Quantification of role reversal in relative parental investment in a bush cricket

SEXUAL differences in courtship roles are thought to depend on the ratio of sexually available females to males 1-3. This 'operational sex ratio,3 should be biased towards the sex investing least in reproduction because they will have the higher potential reproductive rate 4. Thus relative parental investment 1,2 is thought to underlie observed courtship roles. Typically, males have the lower investment and compete for choosy females 2,3,5. But role reversal can occur when males invest parentally 2,3. Recent evidence supports the contentions that role reversal reflects shifts in the potential reproductive rates of males and females 4 and shifts in the operational sex ratio 6. Cases of male investment exceeding female investment in role-reversed species have not been found. In some insects, males invest in reproduction by providing the female with nutrients used for zygote production 7,8. Here I report the measurement of male and female investment in reproduction for a nutrient-provisioning bush cricket (Orthoptera: Tettigoniidae) and demonstrate that reversals in relative parental investment underlie courtship role reversals seen in this species 6,9.