Female mate choice is usually based on traits that signal male quality as a sexual partner. According to the “good parent” hypothesis, female mate choice may also consider male quality as a caregiver in species with male-only care. Because parental activities may be costly, males in good condition should be more attractive to females than those in poor condition. We experimentally manipulated the body condition of non-parental and parental males of the egg-tending harvestman Iporangaia pustulosa and then evaluated how it affected their mating success and ability to protect eggs under field conditions. For non-parental males, individuals in good condition had twice the probability of mating than those in poor condition. For parental males, individuals in good condition had two times more chances of mating and acquired five times more eggs than those in poor condition. Surprisingly, males’ body condition had no effect on the efficiency of egg protection. Although our results indicate that the male condition is a sexually selected trait, we found no support for the “good parent hypothesis” given that an increase in body condition does not improve the survival of the offspring under male care. Instead, these findings are congruent with predictions of the “essential male care” model, which suggests that, when the costs of parental care are low (as is the case of egg attendance), most males can provide the minimum necessary care for offspring survival. However, only males in good condition can allocate surplus energy to advertise their overall quality and attract more mates.
Alissa, L.M., Machado, G. & Requena, G.S. Good body condition increases male attractiveness but not caring quality in a neotropical arachnid with male-only care. Behav Ecol Sociobiol 78, 24 (2024). https://doi.org/10.1007/s00265-024-03439-6