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:
<!-- /* Font Definitions */ @font-face {font-family:Helvetica; panose-1:2 11 6 4 2 2 2 2 2 4; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:536902279 -2147483648 8 0 511 0;} @font-face {font-family:"Arial Narrow"; panose-1:2 11 5 6 2 2 2 3 2 4; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:647 0 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:none; font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-GB; mso-fareast-language:EN-US; layout-grid-mode:line;} p.MsoBodyText, li.MsoBodyText, div.MsoBodyText {margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; text-autospace:none; font-size:12.0pt; font-family:Helvetica; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-GB; mso-fareast-language:EN-US; font-weight:bold;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> 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.