Biology subjects

Gerber, G. P.

Publications and source records attributed to Gerber, G. P..

3 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

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↗