Abstract
Organisms that regularly encounter stressful environments are expected to use cues to develop an appropriate phenotype. Water fleas (Daphnia spp.) are exposed to toxic cyanobacteria during seasonal algal blooms, which reduce growth and reproductive investment. Because generation time is typically shorter than the exposure to cyanobacteria, maternal effects provide information about the local conditions subsequent generations will experience. Here, we evaluate if maternal effects in response to microcystin, a toxin produced by cyanobacteria, represent an inheritance system evolved to transmit information in Daphnia magna. We exposed mothers as juveniles and/or as adults, and tested the offspring's fitness in toxic and non‐toxic environments. Maternal exposure until reproduction reduced offspring fitness, both in the presence and in the absence of toxic cyanobacteria. However, this effect was accompanied by a small positive fitness effect, relative to offspring from unexposed mothers, in the presence of toxic cyanobacteria. This effect was mainly elicited in response to maternal exposure to toxic cyanobacteria early in life and less so during reproduction. None of these effects were explained by changes in egg size. A meta‐analysis using our and others’ experiments suggests that the adaptive value of maternal effects to cyanobacteria exposure is weak at best. We suggest that the beneficial maternal effect in our study is an example of phenotypic accommodation spanning generations, rather than a mechanism evolved to transmit information about cyanobacteria presence between generations.
Highlights
Many organisms regularly encounter conditions that are harmful to their survival or reproduction
Organisms that encounter stressful conditions will often respond in ways that ameliorate some of the negative effects
Evolution of maternal effects is subject to similar considerations; counteracting negative effects by anticipat‐ ing stressful conditions experienced by the offspring (Uller, 2008)
Summary
Females that reproduce under stressful conditions may provide insufficient re‐ sources for their offspring or disrupt their development in other ways, for example, via passive transmission of toxins to the egg or across the placenta (Crump & Trudeau, 2009; Schwindt, 2015; Smith et al, 2007; Tsui & Wang, 2004) Such changes in resource provi‐ sioning or non‐adaptive transfer of harmful compounds neverthe‐ less carry information about the local environment. If conditions are sufficiently recurrent, natural selection should reduce negative effects and strengthen positive effects This may eventually lead to the evolution of a “detection‐based” inher‐ itance systems (sensu Shea, Pen, & Uller, 2011) by which parental responses to the local environment allow reliable transmission of in‐ formation without imposing costs on the offspring (Badyaev & Uller, 2009; McNamara et al, 2016; Uller, 2012). This would be supported if offspring are severely negatively affected by maternal exposure, and any positive effect would be consistent with passing on tolerance built up through pro‐ longed maternal exposure, passively
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