Decreased immune response as a proximate cost of copulation and oviposition in a damselfly

Abstract.Males and females of the Japanese calopterygid damselfly, Matrona basilaris japonica Fester, showed a rapid (within 24 h), and significant reduction in immune system function (encapsulation response) after reproductive activity (copulation or oviposition). A similar, but non‐significant, change occurred in males that conducted energetically costly behaviour (fighting). These data suggest that there may be physiological costs other than energy‐based trade‐offs associated with copulation and oviposition that may have life‐history consequences via their effects on immune system function.