THE HLE HYBRID DYSGENESIS SYNDROME IN THE MIDGE CHIRONOMUS-THUMMI - DIFFERENCES IN THE DYSGENIC POTENTIAL BETWEEN STRAINS

After crossing experiments between two Chironomus subspecies the HLE h ybrid dysgenesis syndrome occurs non-reciprocally in the F1 hybrids if the males of each of the four Ch. th. thummi strains (HL, So, G, Kr) are crossed to females of Ch, th. piger, strain E. In hybrid egg masse s, differences in the strength of the abnormal trait 'reduced egg hatc h' were found between the different piger E female x thummi male inter strain crosses. From the results it is concluded that each thummi stra in has a specific hybrid dysgenesis potential which determines the sev erity of the HLE syndrome in the hybrids. The HLE syndrome occurs also in the hybrids of crosses of different Ch. th. thummi strains. In the se hybrids the syndrome is only obtained if the male parent descends f rom a strain which has a higher HLE hybrid dysgenesis potential than t hat strain from which the female parent is derived. These results demo nstrate that the HLE syndrome is not restricted to the hybrids of the thummi x piger subspecies cross. In the Ch. th. thummi interstrain cro sses the hybrids of that cross direction are normal, which is reciproc al to the cross direction affected by the HLE syndrome. This is in con trast to the thummi x piger subspecies crosses, where the hybrids of o ne cross direction always show the HLE syndrome and the hybrids of the reciprocal cross direction the Rud syndrome. Thus, the present study also demonstrates that the HLE and Rud hybrid dysgenesis syndrome in C hironomus are independent from one another.