Subaculear prong

[Mark Newton]

I thought it would be interesting to see what peoples opinions might be of the subaculear prong. What possible benefit might it give the scorpion? Do you think it might be a specialised adaptation to somehow deal with a particular type of prey item? It appears to only be found in genera with small scorpions such as Lychas and their close relatives, however, it is completely missing in the Isometroides genera I just posted. Isometroides are specialised spider hunters. Any ideas?

Added a scan from a Lychas variatus telson showing subaculear prong.

 

[H. cyaneus]

To open their little cans of grape juice? Hehe...

I think it has something to do with injecting venom, but I have no idea how it would help the process.

Mike

 

[xVOWx]

It might not be an adaptation, it might be the remnants of a second or smaller aculeus that has become unnecessary as these species evolve. I, of course, know almost nothing about the evolutionary history of scorpions so it's just a guess hahaha.

 

[Rigelus]

Maybe Mikes joke is worth more than a chuckle..

As an appendage it certainly looks as if it could be used to add leverage. It has the correct angle and orientation to be used as such. I could imagine that maybe it could help with piercing the thick exoskeleton of beetles for example. Didn't i read somewhere that theres more beetles on the planet than anything else.
In species where the subaculear tooth is further down the telson or not as pronounced or angled differently could this not just simply be an expression of an adaptation to a particular prey item.
Also that it's mostly small species that have these could add weight to the argument. A larger heavier scorpion would be able to thrust with more power.

A dedicated spider hunter would have no need for such an appendage as piercing a spiders body with the aculeus wouldn't present that much of a problem.

/Bryan

 

[Brandelmouche]

According to me it’s for not broken is telson. As it inserts it’s sting in a prey it used as notches of stop for not inserted too deeply the sting and broken the base has. If the end of the telson is broken the scorpion will be able to always use it and nourisches, a cut at the base and is not useful at all, it is just a theory worked out.

 

[skinheaddave]

An interesting thing to consider is that there are many Buthidae that have the subaculear proterberance, but this is also present in the diplocentrids -- currently filed under Scorpionidae. Did these develop in a single event or seperate events? Either way, it should be able to assist us in finding cases of secondary loss, which might provide some insight.

Cheers,
Dave

 

[EAD063]

An interesting thing to consider is that there are many Buthidae that have the subaculear proterberance, but this is also present in the diplocentrids -- currently filed under Scorpionidae. Did these develop in a single event or seperate events? Either way, it should be able to assist us in finding cases of secondary loss, which might provide some insight.

Cheers,
Dave

Isn't there a Vaejovidae with one too? :? Thought I came across that in a paper once.

 

[Mark Newton]

HI Bryan. I have to agree your comments make good sense to me and that is my line of thinking. I thought it might help the scorpion to remove the aculeus in a hard bodied prey item. As you say, with spiders it would not be needed at all. Always open to new ideas though.

So is this form Plesiomorphic (original) or Apomorphic (more recent adaptation). One should consider that far fewer species have this adaptation than those that dont. One should also consider that it is the primitive forms that do have this adaptation.

Is it an adaptation as already suggested it might not be, it might be vestigial and of no use. I tend to think it is a selected adaptation as it is variable and restricted to certain scorpions.

Used as a stop - I think that is a good sugestion too and one that had crossed my mind.

Thanks Dave. Aren't the Diplocentrids considered their own family and thought to be closely related to the Scorpionidae or has that changed? With the presence of the subaculear prong they could not be classified as Scorpionidae in my understanding. (me no taxonomist though :wall: ) Or maybe the Diplocentrids are misplaced phylogenetically. Certainly very Scorpionidae in overall appearance, but that could be parallel evolution. Although of course they are far more closely related to the Scorpionidae than the Buthids if we go by developmental embryology....one that is a little difficult to argue with.

Vaejovidae with this adaptation?? Interesting..anyone?

 

[skinheaddave]

I tend to think it is a selected adaptation as it is variable and restricted to certain scorpions.

It could also be a development imposed by some other adaptive feature.

Thanks Dave. Aren't the Diplocentrids considered their own family

They were all thrown in together in the recent kerfufle over higher level taxonomy. Whether this will stand the test of time, I can't say.

Buthids if we go by developmental embryology....

Agreed. I think it is hard to consider the divide between katoikogenic and apoikogenic scorpions to be anything but highly significant in reconstructing evolutionary history.

Cheers,
Dave

 

[Mark Newton]

It could also be a development imposed by some other adaptive feature.

Could you give me an example of that. What other adaptive feature is there with these scorpions that is not found on others that dont have the prong? Not likely the result of genetic linkage would you think?

Agreed. I think it is hard to consider the divide between katoikogenic and apoikogenic scorpions to be anything but highly significant in reconstructing evolutionary history.

Unless possibly in the Diplocentrids the subaculear prong has either evolved 'again', or a plesiomorphic character gene has been turned on - for a number of possible reasons.

Do you or anyone have any photos of the subaculear prong in the Diplocentrids...would like to see a closeup if possible.

