Abstract
In this study, allometric trajectories for 51 rodent species, comprising equal representatives from each of the major clades (Ctenohystrica, Muroidea, Sciuridae), are compared in a multivariate morphospace (=allometric space) to quantify magnitudes of disparity in cranial growth. Variability in allometric trajectory patterns was compared to measures of adult disparity in each clade, and dietary habit among the examined species, which together encapsulated an ecomorphological breadth. Results indicate that the evolution of allometric trajectories in rodents is characterized by different features in sciurids compared with muroids and Ctenohystrica. Sciuridae was found to have a reduced magnitude of inter-trajectory change and growth patterns with less variation in allometric coefficient values among members. In contrast, a greater magnitude of difference between trajectories and an increased variation in allometric coefficient values was evident for both Ctenohystrica and muroids. Ctenohystrica and muroids achieved considerably higher adult disparities than sciurids, suggesting that conservatism in allometric trajectory modification may constrain morphological diversity in rodents. The results provide support for a role of ecology (dietary habit) in the evolution of allometric trajectories in rodents.
Highlights
A central goal of evolutionary studies is to understand why some clades are more morphologically diverse than others (e.g., Erwin 2007; Pigliucci 2008)
The first two principal component (PC: hereafter, upper case letters denote the axes of allometric space, representing variation among species’ allometric trajectories) axes of allometric space accounted for only 40.7% of variance and an additional 33.8% of variance was spread across PC3–PC6
The quantification of allometric disparity over the course of rodent evolution in this study provides insights into allometric trajectory evolution for the largest mammalian “order”, focusing on patterns in the three major constituent lineages
Summary
A central goal of evolutionary studies is to understand why some clades are more morphologically diverse than others (e.g., Erwin 2007; Pigliucci 2008). Morphological trait covariances have so far been quantified for several clades, and the potential factors underlying these patterns have been explored to assess the role of covariance structure in facilitating or constraining the evolution of traits in complex systems (e.g., Ackermann and Cheverud 2000; Marroig and Cheverud 2005, 2010; Goswami 2006, 2007; Porto et al 2009). These covariance evolution patterns have been central to recent theoretical attempts at conceiving generalized relationships between genotype and phenotype, with the aim of conceptualizing a theory of form (e.g., Erwin 2000; Leroi 2000; Pigliucci and Kaplan 2006; Pigliucci 2008; Rice 2008; Wilson 2012)
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