CARYOLOGIA Vol. 57, no. 1: 67-71, 2004 The variability of the chromosome numbers in Psocomorpha (Insecta, Psocoptera) NATALIA V. G OLUB Natalia V. Golub, Dep. of Karyosystematics, Zoological Institute Russian Academy of Sciences, Universitetskaja emb. 1, 199034, St. Petersburg, Russia. Abstract - Karyotypes of 10 species of Psocoptera of 8 genera and 5 families of the advanced suborder Psocomorpha are reported for the first time. In Stenopsocus aphidiformis End. 2n=23, 24 (22A + X0/XX); in Lachesilla pedic- ularia L., L. tanaidana Roesler, Ectopsocus briggsi McLachl., Elipsocus pumilis (Hagen), Amphigerontia bifasciata (Latr.), Sigmatoneura kolbei End., and Trichadenotecnum sexpunctatum L. 2n=17,18 (16A + X0/XX); in Amphigeron- tia jezoensis Okam. 2n=15, 16 (14A + X0/XX), and in Loensia variegata (Latr.) 2n=13, 14 (12A + X0/XX). The karyotype variability in suborder is estimated. The pathways of the karyotype evolution in Psocomorpha are dis- cussed. Key words: Insecta, Psocoptera, chromosome number, karyotype variability. INTRODUCTION MATERIALS AND METHODS Psocoptera have not been sufficiently inves- Adult males of Stenopsocus aphidiformis End., tigated in respect to their karyotypes. By now, Lachesilla tanaidana Roesler, Amphigerontia jezoen- 66 species (about 2% of world psocopteran sis Okam., and Sigmatoneura kolbei End. were col- lected in the Ussuriyskiy Kray and Vladivostok fauna) of 38 genera, 20 families and all three vicinity (Far East of Russia); adult males of suborders have been karyotyped (ZEFA et al. Trichadenotecnum sexpunctatum L. in Voronezh Re- 1996; GOLUB and NOKKALA 2001; NOKKALA gion (Russia); Ectopsocus briggsi McLachl. in North- and GOLUB 2002, for other references see GOL- western Caucasus and Northern Italy; Lachesilla UB 1999). The overwhelming majority of kary- pedicularia L. in Byelorussia; Elipsocus pumilis (Ha- otyped species (57), genera (32) and families gen), Amphigerontia bifasciata (Latr.), and Loensia (15) fall in the largest and most advanced pso- variegata (Latr.) in the vicinity of Turku (Finland). For karyological studies, the specimens were copteran suborder Psocomorpha. The primi- used either fresh or fixed in mixture of 96% ethanol tive suborder Trogiomorpha as well as the sub- and glacial acetic acid (3:1). Testes were dissected order Troctomorpha, which encloses mainly out of the abdomens and squashed on slides in a specialized species, are still extremely poorly drop of 45% acetic acid. The preparations were examined. made permanent by a dry ice technique (CONGER The present study reports the karyotypes of and FAIRCHILD 1953). After cover slips were re- moved, slides were dehydrated in fresh 3:1, air- 10 additional species form 8 genera and 5 fam- dried and stained by Feulgen-Giemsa procedure ilies of Psocomorpha. (GROZEVA and NOKKALA 1996). Slides were treated in 1N HCl at room temperature for 20 min, hy- drolysed in 1N HCl at 60°C for 7 min, stained with Schiff’s reagent for 30 min, rinsed in distilled water * Corresponding author: fax +7 (812) 328 29 41; e-mail: and then, rinsed in Sorensen’s phosphate buffer, pH [email protected] 6.8. Finally, slides were stained with 5% Giemsa so- 68 GOLUB lution for 30 min. After staining, slides were rinsed vealed (Fig. 1e). Bivalents gradually decrease in briefly with distilled water, air dried, and mounted size; X-chromosome is close in size to a half of in Entellan. one of the smallest bivalents. In the majority of cells X-chromosome is situated at the periph- ery of the metaphase plate. In AI, the homol- RESULTS ogous chromosomes go to the opposite poles and the X divides reductionally as well (Fig. 1f). Family Stenopsocidae The formula of male diploid karyotype has Stenopsocus aphidiformis End. – A dozen of been determined as 2n = 17 (16A + X). males have been examined. In MI, 11 bivalents of autosomes and univalent X-chromosome Family Psocidae have been revealed (Fig. 1a). Bivalents gradu- Amphigerontia bifasciata (Latr.) – Three ally decrease in size; X-chromosome is close in males have been examined. In diakinesis, 8 bi- size to a half of one of the smallest bivalents. In valents of autosomes and X-chromosome have the majority of cells, X-chromosome is situated been revealed (Fig. 1g). X-chromosome is pos- aside the bivalents, at the periphery of the itively heteropicnotic. Every bivalent has a sin- metaphase plate. gle chiasma, the latter being clearly terminal in The formula of male diploid karyotype has six bivalents while subterminal in two others. been determined as 2n = 23 (22A + X). The formula of male diploid karyotype has been determined as 2n = 17 (16A + X). Family Lachesillidae Amphigerontia jezoensis Okam. – Three Lachesilla pedicularia L., and Lachesilla males have been examined. In MI, 7 bivalents tanaidana Roesler – Six males of L. pedicularia of autosomes and X-chromosome have been re- and 8 males of L. tanaidana have been exam- vealed (Fig. 1h). One