Hereditas 105: 287-289 (1986)

Brief report

Achiasmatic male meiosis in Anthucoris nemurum (L.) (Anthocoridae, Hemiptera)

SEPPO NOKKALA and CHRISTINA NOKKALA

Laboratory of Genetics, Department of Biology, University of Turku, SF-20500 Turku, Finland

(Received January 9,1986)

Recent studies have revealed the existence of reveal sixteen chromosomal elements, fourteen au- achiasmatic meiosis in three heteropteran families, Saldidae, Nabidae, and Miridae (NOKKALA and NOK- KALA l983,1984a, 1986). Evidently, the occurrence of achiasmatic meiosis provides a useful cytological marker for the determination of phylogenic af- finities among and inside taxonomic groups. Of the families examined, Saldidae is included in the in- fraorder Leptopodomorpha, whereas Nabidae and Miridae are placed in the Cimicomorpha (see STYS and KERZHNER 1975). The finding of achiasmatic meiosis in two cimicomorphan families led us to ex- pect that more achiasmatic meioses would be found

tosomal bivalents and X and Y univalents. Thus, the chromosome complement can be expressed as a for- mula n = 14A + XY. This is in accordance with an earlier report of SOUTHWOOD and LESTON (1979) on the chromosome number in this species. Metaphase I plate is nonradial (Fig. 4), and bivalents orientate equatorially, homologous chromosomes facing op- posite poles (Fig. 5). The only identifiable element is the slightly negatively heteropycnotic Y chromo- some, which is the smallest chromosome in the com- plement. The X chromosome is of the size of the largest autosomes, and it can not be identified until

within the Cimicomorpha, providing thus a means to clarify the phylogenic relationships within this heterogeneous infraorder.

In the present study, achiasmatic male meiosis is described in Anthocoris nemorum, belonging to the cimicomorphan family Anthocoridae. tional meiosis.

metaphase 11. The metaphase plate at metaphase I1 is radial (Fig. 6), and X and Y chromosomes, which have been divided during the first meiotic division, undergo touch and go pairing in the center of the plate. Hence, sex chromosomes undergo postreduc-

Material and method Discussion

Adult males and nymphs of Anthocoris nemorum (L.) (Anthocoridae, Hemiptera) living on Filipen- dula ulmaria were collected in the vicinity of Turku in late July and early August 1985. Slides were made and stained according to the method described by N O K K A L A ~ ~ ~ NOKKALA (1983).

All families both in the Leptopodomorpha and in the Cimicomorpha possessing achiasmatic male meiosis also share other common cytological char- acteristics. Chromosome numbers are moderately high (see UESHIMA 1979), and as a rule, metaphase I plate is of the nonradial type while metaphase 11 plate is of the radial type. In addition, without ex-

Results

The prophase of male meiosis is characterized by a prominent diffuse stage, during which stage only the heteropycnotic X and Y chromosomes can be iden- tified (Fig. 1). The diffuse stage is the earliest meio- tic stage to be found in adult males. When condens- ing out from diffuse stage (Fig. 2 and 3), the bivalent can be seen to consist of two chromosomes aligned in parallel, no traces of chiasmata can be found, i.e., meiosis is achiasmatic. Nuclei at condensation stage

ception, sex chromosomes undergo postreductional meiosis. In cases where the anaphasic behaviour of chromosomes has been established, e.g., in Nabidae (NOKKALA and NOKKALA 1984a) and Miridae (NOKKALA and NOKKALA 1986), the chromo- somes have been observed to move sideways to- wards the poles, i.e., they are unable to show telokinetic activity. Evidently, the lack of telokine- tic activity is attributable to the fact that, in the case of achiasmatic meiosis, both telomeres of a chromo- some are able to show kinetic activity. This is

288 S . NOKKALA AND C. NOKKALA Hereditas 105 (1986)

Fig. 1-6. Male meiotic chromosomes in Anthocoris nernorurn. Fig. 1. Diffuse stage, X and Y chromosomes are positively hcteropycnotic. Fig, 2. Early condensation stage, showing sixteen chromosomal elements, 14A + XY. Bivalents consist of homologous chromosomes aligned in parallel, no signs of chiasmata are observable. Fig. 3. Late condensation stage. Fig. 4. Metaphase I in polar view, the metaphase plate is nonradial. The Y chromosome is slightly negatively heteropyc- notic. Fig. 5. Metaphase I in side view. The Y chromosome can be identified as a negatively heteropycnotic element. Fig. 6. Metaphase 11. X and Y chromosomes undergo touch and go pairing in the center of a radial metaphase plate. (Bar = 10 p m )

tiereditas 105 (1986) BRIEFREPORT 289

suggested by the finding that in chiasmatic meiosis both telomeres of a chromosome are, potentially, kinetically active, but the kinetic activity of one telomere is suppressed by a terminal or terminalized chiasma (NOKKALA 1985). The m-chromosomes are positively identified both in Saldidae in the Lep- topodomorpha (see UESHIMA 1979; NOKKALA and NOKKALA 1983) and in Miridae in the Cimicomorpha (NOKKALA and NOKKALA 1986). However, chromo- somal complements in Nabidae (NOKKALA and NOK- K A L A 1984a) and Anthocoridae (this study) lack m- chromosomes.

Although not every family within the Cimico- morpha has been studied in detail up till present, it is already obvious that chromosomal characteristics in the family Tingidae differ greatly from those in other cimicomorphan families (see JANDE 1960;

Tingidae, chromosome numbers are low, male meiosis is chiasmatic, sex chromosomes undergo prercductional meiosis, metaphase I plate is radial and metaphase I1 plate is nonradial. These observa-

siders Tingidae as distinct from the Cimicomorpha. Within the Cimicomorpha, achiasmatic meioses

fall into two distinct categories. In Nabidae (NOK- m 1 . A and NOKKALA 1984a) and Anthocoridae (this study), achiasmatic meiosis is of the alignment type, i.e.. homologous chromosomes are held together along all their length during prophase I, whereas in Miridae and perhaps also in Cimicidae, achiasmatic meiosis is of the collochore type (see NOKKALA and NOKKALA 1986), where homologous chromosomes are held together only at certain points via tenacious

U E s H l M A 1979; NOKKALA and NOKKALA 1984b). In

tions favour the Concept Of M A N N A (1984), who con-

collochores. It remains to be seen to what extent these different types of achiasmatic meioses can be used for the determination of phylogenic relation- ships within the Cimicomorpha.

Acknowledgements. -The study was supported by the Academy of Finland.

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