Rising temperatures threaten pollinators of fig trees—Keystone resources of tropical forests

Abstract

Pollinating insects are decreasing worldwide in abundance, biomass, and species richness, affecting the plants that rely on pollinators for fruit production and seed set. Insects are often sensitive to high temperatures. The projected temperature increases may therefore severely affect plants that rely on insect pollinators. Highly specialized mutualisms are expected to be particularly vulnerable to change because they have fewer partner options should one partner become unavailable. In the highly specialized mutualism between fig trees and their pollinating fig wasp, each fig species is pollinated by only one or a few wasp species. Because of their year‐round fruit production, fig trees are considered a keystone resource for tropical forests. However, to produce fruits, wild fig trees need to be pollinated by fig wasps that typically travel a long one‐way trip from the tree donating pollen to the tree receiving pollen. In a few previous studies from China and Australia, increasing temperatures dramatically decreased fig wasp lifespan. Are these grim results generalizable to fig mutualisms globally? Here, we use survival experiments to determine the effect of increasing temperature on the lifespan of Neotropical fig wasps associated with five common Panamanian Ficus species. Experimental temperatures were based on the current daytime mean temperature of 26.8°C (2SD: 21.6–31.7°C) and the predicted local temperature increase of 1–4°C by the end of the 21st century. We found that all tested pollinator wasp species had a significantly shorter lifespan in 30, 32, 34, and 36°C compared to the current diurnal mean temperature of 26°C. At 36°C pollinator median lifespan decreased to merely 2–10 h (6%–19% of their median lifespan at 26°C). Unless wasps can adapt, such a dramatic reduction in lifespan is expected to reduce the number of pollinators that successfully disperse to flowering fig trees, and may therefore jeopardize both fruit set and eventually survival of the mutualism.

Genomic diversity and structure of a Neotropical microendemic fig tree

“…On the other hand, south of the TMVB, specifically in Churumuco, the interplay of high temperatures and low precipitation can pose a significant challenge to the longevity of wasps. Despite their inherent mobility, these wasps, which typically live for a brief period (1–2 days) outside the syconium, are notably susceptible to abiotic stress (Gigante et al., 2021 ; Jevanandam et al., 2013 ; van Kolfschoten et al., 2022 ; Xu et al., 2021 ). Consequently, the environmental conditions in this region might diminish the lifespan of wasps and impact their dispersal capacity (Gigante et al., 2021 ; Xu et al., 2021 ).…”

“…(1-2 days) outside the syconium, are notably susceptible to abiotic stress(Gigante et al, 2021;Jevanandam et al, 2013;van Kolfschoten et al, 2022;Xu et al, 2021). Consequently, the environmental conditions in this region might diminish the lifespan of wasps and impact their dispersal capacity(Gigante et al, 2021;Xu et al, 2021).…”

Comparative Phylogeography of Mexican Rock Fig (Ficus petiolaris) and its Fig Wasp Pollinator: Effects of Abiotic Versus Biotic Factors

“…The variation in genetic connectivity may be due to physiological limitations experienced during traversal of environmental gradients. Heat and humidity constrain fig wasps [Jevanandam et al, 2013;van Kolfschoten et al, 2022;Aung et al, 2022], limiting their navigation abilities. Altitude gradients on Mount Wilhelm in Papua New Guinea have been shown to affect the composition and diversity of wasp communities [SoutoVilarós et al, 2020].…”

Field sampling of fig pollinator wasps across host species and host developmental phase: Implications for host recognition and specificity

“…Given this synchronized development within a host tree and the short lifespan of adult pollinator wasps (around 2-3 days; Kjellberg et al, 1988;van Kolfschoten et al, 2022), most wasps need to travel great distances to encounter a receptive host and finding a suitable receptive host is challenging, especially when the density of host trees is low, as in monoecious neotropical figs (McKey, 1989;Todzia, 1986).…”

“…Due to the synchronized development of syconia within flowering individuals in nearly all Ficus species, there are usually no receptive flowers available for fig wasps at eclosion in their natal tree (Janzen, 1979 ). Given this synchronized development within a host tree and the short lifespan of adult pollinator wasps (around 2–3 days; Kjellberg et al, 1988 ; van Kolfschoten et al, 2022 ), most wasps need to travel great distances to encounter a receptive host and finding a suitable receptive host is challenging, especially when the density of host trees is low, as in monoecious neotropical figs (McKey, 1989 ; Todzia, 1986 ).…”