the Jacky dragon lizard, Amphibolurus muricatus by comparing staining time, contrast specificity and brain tissue shrinkage evaluated at three concentrations (1.25%, 2.5% and 5%). Buffered Lugol's iodine outperformed aqueous PTA by requiring shorter staining times (as short as four days) and providing better white matter-grey matter differentiation, whereas PTA required longer incubation periods of approximately three weeks and produced poorer white-grey matter differentiation. Importantly, buffered Lugol's iodine produced higher brain-to-endocast occupancy estimates than aqueous PTA, suggesting substantially reduced tissue shrinkage. PTA-treated specimens exhibited an estimated 13.3% reduction in occupancy and approximately 20% greater brain tissue shrinkage than buffered Lugol's-treated specimens. Together, these findings demonstrate that buffered Lugol's iodine staining provides the high level of internal tissue contrast required to resolve fine-scale neuroanatomical organisation in three dimensions, preserves the spatial relationships among anatomical structures, and reduces artefacts, all of which result in a closer correspondence between the brain and endocranial cavity. From a practical perspective, the study provides guidance for contrast agent selection in future CT studies and reveals that buffered Lugol's iodine is better suited to fine-scale neuroanatomical, volumetric and geometric morphometric analyses, whereas PTA is advantageous for applications prioritising general soft-tissue or musculoskeletal visualisation.

neuroscience↗

bioRxiv2025

Morphology and distribution of a new scale mechanoreceptor type in olive-headed sea snakes (Hydrophis major)

Snakes are known for their superb sensory specialisations but are not widely appreciated for their sense of touch despite emerging evidence of tactile specialisation among sea snakes. This is partly due to the challenges in quantifying such small and numerous scale mechanoreceptors or scale sensilla across individuals. By using a novel application of gel-based 3D profilometry (GelSight scanner) in combination with scanning electron-and light microscopy, we comprehensively quantified the morphology and distribution of scale mechanoreceptors in a sea snake, Hydrophis major (Hydrophiinae), for the first time. We discovered a new type of scale mechanoreceptor distinguished by its larger size (43.65 {+/-} 22.57 m height) and asymmetrical peak shape, created by a thickening in the cornified outer layers of the epidermis. Asymmetrical peaks contain a dermal papilla with central cells, indicative of meissner-like corpuscles that underlie smooth dome-shaped mechanoreceptors (31.88 {+/-} 19.03 m height) typically found in both sea snakes, but is positioned slightly off centre from the tallest point of the asymmetrical peak. Smooth domes are concentrated anterior-posteriorly on the head with the highest densities on the rostrum and nasal scales (9.83 {+/-} 1.88 and 5.24 {+/-} 2.85 per mm{superscript 2}, respectively). Asymmetrical peaks are rarer; detected only on the dorsal and lateral sides of the head and most common on the postocular scale (mean density 1.26 {+/-} 0.72 per mm{superscript 2}). We suggest functional differences in mechanosensory capabilities: asymmetrical peaks may serve primarily proprioceptive purposes whereas smooth domes are used for hydrodynamic reception.

ecology↗

bioRxiv2022

Enhanced short-wavelength sensitivity in the blue-tongued skink,Tiliqua rugosa

The complex visually mediated behaviors of diurnal lizards are enabled by a retina typically containing five types of opsins with the potential for tetrachromatic color vision. Despite lizards using a wide range of color signals, the limited variation in photoreceptor spectral sensitivities across lizards suggests only weak selection for species-specific, spectral tuning of photoreceptors. Some species, however, have enhanced short wavelength sensitivity, which likely helps with the detection of signals rich in ultraviolet and short wavelengths. In this study, we examined the visual system of Tiliqua rugosa, which has a UV/blue tongue, to determine the spectral sensitivity of the eye and to gain insight into this species visual ecology. Electroretinograms coupled with spectral stimulation showed peak sensitivity at 560 nm with high similarity to other lizards at wavelengths greater than 530 nm. However, at shorter wavelengths, sensitivity is enhanced leading to a spectral sensitivity curve that is 28 nm broader (full width at half height) than other lizards studied so far. The width of the curve is partially explained by a population of photoreceptors that respond more strongly to low temporal frequencies with possible peaks in sensitivity between 460 and 470 nm suggesting that they are SWS2 photoreceptors. The lack of a peak in sensitivity at 360 nm at low temporal frequencies and under a monochromatic light that suppresses the response of LWS photoreceptors, suggests that the SWS1 photoreceptors are red-shifted. In addition, the yellow and green oil droplets that are common in other diurnal lizards appear to be missing and instead, only transparent and pale-yellow oil droplets are present. LWS photoreceptors are likely paired with pale-yellow oil droplets to produce LWS photoreceptors with wider spectral sensitivity curves than in other lizards. Opsin sequencing reveals SWS1, SWS2, RH1, RH2 and LWS opsin genes that are very similar to the visual opsins detected in the green anole, Anolis carolinensis, suggesting there is little change in the spectral sensitivity of photoreceptors compared to other diurnal lizards. Since we only obtained a partial sequence of the SWS1 opsin, we were unable to determine whether amino acid substitution at tuning sites could have played a role in red-shifting the SWS1 photoreceptor spectral sensitivity. Photoreceptor densities are typically higher in central and ventral retinal regions than in the dorsal retina suggesting that higher spatial sampling is necessary at eye level and above the animal than on the ground. However, the SWS1 photoreceptors do not follow this pattern potentially due to their low abundance making them less relevant to high acuity visual tasks. Our findings demonstrate that there are possibly multiple mechanisms acting synergistically in the visual system of T. rugosa to enhance short wavelength sensitivity between 360 and 530 nm. While it is tempting to suggest that this is an adaptation to facilitate the detection of the blue tongues of conspecifics, additional experiments are necessary to determine its ecological relevance. Summary statementColor vision and the distribution of photoreceptor subtypes in T. rugosa

