Impact of immune activation on stored sperm viability in ant queens

Ant queens mate on a single occasion early in life and store millions of sperm cells in their spermatheca. By carefully using stored sperm to fertilize eggs, they can produce large colonies of thousands of individuals. Queens can live for decades and their lifetime reproductive success is dependent on their ability to keep stored sperm alive. Maintaining high sperm viability requires metabolic energy which could trade-off with other costly processes such as immunity. We tested the impact of immune activation on the survival of stored sperm by prompting Lasius niger ant queens to mount a melanization response and subsequently measuring sperm viability in their spermatheca. Since queens face different challenges that influence energy allocation depending on the life stage of their colony, we measured sperm viability after immune activation in both newly mated queens (incipient) and in queens 1 year after mating (established). We found that immune activation reduced sperm viability in established queens but not in incipient queens, showing that the cost of immunity on sperm preservation depends on the life stage. Unexpectedly, established queens had significantly higher sperm viability in their spermatheca compared to incipient queens suggesting that ant queens are able to remove dead sperm from their spermatheca.

The Immune System as a Sensor Able to Affect Other Homeostatic Systems

This chapter deals with the capacity of the immune system to sense the intrusion of external challenges and modifications of self-components, and to provide information to the brain about these disturbances. These properties allow us to classify the immune system as a classical sensory organ. Besides its intrinsic function directed at the elimination of dangerous stimuli, the activation of the immune system also affects the functioning of other homeostatic systems, such as the endocrine and the nervous systems. We also discuss our view of how immune-derived information could be processed by the brain and integrated with other inputs that it permanently receives, leading to a resetting of regulatory adaptive systems. Due to the high energetic cost of immunity, we discuss how brain-borne cytokines, in particular IL-1, could affect glucose homeostasis. Deregulation of these immune-neuroendocrine interactions can affect brain mechanisms that include behavior, cognition, mood, and personality.

Is there a role for antioxidant carotenoids in limiting self-harming immune response in invertebrates?

Innate immunity relies on effectors, which produce cytotoxic molecules that have not only the advantage of killing pathogens but also the disadvantage of harming host tissues and organs. Although the role of dietary antioxidants in invertebrate immunity is still unknown, it has been shown in vertebrates that carotenoids scavenge cytotoxic radicals generated during the immune response. Carotenoids may consequently decrease the self-harming cost of immunity. A positive relationship between the levels of innate immune defence and circulating carotenoid might therefore be expected. Consistent with this hypothesis, we show that the maintenance and use of the prophenoloxidase system strongly correlate with carotenoid concentration in haemolymph within and among natural populations of the crustacean Gammarus pule x.