Biomedical subjects

Judith L Bronstein

Publications and source records attributed to Judith L Bronstein.

5 recordsLinked to original sources

PubMed2006

The evolution of plant-insect mutualisms.

Mutualisms (cooperative interactions between species) have had a central role in the generation and maintenance of life on earth. Insects and plants are involved in diverse forms of mutualism. Here we review evolutionary features of three prominent insect-plant mutualisms: pollination, protection and seed dispersal. We focus on addressing five central phenomena: evolutionary origins and maintenance of mutualism; the evolution of mutualistic traits; the evolution of specialization and generalization; coevolutionary processes; and the existence of cheating. Several features uniting very diverse insect-plant mutualisms are identified and their evolutionary implications are discussed: the involvement of one mobile and one sedentary partner; natural selection on plant rewards; the existence of a continuum from specialization to generalization; and the ubiquity of cheating, particularly on the part of insects. Plant-insect mutualisms have apparently both arisen and been lost repeatedly. Many adaptive hypotheses have been proposed to explain these transitions, and it is unlikely that any one of them dominates across interactions differing so widely in natural history. Evolutionary theory has a potentially important, but as yet largely unfilled, role to play in explaining the origins, maintenance, breakdown and evolution of insect-plant mutualisms.

Animals↗

PubMed2005

Clutch size: a major sex ratio determinant in fig pollinating wasps?

Under local mate competition, sex ratio theory predicts that increasing numbers of ovipositing females (foundresses) on a site should lead to higher proportions of males in their broods. Fig pollinators have confirmed this prediction. It is also predicted that with decreasing clutch size, solitary foundresses should produce increasing proportions of sons. We show this to be true. Further, when several females compete, brood size decreases. As a result, the proportion of males increases, and this could provide a mechanistic explanation of sex ratio response to numbers of colonizing females. Therefore, sex ratio data on fig wasps need to be reassessed to determine whether females 'count' other foundresses, as is generally accepted, or whether they simply 'count' the number of eggs that they lay.

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PubMed2003

Three-way coexistence in obligate mutualist-exploiter interactions: the potential role of competition.

Many mutualisms host "exploiter" species that consume the benefits provided by one or both mutualists without reciprocating. Exploiters have been widely assumed to destabilize mutualisms, yet they are common. We develop models to explore conditions for local coexistence of obligate plant/pollinating seed parasite mutualisms and nonpollinating exploiters. As the larvae of both pollinators and (at a later time) exploiters consume seeds, we examine the importance of intraspecific and (asymmetric) interspecific competition among and between pollinators and exploiters for achieving three-way coexistence. With weak intra- and interspecific competition, exploiters can invade the stable mutualism and coexist with the mutualists (either stably or with oscillations), provided the exploiters' intrinsic birthrate (b(E)) slightly exceeds that of the pollinators. At higher b(E), all three species go locally extinct. When facing strong interspecific competition, exploiters cannot invade and coexist with the mutualists if intraspecific competition in pollinators and exploiters is weak. However, strong intraspecific competition in pollinators and exploiters facilitates exploiter invasion and coexistence and greatly expands the range of b(E) over which stable coexistence occurs. Our results suggest that mutualist/exploiter coexistence may be more easily achieved than previously thought, thus highlighting the need for a better understanding of competition among and between mutualists and exploiters.

Animals↗

PubMed2003

Ecological dynamics of mutualist/antagonist communities.

One approach to understanding how mutualisms function in community settings is to model well-studied pairwise interactions in the presence of the few species with which they interact most strongly. In nature, such species are often specialized antagonists of one or both mutualists. Hence, these models can also shed light on the problem of when and how mutualisms are able to persist in the face of exploitation. We used spatial stochastic simulations to model the ecological dynamics of obligate, species-specific mutualisms between plants and pollinating seed parasite insects (e.g., yuccas and yucca moths) in the presence of one of two obligate antagonist species: flower-feeding insects (florivores) or insects that parasitize seeds but fail to pollinate (exploiters). Our results suggest that mutualisms can persist surprisingly well in the presence of highly specialized antagonists but that they exhibit distinctly different temporal and spatial dynamics when antagonists are present. In our models, antagonists tend to induce oscillations in the mutualist populations. As the number of per capita visits by antagonists increase, the system's oscillatory dynamics become more extreme, finally leading to the extinction of one or more of the three species. When the antagonists exhibit high per capita visitation frequencies and long dispersal distances, significant spatial patchiness emerges within these tripartite interactions. We found surprisingly little difference between the ecological effects of florivores and exploiters, although in general florivores tended to drive themselves (and sometimes the mutualists) to extinction at parameter values at which the exploiters were able to persist. These theoretical results suggest several testable hypotheses regarding the ecological and evolutionary persistence of mutualisms. More broadly, they point to the critical importance of studying the dynamics of pairwise interactions in community contexts.

Animals↗

PubMed2002

Cheating and the evolutionary stability of mutualisms.

Interspecific mutualisms have been playing a central role in the functioning of all ecosystems since the early history of life. Yet the theory of coevolution of mutualists is virtually nonexistent, by contrast with well-developed coevolutionary theories of competition, predator-prey and host-parasite interactions. This has prevented resolution of a basic puzzle posed by mutualisms: their persistence in spite of apparent evolutionary instability. The selective advantage of 'cheating', that is, reaping mutualistic benefits while providing fewer commodities to the partner species, is commonly believed to erode a mutualistic interaction, leading to its dissolution or reciprocal extinction. However, recent empirical findings indicate that stable associations of mutualists and cheaters have existed over long evolutionary periods. Here, we show that asymmetrical competition within species for the commodities offered by mutualistic partners provides a simple and testable ecological mechanism that can account for the long-term persistence of mutualisms. Cheating, in effect, establishes a background against which better mutualists can display any competitive superiority. This can lead to the coexistence and divergence of mutualist and cheater phenotypes, as well as to the coexistence of ecologically similar, but unrelated mutualists and cheaters.

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