Demographic history and biologically relevant genetic variation of Native Mexicans inferred from whole-genome sequencing.

Understanding the genetic structure of Native American populations is important to clarify their diversity, demographic history, and to identify genetic factors relevant for biomedical traits. Here, we show a demographic history reconstruction from 12 Native American whole genomes belonging to six distinct ethnic groups representing the three main described genetic clusters of Mexico (Northern, Southern, and Maya). Effective population size estimates of all Native American groups remained below 2,000 individuals for up to 10,000 years ago. The proportion of missense variants predicted as damaging is higher for undescribed (~ 30%) than for previously reported variants (~ 15%). Several variants previously associated with biological traits are highly frequent in the Native American genomes. These findings suggest that the demographic and adaptive processes that occurred in these groups shaped their genetic architecture and could have implications in biological processes of the Native Americans and Mestizos of today.

Effects of luteectomy in early pregnancy on the maintenance of gestation and plasma progesterone concentrations in the viviparous temperate lizard Barisia imbricata imbricata.

BACKGROUND: Several studies have shown that the corpus luteum is the principal source of progesterone during the gravidity period in reptiles; however, its participation in the maintenance of gestation in the viviparous squamata is in dispute. The effects of ovariectomy or luteectomy vary according to the species and the time at which the procedure is performed. In this paper, we describe the effects of luteectomy during early pregnancy on the maintenance of gestation and progesterone concentrations in the temperate Mexican viviparous lizard Barisia imbricata imbricata. METHODS: Twenty-four lizards were subjected to three different treatments: luteectomy, sham luteectomy or non-surgical treatment, and blood samples were obtained before and after surgical treatment at different stages of gestation to determine the effects of luteectomy on the maintenance of gestation and progesterone concentrations. RESULTS: Spontaneous abortion was not observed in any of the females. However, luteectomy provoked abnormal parturition and a significant reduction in the number of young born alive. Parturition was normal in untreated females as well as those submitted to sham luteectomy. The surgical treatment also caused a significant reduction in progesterone concentrations in luteectomised females during early and middle gestation. However, no significant differences in hormone concentrations were observed among the three groups during late gestation or immediately post-parturition. CONCLUSIONS: Our observations indicate that the presence of the corpus luteum is not necesary for the maintenance of gestation, but that it does participate in parturition control. Moreover, the corpus luteum of the viviparous lizard B. i. imbricata produces progesterone, at least during the first half of pregnancy, and that an extra-ovarian source of progesterone must maintain gestation in the absence of luteal tissue.

Luteal development and progesterone levels during pregnancy of the viviparous temperate lizard Barisia imbricata imbricata (Reptilia: Anguidae).

The relationship between plasma progesterone (P(4)) levels and the formation and degeneration of the corpus luteum (CL) was assessed monthly during gestation of the viviparous lizard Barisia imbricata imbricata. Histochemical activity of the delta(5-4) isomerase 3 beta-hydroxysteroide dehydrogenase (delta(5-4)3beta-HSD) in the luteal tissue and embryonic development were also observed. Females were gravid throughout winter and great part of spring (late November or early December until late May or early June). Corpus luteum development occurred in the first third of gestation (December and January) when the embryo reached developmental stage 27. Four sequential stages were identified during development and three stages during regression of the CL. The follicular and thecal tissue participated in the formation of the luteal cell mass. According to Xavier's classification, the CL of B. i. imbricata is a subtype from Type III. The activity of delta(5-4)3beta-HSD was observed mainly in the luteal cell mass. The first degenerative changes in the CL were observed in the early second third of the gestation and continued gradually until parturition. Progesterone levels increased in early pregnancy and reached its highest level during January (3.07+/-1.04 ng/ml) when mature corpora lutea were present. Gradual diminution in progesterone concentrations occurred in the second and last third of pregnancy and coincided with advanced degenerative changes and diminution in histochemical activity of delta(5-4)3beta-HSD in the luteal tissue. These observations suggest that the CL is the major source of progesterone during pregnancy of B. i. imbricata.