Abstract
BackgroundMorphological evolution may be impacted by both intrinsic (developmental, constructional, physiological) and extrinsic (ecological opportunity and release) factors, but can intrinsic factors be altered by adaptive evolution and, if so, do they constrain or facilitate the subsequent diversification of biological form? Bats underwent deep adaptive divergences in skull shape as they evolved different sensory modes; here we investigate the potential impact of this process on two intrinsic factors that underlie morphological variation across organisms, allometry, and modularity.ResultsWe use comparative phylogenetic and morphometric approaches to examine patterns of evolutionary allometry and modularity across a 3D geometric morphometric dataset spanning all major bat clades. We show that allometric relationships diverge between echolocators and visually oriented non-echolocators and that the evolution of nasal echolocation reshaped the modularity of the bat cranium.ConclusionsShifts in allometry and modularity may have significant consequences on the diversification of anatomical structures, as observed in the bat skull.
Highlights
Morphological evolution may be impacted by both intrinsic and extrinsic factors, but can intrinsic factors be altered by adaptive evolution and, if so, do they constrain or facilitate the subsequent diversification of biological form? Bats underwent deep adaptive divergences in skull shape as they evolved different sensory modes; here we investigate the potential impact of this process on two intrinsic factors that underlie morphological variation across organisms, allometry, and modularity
We predict that the evolution of nasal echolocation reshaped the modularity of the bat cranium as the rostrum took on the new role in sound transmission [37]
Morphological and allometric variation across echolocation modes Without phylogenetic correction, there is a significant relationship between skull size and shape across bats, with size explaining a moderate amount of shape variation (R2: cranium = 18.3%, mandible = 22.3%)
Summary
Morphological evolution may be impacted by both intrinsic (developmental, constructional, physiological) and extrinsic (ecological opportunity and release) factors, but can intrinsic factors be altered by adaptive evolution and, if so, do they constrain or facilitate the subsequent diversification of biological form? Bats underwent deep adaptive divergences in skull shape as they evolved different sensory modes; here we investigate the potential impact of this process on two intrinsic factors that underlie morphological variation across organisms, allometry, and modularity. While the commonly studied ontogenetic allometry describes shape change with growth over an organism’s life, size-shape relationships can be identified at similar age classes across species [17,18,19]. These trends in “evolutionary allometry” may be conserved across highly disparate clades—for example, a pattern of rostrum elongation with larger body size (termed “cranial evolutionary allometry”, CREA) is found across numerous mammalian orders [20,21,22]. Lineages experiencing evolutionary allometry might become constrained in the use of size-mediated ecological resources [19], or exhibit mismatches between performance and realized niches [23]
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