The relationship between the level of inversion polymorphism and the type of water body, the season, and the year of observation in Chironomus plumosus L. (Diptera, Chironomidae)

Data on chromosomal polymorphism in 50 natural populations of Chironomus pl umosus from ecologically different European and Asian water bodies were sum marized. To estimate the inversion polymorphism, two indices were used: the percentage of individuals heterozygous for inversions among the total numb er of individuals in a given sample and the mean number of heterozygous sta tes for inversions per individual. The association between the level of pol ymorphism and the type of water body was studied. Water bodies were divided into four groups: ponds, lakes, reservoirs, and flood plains. Statisticall y significant differences in both polymorphism indices were found between p opulations from two types of water bodies: lakes and reservoirs. In turn, t he populations from ponds fell into two groups: western- and eastern-Europe an. Statistically significant differences in the level of polymorphism were also observed between these two groups. Moreover, the populations from eas tern-European ponds (Russia) and reservoirs are comparable to the populatio ns from the ponds of western Europe (Czech Republic) and lakes in the level of polymorphism. Seasonal variation for heterozygosity was found only in t he lake populations. Long-term (3- to 19-year) studies by different authors on more than ten populations from the ponds and reservoirs that are distan t from one another revealed annual stability (with slight fluctuations) of the polymorphism level. An analysis of the temporal ecological regularities of the maintenance of inversion polymorphism in C. plumosus also revealed surprisingly stable dynamics: the level of polymorphism was significant thr oughout the species range, but it varied among populations and depended on ecological conditions (type of water body, season, etc.).