Mutualism involves exchange of services and rewards between partners, resulting in a net benefit to those involved. In many mutualisms, hosts are larger partners that interact with several individuals of smaller mutualists that live on or within them and are termed symbionts. Partners have an incentive to cheat, leading to possible breakdown of the mutualism. Hosts may regulate interaction by selectively rewarding cooperative symbionts. However, this host-centric view that has dominated mutualism studies, does not explain the role of symbionts in regulating trade within a mutualism. In a mutualism with physiological connection between the host and the symbionts, it is necessary to understand whether the symbionts can influence the resources they receive from hosts. My thesis is an attempt to understand resource allocation patterns and the strategies employed by both partners in a prominent brood-site pollination mutualism between fig trees and their pollinating fig wasps which develop within an enclosed inflorescence termed a syconium.
We determined the pattern of resource partitioning to different components of the fig syconium. We tested the applicability of theories describing resource allocation at the whole plant level to individual organs like the syconium. Results show that the syconial wall, that provides protection to occupants, makes up the majority of the dry mass of a syconium, although it is nutritionally less demanding. Further, a single pollinator wasp is costlier to produce compared to a single seed. We showed that there is no number–mass trade-off for both seeds and pollinator wasps indicating proportional allocation of resources to a syconium.
We measured the elementome of seeds, pollinators and the syconial wall tissue and determined the biogeochemical niche (BN) of syconium occupants by examining concentrations of many important elements. We found that the BN of seeds and pollinators are significantly different suggesting differential nutrient demands and demonstrating how coexistence is possible for seeds and pollinators within the syconium microcosms.
We attempted to understand if individual differences in composition of seeds and pollinators result in differential allocation of resources to the syconium. We experimentally manipulated pollinators (foundresses) to produce syconia containing only seeds (S), only pollinators (G) and both seeds and pollinators (SG). We found that overall, the presence of both seeds and pollinator galls increased resource
allocation to a syconium. Since pollinators are gallers, we attempted to understand the role of plant growth hormones in the differential effects of seeds and pollinators on resource allocation. We measured the concentrations of indole-3-acetic acid (IAA), an auxin and trans-Zeatin (tZ), a cytokinin, in S, G and SG syconia during early and mid-phases of their development. We found that IAA and tZ concentrations did not differ between S and G syconia suggesting that galls mimic seeds to garner resources. Further, SG syconia had higher hormone levels correlating with its increased size reported in the previous chapter. Syconia that contain both seeds and galls are rewarded with more resources, which can also ensure cooperation between the partners.