HERITABILITY OF PRE-ADULT VIABILITY DIFFERENCES CAN EXPLAIN APPARENT HERITABILITY OF SPERM DISPLACEMENT ABILITY IN DROSOPHILA-MELANOGASTER

Sperm displacement has been the subject of a large number of evolution ary studies because of its effects on relative male reproductive succe ss. To understand better the evolutionary role of variation in sperm d isplacement ability (SDA), an obvious aim is to measure its heritabili ty. In this paper, we show that a standard method used to measure the heritability of SDA can be misleading. First, we show that using conve ntional methods (based on counts of adult offspring of multiply mated females), SDA appears to be heritable. However, an examination of pote ntially confounding variables strongly suggests that this result is mi sleading, and that the heritable component is more likely to be pre-ad ult viability. Consequently, it is likely that there is little measura ble heritable genetic variation for SDA in D. melanogaster. We conclud e that, although conventional methods of measuring sperm displacement will usually be adequate for phenotypic measurements, greater care mus t be taken when measuring genetic variances.