The Effects of Water Temperature on Mate Choice For Convict Cichlids (A. Nigrofaciata) Juan M. Ortiz Jr. Faculty Mentor: Ron Coleman, Ph.D. McNair Scholars Journal s Volume 17 Abstract Mate Choice is a complex issue in the study of animal behavior. Most studies have focused on the morphology of potential mates, e.g., males with brighter colors, etc. Unfortunately, the effect of temperature has been overlooked. Recent research suggests that temperature can have profound effects on behavior. In this study, it was hypothesized that temperature can affect mate choice in convict cichlids. Female behavior was analyzed by observing the mate choice of females against a paired situation of males experiencing different temperatures. The results supported the hypothesis. Future research should analyze how this factor affects mate choice in other species. Introduction Why do sharks attack people? Why do beavers build dams? Why do animals behave the way they do? The answers to these and many other questions lie in studying animal behavior. According to Charles T. Snowdon (1995), a former president of the Animal Behavior Society at California State University, Northridge, Animal behavior is the bridge between the molecular and physiological aspects of biology and the ecological. Behavior is one of the most important properties of animal life (par. 1). In retrospect, animal behavior can be explained by how their anatomy interacts with the ecosystem. For example, a hawk has wings but why do they fly? The answer is relatively simple; hawks fly in order to gain altitude. In turn, the higher altitude gives the hawk a wider scope of the land and raises the probability of spotting prey. In other words, the reason a hawk has wings (anatomy) is so that it can catch prey (ecosystem) and to do this it needs to use its wings to fly (behavior). In order to answer questions regarding behaviors displayed by animals, further research must take this kind of approach, especially for some of the most critical behaviors such as sexual selection or even dominance struggles. Mate choice can be best defined as a form of natural selection in which the male or female is attracted by certain characteristics such as form, color, behavior, etc of a potential mate (Farlex 2012). In every species of animal, there are certain characteristics that each gender within that species tends to search for in the 79
California State University, Sacramento opposite sex when reaching a consensus on mate choice. Some of the most common characteristics that females look for are parental abilities, resources, and courtship display (Bateson and Holliday, 1983). For example, in species where males carry out some or all of the parental care of the young (Bateson and Holliday, 1983), there is a higher chance for a male to be selected depending on the amount of parental care a male can display before having any offspring of its own. This particular trait is important because females from certain species want a male that can keep both eggs and offspring safe from predators. For many fish species, females seek males that are capable of displaying their dominance over a territory and simultaneously being able to nurture the fry. In this study, the observational unit in question is the convict cichlid (Archocentrus nigrofasciatus), specifically the females. Cichlids are considered to be a model subject in behavioral studies because many cichlid species are easily accessible and maintained (Barley & Coleman 2010). In this regard, they can easily grow and breed within a lab setting. According to Coleman (2008), once cichlids become comfortable with living in a prepared fish tank, they can begin to nest eggs in as little as a day if given the necessary resources (e.g., available space, food). However, this is only the case when the female is paired with one male cichlid in the tank. If the female is exposed to two different males within the same tank simultaneously, then she is forced to choose between the males. A typical mate choice apparatus divides a tank into three compartments as to isolate one gender from another. It also serves to minimize for certain external factors such as dominance and only examine the factor in question. For example, Kennedy et al. (1987) analyzed how variation in male infestation of nematodes effects female mate choice. They found males who had higher burden of parasite infestation almost always had a lower courting rate and suggested that females may be using courting as a cue for mate choice. They also suggested that there may have been an unknown effect from the parasites that could have made the females discriminate against the heavily infested males. For their experiment, Kennedy et al. used a mate choice apparatus similar to the one for this experiment in order to measure the amount of time that the females spent with each male. One of the most common topics of studies relating to cichlid mate choice is the size distribution that female convict cichlids use to select their respective male convicts. In one study, Robart (2011) hypothesized that a female will naturally increase investment in reproduction in the presence of a high quality partner. Robart s results supported her theory, indicating that as male size increased, so did the amount of time a female invested on reproduction. Because female fish spend a majority of their time focused on the development of eggs, it was concluded a potential mate is very important. There are several studies that describe the relationship between female mate choice and the size of males, but rarely do these 80
