The net effects of guarding on egg survivorship in the flagfish, Jordanella floridae

We investigated the effects of male nest guarding on egg survival in the flagfish, a species in which paternal care is thought to be relatively recently evolved. Thus, we characterized the fitness consequences of a major component of paternal care when secondary adaptations to care are likely to be minimal. The effects of guarding under three predation regimes were examined by exposing eggs to treatments in which no predators, conspecific females, and conspecific females and the egg predator Gambusia affinis were present. These were crossed with the presence and absence of parental males. We expected that guarding would result in an increase in egg survival in the presence of egg predators, but considered that in their absence the benefit might be decreased or absent, as a result of filial cannibalism. We also examined effects on egg survivorship stemming from filial cannibalism and egg-directed components of care (i.e. cleaning and fanning); the effects of these behaviours were examined through treatments in which males had full access to eggs (i.e. complete care), males were separated from their eggs by a screen (i.e. egg fanning and no cannibalism), and males were absent (i.e. no care and no cannibalism). In accordance with our expectations, guarding increased egg survivorship in the presence of females and Gambusia. However, egg survivorship when males were alone with eggs was low. Indeed, significantly more eggs were eaten than became diseased, suggesting that males cannibalize healthy eggs. Neither fanning nor cleaning resulted in an increase in egg survivorship. Thus, in flagfish, there may be costs of care when predators are absent. We discuss our findings in relation to sexual selection and the early evolution of parental care.