A global synthesis of offspring size variation, its eco‐evolutionary causes and consequences

Abstract

Offspring size is a key functional trait that can affect all phases of the life history, from birth to reproduction, and is common to all the Metazoa. Despite its ubiquity, reviews of this trait tend to be taxon‐specific. We explored the causes and consequences of offspring size variation across plants, invertebrates and vertebrates. We find that offspring size shows clear latitudinal patterns among species: fish, amphibians, invertebrates and birds show a positive covariation in offspring size with latitude; plants and turtles show a negative covariation with latitude. We highlight the developmental window hypothesis as an explanation for why plants and turtles show negative covariance with latitude. Meanwhile, we find evidence for stronger, positive selection on offspring size at higher latitudes for most animals. Offspring size also varies at all scales of organization, from populations through to broods from the same female. We explore the reasons for this variation and suspect that much of this variation is adaptive, but in many cases, there are too few tests to generalize. We show that larger offspring lose relatively less energy during development to independence such that larger offspring may have greater net energy budgets than smaller offspring. Larger offspring therefore enter the independent phase with relatively more energy reserves than smaller offspring. This may explain why larger offspring tend to outperform smaller offspring but more work on how offspring size affects energy acquisition is needed. While life‐history theorists have been fascinated by offspring size for over a century, key knowledge gaps remain. One important next step is to estimate the true energy costs of producing offspring of different sizes and numbers. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13099/suppinfo is available for this article.

The association between mitochondrial genetic variation and reduced colony fitness in an invasive wasp

“…Larger, high‐quality queens are more successful in the colony founding stage, have more fat reserves to survive winter hibernation (Archer, ; Harris & Beggs, ) and may represent a trait that is beneficial during range expansion and invasion. Plasticity in offspring size is found in many taxa: mothers can adjust offspring size to maximize fitness (Marshall, Pettersen, & Cameron, ). Competition has been shown to affect quality as well as quantity of workers and new queens produced by social insect colonies (Beggs et al, ; Tibbetts & Curtis, ).…”

Can competitive asymmetries maintain offspring size variation? A manipulative field test

“…; Marshall et al. ). For example, two offspring can differ fivefold in the resources they receive from the same parent (Lips ; Turnbull et al.…”

“…The size of offspring at independence from their parents reflects this provisioning—larger offspring receive more parental resources than smaller offspring (reviewed in Bernardo ; Marshall et al. ; Mousseau and Dingle ). Offspring vary remarkably in size across time and space, and all scales of organization (reviewed in Krist ; Leishman et al.…”

“…; Krist ; Marshall et al. ). Overall then, offspring‐size effects are ubiquitous, pervasive, and of fundamental interest to life‐history theory.…”

“…Once feeding commences, larger offspring typically access more resources than smaller offspring (Leishman ; Martin and Pfennig ; Stanton ), though it is unclear whether they access disproportionately more resources (Marshall et al. )—a requirement of asymmetric competition (Weiner ). Furthermore, while larger individuals acquire more resources, smaller individuals often have lower resource requirements and may tolerate resource depletion better than their larger neighbors (Persson ).…”