A TEMPERATURE CLINE IN COPY NUMBER FOR 412 BUT NOT ROO B104 RETROTRANSPOSONS IN POPULATIONS OF DROSOPHILA-SIMULANS/

The copy number of the retrotransposable element 412 of Drosophila sim ulans from populations collected worldwide shows a negative correlatio n with minimum temperature. No association was detected for the roo/B1 04 element. The possibility that selective pressures might regulate th e 412 copy number in these natural populations is supported by detecti on of selection against the detrimental effects of 412 insertions (est imated by the proportion of insertions on the X chromosome in comparis on with the autosomes) hut not roo/B104. These data reveal different s patial patterns for two element families, and strongly suggest that so me factors in the environment, such as temperature, may interfere with the control of retrotransposition, thus affecting important aspects o f genomic evolution.