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| Author(s): |
Amália Torrezan Lopes
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Rio Claro. 2016-05-03. |
| Institution: | Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro |
| Defense date: | 2016-04-04 |
| Advisor: | Marielle Cristina Schneider |
| Abstract | |
The beetles of the subfamily Cassidinae s.l. are commonly known as tortoise beetles, due to the peculiar shape of the elytra. This subfamily possesses more than 6000 taxonomically described species, of which less than 2% were cytogenetically studied. The cassidines showed diploid number ranged from 2n=16 to 2n=51, and sex chromosome systems of the Xyp, X0, Xy, Xyc, Xyr, neoXY, Xyyp, XpneoXneoYp types, in addition to other multiple systems. Despite the occurrence of this karyotype diversity, about 85% of the species presented the karyotype 2n=16+Xyp. However, this karyotype homogeneity may be related to the low number of species examined, the analyses with species included in the same genus and/or tribe, as well as the scarcity or lack of studies with techniques that identify specific chromosomal regions. The aim of this work is to discuss about the mechanism of chromosome evolution in species of Cassidinae. The chromosomal analysis were performed in 19 species of Cassidinae from Brazilian fauna, using standard staining, C-banding and fluorescent in situ hybridization (FISH) with probes of 28S rDNA, 5S rDNA, (TTAGG)n and (TCAGG)n telomeric clusters, and U2 small nuclear RNA (snRNA). The cytogenetic studies in 19 cassidine beetles revealed a high diversity of diploid number - Cassidini: 2n=38+Xyp in Agroiconota inedita, 2n=20+Xyp in Charidotella immaculata, Charidotella sexpunctata and Microctenochira stigmatica, 2n=16+Xyp in Deloyala cruciata, Microctenochira aciculata, Microctenochira optata and Microctenochira quadrata, 2n=18 in Microctenochira gnata; Goniocheniini: 2n=16+Xyp in Chlamydocassis cribripennis; Ischyrosonychini: 2n=16+Xyp in Cistudinella obducta; Mesomphaliini: 2n=34+Xyp in Botanochara tesselata, 2n=20+Xyp/Xyr in Chelymorpha cribraria, 2n=20+Xyp in Chelymorpha inflata, 2n=20 in Cteisella magica, 2n=38+Xyp in Cyrtonota cyanea, 2n=40+Xyp in Paraselenis flava, 2n=22 in Stolas areolata, and 2n=24+Xyp in Stolas redtembacheri. The karyotype 2n=16+Xyp ocurred in 26% of the analyzed species, belonging to the tribes Cassidini, Goniocheniini and Ischyrosonychini. The Xyp sex chromosome system (SCS) was the most frequent, occurring also in Mesomphaliini that exhibit the highest diversity of SCS within the Cassidinae. In relation to the pattern of constitutive heterochromatin, 12 species showed chromosomes with pericentromeric bands, which were present in some or all elements of the diploid set. Additionally, four species revealed heterochromatic blocks in the interstitial and terminal regions of some autosomal and/or sex chromosomes. In 10 of the 11 species investigated, the 28S ribosomal gene showed a similar pattern, occurring in only one autosomal pair. However, differences regarding the localization of the 28S rDNA sites were observed among the species, mainly in representatives of Cassidini, which showed the highest karyotype homogeneity. Among the 12 species studied for the presence of the (TTAGG)n and (TCAGG)n telomere clusters, only nine showed (TTAGG)n positive signals, but with variations regarding the number of chromosomes with the telomere sites. This result probably indicates that the TTAGG telomere sequence have repeatedly been lost during the chromosome evolution of this subfamily. The FISH with 5S rDNA probes did not revealed positive sites in all investigated species, with the exception of Cha. immaculata that exhibited a tenuous signal in interphase nuclei. The U2 snRNA gene was visualized in only one autosomal pair, but with variation in chromosomal location among the species. (AU) | |
| FAPESP's process: | 12/12619-2 - Mechanisms of chromosomal differentiation in beetles of the subfamily Cassidinae s.l. (Polyphaga, Chrysomelidae) |
| Grantee: | Amália Torrezan Lopes |
| Support Opportunities: | Scholarships in Brazil - Doctorate |