McNair Scholars Journal s Volume 17 studies account for water temperature. In particular, these studies seem to neglect to mention whether temperature was controlled throughout the experiment. There are a few studies that analyze the effects of temperature on cichlid behavior. For example, a study conducted by Jesse Heckendorf (2014) observed mother cichlids behavior towards intruders when placed in warm water temperatures and cold water temperatures. Heckendorf (2014) found that when a mother cichlid was bombarded by intruders at a warmer water temperature, there were more bites inflicted on the intruder than when the mother cichlid encounters intruders in colder water temperatures. In another study, Bell and Shanklin (2011) analyzed aggressive behavior at different temperatures, measuring the amount of bites and the time spent chasing between a pair of female convict cichlids. The observed results demonstrated that on both measurements, the values increased when the pair of females were placed at warmer water temperatures. Both of these studies demonstrate how convict cichlid activity increased when the temperature of the water also increased. If increasing temperature causes fish activity to increase, and females have a higher preference for males that tend to express higher activity levels, then there exists a chance that previous experiments demonstrating a lack of water temperature control may have confounded data because of the effects of temperature. The aim of this study is to measure the frequency by which female convict cichlids will choose between two male cichlids when placed in the same tank at different water temperatures. The goal of the is to determine if female convict cichlids prefer males in warmer water. Study Species The study species used for this research was Archocentrus nigrofasciatus. The convict cichlid is a small fish that is native to the waters of Central America such as Guatemala, El Salvador, Nicaragua, Costa Rica, and Panama (Barley & Coleman 2010). It is one of the few fishes that have gone through extensive studies in behavioral science because they are capable of simple tank maintenance, quick reproduction cycles, and manipulation (Galvani & Coleman 1998). Methodology In biology, the majority of experiments tend to take place out in the field or in a laboratory. Biological experiments allow biologist the opportunity to control factors in an animal s environment and see how the animal may react by observing the behavior. It is through the use of experiments and observations that biologists can determine the different types of environmental factors that contribute to animal behavior. Some of the key variables that influence animal 81
California State University, Sacramento behavior the most include the amount of exposure to light, the population number, or the presence of predators. For this experiment, the focus will be on the consequences in the level of attraction when two convict cichlids of the opposite gender are exposed to warm or cold water temperatures. This experiment took place in the Evolutionary Ecology of Fishes Laboratory at California State University, Sacramento. The laboratory itself is maintained to have a light: dark cycle of 12:12 in order to mimic a normal day. This experiment allows the scientist to derive general conclusions about convict cichlids, and gain specific details about the behavioral changes displayed. The results will serve as a step in better understanding animal behavior and potentially population conservation of the convict cichlid. Experimental Design Apparatus and Tank Set-Ups In this experiment, three tanks were needed. The first tank was labeled as the Experimental Tank. This tank is a fifty-gallon tank that has both clear and black barriers added to them. The clear barriers were placed approximately ten metric inches from the sides and separated the tank into 3 different and independent sections. In the middle there were two black barriers that did not run completely across the tank but instead created a passage from one clear barrier to another approximately 5 metric inches away from one another. Once the barriers were in place, approximately three metric inches of gravel was inserted into the tank measuring from the tank