By: Elizabeth Constantine, Mackenzie Gomes, Brianna Roy, Yasmine Sudhu (Stonehill College, BIO323 Evolution, Fall 2018)
In our own lives, we choose mates based on qualities that attract us. Typically, these traits are a mix of both physical and emotional characteristic, but regardless this preference is animalistic and instinctive. Fish, which are our distant relatives, exhibit similar mating strategies. In the Atlantic molly, female mollies choose to mate with males who are large in size, aggressive in nature and display a vibrant color pattern. The intensity of sexual selection is predator-induced. Female preference changes when predators are introduced into the equation. Seems hypocritical, until you see why.
A team of researchers, led by David Bierbach, were interested in how predators influence mating preferences in female Poecilia mexicana. Poecilia mexicana, Atlantic Mollies, are small fish that estimate to be about 1.6 inches long. The males often vary in their color and size, of which the females prefer the larger, more colorful ones. In this study, the mating preferences of predator naïve and predator experienced females were tested in the presence and the absence of large predators. The lab reared mollies were sampled and taken from Río Oxolotán in Mexico and reared about six thousand litters that stayed in fish-cultured tanks until the experiment began. The wild caught mollies were taken from the stream of Río Ixtapangajoya, about 20 kilometers of the lab-reared mollies. All the females in this study were most likely in or around their reproductive stage. The post-partum females were taken out and excluded in this study.
Female mollies were held in a large tank with two small tanks attached on opposite ends, that held one male molly at a time. The attached tanks were made of clear material, so the females were able to view the male mollies but were not able to interact with them. In the middle of the large female holding tank, a third clear tank was attached. This tank contained one of four predators, which were introduced to the females at separate times. In treatment one (1), a green swordtail female served as the control since it is morphologically similar to mollies. Treatment two (2) consisted of the the Nile tilapia, a filter feeder that ingest plants, dead organic materials, and insects. The third treatment (3), involved a Vieja bifasciata , a large fish which consumes algae and dead organic material. The final treatment (4), used an omnivore that includes mollies in their diet, the Cichlasoma’ salvini.
In all four treatments, the wild-caught mollies spent significantly more time near the larger male molly. Analysis of the fourth treatment (4) showed that the data was not statistically significant from the control preference experiment where no predator was introduced. The lab-reared female mollies spent the most time near larger males in treatment one (1). Treatments (2) and (3) indicated that females spent more time with the smaller males, but both were statistically insignificant from the control. The fourth treatment (4) revealed that the females spent an ample amount of time with the smaller males. In conclusion, the presence of a predator will altered the mating preference of a female Atlantic molly.
Citation: Bierbach et al.: Predator-induced changes of female mating preferences: innate and experiential effects. BMC Evolutionary Biology 2011 11:190.
Author’s website: http://www.davidbierbach.com/
Music: Holmes , Scottian. “Corporate & Motivational Music 2.” Free Music Archive, 20 Aug. 2018, freemusicarchive.org/music/Scott_Holmes/Corporate__Motivational_Music_2/.
Twitter account: Millie the Atlantic Molly
Essay question: Do you think that this an effective survival strategy among Atlantic female mollies? Why or Why not?
b. Female mollies want to survive in order to pass on their genes
c. Why do female mollies prefer small, dull males when a predator is near?
iii. To protect themselves
iv. Small, dull males are more attractive
v. Large, colorful males mistreat the females
d. Under normal environmental conditions, what traits do female mollies prefer?
vi. Small and dull
vii. Large and dull
viii. Large and colorful
ix. Small and colorful