PATTERNS OF SPERM STORAGE IN 2 SPECIES OF TITS

The morphology of the sperm-storage tubules (SSTs) and the patterns of sperm storage within the SSTs was studied in two related species, the Great Tit (Parus major) and the Blue Tit (Parus caeruleus). Sperm com petition is important in both species, but Blue Tits have a much highe r copulation rate than Great Tits and therefore differences in the spe rm-storage organs could be expected. The female reproductive organs of three Blue Tits and three Great Tits were examined during laying. Con trolling for female body mass, no differences were found between the t wo species in the number of sperm-storage tubules (SSTs), the form and size of the SSTs, or the proportion of SSTs filled with sperm. The to tal sperm load was somewhat higher in Great than in Blue Tits but the significance of this difference is not clear. The structure of the SST s and the sperm storage capacity of both tit species are similar to th ose of other passerines.