Biology subjects

Colosimo, G.

Publications and source records attributed to Colosimo, G..

6 recordsLinked to original sources

bioRxiv2026

How small is too small? Genetic signatures from naturally small populations of a large island vertebrate, the Turks and Caicos Rock Iguana

Small populations are increasingly common on the landscape, and many face rising probabilities of extinction. Demographic factors alone can drive a small population into an extinction vortex, but genetic factors such as inbreeding and genetic drift lead to reductions in genetic diversity and expression of deleterious alleles, further impacting fitness. Populations on islands are also impacted by founder effects, minimal gene flow, and habitat constraints, yet naturally small, island populations have persisted through many generations despite all these factors. This suggests that island biota may operate at smaller viable population sizes than their mainland counterparts while avoiding extinction vortices. Using 26 microsatellites, we describe the genetic diversity and population structure of 13 subpopulations of a large island vertebrate, the endangered Turks and Caicos rock iguana (Cyclura carinata), found on a range of small cays (0.151-374ha). Most subpopulations had decreased genetic variation but limited evidence of inbreeding despite small island size. Even with water barriers limiting gene flow, some subpopulations in geographical proximity are functioning as a metapopulation while others are not. These subpopulations are not in danger of extirpation, even though census size could be as low as 10 individuals. We believe this study shows that C. carinata has a low population size threshold for long-term persistence that can inform the species' future management, such as with conservation translocations. Furthermore, this project anecdotally adds more evidence to how island populations persist through selection despite genetic drift.

genetics↗

bioRxiv2026

Why they move: breeding-site availability drives partial migration in a large terrestrial reptile

1. Migration is a widespread phenomenon across taxa, yet the ecological mechanisms underlying its evolution and maintenance, particularly whether migratory behaviors are primarily driven by access to spatially restricted breeding sites or by seasonal tracking of trophic resources, remain poorly documented outside birds and large mammals. Despite increasing evidence that reptiles perform seasonal migrations, the ecological mechanisms underlying these movements have rarely been formally tested. 2. The critically endangered Galapagos pink land iguana (Conolophus marthae), endemic to Wolf Volcano, Isabela Island, exhibits partial migration along a steep altitudinal gradient, providing an opportunity to disentangle the relative roles of breeding-site availability, trophic resource dynamics, and thermoregulatory conditions as drivers of migration. 3. We used GPS tracking data from 22 individuals (7 males, 15 females) monitored between 2019 and 2023, combined with high-resolution spatio-temporal models of vegetation productivity and air temperature across the species' altitudinal range, to characterize population-level movement patterns and evaluate competing hypotheses explaining the evolution of this migratory behavior. 4. Movement models revealed a clear pattern of partial migration: 16 out of 22 tracked individuals performed seasonal altitudinal movements between a restricted high-elevation mating area and a larger dispersal area at lower elevation, with males reaching the mating area approximately 48 days earlier than females. The dispersal area remained consistently more productive than the mating area throughout the year, rejecting the prediction that individuals should track the shifting trophic resource peaks. Instead, the mating season coincided with the local productivity peak within the mating area, whereas temperature differences between areas were small (ca. 2{degrees}C) and did not explain migration timing. 5. These results support a site-dependent hypothesis of partial migration over a resource-tracking hypothesis, indicating that access to spatially restricted breeding sites is the primary driver of migration in this species, with local trophic resource dynamics fine-tuning reproductive timing. Providing empirical evidence for the ecological mechanisms underlying migration in a large terrestrial reptile, our results extend site-dependent theories of migration beyond birds and mammals and identify breeding-site availability as a key ecological driver of migratory behaviors across taxa.

ecology↗

bioRxiv2026

The impact of serial translocations on the genetic diversity of Anegada iguanas (Cyclura pinguis) in the British Virgin Islands

Animal translocations are becoming increasingly popular as a tool for conservationists. Demographic factors can be crucial determinants dictating translocation viability in the short term. Translocated populations pass through artificial bottlenecks and can suffer from founder effects. Reduction in genetic variation relative to their source populations is likely, limiting their adaptive potential. Founder events can increase frequencies of deleterious alleles due to elevated rates of inbreeding and inbreeding depression. Here, we describe the effects of human-driven, serial population translocations on the genetic diversity of critically endangered Anegada iguanas (Cyclura pinguis) in the British Virgin Islands. Though founding populations were extremely small (N=8, N=4), the census sizes of translocated iguana populations increased dramatically over the first twenty years. This implies that these translocations were successful from a demographic perspective despite the small number of animals used, indicating a genetic paradox. To quantify genetic signatures in these bottlenecked populations, blood samples were collected from the source population and two translocated populations and genotyped at 21 microsatellite loci. We found that allele frequencies in translocated populations differed significantly from those of the source, with the translocated populations having less genetic diversity. However, common methods for estimating presence of genetic bottlenecks were non-significant. Estimates of internal relatedness by age class suggest that inbreeding depression may be elevated after translocation, likely reflecting the small initial population sizes associated with these translocation events. Anecdotally, our work shows that translocations may result in subtle genetic erosion that has long-term population viability impacts, even when census size indicates success.

