Hey Conch-Lers,
I received an interesting request recently about age rings in freshwater
mollusks. The answer is not an easy one and I have included my attempt at
an answer. If anyone else can help this individual please respond to him
directly ([log in to unmask] and PLEASE info me as I would be most
interested - in fact, a lot of Conch-Lers might also be interested).
Thanks,
Tom Eichhorst
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Tuesday, December 14, 2004 10:01 PM
> To: [log in to unmask]
> Subject: Freshwater Shell Growth Rings
>
>
> I am attempting to locate a specialist who tell me something
> about what is known about the growth rings of freshwater
> shells in this case from the Yucatan, Mexico with particular
> attention to one species, Pomacea flagellata.
>
> The question has to do with the degree to which it is known
> whether each growth "ring" in this species is annual.
>
> I have obtained some radiocarbon measurments on a segment of
> one of these shells and am attempting to understand the
> numbers I have been getting.
>
> Any information would be appreciated.
>
> R. E. Taylor
> Professor
> University of California, Riverside
Dr. Taylor,
The standard answer on growth lines in the majority of mollusks is that they
are not usable as an age determinant, especially in tropical conditions.
Many mollusks are short lived and in a year will lay down a multitude of
growth lines, often dependant upon food supply. But after saying this, I
must add that your freshwater snail may be different. It may be possible to
link growth lines in your snail to rainy and dry periods. To my knowledge,
this has not been done with apple snails and would require a mark and
recapture program to prove out with your Pomacea. This was accomplished
with a neritid, Clithon retropicta (von Martens, 1879) in Japan. Shigemiya
and Kato (2001) conducted a study of this species with some surprising
results. Using a mark and recapture program they established that Clithon
retropicta displays measurable annual growth lines [a response to seasonal
temperature and/or food fluctuations?]. These growth lines showed an
unusually long life span of 20 years for this species (easily in the top 5%
of freshwater mollusks). I was interested in their study as I am working
with world wide Neritidae, a family with life spans of 1-2 years (Theodoxus
and many of the other freshwater genera) to 4-5 years (Nerita, the marine
genus).
I am sorry I cannot really help you with this matter, but I will pass along
your request to a mollusk list serve I am on and see if someone has some
knowledge that may help.
Tom
Thomas E. Eichhorst
4528 Quartz Dr NE
Rio Rancho, NM 87124-4908
USA
Shigemiya, Yusuke and Kato, Makoto. 2001. Age distribution, growth, and
lifetime copulation frequency of a freshwater snail, Clithon retropictus
(Neritidae). Population Ecology 43(2):133-140.
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