. "7 Critical Review of Host Specificity and Its Coevolutionary Implications in the Fig/Fig-Wasp Mutualism--CARLOS A. MACHADO, NANCY ROBBINS, M. THOMAS P. GILBERT, AND EDWARD ALLEN HERRE." Systematics and the Origin of Species: On Ernst Mayr's 100th Anniversary. Washington, DC: The National Academies Press, 2005.
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Systematics and The Origin of Species: On Ernst Mayr’s 100th Anniversary
Both ecologically and evolutionarily, mutualisms represent one of the most influential of all biological interactions, with fundamental consequences for the evolution and maintenance of biotic diversity (Boucher, 1985; Bronstein, 2001; Douglas, 1994; Herre et al., 1999; Margulis and Fester, 1991; Maynard Smith and Szathmáry, 1995; Thompson, 1994). The long-term stability of mutualisms poses a considerable and, as yet, not fully resolved challenge to evolutionary theory. However, the obvious fact of long-term stability coupled with the proliferation and diversification of many mutualisms raises a set of interesting questions concerning coadaptation and speciation among the partners in the interaction. The obligate mutualisms between flowering plants and their insect pollinators (Corner, 1952; Kato et al., 2003; Pellmyr, 2003; Wiebes, 1979) constitute fascinating extreme cases of interspecific mutualisms. Most obligate plant–pollinator mutualisms show high levels of reciprocal species or taxon specificity. Usually, the insect requires the plant for food or other substances to complete its life cycle successfully, and the plant requires the insect for pollination. Further, it is the insect’s recognition and choice of hosts that determine the patterns of host gene flow. Although there are relatively few cases of obligate pollination mutualisms (Corner, 1952; Kato et al., 2003; Pellmyr, 2003; Wiebes, 1979), these few cases are often marked by high to extreme speciation and diversification in both partners, raising the question of how host specificity and control of gene flow affects patterns of speciation in one or both partners.
Figs (Ficus spp., Moraceae) and their pollinating wasps (Agaonidae, Chalcidoidea) constitute perhaps the most tightly integrated pollination mutualism that is known (Cook and Rasplus, 2003; Corner, 1952; Galil and Eisikowitch, 1968; Janzen, 1979; Ramirez, 1970a; Weiblen, 2002; Wiebes, 1979). Ficus is one of the most diverse genera of flowering plants in number of species and growth and life forms (Berg and Wiebes, 1992; Harrison, 2005). The nearly 750 described species of Ficus (Berg, 1989) occur worldwide in tropical and subtropical regions, and they are considered “keystone” species in tropical forests because of their year-round production of fruit that is essential to a large number of frugivores (Kalko et al., 1996; Korine et al., 2000; McKey, 1989; Terborgh, 1986). Figs depend on minute, pollen-bearing female wasps to pollinate the flowers and thereby initiate seed production (Corner, 1952; Eisikowitch, 1968; Galil, 1977; Galil and Ramirez, 1974; Herre, 1989, 1999; Herre and West, 1997). The mated female wasps, in turn, depend on the developing fig inflorescence for the production of their offspring, because each wasp larva consumes the contents of one would-be seed. The cycle begins when mated female wasps locate a receptive tree and enter the enclosed fig inflorescences (Syconia). As the females search for oviposition sites, they pollinate the flowers. Usually the foundresses die inside the syconium, and