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.

THE GENETIC COMPOSITION OF PHILAENUS SPUMARIUS POPULATIONS IN ISLAND HABITATS VARIABLY AFFECTED BY VOLES

Gentics of hilanenus colour polymorphism: the 28 genotypes.

Abundance of Philaenus spumarius in relation to types of plant community in the Tvärminne archipelago, southern Finland

Eight main types of plant community capable of supporting populations of the meadow spittlebug (Philaenus spumarius (L.), Homoptera), were distinguished on the islands of the Tvärminne archipelago, off the south coast of Finland. The area is subject to land upheaval amounting to about 42 cm in 100 years. The flora and vegetation of the island meadows develop through successive stages determined by edaphic, climatic and biotic factors which themselves are changed by land upheaval. The meadows are mostly very small. The secular succession of the vegetation is rendered irregular by yearly and longer-term fluctuations in climate. Changes in the vegetation affect the choice of food-plants availa…

Radial and peripheral clines in northern polymorphic populations of Philaenus spumarius

Geographic variability in the colour polymorphism of Philaenus spumarius (Homoptera) was investigated in the northern parts of Finland, Norway and Sweden. The investigation was directed mainly at peripheral populations south of the Baltic—Arctic divide. The colour phenotypes were found to differ in their “north tolerance”. The phenotypes typ (pt/pt) and lat (pt/pt) were the most, and the phenotype tri (pt/pT) the least tolerant to marginal conditions. Differences in “north tolerance” between the phenotypes cause radial clines to be present in allele frequencies. The radial clines may be caused by the combined effect of several different factors. These include shortness of the thermal growth…

The founder principle, founder selection, and evolutionary divergence and convergence in natural populations of Philaenus

Parts of the archipelago of the Baltic Sea are rising above the water level at a steady, slow rate. Plant species appear on the emerging islands in a definite order, and an early stage and a late stage can be distinguished in the development of meadows on the islands. In 1969–1973 four populations of Philaenus spumarius living in meadows at the early stage had widely different frequencies of the alleles determining colour polymorphism. In the same years three Philaenus populations living on islands with meadows at the late stage had closely similar allele frequencies. The differences between the Philaenus populations in the early stage meadows are ascribed partly to the founder principle an…

The genetic basis of balanced polymorphism in Philaenus (Homoptera)

In Philaenus spumarius (Homoptera), colour polymorphism is mainly determined by a series of allelic genes. The dominance and co-dominance relationships of the following seven alleles were analysed: T (trilineatus), M (marginellus), F (flavicollis-F), L (lateralis), C (flavicollis-C, gibbus and leucocephalus), O (quadrimaculatus, albomaculatus and leucophthalmus) and t (typicus). The colour phenotypes are indicated in brackets. On the basis of partly direct and partly indirect evidence, T was found to be the top dominant and t the bottom recessive allele in the female sex. In the males, T is also the top dominant, but t comes second in the hierarchy. Conclusive evidence of the dominance of T…

Transfer of individuals as a means of investigating natural selection in operation.

Populations of Philaenus spumarius (Homoptera) displaying colour polymorphism at stable equilibrium were subjected to the introduction of alien phenotypes. In an exchange experiment between populations of isolated islands, 2/3 of population A, from Allgrundet, was transferred to Porskobben, and 2/3 of population P from Porskobben to Allgrundet. The immediate result of the transfer was A-type allele frequencies on Porskobben and P-type frequencies on Allgrundet. After four generations, the pre-transfer frequencies were almost completely restored. This change implies strong island-specific selection pressures. The process was remarkably rapid in view of the mixed composition of the gene pools…