Morphological Integration, Evolutionary Constraints, and Extinction: A Computer Simulation-Based Study

Villmoare, Brian

doi:10.1007/s11692-012-9186-3

Cited by 29 publications

(32 citation statements)

References 42 publications

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“…A consequence of this mechanism is that skull morphology is highly constrained. Interestingly, animals that demonstrate high levels of integration are less able to respond to shifting selective pressures because they are locked in to a particular dimension of variation (47,49): in this case, size. Consequently, raptors may be particularly vulnerable if changing environmental conditions result in an adaptive peak that they cannot reach by simply sliding along their allometric trajectory.…”

Section: Discussionmentioning

confidence: 99%

The shapes of bird beaks are highly controlled by nondietary factors

Bright

Marugán‐Lobón

Cobb

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

209

274

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Bird beaks are textbook examples of ecological adaptation to diet, but their shapes are also controlled by genetic and developmental histories. To test the effects of these factors on the avian craniofacial skeleton, we conducted morphometric analyses on raptors, a polyphyletic group at the base of the landbird radiation. Despite common perception, we find that the beak is not an independently targeted module for selection. Instead, the beak and skull are highly integrated structures strongly regulated by size, with axes of shape change linked to the actions of recently identified regulatory genes. Together, size and integration account for almost 80% of the shape variation seen between different species to the exclusion of morphological dietary adaptation. Instead, birds of prey use size as a mechanism to modify their feeding ecology. The extent to which shape variation is confined to a few major axes may provide an advantage in that it facilitates rapid morphological evolution via changes in body size, but may also make raptors especially vulnerable when selection pressures act against these axes. The phylogenetic position of raptors suggests that this constraint is prevalent in all landbirds and that breaking the developmental correspondence between beak and braincase may be the key novelty in classic passerine adaptive radiations.geometric morphometrics | integration | allometry | birds | modularity T he avian beak offers a classic example of adaptation to feeding ecology, with beak morphology frequently considered to represent evolutionary adaptation to specialized trophic niches [e.g., Galápagos finches (1), Hawaiian honeycreepers (2), and Madagascan vangas (3)]. Despite this axiom, we lack quantitative data on the degree to which skull and beak morphology is influenced not only by feeding ecology, but also by other sources of variation or constraint (4). Although the beak is often seen as the target of selection mechanisms closely allied to feeding ecology, such as prey type, feeding style, or beak use, evidence also suggests that beak morphology and variation may be constrained by a number of other factors, including evolutionary history (phylogeny) and development on the component parts of the entire skull. Breakthrough experiments in molecular genetics have shown that the mechanisms driving beak shape variation encompass modifications to the timing of expression of conserved developmental pathways (5-9), resulting in beak diversity described by a few relatively simple geometric transformations (10). However, pleiotropic associations between different skull structures can also contribute to the shape of the avian beak (11), and Sonic hedgehog signaling from the forebrain also relates to the spatial organization of, and changes to, face and beak shape (12)(13)(14). Furthermore, assessments of bird skull phenotypic variation suggest that beak morphology may evolve cohesively with cranial morphology (15,16). Size is also an important consideration when assessing morphological variation. Larger animals gene...

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Section: Discussionmentioning

confidence: 99%

The shapes of bird beaks are highly controlled by nondietary factors

Bright

Marugán‐Lobón

Cobb

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

209

274

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“…By relaxing constraint, hybridization may first facilitate the expansion to new areas in morphospace in response to ecological release, and second adaptive diversification in response to new diversifying selection in such environments. Hybrid populations may thus be able to evolve along a wider variety of morphological trajectories and respond more quickly to novel selection regimes (Grant & Grant, 1994;Deng et al, 1999;Young et al, 2010;Hallgrimsson et al, 2012;Villmoare, 2013).…”

Section: Discussionmentioning

confidence: 99%

Relaxed trait covariance in interspecific cichlid hybrids predicts morphological diversity in adaptive radiations

Selz

Lucek

Young

et al. 2013

J of Evolutionary Biology

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The process of adaptive radiation involves multiple events of speciation in short succession, associated with ecological diversification. Understanding this process requires identifying the origins of heritable phenotypic variation that allows adaptive radiation to progress. Hybridization is one source of genetic and morphological variation that may spur adaptive radiation. We experimentally explored the potential role of hybridization in facilitating the onset of adaptive radiation. We generated first-and second-generation hybrids of four species of African cichlid fish, extant relatives of the putative ancestors of the adaptive radiations of Lakes Victoria and Malawi. We compared patterns in hybrid morphological variation with the variation in the lake radiations. We show that significant fractions of the interspecific morphological variation and the major trajectories in morphospace that characterize whole radiations can be generated in second-generation hybrids. Furthermore, we show that covariation between traits is relaxed in secondgeneration hybrids, which may facilitate adaptive diversification. These results support the idea that hybridization can provide the heritable phenotypic diversity necessary to initiate adaptive radiation.

