Reptile & Amphibian Forums

Hi BGF,

Long time no chat... did you ever get any Madagascarophis specimens for your studies? In case you don't remember I was supposed to send you several specimens a few years back before 9/11/01 messed up international shipping.

But I digress.

In a recent discussion I used the evolution of opistoglyph dentition (OD) as an example of convergent evolution based on your suggestion that OD is a homoplasic trait.

During that discussion I started to fumble the terms analagous, homoplasic, parallelism and convergence and seek your clarification. After being out of the lab for almost two years I'm a bit "rusty" in science speak. My science library was lost in a flood last year so I have no immediate reference source.

I'd appreciate your comments on the following hypothetical example.

In this example we have two species of aglyphous snakes that give rise to two separate lineages of snakes with OD.

The two snakes species are closely related enough that the specific teeth giving rise to the OD are homologous.

Would the resultant OD be an example of homoplasy since they were independent origins?

Or would they be an example of parallelism since OD evolved through an identical evolutionary pathway, albeit independent of each other?

I hope this makes sense.

And to digress again...

I know you like Gonyosoma. Here's a picture of one of my females imported from Java. This picture was taken after her first shed in my care. She really was this orange. Actually, I had to dim the picture down in photoshop to better duplicate her actual color. The original photo was an even brighter orange.

She changes color with every shed so I never know what snake I'm going to see. Awesome animals.

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1.1 Gonyosoma oxycephala - (Silver/Yellow)

3.4 Gonyosoma oxycephala - (Green)

2.1 Gonyosoma janseni - (Black)

>>During that discussion I started to fumble the terms analagous, homoplasic, parallelism and convergence and seek your clarification. After being out of the lab for almost two years I'm a bit "rusty" in science speak. My science library was lost in a flood last year so I have no immediate reference source.
>>
>>I'd appreciate your comments on the following hypothetical example.
>>
>>In this example we have two species of aglyphous snakes that give rise to two separate lineages of snakes with OD.
>>
>>The two snakes species are closely related enough that the specific teeth giving rise to the OD are homologous.
>>
>>Would the resultant OD be an example of homoplasy since they were independent origins?

The opisthoglyphous dentition in the two lineages would be a case of homoplasy, since the opisthoglyphous dentition would have evolved simultaneously. On the other had, the posterior maxillary teeth involved would be homologous in the sense that they are both posterior maxillary teeth.

A parallel example would be the wings of a bird and a bat: their function as wings is a case of homoplasy, since it evolved independently, but they are homologous in the sense that they are both types of vertebrate forelimb.

>>Or would they be an example of parallelism since OD evolved through an identical evolutionary pathway, albeit independent of each other?

That as well. Parallel evolution is a type of homoplasy. Homoplasy is basically the catch-all term for "noise" in a phylogenetic analysis. Homoplasy is caused by 3 phenomena:

- convergence, where two lineages arrive at sharing a derived condition from a different starting point (e.g., green pattern with white spots in Corallus caninus and Morelia viridis, evolved from somewhat different ancestral patterns).

- parallel evolution, where two lineages independently acquire the same derived character state from the same starting point (e.g., flat tail in Laticauda and sea snakes)

- reversal, where a derived condition is lost again (e.g., venom in North American rat and king snakes).

In practice, parallel evolution and convergence can be difficult to distinguish, but, in any case, result in a derived condition being acquired independently by multiple lineages.

Hope this helps.

Cheers,

Wolfgang
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WW Home

hi..i was wondering..is this the kinda stuff i'll be studying if i major in herpetology? what else might be included in a herpetology course?

Depends on what you want to do and what area interests you most. Herpetology could be defined to include everything in between watching a skink get predated on by a bird or studying a snake toxin. So your speciality could be biology, biochemistry, molecular biology, ecology or whatever. Really comes down solely to you.

Cheers
Bryan
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Dr. Bryan Grieg Fry
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Australian Venom Research Unit,
University of Melbourne
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Population and Evolutionary Genetics Unit,
Museum Victoria
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http://www.venomdoc.com