Selective Spin-State Switch and Metal-Insulator Transition in \boldmath GdBaCo2O5.5\rm GdBaCo_2O_{5.5}

Ultra-high resolution synchrotron diffraction data for $\rm GdBaCo_2O_{5.5}$ throw new light on the metal-insulator transition of Co$^{3+}$ Ba-cobaltites. An anomalous expansion of CoO$_6$ octahedra is observed at the phase transition on heating, while CoO$_5$ pyramids show the normal shrinking at the closing of the gap. The insulator-to-metal transition is attributed to a sudden excitation of some electrons in the octahedra ($t_{2g}^6$ state) into the Co $e_g$ band (final $t_{2g}^4e_g^2$ state). The $t_{2g}^5e_g^1$ state in the pyramids does not change and the structural study also rules out a $d_{3x^2-r^2}/d_{3y^2-r^2}$ orbital ordering at $T_{MI}$.Comment: Phys. Rev. B (to appear

Evidence for a Low-Spin to Intermediate-Spin State Transition in LaCoO3

We present measurements of the magnetic susceptibility and of the thermal expansion of a LaCoO$_3$ single crystal. Both quantities show a strongly anomalous temperature dependence. Our data are consistently described in terms of a spin-state transition of the Co$^{3+}$ ions with increasing temperature from a low-spin ground state to an intermediate-spin state without (100K - 500K) and with (>500K) orbital degeneracy. We attribute the lack of orbital degeneracy up to 500K to (probably local) Jahn-Teller distortions of the CoO$_6$ octahedra. A strong reduction or disappearance of the Jahn-Teller distortions seems to arise from the insulator-to-metal transition around 500 K.Comment: an error in the scaling factor of Eq.(4) and consequently 2 values of table I have been corrected. The conclusions of the paper remain unchanged. See also: C. Zobel et al. Phys. Rev. B 71, 019902 (2005) and J. Baier et al. Phys. Rev. B 71, 014443 (2005

High Levels of Diversity Uncovered in a Widespread Nominal Taxon: Continental Phylogeography of the Neotropical Tree Frog

Species distributed across vast continental areas and across major biomes provide unique model systems for studies of biotic diversification, yet also constitute daunting financial, logistic and political challenges for data collection across such regions. The tree frog Dendropsophus minutus (Anura: Hylidae) is a nominal species, continentally distributed in South America, that may represent a complex of multiple species, each with a more limited distribution. To understand the spatial pattern of molecular diversity throughout the range of this species complex, we obtained DNA sequence data from two mitochondrial genes, cytochrome oxidase I (COI) and the 16S rhibosomal gene (16S) for 407 samples of D. minutus and closely related species distributed across eleven countries, effectively comprising the entire range of the group. We performed phylogenetic and spatially explicit phylogeographic analyses to assess the genetic structure of lineages and infer ancestral areas. We found 43 statistically supported, deep mitochondrial lineages, several of which may represent currently unrecognized distinct species. One major clade, containing 25 divergent lineages, includes samples from the type locality of D. minutus. We defined that clade as the D. minutus complex. The remaining lineages together with the D. minutus complex constitute the D. minutus species group. Historical analyses support an Amazonian origin for the D. minutus species group with a subsequent dispersal to eastern Brazil where the D. minutus complex originated. According to our dataset, a total of eight mtDNA lineages have ranges >100,000 km2. One of them occupies an area of almost one million km2 encompassing multiple biomes. Our results, at a spatial scale and resolution unprecedented for a Neotropical vertebrate, confirm that widespread amphibian species occur in lowland South America, yet at the same time a large proportion of cryptic diversity still remains to be discovered

Colección herpetológica de Latinoamérica en la Estación Biológica de Doñana

Comunicación presentada en el XII Congreso Latinoamericano de Herpetología, 30 de octubre al 3 de noviembre 2023, Cochabamba, Bolivia.La Colección científica de Vertebrados de la Estación Biológica de Doñana (EBD) es la segunda más grande y completa de España. Fundada en 1964, actualmente sus fondos conservan unos 150.000 ejemplares de vertebrados, la mitad testigos de la biodiversidad española y la otra mitad del mundo. La colección de Herpetología destaca con 41.000 ejemplares representativos de unas 650 especies de anfibios y reptiles, con preparaciones en seco (huesos, caparazones, pieles) o en etanol, además de muestras de tejidos y ejemplares naturalizados de gran valor histórico. Durante las décadas de los 70 y 80, la EBD realizó estudios pioneros sobre la biodiversidad de algunos ecosistemas de América y África, aportando material a las colecciones. Un recuento actualizado de los fondos herpetológicos de la EBD da cuenta de unos 5.100 ejemplares provenientes de Latinoamérica, resaltando por su contribución numérica y cobertura taxonómica las muestras de Bolivia (2.376 ejemplares de 223 especies de anfibios y reptiles), Venezuela (1.288 ejemplares/116 especies) y Nicaragua (686 ejemplares/52 especies) que, en conjunto, representan el 85% del total de muestras de esta región. El 15% restante provienen principalmente de México, Paraguay, Argentina, Perú y Uruguay. En la EBD se custodia material tipo (6 holotipos y 30 paratipos) de 14 especies descritas para Bolivia y Venezuela. La colección está abierta a consulta y muy pronto la información asociada a los ejemplares estará disponible en portales globales de biodiversidad.Peer reviewe

First record of the treefrog Myersiohyla neblinaria (Anura: Hylidae) for Cerro Aracamuni, in the south of the Venezuelan Amazon

Abstract. Until now, the treefrog Myersiohyla neblinaria was only known from four highland localities on the northern slope of Cerro de la Neblina, in the southern part of Amazonas state, Venezuela. In this note we document the first record of this species for the summit of Cerro Aracamuni, a table-top mountain located ca. 40 km north from Cerro de la Neblina. This is the fourth anuran species known for the poorly explored Aracamuni. We briefly discuss some implications of this new finding.Primer registro de la rana arborícola Myersiohyla neblinaria (Anura: Hylidae) para el Cerro Aracamuni, en el sur de la Amazonia venezolana Resumen. Hasta ahora, la rana arborícola Myersiohyla neblinaria era conocida solo de cuatro localidades en la ladera norte del Cerro de la Neblina, en la parte sur del estado Amazonas, Venezuela. En esta nota documentamos el primer registro de la especie para la cima del Cerro Aracamuni, un tepui localizado a unos 40 km al norte del Cerro de la Neblina. Esta es la cuarta especie de anuro conocida para el poco explorado Aracamuni.  Discutimos brevemente algunas de las implicaciones de este nuevo hallazgo