floor. The tank was filled with water at about 5 metric inches from the top of the tank. As displayed in Figure 1, each independent section was labeled as 1, 2, or 3. Four plastic hygrophilia plants were then placed in the tank: two on the side areas labeled 1 and 3 and then two in the middle section closest to the clear barriers within section 2. The hygrophilia were twelve inches tall and were produced by Tetra Water Wonders Decorative Aquarium plants. A water heater was inserted in each section. In this experiment, two Eheim Jager 50W Heaters and one Jager 100W Heater were used and the first two are placed in sections 1 and 2 while the last heater is placed in section 3. The first two heaters were set to 23 Celsius and the last heater was set to 30 Celsius. Each section had a thermometer in order to ensure that temperature was accurate for each section. Finally, a sponge filter was placed in the back of each section. 82
McNair Scholars Journal s Volume 17 Figure 1 Front View of Experimental Tank Figure 1 Birds Eye View of Experimental Tank The next two tanks will be labeled as the Used Male Convict Cichlids and Used Female Convict Cichlid. Each tank was given an Eheim Jager Heater that was set at 23 Celsius and a sponge filter. These tanks were used after each trial to place the convict cichlids that have already been tested. Experimental Protocol The experiment was conducted with twenty-one convict cichlids, 3 for each trial. For each trial, 2 mature male convict cichlids of similar size (no more than one millimeter difference in size) and 1 mature female convict cichlid were obtained. A caliper was used to measure the total length (tip of the nose to the end of the tail) and the standard length (tip of the nose to the base of the tail) for all convict cichlids. A mass balance was used to measure the mass of all the convict cichlids. Once measurements were taken, one male was placed in section 1, the other male in section 3, and the female in section 2. The cichlids were given two to twentyfour hours for the convict cichlids to adjust to the Experimental tank. 83
California State University, Sacramento Once the time of adjustment for the convict cichlids passed, two stopwatches and a timer were obtained. One stopwatch was set at the clear barrier between sections 1 and 2 while the other was set between sections 2 and 3. The timer was then set to fifteen minutes and the stopwatches were zeroed out. The timer was then initiated and the stopwatches were started every time the female was in close proximity to the clear barriers and then stopped once she exits that area. After fifteen minutes, the time displayed on the stopwatches was recorded. For this experiment, we can assume that the female convict cichlid will spend more time in the area closest to the more favorable male convict cichlid. Data collection lasted for a total of 3 days. At the end of the third day of data collection, a fish net was used to transport the males and female convict cichlids to their respectively labeled used convict cichlid tanks. The experimental procedures were repeated for six additional trials, replacing the convict cichlids with new cichlids and alternating the location of the heaters in the male sections so that the water temperatures in section 1 and 3 alternated. Once the experiment was completed, the sponge filters were rinsed with tap water and the Experimental tank was cleaned of any fish waste using a water syphon as a vacuum. All labels were removed from the Experimental Tank and the tank was left open for any other experiments. Data Analysis Once the experiment was over, all measurements of time were converted into seconds for uniform units. The times for the stopwatch that represented the convict cichlid at 30 Celsius in each trial were averaged; the times for the stopwatch that represented the convict cichlid at 23 Celsius for each trial were also averaged. The data were then graphed on a bar graph to display the differences between the times in each trial. A paired t-test was run using the collected data to determine if a significant statistical difference existed with the results in the time the female spent next to the two males at different water temperature. Figure 3 The graph displays the results of this experiment in the form of a graph. 84
