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Brain lateralization on Pearl cichlid in Detour Task
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Ciklido
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Joined: 06 Aug 2005
Location: Ontario, Canada

PostPosted: 2010.07.26(Mon)15:05    Post subject: Brain lateralization on Pearl cichlid in Detour Task Reply with quote

With all the uproar of importance about being right or left handed or which way a shrimp will jump I thought I'd jump in the direction which I think is actually relevant and important. This topic of right or left is not important as compared to a broader subject of the importance of brain lateralization.

Is it beneficial? The human brain and almost every vertebrate animal has some form of lateralization. In this article review one could discuss the biological aspect of being lateral organisms with behaviour, specifically in the Pearl Cichlid convict SA cichlid. As well, a common experiment among researchers which everyone can become familiar with is the Detour Task.

A study by Reddon et al (2009) of University of Alberta conducted this experiment using 26 convcts, 15 male and 11 female.

The main method was The Detour task. Since the fish were born and raised in lab aquariums and came from same hatch, the Detour task was a novel event presented to them.

The detour task is a method in which a rather lengthy aquarium is divided into two along its length with an opaque entrance door at one end of the "runway" or lane. Like two blowling alleys side by side, and a small entrance at one end. Note that just before the entrance there is a barrier that must be swimmed around using only one hemisphere of the brain and thus one eye. Fish are slowly chased from the start of the lane until they reach the barrier, depending on which eye they use one can infer which hemisphere is responsible for crossing over to the other side and which is not. Which eye is preferred right, or left depnding which eye they use to cross over and the consistency of that relationship.

The researchers indicated they decapitated the head ( Laughing ) immedietly after behavioural testing to extract the brain and analyze the neuroanatomy of the brain and probably the habenular nucleus. (mainly thought to be responsible for asymetries and brain lateralization)

The results were interesting firstly because as a species, they don't tend to be lateralized, that is, preferably right or left brained, when performing the detour task. However, each individual fish did tend to have this preferentiability for either right or left.

There is a correlation between the size of the fish and right habenular, or left habenular hemisphere size. The larger Pearls will typically have larger right habenular hemisphere while smaller fish will have larger LEFT habenulae.

In terms of sex, there was no relationships between size of the fish and sex.

It is thought that faster growing convict males would show more right-habenular assymetry, and females having have slower growth rates than male convicts show more left-habenular assyemtry.

One interesting finding which the authors noted is that males are right biased and females are left biased. They suggested this could be because of sexual correlations having to do with faster or slower growth rates.

The question is, does sex determine growth rate? In the Midas, as the authors suggested, the sex is determined by the position among the hierarchy of fish. Thus it is speculated growth rate determines sex and not vice versa. Faster growing fish will behave more laterally and conatin greater habenular assymetry thus impacting the differentiation of sexual development. It seems to fir in with what natural selection would show.

This is supported by studies which show that testosterone in chicks increases rightward bias among females, but has no effect in males.

In terms of eovlution, a faster growth rate and incrased sexual differentiation means a more risky lifestyle in order to compensate for rapid energy uses and secure the strength and position in the hierarchy as a male.
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Last edited by Ciklido on 2010.07.26(Mon)23:51; edited 1 time in total
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diademhill
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Joined: 18 Apr 2007

PostPosted: 2010.07.26(Mon)18:11    Post subject: Reply with quote

Which species was actually used and have the researchers considered that handedness may have an impact on spawning procedure?
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unissuh
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Joined: 29 Mar 2005
Location: Melbourne, Australia

PostPosted: 2010.07.26(Mon)22:21    Post subject: Reply with quote

A link to the article for people who aren't McMaster students. Razz
link

It's strange they claim there is a relation between fish size and lateral preference, sex and lateral preference...however none between fish size and sex. Especially when you look at their graph (Figure 3) the *smallest* male is bigger than their *largest* female. Seems to be either an "oops typo" or an epitome of the phrase "There are lies, there are filthy lies, and there are statistics."

Essentially what the conclusion was is that there is a correlation (and a pretty weak one too looking at their graph IMO) between absolute habenular nuclei (for those not familiar with jargon, it's one of the regions that has been proposed to control "handed-ness") size and absolute laterality preference I.e. there is no correlation between left nuclei being larger and left or right lateral preference, only in the degree of bias present.

So heres a question for you: If you consider lateral preference to be useless so to say, why is the relative size of habenular nuclei important?
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Ciklido
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Joined: 06 Aug 2005
Location: Ontario, Canada

PostPosted: 2010.07.27(Tue)1:29    Post subject: Reply with quote

The fish used was Geophagus brasiliensis, Pearl SA cichlid.

In terms of spawning its likely that the male will go with the preferred side which he is naturally inclined to go. Probably begin in direction of his right.

The relationships seem strange as written on the paper regarding sex and size relationships. This paper is not as good lol This is probably because they attempted to try to find a direct correlation between a specific behaviour (repeated and consistent but not very definitive in terms of specifing right or left eye use), against a morphological observation which was already generally known but not well understood. Other studies have used both detour and mirror viewing but this one just one. They did not indicate which side was used in accordance to which eye.

Quote:
So heres a question for you: If you consider lateral preference to be useless so to say, why is the relative size of habenular nuclei important?


An asymetric habenular formation appears to be responsible for a whole series of other relationships. Some studies find that the larger habenular side will contain certain specific types of neurons R branched or L branched. What is important is the relative difference in size of the habenular sides. How is it that one side comes to develop faster and thus bigger? The habenunlar structure is very important as it has sown that perhaps unique neurotransmitters exist in specific sides or just as well that the structure of both sides is equal but in different proportions and possibly causing further effects leading to lateralization in behaviour.

Lateral preferences I suppose were one of the possible features which are linked to habenular asymetries. Which side is naturally preferred I think can only be as important as which type of behaviour is necessary in novel situations. Supposedly more lateralized organisms behave more risky in new sitations which would make an ideal characteristic for a male. For a female probably less ideal. But this difference among males and females of directional bias I think has not been reported elsewhere? it may be faulty.

A more popular study found that zebra fish will tend to analyze novel stimuli with their right eye, and familiar stimuli will be observed with the left eye.

Another study which also supports the previous shrimp one, that lateral bias is genetically passed down. Similar detour task performing G falcatus were bred and their offspring tested for direction bias and it strongly correlates with that of the parents.
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