Chromosomal Data of Two Pholcids (Araneae, Haplogynae): A New Diploid Number and the First Cytogenetical Record for the New World Clade

Abstract

Mesabolivar luteus (Keyserling 1891) and Micropholcus fauroti (Simon 1887) specimens were collected in Ubatuba and Rio Claro, both in the state of Sao Paulo, Brazil. Mesabolivar luteus showed 2n (d) = 15 = 14 + X and 2n (?) = 16 = 14 + XX in mitotic metaphases and 7II + X in diplotenic cells. During late prophase I, all bivalents presented a ring shape, evidencing two chiasmata per bivalent. In this species, some diplotenic cells appear in pairs, maybe due to specific characteristics of the intercellular bridges. The metaphases II showed n = 7orn = 8 = 7 + X chromosomes. Micropholcus fauroti evidenced 2n (d) = 17 = 16 + X in spermatogomal metaphases and 8II+X in diplotenic cells, with only one chiasma per bivalent, contrasting with M luteus. In both species, all chromosomes were metacentrics. The sexual chromosome X was the largest element and appeared as a univalent during meiosis 1. These are the first cytogenetical data for the genera Mesabolivar and Micropholcus. Additionally, M. luteus is the first chromosomally analyzed species of the New World clade and the observed diploid number for M. fauroti had not yet been recorded in Pholcidae.

Mesabolivar brasiliensis (Moenkhaus 1898) and Mesabolivar cyaneotaeniatus (Keyserling 1891) (Araneomorphae, Pholcidae): close relationship reinforced by cytogenetic analyses

“…With regard to the SCS, the X type in males and XX in females found in both species here studied was also encountered in nine other pholcids (Bole-Gowda 1958;Cokendolpher 1989;Xiuzhen et al 1997;Araujo et al 2005;Krá l et al 2006;Oliveira et al 2007), and thus may be the most prevalent form in this family. In species of Pholcidae with X/XX system, the X chromosome seems to be the largest or nearly the largest element of the karyotype.…”

“…Our comparison of the karyotype of M. luteus obtained by Araujo et al (2005) with M. brasiliensis and M. cyaneotaeniatus revealed similar chromosomal morphology with biarmed elements (meta/submetacentrics) and the same SCS of the X/XX type. However, the diploid number differed among these three Mesabolivar species, that is, 2n L 5 15 in M. luteus and 2n L 5 17 in both species examined here.…”

“…Concerning the diploid number, 2n L 5 17 was first described for the pholcid Micropholcus fauroti (Simon 1887) (Araujo et al 2005). However, the present addition of two more pholcids with the same number of chromosomes indicates that this diploid number could be as widespread as the 2n L 5 15, which has been recorded from five species of the family.…”

“…It is possible that the morphology of the sex chromosomes has been interpreted incorrectly as acrocentric due to low chromosomal preparation quality. The problem of preparation quality in pholcid cytogenetical research has been highlighted by several authors (see Araujo et al 2005). As an alternative to describe chromosomal morphology in species of this family, metaphase II chromosomes have been used (Araujo et al 2005;Krá l et al 2006;Oliveira et al 2007; this work).…”

“…The meta/submetacentric morphology of the chromosomes predominates in the species karyotyped (see Oliveira et al 2007). Mesabolivar luteus (Keyserling 1891), a representative of the ''miscellaneous group,'' is the single species of Mesabolivar characterized chromosomally and its diploid complement was described as 2n L 5 15 5 14 + X (Araujo et al 2005). Considering that M. brasiliensis and M. cyaneotaeniatus belong to the same Mesabolivar operational group, the aim of the present work was to determine and compare the mitotic and meiotic chromosomal characteristics of both species and to discuss the cytogenetic similarities with M. luteus, the karyotype of which was previously described by Araujo et al (2005).…”