Abstract
Understanding the evolution of various forms of parental care is a key question in the field of evolutionary ecology. The study of parental behavior is inseparable from Williams' principle and parental decisions should be analyzed in terms of present reproductive costs diminishing the expected future reproduction of an individual. Due to the diversity in parental behavior exhibited within the family, cichlid fishes present an excellent opportunity to study the evolution of parental care.
The experiments presented herein address two different aspects of the evolution of mouthbrooding in cichlid fishes: first, if mouthbrooding may have had its origins as a response to predation pressure; and second, if these fishes are able to adjust their investment in offspring defense in relation to the perceived risk for their young. By presenting potential predators of their offspring to parenting females of two different species of Neotropical cichlids, I studied the changes in their parental response.
When they perceived high risk for their offspring, females of the substrate spawning convict cichlid (Archocentrus nigrofasciatus) used their mouths significantly more in offspring retrieving, a behavior that can be considered an incipient state of mouthbrooding. This may constitute evidence that high predation threat on the young acted as a selective pressure promoting mouthbrooding.
Delayed mouthbrooder Gymnogeophagus balzanii females were capable of adjusting their investment in parental care by delaying by 33.9% the time of first releasing their offspring in response to the perception of predation risk for her young. Delayed mouthbrooding is considered to be an intermediate state between substrate spawning and immediate or pure mouthbrooding.
Together, these results prove that female cichlids are capable of adjusting the amount of parental investment in response to predation threat for their offspring and suggest that in some Neotropical cichlids, maternal mouthbrooding may have evolved from biparental substrate spawning as a result of male desertion in environments with high predation upon fry.