Análise citogenética na aranha Micrathena aff. triangularis (Araneae, Araneidae)

Abstract

Spiders constitute a megadiverse group, currently composed of 50,412 taxonomically described species, distributed in 132 families. Despite this enormous diversity, there are only 849 species studied from the point of view of cytogenetics, which represents less than 1.7% of known species. Cytogenetics provides data such as diploid number, chromosomal morphology, type of sexual chromosome system (SCS), among others, which can be used to compare species. Micrathena Sundevall, 1833 (Araneidae) is an extremely specious genus, with 119 described species, but only 11 species analyzed by cytogenetics, in which the diploid number varies between 2n♂=11=10+X in Micrathenaplana (C.L. Koch, 1836) and 2n♂=51=46+X1X2X3X4X5 in Micrathena sanctispiritus (Brignoli, 1983), with predominantly telocentric morphology and SCS X1X2X3X4 in males and X1X1X2X2X3X3X4X4 in females. This work cytogenetically analyzed Micrathena aff. triangularis (flat group), which presented 2n♂=48=44+X1X2X3X4, with an exclusively telocentric morphology, which differs from the karyotypes with lower chromosome numbers and chromosomes with two arms found in two other species in this group. Therefore, two hypotheses were proposed for the chromosomal evolution of the flat group, one with two independent reductions and the other involving a reduction and a new increase in diploid number.