To the FWGNA group:
I am pleased to report that the annual meeting of the American
Malacological Society, held in late June at the Asilomar Conference
Center near Monterey, CA, was a great success. The registered
attendance of about 150 well-assorted malacologists combined to present
120 papers and posters, including 10 on freshwater snails, as appended
to the end of this message. Abstracts
are available from the AMS web site.
The quality of the papers was generally excellent. And on Monday
morning June 27, Yoichi Yusa of Nara Women’s University
(yusa@cc.nara-wu.ac.jp) may have presented the most important research
results I have ever heard in my 29 years of scientific meetings.
Although most mollusks are gonochoristic (sexes separate), great
mystery has long surrounded molluscan mechanisms of sex
determination. There have been a couple scattered reports of sex
chromosomes in prosobranch gastropods. The research of Stan
Allen, Ximing Guo and their colleagues in the 1990s suggested that sex
determination in (partially protandric) oysters seems to be controlled
by a single locus with a dominant male allele. But population sex
ratios are often way off 1:1 in the Mollusca, and sometimes the bias
may be attributable to differential growth or survivorship in the
sexes, or partial protrandry, and sometimes it clearly isn’t.
At Asilomar Yusa described an impressive series of breeding experiments
strongly suggesting that gender in Pomacea
canaliculata is controlled by a small number of additive
sex-determining genes, apparently scattered through the genome,
inherited from both parents. Such an oligogenic sex determining
mechanism has never before been suggested for the Mollusca. It
seems clear to me that sex ratios might easily vary from 1:1 in this
situation, especially in populations subject to drift and bottlenecks,
such as many freshwater prosobranch snails. The evolutionary
implications are profound.
While we’re on the subject of the Ampullariidae, I should also report
that Ken Hayes (working with Rob Cowie at the University of Hawaii –
Manoa, khayes@hawaii.edu) has been sequencing the daylights out of the
family. He has (to this point) sampled somewhere around 9 – 13 Pomacea species from the Americas,
as well as representatives of the genera Marisa, Asolene, Lanistes and Pila. His database currently
includes about 435 individual CO1 sequences, from 40 populations in
their native ranges and 80 introduced populations.
The big headline (from my outside perspective) is that Ken seems to
find that sequence methods are useful in discriminating Pomacea species. Freshwater
and terrestrial gastropods both typically show great intrapopulation
sequence variation, to the point that the distinction between
populations known to constitute valid biological species may be
swamped. But Ken reports that the mean maximum intraspecific
sequence divergence in his Pomacea
data set is around 5%, while mean minimum interspecific divergence is
around 10%, suggesting that sequence data may prove to be a useful tool
for specific diagnosis in the Ampullariidae.
Although the various Pomacea
species are not terribly difficult to culture, I don’t believe that Ken
has breeding data of sufficient quality to absolutely confirm the
biological status of his nominal species groups. Thus his
sequence data, strictly speaking, remain uncalibrated. But he
reassures me that anatomical morphology supports the specific
distinctions being made by his CO1 sequences in all cases where they’ve
looked. Regardless, it’s nice to see sequence data find some
application not dependent on the tenuous assumptions of phylogenetic
reconstruction.
We’ll keep in touch,
Rob
Freshwater gastropod
presentations at AMS 2005, Asilomar:
Robert T. Dillon, Jr., John D.
Robinson, and Amy R. Wethington. Empirical Estimates of
Reproductive Isolation Among the Freshwater Pulmonate Snails Physa acuta, P. pomilia, and P. hendersoni.
Kenneth A. Hayes.
Preliminary phylogenetic assessment of invasive apple snails in Asia
and beyond.
Cynthia G. Norton and Jennifer M.
Bronson. The relationship between body size, growth, and
egg production in the hermaphroditic freshwater snail, Helisoma trivolvis.
Robert S. Prezant and Eric J. Chapman.
Temporal Community Structure and Biodiversity of Malacofauna from an
Urban New Jersey Pond.
David C. Richards, C. Michael Falter,
Gary T. Lester, Ralph Myers. Mollusk Survey and Basic
Ecological Studies in Hells Canyon, Snake River, USA.
Ellen E. Strong. New
morphological data for Pleuroceridae (Gastropoda, Cerithioidea):
implications for monophyly and affinity of the family.
Andries Ter Maat, Cora Montagne-Wajer
and Joris M. Koene. The year of the pond snail.
Lori Tolley-Jordan.
Impacts if urbanization on the biodiversity of the imperiled snail
fauna (Gastropoda: Prosobranchia: Pleuroceridae) of the Cahaba River,
Alabama, USA.
A.R. Wethington, M.K. Smith, G.
Oliveira, F. Lewis, and D.J. Minchella. Genetic Structure
of Biomphalaria glabrata
populations sampled from a schistosomiasis endemic region.
Yoichi Yusa. Genetics of
Sex Ratio Variation in the Apple Snail, Pomacea canaliculata.
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