Evolution of alternative insect life histories in stochastic seasonal environments

Abstract

Deterministic seasonality can explain the evolution of alternative life history phenotypes (i.e., life history polyphenism) expressed in different generations emerging within the same year. However, the influence of stochastic variation on the expression of such life history polyphenisms in seasonal environments is insufficiently understood. Here, we use insects as a model and explore (1) the effects of stochastic variation in seasonality and (2) the life cycle on the degree of life history differentiation among the alternative developmental pathways of direct development and diapause (overwintering), and (3) the evolution of phenology. With numerical simulation, we determine the values of development (growth) time, growth rate, body size, reproductive effort, adult life span, and fecundity in both the overwintering and directly developing generations that maximize geometric mean fitness. The results suggest that natural selection favors the expression of alternative life histories in the alternative developmental pathways even when there is stochastic variation in seasonality, but that trait differentiation is affected by the developmental stage that overwinters. Increasing environmental unpredictability induced a switch to a bet‐hedging type of life history strategy, which is consistent with general life history theory. Bet‐hedging appeared in our study system as reduced expression of the direct development phenotype, with associated changes in life history phenotypes, because the fitness value of direct development is highly variable in uncertain environments. Our main result is that seasonality itself is a key factor promoting the evolution of seasonally polyphenic life histories but that environmental stochasticity may modulate the expression of life history phenotypes.

Variation in dung removal by dung beetles in subtropical Atlantic Rainforests

“…The approach of summer conditions linked with an increase in temperature and precipitation is the best seasonal predictor, although its pure explanatory capacity can be considered negligible due to the correlation between this seasonal predictor and those reflecting environmental conditions. This could mean that developmental constraints linked to seasonal changes (Kivelä et al., ) would have a minor influence in dung removal rates in tropical forests, and that the seasonal variation in these rates (Amézquita & Favila, ) is mainly related to the associated environmental and temperature changes (Hernández & Vaz‐de‐Mello, ; da Silva et al., ).…”

“…Similarly, local habitat and climatic variables have also been linked to the activity of dung beetle species and their seasonal and spatial distribution (Numa et al, 2012;Kaspari et al, 2015;da Silva et al, 2018), as all organisms have a thermo-comfort zone and limits of environmental conditions that cannot be surpassed (Angilletta, 2009). Seasonal variation can be another important variable in dung removal by dung beetles, not only because of the associated change in climatic conditions, but also as a consequence of the species specific time required to complete a specific instar (Bull, 1987;Kivel€ a et al, 2016).…”

Seasonal polyphenism in body size and juvenile development of the swallowtail butterfly Papilio xuthus (Lepidoptera: Papilionidae)

“…A shorter larval development time may result in the smaller body size of the spring form. Kivelä et al (2016) also show that environmental uncertainty is the Fig. 2.…”

Developmental plasticity in metabolism but not in energy reserve accumulation in a seasonally polyphenic butterfly

“…Hence, a developmental switch (Nijhout, 2003) resulting in alternative developmental pathways – one leading to overwintering and delayed maturation and one leading to direct maturation – evolves. Because individuals completing their life cycles during the favourable season face different selection pressures compared to overwintering individuals, the evolution of alternative developmental pathways should result in phenotypic divergence (polyphenism) between directly developing and overwintering individuals (Moran, 1992; Kivelä et al, 2013, 2016a).…”