Changes in offspring vulnerability account for the increase in convict cichlid defensive behaviour with brood age: evidence for the nest crypsis hypothesis

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Several hypotheses have been proposed to explain the increase in parental defensive behaviour with brood age: parent re-nesting potential, age-investment, predator revisitation and nest crypsis hypotheses. However, these hypotheses are difficult to separate experimentally because many variables covary with brood age and all hypotheses predict an increase in effort with brood age. In this study, an attempt was made to determine which of these variables convict cichlid,Cichlasoma nigrofasciatum, parents assess in determining their defence levels at each developmental stage: egg (embryo), wriggler (free-embryo) and fry (larvae). The type of offspring parents had at each stage was manipulated. The experimental group was repeatedly given eggs until the offspring in the control group reached the fry stage, at which time the experimental eggs were allowed to develop. At each stage, parental behaviour was observed to determine whether the groups differed in past investment. Subsequently, a model predator was presented to determine whether the groups differed in defensive behaviour. The results suggest that the increase in parental defence in this species is due to the increased vulnerability of their offspring at the fry stage (nest crypsis hypothesis).