Science 248: 1631-1633. (1990)
Influence of environmental quality on pollen competitive ability in wild radish.
Helen J. Young and Maureen L. Stanton

Abstract
Pollen of Raphanus raphanistrum produced under low nutrient conditions sired fewer seeds than pollen produced under better conditions when the two types were applied on a stigma together. No difference was seen in single-donor crosses. Male mating success can be strongly influenced by the environmental conditions of pollen-bearing plants, a factor overlooked in studies of plant reproductive biology and in standard quantitative genetic crossing designs, where effects of male parent are equated with heritable genetic variation.


ENVIRONMENTAL EFFECTS ON FEMALE reproductive success in plants are well documented (1). Environmental conditions can also affect pollen characters that may, in turn, influence paternal success. The microenvironment of pollen-producing plants has been shown to affect pollen production (2), pollen size (3), pollen germination (4), and pollen tube growth rate (5), but the relations between each of these pollen traits and male success remain unknown. In general, environmental effects on pollen traits are ignored in studies of variation in male success, sexual selection, and classical crossing designs (6). The assumption of no paternal environmental effects overestimates genetic variance and response to selection in the evolution of characters that influence paternity, if the environmental variance for these traits is not zero.

We show that pollen quality, measured as the number of seeds sired, is influenced by environmental conditions during pollen development. We performed two types of crosses to compare seed production resulting from low levels of pollen competition (single-donor crosses) versus a higher degree of pollen competition (multiple-donor crosses).

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There were significant differences in pollen size and number among the four sets of full sib donors; however, there was no consistent relation with nutrient treatment (Fig. 3). Family differences for both traits were larger than treatment differences.

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If paternity is more strongly influenced by less visible pollen traits (pollen nutrients), then measuring pollen number and size is not sufficient for estimating male fitness.