Abandoning the ship using sex, dispersal or dormancy: multiple escape routes from challenging conditions

Abstract

Natural populations often experience environments that vary across space and over time, leading to spatio-temporal variation of the fitness of a genotype. If local conditions are poor, organisms can disperse in space (physical movement) or time (dormancy, diapause). Facultatively sexual organisms can switch between asexual and sexual reproduction, and thus have a third option available to deal with maladaptedness: they can engage in sexual reproduction in unfavourable conditions (an 'abandon-ship' response). Sexual reproduction in facultatively sexual organisms is often coupled with dispersal and/or dormancy, while bet-hedging theory at first sight predicts sex, dispersal and dormancy to covary negatively, as they represent different escape mechanisms that could substitute for each other. Here we briefly review the observed links between sex, dormancy and dispersal, and model the expected covariation patterns of dispersal, dormancy and the reproductive mode in the context of local adaptation to spatio-temporally fluctuating environments. The correlations between sex, dormancy and dispersal evolve differently within species versus across species. Various risk-spreading strategies are not completely interchangeable, as each has dynamic consequences that can feed back into the profitability of others. Our results shed light on the discrepancy between previous theoretical predictions on covarying risk-spreading traits and help explain why sex often associates with other means of escaping unfavourable situations.This article is part of the theme issue 'Linking local adaptation with the evolution of sex differences'.

Transgenerational Plasticity and Bet-Hedging: A Framework for Reaction Norm Evolution

“…This ignores that CBH and DBH are often nearly equally suited strategies to cope with environmental uncertainty (Starrfelt and Kokko, 2012), i.e., the shape and curvature of the geometric mean fitness curve ( Figure 1A) requires further consideration. Secondly, we have restricted our arguments to binary transgenerationally inherited traits, as these are commonly treated both empirically (Venable, 2007;Maxwell and Magwene, 2017;Scholl et al, 2020) and theoretically (Cohen, 1966;Halkett et al, 2004;Starrfelt and Kokko, 2012;Kivelä et al, 2016;Gerber and Kokko, 2018). For continuous traits, e.g., offspring size (Marshall et al, 2008), our calculations may not apply, because AMM, DBH and CBH need not lie on a linear gradient (i.e., intermediate trait values need not incur highest trait variance).…”

“…Bet-hedging can be achieved by avoiding risky investments (conservative bet-hedging), or by spreading the risk among one's offspring (diversified bet-hedging), i.e., producing offspring with varying phenotypes (Seger and Brockmann, 1987;Starrfelt and Kokko, 2012). Although empirical evidence is difficult to obtain (Simons, 2011), bet-hedging is a likely explanation for high trait variance or unexpected trait means in many systems, such as the seed dormancy of desert annuals (Cohen, 1966), diapausing strategies of insects (Hopper, 1999) and annual killifish (Furness et al, 2015), wing dimorphisms (Grantham et al, 2016), facultative sexual reproduction (Gerber and Kokko, 2018), dispersal and partial migration (Goossens et al, 2020).…”

When Synchrony Makes the Best of Both Worlds Even Better: How Well Do We Really Understand Facultative Sex?

“…When viewed across a broad-enough taxonomic lens, sex also does not necessarily associate with the production of males. Sexual conflict, where males benefit from mating while females might not, can complicate the maintenance of facultative sex (Gerber and Kokko 2016;Burke and Bonduriansky 2017), but this argument only applies to species with males (anisogamy). Science has made some progress toward understanding why anisogamy associates with being large and multicellular (Lehtonen and Parker 2019); why this should also often associate with obligate sex is an obvious followup question.…”

Sex Allocation Theory for Facultatively Sexual Organisms Inhabiting Seasonal Environments: The Importance of Bet Hedging

“…While our model (and that of Spencer et al 2001) is silent on why this link exists, an obvious next question is whether there is an adaptive reason to expect dormant forms to be sexually produced, while directly developing offspring result from parthenogenesis-especially because some exceptions exist (for an obligately asexual Daphnia lineage that can produce dormant stages asexually, see Innes et al 2000; bdelloid rotifers behave similarly; see Caprioli and Ricci 2001). We address this question by relaxing the assumption of a preexisting constraint (Gerber and Kokko 2018).…”