Effect of Brood Developmental Stage on Parental Defense by Female Convict Cichlids
A common pattern in parental investment has been observed in various taxonomic groups: investment peaks early in the brood cycle and gradually diminishes through time. Previous studies suggest that brood age, in terms of development stage, is one factor that influences this pattern. However, results of previous studies may have been confounded by differences in past investment, perception of a predator model as a threat to the parents, interactions between the parents, and use of unrelated offspring as surrogates for the parent’s natural brood. With modifications to previous study designs, I controlled these factors. My objective was to investigate why parental care changes over the life cycle of a brood in a short-lived ectotherm, the convict cichlid, Archocentrus nigrofasciatus. I predicted that brood developmental stage affects parental defense of offspring by female convict cichlids. Specifically, I expected females to defend larvae (wrigglers) less than fry, a later developmental stage, primarily because fry are more mobile and visible to predators. The research was conducted in the Evolutionary Ecology of Fishes Laboratory at California State University, Sacramento from October 2004 through February 2005. Adults were paired in individual tanks for spawning. After each spawning, the male was removed, and 90 eggs were left with the female. Eggs in excess of 90 were moved to a separate brood tank for either the control or experimental treatment. Developmental stage in separate brood tanks was controlled by manipulating water temperature. In the parent tanks, parental defense was measured daily as number of bites on a predator model. On Day 6, after testing, the surviving brood (fry) in the parent tank was removed and replaced with the same number from its corresponding brood tank (control = fry; experimental = wrigglers). The difference in defense (number of bites on Day 7 minus number of bites on Day 6) was calculated for each sample. As predicted, defense was significantly lower (p=0.002) for the experimental than for the control group. Results show that parental investment by female convicts is affected by brood developmental stage. This experiment provides a new method for testing the effect of brood developmental stage on parental investment without using surrogate offspring from other parents. Similar research applied to different taxonomic groups, life histories, and life stages would provide empirical data for new or improved models to predict evolutionary trends in the past or future under various selective pressures.
Kogut, Nina J. (2005) Effect of Brood Developmental Stage on Parental Defense by Female Convict Cichlids. Masters thesis, Department of Biological Sciences, California State University, Sacramento.
Nina is holding a leopard shark
Nina joined the lab in January of 2002 and finished her degree in May of 2005.