Pollen Dispersal and Mating Patterns in Animal-Pollinated Plants

Abstract

Immobility complicates mating by angiosperms because the transfer of male gametes between individuals requires pollen vectors. Although abiotic and biotic vectors can transport pollen considerable distances (Bateman. 1947a; Squillace. 1967; Kohn and Casper. 1992; Godt and Hamrick, 1993), the resulting pattern of pollen dispersal does not intrinsically maximize the number and quality of matings. Consequently, floral evolution generally involves two classes of adapta- tions that promote mating success. The morphological traits that characterize floral design and display modify the actions of pollen vectors so as to enhance fertility (see below). In contrast, physiological traits mitigate unsatisfactory pollen dispersal by rejecting unsuitable male gametophytes (lones, 1928; de Nettancourt, 1977; Marshall and Ellstrand, 1986; Seavey and Bawa, 1986: Barrett, 1988; Snow and Spira, 1991; Walsh and Charlesworth, 1992) or zygotes (Stephenson, 1981; Casper, 1988; Becerra and Lloyd. 1992; Montalvo, 1992). As a result of postpollination processes, the realized mating pattern does not simply mirror the pattern of pollination (e.g., Campbell. 1991; also see Waser and Price, 1993). However, these processes can only filter the incipient mating pattern established during pollination, so that pollination fundamentally determines the maximum frequency and diversity of mating opportunities. Consequently. the role of pollina- tion in governing the scope for mating inextricably links the evolution of pollina- tion and mating systems.