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| A. brunneum holotype |
Although knowledge of the composition and
phylogenetic placement of Thiaridae has increased due to recent studies (Strong
et al., 2011 and citations therein), modern taxonomic and systematic treatment
is still needed within the family.
Recently, Roberto Vogler, Ariel Beltramino, Juana Peso, and Alejandra Rumi
provided a redescription of one species and a description of a new species from
Argentina and Paraguay in an attempt to provide useful data towards future
comparative studies. The paper entitled “Threatened
gastropods under the evolutionary genetic species concept: redescription and
new species of the genus Aylacostoma
(Gastropoda: Thiaridae) from High Paraná River (Argentina-Paraguay)” begins
with an introduction to thiarids and a history of available genus-group names
that are available for Neotropical thiarids.
The authors describe that in Argentina and Paraguay three species of Aylacostoma were recorded in the High
Paraná River at the border area between Argentina and Paraguay, but
regrettably, their highly oxygenated habitat disappeared due to the
construction of a dam that formed the Yacyretá Reservoir. The authors suggest that Aylacostoma guaraniticum and A.
stigmaticum could now be categorized as extinct while A. chloroticum and the newly described species exist due to an ex situ conservation program.
Vogler et al. examined specimens from the
Museo de La Plata and Museo Argentino de Ciencias Naturales and live specimens
from the ongoing ex situ conservation
program taking place at the Universidad Nacional de Misiones. They took seven shell measurements and
examined the protoconchs, operculate, and radulae using scanning electron microscopy. They also obtained mitochondrial Cyt b
sequences from five individuals and conducted phylogenetic analyses of mitochondrial
COI data of 37 A. chloroticum and six A. new sp. as well as six outgroup taxa.
The authors used the Evolutionary Genetic
Species Concept to determine if well-supported sister clades could be different
species. The method, which has been
developed for asexual species states that if phylogenetic analysis shows that small
samples from two populations are reciprocally monophyletic , and if the mean
sequence difference between them is more than four times θ=2Neµ estimated
from the within-sample variation, then the samples came from different species (Birky
et al., 2010). The authors found
support for the recognition of the redescribed A. chloroticum and new
species, which they named A. brunneum Vogler & Peso. Aylacostoma
brunneum could also be distinguished
from A. chloroticum by its distinctive coloration pattern being dark brown
with alternating lighter brown bands, while A.
cloroticum is greenish-yellow to mid
greenish-brown.
Unfortunately, only a single relict population
of A. chloroticum is known in the wild, and wild populations of A. brunneum
are probably extinct (although further survey work is necessary). It is a sad state of affairs that as scientists begin
to gain knowledge of this poorly studied group, they are disappearing from the
wild.
Literature
Cited
Birky, C.
W., Jr., J. Adams, M. Gemmel, and J. Perry.
2010. Using population genetic
theory and DNA sequences for species detection and identification in asexual
organisms. PLoS ONE 5: e10609. Doi:10.1371/journal.pone.0010609.
Strong, E. E., D. J. Colgan, J. M. Healy, C. Lydeard, W. F. Ponder, and M. Glaubrecht. 2011. Phylogeny of the gastropod superfamily Cerithioidea using morphology and molecules. Zool. J. Linnean Society 162:43-89.
Vogler, R. E., A. A. Beltramino, J. G. Peso, and A. Rumi. Threatened gastropods under the evolutionary genetic species concept: redescription and new species of the genus Aylacostoma (Gastropoda: Thiaridae) from High Parana River (Argentina-Paraguay). Zool. J. Linnean Society 172:501-520.