McNair Scholars Journal s Volume 17 Results Females clearly spent more time next to the male in the warm water. The paired t-test results are as follows: t=6.11, df=5, and p<0.001. Discussion The data demonstrated that there was a preference for female convicts to choose males that were exposed to higher water temperatures. One of the greatest factors that contributed to this outcome was that the males at a higher water temperature consistently displayed greater observable levels of activity. Limitations Throughout the entirety of the experiment, there were a few implications that arose along the way. In the beginning, this researcher thought that the ultimate way to test for mate choice was to wait and observe if the female would eventually lay eggs along the area closest to the male that she would choose as her mate. After several weeks of waiting for the female to nest, an assumption was made that the female will not lay eggs unless she was physically able to have contact with the male of her choice. As a result, another way of measuring mate choice needed to be created in order for this experiment to progress. Eventually, it was determined that mate choice can be measure by the amount of time the female spent with the male convict cichlid. It can be assumed that if an individual has a preference for a potential mate then they would spend more time observing them. Another implication that arose in this experiment came from the pots that were added into the tank to provide a shelter for the female. There were a few occasions where a specific pot would be placed in the apparatus and the female would be inclined to only spend time within that pot and not observe either male. During these times, the pots would be switched out with another one and then the female was given time to adjust to the new pot. Conclusion In this experiment, there was a clear significant difference in female convict cichlid mate choice between males that were subjected to different water temperature. The results displayed a higher female preference for males that were located in higher water temperature than those at equal or lower temperatures as the female. Those at higher water temperatures may have likely been chosen more often because they displayed higher levels of activity, which is one of the many factors that have been known to correlate into mating for convict cichlids. Higher activity levels in males are correlated with 85
California State University, Sacramento greater efficiency in defending both territory and fry as compared with males displaying average or low levels of activity. For this study, other researchers may argue that the female may have possible just wanted to be warmer and so chose to be closer to the barrier next to warmer water. In order to counter this argument, I conducted a separate study to test whether a temperature gradient would arise from barrier housing the warmer water. I placed thermometers in one metric inch intervals away from the warm water barrier between sections 1 and 2. I did the same thing at the barrier between section 2 and 3. The results demonstrated that there was no temperature gradient within section 2. The temperature stayed constant throughout the entire section. Thus it would discredit any argument that the female chose to be closer to the male at a higher water temperature in order to stay warm. Future Studies After conducting this experiment and observing how convict cichlids behave, this researcher believes that the knowledge gained from this experiment can be used from a genetic perspective. By manipulating which female mates with which male, important genes can be maintained while others can be enhanced or even new genes can be expressed This will allow the researcher to determine how similar marine life behavior is to one another and how this behavior either exists or doesn t in humans or other land born animals. 86
McNair Scholars Journal s Volume 17 References Barley, Anthony J., and Ronald M. Coleman. Habitat Structure Directly Affects Aggression in Convict Cichlids Archocentrus Nigrofasciatus. Current Zoology 56.1 (2010): 52-56. Bateson, P., and T.R. Halliday. The Study of Mate Choice. Cambridge University Press (1983): 3-32. Bell, Nate, and Nate Shanklin. Effect of Temperature on Aggression of the Convict Cichlid. Undergraduate Research Reception and Poster Presentation. Sacramento State: College of Natural Sciences & Mathematics. Sacramento State, Sacramento, CA. 4 Oct. 2011. Poster Presentation. 23 May 2016 Coleman, Ronald M. Cichlid Research Home Page: Introducing the Cichlids Cichlid Research. California State University, Sacramento, 18 Dec. 2008. Retrievd from http://cichlidresearch.com/introducingcichlids.html. Galvani, Alison P., and Ronald M. Coleman. 1998. Do Parental Convict Cichlids of Different Sizes Value the Same Brood Number Equally? Animal Behaviour 56: 541-46. Heckendorf, Jesse. Mother Convict Cichlid Inflict More Bites Upon an Intruder in Hot Temperatures. Digitalcommons.calpoly.edu. STAR Program Posters, 1 Aug. 2014. Retrieved from http://digitalcomons.calpoly.edu/star/296/. Kennedy, C.E.J., J.A. Endler, S.L. Poynton, and H. McMinn. 1987. Parasite load predicts mate choice in guppies. Behav. Ecol. Sociobioly. 21: 291-295 Mate choice. (n.d.) Farlex Partner Medical Dictionary. (2012). Retrieved 2015 from http://medical-dictionary.thefreedictionary.com/mate+choice Robart, Ashley R. Effect of Mate Size on Maternal Reproductive Effort in the Convict Cichlid Amatitlania siquia. Current Zoology 58.1 (2011): 66-72. 87