Chromosomes and their Meiotic Behavior in Two Families of the Primitive Infraorder Dipsocoromorpha (Heteroptera)

Abstract

Five species belonging to the two families of Dipsocoromorpha were studied: three species from the family Dipsocoridae ~ Cryptostemma pusillimum J . Sb. (2n = 16 + 2m + XY, Yz), C. hickmani Hill (2n = 18 + 2m + XU), and C. ca.ytuneouitreus Linnavuori (2n = 18 + m? + XU) and two species from the family Schizopteridae Pateenu elimata Hill (2n = 30 + 2m + X O ) and Rectilamintl australis Hill (2x1 = 30 + 2m + X0). In all species, autosomes formed chiasmate bivalents in spermatogenesis, and the sex chromosome univalent(s) divided at the first meiotic division and segregated at the second. The evolution of autosomal number, m-chromosomes, and sex chromosome systems within the Dipsocoromorpha and in the whole Heteroptera was discussed. Seppo FinlandThe Dipsocoromorpha is one of the most primitive infraorders within Heteroptera ( STYS and KERZH-NER 1975), and its study is important for understanding the phylogeny of the entire order. Karyological and anatomical (especially, the male reproductive system) characters of the Dipsocoromorpha are poorly studied. So far, only one species, Cryptostemma (as Pachycoleus) rujescens, has been briefly reported as 2n = 20 + X0 by COBBEN (1968). No detailed information on chromosome behavior, nor any information on follicle numbers in this infraorder is available, though the latter has been used for long time as an additional character in taxonomic and phylogenetic studies ( PENDER-GRAST 1957;GROZEVA and KUZNETSOVA 1992).There are several chromosomal characteristics in the Heteroptera like holokinetic chromosomes, diversity of sex chromosome systems (X0, XY, multiple sex chromosomes), alternative sequences of the meiotic reduction for autosomes and sex chromosomes, existence of a pair of m-chromosomes, and occurrence of chiasmatic and achiasmatic meioses. It is very important from the phylogenetical point of view to know to what extent these characteristics exist within the infraorder Dipsocoromorpha.In the present study information on the karyotypes and meiotic behavior of the chromosomes of five species, belonging to two families of Dipsocoromorpha, Dipsocoridae and Schizopteridae, is reported for the first time. Also information on the follicle number of some species is given. Material and methodsThe material for this study has been collected from Finland (Cryptostemma ( s . str.) pusillimum J. Sb.), Tasmania (C. (s. str.) hickmani Hill, Pateena elimata Hill, Rectilumina australis Hill), and Bulgaria (C. (Harpago) castaneouitreus Linnavuori).Specimens were fixed in an ethano1:glacial acetic acid mixture (3:l). The gonads of Bulgarian and Tasmanian material were stained in acetoorcein and squashed in a drop of 45 YO acetic acid.The gonads of the Finnish species were dissected out in 1% sodiumcitrate solution, fixed briefly, about 30 s, in a methano1:glacial acetic acid mixture (3:1), and squashed in a drop of 45% acetic acid. After removing cover slips, slides were dehydrated by immersing in glacial acetic acid for 25 s (or alternatively in fresh 3:l -fixative for 15 min) and air...

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