of the bivalents is signifi- ined. In MI of both species, 8 bivalents of au- cantly larger then the others which gradually de- tosomes and X-chromosome have been re- crease in size; X-chromosome is close in size to vealed (Fig. 1b, 1c). Bivalents gradually de- a half of one of the middle-sized bivalents. In crease in size; X-chromosome is close in size to the majority of cells, X-chromosome is situated a half of one of the smallest bivalents in L. at the periphery of the metaphase plate. pedicularia, however to a half of one of the mid- The formula of male diploid karyotype has dle-sized bivalents in L. tanaidana. In the ma- been determined as 2n = 15 (14A + X). jority of cells, X-chromosome is situated at the Sigmatoneura kolbei End. – Two males have periphery of the metaphase plate. been examined. In MI, 8 bivalents of auto- For every species, the formula of male somes and X-chromosome have been revealed diploid karyotype has been determined as 2n = (Fig. 1i). Bivalents gradually decrease in size; 17 (16A + X). X-chromosome is close in size to a half of one of the middle-sized bivalents. In the majority of Family Ectopsocidae cells X-chromosome is situated at the periph- Ectopsocus briggsi McLachl. – Five males ery of the metaphase plate. have been examined. In MI, 8 bivalents of au- The formula of male diploid karyotype has tosomes and X-chromosome have been re- been determined as 2n = 17 (16A + X). vealed (Fig. 1d). Bivalents gradually decrease Trichadenotecnum sexpunctatum L. – Two in size; X-chromosome is close in size to a half males have been examined. In MI, 8 bivalents of one of the middle-sized bivalents. In the ma- of autosomes and X-chromosome have been jority of cells X-chromosome is situated at the revealed (Fig. 1j). Bivalents gradually decrease periphery of the metaphase plate. in size; X-chromosome is close in size to a half The formula of male diploid karyotype has of one of the middle-sized bivalents. In the ma- been determined as 2n = 17 (16A + X). jority of cells, X-chromosome is situated at the periphery of the metaphase plate. Family Elipsocidae The formula of male diploid karyotype has Elipsocus pumilis (Hagen) – Four males been determined as 2n = 17 (16A + X). have been examined. In MI, 8 bivalents of au- Loensia variegata (Latr.) – Six males have tosomes and X-chromosome have been re- been examined. In early metaphase I, six biva- CHROMOSOME NUMBERS IN PSOCOMORPHA 69 Fig. 1 – Male meiotic karyotypes in Psocomorpha. (a) Metaphase I in Stenopsocus aphidiformis, (b) Metaphase I in Lachesil- la pedicularia, (c) Metaphase I in L. tanaidana, (d) Metaphase I in Ectopsocus briggsi, (e) Metaphase I, and (f) Anaphase I in Elipsocus pumilis, (g) Diakinesis in Amphigerontia bifasciata, (h) Metaphase I in Sigmatoneura kolbei, (i) Metaphase I in Trichadenotecnum sexpunctatum; (j) Metaphase I in Amphigerontia jezoensis, (k) Diakinesis in Loensia variegata. X-chromo- some is arrowed. Scale bar corresponds to 5 µm. 70 GOLUB lents of autosomes and X-chromosome have parthenogenetic females of T. majus 2n = 18 been revealed (Fig. 1k). One of the bivalents is (16 + XX), that is in fact the same pattern. The nearly twice as large as any other. X-chromo- data obtained for the genera Sigmatoneura and some is close in size to a half of one of the Amphigerontia represent the first ones for these smallest bivalents. Every bivalent has a single genera. S. kolbei and A. bifasciata display 2n = chiasma, the latter being clearly terminal in 17 (16 + X) like the majority of the above men- four bivalents while subterminal in two biva- tioned species whereas A. jezoensis has 2n = 15 lents. (14 + X). In the genus Loensia, L. picicornis and The formula of male diploid karyotype has L. moesta, both with 2n=16 (17 + X) have been been determined as 2n = 13 (12A + X). karyotyped previously (MEINANDER et al. 1974; GOLUB et al. 1996). L. variegata from our ma- terial shows the different karyotype 2n = 13 (12 DISCUSSION + X), which represents the lowest chromosome number found so far in Psocoptera as a whole. A total of 10 species have been studied. The At present, in Psocomorpha, data on the species belong to the genera Stenopsocus (1 karyotypes are available for 67 species, 34 gen- species) of Stenopsocidae, Lachesilla (2) of era and 15 families. As many as 6 values of Lachesillidae, Ectopsocus (1) of Ectopsocidae, chromosome number and two various sex de- Elipsocus (1) of Elipsocidae, and Amphigeron- termining systems have been revealed. The tia (2), Sigmatoneura (1), Trichadenotecnum (1), karyotype 2n = 17, 18 (16 + XX/X0) found in and Loensia (1) of Psocidae. The species stud- 59 species, 31 genera and 14 families (except ied showed as many as four values of chromo- Amphipsocidae) is regarded as the modal and some number: 2n = 17 (16 + X), 2n = 23 (22 + initial karyotype in this suborder (WONG and X), 2n = 15 (14 + X), 2n = 13 (12 + X); the first THORNTON 1966; MESA et al.