 

[EAD063]

Hello Mark, I did find the reference I spoke of before. The species is V pequeno. After re-reading the article it becomes clear that the ST is basically inexsistent, "minute" as quoted from the author. But I do wonder what margin is considered acceptable, some have a larger, more defined ST than others. The fact that Vaejovidae is confined to North America in my uneducated wager would suggest that it is evolutionary, seeings none of the other members of the vaejovidae family show a ST. I'm confused whether or not the ST evolved "IN" to these specific species, or "out" of the species that do not show the tooth. I thought Polis' book had a decent write up on the subaculear but unfortunately I don't have the book any longer.

The article for V pequeno can be accessed here.
http://core.ecu.edu/biol/bondja/publications/henrixson2001.pdf

Hmm. So if this could be considered a non-buthid with a ST, wouldn't that give your idea of a plesiomorphic gene being "turned on", some weight? The only problem is that it seems the ST spreads striaght across the genus' that have them, not true with this vaejovis.

 

[redhourglass]

Hi.

In reference to the family Vaejovidae, two species have this st:

Vaejovis mumai and V. spicatus sare the only two vaejovid species possessing a distinct, spinoid subaculear tooth on the telson vesicle (Serradigitus joshuaensis has a conspicuous tubercle, but not a spinoid tooth).

1993. The Journal of Arachnology 21 :64—68


Sinc. Chad

 

[Mark Newton]

Hmm. So if this could be considered a non-buthid with a ST, wouldn't that give your idea of a plesiomorphic gene being "turned on", some weight? The only problem is that it seems the ST spreads striaght across the genus' that have them, not true with this vaejovis.

The Vaejovidae are more closely related to the Buthidae than the Diplocentridae according to embryology at least....which as stated before is a little hard to argue with. So, I would expect to see a Vaejovid with the ST before a Diplocentrid.

Very difficult to be sure isnt it. I guess that because we see this character occuring mainly in more primitive forms we consider it plesiomorphic. But for what reason has it been maintained in these scorpions? If it is plesiomorphic then surely it can arise as a new character in groups that have lost it. It may well be an apomorphy that has predominated in the more primitive forms due to some aspect of the way they live.

My gut feeling is that it's plesiomorphic and is generally lost in more recent lineages. For some reason its selective advantage remans high in the primitive forms such as the Buthids but not in later lineages. The Diplocentrids may be an example of it either reappearing or being maintained throughout an evolving lineage..... What do the Diplocentrids have in common with the Buthids that is not common to groups not showing the ST?

 

[skinheaddave]

Could you give me an example of that. What other adaptive feature is there with these scorpions that is not found on others that dont have the prong? Not likely the result of genetic linkage would you think?

I cannot concieve of a decent explanation along those lines. I was simply suggesting it as a possibility. Maybe a substantial piece of exoskeleton is required as a muscle attachment point for stronger telson contractions. Okay, that isn't overly plausable -- but an example of the type of causality I'm talking about. And no, I doubt genetic linkage is involved with what one would think is a relativley complex structure goverened by more than a snippet of genetic code.

Of course if it is plesiomorphic, it may also be possible that it is a disadvantage and has been selected against in some lineages.

Cheers,
Dave

 

[EAD063]

Of course if it is plesiomorphic, it may also be possible that it is a disadvantage and has been selected against in some lineages.

So basically thats sort of what I was saying I belive. About wondering if either it evolved in, or out of these genus. Using one theory from above, if the ST was used to better accomadate the true aculeus, either by giving it more leverage, or controlling how far the aculeus penetrates skin, wouldn't the scorpion need to be a lot bigger to actually make use of the ST if this were the case? I speculate that the larger the scorpion is, the farther foward the metasoma needs to be extended, thus, in the case of a scorpion that is very large, it would need a larger segment of it's body off the ground to alow the metasoma to reach it's prey, once the metasoma is extended enough to where the back pairs of legs leave the ground, a ST would act as leverage to prevent the scorpion from flipping over. Like I said, this would be of use for species who are VERY large, larger than all of the species today, so if thats what it is used for, then the argument could be made that this is an adaptation which is on it's way out evolutionary speaking.

 

[John Bokma]

http://johnbokma.com/mexit/2006/04/25/diplocentrus-species-scans.html has a close up of SAT of Diplocentrus sp.

 

[Mark Newton]

http://johnbokma.com/mexit/2006/04/25/diplocentrus-species-scans.html has a close up of SAT of Diplocentrus sp.

Thanks John. Some good scans there. Incredibly short aculeus. Looks like you found 2 males that time.

 

[pandinus]

i have noticed differences in the size of subaceular tubercles in a single species. mostly (theorizing from personal experience) dependant on range, i have witnessed that the size of the subaceular tubercle is variable among C. vittatus, going from a mild tubercle, to being all but nonexistent in other ranges.



John

 

[Mark Newton]

i have noticed differences in the size of subaceular tubercles in a single species. mostly (theorizing from personal experience) dependant on range, i have witnessed that the size of the subaceular tubercle is variable among C. vittatus, going from a mild tubercle, to being all but nonexistent in other ranges.



John

Interesting John. Any ideas as to what the reason might be?

 

[John Bokma]

Thanks John. Some good scans there. Incredibly short aculeus. Looks like you found 2 males that time.

Hi Mark, thanks, but I am very sure that both are females, especially since one gave birth (but died very shortly after doing so).

http://johnbokma.com/mexit/2006/04/23/diplocentrus-terrarium.html has more photos, and http://johnbokma.com/mexit/2006/05/02/sony-cyber-shot-dsc-s600-test.html a bit better ones.