Abstract
The potential of artificial selection to dramatically impact phenotypic diversity is well known. Large-scale morphological changes in domestic species, emerging over short timescales, offer an accelerated perspective on evolutionary processes. The domestic horse (Equus caballus) provides a striking example of rapid evolution, with major changes in morphology and size likely stemming from artificial selection. However, the microevolutionary mechanisms allowing to generate this variation in a short time interval remain little known. Here, we use 3D geometric morphometrics to quantify skull morphological diversity in the horse, and investigate modularity and integration patterns to understand how morphological associations contribute to cranial evolvability in this taxon. We find that changes in the magnitude of cranial integration contribute to the diversification of the skull morphology in horse breeds. Our results demonstrate that a conserved pattern of modularity does not constrain large-scale morphological variations in horses and that artificial selection has impacted mechanisms underlying phenotypic diversity to facilitate rapid shape changes. More broadly, this study demonstrates that studying microevolutionary processes in domestic species produces important insights into extant phenotypic diversity.
Highlights
The phenotypic diversification of domestic species provides a unique and accelerated perspective on evolutionary processes
The multivariate regression of the shape against the log10-transformed centroid size (CS) indicates significant and strong impact of size on shape (R2 = 0.93). This strong influence of allometry on shape variation is reflected by the distribution of the specimens according to size along PC1
As already shown in several taxa, we found that this drastic diversification did not rely upon changes in modularity patterns but rather upon variations in the magnitude of integration between morphological features
Summary
The phenotypic diversification of domestic species provides a unique and accelerated perspective on evolutionary processes. Sustained selection by breeders (e.g. for specific morphological, functional or behavioral features) can generate novel shape variation and contribute to large-scale phenotypic diversification in a few. This ability of artificial selection to strongly impact the morphological features of domestic animals raises the issue of the existence of microevolutionary mechanisms facilitating rapid shape changes [11]. Hanot et al BMC Ecol Evo (2021) 21:178 of organisms are known to influence patterns of morphological variation [12,13,14]. Selective processes may cause changes in modularity patterns or in magnitude of integration, and these can be examined as a way to understand how interactions among traits drive or limit the generation of variation in evolution [15, 19]
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