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Mating success and energetic condition effects driven by terminal investment in a short-lived insect

Tuesday, 25 June 2013
South Hall (Herradura San Jose)
Daniel M González-Tokman , Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico
Alejandro Córdoba-Aguilar , Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico
When animals perceive that the probability of mortality is high and there are low chances of reproducing in the future, they should expend a high amount of resources in current reproduction. This idea, known as the terminal investment hypothesis, has two predictions: in the face of an infection (i) mature males will increase investment to traits that enhance mating success, and such investment will be lower in young males; (ii) physiological costs of resource reallocation will be more severe for infected mature males than for infected young males. Although these predictions have been tested in long-lived vertebrates, prior studies have not examined actual resource allocation conflicts. Here, we have tested the above predictions and have investigated the energetic costs of increased mating by old males, using a short-lived invertebrate, the damselfly Hetaerina americana. Males of this species defend territories as the main way to obtain access to females. Using groups of infected vs. noninfected males of two different ages, we found that compared to young infected males, mature infected males defended territories for longer, had higher mating success and directed agonistic behaviour to conspecific males more frequently. Despite similar immune responses by mature and young males, infected mature males ended up with less fat reserves compared to infected young males. This suggests that resource allocation conflicts are more severe for mature than for young males. In general, these results suggest that the terminal investment hypothesis applies in males of short-lived invertebrates and that a cause of increased mating success for males of advanced ages is reduced energetic stores. Aging is an understudied but ecologically relevant process that deserves to be studied in tropical species. Insect pests, infectious disease vectors and pollinators are subject to aging and could be good research models.