Interaction of temperature and an environmental stressor: Moina macrocopa responds with increased body size, increased lifespan, and increased offspring numbers slightly above its temperature optimum Antonia Engert a , Shumon Chakrabarti a , Nadine Saul a , Michal Bittner b , Ralph Menzel a , Christian E.W. Steinberg a,⇑ a Humboldt-Universität zu Berlin, Department of Biology, Laboratory of Freshwater and Stress Ecology, Arboretum, 12437 Berlin, Germany b Masaryk University, Research Centre for Toxic Compounds in the Environment, Kamenice 3, 625 00 Brno, Czech Republic highlights " Temperatures below and above 20 °C reduce the antioxidative capacity. " Additions of humic substances (HSs) increase body length. " At 15 and 20 °C, additions of HS decrease mean lifespan. " At 25 °C rising HS-concentration, increase lifespans and offspring numbers. " The mitohormesis hypothesis comprises lifespan, but with Moina it may be extended also to offspring numbers. article info Article history: Received 19 April 2012 Received in revised form 19 October 2012 Accepted 22 October 2012 Available online 1 December 2012 Keywords: Moina macrocopa Humic substances Lifespan Reproduction Oxidative stress Mitohormesis abstract For organisms, temperature is one of the most important environmental factors and gains increasing importance due to global warming, since increasing temperatures may pose organisms close to their environmental tolerance limits and, thus, they may become more vulnerable to environmental stressors. We analyzed the temperature-dependence of the water-soluble antioxidant capacity of the cladoceran Moina macrocopa and evaluated its life trait variables with temperature (15, 20, 25, 30 °C) and humic sub- stance (HS) concentrations (0, 0.18, 0.36, 0.90, 1.79 mM DOC) as stressors. Temperatures below and above the apparent optimum (20 °C) reduced the antioxidative capacity. Additions of HSs increased body length, but decreased mean lifespan at 15 and 20 °C. There was no clear HS-effect on offspring numbers at 15, 20, and 30 °C. At 25 °C with increasing HS-concentration, lifespan was extended and offspring num- bers increased tremendously, reaching 250% of the control. Although the applied HS preparation pos- sesses estrogenic and antiandrogenic activities, a xenohormone mechanism does not seem plausible for the reproductive increase, because comparable effects did not occur at other temperatures. A more convincing explanation appears to be the mitohormesis hypothesis which states that a certain increase of reactive oxygen production leads to improved health and longevity and, with Moina, also to increased offspring numbers. Our results suggest that at least with the eurythermic M. macrocopa, a temperature above the optimum can be beneficial for several life trait variables, even when combined with a chemical stressor. Temperatures approximately 10 °C above its optimum appear to adversely affect the lifespan and reproduction of M. macrocopa. This indicates that this cladoceran species seems to be able to utilize temperature as an ecological resource in a range slightly above its thermal optimum. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Climatic parameters with temperature belong to the most important environmental factors influencing all biological pro- cesses, such as reproduction, growth, migration patterns, and phe- nology, particularly in ectothermic animals (Lushchak, 2011). Temperature structures the distribution of taxa and shapes com- munities (Daufresne et al., 2009; Yvon-Durocher et al., 2011). As a result of global warming, this abiotic factor has gained increasing importance and consideration as an ecological driving force (Brucet et al., 2010). A central belief in ecophysiology is that organisms liv- ing under conditions close to their environmental tolerance limits appear to be most vulnerable to additional stressors (Heugens 0045-6535/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2012.10.099 ⇑ Corresponding author. Tel.: +49 30 6322 4715; fax: +49 30 6369 446. E-mail address: christian_ew_steinberg@web.de (C.E.W. Steinberg). Chemosphere 90 (2013) 2136–2141 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere