Gall Aposematism
Galls are abnormal plant growths induced by various parasitic organisms, mainly insects. Many herbivorous insects induce galls on various plant organs such as leaves, shoots and flowers. Gall-inducers manipulate and exploit the development, anatomy, morph
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Gall Aposematism
Galls are abnormal plant growths induced by various parasitic organisms, mainly insects. Many herbivorous insects induce galls on various plant organs such as leaves, shoots and flowers. Gall-inducers manipulate and exploit the development, anatomy, morphology, physiology and chemistry of the host plant to their own benefit (Weis et al. 1988; Shorthouse and Rohfritsch 1992). Galls, being plant tissues, act as physiological sinks for mobilized plant resources, resulting in increased nutritional values for their inducers. They serve as “incubators” for the developing insects that gain protection from both abiotic factors (e.g., sun irradiation, wind, dessication, rain and snow) and natural enemies such as pathogens, predators and parasitoids, or even from accidental consumption by large herbivores (Price et al. 1987; Stone and Schonrogge 2003). Since the inducing insects control gall formation up to the smallest details, galls are commonly considered as their extended phenotype (Dawkins 1982; Crespi and Worobey 1998; Stone and Schonrogge 2003; Inbar et al. 2004). An earlier (but less likely) hypothesis, suggested that galls could represent adaptations of the host plants; restricting insect damages to specific organs (see Stone and Schonrogge 2003). The evolutionary and ecological contexts of many gall traits have been intensively studied (e.g. Stone et al. 2002; Raman et al. 2005). Numerous studies have examined the biochemical composition of gall tissues both from the nutritional and defensive points of view (e.g., Inbar et al. 1995; Nyman and Julkunen-Titto 2000). Defensive gall traits against natural enemies attracted much attention from ecologists and evolutionary biologists (e.g., Cornell 1983; Abrahamson et al. 1989; Schonrogge et al. 1999). Galls are typically armed with high levels of defensive secondary metabolites of plant origin. For example, the high levels and compartmentalizing of defensive phenolics and tannins in galls are explained as an adaptive trait that protects the gall-inducing insects without compromizing the nutritive values of inner gall parts (Cornell 1983; Hartley 1998). Inbar et al. (2010a) posited that conspicuousness is a striking and common gall trait. Many galls may be conspicuous because of their size and shape, which differ from the background plant organs. Galls are often characterized by bright or contrasting (red, yellow, etc.) colors © Springer International Publishing Switzerland 2016 S. Lev-Yadun, Defensive (anti-herbivory) Coloration in Land Plants, DOI 10.1007/978-3-319-42096-7_43
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Gall Aposematism
Fig. 43.1 Colorful Forda sp. galls on Pistacia terebinthus tree growing in Makri, northern Greece
(Figs. 43.1, 43.2, 43.3 and 43.4) (Russo 2007) as a result of an accumulation of plant-derived pigments in their tissues. Since many galls are colorful, they can be clearly distinguished visually from the surrounding host plant organs. For example, the red galls of wasps (Cynipidae) induced on oaks contain high levels of carotenoids (Czeczuga 1977).
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