Re: On a sea horse,what purpose does the coronet have?

Dear Ms. Gorey:

What a fantastic question!  I studied mate choice in seahorses in Dr. Sara 
M. Lewis' lab at Tufts University, which is likely why I was chosen to 
answer this question.  The coronet of the seahorse, which is formed by the 
bony plates of the seahorse skeleton, doesn't serve any overt function.  
Seahorses don't, for example, use the coronet to ram each other or for 
capturing prey.  There are, however, two possible uses for the coronet which 
have recently come to light.

First, seahorses (Hippocampus spp.) make audible clicks while feeding.  Work 
by SM Lewis' group (1) has shown that the coronet is involved in producing/
amplifying this sound.  The clicks that the seahorses make may also allow 
them to communicate with one another or at least allow them to detect the 
presence of other seahorses nearby.  Seahorses live in dense mats of sea 
grasses, and are well-camoflauged, which may make it difficult to find a 
mate.  Audible clicks may overcome this barrier.

Second, seahorses are unusual in the animal world in the fact that the males 
become pregnant.  Male and female seahorses mate monogamously (2-5), a bond 
reaffirmed each morning by a quivering "dance" of greeting.  Because they 
mate monogamously, it is important for a seahorses to choose a good mate.  
One of the parameters the female seahorses select on (and possibly vice-
versa) is mate size.  The larger the male, the larger his pouch is likely to 
be, and thus the more eggs he is able to incubate.  A large mate is likely a 
more "fit" mate, to use the evolutionary term.  If the coronet makes an 
individual seahorse appear larger, taller, then that individual may be 
selected over its competitors.  In this way, a tall coronet might impart a 
selective advantage to the animal that possesses it, in the same fashion 
that a male peacock's long feathers impart a selective advantage to him.  
So, another way the coronet might serve a purpose is to provide a positive 
selective advantage to the animal that possesses it due to mate selection.

I hope this answers your question.  If it did not, or if you have more 
questions, please feel free to e-mail me at: 
ingrid_dodge@student.hms.harvard.edu.

Have a good day!
Ingrid 

References:

1) Jones et al, Molecular Ecology 7(11):1497-1505, 1998 Nov.
2) Vincent et al, Animal Behaviour 50(part 6):1557-1569, 1995 Dec.
3) Masonjones and Lewis, Copeia (3):634-40, 1996 Aug 1.
4) Vincent, Animal Behaviour 49(1):258-260, 1995 Jan.
5) Vincent, Behaviour 128(part1-2):153-167, 1994 Feb.