This IA achieved a 23/24 in May 2022. It is a HL Biology IA on ecology done with a simulation.
Title: An Investigation Into the Effect of Predator Density on the Simulated Phenotypes of Guppies,
Poecilia reticulata.
An Investigation Into the Effect of Predator Density on the Simulated Phenotypes of Guppies,
Poecilia reticulata.
EXPLORATION
RESEARCH QUESTION
How does the predator density affect the simulated population number of the Wildtype and Golden phenotypes of
guppies, Poecilia reticulata in sandy environments over 30 generations?
INTRODUCTION
The phenotypes of guppies have been thoroughly
investigated and observed by several biologists. When we
studied population adaptations and the frequency of
characteristics, I often wondered the extent to which
external factors affect evolutionary changes. This
simulation developed my curiosity because our school’s
science department is fortunate enough to care for several
fish tanks. One of which holds guppies, as demonstrated
in Figure 2. Ever since I began my classes last year in the
rooms that hold fish tanks, I have taken any opportunity
that comes my way to interact with the fish, whether it be feeding, cleaning the tank, or even buying them accessories
for environmental enrichment, as seen in Figure 1. Even more astonishing, when I returned from summer break, there
was a new generation of fish, each with slightly different colouring patterns and fin shapes. This prompted my interest
in the evolutionary adaptations of guppies.
BACKGROUND INFORMATION
Poecilia reticulata, more commonly referred to as guppies, are small freshwater fish native to South America.
Evidence of various colour expressions in guppies has been primarily investigated in the Caribbean island of Trinidad.
The two phenotypes that have been most commonly studied are the Wildtype and Golden guppies. A visual
demonstration of these two phenotypes can be seen in Figures 3 and 4. Kottler et al. found that mutations in the type
III receptor tyrosine kinase, produced by the Kita gene, is responsible for the Golden phenotype. The mutation causes
a lack of dendritic melanophores, which may explain the uni coloured, Golden phenotype (Kottler).
The simulation Guppy Evolution: Natural Selection, Sexual Selection, and Genetic Drift, created by Jon Darkow, aims
to model how the evolutionary behaviour of the P. reticulata is affected in response to the alteration of several factors.
In this simulation, Darkow has allowed for conditions such as salinity, environment, mutation rate and predator
density to be adjusted. Though these are all exciting inquiries of investigation, the alteration of predator density
seemed to be most pertinent to me because I was interested in seeing how these two distinguished phenotypes would
be selected under different predator conditions. A simulation is useful in the discussion of evolutionary changes
regarding animals, as live experiments are not always feasible.
The predator modelled for this investigation is described to be Pike Cichlids, Crenicichla lepidota. Pike Cichlids are
also freshwater fish native to South America (Torres). It has been observed that Pike Cichlids are a primary predator
for the guppies (Magurran). Considering the hypothesized behaviours of a predator, the phenotypes of the guppies
may play a huge role in their chances of survival. This may also be dependent on the environment, as guppies that
predators can easily spot are less likely to survive.
1
, For this reason, natural selection is an essential concept to this investigation because it describes how populations of
living organisms adapt and change depending on their environment. Natural selection can only occur if variation exists
among members of a population of the same species. In the case of the guppies, there is biological variation due to a
mutation (Kottler). According to the theory of natural selection, organisms that are better adapted to their environment
tend to survive and produce more offspring, passing on their characteristics. This contributes to the idea of survival of
the fittest, describing how the fittest members will progressively become more predominant in the population because
their adaptation offers an advantage. The number of members who do not have this advantage will gradually decrease
as the gene pool changes. This can be applied to the Poecilia reticulata. As, depending on the environment, one of the
phenotypes may be better adapted to camouflage, decreasing the chances of being spotted by a Pike Cichlid. For this
reason, only the phenotypes of the guppies will be examined in this investigation, as opposed to the genotypes.
This is relevant to the simulation because Jon Darkow offers a choice between a sandy or coarse gravel environment.
The difference between these two conditions can be seen in Figures 4 and 5.
As can be observed, the Golden phenotype is much better suited to sandy environments, while the Wildtype is easily
visible. The coarse gravel condition contrasts this as the Wildtype phenotype is better adapted. This investigation will
only observe the evolutionary behaviour of the guppies in sandy environments when responding to an increase in
predator density. Such analysis may lead to valuable discussions of the decline of specific phenotypes or the species in
its entirety in response to a significant increase in Pike Cichlids.
HYPOTHESIS
Applying the afore-mentioned information, the alternative hypothesis describes that there will be a negative
correlation between the predator density and the population of Wildtype guppies after 30 generations in sandy
conditions. While in the same conditions, there will be a positive correlation between the predator density and
population of the Golden phenotype. While the null hypothesis predicts no relationship between the two variables.
VARIABLES
Independent Variable:
The independent variable can be described as Predator Density of Pike Cichlids. The predator density will be
discussed in terms of /m3, as it describes the relative amount of Pike Cichlids in an an enclosed habitat. The densities
include 0, 10, 20, 30, 40, 50, 60, and 70/m3. Observational pre-trials using the simulation delimited the range of
densities. It was observed that past the density of 70, there was little to no change in the dependent variable,
demonstrating that 70 is approximately the capacity of survival conditions for guppies of both phenotypes. Following
this, the predator density of 0 would accurately control the guppy population’s phenotype changes without considering
predation. The following densities were chosen by adding 10 to the successor of each condition as it gave an extensive
range of variables, each equally distanced from one another, which would allow for consistent data points.
Dependent Variable:
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