MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Species and Population boundaries in a changing environment in the South American subterranean rodent Ctenomys
Autor/es:
MIROL PATRICIA
Lugar:
Mendoza, Argentina
Reunión:
Congreso; 10th International Mammalogical Congress; 2009
Resumen:
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Species of
subterranean rodents of the genus Ctenomys
constitute an interesting model to assess the effects of habitat fragmentation
at the interface between population genetics, ecology, historical biogeography
and species boundaries. Because of their fossorial habits, they only occur in a
small number of highly fragmented areas of well drained and friable soils. The
Corrientes group is a complex of three species (C. roigi, C. perrensi and
C. dorbigny), and several forms (perrensi complex) whose taxonomic status
has not yet been determined. The three named species have diploid numbers of
2n=48, 50 and 70, respectively, while the perrensi complex exhibits 2n
ranging from 40 to 65. The high karyotypic variability of the perrensi
complex, together with the distribution of their populations in isolated demes,
encourages the thought that chromosomal evolution is an ongoing active and
recurrent process in these genomes. Boundaries of the distribution areas of
named species seem to be well established, but populations of the perrensi complex
are patchy distributed in dry areas around the Esteros .
The
Esteros is a wetland that covers more than 12,000 km2 that is fed by
inland rain and groundwater. It is located between three large rivers, the Rio
Paraná alto, the Rio Paraná medio and the Rio Uruguay, with no surface
connection to any of the three. The wetland consists of a vast mosaic of
marshes, swamps and lagoons, of which nearly 60% are permanently inundated.
Because of the soil requirements for their fossorial life, tuco-tucos can only
form patchy populations where the habitat is favorable in the wetland.
Fluctuations in the area of the lagoons that form the esteros produce changes
in the suitability of habitat for the rodents. Populations can become connected
or isolated depending on the precipitation regime and other climatic
alterations of the environment.
We
have been investigating the species and populations of the "perrensi"
complex during the last 10 years, through chromosomal, mitochondrial and
microsatellite analysis. In the symposium, I would like to present our main
results regarding species and population boundaries, with the purpose of answering
the questions of how many evolving units of Ctenomys
is possible to define in the Corrientes area, and which criterion can we apply
to delimit boundaries for those units. Although results obtained with
mitochondrial DNA (cytochrome b and
D-loop sequences), karyotypes and microsatellites are sometimes in conflict,
they clearly depict a complex hybridization scenario, where:
1- C. dorbignyi, despite conserving
chromosomal numbers, seems to be constituted by two evolutionary separated
lineages geographically isolated at the north and south of Corrientes.
2- C.
roigi constitutes a compact entity represented by only one population located
at the margin of the Paraná River, which, although not depauperated
genetically, needs to be monitored through time due to habitat instability
during flood periods. However its genetic pool is also present in a group of C. sp populations, which are probably
the result of hybridization between that species and C. dorbignyi north.
3- C. perrensi also appears separated into two different lineages, one
located between the Paraná and Santa Lucía Rivers, and the other between the
Santa Lucía River and the Iberá marsh. Each lineage is associated to a group of
derived populations. One of them, probably the result of hybridization with C. dorbignyi south, is characterized by
a high number of chromosomal polymorphisms and polytypisms,
4- There is a northern group
of C. sp populations located north of
Corrientes and characterized by some of the lowest diploid numbers, which
appears quite differentiated from the rest, although distantly related to the
south lineage of C. dorbigny.
5- The only two populations of C. sp located east of the Iberá marsh
are the result of recent
founding events, whose source population needs still to be found.
As stated by Hey et
al (2003), sometimes it is better to present the full picture that research has
revealed, which will show all its complexity, rather than to reduce that
complexity artificially. The nature of the Corrientes lineages, with its
patterns of divergence within species without karyotypic change, and
hybridization between species accompanied by intensive chromosomal rearrangements
is better understood within this framework.
The
"perrensi" group of species constitutes in this way a very
interesting model to understand evolutionary processes actually occurring, as
well to analyze the incidence of habitat fragmentation and instability on the
shaping of evolutionary lineages. By other hand, studying Ctenomys in this naturally and humanly altered environment, as a
representative of a varied small mammals community, can contribute to the
establishment of management strategies leading to the conservation of one of
the most important aquifers of South America.