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Mattheau S. Comerford, Scott. P. Carroll, and Scott P. Egan: Read the article
Comerford et al. uncover the red-shouldered soapberry bug as the first Hemipteran pollinating seed predator, reshaping our understanding of this guild and its role in evolution and ecological resilience. A discovery bridging natural history and evolution!
When we examine organisms in nature, we tend to typecast them into ecological roles: producers, herbivores, invasives, mutualists, and so on. However, the ecological roles of organisms often vary with circumstances such as the availability of resources and the stability of the environment. Further, the full gamut of their interactions may yet be undescribed by science.
The red-shouldered soapberry bug, Jadera haematoloma, is reminiscent of a male red-winged blackbird: black in colour with eponymous bright red “shoulders”. It is widely distributed across the United States, and its range extends into northern South America. The nymphs and adults are dietary specialists, feeding on the seeds of plants in the soapberry family, Sapindaceae. The authors noticed that this species was often found feeding on the nectar of its host plant’s flowers, so they set out to test if they were viable pollinators.
Until now, it was thought that the members of the true bug subfamily Serinethinae were primarily seed predators of plants in the soapberry family, Sapindaceae. When we think of pollinating seed-predators, the organisms that come to mind are fig wasps or yucca moths, which participate in tightly coevolved partnerships with their plant hosts. The insects provide targeted pollen delivery, while the plant partners sacrifice a few developing seeds as food or lodging for the developing insect offspring. In such cases, the costs and benefits to each partner are clear. From the plant’s perspective, could the pollination benefit, provided by the bugs, although not as targeted, make up for the cost they impose by eating seeds?
Comerford et al. set out to see if the red-shouldered soapberry bug is a different kind of pollinating seed-predator—one that is a generalist nectar feeder, while being a dietary specialist seed-predator. To do this, they examined various records and conducted experiments to test if J. haematoloma consumed nectar, collected host pollen, and contributed to successful seed-set in host plants both in the greenhouse and the field. They also quantified the benefit of consuming nectar to J. haematoloma, and cost of harbouring a pollinating seed-predator to the host plant.
Surveys of museum records, community science databases, online images, and literature revealed widespread nectar feeding in J. haematoloma and some of its relatives worldwide. Experiments confirmed that J. haematoloma consumed nectar, carried pollen and successfully pollinated their host plant, leading to viable seed set. A diet supplemented with synthetic nectar extended insect lifespan, highlighting nectar’s value as a supplement to seeds. However, seed predation experiments showed that offspring consumed far more seeds than the ovules they fertilized, indicating that the interaction with host plants is primarily antagonistic.
These findings reframe our understanding of both the ecology and evolution of this species. Assumed to be exclusively seed feeders until now, these findings suggest that feeding on nectar opportunistically could enable this species to tide over spells of low seed availability and environmental variability. When the flamegold rain tree (Koelreuteria elegans) was introduced to the US from southeast Asia in the 1950s, populations of J. haematoloma were quick to adapt to feed on the seeds of this novel host (Carroll et al. 2001). Considering Comerford et al.’s findings, it’s possible that the ability of this species to feed on nectar may have facilitated its co-expansion into new ranges in tandem with this new host. The findings also prompt us to reconsider the factors shaping the morphology of J. haematoloma’s mouthparts – could nectar consumption be an important driver, in addition to seed predation?
This study also highlights the importance of natural history observations in uncovering surprising aspects of the biology even of well-studied species. In this age of artificial intelligence and big data, observations of organisms in their natural environment continue to serve as wellsprings of inquiry and remain essential to map processes to patterns in ecology, evolution and biodiversity. Studies like this inspire us to don our field biologist hats and just observe our study organisms in nature – who knows what we might discover?
Pooja Nathan is a PhD candidate in the Department of Ecology and Evolutionary Biology at the University of Toronto, where she studies plant-ant mutualisms. Pooja's research focuses on the ecology and evolutionary biology of the mutualism between ants and plants mediated by extrafloral nectaries, but she is excited by all kinds of plants, insects and their interactions. In her free time, Pooja enjoys learning to cook dishes from different cuisines, embroidery, and taking nature walks.
