Multivariate structural statistics in natural history

Valen, Leigh Van

doi:10.1016/0022-5193(74)90053-8

Cited by 140 publications

(120 citation statements)

References 9 publications

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“…Morphological disparity was calculated for each fossil population and for the modern species using the sum and the product of the variances on PC1 and PC2 (48,49).…”

Section: Methodsmentioning

confidence: 99%

Morphological stasis in an ongoing gastropod radiation from Lake Malawi

Bocxlaer

Hunt²

2013

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

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Evolutionary processes leading to adaptive radiation regularly occur too fast to be accurately recorded in the fossil record but too slowly to be readily observed in living biota. The study of evolutionary radiations is thereby confronted with an epistemological gap between the timescales and approaches used by neontologists and paleontologists. Here we report on an ongoing radiation of extant Bellamya species (n = 4) from the African Rift Lake Malawi that provides an unusual opportunity to bridge this gap. The substantial molecular differentiation in this monophyletic Bellamya clade has arisen since Late Pleistocene megadroughts in the Malawi Basin caused by climate change. Morphological timeseries analysis of a high-resolution, radiocarbon-dated sequence of 22 faunas spanning the Holocene documents stasis up to the middle Holocene in all traits studied (shell height, number of whorls, and two variables obtained from geometric morphometrics). Between deposition of the last fossil fauna (∼5 ka) and the present day, a drastic increase in morphological disparity was observed (3.7-5.8 times) associated with an increase in species diversity. Comparison of the rates of morphological evolution obtained from the paleontological time-series with phylogenetic rates indicates that the divergence in two traits could be reconstructed with the slow rates documented in the fossils, that one trait required a rate reduction (stabilizing selection), and the other faster rates (divergent selection). The combined paleontological and comparative approach taken here allows recognition that morphological stasis can be the dominant evolutionary pattern within species lineages, even in very young and radiating clades.speciation | rates of evolution | punctuated equilibrium | Viviparidae E volutionary radiations are potentially responsible for much of the ecological and phenotypic diversity on earth (1, 2). Beyond rapid speciation through lineage splitting, radiations are often characterized by exceptional diversification into a variety of ecological niches, with divergence, at least in traits under selection, regularly occurring very rapidly (e.g., refs. 3 and 4). However, the controls on diversification may be complex and include historical contingencies, as well as ecological, genetic, and developmental factors (5, 6). One major challenge is that processes leading to evolutionary radiations occur regularly too fast to be accurately recorded in the fossil record where temporal resolutions finer than ∼10 4 y are unusual, but perhaps still too crude to see speciation and radiation unfold. On the other hand, speciation generally occurs too slowly to be readily observed in living biota, resulting in an "epistemological gap" between the timescales and approaches used by neontologists and those that paleontologists adopt for the study of organismal evolution (7,8). Moreover, it can be difficult to assess the adaptive significance of phenotypic variation among fossil taxa (e.g., ref. 9), partly because ecological, behavioral, physiological, ...

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“…Morphological disparity was calculated for each fossil population and for the modern species using the sum and the product of the variances on PC1 and PC2 (48,49).…”

Section: Methodsmentioning

confidence: 99%

Morphological stasis in an ongoing gastropod radiation from Lake Malawi

Bocxlaer

Hunt²

2013

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

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“…Complexity is often defined as the number of independent parameters necessary to describe an organism's morphology (58)(59)(60)(61). According to this definition, functional specialization then clearly corresponds to an increase in complexity because once θ 1 ≠ θ 2 , two parameters instead of one are necessary to describe the phenotype of the two modules.…”

Section: Discussionmentioning

confidence: 99%

Evolution of functional specialization and division of labor

Rueffler

Hermisson²,

Wagner³

2012

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

157

170

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Division of labor among functionally specialized modules occurs at all levels of biological organization in both animals and plants. Well-known examples include the evolution of specialized enzymes after gene duplication, the evolution of specialized cell types, limb diversification in arthropods, and the evolution of specialized colony members in many taxa of marine invertebrates and social insects. Here, we identify conditions favoring the evolution of division of labor by means of a general mathematical model. Our starting point is the assumption that modules contribute to two different biological tasks and that the potential of modules to contribute to these tasks is traded off. Our results are phrased in terms of properties of performance functions that map the phenotype of modules to measures of performance. We show that division of labor is favored by three factors: positional effects that predispose modules for one of the tasks, accelerating performance functions, and synergistic interactions between modules. If modules can be lost or damaged, selection for robustness can counteract selection for functional specialization. To illustrate our theory we apply it to the evolution of specialized enzymes coded by duplicated genes.complexity | fitness landscape | saddle point

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“…This is equivalent to the average sum of squares of the Cartesian distances of the values in each dimension from their joint mean (Van Valen, 1974). It is referred to as the total variance, as opposed to the generalized variance, which is the determinant of the covariance matrix for the variables.…”

Section: Introductionmentioning

confidence: 99%

Test of association of morphological variation with heterozygosity in the snail Cepaea nemoralis

Cook

Gao

1996

Heredity

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It has been suggested that the polymorphism for shell colour and pattern in Cepaea may be unrelated to the visible appearance of the shells, but maintained by heterosis or heterozygote advantage. A possible way to test this supposition is to examine whether phenotypic variance is lower in the morph exhibiting the dominant phenotype than in that with the recessive phenotype. This has been tested in two samples of shells involving totals of 1792 and 5423 individuals, respectively. Overall, there is a significantly greater variance in the recessive than the dominant class (P <0.05). Correlation between measurements on the same shell was also examined. No evidence of difference between phenotypes was found. If the difference in variance is real it may indicate either: (i) that visible appearance is not important and the polymorphism is maintained by a heterozygous balance; or (ii) evolution of such a balance in a polymorphism maintained over a long time span by selection acting on visible attributes of the shells.

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Multivariate structural statistics in natural history

Cited by 140 publications

References 9 publications

Morphological stasis in an ongoing gastropod radiation from Lake Malawi

Morphological stasis in an ongoing gastropod radiation from Lake Malawi

Evolution of functional specialization and division of labor

Test of association of morphological variation with heterozygosity in the snail Cepaea nemoralis

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