BIOL112 Animal Biology


The experiment was conducted using the Evobeaker(r), computer simulation program “How a Guppy Got Its Spots”, (Simbio Virtual Labs(r).)

It included five study locations (Upper West Stream, Lower West Stream, Upper East Stream, Lower East Stream, Meir Creek ), with and without predators. There was one holding cooler and three tanks.

Simulations were run for about four to eight generation, including before and following the removal of predators and before and during transplantation.

The simulations involved 15 males randomly sampling and recording their spot brightness on a scale ranging from 0-20.

Each simulation was repeated 21 times. The results were visualised with histograms, and two-sample statistical t-tests were used to verify the validity of each.

To verify the hypothesis that male spots brightness is determined in part by adult predator risk (AH1), we calculated that a decreased or increased predation rate would cause a decrease (or increase) in the average male spot luminosity over time (P1). The male spot brightness of males was measured before, 1000 days after, and 1000 after, the addition of a predator, Cichlid A, to Upper East Stream and after, the removal (Cichlid A), from Lower East Stream.

East Stream

To test the hypothesis of male spot brightness being determined by sexual choice (AH2), we predicted that male spot luminosity would rise over time in a population that is free from adult predators (P2): Male spot brightness was recorded 800 day after 15 dull males (brightness scores =7) were transferred to a predator-free aquarium.

To verify the hypothesis that male spots brightness is determined geographically (AH3), we predicted that males would have an average spot luminosity similar to their original inhabitants (P3). We recorded male spot brightness in the Upper West Stream as well as in the Lower East Stream prior to removing all fish from Upper West Stream. All fish were then transplanted from the Lower East Stream into the Upper West Stream.

1000 days after transplantation, the male spot brightness in Upper West Stream was documented.

Also, we used P1-P3 for testing the hypotheses about male spot lighting being determined by a combination predation risk and sexual selection (AH4) or random with respect predation and sexual selection (AH5). If one or more of these predictions are true, then support AH4. However, if none are true, support AH5.


Charles Darwin’s theory of evolution proposed a theory that justified descent with modification.

According to this theory, if a particular population of organisms shows inheritance, variation, or differential reproductive success, it is likely that its composition will change significantly over time (Laland and al., 2014).

Guppies (Poeciliareticulata), aquarium fish are highly patterned.

While wild males may not have extravagant ornamentation, they are still stunning.

They wear spots, stripes and splashes of many vibrant colours such as yellow, orange, black and orange (Kodric Brown 1985).

John Endler, the famous evolutionary biologist, was fascinated by the colouful patterns displayed by wild guppies in Trinidad during the 1970s.

Deacon & Magurran (2016) found that male guppies in one pool were characterized by bright orange and blue splotches along their sides. While those who live downstream had only small dots at the tails, Endler noted this.

There were also differences in the distribution of guppy prey.

Endler performed the research to test the hypothesis that the diversity among the populations could be due to the presence of predators in the aquatic system.

This was due to the fact that the guppy that lived in the stream with the predatory cichlids had fewer spots on their bodies than the guppies that were living with Rivulus. (Endler, 1980).

The current laboratory work challenged learners to design a study that could document evolution by natural selection in the wild.

It was necessary to conduct a field investigation on wild guppies, and to assess the variation between males in various wild populations.

John Endler’s definitive study on natural selection in guppies was the foundation of the EvoBeaker simulations.

The purpose of this research is to examine the variation in guppy males across different populations.


Study results showed that predators in streams significantly decrease the average brightness for the male spot.

Alternately the stream had fewer predators, which led to a significant increase in the average brightness of male spots.

According to the first hypothesis, the male spot brightness can be determined by the risk of adult predators (AH1)

It was proven that the prediction regarding increased or decreased risk of predation would cause a respective reduction or an elevation in the average brightness male spot with time (P1) is true.

Similar to the above, male spot brightness increased significantly when females and males were kept in predator-free tanks.

Therefore, the second hypothesis (AH2) that explained the brightness of male spot through sexual selection was accepted.

The prediction that the average spot brightness of males within a population would rise over time, even without predators that have become adults (P2) was proved to be correct.

A significant difference in the average brightness of spots in male guppies after and before the transplanting factor was observed.

However, there was a marked difference in the average brightness for spot in males living in Lower East Streams after they were transplanted to Upper West Streams and removed the males that had been previously found there.

The geographically-located hypothesis (AH3) that spot brightness is determined by geography was rejected.

The prediction that the average spot brightness would be the same for males who move to a new area is false (P3).

The fourth hypothesis view was based upon the calculation of spot brightness in males using combined risk of predatory, sexually selective and geographical location (AH4).

AH4 was supported as two of the three predictions proved true.

The results of this study support the theory that natural selection, specifically sexual selection, is possible.

The process of sexual selection, which is a form natural selection, occurs when certain organisms produce offsprings more efficiently than others so that they are more likely to be selected for mating (West Eberhard and al. 2014).

Guppies adopt the sexual selection theory because they are not fighting for their existence but to find the right mating partner.

There are either no or very few offspring as a result of the struggle between male and female guppies to have females.

Evolutionary pressures cause male guppies in order to be more attractive to females (Wilson, et al. 2014).

A male guppy who is more attractive to females would indicate that she will be more likely to choose him for her preferred mate. This would allow him to pass on the genes to future generations.

When predators are high in water bodies, evolutionary pressure is on guppy species to camouflage themselves to avoid being prey.

Because the priority in these cases is to survive and not reproduce, the brightness of body spots does not matter (Tefertiller (2016)).

The study found valuable evidence supporting long-standing models for sex chromosome evolution, which suggests sexual selection in conjunction with sexual conflict during genome evolution.

The discussion can therefore conclude that spots in guppies result from natural selection theory as proposed by Darwin.

This supports the theory about sexual selection.

Linking reproduction and locomotion in the Trinidadian puppy (Poeciliareticulata).

15 How behaviour contributes to an Invasive Poeciliid Fisch’s Success: The Trinidadian Guppy is a Model Species.

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Natural selection and color patterns in Poeciliareticulata.

How size and color affect Mate Selection in Poeciliareticulata.

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Behavioral Ecology & Sociobiology 17(3), 199–205.

Do evolutionary theories need to be rethought?

Studying male guppy mating behavior.

Journal of Introductory Biology Investigations. 5(4).

Darwin’s forgotten idea. The social essence sexual selection.

Dynamic social networks among guppies (Poecilia.reticulata).

Behavioral ecology, sociobiology, 68(6) 915-925.

Convergent recombination suppression supports the role of sexual selection for guppy sex-chromosome formation.

Nature Communications 8, 14251.