Mitotic and meiotic chromosomes of a southern Brazilian population of Boophilus microplus (Acari, Ixodidae)

Abstract

Using conventional staining with acetic orcein and C-banding techniques it was investigated constitutive heterochromatin chromosomal polymorphisms and the mitotic and the meiotic behavior of male and female chromosomes of Boophilus microplus (Canestrini, 1887). Some differences were detected in the population of southern Brazil as compared to the data of other authors for populations in other latitudes. The differences being mainly concerned with the distribution of constitutive centromeric heterochromatin and variation in the length of heterochromatic blocks in the pericentromeric regions of some chromosome pairs.

The position of repetitive DNA sequence in the southern cattle tick genome permits chromosome identification

“…In addition, we observed apparent end-to-end pairing of homologous R. microplus chromosomes in meiosis I and sister chromatids in meiosis II (data not shown), which is consistent with other holocentric arthropods (Pérez et al 1997(Pérez et al , 2000Mandrioli 2002Mandrioli , 1999Bongiorni et al 2004). The studies of Hilburn et al (1989) and Garcia et al (2002) concluded that R. microplus constitutive heterochromatin bands were centromeric, where as our observations suggest that the heterochromatin actually occurs in the R. microplus telomeres. The localization of repetitive DNA in telomeric regions is a common feature of holocentric chromosomes (Schweizer and Loidl 1987).…”

“…These results are also consistent with chromosome numbers in Mexican (Newton et al 1972;Hilburn et al 1989) and Brazilian (Garcia et al 2002) R. microplus populations. Although R. microplus karyotypes have been developed using traditional C-banding techniques (Hilburn et al 1989;Garcia et al 2002), chromosome identification is complicated by the fact that the autosomes are similar in size, lack distinguishing morphological traits, and possess relatively uniform C-banding patterns. Our DAPI staining results suggest that significant amounts of heterochromatin are associated with the termini of chromosomes, but the distribution was too uniform to permit identification of individual chromosomes.…”

“…Previous studies have reported acrocentric chromosomes in R. microplus (Oliver and Bremner 1968;Hilburn et al 1989;Garcia et al 2002) with the presumed centromere occurring at the tip of the chromosome and the 'short' arm being indistinguishable (Hilburn et al 1989). Using FISH and high-resolution digital images, we identified several lines of evidence that suggest that R. microplus chromosomes are actually holocentric.…”

“…Rhipicephalus microplus chromosomes lacked a clearly defined centromere in all spreads examined. Garcia et al (2002) also failed to identify a clearly defined centromere in R. microplus chromosomes using conventional acetic orcein staining. In addition, we observed apparent end-to-end pairing of homologous R. microplus chromosomes in meiosis I and sister chromatids in meiosis II (data not shown), which is consistent with other holocentric arthropods (Pérez et al 1997(Pérez et al , 2000Mandrioli 2002Mandrioli , 1999Bongiorni et al 2004).…”

“…Early tick cytogenetics is reviewed by Oliver (1977) who reported that R. microplus has an XX:XO sex determination system with 22 diploid chromosomes in females and 21 in males. Preliminary C-banding karyotypes have also been developed for R. microplus (Hilburn et al 1989;Garcia et al 2002). Unfortunately, these are of limited utility for chromosome identification due to uniformity of autosome length and morphology.…”