Resources mediate selection on module longevity in the field

Abstract

The life histories of modular organisms are complicated, where selection and optimization can occur at both organismal and modular levels. At a modular level, growth, reproduction and death can occur in one module, independently of others. Across modular groups, there are no formal investigations of selection on module longevity. We used two field experiments to test whether selection acts on module longevity in a sessile marine invertebrate and whether selection varies across successional gradients and resource regimes. We found that selection does act on module longevity and that the strength of selection varies with environmental conditions. In environments where interspecific competition is high, selection favours colonies with longer zooid (module) longevity for colonies that initially received high levels of maternal investment. In environments where food availability is high and flow rate is low, selection also favours colonies with longer zooid longevity. These patterns of selection provide partial support for module longevity theory developed for plants. Nevertheless, that selection on module longevity is so context-dependent suggests that variation in module longevity is likely to be maintained in this system.

Resource level modifies heatwave responses in the freshwater snail Lymnaea stagnalis

“…In addition to its potential ecological effects, the condition‐dependence of organisms' heatwave responses could influence evolutionary processes relevant to the ability of natural populations to adapt to climate change. This is because both the form and strength of selection (Monro et al., 2010; Svanfeldt et al., 2018) and the expression of genetic variation (i.e., evolutionary potential) in phenotypic traits subject to selection (Saltz et al., 2017; Valdar et al., 2006) can be condition dependent. Among‐individual variation in organismal resource levels could increase variation in phenotypic responses to high temperatures and their fitness consequences, thus strengthening heatwave‐mediated selection in organisms.…”