Aim: Geographic range expansion depends on ecological and evolutionary processes that may hamper local adaptations in populations living at range edges by constraining phenotypic variability. This study investigates the spatial patterns of the intraspecific variability of skull traits throughout the geographic range of a marsupial from the Brazilian Atlantic Forest. We aimed to answer whether the distance from the range edge and the environmental suitability explain the geographic variation of morphological variability of the species.

Location: Atlantic Forest, Brazil.

Taxon: Marmosops incanus (Didelphimorphia, Didelphidae).

Methods: We analysed adult specimens deposited in the main biological collections in southeastern Brazil. The morphological variability extent and integration within populations were characterised by 13 linear measures of the skull, using a multivariate approach. Environmental suitability for the species’ occurrence was estimated by Ecological Niche Models, using climatic and vegetation productivity as predictors and three different modelling methods. Distance from the range edge was calculated based on the minimum linear distance between populations and the closest range limit. We fitted linear regressions and selected the best models that explained the spatial variation of morphological variability based on the Akaike information criterion.

Results: The extent of morphological variability of M. incanus is positively correlated with morphological integration and increases with local environmental suitability and distance from the range edges. However, the relationship between morphological variability and environmental suitability depends on the niche modelling method.

Main conclusions: Unfavourable environmental conditions constrain morphological variability within populations of the Gray slender opossum and may hamper local adaptation in peripheral populations living in less suitable environments. In addition to environmental conditions, geographic location of populations also plays an important role in phenotypic variability among populations. We stress the boundary effect of the species range on the local adaptation of peripheral populations and its possible consequences for the range expansion dynamics.

Please see the README.md document and the metadata.txt located within the /data directory for data collection and analysis information. More details on methods can be found in the accompanying published article: Braz, A.G.; Figueiredo, M.S.L.; Weber, M.M.; Grelle, C.E.V. 2023 Morphological variability decreases in populations living in less suitable environments and close to the range edges. Journal of Biogeography, doi: 10.1111/jbi.14687

All datasets, outputs and codes were created and/or processed in R language. Please see the README.md document and the metadata.txt located within the /data directory for data collection and analysis information. More details on methods can be found in the accompanying published article: Braz, A.G.; Figueiredo, M.S.L.; Weber, M.M.; Grelle, C.E.V. 2023 Morphological variability decreases in populations living in less suitable environments and close to the range edges. Journal of Biogeography, 10.1111/jbi.14687