Correlational selection on size and development time is inconsistent across early life stages
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Correlational selection on size and development time is inconsistent across early life stages Evatt Chirgwin1 · Keyne Monro1 Received: 29 January 2020 / Revised: 14 July 2020 / Accepted: 4 August 2020 © Springer Nature Switzerland AG 2020
Abstract Size and development time are universally important traits. Yet evolutionary trends in development time are often viewed as allometric and physiological by-products of initial size, when life-history theory predicts that both traits are targets of selection and evolve adaptively through opposing effects on fitness. Surprisingly, this prediction has rarely been tested by disentangling the direct and indirect effects of size and development time on fitness, as necessary to understand selection on each trait. Here, in a marine external fertiliser that provides novel scope for such tests, we measure directional, quadratic, and correlational selection acting on early size (of embryos and post-hatch larvae) and development time (from fertilisation to hatching) through survival of juveniles in the field. We find little directional selection acting on traits during this selective episode. Rather, selection is primarily correlational, targeting combinations of development time and post-development size in a way that acts against their already-weak positive correlation, and could eventually drive a negative correlation between them if persistent enough. Lack of correlational selection on combinations of embryo size and development time, in contrast, suggests that physiological or allometric constraints more likely explain their positive association. Hence, neither life-history theory nor principles of allometry and physiology alone may predict the evolution of size and development time, warranting greater appreciation of the tension between adaptive and non-adaptive explanations for evolutionary trends in these traits. Keywords Evolution · Phenotypic selection · Life history theory · Offspring size · Biological rates · Marine invertebrates
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1068 2-020-10065-x) contains supplementary material, which is available to authorized users. * Evatt Chirgwin [email protected] 1
School of Biological Sciences, Monash University, Melbourne, VIC, Australia
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Evolutionary Ecology
Introduction Whether microevolutionary processes (e.g., selection, inheritance) within populations can explain macroevolutionary patterns at larger scales remains a key problem in evolutionary biology (Arnold et al. 2001; Futuyma 2010). Among species, size is often correlated with biological rates and times at a given temperature, and is positively correlated with development time from one life stage to the next (Pauly and Pullin 1988; Gillooly et al. 2002; but see Church et al. 2019). Consequently, variation in species’ development times has been declared the evolutionary by-product of allometric and physiological constraints arising from variation in size (Gillooly 2000; Gillooly e
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