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The South American plains vizcacha, Lagostomus maximus inhabits primarily the Pampean and adjoining Espinal, Monte and Chaquenean regions of Argentina. In order to study the population genetic structure of L. maximus, a fragment of 560 bp of the mitochondrial DNA hypervariable region 1from 90 individuals collected from the 3 subspecies and 8 groups along Argentina was amplified and analyzed. We found 9 haplotypes. The haplotype network did not show an apparent phylogeographical signal. Although low levels of genetic variation were found in all the subspecies and groups analyzed, a radiation of L. maximus would have occurred from the North and Center of the Pampean region toward the rest of its geographic range in Argentina. Low levels of genetic diversity, the existence of a single genetically distinct population in Argentina and changes of its effective size indicate that metapopulation processes and changes in human population dynamics during the late-Holocene were important factors shaping the population genetic structure of L. maximus in Argentina. [ABSTRACT FROM AUTHOR]

Highlights • The involvement of estrogen receptors on LH surge during gestation was evaluated. • ERα, but not ERβ, showed significant increment from mid-gestation. • LH pulsatility showed a significant increase at mid-pregnancy. • Stimulation of ERα induced significant increase in the total mass of LH released. • LH pulsatility rise at mid-pregnancy would be enabled by ERα action. Abstract The South American plains vizcacha, Lagostomus maximus , is a caviomorph rodent native from Argentina, Bolivia and Paraguay. It shows peculiar reproductive features like pre-ovulatory follicle recruitment during pregnancy with an ovulatory process at around mid-gestation. We have described the activation of the hypothalamic – pituitary – ovarian (HPO) axis during pregnancy. A progressive decrease of progesterone (P4) at mid-pregnancy elicits the delivery of gonadotropin-releasing hormone (GnRH) with the consequent secretion of follicle stimulating hormone (FSH) and estradiol (E 2) followed by luteinizing hormone (LH) release resulting in follicular luteinization and the P4 concentration recover. Pituitary gland is the central regulator of the HPO axis being E 2 a key hormone involved in the regulation of its activity. In this work we analyzed the action of E 2 on the pituitary response to the GnRH wave as well as its involvement on LH secretion at mid-gestation in L. maximus. The expression of GnRHR at the pituitary pars distalis showed a significant decrease at mid-pregnancy compared to early- and term-gestating females. ERα showed a significant increment from mid-gestation whereas ERβ did not show variations throughout pregnancy; whereas the LH expression in the pituitary pars distalis showed a significant increase at mid-gestation, concordantly with serum LH, which was followed by a decrease at term-gestation with similar values than at early-pregnancy. The number of cells with co-localization of ERα and GnRHR showed a decline at mid-pregnancy related to early- and term-gestation, whereas the cells with co-localization of ERα and LH increased at mid- and term-pregnancy. On the other hand, ex vivo measuring of LH pulsatility showed a significant increment in the total mass of LH delivered at mid-pregnancy followed by a decrease at term-gestation. The stimulation of ERα with the PPT specific agonist induced a significant increment in the total mass of LH released, whereas no changes were determined when ERβ was stimulated with its specific agonist MPP. These results suggest that LH pulsatility rise at mid-pregnancy would be enabled by the increase of E 2 acting through ERα. [ABSTRACT FROM AUTHOR]

The karyotype of specimens identified as Calomys lepidus, trapped at 3600 m above sea level in the Puna region, northwestern Argentina, was studied. All specimens analysed showed a 2n = 44 (NF(a) = 68) asymmetrical karyotype with 13 pairs of metacentric/submetacentric autosomes and 7 pairs of telocentric chromosomes. The X was a medium-sized submetacentric and the Y a small submetacentric chromosome. This karyotype was quite different from that previously described for C. lepidus from Peru (2n = 36, NF(a) = 68). However, both karyotypes may be easily interrelated by means of four centric fusions, and the chromosome complement of Punian C. lepidus fitted into a previously proposed chromosomal phylogeny of the genus. In addition, the spermatozoa of specimens corresponded to a morphological pattern previously described for other species of Calomys.