neuroscience↗

bioRxiv2021

Morphometric Analysis of Lungfish Endocasts Elucidates Early Dipnoan Palaeoneurological Evolution

Lungfish (Dipnoi) are lobe-finned fish (Sarcopterygii) that have persisted for over 400 million years from the Devonian Period to present day. They are the extant sister group to tetrapods and thus have the ability to provide unique insight into the condition of the earliest tetrapods as well as their own evolutionary history. The evolution of their dermal skull and dentition is relatively well understood, but this is not the case for the central nervous system. While the brain itself has very poor preservation potential and is not currently known in any fossil lungfish, substantial indirect information about it and associated structures such as the inner ears can be obtained from the cranial endocast. However, before the recent development of X-ray tomography as a palaeontological tool, these endocasts could not be studied non-destructively, and few detailed studies were undertaken. Here we describe and illustrate the endocasts of six Palaeozoic lungfishes (Iowadipterus halli, Gogodipterus paddyensis, Pillararhynchus longi, Griphognathus whitei, Orlovichthys limnatis, and Rhinodipterus ulrichi) from tomographic scans. We combine these with six previously described lungfish endocasts (4 fossil and 2 recent taxa), also based on tomographic studies, into a 12-taxon data set for multivariate morphometric analysis using 17 variables. We find that the olfactory region appears to be more highly plastic than the hindbrain, and undergoes significant elongation in several taxa. Further, while the semicircular canals covary as an integrated module, the utriculus and sacculus of the inner ear instead vary independently of each other. The functional and phylogenetic implications of our findings are discussed.

paleontology↗

bioRxiv2017

Retinal specializations to a micro-predatory and crypto-benthic life-style in the Mediterranean triplefin blenny Tripterygion delaisi

The environment and lifestyle of a species are known to exert selective pressure on the visual system, often demonstrating a tight link between visual morphology and ecology. Many studies have predicted the visual requirements of a species by examining the anatomical features of the eye. However, among the vast number of studies on visual specializations in aquatic animals, only a few have focused on small benthic fishes that occupy a heterogeneous and spatially complex visual environment. This study investigates the general retinal anatomy including the topography of both the photoreceptor and ganglion cell populations and estimates the spatial resolving power of the eye of the Mediterranean triplefin Tripterygion delaisi. Retinal wholemounts were prepared to systematically and quantitatively analyze photoreceptor and retinal ganglion cell densities using design-based stereology. To further examine the retinal structure, we also used magnetic resonance imaging and histological examination of retinal cross sections. Observations of the triplefin's eyes revealed them to be highly mobile, allowing them to view the surroundings without body movements. A rostral aphakic gap and the elliptical shape of the eye extend its visual field rostrally and allow for a rostro-caudal accommodatory axis, enabling this species to focus on prey at close range. Single and twin cones dominate the retina and are consistently arranged in one of two regular patterns, which may enhance motion detection and color vision. The retina features a prominent, dorso-temporal, convexiclivate fovea with an average density of 104,400 double and 30,800 single cones per mm2, and 81,000 retinal ganglion cells per mm2. Based on photoreceptor spacing, spatial resolving power was calculated to be between 6.7 and 9.0 cycles per degree. Location and resolving power of the fovea would benefit the detection and identification of small prey in the lower frontal region of the visual field.

animal behavior and cognition↗