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Animals often increase their investment in reproduction in response to a threat to their survival (e.g. an infection), a life history strategy known as terminal investment. The dynamic terminal investment threshold model proposes that the tendency of an individual to terminally invest depends on other factors that alter an individual’s residual reproductive value. Here, we test the dynamic terminal investment model in burying beetles, insects that bury small vertebrate carcasses as a source of food and that provide extensive biparental care. We injected males at two different ages with heat-killed bacteria and measured their reproductive effort, predicting that immune-challenged males would show a longer period of parental care, consume less of the carcass, and produce a greater number of larvae in the current reproductive attempt compared with control males. We further predicted that older males would be more likely to terminally invest than younger ones. Males, when challenged with heat-killed bacteria as virgins prior to their first reproductive attempt, did not terminally invest, whereas these same individuals when challenged in a subsequent reproductive bout produced a greater number of offspring. Older, immune-challenged individuals gained less mass during their time on the carcass than control males, suggesting that terminal investment was subsidized by their consuming less of the carcass than they might have otherwise done in the absence of an immune challenge, leaving more for their offspring to consume. We conclude, that the age-specific terminal investment shown by immune-challenged males in the current study supports the dynamic terminal investment model.
Farchmin, Paige, "Dynamic Terminal Investment In Male Burying Beetles" (2021). Biology. 13.