Evolution of Mutualistic Life-Cycles: Yucca Moths and Fig Wasps

Abstract

The study of mutualism is shifting from emphasizing the identification of systems that are mutualistic to attempting to understand the origin, maintenance and breakdown of mutualistic systems. Many different approaches are being used in this effort, including cost-benefit models (Roughgarden 1975), phylogenetic analyses (Thompson 1982), models of population dynamics (Addicott 1981; Wolin 1985), and the approach that we adopt in this chapter, the analysis of lifehistories. We focus on two aspects of life-histories important for understanding the origin, maintenance and breakdown of mutualistic interactions: the probability of successful association between potential symbiont and host, and the comparative fitness of mutualistic and non-mutualistic symbionts when successfully associated with their host (Roughgarden 1975). More specifically, we ask two questions. (a) How does synchronization of life-cycles within and between symbiont and host populations influence the probability of successful association between mutualists and ultimately the maintenance of mutualism? (b) Under what conditions would "cheating" by potentially mutualistic individuals be favoured over strictly mutualistic behaviour? To address these questions we analyse the life-histories of species in two obligate pollination-seed predation mutualisms: the yucca-yucca moth interaction and the fig-fig wasp interaction. Two factors affect the probability of association between symbionts (e.g. yucca moths or fig wasps) and their hosts (e.g. yuccas or figs). First, symbionts must be able to recognize their hosts. Recognition is usually based on various combinations of visual (e.g. Brown and Kodric-Brown 1979) or chemical (e.g. Dodson et al. 1969) cues. Second, there must be synchronization between the appropriate life-history stages of host and symbiont. For example, pollinators must be active when female flowers are receptive to pollen. Asynchrony of appropriate lifehistory stages between individual hosts and symbionts should lead to a lower probability of association, and decreased fitness for individual hosts and F. Gilbert (ed.), Insect Life Cycles

The evolution of obligate pollination mutualisms: senita cactus and senita moth

“…As predicted by theory (Addicott et al 1990;Thompson 1994;Waser et al 1996), both systems feature pollinators whose life cycles are intimately associated with long-lived plants with seasonal¯owering cycles. We propose that three of their common features±nocturnal¯ower opening, selfincompatability, and resource-limited fruit set±have A total of 2,290¯owers on 60 plants was tagged.…”

“…Classic examples of these kinds of mutualisms include yuccas (Yucca) and yucca moths (Tegeticula, Parategeticula) (Riley 1892;Aker and Udovic 1981;Pellmyr et al 1996), and ®gs (Ficus) and ®g wasps (Agaonidae) (Janzen 1979;Wiebes 1979;Addicott et al 1990). In both of these mutualisms, females actively pollinate¯owers by deliberately collecting pollen and depositing it on or in receptive stigmas.…”

“…These insects thus are pollinators and seed predators and simultaneously interact with their host plants as mutualists and antagonists. In addition to a net positive e ect on seed set, conditions favoring the evolution of such specialized pollination mutualisms are thought to include a close physical relationship between large, long-lived plants and pollinators whose life cycles are synchronized with¯owering phenology (Addicott et al 1990;Bronstein 1992;Pellmyr and Huth 1994;Thompson 1994;Waser et al 1996). Although co-pollinators are absent in the ®g and yucca mutualisms, Pellmyr et al (1996) predicted that active pollination can evolve in the presence of co-pollinators when specialized pollinator/seed predators provide higher-quality pollination than generalists.…”

On Mutualists and Exploiters: Plant–insect Coevolution in Pollinating Seed–parasite Systems

“…Beyond its demographic signi"cance, phenological timing strongly in#uences the outcome of the biotic interactions that an organism is likely to experience. Phenologies in#uence the likelihood that prey will be able to avoid predators (Ohkawara et al, 1997), predators will be able to locate prey (Hunter, 1990), hosts will be able to resist diseases (Parker, 1991;Marr, 1997), mimics will coincide with models (Brodie, 1981), competitors will be able to avoid each other (Stone et al, 1998), and mutualists will be able to "nd each other (Addicott et al, 1990).…”

Forty million years of mutualism: Evidence for Eocene origin of the yucca-yucca moth association

“…Obligate mutualisms have attracted particular interest in terms of their stability and endurance (10,51 (53) suggest that this mutualism has persisted as long as the yucca-yucca moth association. Furthermore, many associations between specific yuccas and yucca moths have persisted since the evolution of derived cheater yucca moths, which dramatically increased the cost to the plants (11), suggesting that these mutualisms retain evolutionary stability over long time spans.…”