Pimiento C et al. (2018), Assessing canalisation of intraspecific variati...

ECB-ART-49967

PeerJ 2018 Jan 01;6:e4899. doi: 10.7717/peerj.4899.

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Assessing canalisation of intraspecific variation on a macroevolutionary scale: the case of crinoid arms through the Phanerozoic.

Pimiento C , Tang KL , Zamora S , Klug C , Sánchez-Villagra MR .

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Clades that represent a new 'Bauplan' have been hypothesised to exhibit more variability than more derived clades. Accordingly, there is an expectation of greater variation around the time of the origin of a clade than later in its evolutionary history. This 'canalisation' has been tested in terms of morphological disparity (interspecific variation), whereas intraspecific variation in macroevolution is rarely studied. We analysed extensive data of brachial counts in crinoid populations from the Ordovician to the Recent to test for canalisation in morphological intraspecific variation. Our results show no support for the canalisation hypothesis through the Phanerozoic. This lack of pattern is maintained even when considering crinoid subclades separately. Our study is an example of the lack of universality in such macroevolutionary patterns both in terms of organisms and in terms of modules within them. It is also an example on the challenges and limitations of palaeontological studies of macroevolutionary processes.

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	Figure 1. Intraspecific variation in primibrachials of Cupulocrinus jewetti.Crinoid Cupulocrinus jewetti (USNM S2249) from the Ordovician of Kentucky (USA) showing intraspecific variation in the number of primibrachials. (A) Camera lucida drawing of specimen figured in (B) with indication of anatomical parts (only two frontal arms coloured). (B–D) Different specimens of C. jewetti showing variation in the number of primibrachials, ranging from three to five per branch. All scale bars represent 1 cm. Photographer: S Zamora.
	Figure 2. Relationship between intraspecific variation and sampling size.(A) Intraspecific variation is measured as species’ coefficient of variation (CV) and sample size is regarded as the number of specimens per species (adjusted R2 = −0.01, p-value: 0.9). (B) Intraspecific variation is measured as mean CV per time bin and sample size is regarded as the number of species per time bin (adjusted R2 = 0.12, p-value: 0.18).
	Figure 3. Crinoid intra- and inter-specific variation throughout the Phanerozoic.(A) Intraspecific variation measured as the coefficient of variation (CV = standard deviation/mean) through time bin. Black solid line shows the linear regression (R-squared = 0.10; p-value = 0.001). Grey polygon denotes the 95% confidence intervals of the linear regression. Upper dashed line shows the linear regression excluding invariant species (CV = 0). Lower dashed line shows the linear regression excluding the extremely high CV values of the Carboniferous (323 Ma). Red curve shows the local regression fitting (LOESS), and the red polygon shows its confidence intervals. (B) Intraspecific variation (CV) trajectory over time. Bars represent standard errors on the mean. Inserted table show support of three evolutionary models tested (C). Interspecific variation measured as the mean pairwise character (=range of the number of primibrachials) distance (MPD) between species over time. Time bins are shown as mid age (see Methods).

References [+] :

Baumiller, Testing predator-driven evolution with Paleozoic crinoid arm regeneration. 2004, Pubmed, Echinobase