The evolution of striking phenotypes on islands is a well-known phenomenon, and there has been a long-standing debate on the patterns of body size evolution on islands. The ecological causes driving divergence in insular populations are, however, poorly understood. Reduced predator fauna is expected to lower escape propensity, increase body size and relax selection for crypsis in small-bodied, insular prey species. Here, we investigated if escape behaviour, body size and dorsal coloration have diverged as predicted under predation release in spatially replicated islet- and mainland populations of the lizard species Podarcis gaigeae. We show that islet lizards escape approaching observers at shorter distances and are larger than mainland lizards. Additionally, we found evidence for larger between-population variation in body size among the islet populations than mainland populations. Moreover, islet populations are significantly more divergent in dorsal coloration and match their respective habitats poorer than mainland lizards. These results strongly suggest that predation release on islets has driven population divergence in phenotypic and behavioural traits and that selective release has affected both trait means and variances. Relaxed predation pressure is therefore likely to be one of the major ecological factors driving body size divergence on these islands.
DataDescriptionRunemark et al
This file describes the contents of the other files associated with this manuscript uploaded to Dryad. It also contains general information about the manuscript.
FID
Flight initiation distances (measured in meters) per habitat (island I or mainland M) and population (location).
PC1size
Body size (measured as the first Principal Component, PC1) per habitat (I island or M mainland), sex, and location (population). Higher values of PC1 reflect larger body sizes.
Greenness
Greenness (measured as mean (Green-Red)/(Green+Red))) of the lizard dorsal area per habitat (I island and M mainland), sex (M male and F female) and location (population).
SizeRawDataPCAScores
Raw size measurements (in millimeters for length characters and grams for weight) of the morphological characters the Principal Component Analysis (PCA) of size is based on, as well as the factor scores for PC1-9 per individual, per habitat (I: island, M: mainland), sex and population.
ColorPCAscores
Factor scores for PC1-20 for dorsal coloration per individual, per habitat (I: island, M:mainland), Population/Location (e.g. the Pop column) and sex (M: male, F: female). The PCA is based on 2D-histograms of the pixels in RGB-space, see (Brydegaard, M., A. Runemark, and R. Bro. 2012. Chemometric Approach to Chromatic Spatial Variance. Case study: Patchiness of the Skyros Wall Lizard. J.Chemometr. 26: 246-255) for a description of how these are obtained from raw images. These are the PCs the correlations between populations as well as between populations and habitats are based on. A subset of the PCs are also included in the variance component analysis and for preparing figure 3.
PopulationCorrelationColor
Pair-wise correlation between two populations (Population_1 and Population_2) per habitat category (M: two mainland populations, IM: one mainland and one islet population, I: two islet populations).
PopulationHabitatCorrelationColor
Pair-wise correlations reflecting multivariate colour similarity between populations (e.g. lizard dorsal coloration)- and habitat squares (1 square meter areas photographed from above). Data is divided into Own-or-Not where 1 reflects that the lizards and the habitat are the same, whereas 0 reflects that lizards come from a different location than the habitat squares. Habitat category reflects if the pair are both from an islet population (I), both from a mainland population (M) or from one islet- and one mainland population (IM).
FST
Pair-wise FST-values based on the 16 microsatellite markers: Lv 319, Pb10, B4, C9, Lv 472, Pod1B, B6, Pb73, Lv 4alfa, Pod 2, Po47, Po56, Po55, Po22, Po43 and Po51 used in Runemark, A., B. Hansson, P. Pafilis, E. Valakos, and E. Svensson. 2010. Island biology and morphological divergence of the Skyros wall lizard Podarcis gaigeae: a combined role for local selection and genetic drift on color morph frequency divergence? BMC Evol. Biol. 10:269. doi: 10.1186/1471-2148-10-269. and originally published in Runemark, A., Gabirot, M., Bensch, S., Svensson, E.I., Martín, J., Pafilis, P., Valakos, E.D. & Hansson, B. Cross-species testing of 27 pre-existing microsatellites in Podarcis gaigeae and P. hispanica (Squamata: Lacertidae) Mol. Ecol. Recourses 8(6):1367-1370. and Wellenreuther, M., Runemark, A., Svensson, E. & Hansson, B. 2009. Ten variable polymorphic microsatellite loci for the Skyros Wall Lizard Podarcis gaigeae (Squamata: Lacertidae). Mol. Ecol. Recourses 9(3):1005-1008.