INHERITANCE AND FITNESS EFFECTS ANALYSIS FOR A EUCHROMATIC SUPERNUMERARY CHROMOSOME SEGMENT IN SCILLA-AUTUMNALIS (LILIACEAE)

A large euchromatic supernumerary segment (ss) occurs at a high freque ncy in a natural population of Scilla aulumnalis from the west of the Iberian Peninsula. Mother-offspring analyses have shown random pollina tion of all bulbs lacking the extra segment but nonrandom pollination of some bulbs carrying it. With a single exception, ss transmission ap peared to be Mendelian through the eggs of heterozygous bulbs, which w as consistent with results of controlled crosses. An analysis of the e ffects of this ss on some female fitness components demonstrated signi ficant differences between genotypes for mean seed weight. Heterozygou s bulbs yielded significantly heavier seeds than standard homozygous b ulbs, and slightly (but not significantly) heavier seeds than segment homozygotes. No trade-off was observed between seed number and seed si ze in this population. In heterozygotes there was a surprising positiv e correlation between fruit fertility (number of seeds per fruit) and seed weight. These results are discussed in relation to the maintenanc e of the segment in natural populations. (C) 1995 The Linnean Society of London