Reproduction in risky environments: the role of invasive egg predators in ladybird laying strategies
Public Library of Science (PLoS)
Reproductive environments are variable and the resources available for reproduction are finite. If reliable cues about the environment exist, mothers can alter offspring phenotype in a way that increases both offspring and maternal fitness ('anticipatory maternal effects'-AMEs). Strategic use of AMEs is likely to be important in chemically defended species, where the risk of offspring predation may be modulated by maternal investment in offspring toxin level, albeit at some cost to mothers. Whether mothers adjust offspring toxin levels in response to variation in predation risk is, however, unknown, but is likely to be important when assessing the response of chemically defended species to the recent and pervasive changes in the global predator landscape, driven by the spread of invasive species. Using the chemically defended two-spot ladybird, Adalia bipunctata, we investigated reproductive investment, including egg toxin level, under conditions that varied in the degree of simulated offspring predation risk from larval harlequin ladybirds, Harmonia axyridis. H. axyridis is a highly voracious alien invasive species in the UK and a significant intraguild predator of A. bipunctata. Females laid fewer, larger egg clusters, under conditions of simulated predation risk (P+) than when predator cues were absent (P-), but there was no difference in toxin level between the two treatments. Among P- females, when mean cluster size increased there were concomitant increases in both the mass and toxin concentration of eggs, however when P+ females increased cluster size there was no corresponding increase in egg toxin level. We conclude that, in the face of offspring predation risk, females either withheld toxins or were physiologically constrained, leading to a trade-off between cluster size and egg toxin level. Our results provide the first demonstration that the risk of offspring predation by a novel invasive predator can influence maternal investment in toxins within their offspring.
S.C. Paul was funded by a Natural Environment Research Council PhD studentship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. JK Pell Consulting is the trading name of author J.K. Pell, who is a self employed science consultant (sole trader) in UK; this author contributed to study design and interpretation, decision to publish and preparation of the manuscript. The specific roles of the authors are articulated in the ‘author contributions’ section.
This is the final version of the article. Available from PLOS via the DOI in this record.
We have made the data for this publication freely available from the University of Exeter Repository: URL http://hdl.handle.net/10871/18252.
Vol. 10, e0139404
PubMed Central ID
Place of publication