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Scototaxis Behavior In Courting Male P. latipinna (Sailfin Molly)
Scototaxis is the behavioral preference for a darker environment as opposed to a well light or lighter background environment (Maximino). This behavior can be observed in many organisms in the animal kingdom, most notably, in teleosts. Some researchers believe this behavior has been evolutionarily re-enforced throughout the generations as a means of predator avoidance, and to ensure an individual’s safety. Many experiments have shown a strong correlation between a teleost being in an environment with a white background and observable anxiety-like behavior, with the fish erratically swimming around, apparently trying to find a darker area to “hide” in. This experimental setup will test if our local (Brownsville, Texas Resaca inhabiting) courting male sail-fin mollies (Poecilia latipinna) exhibit this same behavior.
The purpose of this research experiment is to assess whether or not P. latipinna showcase scotaxic behavior, even though our local population lives in very turbid aquatic environments. A study done on the mate selection preferences of female sailfin’s by way of symmetrical bar lines shows that this species relies heavily on eyesight during mate selection and courting. Females are shown to choose males that are more brilliantly colored and have symmetrical bar and coloration patterns along their bodies. One can only reason that in order for these preferences to have evolved and been re-enforced, is by females having the ability to see their mates when making a selection. The use of eyesight to aid in mate selection strongly urges the point that visibility and lighting play a strong role in this species mating strategy, and may have had behavioral changes secondarily changed to accommodate this lifestyle. “Using both live stimulus males and silicon models, we found that females have significant preferences both for bars per se and for males with symmetrical bars. The total number of bars and the degree of fluctuating asymmetry were negatively related so fluctuating asymmetry in bars may be an honest signal. This phenomenon may have influenced the evolution of the male courtship display in P.latipinna” (Schluter ’97). If these male morphs of this species have to display in order to attract mates, then behaviors to select better-lit areas in order to attract mates may have overtaken and spread across the local population.
Another study that suggests courting male sailfins may exhibit anti-scototaxic behavior, is research done by Klaudia Witte and Kirsten Ueding. Their research shows that female sailfins will copy the mate selection choices of other females in the area as a means of selecting the best mate possible. Essentially, this selection behavior is one that relies on the fact that more sets of eyes are better than one. If several females are selecting a single male out of all the available males in the population, this must mean there is a trait or set of traits that particular male possesses, that has a pre-established female bias. All females in the population are vying for the best mate to produce healthy offspring, done by scrutinizing the visible traits of potential mates within the available population. Again, this behavior is reliant on the ability of the female to see subtle differences between males, indicating that a male presenting itself in a well-lit area has a better chance of mating than one that is in a shaded environment. Witte and Ueding constructed tanks that allowed sailfins of opposite sex to see one another but not actually come into physical contact with one another or each other’s water; eliminating any olfactory or secreted hormonal queues. This experiment was wholly based on the premise that sight alone can be a determining factor when females select a mate. Males that were selected by multiple females (multiple females staying in areas next to male in his own area) where consistently selected by other females as opposed to those males that received less female attention, noted as rejection. Witte and Ueding concluded that females not only rely on the judgment of other females to select a better mate, females also rely on the scrutiny of other females in rejecting “less desirable” mates. “This is the first study showing that females copy another female’s rejection of a male. This is a novel aspect in mate choice copying. In our experiment, sailfin molly females spent significantly less time close to a video showing an attractive male after these females had observed another female that always escaped from that male when he tried to court her, that is, rejected that male. Interestingly, females not only spent less time with those males but also significantly reversed their preferences after observation of the escaping female and spent more time with the male they had previously found less attractive” (Witte & Ueding 2002).
Previous research and literature show that female bias, visual stimuli, and queues dictate much of the reproductive strategy in sailfin mollies. With this given information, I hypothesize that the courting male of this species may have lost this “dark environment favorability” due to the poor water clarity of its habitat, and dependence on courting behavior. If a reproductive female cannot see a courting male, this may significantly lower his chances of securing a mate, and cause a previously advantageous survival behavior, to become a reproductive hindrance.
The concept of this experiment is based on Caio Maximino’s (with the help of several collaborators) protocol for testing scototaxis behavior in fish. His 2010 publication in “Nature Protocol” attests to his team’s experimental tank construct validity. “ The construct validity of most anxiety models rely on linking them to species-specific defense reaction. In this model, a behavioral co-adaptation to heightened dorsal distribution of melanophores (i.e., preference for dark substrata to enable crypsis) is central to the construct in question” (Maximino 2010). He goes on to say that this model allows researchers to observe exploratory behaviors with out predator avoidance behaviors, but more along the lines of assessing the “risk” of the environment. You can view the tank setup in the figures section of this paper. Logitech c270 webcams were secured to ring stands that were fixed with clamped 80-watt light fixtures, and used to record behaviors during testing that would later be analyzed. The felt used to coat the inside of the tanks was the same for all four, 10-gallon testing tanks in this experiment. The felt was secured with hot glue and allowed to set for a week before testing. The tanks were rinsed several times before initial testing began to ensure no chemical residue was present. The water provided for this experiment was a mixture of distilled and Resaca water with a ratio of about 20:1 in favor of distilled. This mixture was chosen for clarity purposes, due to the fact that if too much turbid Resaca water was used, behavior could not be observed at all, and that if there were no dissolved solids in the water, it may have had an adverse affect on the specimens.
