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Need help with another write up.

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Need help with another write up.

Postby Cerebral_Artist » Mon Dec 03, 2007 5:20 am

I honestly don't even know where to start with this one. We haven't gone over the necessary lectures to answer this one yet, but it still due monday since it's our final week before finals.

Not really sure how to go about in answering these.

1. A graduate student is interested in studying a rare group of damselfishes endemic to Papua New Guinea (PNG). She arranges for a sampling trip to PNG but is successful in collecting a good number of specimens that she preserves in alcohol. Once back, she begins characterizing a suite of morphological characters and also collects mitochondrial DNA (mtDNA) sequence data for each individual (a portion of the cytochrome b gene).

(a) Briefly describe two approaches for how the student could decide how many species are represented in the collection.

(b) Suppose numbers of species identified using the morphological characters differed from that suggested by the mtDNA. What factors may have caused this discrepancy?

Thanks to any and all help


EDIT: alright, I did some reading online, and I'm prett sure I was able to find the answer I was looking for. There is a list of a bunch of different species concepts. So I just chose two out of that:

Phenetic species concept: a set of organisms that are phenotypically similar and look different from other sets of organisms.

Phylogenetic species concept: a species is a “tip” on a phylogeny, the smallest set of organisms that share an ancestor and can be distinguished from other such sets. Under this definition, a ring species is a single species that encompasses a lot of phenotypic variation.


But for part 2, I'm not sure what to say. Could it have been due to human error (or is that too simple a reason)? Maybe a bad diet which changes a species from looking like others from it's family?
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Postby mith » Mon Dec 03, 2007 6:32 am

cytochrome gene is pretty slow evolving fyi. A different gene with extensive introns within it should be picked.
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Postby Cerebral_Artist » Mon Dec 03, 2007 7:01 am

mith wrote:cytochrome gene is pretty slow evolving fyi. A different gene with extensive introns within it should be picked.


I'm pretty sure he was just trying to give an example. The main part of the assignment is just to list two different ways to identify the species (which I've listed), and the second part of the question asks how the morphological aspect could give differing results from the genetically based testing.

I just need ideas as to why the numbers of species identified using the morphological characters differed from those done by mtDNA.

Could it be due to some fish possibly lacking the necessary diet, so their morphological features differ from others in its species leading to a possible alteration in size, making it look similar to another species in size at least.

I can't think of other reasons. I was thinking it could even be due to natural selection. Some of the fish might still be the same species but differ morphologically due to their locations, which could lead to a change physically, similar to the situation with Darwin's finches.
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Postby mith » Mon Dec 03, 2007 7:57 am

sexual dimorphism, intraspecies variation,

remember that morphology is somewhat subjective so that some people may think people of difference races are of different species based on physiology.

You should also think of the other case where DNA is very different but they are similar morphologically.
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Postby Cerebral_Artist » Mon Dec 03, 2007 8:16 am

Awesome, thanks a lot for the help! This board has been very helpful, if only I had known about this place earlier!
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