BRIEF COMMUNICATION
doi:10.1111/j.1558-5646.2011.01240.x
PREDATOR-INDUCED DEFENSE MAKES DAPHNIA MORE VULNERABLE TO PARASITES
Mingbo Yin,1 Christian Laforsch,1,2 Jennifer N. Lohr,1,3 and Justyna Wolinska1,4 1Ludwig-Maximilians University Munich, Department Biology II, Großhaderner Str. 2, D-82152 Planegg-Martinsried, Germany 2Ludwig-Maximilians University Munich, Geo Bio-Center, Munich, Germany 4E-mail: [email protected]
Received September 16, 2010 Accepted January 10, 2011
Inducible defensive traits against herbivores or predators are widespread in plants and animals. Theory predicts that defended morphs have greater fitness in the presence of predators, but lower fitness than undefended morphs in the absence of predators. If such costs did not exist, then a constitutively defended morph would be favored by natural selection; yet, evidence for such costs has been elusive. Our current work reveals a significant cost to inducible defenses. Using the waterflea (Daphnia) model system, we show that induced defended morphs are significantly more vulnerable to infection by a virulent yeast parasite than undefended morphs. In two independent experiments, the proportion of successful infections and the number of parasite spores were higher among defended versus undefended Daphnia. Thus, by demonstrating a previously unknown and environmentally relevant cost to inducible defenses, this study enhances our understanding of adaptive phenotypic plasticity and its evolution.
KEY WORDS: Inducible defenses, kairomones, Metschnikowia, phenotypic plasticity.
Predation is a major driver of natural selection. Phenotypic plas- (e.g., Tollrian 1995; DeWitt 1998; Scheiner and Berrigan 1998; ticity for the induction of defensive traits has proven to be a Van Buskirk 2000; Relyea 2002; Van Kleunen and Fischer 2005; widespread mechanism for plants and animals to cope with the risk Van Buskirk and Steiner 2009; Auld et al. 2010). For example, of consumption by herbivores and predators (Agrawal 2001). On life-table experiments conducted on the rotifer Brachionus caly- theoretical grounds, inducible defenses are most likely to evolve ciflorus showed that neither the possession of long spines nor the when there is spatial or temporal heterogeneity in predation, and production of offspring with long spines interfered with rotifer when there are reliable cues that can be used to indicate the fu- survivorship, fecundity, or reproductive potential (Gilbert 1980). ture risk of attack (Lively 1986; Riessen 1992; Frank 1993; Hazel It has been suggested that the primary cost of inducible et al. 2004). Present models for the evolutionary stability of in- defenses is a reduction in growth and development (Clark and duced defense suggest that there must be a cost associated with Harvell 1992; Tollrian and Harvell 1999). For example, tadpoles the defended morph in the absence of predators; otherwise we build large tails to escape predators, but this comes at the cost of would expect the defense to be constitutively expressed (Lively slower growth (meta-analysis in Van Buskirk 2000). Small plank- 1986; Van Tienderen 1991; Clark and Harvell 1992; Moran 1992; tonic waterfleas (Daphnia) with induced neck spines (called neck- Riessen 1992; Frank 1993; Hazel et al. 2004). Nonetheless, em- teeth) have an approximately 5–15% delay in reproduction com- pirical studies in some systems have revealed only weak costs pared to undefended morphs (Black and Dodson 1990; Riessen and Sprules 1990). However, these observations of growth and de- 3Present address: Unite´ d’Ecologie et d’Evolution, Departement´ velopmental costs have been questioned. Tollrian (1995) argued de Biologie, Universite´ de Fribourg, Chemin du Musee´ 10, 1700 that the increased time to maturity is not the result of a direct phys- Fribourg, Switzerland. iological cost but a trade-off for larger body size. Consequently,