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EECG Embarkation 2024: Microgeographic adaptation and landscape connectivity in two anoles from the small, environmentally heterogeneous island of St. Martin

About the author

Michael Yuan (he/him) is a postdoctoral researcher at the Institute for Biodiversity Science and Sustainability at the California Academy of Sciences working with Dr. Rayna Bell and Dr. Lauren Esposito. His work is focused on the evolutionary ecology and conservation of reptiles and amphibians, particularly in the Caribbean. Learn more at his website

My work is broadly interested in the response of generalist species to environmental variation across the landscape. In particular, I am currently interested in questions of scale in local adaptation and how local adaptation can help or hurt a population’s ability to respond to environmental change. Microgeographic adaptation is local adaptation occurring across the dispersal neighborhood of individuals (Richardson et al. 2014). This variation is likely underappreciated but holds valuable insights into the generation and maintenance of intraspecific diversity. Additionally, the presence of local adaptation suggests that conservation efforts for threatened species should include finer-scale management actions. This is particularly relevant in small island systems where the spatial scale is limited despite high environmental heterogeneity and available land for conservation is scarce.

Figure 1. Male individual of Anolis pogus on the island of St. Martin. Photo credit: Edward Myers

The AGA EECG funds support my research on microgeographic adaptation using two species of anoles (Anolis gingivinus and A. pogus; Fig 1-2) found on the island of St. Martin (88 km2). St. Martin provides a compelling system in which to study local adaptation because its volcanic nature means that environmental turnover occurs rapidly despite its small overall size (Fig 3). Despite the limited geographic area, anoles exhibit several differences across this heterogeneous landscape such as covariation between color and habitat (Yuan et al. 2023) despite a lack of coincident population structure (Jung et al. In Press). Ongoing work also suggests that blood pathogen loads vary across the island with the environment. Thus, the two main questions this project will ask are:

  • Do we observe evidence for microgeographic adaptation in anoles across St. Martin?
  • Does urbanization differentially influence population connectivity and structure in these two species?
Figure 2 Male individual of Anolis gingivinus sampled from a satellite island of St. Martin, Caye Verte.

In addition to the above goals, this project seeks to evaluate the conservation status and ecology of A. pogus, which is currently classified as near threatened by the IUCN Red List and is of local conservation concern to both Sint Maarten and Saint-Martin (the two jurisdictions which comprise the island). Our conservation-focused efforts combine landscape genomics analyses with abundance surveys conducted throughout the island of St. Martin. These surveys confirm that A. pogus occurs in all environments across the islands, however, their abundances are substantially higher in closed canopy and higher elevation sites than in urbanized areas. Comparatively, A. gingivinus is abundant throughout the entirety of the island’s habitats including more urbanized sites. We are also reviewing the proposed fossil evidence that A. pogus went extinct on the neighboring island of Anguilla (Pregill et al. 1994). Preliminary evidence suggests that fossils of anoles on Anguilla actually correspond to male and female A. gingivinus without evidence for the presence of A. pogus. Our aim is for our findings to contribute to ongoing management efforts for A. pogus across the archipelago

Figure 3 Coastline of the island of St. Martin showing coastal xeric habitat, urban development, and forested mountains habitats. Both species of anoles occur in across all of these habitats.

This project is part of the broader Islands 2030 initiative at the California Academy of Sciences, which aims to provide biodiversity science, environmental learning, and collaborative engagement to equip island communities to combat biodiversity loss. The results of this study will also provide guidance for conservation actions and educational activities of our partner organizations, including the Nature Foundation Sint Maarten and the Réserve Naturelle de Saint-Martin.


Jung C, Frederick JH, Graham NR, Wang IJ, Fenton C, de Queiroz K, Bell RC, Yuan ML. (In Press) Environmentally-associated color divergence does not coincide with population structure across Lesser Antillean anoles. Biological Journal of the Linnean Society. 

Pregill GK, Steadman DW, Watters DR (1994) Late Quaternary vertebrate faunas of the Lesser Antilles: historical components of Caribbean biogeography. Bulletin of Carnegie Museum of Natural History. 30. 1–51.

Richardson JL, Urban MC, Bolnick DI, Skelly DK (2014) Microgeographic adaptation and the spatial scale of evolution. Trends in Ecology and Evolution. 29. 165–176.

Yuan ML, Jung C, Frederick JH, Fenton C, de Queiroz K, Cassius J, Williams R, Wang IJ, Bell RC (2023) Parallel and non-parallel phenotypic responses to environmental variation across Lesser Antillean anoles. Evolution 77:1031–1042.

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