Karyotype, sex chromatin and sex chromosome differentiation in the carob moth,Ectomyelois ceratoniae(Lepidoptera: Pyralidae)

Abstract

-This paper reports results of the first cytogenetic investigation carried out in the carob moth, Ectomyelois ceratoniae Zeller, the serious polyphagous pest of both stored products and field crops in the Mediterranean basin and Near East regions. Preparations of mitotically dividing spermatogonia and oogonia revealed that the carob moth karyotype consists of 2n = 62 chromosomes. As typical for Lepidoptera, the chromosomes were of a holokinetic type, only slightly differed in their sizes, and displayed no morphological structures including primary constrictions (the centromeres) that could enable us their identification. Metaphase I spermatocytes showed 31 bivalents. Accordingly, 31 chromosome elements were observed in metaphase II spermatocytes. Hence the haploid chromosome number is n = 31. In pachytene complements, two NOR bivalents were observed. In highly polyploid nuclei of the Malpighian tubule cells and silk glands, females showed a heterochromatin body, the so-called sex chromatin or W chromatin, that was absent in male nuclei. This indicated that the carob moth possesses a WZ/ZZ sex chromosome system. However, we failed to identify the sex chromosome bivalent WZ in pachytene oocytes. In order to differentiate the sex chromosomes, we employed genomic in situ hybridization (GISH) and comparative genomic hybridization (CGH). GISH detected the W chromosome by strong binding of the Cy3-labelled, female-derived DNA probe. With CGH, both the Cy3-labelled female-derived probe and Fluor-X labelled male-derived probe evenly bound to the W. This suggested that the W is composed predominantly of repetitive DNA sequences occurring scattered in other chromosomes but accumulated in the W chromosome.

Probing the W chromosome of the codling moth, Cydia pomonella, with sequences from microdissected sex chromatin

“…In this respect, it resembles the W chromosomes in birds, which also show heterosynapsis with the Z chromosomes (Pigozzi 1999). Unlike generally small Y chromosomes in many animals, such as beetles, flies, and mammals (Virkki et al 1991;Graves 2005;Steinemann and Steinemann 2005), and small W chromosomes in carinate birds (Pigozzi 1999), the lepidopteran W is more or less comparable in size with the Z chromosome, and the WZ pair often belongs to the largest chromosomes in the genome (Traut and Marec 1997;Traut et al 1999;Mediouni et al 2004;Fuková et al 2005;Yoshido et al 2005). The females of Lepidoptera lack crossing-over, and their meiosis is achiasmatic (Marec 1996 and references therein).…”

Resolution of sex chromosome constitution by genomic in situ hybridization and fluorescence in situ hybridization with (TTAGG) n telomeric probe in some species of Lepidoptera

“…In some species, sex chromosome differentiation can be studied by using a pachytene mapping technique (Traut and Marec 1997). In preparations of pachytene oocytes, this simple method makes possible identification of sex chromosome bivalent (or trivalent) according to the W chromosome heterochromatin but fails if the W heterochromatin is not seen as, for example, in the carob moth, Ectomyelois ceratoniae (Mediouni et al 2004). In addition, lepidopteran sex chromosomes pair during female meiosis and, although largely non-homologous, form a synaptonemal complex (SC), which is often not discernible from autosome SCs due to a complete synaptic adjustment of chromosomes involved in the SC (Marec and Traut 1994).…”

Neo-sex chromosomes and adaptive potential in tortricid pests

“…Meiotic chromosomes were prepared from gonads of male and female larvae by the spreading technique as described in ref. 60. For FISH, BAC-DNA was labeled using a Nick Translation Kit (Abbott Molecular).…”