Date of Award
Doctor of Philosophy
Ecology, Evolution, and Organismal Biology
Ecology and Evolutionary Biology
John D. Nason
All living organisms interact with different degrees of interdependence and in ways that are integral to their ecology and evolution. Of the many forms of species interaction, mutualism is one in which species reciprocally obtain benefits from their interactions. Because mutualism is ubiquitous in nature, mutualists are commonly associated with a broader community of species whose interactions vary across a mutualist–antagonist spectrum and in space and time, and so they play a broadly important role in ecosystem function and species evolution. Flowering plants are widely distributed, typically primary producers, and thus foundational ecosystem elements. They are also ubiquitously associated with a diverse assemblage of insects, including diffuse to species-specific associations with pollinators (mutualists) and herbivores and seed predators (antagonists), which are interactions that effect the reproductive fitness of both plants and insects. The main goal of this dissertation is to investigate the effects of past and current environmental variation on the dynamics of species involved in obligate plant-insect interactions, and to model this dynamic in the context of future climate scenarios. This goal was addressed studying a fig–fig wasp system as a biological model. Fig trees (Ficus, family Moraceae) are a well-known example of obligate symbiosis in which the plants serve as hosts to pollinator and non-pollinator fig wasps and other insects whose larva develop within fig fruits. Ficus petiolaris is a rock-strangler fig tree, endemic to Mexico, and hosts nine species of chalcidoid fig wasps: one pollinator plus eight species of non-pollinators that are antagonistic to the plant, pollinator or both. In addition, F. petiolaris fruit (including developing seeds and wasps) are subject to predation by a species of a lepidopteran larva. Past climatic fluctuations and the geological history of the region are factors that have influenced the co-distribution of these species, a history that can be revealed through the analysis of their contemporary genetic structure. Using single nucleotide polymorphism (SNP) molecular data, population genetics, phylogenetics, and species distribution modeling, I investigated how the geology, geography and historical climate in western Mexico shaped the genetic landscape of F. petiolaris, revealing that northern range limits of F. petiolaris shifted to the south during the late Pleistocene, with subsequent range expansion resulting in a contemporary contact zone in coastal northwestern Mexico between previously isolated populations in Baja California and mainland Mexico. I then investigated present day associations between biotic and abiotic ecological variables and local and landscape-level dynamics in fig wasp community composition and lepidopteran fruit predation. The results indicate that variation in F. petiolaris reproductive phenology and tree density differentially influence the relative proportions of pollinating and parasitic wasps, as well as the rate of damage cause by the lepidopteran larvae. Furthermore, I found that increasing local temperature and precipitation strongly benefit pollinator reproductive success, and hence pollen dispersal, at the expense of non-pollinator production. Finally, global climate change scenarios in Mexico predict substantial near-future geographical changes in temperature and rainfall. Using future climate modeling, I projected the distribution of F. petiolaris and predicted changes in pollinator versus non-pollinator reproductive success to assess implications of climate change for the fig–fig wasp mutualism. Because rapid, human-mediated global environmental change is threatening biodiversity, it is crucial to understand the effect of spatial and temporal environmental variation on species interactions and their consequences. Projections of the F. petiolaris system indicate that near-term climate change has the potential to disadvantage the mutualism by decreasing pollinator reproduction success over an expanded geographical area. This dissertation provides new insight into the fig–fig wasp symbiosis and its relationship with its past and current environment, and present for the first time a joint, climate-based projection of a fig’s geographical distribution, wasp community composition, and mutualism dynamics into the future.
Piatscheck, Finn, "Past, present and future: Geographic and temporal variation in a fig–fig wasp mutualism" (2019). Graduate Theses and Dissertations. 17541.