Floral Evolution: Attractiveness to Pollinators Increases Male Fitness

Abstract

Because availability of resources often limits seed or fruit set, increased visits by pollinators may not always lead to increases in maternal reproduction. This observation has led evolutionary biologists to hypothesize that a plant's ability to attract pollinators may have its primary impact on male fitness achieved through the fertlization of ovules. This interpretation of angiosperm reproductive ecology is supported by field experiments. Pollinating insects strongly discriminated between two Mendelian petal-color morphs in Raphanus raphanistrum, a widespread, self-incompatible crucifer. In experimental populations composed of petal-color homozygotes. color discrimination by naturally occurring pollinators had no statistically significant effect on relative maternal function (fruit and seed production) in the two morphs. In contrast, yellow-flowered individuals were far more successful as fathers (pollen donors) than were the less visited whites. These results suggest that the evolution of floral signals such as petal color may be driven primarily by selection on male function.

The biology of Canadian weeds. 132. Raphanus raphanistrum L.

“…In a hand-pollination experiment, fruit set of wild radish increased with receipt of supplemental pollen, but seed set did not (Pfennig and Conner 1997). Stanton et al (1986) found that while colour discrimination by pollinators had no significant effect on relative maternal function (fruit and seed production), yellow-coloured flowers were much more successful as pollen donors.…”

Seed paternity in flowering plants: an evolutionary perspective

“…Thus a potential caveat for the interpretation of results is that both phenotypic markers and isozymes have potential limitations, due to the fact that the markers themselves may directly affect paternity success. For instance, in Raphanus raphanistrum, pollinators preferentially visit the yellow petal-colour morph over white-petal flowers (Stanton et al 1986). Similar effects can occur for different alleles at isozyme loci, that can affect paternity, via linked loci or directly (Travers & Holtsford 2000;Travers & Mazer 2001).…”

“…Heritable markers include phenotypic markers with a mendelian genetic basis, such as flower and leaf colour (e.g. Stanton et al 1986;Snow & Mazer 1988;Cowan et al 2000), allozymes and other molecular markers. To date, it is isozyme electrophoresis that still makes the major methodological contribution to the body of published studies on paternity shares within fruits in plants (Table 1).…”

Plant hybridization

“…Waser & Price, 1983 ;Stanton, Snow & Handel, 1986 ;Nilsson, 1988 ;Campbell et al, 1991, Campbell, Waser & Price, 1996. Pollinator choice is determined by the presence of rewards (e.g.…”