Does the size of a predator influence the willingness of a parent
cichlid to defend its offspring?
Esther Tracy
Supervisor : Dr. Ron Coleman
Department of Biological Sciences
Abstract
The extent of parental investment is partly based on
maximizing lifetime reproductive success. When
confronted with a predator, a female cichlid must make a
choice to protect her current offspring or to call it a loss
and survive until her next chance at reproduction. In this
study, I tested the aggressive behavior of a female
convict cichlid (Archocentrus nigrofasciatus) toward
models of a predator of two different sizes to determine if
the predator size affects her willingness to defend her
offspring.
Background
Convict cichlids (Archocentrus nigrofasciatus) show significant
parental investment by protecting their offspring. Convict cichlids
have been shown to change their aggressive response due to
temperature, prior residence, conspecific density, risk of
predation, and even time elapsed since last mating (Fitzgerald
and Keenleyside, 1978; Cole et al., 1980; Ratnasabapathi et al.,
1992; Wisenden and Sargent, 1997; Kim et al., 2004). The extent
and kind of care-giving a cichlid gives may interfere with future
mating opportunities (Kuwamura, 1986). Because the goal of any
animal is to maximize its lifetime reproductive success, the
female convict has to make a decision whether to continue
attacking a predator or abandon her offspring and have an
opportunity for future reproduction. In nature, predators come in
all different sizes, the larger the predator the greater the threat to
the wrigglers and to the cichlid providing the care.
California State University, Sacramento
Methods
Each pair of convict cichlids was placed in a 76 liter tank
with two terra cotta pots and two plastic plants to provide
shelter. Tanks were filtered using a sponge filter and
heated using a 150 watt heater set to 27 degree Celsius.
The bottom was covered with medium sized gravel. A pair
of cichlids was placed in these tanks until the eggs were
laid, at which point the male was removed from the tank so
the female was the only one providing the parental care.
Various sized female convict cichlids were used in order to
test if parental size affected the aggressiveness of the
female. To test parental investment in convict cichlids,
female convict cichlids were presented with two different
sized models of Amphilophus hogaboomoruma, a species
of cichlid found naturally with convict cichlids. The small
model measured 5.5 cm while the large model measured
7.2 cm in length. The model predator was placed in front of
the three day old hatchlings, and moved in a figure eight
pattern in rhythm to a metronome set at 80 beats per
minute.
Aggressive behavior was measured using a clicker
counter recording the number of bites that the female
delivered onto the models for a 30 second period. Each
female was observed for 10 days after the eggs had
hatched.
Preliminary data shows a bell shaped curve pattern in the
number of bites a female delivers during the development of
her offspring. The highest peak in aggressiveness from the
female comes at about day five or six. The days prior and
after the peak taper off.
A one-tailed paired t-test on the data points collected so far
show a p-value of 0.280 with the degrees of freedom being 3
This does not show that there is a significant statistical
difference between the attacks on a large versus small
predator model.
Fig 4. The number of bites delivered by the female convict cichlids on the small
versus large models
Hypothesis
Discussion
I hypothesize that a female convict cichlid will increase her
attacks on a larger model versus a smaller model in order to
protect her offspring.
6
Figure 2 Experimental tank set up
Figure 3 Presenting a female cichlid with a model of the predator
Figure 1 Different sized models of Amphilophus hogaboomorum representing the predators
Preliminary Results
With a p-value> 0.05, preliminary statistical analysis
shows that there is no statistical difference in the number of
bites exerted onto a certain sized model. This suggests that
female convict cichlids don’t assess one of the models as
more of a threat than the other.
It has been hard to gather data because four of the
females have spawned but have not attacked the models.
One reason could be that the models are not realistic enough
and the fish don’t feel threatened. The difference between the
two models could not be large enough to merit more
aggressive behaviors. Another reason could be that the
females have not spawned previously and still are trying to
figure out how to be mothers, or it could be due to the fact
that the females have bred before and feel like their
reproductive success is sufficient.
We thank the Summer Undergraduate Research Experience Award of the College
of Natural Sciences and the Department of Biological Science, CSUS, for support.