genetics↗

bioRxiv2025

A genomic perspective on the origins, evolution and adaptation of Galapagos iguanas

Island taxa provide opportunities to explore the genomic basis of species diversification and trait evolution arising from adaptation to new environmental conditions and ecological niches. Here we generate the first genomic sequences for the four endemic Galapagos iguana species to reconstruct their evolutionary history and to identify genes which may contribute to their unique adaptations. We show that the marine (Amblyrhynchus) and land (Conolophus) lineages evolved in situ on now submerged islands, following a single colonisation event 9 - 12.4 million years ago. Genomic selection scans identified genes linked to traits potentially facilitating adaptation to the Galapagos environment, including specialised pigmentation phenotypes (e.g. ASIP, BCO2 and KITLG), DNA damage and UV irradiation inflammation responses (e.g. MAPK14 and BRAF), which may contribute to increased resilience to elevated UV exposure at equatorial latitudes. A shift from eumelanin (dark) to pheomelanin (yellow-orange) dominated colouration in Conolophus species may be attributable to fixed substitutions in the MC1R gene that influence protein structure and interactions, with the depigmented skin phenotype of the pink iguana additionally linked to positive selection in regulators of MITF activity, melanosome transport and dermal vasculature unique to that lineage. Further genes with signatures of positive selection in marine iguanas have putative functions including hypoxia response, that may be associated with their transition to underwater foraging (e.g. HBA, HMOX2, HIF), as well as their unique ability to repeatedly shrink and grow in body size through tissue and bone remodelling (e.g. AREG, BMP2, CPNE7). Genome-wide patterns of genetic diversity indicate recent inbreeding coincident with the timing of human settlement. Our study provides insights into the origins and diversification of the iguanas and the molecular basis of adaptation to life in the Galapagos, facilitating future conservation genomic management of threatened iguanid populations.

evolutionary biology↗

bioRxiv2021

Health assessment of the pink land iguana, Conolophus marthae.

The pink land iguana, Conolophus marthae, is one of four species of iguanas (three terrestrial and one marine) in the Galapagos Islands, and the only one listed as critically endangered by the IUCN. The species can only be found on the north-west slopes of the highest volcano on the island of Isabela and was first described to science in 2009. As part of a population telemetry study, a health assessment was authorized by the Galapagos National Park. Wild adult iguanas were captured on Wolf Volcano in September 2019 and April 2021 to record morphological and physiological parameters including body temperature, heart rate, body measurements, intraocular pressures, tear formation, and infrared iris images. Blood samples were also collected and analyzed. An i-STAT portable blood analyzer was used to obtain values for base excess in the extracellular fluid compartment (BEECF), glucose, hematocrit, hemoglobin, ionized calcium (iCa), partial pressure of carbon dioxide (pCO2), partial pressure of oxygen (pO2), percent oxygen saturation (sO2%), pH, potassium (K), and sodium (Na). Standard laboratory hematology techniques were employed for packed-cell-volume (PCV) determination. When possible, data were compared to previously published and available data for the other Galapagos iguanas. The results reported here provide baseline values that may be useful in detecting changes in health status among pink land iguanas affected by climate change, invasive species, anthropogenic threats, or natural disturbances.

zoology↗

bioRxiv2020

All is fish that comes to the net: metabarcoding for rapid fisheries catch assessment

Monitoring marine resource exploitation is a key activity in fisheries science and biodiversity conservation. Since research surveys are time-consuming and costly, fishery-dependent data (i.e. derived directly from fishing vessels) are increasingly credited with a key role in expanding the reach of ocean monitoring. Fishing vessels may be seen as widely ranging data-collecting platforms, which could act as a fleet of sentinels for monitoring marine life, in particular exploited stocks. Here, we investigate the possibility of assessing catch composition of single hauls carried out by trawlers by applying DNA metabarcoding to the "slush" collected from fishing nets just after the end of hauling operations. We assess the performance of this approach in portraying {beta}-diversity and examining the quantitative relationship between species abundances in the catch and DNA amount in the slush (reads counts generated by amplicon sequencing). We demonstrate that the assemblages identified using DNA in the slush mirror those returned by visual inspection of net content and detect a strong relationship between read counts and species abundances in the catch. We therefore argue that this approach could be upscaled to serve as a powerful source of information on the structure of demersal assemblages and the impact of fisheries.

ecology↗