Lab report
The Selection of Guppies (Poecilla reticulata) to determine reasons for differences between male
spot brightness in different locations.
Introduction
Sexual Selection in Guppies (Poecilla reticulata) may explain why the sexual trait of male’s spot
brightness are well developed in male guppy populations as the female population tends to prefer
males that express larger amounts of spot brightness (Houde and Endler 1990). Differences in this
sexual trait also has a large impact from predation as in high predation environments Guppies that
express a high degree of colourisation are more likely to be targets of predation therefore in high
predation environments Guppies tend to express lower levels colourisation than in low predation
environments (Lindholm et al. 2014). Because of this the colour variation of Guppies is often
comprised of sexual selection and predation avoidance or some sort of combination of the both
(Endler 1991).
This is important to understand as in any given environment there is various other species living
alongside Guppies which also impact them as well. In low predation environments Guppies tend to
have higher degree of body coloration and Guppies being introduced from high predation
environments to a low predation environment can adapt within 50 years (Gordon et al. 2012).
Guppies also serve as a good example of sexual selection and according to current literature female
preference co-evolves with male colourisation, this means that in low predation environments
females are looking for a high degree of colourisation in males and in high predation areas they are
more lenient, therefore looking for a lower degree of colourisation in male Guppies (Sandkam.B
2015). This information is important for our study as it gives us a rational look on the reasoning for
the colouring of male Guppies and potential environmental differences that occur in different
Guppies habitats, like number of predators or lack of predators in any given Guppies environment.
Our studies aim was to research and address potential factors like sexual selection, predation,
habitat or combination of these factors and how they impact male spot brightness in different
locations, and draw conclusions based on results from experiments and reflect on our various
hypothesis. This research is important as it sheds light on why males spot brightness is different in
different locations and gives potential reasons for this and is also important in understanding the
various factors acting on Guppies (Poecilla reticulata).
Discussion
Prediction one’s results collected showed that the mean spot brightness decreased by 6.7 in upper
east stream after predators were added, then after the predators were removed mean spot
brightness increased significantly by 8.6, from this alternative hypothesis one appears to be
supported as the more predators the more the guppies needed to blend therefore reducing spot
brightness to avoid predation. From prediction two males mean spot brightness at start was 6.3 then
after 800 days with no predators it increased to 18.8 which is a significant increase. From this
evidence collected from the results we would support alternative hypothesis two as with no threat of
predation male spot brightness will increase to attract females. Prediction three showed after 1000
days after transplantation the mean spot brightness was 6.1 which was closer to the lower east
stream average of 7.7 rather than their original habitat which was 15.7 which shows a large drop
from their original habitat. From this data I would not support alternative hypothesis three as spot
brightness is determined by past heritage not habitat as seen in data above. Overall from the data
collected above it appears to be a combination of alternative hypothesis one and hypothesis two
which are the main causes of differences in male Guppies brightness in different areas which means I
would support alternative hypothesis four as the data collected suggests that at least two of the first
three hypothesis are supported.
Prediction one reinforced information regarding predations effects on guppies from the introduction
therefore supporting alternative hypothesis one. Predator induced plasticity is certainly clear from
the results as guppies respond in correlation to low or high predator environments by reducing spot
brightness to blend in to their environment to avoid predation and in the absence of predators they
increase in brightness to attract females (Torres-Dowdall et al. 2012). Natural selection also has a
massive impact on Guppy populations as the potential for an individual’s genotype to produce
different phenotypes is very dependent on the environment and their response to variation within
that given environment, like high or low predation environments and if the plasticity of these
changes is adaptive or non-adaptive (Ghalambor et al. 2015). Prediction two’s results correlated with
literature from the introduction as with the significant increase in male spot brightness from 6.3 to
18.8 supports alternative hypothesis two as variation of male spot brightness increase over a number
of generations to attract females this information showing certain sexual selection within Guppy
populations and that males with rare of larger colourisation(spot brightness) have larger
reproductive fitness among the population leading to an increase in spot brightness as long as other
environmental variation complies(Hughes et al.2013). Prediction threes results were interesting as
lower east stream males were more closely resembled by their previous spot brightness than the
males that originally inhabited the upper west stream, which provides evidence that habitat isn’t to
count for mean spot brightness therefore we would reject alternative hypothesis four. This could be
potentially because eco-evolution requires a feedback loop in which organisms react to their
environment and adapt to fill certain niches then pass on these traits as heritable adaptation to the
next generation and that the largest factors which act on this include predation, food supply and
changes within a habitat and how organisms respond to these changes not just simply the
environment itself as heritable factors also have a crucial role in an organism adapting to any given
environment(Post and Palkovacs 2009).
Spot brightness or colourisation of Guppies in different locations as suggested from results is some
sort of combination as at least two of the first three alternative hypothesis were supported. Guppies
provide a good example of understanding interplay between natural selection caused by predation
and sexual selection, as stated in the introduction in high predation environments females prefer
lower levels of colourisation and in low predator environments females prefer a higher degree of
colourisation in male Guppies. This shows a direct linkage between predation and sexual selection
among Guppies populations (Elgee et al. 2010).
In conclusion two of the first three alternative hypothesis were supported which means that
alternative hypothesis four was supported and that the null (alternative hypothesis five) was not
supported as at least one of the first three hypothesis was supported. So overall from the evidence
provided it appears to be a combination of sexual selection and predation which determine the
differences in spot brightness in male Guppies (Poecilla reticulata) from location to location as
different degrees of predation impact spot brightness and this appears to be paired with sexual
selection which are the driving factors in differentiation of spot brightness within male Guppy
populations.
Literature Cited
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