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 reduces 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 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.
Maternal effects experiments
Data from all 5 maternal effects experiments. eid = experiment number (1-5), iid = individual identity, gid = genotype identity, trt = treatment (C = control, CC = control/control, CM = control/full, E = early, EC = early/control, EM = early/full, F = full, FC = full/control, FM = full/full, L=late, LC = late/control, LM = late/full, M = full, MC = full/control, MM = full/full) mid = mother identity, ar1 = age at first brood, ar2 = age at second brood, ar3 = age at third brood, bs1 = size first brood, bs2 = size second brood, bs3 = size third brood, txp = toxicity as the proportion of cyanobacteria in the food (measured as the fraction of total organic carbon weight per liter medium), txc = toxicity as the concentration of cyanobacteria (measured as mg of organic carbon per liter of medium), txm = toxicity as the concentration of microcystin (ug/L), gr2 = fitness estimate after 2 broods, gr3 = fitness estimate after 3 broods.
Radersma_et_al_experimental_data.csv
Data from the meta-analysis
Data collected from 6 studies and our 5 maternal effects experiments. study = study identity (see figure 4, mean text), species = species of Daphnia, clone = identity of clone line, tox.prop = toxicity as the proportion of cyanobacteria in the food (measured as the fraction of total organic carbon weight per liter medium), tox.conC = toxicity as the concentration of cyanobacteria (measured as mg of organic carbon per liter of medium), tox.conM = toxicity as the concentration of microcystin (ug/L), trait = description of trait, tr.cat = trait category (see figure 4 in main text), stat.type = type of statistic (t = t-test, z = z-test, OD = odd ratio), stat = value of statistic, df = degrees of freedom, direction = direction of effect (C = offspring from control mothers have higher mean, M = offspring from exposed mothers have higher mean), mnC = mean offspring control mothers, sdC = standard deviation offspring control mothers, seC = standard error offspring control mothers, nC = sample size offspring from control mothers, mnM = mean offspring exposed mothers, sdM = standard deviation offspring exposed mothers, seM = standard error offspring exposed mothers, nM = sample size offspring from exposed mothers, pooled.sd = pooled standard deviation, cohens.d = Cohen’s d, var.cd = variance for Cohen’s d, hedges.g = Hedges’ g, var.hg = variance for Hedges’ g, effect = effect size (Hedges’ g corrected for the direction of the effect), sid = study identity number, cid = clone identity number, tid = trait class identity number.
Radersma_et_al_meta-analysis.csv
Egg sizes - data for mothers
Data of the mothers for which egg sizes were measured. iid = individual identity of the mother, tox = treatment of the mother (0 = non-toxic, 1 = toxic), gid = genotype identity, avt = z-score for the average time interval between the first and second, and second and third brood, abs = z-score for the average size of the second and third brood.
Radersma_et_al_egg_size-mothers.csv
Egg sizes - egg size measurements
Data of the egg size measurements. iid = individual identity of the mother, mid = row number of the mother in the data file with mothers, are = area of the egg (mm^2), per = perimeter of egg (mm), mxr = semi-major axis (mm), mnr = semi-minor axis (mm).
Radersma_et_al_egg_size-egg_size_measurements.csv