In order to collect courting sailfin mollies from the local aquatic environments, I employed the use of a mobile electro-fishing unit that was made available to me by Dr. Richard Kline during the course of this study. Individuals were collected from Resaca’s within the Brownsville city limits. These Resaca’s include, one found on our own campus here at UTB behind the Barnes & Noble bookstore, the Dean Porter Park Resaca, and from the Sabal Palm wildlife sanctuary on Southmost road. Adjustments were made to the voltage output in order to safely collect specimens without any unnecessary harm or discomfort to them. Unfortunately courting sailfin mollies were few and far between during electro-fishing trips to secure test subjects. These individuals that were collected for this experiment were allowed to acclimate and settle for a 24-hour period before subjected to any behavioral observations or testing. Specimens were housed in a 150-gallon live well tank equipped for proper water chemistry, aeration, and circulation appropriate for biotic needs. This setup posed a slight flaw in design as I was unable to distinguish individuals by origin of location, thus eliminating any chance of noticing any discernable patterns within individuals from a given cite. If given the chance, I would rectify this problem by utilizing several smaller tanks to keep like groups separated from one another.
After the allotted 24-hour acclimation time had been reached, each specimen was introduced into a novel environment (the terror tank filled with 10cm of water) in order to observe the individual’s scototaxic behavior. Before the scototaxis test was administered, the individual was corralled to the middle of the tank and on the defining line (light and dark divide), where they were enclosed using black and white felt covered acrylic “walls” (spaced 5cm apart) to effectively hold the specimen in place while not changing the perception of the environment. The test subjects where allotted a 10-minute settling period to acclimate to their new novel environment before observations began. After the appropriate settle period, video recording from overhead-secured external webcams, recorded the test subject’s behavior as the walls were removed, for a period of 15-minutes. Once the “walls” of each tank had been removed, in order to administer testing, the lab was vacated entirely to ensure no outside stimulus, other than normal lab acoustics that the subjects have already had time to get acquainted with. Once the fifteen-minute recording period had elapsed, the lab was re-entered, the webcams were deactivated, videos were appropriately labeled and stored, and the test subjects were moved to a secondary holding period to await release back into the wild. This process was repeated with freshly changed water, for all test subjects during the experiment. The video recordings were later analyzed for total time spent on either side of the tank.
Twenty courting P. latipinna males, ranging in length from 3.8 – 5cm, were tested and recorded in the terror tank setup with some interesting results (Figure 2). None of the individuals spent more than thirty percent of their time exploring the light side of the tank; with four males spending the entire observation time in the dark side of the tank. While this data may seem a little anti-climactic, we can infer from the given data that these individuals did in fact exhibit scototaxis behavior.
The data collected does not support the initial hypothesis of this experiment; courting P. latipinna males do still exhibit scototaxis behavior. Whether this is due to the introduction of a novel environment or the lack of females present still remains unclear. Further testing and analysis is still needed to come up with any kind of definitive answer.
The modeled protocol was adjusted in order to accommodate the time constraints of a single semester class and limited resources. Instead of the 30-day holding period for acclimation, this process was cut down to a single day in order to adjust to multiple students utilizing very limited work area and resources allotted towards the project. For the intensive purposes of acknowledging good science and in good conscience, given the opportunity, I would have adhered to the original protocol to ensure unbiased or skewed data. I feel it is in the best interest of the reader for me to acknowledge that due to the severe change in protocol, I cannot attest for the level of scientific merit of this experiment as the parameters have been changed. The data collected should be viewed as rough observations, and inadmissible by scientific standards.
Maximino, Caio, Thiago Marques de Brito, Rafael Colmanetti, Alvaro Pontes, and Henrique Castro. “Parametric Analyses of Anxiety in Zebrafish Scototaxis.” Behavioral Brain Research 210 (December 22, 2009): 1–7.
Maximino, Caio, Thiago Marques de Brito, Claudio Alberto Gellis de Mattos Dias, Amauri Gouveia Jr., and Silvio Morato. “Scototaxis as Anxiety-like Behavior in Fish.” Nature Protocols 5, no. 20 (2010): 221–28.
Schluter, Anne, Jakob Parzefall, and Ingo Schlupp. “Female Preference for Symmetrical Vertical Bars in Male Sailfin Mollies.” Animal Behavior 56, no. 1 (1997): 147–53.
Witte, Klaudia, and Kirsten Ueding. “Sailfin Molly Females (Poecilia Latipinna) Copy the Rejection of a Male.” Behavioral Ecology 14, no. 3 (2002): 389–95.
Courting Sailfin Molly (P. latipinna) Male Scototaxis Behavior