Biology subjects

Crowe-Riddell, J. M.

Publications and source records attributed to Crowe-Riddell, J. M..

3 recordsLinked to original sources

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↗

bioRxiv2026

Seascape genomics reveals shared spatial genetic structure in three co-occurring sea snakes

Marine species with broad distributions often exhibit complex patterns of genetic connectivity, shaped by historical and contemporary processes. Understanding these patterns is critical for conserving taxa threatened by ongoing and future environmental change. Here, we use reduced-representation and whole-genome sequencing to investigate population genetic patterns in three co-occurring sea snake species (Hydrophis stokesii, Hydrophis major, and Aipysurus laevis) across northern Australia and New Caledonia. Broadscale analyses revealed major genetic breaks across all species between: (1) Australia and New Caledonia, (2) northwestern and northeastern Australia, and (3) the offshore Timor Sea reefs and adjacent northwestern continental shelf of Australia. More subtle genetic differentiation was observed between Shark Bay in Western Australia and northern localities. All species showed relatively large effective population sizes and broadscale connectivity across ~1,300 km of Australia's northwestern continental shelf. This likely reflects substantial historical range expansion over late Quaternary timescales, which may have contributed to the observed genetic connectivity across the region. However, subtle patterns of isolation by distance emphasised the contribution of species-specific traits in shaping connectivity. The isolated offshore reef populations are genetically distinct and potentially threatened by environmental change. Disjunct populations in Shark Bay and the Timor Sea maintain similar levels of genetic diversity to the extensive continental shelf populations, while New Caledonian populations exhibit reduced diversity. Our results support the delineation of spatial units for sea snake conservation based on shared phylogeographic structure, while also finding important population- and species-specific differences in connectivity at finer spatial and temporal scales.

genomics↗

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↗