Dynastinae is a subfamily of scarab beetles known as Rhinoceros beetles. The Dynastine beetles within the tribe Cyclocephalini ("round-head"), however, are characterized by a lack of horns. Thus the origin for the title of this blog. Welcome to the world of taxonomy!
My thesis research project's goals are to sort out the phylogeny (create a family tree) of the tribe Cyclocephalini. This tribe includes 15 genera and a little over 500 species, although new species are being described all the time. All but two of the genera are found in the New World, primarily in the tropics. The two exceptions are Ruteloryctes Arrow, found in Western Africa, and Peltonotus Burmeister, found in Southeastern Asia. The largest genus is Cyclocephala Latreille with about 350 species.
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Are there any reasons for the lack of horns on these beetles?
ReplyDeleteThat is a really good question that I don't have an answer to. I just asked Dr. Jameson and she doesn't really have an answer either.
ReplyDeletehttp://dbs.umt.edu/research_labs/emlenlab/documents/EmlenetalPNAS2007.pdf
The above link goes to a paper by Doug Emlen in which he states that the ancestral scarab had horns, meaning that all scarabs without horns (including Cyclocephalini) lost this trait. My guess would be that, as cyclocephalines are often associated as pollinators of aroids, that horns got in the way of getting inside the flower, so gradually the horns reduced in order for access to be easier. But, again, I don't have a good answer to a very good question.
I seem to remember maybe watching some Discovery channel episode where the horned rhino beetles were ferocious and would "battle" with each other. Is that true?
ReplyDeleteAnd weren't golden scarabs used in ancient Egypt? or maybe even today? I guess I didn't make a connection when i saw that that they were actually horned!!! Maybe those scarabs aren't really related to the hornless rhino beetle.
My question from reading your blog is similar to all previous comments. How about this: what is the purpose of horns in other scarab beetles? If they are for fighting, what is the fighting for? Territory?
ReplyDeleteI would propose the horns are a sexual display. If for whatever reason they were to lose the horns for a more advantageous survival of species situation, I would think they would evolve a new sexual display. This could aid in differentiation from other "horned" variety of scarabs.
Another comment on horns for fighting. Such ornamentation is uncommon among 'fighters' in nature. Dr. Burke: "Imagine sticking some guy with that horn just to have him skewer your eyes out as he dies."
ReplyDeleteIs the horn always for fighting? Could it be for burrowing or digging perhaps maybe some kind of tool.
ReplyDelete