Keyword: karyotype

Chromosomal characterization of Irenomys tarsalis (Rodentia, Cricetidae, Sigmodontinae)

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The systematics of I. tarsalis is far from being understood. Morphological and molecular analyses have given contradictory results, pointing towards its inclusion or exclusion from the Phyllotini. The karyotype of Irenomys tarsalis, as well as its C-bands, are reported for the first time. The species has 2n = 64 chromosomes (FN = 98) and a C-banding pattern characterized by small amounts of centromeric heterochromatin. Although the high diploid number and the C-bands of I. tarsalis support the notion of the species’ ancestral karyotypic condition, its affiliation within the sigmodontines cannot be discerned by the data.

Caracterización cromosómica de Irenomys tarsalis (Rodentia, Cricetidae, Sigmodontinae). Las relaciones sistemáticas de I. tarsalis están poco comprendidas. Los análisis morfológicos y moleculares han dado resultados contradictorios, que indican su pertenencia o exclusión de la tribu Phyllotini. Se describe por primera vez el cariotipo de Irenomys tarsalis, así como la distribución de la heterocromatina C-positiva. La especie tiene 2n = 64 cromosomas (FN = 98) y un patrón de bandas C pequeñas y centroméricas. Si bien el alto número diploide y la distribución de la heterocromatina apoyan la condición cariotípica ancestral de I. tarsalis, su afiliación dentro de los sigmodontinos no puede ser discernida solamente por estos datos.

Karyotypes of Brazilian representatives of genus Zygodontomys (Rodentia, Sigmodontinae)

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In this article we are reporting two cytotypes found in representatives of Zygodontomys genus trapped in two localities of Brazilian Amazon. From the locality of Surumú (Roraima) were analyzed 12 individuals (cytotype 1) which showed 2n = 86 / FN = 96–100, presenting the two largest pairs (1 and 2) as subtelo-submetacentrics, 4 or 5 medium to small biarmed pairs, the remainder being acrocentric. In Tartarugalzinho (Amapá) 7 specimens which displayed 2n = 84 / FN = 96–98 (cytotype 2) were caught. In both cytotypes the sexual pair is composed by a large submetacentric X chromosome and a median subtelocentric Y chromosome. By G-banding the largest pairs as well as the sex chromosomes could be identified. The C-bands occurred at the centromere of the majority of the autosomes and the short arm of the X and the whole Y chromosomes were heterochromatic. The NOR-bands were prevalently seen at the short arm of one medium and one small acrocentric pairs. Comparing the individuals studied in Brazil with those reported in Venezuela is observed that, although the same or similar diploid numbers, the morphology of the chromosomes of these taxa is quite different, the karyotypes of the specimens from Brazil having a smaller number of biarmed elements.The sexual pair is distinct also, the difference basically concerning to the size of the Y chromosome. Whether these karyotype differences may correspond to different morphological taxa is a subject that deserves further investigations.

Lestodelphys halli: new information on a poorly known Argentine marsupial

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Lestodelphys halli is a small, terrestrial didelphid marsupial known only from a few widely scattered, semidesert localities from Mendoza south to Santa Cruz in Argentina. We have updated the distribution map based on 17 traditional specimens and 31 catalogued and more than 15 uncatalogued individuals and lots of osteological remains recovered from owl pellets. Images taken from a videotape of a captive L. halli document the killing and partial consumption of a mouse, strongly supporting Thomas’ (1921) hypothesis that the species is predaceous. The karyotype consists of 14 chromosomes and is generally similar to that of other 2N = 14 marsupials. Study of a 281-base pair region of the cytochrome b gene compared to the same region in other South American didelphids suggests that Lestodelphys is most closely related to Thylamys, another small South American didelphid that occurs in southern Argentina, but does not elucidate the relationship of this clade to other genera previously hypothesized to be closely related to Lestodelphys.

Lestodelphys halli: nueva información sobre un marsupial argentino muy poco conocido. Lestodelphys halli es un marsupial didélfido de pequeño tamaño conocido solo por unas pocas y dispersas localidades en semidesiertos de Argentina, desde Mendoza hasta Santa Cruz. Nosotros hemos actualizado el mapa de distribución de la especie sobre la base de los 17 especímenes regulares y sobre evidencias adicionales obtenidas de 31 especímenes y lotes catalogados y al menos 15 especímenes obtenidos ambos de regurgitados de lechuzas. Una serie de fotografías obtenidas de una videofilmación de un Lestodelphys halli en cautiverio documenta la muerte y consumo parcial de un ratón, apoyando la sugerencia de Thomas (1921) sobre los hábitos de predador de esta especie. El cariotipo es de 14 cromosomas y es similar al 2N = 14 de otros marsupiales. Estudios utilizando regiones del ADN mitocondrial de esta especie, comparados con las mismas regiones del ADN mitocondrial de otros didélfidos sudamericanos, sugieren que Lestodelphys es la especie más cercanamente relacionada a Thylamys, otro pequeño didélfido que habita el sur de Argentina. Las relaciones filogenéticas de este ciado con otros géneros, previamente hipotetizados como cercanamente emparentados, permanecen sin resolver en nuestro estudio.