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Whitney Ginn
Techniques in Science
Analysis of Poeciliid Fishes Article
Lindholm, Anna. 2002. “Sex Chromosomes and Sexual Selection in Poeciliid Fishes”.
The American Naturalist. 160: S214-S224.
Poeciliid fish are able to give birth to live babies and whose species varies
between their sex chromosomes and how they chose to select mates. This research paper
goes into great depth about how certain traits are Y-linked in males, and how females are
possibly attracted to certain traits located on a sex chromosome versus other similar traits.
These traits may not as unique as some of the other ones found on the sex chromosomes
in other male fish. Also mentioned is how certain X-linked traits are more attractive to
the females when presented on the male species due to crossover. Due to the preference
of these traits on fish, certain fish may gain a positive advantage. Other male fish,
however, will have a disadvantage because of their lack of a certain preferred sexuallylinked trait. In order to check this theory, studies comparing homogametic and
heterogametic fish may help scientists understand how the male species have changed
over time.
Much studying of gene mapping has to be done in order to prove the theory of
physical linkage of genes and their effect on the female population. The frequency of
certain physical traits showed that some characteristics could be beneficial to one sex and
harmful to the other. Gathering on all this information, the Y chromosome is very
possibly degenerating throughout time and evolution due to the lack of chromosomal
information.
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Although this may be a possibility, females are certainly attracted to specific male
traits. The characteristics researched showed certain species of fish had attraction to
particular types of pigmentation, fin shape and size, as well as body size. Body size has
not been shown to be sex-linked; therefore it has been omitted from the study. The
experiment of the paper wants to see if the Y-linked traits affect the female’s preference
because of the male’s phenotype.
In Lindholm and Breden’s experiment, an eight liter tank was acquired and filled.
One male guppy, which showed low-coloration, which was obtained from the Rio San
Miguel in Venezuela, was placed on one end of the tank, and another male guppy, was
placed on the other end of the tank. The latter of the two male guppies is considered a
high-coloration fish. He is known as an Endler’s live-bearer (ELB), who are known for
their bright contrasting black and orange body patterns. This fish is also from Venezuela.
The female fish was bred from one parent of a highly colored fish and the other
parent was one that was considered a low colored fish. A reciprocal cross was also
performed, giving two types of F1 generation females. One female of these crosses was
placed in the center of the tank. The three fish (one female, two male) were allowed to
become adjusted to the environment for a few hours in the dark. A halogen light was
placed above the tank, left for an hour so fish could reacquaint themselves, this time in
the light. The twenty minutes afterwards was used for observation. This test was
repeated a number of unmentioned times.
Statistics for the experiment showed that neither of the guppies of various color
variation were not significantly different. For the low colored fish, there was no
significant difference in the choosing of the males (X=0.05, N=11, P>0.2). However, for
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the high coloration of the ELB males, there was a significant difference (X=0.66, N=11,
P<0.001). Taking these tests into consideration, it does show that the extent of the male
coloration does have an affect on the female preference. When the researchers performed
a backcross from the F1 generation, it showed that there was a regression back towards
the parental preference (X=-0.07, N=7, low-coloration backcross, X=0.69, N=3, high
coloration backcross). With these numbers the beginning of showing genetic linkage
may occur, but with so few test numbers, it is not able to say for sure whether the linkage
is true or not.
Research performed for this paper is excellent, however, very little of it seems
relevant to the actual experiment. The experiment was very simple and straightforward,
and could easily be done by any undergraduate. The scientists’ research goes into great
detail about the Y-chromosome and how it may be degenerating and about how some of
the genes may actually be X-linked. The experiment only goes into the simple
observation of the preference between color, it does not go into how the genes may have
been X-linked, and did not do any sort of comparison to the heavily talked about
homogametic species of fish.
Another disappointment was that the researchers did not go at all into the gene
mapping of their particular experiment. It is unknown which genes they observed and if
these genes may have been X-linked and experienced crossover. Very little seemed to be
known about what the actual experiment entailed. More research should have been done
to pinpoint what the actual experiment dealt with. The record taking of the actual
experiment had much lacking as well. The record of the F1 generation of the female fish
was not mentioned, as well as how many times the experiment was performed and the
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results of each individual experiment. All of this data would have been easily able to be
put into a table.
The data collected from the experiment was indeed relevant to the hypothesis;
however, the paper seemed to be more hype than anything. A possible way to make this
experiment more relevant would have been to also test homogametic fish species
preferences, and try to do some gene mapping between the two of them. Also, instead of
just doing color, the researchers could have worked with other traits which have been
known to sway the female preference, such as size, and characteristics dealing with the
caudal fin. This may be helpful to see if there are certain male characteristics that are
more attractive to females than others. It would be nice to see the scientists build on their
research and try to find new and different results which support the other studies.
The review is able to be understood very easily. The words and context were not
difficult to understand. A brief brush-up on certain terms may be required; however, the
authors do include a short glossary which may aid the reader. Results of the two types of
the research conducted were placed in two separate, easily understandable tables. The
math is easy to understand, and organization of the paper is excellent.
The paper is interesting because of how it does try to show the physical linkage
between genes and fish. Included in the table are a list of the Y-linked, X-linked, and the
X and Y-linked chromosomes divided into different genus of fish, and gives references to
where more information could be found.
In conclusion, the paper is well written and easily able to be understood. If an
undergraduate would want to copy the scientists’ experiment, there would be no problem.
The mathematical data would also be easy to reproduce and able to be expanded on. A
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separate trial should be conducted with homogametic fish and try to see how the
difference of gene placement would be between the homogametic fish and heterogametic
fish. This paper should be recommended for a basic understanding of fish genes and their
physical linkage, but not for a basis for another research project. The articles used for the
author’s research for this paper would probably be more ideal for that situation. Yet, this
would be a nice start for a basic synopsis of the sexual selection and sex chromosomes in
fish for anyone.