Danielle de La Porte
Effects of Predator Size and Experience with Predators on Parental Investment in Female Convict Cichlids (Archocenturs nigrofasciatus)
Although parental care increases the chances of offspring survival and reproduction, a parent incurs a cost of providing investment because it compromises its own future reproductive success. A parent has to effectively make split-second decisions regarding nest making, foraging, offspring defense, etc. in order to make the most of its time and energy allocations. To maximize the benefits in parental investment trade-offs, a parent makes investment decisions based on brood characteristics such as size, quality, and age as well as its past investment in the current brood. The effects of brood characteristics and past investment in the current brood have been studied extensively. However, there is an absence in the literature regarding the effects predator characteristics have on parental decisions and investment. I studied the parental responses to predator threats on offspring by guarding convict cichlids, Archocentrus nigrofasciatus. To better understand parental decisions in relation to predator characteristics, threats by a heterospecific model predator to offspring were made with variable wait times between attacks and by model predators of various sizes.
A parent may face repeated encounters with the same predator; how should it respond to defending against the same predator again? Because when investing in its offspring a parent incurs costs, the parent should put forth only enough effort and defense to repel the predator. Any extra effort put into the defense could compromise the parent's potential future reproductive success. If a predator does reappear quickly, the parent should increase its investment to ensure the predator is deterred. As the wait time between predator attacks increases, the cost of retaining information about prior encounters increases, while the value of that information decreases. Therefore, I predicted that when times between threats by the same predator are at or less than one minute, a female should increase her parental defense; whereas, if the time between attacks is longer than one minute, a female should not increase her parental defense. To test this, I threatened the offspring of 16 females using the following times between attacks: 0.5, 1, 2, or 5 minutes.
Breeding pairs of convict cichlids were placed in 76 liter fish aquaria (water ranging in temperature from 25-28 degrees Celsius) with six plastic plants and one terracotta flower pot. Within the first day of a pair’s spawning, the male was removed, leaving the female to guard the eggs. Removal of the male allowed for a more precise measurement of parental investment since the investment of only one parent was monitored. On days 4 through 11 of the brood cycle, I threatened the fry with a model predator and recorded the number of times the guarding female bit the model. I then waited the amount of return time specified by the treatment, and then retested the female. Results show that female convict cichlid parents did not significantly modulate their defense efforts in relation to the various wait times between threats toward their offspring.
I also predicted that predator size should influence a parent's investment decisions—the reasoning behind it being a parent would need to expend more effort to deter a larger predator. To test this, I threatened the offspring of 15 females using a large predator model and a small predator model and then recorded the number of times the female bit each model in an experimental setup similar to that of the first experiment. In this experiment, however, the time between predator attacks remained constant (5 minutes), but the size of the predator varied between “large” and “small” (the average adult female standard length is about 50mm; therefore, “large” indicates greater than 50mm and “small” indicates less than 50mm). Each female was subjected to both models, and results show that female convict cichlids defend more aggressively against larger predators.
These experiments provide insight into the effects predator characteristics have on parental investment decisions. Although the wait times used in the first experiment had no significant effect on females’ parental investment, further research could compare wait times with greater differences to find if there exists any consistency or strategy in defending against a returning predator. The second experiment offered insight into a guarding female’s perception of a heterospecific’s predatory ability. From this, further investigations of a parent’s perceived threat to its offspring and a parent’s perceived threat to its own safety could be explored by varying predator size, morphology, marking and coloration, and attack behavior.
Delaporte, Danielle Lara. (2007) Effects of Predator Size and Experience with Predators on Parental Investment in Female Convict Cichlids (Archocentrus nigrofasciatus). Masters thesis, Department of Biological Sciences, California State University, Sacramento.
Danielle joined the lab in March of 2003 and finished her degree in December 2007.