Multiple interstitial ribosomal sites (NORs) in the Brazilian squirrel Sciurus aestuans ingrami (Rodentia, Sciuridae) with 2n = 40: an overview of Sciurus cytogenetics

Valéria Fagundes,Renata Cecília Amaro-Ghilard,Yatiyo Yonenaga-Yassuda,Daniel R Scheibler,Alexandre Uarth Christoff

doi:10.1590/s1415-47572003000300007

Abstract

This is the first time the karyotype of the Brazilian squirrel Sciurusaestuans ingrami, with 2n = 40, is described. The karyotype of this species comprises 18 pairs of biarmed and one minute pair of acrocentric autosomes, a medium-sized submetacentric X and a medium-sized acrocentric Y. Four pairs have an interstitial secondary constriction, co-located with nucleolar organizer regions (NORs), identified by silver-staining technique and fluorescent in situ hybridization (FISH) with ribosomal 18S/28S probes. The occurrence of multiple interstitial NORs is rare in rodents, and this is one of the few examples, identified by a molecular cytogenetics approach.

Highlights

Squirrels of the genus Sciurus Linnaeus (1758), especially those from Central America, present a wide geographical variation in pelage coloration
There are some taxa included in S. aestuans which have been considered as full species by some authors: S. a. aestuans, found mainly in the northern Amazon; S. a. gilvigularis, from the southern Amazon and Venezuela; S. a. alphonsei, found along the coast, from southern Pará to Pernambuco; and S. a. ingrami, found all along eastern Brazil, from Bahia to Rio Grande do Sul (Emmons, 1997)
We present the karyotype of two Brazilian S. a. ingrami (2n = 40) females and one male, which presented a pattern of multiple interstitial nucleolar organizer regions (NORs) that is unusual in rodents

Summary

Introduction

Squirrels of the genus Sciurus Linnaeus (1758), especially those from Central America, present a wide geographical variation in pelage coloration. Systematics of this group is rather puzzling. 50 genera and 273 species of squirrels are recognized in the world. 4 genera and 19 species from Neotropical forests were known. Hoffmann et al (1993) recognized four species in Brazil: S. ignitus (westernmost region), S. igniventris (Amazon region), S. spadiceus (southern Amazon), and S. aestuans. There are some taxa included in S. aestuans which have been considered as full species by some authors: S. a. Aestuans, found mainly in the northern Amazon; S. a. Gilvigularis, from the southern Amazon and Venezuela; S. a. There are some taxa included in S. aestuans which have been considered as full species by some authors: S. a. aestuans, found mainly in the northern Amazon; S. a. gilvigularis, from the southern Amazon and Venezuela; S. a. alphonsei, found along the coast, from southern Pará to Pernambuco; and S. a. ingrami, found all along eastern Brazil, from Bahia to Rio Grande do Sul (Emmons, 1997)

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