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 Península de Paraguaná 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.

[Molecular characterization of Sigmodon hirsutus (Rodentia: Cricetidae) populations in Venezuela]. / Caracterización molecular de poblaciones venezolanas de Sigmodon hirsutus (Rodentia: Cricetidae).

Recent phylogenetic studies based on cytochrome b gene sequence, have determined that the species historically known as Sigmodon hispidus (Rodentia) from South America comprises a species S. hirsutus of paraphyletic origin. The aim of this study was to test the hypothesis that populations from Venezuela, represent the sensu strict form, ancestral haplotypes, and monophyletic subspecieS. For this, 12 individual sequences from three localities of different biogeographic regions in Venezuela were evaluated and sequenced based on cyto b. Additionally, the sequences were used to develop a cladistic analysis and genetic distance calculations, and to compare this information with two individual sequences of Sigmodon specimens available in Genbank. Phylogenetic analyses show that the three populations of S. hirsutus of Venezuela form an ancestral and monophyletic subclade supported by high bootstrap values and significant genetic distance between subclade within the S. hirsutus. Besides, the existence of two lineages suggests two subspecies, S. hirsutus hirsutus from Venezuela, and S. hirsutus mexicanus from Mexico-Central America, but, both species need formal description.

Caracterización molecular de poblaciones venezolanas de Sigmodon hirsutus (Rodentia: Cricetidae)

Molecular characterization of Sigmodon hirsutus (Rodentia: Cricetidae) populations in Venezuela. Recent phylogenetic studies based on cytochrome b gene sequence, have determined that the species historically known as Sigmodon hispidus (Rodentia) from South America comprises a species S. hirsutus of paraphyletic origin. The aim of this study was to test the hypothesis that populations from Venezuela, represent the sensu strict form, ancestral haplotypes, and monophyletic subspecies. For this, 12 individual sequences from three localities of different biogeographic regions in Venezuela were evaluated and sequenced based on cyto b. Additionally, the sequences were used to develop a cladistic analysis and genetic distance calculations, and to compare this information with two individual sequences of Sigmodon specimens available in Genbank. Phylogenetic analyses show that the three populations of S. hirsutus of Venezuela form an ancestral and monophyletic subclade supported by high bootstrap values and significant genetic distance between subclade within the S. hirsutus. Besides, the existence of two lineages suggests two subspecies, S. hirsutus hirsutus from Venezuela, and S. hirsutus mexicanus from Mexico-Central America, but, both species need formal description. Rev. Biol. Trop. 59 (2): 795-807. Epub 2011 June 01.

Recientes estudios filogenéticos basados en la secuencia del gen del citocromo b, han determinado que la especie conocida históricamente como Sigmodon hispidus (Rodentia) en Suramérica incluye una especie S. hirsutus de origen parafilético. El objetivo de este estudio fue probar la hipótesis de que las poblaciones de Venezuela, representan la forma sensu estricto, los haplotipos ancestrales y una subespecie monofilética. La metodología consistió en un análisis cladístico y cálculos de distancia genética, a partir de secuencias de citocromo b en 12 individuos de tres localidades en Venezuela que pertenecen a diferentes regiones biogeográficas, y a su vez compararlas con las dos secuencias disponibles en Genbank de especies del género Sigmodon. Los análisis filogenéticos indican que las tres poblaciones de S. hirustus de Venezuela forman un subclado ancestral y monofilético con el apoyo de valores de bootstrap altos y con significativa distancia genética, entre subclados dentro de S. hirsutus. La existencia de dos subclados dentro de S. hirsutus sugiere dos subespecies, S. hirsutus hirsutus en Venezuela y S. hirsutus mexicanus en México y Centroamérica. Sin embargo, ambas subespecies necesitan una descripción formal.

Comparative chromosome painting in Aotus reveals a highly derived evolution.

The genus Aotus represents a highly diverse group with an especially intricate taxonomy. No standard cytogenetic nomenclature for the genus has yet been established. So far, cytogenetic studies have characterized 18 different karyotypes with diploid numbers ranging from 46 to 58 chromosomes. By combining G-banding comparisons and molecular cytogenetic techniques, we were able to describe the most likely pattern of chromosome evolution and phylogenetic position of two Aotus karyomorphs (KMs) from Venezuela: Aotus nancymai (KM3, 2n=54) and Aotus sp. (KM9, 2n=50). All of the proposed Platyrrhini ancestral associations (2/16, 3/21, 5/7, 8/18, 10/16, 14/15) were found in the Aotus KMs studied, except 2/16 and 10/16. In addition, some derived chromosomal associations were also detected in both KMs (1/3, 1/16, 2/12, 2/20, 3/14, 4/15, 5/15, 7/11, 9/15, 9/17, 10/11, and 10/22). Although some of these associations have been found in other New World monkeys, our results suggest that Aotus species have undergone a highly derived chromosomal evolution. The homologies between these two Aotus KMs and human chromosomes were established, indicating that KM3 has a more derived karyotype than KM9 with respect to the ancestral Platyrrhini karyotype.