Protective Ant-Plant Interactions as Model Systems in Ecological and Evolutionary Research

Abstract

Protective ant-plant interactions, important in both temperate and tropical communities, are increasingly used to study a wide range of phenomena of general interest. As antiherbivore defenses "worn on the outside," they pose fewer barriers to experimentation than do direct (e.g., chemical) plant defenses. This makes them tractable models to study resource allocation to defense and mechanisms regulating it. As multi-trophic level interactions varying in species specificity and impact on fitness of participants, ant-plant-herbivore associations figure prominently in studies of food-web structure and functioning. As horizontally transmitted mutualisms that are vulnerable to parasites and "cheaters," ant-plant symbioses are studied to probe the evolutionary dynamics of interspecies interactions. These symbioses, products of coevolution between plants and insect societies, offer rich material for studying ant social evolution in novel contexts, in settings where colony limits, resource supply, and nest-site availability are all more easily quantifiable than in the ground-nesting ants hitherto used as models. PROTECTIVE ANT-PLANT MUTUALISMS 427 Other plants lack obvious ant-specialized traits but frequently harbor ant-tended hemipteran trophobionts. Recent reviews of ant-hemipteran interactions are provided by Delabie (2001), Gullan (1997), and Gullan & Kosztarab (1997). Most ant-tended hemipterans are phloem-feeders and excrete excess liquid as sugarrich honeydew. An important resource for ants, honeydew-producing hemipterans are often monopolized by territorial, ecologically dominant ants (Blüthgen et al. 2000). These generalist predators can strongly reduce densities of phytophagous insects.

The Direct and Ecological Costs of an Ant-Plant Symbiosis

“…Ant-plant interactions are classic examples of mutualism (e.g., Janzen 1966) and have figured prominently in the literature on the evolution of mutualism (Bronstein 1998;Yu 2001;Heil and McKey 2003;Sachs et al 2004;Heil et al 2009;Weyl et al 2010). Numerous plant species make food or housing to attract ants, which defend the plants against herbivores or other enemies (reviewed by Heil and McKey 2003).…”

Plant-ants use symbiotic fungi as a food source: new insight into the nutritional ecology of ant–plant interactions

“…Ants and plants are among the most dominant taxa in tropical ecosystems, and the ecological importance of their mutualistic interactions is brought to light by two considerations: these interactions structure food webs [1] and the mutualistic benefits exchanged can convey ecological advantages to the partners [2]. Yet the nutritional ecology of these interactions is still poorly understood [3].…”

Mutualism favours higher host specificity than does antagonism in plant–herbivore interaction

“…Although many mutualisms do not evolve to exhibit high degrees of specificity (e.g. most plantpollinator and plant -seed disperser interactions), reciprocal partner specialization is often found in intimate mutualisms, such as those between myrmecophytic plants and their resident ants (Davidson & McKey 1993;Heil & McKey 2003;Guimarães et al 2007), ants/termites and their cultivated fungi (Mueller et al 1998;Aanen et al 2002;Currie et al 2003) or various invertebrates and their endosymbiotic micro-organisms (Moran & Telang 1998;Hosokawa et al 2006). Both ultimate and proximate causes of specialization have been proposed, including selection for elimination of less-cooperative partners (Heil et al 2005;Poulsen & Boomsma 2005) and chemical or physical mechanisms of partner discrimination (Federle et al 1997;Brouat et al 2001;Edwards et al 2006;Grangier et al 2009).…”