Abstract
The aim of this work is to characterize Nephilengys cruentata in relation to the diploid number, chromosome morphology, type of sex determination chromosome system, chromosomes bearing the Nucleolar Organizer Regions (NORs), C-banding pattern, and AT or GC repetitive sequences. The chromosome preparations were submitted to standard staining (Giemsa), NOR silver impregnation, C-banding technique, and base-specific fluorochrome staining. The analysis of the cells showed 2n = 24 and 2n = 26 chromosomes in the embryos, and 2n = 26 in the ovarian cells, being all the chromosomes acrocentric. The long arm of the pairs 1, 2 and 3 showed an extensive negative heteropycnotic area when the mitotic metaphases were stained with Giemsa. The sexual chromosomes did not show differential characteristics that allowed to distinguish them from the other chromosomes of the complement. Considering the diploid numbers found in N. cruentata and the prevalence of X1X2 sex determination chromosome system in Tetragnathidae, N. cruentata seems to possess 2n = 24 = 22 + X1X2 in the males, and 2n = 26 = 22 + X1X1X2X2 in the females. The pairs 1, 2 and 3 showed NORs which are coincident with the negative heteropycnotic patterns. Using the C-banding technique, the pericentromeric region of the chromosomes revealed small quantity or even absence of constitutive heterochromatin, differing of the C-banding pattern described in other species of spiders. In N. cruentata the fluorochromes DAPI/DA, DAPI/MM and CMA3/DA revealed that the constitutive heterochromatin is rich in AT bases and the NORs possess repetitive sequences of GC bases.
Highlights
The Araneae order has about 38,000 taxonomically known species distributed in 109 families (Platnick, 2002)
Karyotype description Mitotic metaphases of N. cruentata submitted to the standard staining, C-banding, Nucleolar Organizer Regions (NORs) silver impregnation and fluorochrome technique showed 2n = 24 in the male embryos (Fig. 1A) and 2n = 26 in the female embryos and in the oogonials of the young specimens (Fig. 1B)
Standard staining The analysis of embryonic and oogonial metaphases evidenced that the chromosomes of the pairs 1, 2 and 3 have a prominent negative heteropycnotic region which extends from the median until the telomeric region of the long arm (Fig. 2A, B)
Summary
The Araneae order has about 38,000 taxonomically known species distributed in 109 families (Platnick, 2002) Of these approximately 460 species have been studied from the cytogenetic point of view, being 32 belonging to the Neotropical region (Hackman, 1948; Suzuki, 1954; Bole-Gowda, 1958; Brum-Zorrila & Cazenave, 1974; Benavente & Wettstein, 1980; Brum-Zorrila & Postiglioni, 1980; Silva, 1988; Scioscia, 1997; Sbalqueiro et al, 1998; Chen, 1999). 3 species possess the type X X X X /XXXXX 1234 11223
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