Plant–animal interactions are a key to understand biodiversity

For centuries, plant and animal studies progressed along mostly separate scientific pathways. However, ever since Darwin’s famous quote “plants and animals, most remote in the scale of nature, are bound together by a web of complex relations” (The Origin of Species, 1859), naturalists have started to realize that plant–animal interactions are a powerful evolutionary force sustaining biological diversity in all terrestrial ecosystems. Recently, this cross-disciplinary subject has attracted researchers from different fields: plant biologists, behavioral zoologists, evolutionary ecologists, etc. In this issue of Acta Agrobotanica, we present a selection of papers extending our understanding of the various adaptations in plant–animal relationships. Among all, the contributions include the role of pollinators in shaping plant reproductive success, micromorphological adaptations of the flower and nectar characters to attract pollinators as well as the role of ecological stoichiometry in plant–animal interactions and the function of microorganisms in plant–animal interactions. The observations carried out by Odintsova and Fishchuk [1] from Ukraine have revealed diversity of micromorphological adaptations to the pollination mode in closely related species from Convallariaceae (Polygonatum multiflorum, Maianthemum bifolium, and Convallaria majalis). They report the presence of a long septal nectary in the ovary and epidermal trichomes on the inner perigonium surface and on the filaments in the flower of P. multiflorum and suggest that the flower potentially functions as a xenogamous nectar and pollen flower. The disc-shaped flower of M. bifolium is morphologically adapted to generalist pollinators and self-pollination. In M. bifolium, a rudimentary external septal nectary was described for the first time. In contrast, the C. majalis flower is polleniferous with no nectaries or other morphologically distinct secretory structures. The new perspectives in nectar evolution and ecology have been discussed by Nepi [2] from Italy in his fascinating review article. Nectar is considered as a main reward offered by plants to animals in exchange for benefits, mainly pollination and indirect defense against herbivores. Some nectar components (proteins and nectar secondary metabolites, e.g., nicotine and benzyl acetone or non-protein amino acids) have no primary nutritious function but are involved in plant–animal relationships in other ways. Proteins protect against proliferation of microorganisms and infection of plant tissues by pathogens. Nectar secondary compounds can be involved in modulating the behavior of nectar feeders, maximizing benefits for the plant. Nectar-dwelling microorganisms (mainly yeasts) have recently been revealed as a third partner in the scenario of plant–animal interactions mediated by nectar. There is evidence that yeast has a remarkable impact on the nectar feeder behavior, although the effects on plant fitness have not yet been clearly assessed. The experiment conducted by Peters et al. [3] brings an important contribution to the interpretation of the role of bacteria in plant–animal interactions. The authors suggest a prominent role of bacteria in shaping the behavior of organisms at higher trophic levels, e.g., herbivory in natural, horticultural, and agricultural systems. In their survey, the authors reveal that the feeding behavior of the common slug Arion vulgaris is modified by bacteria associated with both plants and animals. DOI: 10.5586/aa.1711