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

Abstract

Pholcidae is the most diverse family among haplogyne spiders but only 15 species have been analyzed cytogenetically. These studies revealed that the diploid number varies from 2n 5 15 to 2n 5 32, that there are three types of sex chromosome systems in males (X, X1X2 and X1X2Y), and that the chromosomes are predominantly biarmed. Within the genus Mesabolivar, only Mesabolivar luteus (Keyserling 1891) has been karyotyped, and it showed 2n 5 15 5 14 + X, with all chromosomes being metacentric. In the present work, we characterize the mitotic and meiotic chromosomes of Mesabolivar brasiliensis (Moenkhaus 1898) and Mesabolivar cyaneotaeniatus (Keyserling 1891). Male mitotic metaphases of the two species showed the diploid number 2n 5 17 5 16 + X; oogonial cells of M. brasiliensis showed 2n 5 18 5 16 + XX. In both species, the chromosomes were exclusively biarmed, and the X chromosome was the largest element of the karyotype. Diplotene spermatocytes of the two species exhibited 8II + X and the occurrence of only one terminal or interstitial chiasma per bivalent. In M. cyaneotaeniaus, metaphases II with n 5 9 5 8 + X and n 5 8 were found, indicating the regular segregation of all chromosomes during meiosis I. Mitotic metaphases of M. brasiliensis stained with CMA3/DA/ DAPI revealed GC-rich chromatin in the terminal region of almost all autosomes, especially in pair 2. An earlier revision of the New World pholcids grouped M. brasiliensis and M. cyaneotaeniatus in a ''southern group'' and placed M. luteus in a ''miscellaneous group.'' A molecular study showed a closer relationship between M. brasiliensis and M. cyaneotaeniatus than between M. luteus and either of these two species. The 2n 5 17 found in M. brasiliensis and M. cyaneotaeniatus corroborates this hypothesis, given that M. luteus has a diploid number of 2n 5 15. According to Platnick (2008), the family Pholcidae Koch 1851 includes 999 extant species, and thus constitutes the most diverse family among haplogyne spiders. A phylogenetic analysis based on morphological characters separated pholcids into four clades: ''ninetines,'' ''pholcines,'' ''holocnemines,'' and the ''New World clade'' (Huber 2000). The genus Mesabolivar Gonzalez-Sponga 1998, which ranges from northern South America to northern Argentina, is included in the ''New World clade'' and possesses 45 species (Huber 2000, 2008). Moreover, the genus is divided into four operational groups based on morphological characters: a ''northern group with spines on male metatarsi,'' a ''northern group without spines on male metatarsi,'' a ''southern group,'' and a ''miscellaneous group.'' The species Mesabolivar brasiliensis (Moenkhaus 1898) and Mesabolivar cyaneotaenia- tus (Keyserling 1891), both part of the ''southern group,'' are distributed in southern and eastern Brazil and northern