Habitat Stability Does Not Influence Size Variation in Morphological Features of Lizards
Global climatic fluctuation has significantly impacted biodiversity by shaping adaptations across numerous species. Pleistocene climate changes notably affected species’ geographic distributions and population sizes, especially fostering post-glacial expansions in temperate regions. Evolutionary theory suggests spatial sorting of morphological traits associated with dispersal in recently expanded species. However, evidence of predicted intraspecific trait variation is scant. We investigated intraspecific trait variation in five lizard species along a forest-savanna gradient affected by Pleistocene climate. Lizards serve as an ideal group to test these ideas due to climate’s known influence on their morphological traits linked to essential functions like feeding and locomotion. We assessed two hypotheses: (i) niche variation and (ii) spatial sorting. For the niche variation hypothesis, we predicted increased intraspecific variability in head dimensions with distance from stable areas. For spatial sorting, we anticipated larger hind limb sizes with increased distance from stable areas. We gathered data on five quantitative traits from 663 samples across species. There was no evidence supporting either hypothesis across the five species. Limited sample sizes, challenges in habitat modeling, or other factors might explain this lack of support. Nonetheless, our study illuminates complexities in exploring trait variation within species. The data collected here, although inconclusive, represent a crucial test for evolutionary theory.ABSTRACT
An example of steps used for production of stability maps for our focal species: (A) combination and average of three time slice maps; (B) separation of 95th percentile of high suitability regions; (C) exclusion of areas with less than 500 pixels of size and estimation of high stability areas’ centroids, and (D) final map showing niche suitability, with areas of high climatic stability through time in yellow, and areas with low climatic stability in dark blue. Black circles and their associated numbers are climatically stable areas, triangles are occurrence points of T. teguixin which have associated morphological data.
Iguana iguana. Map of stability (A); numbers 1–8 correspond to centroids of stable areas; triangles correspond to localities at which we have morphological data. Plots (B–E) correspond to linear mixed-effects models and linear models for each trait: (B) residual from HLS and SVL linear model (P-value: 1); (C) variation of HD (P-value: 1); (D) variation of HL (P-value: 1); (E) variation of HW (P-value: 0.744). Abbreviations: HLS (hind limb size); SVL (snout-vent length); HD (head depth); HL (head length); HW (head width); Stdv (standard deviation).
Micrablepharus maximiliani. Map of stability (A); numbers 1–6 correspond to centroids of stable areas; triangles correspond to localities at which we have morphological data. Plots (B–E) correspond to linear mixed-effects models and linear models for each trait: (B) residual from HLS and SVL linear model (P-value: 1); (C) variation of HD (P-value: 1); (D) variation of HL (P-value: 0.97852); (E) variation of HW (P-value: 0.259228). Abbreviations: HLS (hind limb size); SVL (snout-vent length); HD (head depth); HL (head length); HW (head width); Stdv (standard deviation).
Notomabuya frenata. Map of stability (A); numbers 1–4 correspond to centroids of stable areas; triangles correspond to localities at which we have morphological data. Plots (B–E) correspond to linear mixed-effects models and linear models for each trait: (B) residual from HLS and SVL linear model (P-value: 1); (C) variation of HD (P-value: 1); (D) variation of HL (P-value: 1); (E) variation of HW (P-value:1). Abbreviations: HLS (hind limb size); SVL (snout-vent length); HD (head depth); HL (head length); HW (head width); Stdv (standard deviation).
Tropidurus oreadicus. Map of stability (A); numbers 1–3 correspond to centroids of stable areas; triangles correspond to localities at which we have morphological data. Plots (B–E) correspond to linear mixed-effects models and linear models for each trait, (B) residual from HLS and SVLe linear model (P-value: 1), (C) variation of HD (P-value: 1), (D) variation of HL (P-value: 1), (E) variation of HW (P-value: 1). Abbreviations: HLS (hind limb size); SVL (snout-vent length); HD (head depth); HL (head length); HW (head width); Stdv (standard deviation).
Tupinambis teguixin. Map of stability (A); numbers 1–7 correspond to centroids of stable areas; triangles correspond to localities at which we have morphological data. Plots (B–E) correspond to linear mixed-effects models and linear models for each trait, (B) residual from HLS and SVL linear model (P-value: 1), (C) variation of HD (P-value: 1), (D) variation of HL (P-value: 1), (E) variation of HW (P-value: 1). Abbreviations: HLS (hind limb size); SVL (snout-vent length); HD (head depth); HL (head length); HW (head width); Stdv (standard deviation).
Map showing stable habitat areas (13 areas) in South America, selected using the Costa et al. (2018) stability map, which had more than 95% stability and were bigger than 1000 pixels. X-axis denotes longitude in degrees, y-axis represents latitude in degrees. Each color represents one continuous area; black circles are stable habitat area centroids.
Boxplots illustrating the distribution of morphological traits across different species. The plots depict (A) hind limb size (HLS), (B) head depth (HD), (C) head length (HL), and (D) head width (HW). Each species is represented by a unique color, as indicated in the legend. In each boxplot, the central line represents the median, the box encompasses the interquartile range (IQR), and whiskers extend to 1.5 times the IQR. Data points beyond the whiskers are considered outliers and are shown as individual dots.
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