Trait–fitness associations do not predict within-species phenotypic evolution over 2 million years
Description
Long-term patterns of phenotypic change are the cumulative results of tens
of thousands to millions of years of evolution. Yet, empirical and theoretical
studies of phenotypic selection are largely based on contemporary populations.
The challenges in studying phenotypic evolution, in particular
trait–fitness associations in the deep past, are barriers to linking microand
macroevolution. Here, we capitalize on the unique opportunity offered
by a marine colonial organism commonly preserved in the fossil record to
investigate trait–fitness associations over 2 Myr. We use the density of
female polymorphs in colonies of Antarctothoa tongima as a proxy for fecundity,
a fitness component, and investigate multivariate signals of trait–fitness
associations in six time intervals on the backdrop of Pleistocene climatic
shifts. We detect negative trait–fitness associations for feeding polymorph
(autozooid) sizes, positive associations for autozooid shape but no particular
relationship between fecundity and brood chamber size. In addition,
we demonstrate that long-term trait patterns are explained by palaeoclimate
(as approximated by ∂18O), and to a lesser extent by ecological interactions
(i.e. overgrowth competition and substrate crowding). Our analyses show
that macroevolutionary outcomes of trait evolution are not a simple
scaling-up from the trait–fitness associations.
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Di Martino & Liow, 2021.pdf
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