Coronal voids and their magnetic nature

Context. Extreme ultraviolet (EUV) observations of the quiet solar atmosphere reveal extended regions of weak emission compared to the ambient quiescent corona. The magnetic nature of these coronal features is not well understood.Aims. We study the magnetic properties of the weakly emitting extended regions, which we name coronal voids. In particular, we aim to understand whether these voids result from a reduced heat input into the corona or if they are associated with mainly unipolar and possibly open magnetic fields, similar to coronal holes. Methods. We defined the coronal voids via an intensity threshold of 75% of the mean quiet-Sun (QS) EUV intensity observed by the high- resolution EUV channel (HRIEUV) of the Extreme Ultraviolet Imager on Solar Orbiter. The line-of-sight magnetograms of the same solar region recorded by the High Resolution Telescope of the Polarimetric and Helioseismic Imager allowed us to compare the photospheric magnetic field beneath the coronal voids with that in other parts of the QS.Results. The coronal voids studied here range in size from a few granules to a few supergranules and on average exhibit a reduced intensity of 67% of the mean value of the entire field of view. The magnetic flux density in the photosphere below the voids is 76% (or more) lower than in the surrounding QS. Specifically, the coronal voids show much weaker or no network structures. The detected flux imbalances fall in the range of imbalances found in QS areas of the same size. Conclusions. We conclude that coronal voids form because of locally reduced heating of the corona due to reduced magnetic flux density in the photosphere. This makes them a distinct class of (dark) structure, different from coronal holes

Morphometric evaluation of the spermatogenesis in trahira Hoplias malabaricus (Bloch) (Characiformes, Erythrinidae)

The Erythrinidae trahira, Hoplias malabaricus (Bloch, 1794), is widespread throughout South America river basins. We determined Sertoli cell supporting capacity (ratio of primary spermatocytes: Sertoli cells and spermatids: Sertoli cells), meiotic index (ratio of spermatids: primary spermatocytes) and the number of spermatogonial mitotic generations of this fish. The fish were captured in the Igarapava reservoir, Grande River, Alto Paraná River basin, Brazil. Testis fragments of three sexually mature trahiras were fixed in 5% buffered glutaraldehyde solution and embedded in glycol methacrylate. Serial sections of 2 and 3 µm in thickness were stained with 0.5% toluidine blue. Histological counts from cysts of primary spermatocytes and spermatids revealed, respectively, 326 ± 99 and 468 ± 73 nuclei of these cells. Sertoli cell supporting capacity was considerably higher for spermatids (113.3 ± 16:1) when compared to primary spermatocytes (71 ± 5:1). Between eight and ten spermatogonial generations were formed to give rise to primary spermatocytes. These values were within the generation range of those already found in freshwater teleosts of external fertilization. Correlation between the number of Sertoli cells and primary spermatocytes per cyst, and Sertoli cells and spermatids per cyst were statistically significant (p < 0.05).<br>A traíra, Hoplias malabaricus (Bloch, 1794), da família Erythrinidae, encontra-se espalhada pelas bacias fluviais da América do Sul. Determinou-se a capacidade de suporte das células de Sertoli (espermatócitos primários: células de Sertoli e espermátides: células de Sertoli), índice meiótico (espermátides: espermatócitos primário) e o número de gerações mitóticas de espermatogônias desse peixe. Os indivíduos foram capturados no reservatório de Igarapava, rio Grande, bacia do Alto Paraná, Brasil. Fragmentos dos testículos de três traíras sexualmente maduras foram fixados em glutaraldeído a 5%, e incluídos em metacrilato. Cortes seriados de 2 e 3 µm de espessura foram corados em azul de toluidina a 5%. Contagens histológicas feitas em cistos de espermatócitos primários e espermátides revelaram, respectivamente, 326 ± 99 e 468 ± 73 núcleos destas células. A capacidade de suporte das células de Sertoli foi consideravelmente mais alta para espermátides (113,3 ± 16:1) do que para espermatócitos primários (71 ± 5:1). Ocorreram entre oito e dez gerações de espermatogonias antes de darem origem aos espermatócitos primários. Esses valores encontravam-se dentro da amplitude de gerações já registrada para teleósteos de água doce de fertilização externa. Correlações entre o número de células de Sertoli por cisto e de espermatócitos primários e entre células de Sertoli e espermátides por cisto foram estatísticamente signficativas (p < 0,05)

Species richness and areas of endemism of oryzomyine rodents (Cricetidae, Sigmodontinae) in South America: an NDM/VNDM approach

Aim. To infer areas of endemism for the tribe Oryzomyini in South America by employing a database of species richness and geographical distribution, and to compare these results with areas of endemism and species richness proposed in the literature for other taxa. // Location. We analysed specimens of the tribe Oryzomyini distributed throughout South and Central America, which are housed in European, North and South American museums and collections. // Methods. We analysed 2768 occurrence records for 102 species of the tribe Oryzomyini using the NDM/VNDM algorithm and three different grid sizes to assess the possible effects of grid cell area on the results. // Results. Using the overlap of consensus areas in South America, we identified three generalized areas of endemism for the Oryzomyini: north-western South America (NWSA), eastern South American (ESA), and northern South America (NSA); we also identified the Galápagos archipelago (GA) as an area of endemism.// Main conclusions Areas of endemism detected in the continental portion of South America include its three main mountain chains: the Andes Cordillera, the Guyanan Shields, and an area east of the Brazilian Shield named Serra do Mar. Each of these regions encompasses many different types of vegetation, and the species richness and composition of the areas of endemism of the tribe are directly related to this environmental diversity. Different grid sizes affected the distributional heterogeneity of the consensus areas. The smallest grid cell size identified mainly Andean areas, which contain a higher number of more exclusive species in a small area along a steep elevational gradient. In contrast, the largest grid size identified areas of endemism along an environmental gradient that co-varied with latitude and longitude. The identified areas of endemism are corroborated by previous studies on other taxa.Fil: do Prado, Joyce R.. Universidade Do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz Esalq; BrasilFil: Brennand, Pamella G. G.. Universidade Do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz Esalq; BrasilFil: Perez Godoy, Leandro. Universidade Do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz Esalq; BrasilFil: Simoes Libardi, Gustavo. Universidade Do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz Esalq; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: de Abreu Junior, Edson Fiedler. Universidade Do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz Esalq; BrasilFil: Roth, Paulo R. O.. Universidade Do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz Esalq; BrasilFil: Chiquito, Elisandra A.. Universidade Do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz Esalq; BrasilFil: Percequillo, Alexandre R.. Universidade Do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz Esalq; Brasi