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“…The evolutionary simulations were based on viability selection, where the probability of individuals surviving and contributing to the next generation depends on their distance to an adaptive peak, with individuals further away more likely to be eliminated from the population (Salazar‐Ciudad and Marin‐Riera ; Villmoare ; Rolian ). As a proxy for evolvability, the simulations quantified the time taken for a given species to evolve toward the mean phenotype of every other species, including the reciprocal of a given pair (i.e., gorilla‐like to human‐like and vice‐versa).…”

Section: Methodsmentioning

confidence: 99%

“…; Jones et al. ; Salazar‐Ciudad and Marin‐Riera ; Villmoare ; Rolian ) to limb bone lengths in a functionally diverse group of catarrhine primates (Old World monkeys, apes, and humans), in order to determine how intrinsic factors such as morphological integration, limb specialization, and body size impact the rate at which species can evolve new morphologies, and the likelihood of going extinct in response to selection.…”

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confidence: 99%

Ecomorphological specialization leads to loss of evolvability in primate limbs*

Rolian

2020

Evolution

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Primate limb morphology is often described as either generalized, that is, suited to a range of locomotor and positional behaviors, or specialized for unique locomotor behaviors such as brachiation or bipedalism. The evolution of highly specialized limb morphology may result in loss of evolvability, that is, in a decreased capacity of the locomotor skeleton to evolve in response to selection towards alternative ecomorphological niches. Using evolutionary simulations, I show that the highly specialized limb anatomy of hominoids is associated with a significant loss of evolvability, defined as the number of generations to reach alternative adaptive peaks, and in parallel an increased risk of extinction, particularly in simulated evolution toward generalized quadrupedal limb proportions. Loss of evolvability in apes and humans correlates with three factors: (1) decreased correlation among limb bone lengths(i.e., integration), which slows the rate of change along lines of least evolutionary resistance; (2) limb specialization, which places apes and humans in relatively remote areas of morphospace; and (3) increased skeletal size as a proxy for body size. Thus, locomotor over-specialization can lead to evolutionary dead-ends that significantly increase the probability of hominoid populations going extinct before evolving new adaptive morphologies. K E Y W O R D S : Fitness, macroevolution, models/simulations, morphological evolution, quantitative genetics.Primates have diverse limb proportions, reflecting a range of locomotor modes and ecological niches (Fleagle 1999;Fleagle and Lieberman 2015). Primates can be divided into two broad groups based on limb ecomorphology: (1) a group of generalized arboreal and terrestrial quadrupeds in which the fore-and hindlimbs are approximately equal in length, and (2) a phylogenetically disparate group in which derived limb proportions are associated with specialized modes of locomotion. For example, vertical clinging and leaping strepsirrhines (e.g., lemurs, galagos) have longer hind limbs relative to forelimbs, which may improve locomotor performance in leaping across substrate gaps (Legreneur et al. 2010). Among apes, brachiating gibbons and siamangs have much longer forelimbs than hindlimbs, which is hypothesized to facilitate their ricochetal suspensory locomotion, while humans have elongated hindlimbs that reduces the energetic cost of habitual bipedal locomotion (Steudel-Numbers and Tilkens 2004;Pontzer et al. 2009) . * This article corresponds to Olivia, S. Limb specialization reduces evolvability. Evolution. https://doi.

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Morphological Integration, Evolutionary Constraints, and Extinction: A Computer Simulation-Based Study

Cited by 29 publications

References 42 publications

The shapes of bird beaks are highly controlled by nondietary factors

The shapes of bird beaks are highly controlled by nondietary factors

Relaxed trait covariance in interspecific cichlid hybrids predicts morphological diversity in adaptive radiations

Ecomorphological specialization leads to loss of evolvability in primate limbs*

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