O. Halkka

Enzyme gene heterozygosity in small island populations of Philaenus spumarius (L.) (Homoptera)

Genetic polymorphism at about twenty enzyme loci in one mainland and in six differentially isolated island populations of Philaenus spumarius (L.) was studied by starch gel electrophoresis. The populations have different average degrees of heterozygosity, so that the most isolated population is the least polymorphic. The differences in heterozygosity seem to be correlated to the size of the population and the degree of isolation from other populations. With a single exception, the most common allele in each locus is the most common one everywhere. The results are compared with the differences observed in the color polymorphism of Philaenus island populations. The allele frequencies of enzyme loci are maintained by selection; the fact that the prevalent allele is the same in all populations may be due to selection and founder principle.

RNA and Protein in Nucleolar Structures of Dragonfly Oocytes

Dragonfly and damselfly oocytes regularly contain two nucleolus like bodies of different sizes, a primary nucleolus and a secondary nucleolus. The primary nucleolus stains more deeply with RNA stains than with an arginine stain; the seconidary nuicleolus stains conzversely. The primary nulcleolus incorporates uridine under all conditions tested; the secondary, only after precautions have been taken to preserve soluble RNA. Both inicorporate lysine.

The mode of meiosis in the Psyllina

Summary1.The spermatogenesis of six psyllids and the oogenesis of Psylla försteri have been studied. The haploid number n=13 was found in 4 species, all with an XO system of sex determination. 13 may well be the modal haploid number in the genus Psylla.2.The chromosome complement of the only XY species, Psylla corcontum, with n=11, is probably the result of two chromosomal rearrangements which have led to the formation of a neo-XY pair.3.Psylla försteri is an XO species in which the haploid set consists of only 8 chromosomes, one of which is very large. As the amount of DNA in this species is approximately equal to that in the 13-chromosome species P. sorbi, the large chromosome obviously corresponds to 5 or 6 chromosomes of P. sorbi.4.A diffuse stage, which leads to a considerable increase of nuclear size, is typical of late pachytene to late diplotene of spermatogenesis.5.In contrast to the other cytologically studied Homoptera Sternorrhyncha, the bivalents of psyllids co-orientate at the first metaphase of spermatogenesis. The following anaphase is therefore prereductional.6.In the oogenesis of Psylla försteri the bivalents always seem to have auto-orientation, which means morphological postreduction at first anaphase.7.The karyological picture is that of an organism with a diffuse kinetochore.8.The Hemiptera and the plant genus Luzula both have diffuse kinetochores. The reason that the chromosome numbers in Hemiptera vary far less than in the genus Luzula may lie in the existence in the Hemiptera of a delicate system of sex determination sensitive to any change in chromosome number and structure.9.Cytologically, the Psyllina lie between the suborders Sternorrhyncha and Auchenorrhyncha.

The Selection Regime of Philaenus Spumarius (L.) (Homoptera)

In visual polymorphisms, as a rule there exist geographical and local discontinuities in the frequencies of the genes responsible for colour variability. Many of these discontinuities cannot be satisfactorily explained on the assumption of discontinuities in the intensity of visual selection. For types of selection other than visual, it is often justifiable to suppose at least linkage disequilibrium (see Frydenberg 1963), if not supergene linkage (see Turner 1967), between the “visual” genes and the genes subject to other types of selection.

X-ray-induced changes in the chromosomes of Limotettix (Homoptera)

SummaryMale specimens of the Homopteran Limotettix were irradiated with a 400 r dose of X-rays. This treatment produced a variable number of chromosome fragments per cell. These fragments survived over a period of 7 days, which is probably equivalent to more than one cell generation.A striking difference was observed in the manifestation of irradiation effects at the anaphase stages of the two maturation divisions. At the first division anaphase, bridge formations and laggard chromosomes were frequently found, while both these types of disturbance were practically absent at the second division.After consideration of an alternative explanation, the conclusion is reached that all the peculiarities of irradiated leafhopper testicular cell progenies are best explained if it is assumed that1)the chromosomes are holokinetic2)the mode of meiosis is prereductional.

Conditions requisite for stability of polymorphic balance in Philaenus spumarius (L.) (Homoptera)

Frequencies of colour morphs were recorded in 1969–74 in 5 island populations of Philaenus spumarius. The polymorphic balance was accurately maintained in three of them, but less constantly in the other two. One of the latter populations experienced a great fluctuation in size, and this was accompanied by a profound alteration in morph frequencies.One of the five populations consists of two subpopulations about 5 m apart. Although differing in the same island-specific respects from the populations of the other islands, the subpopulations were significantly unlike in the detailed distribution of the morph frequencies. These differences were probably due to the dissimilar distribution of the subniches available to the subpopulations. The dissimilar, island-specific patterns of morph frequences recorded in the other four populations may also be due to dissimilar subniche distribution. Migration between islands occurs at too slight a rate to cause an appreciable dysmetric load in the populations. In general, the rate of migration in Philaenus appears to be governed by the need for a balance between effective ability to colonize and effective subniche-specific protection of polymorphism.

Lamellate bodies in the nuclei of dragonfly (odonata) oocytes

SummaryConcentrically lamellate spherical bodies have been observed in the oocyte nuclei of the anisopterous dragonflyCordulia aenea. In their ultrastructure, these bodies resemble the “cortical granules” reported from the cytoplasm of the sea urchin oocytes. The lamellate bodies ofCordulia are compared with other lamellate systems known to exist in nuclei. It is suggested that the nuclear lamellate spheres ofCordulia may be homologous with the somewhat less regular lamellate bodies described from maize microspores.