Are we overestimating the niche? Removing marginal localities helps ecological niche models detect environmental barriers

Correlative ecological niche models (ENMs) estimate species niches using occurrence records and environmental data. These tools are valuable to the field of biogeography, where they are commonly used to infer potential connectivity among populations. However, a recent study showed that when locally relevant environmental data are not available, records from patches of suitable habitat protruding into otherwise unsuitable regions (e.g., gallery forests within dry areas) can lead to overestimations of species niches and their potential distributions. Here, we test whether this issue obfuscates detection of an obvious environmental barrier existing in northern Venezuela – that of the hot and xeric lowlands separating the Penınsula de Paraguana from mainland South America. These conditions most likely promote isolation between mainland and peninsular populations of three rodent lineages occurring in mesic habitat in this region. For each lineage, we calibrated optimally parameterized ENMs using mainland records only, and leveraged existing habitat descriptions to assess whether those assigned low suitability values corresponded to instances where the species was collected within locally mesic conditions amidst otherwise hot dry areas. When this was the case, we built an additional model excluding these records. We projected both models onto the peninsula and assessed whether they differed in their ability to detect the environmental barrier. For the two lineages in which we detected such problematic records, only the models built excluding them detected the barrier, while providing additional insights regarding peninsular populations. Overall, the study reveals how a simple procedure like the one applied here can deal with records problematic for ENMs, leading to better predictions regarding the potential effects of the environment on lineage divergence

Dose-Dependent Limitation of Arterial Enlargement by the Matrix Metalloproteinase Inhibitor RS-113,456

Background. Arterial diameter changes in response to flow. Chronic flow-mediated arterial enlargement may be mediated through metalloproteinase activity in the extracellular matrix of the arterial wall. We examined flow-mediated enlargement in the setting of increasing competitive matrix metalloproteinase (MMP) inhibition and with respect to gelatinase A and B expression and activity. Methods. Left common femoral arteriovenous fistulas (AVFs) were created in dose–response (52) and time course (34) cohorts of rats. Dose–response rats received either vehicle alone or 12.5, 25, or 37.5 mg/kg b.i.d. RS 113,456, a competitive MMP inhibitor. Heart rate, blood pressure, and weight were measured at intervals following AVF construction. Aortic and common iliac diameters were measured on postoperative day (POD) 21. Untreated time course rats were sacrificed on PODs 0 (no AVF), 3, 7, 14, and 21. Aortic diameter was measured and the vessels were harvested for tissue analysis. Equal amounts of aortic RNA underwent reverse transcription and polymerase chain reaction with primers for MMP-2, MMP-9, and GAPDH. Zymography was performed on iliac artery tissue to measure gelatinolytic activity. Results. A significant, stepwise reduction in flow-mediated aortic and left common iliac enlargement following left femoral AVF creation was noted with progressively higher doses of RS 113,456 without apparent hemodynamic or toxic effects. Right common iliac diameter was unchanged. Over 21 days following AVF creation, there was an upward trend in expression and activity for MMP-2 not evident for MMP-9. Conclusion. Flow-mediated arterial enlargement is limited by competitive MMP inhibition in a dose-dependent fashion. MMP-dependent flow-mediated enlargement may involve differential expression and activity of MMP-2 and MMP-9

Cytogenetics of the Brazilian whiptail lizard Cnemidophorus littoralis (Teiidae) from a restinga area (Barra de Maricá) in Southeastern Brazil

Chromosomes of Cnemidophorus littoralis, a new species of teiid lizard recently described, were studied. The animals are from a restinga area in Barra de Maricá, RJ. The karyotype presents a diploid number of 2n = 46 chromosomes and a chromosomal sex determination mechanism of the type XX:XY. Nucleolar organizer regions, Ag-NORs, are at the sixth pair of chromosomes; there is variability of size and number of the Ag-stained nucleoli on the 50 interphase nuclei for each specimen analyzed. These nucleoli are related to NOR patterns that also demonstrated variability in size and number. This paper presents the first description of the karyotype of Cnemidophorus littoralis and of a chromosomal sex determination mechanism of the XX:XY type in the genus Cnemidophorus from Southeastern Brazil