by Jo Ohm
In the Chihuahuan desert, it’s an insect-eat-plant world. Cacti are facing a formidable environment, rife with insect herbivores, lacking in water resources and covered by rocky terrain. Luckily, for Opuntiae imbricata, a type of extra-floral nectar bearing cactus, clever strategies and community partnerships make desert life a bit more bearable.
O.imbricata plants team up with ant mutualists in a facultative relationship in which both ants and cacti benefit from the interaction. For ants, the plants supply an unusual carbohydrate source: extra-floral nectar or EFN which is nectar produced at nectaries away from the flowers. EFN is unusual because its purpose is not to attract pollinators, as normal floral nectar usually does. For cacti, the presence of ants has been shown to decrease rates of herbivory. However, in this particular system, there are two competing ant species vying for access to EFN on host plants. Ants in the genera Crematogaster and Liometopum are competitors, the question is, do the plants have a preference for their mutualists? Crematogaster and Liometopum ants differ in their behavior, most notably in their levels of aggression. Higher aggression correlates with better defense for plant hosts, as aggressive ant-tenders are more likely to consume herbivores. But is their also a cost to having aggressive ant tenders? Could aggression deter pollinators? Perhaps there is evidence of a growth-reproduction trade-off.
This blog is dedicated to exploring the mutualist interactions of O. imbricata plants and ants and to prompt discussion on the cost of aggression in other systems. Blog posts will also feature topics related to how we define mutualist vs. parasitic relationships, how scientists approach understanding community interactions and will encourage public interest in the exciting realm of ecology research!