CARYOLOGIA Vol. 57, no. 1: 67-71, 2004

The variability of the chromosome numbers in Psocomorpha (Insecta, )

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., pumilis (Hagen), 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 ; 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 (). 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 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 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. 1991; GOLUB number was found in 7 species whereas three 1999). Two parthenogenetic species, Valenzuela other numbers were found in one species each. flavidus (Caeciliusidae) and Peripsocus subfas- The chromosome number 2n = 13 is reported ciatus (Peripsocidae) fall in fact in this group. for the first time in Psocoptera as a whole. Their karyotype is triploid, expressed by 2n = Stenopsocus aphidiformis shows 2n = 23 (22 3x = 27 (24 + XXX). It includes the modal + X) and shares its karyotype with S. lachlani number 2n = 18 (16 + XX) and one more (MEINANDER et al. 1974). However, the third added haploid set n = 9 (8 + X) (NOKKALA and studied species of this genus, S. immaculatus, GOLUB 2002). has a different karyotype 2n = 17 (16 + X) Seven species have karyotype deviating from (GOLUB et al. 1996). This karyotype was found the modal one. Amphipsocus japonicus (Am- in Lachesilla pedicularia and L. tanaidana, phipsocidae) displays 2n = 16 (14 + neo- which share this pattern with the only previ- XX/XY) and represents the only finding of neo- ously studied representative of this large genus XY system known in Psocoptera (GOLUB and L. quercus (GOLUB et al. 1996). Ectopsocus brig- NOKKALA 2001). S. lachlani and S. aphidiformis gsi from our study also shows 2n = 17 (16 + X) (Stenopsocidae) display 2n = 23 (22+X), which as well as the only previously studied represen- number represents the highest one revealed so tative of this genus E. maindroni (WONG and far in Psocomorpha (MEINANDER et al. 1974; THORNTON 1966). Elipsocus pumilis from our present study). Noteworthy, that the highest material with 2n = 17 (16 + X) shares its kary- number in Psocoptera 2n = 29 was found in otype with E. abdominalis and E. westwoodi so Psocatropos sp. from Trogiomorpha (WONG and far studied in this genus (MEINANDER et al. THORNTON 1966). As we have mentioned above, 1974). Trichadenotecnum sexpunctautum has 2n Loensia variegata (Psocidae) displays 2n = 13, = 17 (16 + X). In the large genus Trichade- that is the lowest chromosome number not only notecnum three further bisexual and one facul- for Psocomorpha, but for Psocoptera as a whole. tatively parthenogentic species T. majus have Finally, Pseudocaelius maculosus* (Pseudocae- been previously karyotyped (WONG and ciliidae), Amphigerontia jezoensis and Mety- THORNTON 1966; ZEFA et al. 1996; NOKKALA and GOLUB 2002). Bisexual species were found * In original paper the species was wrongly named as Dasyp- to have 2n = 17 (16 + X) in males and the socus japonicus End. CHROMOSOME NUMBERS IN PSOCOMORPHA 71 lophorus nebulosus (Psocidae) display 2n = 15 REFERENCES (MEINANDER et al. 1974; GOLUB 1999; GOLUB and NOKKALA 2001; present study). CONGER A.D. and FAIRCHILD L.M., 1953 – A All diverged karyotypes could have arisen quick-freeze method for making smear slides per- from the modal 2n = 17 by different ways. Fis- manent. Stain. Techn., 28: 289-293. sion of the autosomes has resulted in the in- GOLUB N.V., 1999 – Review of karyological data on creasing autosome number in S. lachlani and in psocids (Psocoptera) and description of kary- S. aphidiformis. Autosome fusions have proba- otypes of 13 species. Entomol. Rew., 79: 412-424. bly resulted in the karyotype of M. nebulosus, P. GOLUB N.V., GROZEVA S.M. and KUZNETSOVA V.G., 1996 – Karyotypes of Psocoptera: A review maculosus, A. jezoensis and L. variegata. As a re- and new data. In: V.E. Gokhman, V.G. sult of fusions, these species acquired a large Kuznetsova (Eds) “Karyosystematics of the in- chromosome pair, which is absent in their rel- vertebrate ”, Vol. sci. papers n. p. 20- atives with 2n = 17. A fusion between an auto- 22. M.: Publ. Bot. Garden, Moscow St. Uni- some and X-chromosome led to decreasing au- versity. tosome number and appearing neo-XY mecha- GOLUB N. and NOKKALA S., 2001 – The karyotypes nism in A. japonicus. Fusions seem to have pre- of two bark-lice species (Psocoptera, Psocomor- vailed in karyotype evolution of Psocomorpha pha, Amphipsocidae): the first description of neo- resulting in four various chromosome numbers XY sex chromosome system in Psocoptera. Folia in different families. Polyploidy has resulted in biologica, 49: 153-156. three-fold increase of chromosome number in GROZEVA S. and NOKKALA S., 1996 – Chromo- parthenogenetic V. flavidus and P. subfasciatus. somes and their meiotic behavior in two families Over many years it has been assumed, that of the primitive infraorder Dipsocoromorpha Psocoptera have highly conservative chromo- (Heteroptera). Hereditas, 125: 31-36. MEINANDER M., HALKKA O. and SÖDERLUND V. some systems (WONG and THORNTON 1966; 1974 – Chromosomal evolution in the Pso- MESA et al. 1991; GOLUB 1999). However, re- coptera. Not. Entom., 54: 81-84. cent data allow the suggestion that Psocoptera MESA A., FONTANETTI C.S. and ZEFA E., 1991 – are actually characterized by fairly variable First contribution to the cytogenetics of Brazil- chromosome systems. New examples of devi- ian Psocoptera. Rev. Brazil. Genet., 14: 913-919. ating chromosome numbers will expected to be NOKKALA S. and GOLUB N., 2002 – Cytogenetical found during future studies on this group. study of three parthenogenetic psocid species (Pso- coptera, Psocomorpha). Hereditas, 137: 198-201. Acknowledgements – The author is very grate- ZEFA E., FONTANETTI C.S. and MESA A., 1996 – ful to Dr. V. G. Kuznetsova for the valuable com- Cytogenetics of six Brazilian species of Pso- ments during the preparing of the manuscript. The coptera. Brazilian J. Genetics, 19: 597-598. author also thankful to Dr. Yoshizawa for the help WONG S.K. and THORNTON I.W.B., 1966 – Chro- with re-determination of the species from the fam- mosome numbers of some Psocid genera (Pso- ilies Amphipsocidae and Pseudocaeciliidae. coptera). Nature, 211: 214-215. The study was supported by the Russian Foun- dation for Basic Research Grant 02-04-48649. Received July 3, 2003; accepted August 28, 2003