Labidura Riparia (Dermaptera, Labiduridae) from Brazil: Karyotype and C-Banding Rita M

C 2000 The Japan Mendel Society Cytologia 65: 93-96, 2000 Labidura riparia (Dermaptera, Labiduridae) from Brazil: Karyotype and C-banding Rita M. P. Avancini 1, Shirlei M. Recco-Pimentel2 and AngeloP. Prado1 1Departamento deParasitologia and2Departamento deBiologia Celular , InstitutodeBiologia, UniversidadeEstadual deCampinas (UNICAMP), CaixaPostal 6109, 13083-970 Campinas, SP,Brasil AcceptedDecember 6,1999 SummaryThe karyotype of Labidurariparia from Brazil is 2n=5A+XYfor malesand 2n=5A+XXfor females. The chromosomes canbe grouped into 3 largeand 3 smallpairs, the latter includingthe sex chromosomes. TheY chromosomeis entirely C-band positive and remains het- eropycnoticduring most of the division cycle. The X chromosome, which is longer than the Y chromosome,presents no C-banding. Thelongest chromosome ofthe complement hasvery noticeable C- bandsat oneof its terminal. Only one nucleolus was seen in the preparations examined. These re- sultson the general chromosomal morphology arevery similar to the karyotype described for L. ripariain the USA. The most significant similarity isthat chromosome number 1is about 20% longer thanchromosome 2,a feature not observed inthe karyotypes ofL. riparia from other regions of the world.In addition, the difference insize between the chromosomes Xand Y of Brazilian and US L. ripariais not as large as that for other populations. Keywords Earwigs,Karyotype, Heterochromatin, Holocentric chromosomes. Thesystematics ofmembers of thegenus Labidura Leach 1815 has been the objectof discus- sionespecially because of theuncertain status of Labidura riparia Pallas 1773 (Brindle 1966). The Labiduracomplex has often been considered to be a singlespecies with extreme morphological variability,which has rendered it withup to 41 synonyms.In studyingthis complex some authors havefocused mainly on karyotypeanalysis since it providesa morereliable indicator of biological differencesthan the variable external phenotype (Giles and Webb 1972). Formsof L. ripariawith different karyotypes from various parts of the speciesrange have beendescribed and were summarized by Kuznetsova(1979) and later by Hoshibaet al. (1988).The trueL. ripariaPall. has 2n=12 (5A+XY) (Kuznetsova 1979) and is foundin the former USSR (W. Siberia),USA, Bahamas, Spain and India. L. truncata, once considered a variant of L. riparia,was re-erectedby Gilesand Webb (1972), has 2n=10 (4A+XY) and is foundin Australia.There is also a specieswith 2n= 14, described as L. riparia (Asana and Makino 1934, Giles and Webb 1972, Mit- tal et al. 1974)but reviewed as L. bengalensisor simplyas Labidurasp. by Kuznetsova(1979), de- pendingon theorigin of the specimens (India, Japan or NewGuinea). Thefirst record of L. ripariain Brazilis froma surveyin Riode Janeiro(Moreira 1930). The introductionof this species to continentalUSA is consideredvery recent (Schlinger et al. 1959)and thesame situation may be true of Brazil,although the route and date of introductionare unknown. Thekaryotype of Brazilian L. riparia has not been investigated even though the speciesoccurs in considerablenumbers in certainhabitats such as in caged-chickenmanure (Guimaraes et al. 1992,A. P. Prado, pers. com.). In the present study we investigated the karyotype of a populationof L.riparia from Brazil and compared the findings with other reports on L. riparia. 94 Rita M. P. Avancini, Shirlei M. Recco-Pimentel and Angelo P. Prado Cytologia 65 Materials and methods Specimens of L. riparia were removed manually from chicken manure collected on a poultry facility in Monte Mor county, state of Sao Paulo, southeastern Brazil. Testes and ovaries were dissected from adult males and females (n=55), respectively, and pre- pared according to Imai et al. (1988). Some slides were stained with conventional Giemsa to ob- serve the basic chromosome morphology. C-banding was performed as described by Summer (1972) with a few modifications. Some slides were treated with 0.1% solution of RNAse at 37°C for 1 h, followed by 0.025% toluidine blue in Mcllvaine buffer, pH 4.0, for 15 min. Results and discussion The males and females examined had 2n= 12 (5A+XY, 5A+XX, respectively) (Figs. 1, 2). Five autosomal bivalents and a heteromorphic pair (XY) were apparent in the early anaphase I (Fig. 3). No primary or secondary constriction was observed in any of the chromosomes and C-banding did not identify any potential "pericentromeric" heterochromatic regions (Fig. 1). The behavior of the chromosomes during meiosis was typical for chromosomes with no identifiable centromere (Fig. 4). Therefore, this lack of centromere agrees with the observations by White (1971) that holocentric chromosomes are characteristic of dermapterans. The chromosomal set can be grouped into large and small chromosomes (Fig. 4, upper set). Three pairs are obviously bigger than the others, including in the later group, the sex pair. The sex chromosomes are the fifth in size, and, therefore, not the smallest of the complement. The karyotype observed here is very similar to that described by Morgan (1926) for specimens collected mostly in St. Petersburg (Florida) but also in Dundee (Florida), New Orleans (Lousiana), and the Bahama Islands. This similarity includes a chromosome number of 2n=12 and, most re- markably, a noticeably longer chromosome 1 (Figs. 1, 2). The species denominated L. bidens Oliv. by Morgan (1928) was considered as a synonym of L. riparia by Brindle (1966). Although the karyotypes for L. riparia described by Kuznetsova (1979) and Mittal et al. (1974) also showed 2n= 12, chromosome number 1 was not about 20% longer than chromosome 2, in contrast to that observed here. The difference in size between the X and Y chromosomes (Fig. 1) of L. riparia is not as marked as in the form of L. riparia described by Kutznetsova (1979) and Mittal et al. (1974). These results indicate that the general karyotypic morphology of Brazilian L. riparia is more similar to North American populations. The amount of constitutive heterochromatin in the autosome set as detected by the C-banding was not large. Indeed, heterochromatin was only very noticeable in one of the terminal regions of pair 1, although in some cases much smaller bands were seen in other autosomes (Fig. 5). Terminal C bands at one or both ends were also reported by Hoshiba et al. (1984a, b) for the autosomes of two species of Demaptera, Anisolabis maritima and L. riparia japonica, respectively. The Y chromosome is entirely heterochromatic (Figs. 1, 5 , 7). This feature has already been described for A. maritima (Anisolabididae) (Hoshiba et al. 1984a) whereas these same authors (1984b) found that in L. riparia japonica, the Y chromosome was not stained by C-banding tech- nique. The results of the present study agree more with those for A. maritima than for L. riparia japonica, despite the fact that the latter belongs to the same genus as the species investigated here. Hoshiba et al. (1984b) found that in L. riparia japonica the X chromosome showed strong C- banding at one of its terminals. Similar staining was also observed for one of the two X chromosomes of A. maritima (Hoshiba et al. 1984a). During early first meiotic prophase, the X and Y chromosomes are tightly associated, forming 2000•@ Labidura riparia from Brazil: Karyotype and C-banding 95 Figs. 1-8. Chromosomes of Labidura riparia. 1, 2) Mitotic metaphases 2n= 12. 1. male, C-banding; Y chromosome is C-band positive (•~2050). 2. Female, Giemsa (•~2600). Note chromosome 1 longer than others. Meiosis in male, Giemsa. 3) Anaphase; arrow head: sex bivalent (XY) (•~1500). 4) Metaphases I; two groups of chromosomes can be observed: one with three small and other with three large chromosomes (upper set) (1500•~). 5-7) C-banding (•~2000). 5. Diplotene; arrow head: Y chromosome is C- band positive; arrow: terminal C-bands in chromosome 1; smaller C-bands in other autosomes. 6. Diplotene; arrow head: sex chromosomal pair strongly condensed. 7. Pachytene; arrow head: sex bivalent is heteropycnotic. 8, 9) Leptotene: Arrow: nucleolus; arrow head: sex chromosome body. 8. Giemsa (•~2000). 9. RNAse treatment followed by toluidine blue staining; the nucleolus is not seen (•~1500). a roundish dense chromatin body that is positively heteropycnotic until diakinesis (Figs. 5-7). Throughout the first meiotic prophase there are significant differences in the condensation cycle between the sex and autosomal chromosomes (Figs. 6-9). Similar behavior has been observed in other order of insects (Gonzalez-Garcia et al. 1996). This condition may have been misinterpreted by Morgan (1928) who may have considered this association of sex chromosomes as a second nucleolus. In all of slides examined we never observed the presence of two nucleoli mentioned by Morgan 96 Rita M. P. Avancini, Shirlei M. Recco-Pimentel and Angelo P. Prado Cytologia 65 (1928). After treatment of some slides with RNAse followed with toluidine blue, the nucleolus is no longer seen. However, the sex chromosome body is still visible after such treatment, confirming the different nature of these two structures (Fig. 9). Acknowledgements We thank Mr. Odair Francisco, M. Sc., for providing some of the specimens, and Ms. Klelia A. de Carvalho for her help with banding of female meiosis. References Asana,J. J.and Makino, S. 1934.The idiochromosomes of an earwig, Labidura riparia. J.Morphol. 56: 361-369. Brindle,A. 1966.A revisionof the subfamilyLabidurinae (Dermaptera, Labiduridae). Ann. Mag. nat. Hist.ser. 13 9: 239-269. Giles,E. T. andWebb, G. C. 1972.The systematics and karyotype of Labidura truncata Kirby, 1903 (Demaptera: Labiduri- dae). J.Aust. Ent. Soc. 11: 253-256. Gonzalez-Garcia,J. M., Antonio, C., Suja,J. A. andRufas, J. S. 1966.Meiosis in holocentricchromosomes: kinetic activity is randomlyrestricted to thechromatid ends of sexunivalents in Graphosomaitalicum (Heteroptera). Chrom. Res. 4:124-132. Guimaraes,J. H.,Tucci, E. C. andGomes, J. P.C. 1992.Demaptera (Insecta) associados a aviarios industriais no estadode SaoPaulo e suaimportancia como agentes de controle biologico de pragasavicolas. Revta bras. Ent. 35: 527-534. Hoshiba,H., Sakai, S.

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