Abiotic pollen and pollination: ecological, functional, and evolutionary perspectives
The transport and capture of pollen in ∼ 20% of all angiosperm families occurs in air and water. In other words, pollination is abiotic and occurs via the fluid media, not an animal vector. Whereas some early concepts considered abiotic pollination to be
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Abstract. The transport and capture of pollen in ",20% of all angiosperm families occurs in air and water. In other words , pollination is abiotic and occurs via the fluid media, not an animal vector. Whereas some early concepts considered abiotic pollination to be largely a stochastic phenomenon, there is sufficient evidence to indicate that wind pollination (i.e. anemophily) and water pollination (i.e. hydrophily) have deterministic features and are sophisticated fluid dynamic solutions to the problem of pollen release, dispersal , and capture. An abiotic pollination syndrome is defined in which there is spatial or temporal separation of carpellate and staminate flowers, which are drab, a reduction in perianth parts, stigmas and anthers are exposed to the fluid, and typically unclumped pollen may be produced in large amounts. Separate pollination syndromes are defined for anemophilous (i.e. wind-pollinated), ephydrophilous (i.e. surface-pollinated), and hydrophilous (i.e. submarine-pollinated) plants. Distinctions are based on habitat and physical conditions for pollination, pollen size, shape, and ultrastructure, morphology and ultrastructure of stigmas, and outcrossing rates . For example, anemophilous pollen are spherical and small, ephydrophilous pollen are spherical or reniform and large, while hydrophilous pollen are filiform (i.e. filamentous) or functionally filiform . The pollination mechanisms and mechanics associated with these syndromes reveals a strong evolutionary relationship between plant morphology and fluid dynamics.
Key words: Anemophily, hydrophily, wind pollination, water pollination, biomechanics, fluid dynamics , ephydrophily, hyphydrophily, dicliny, dichogamy, autogamy.
Whereas pollination biology has focused on biological vectors of pollen transfer, there has been an increased interest in abiotic pollination systems, in which pollen transfer occurs via physical (i.e. wind and water) rather than biological agents. This is especially true for water pollination. Unfortunately, a recent review of abiotic pollination is lacking. The purpose of this chapter therefore, is to : (1) examine the systematic distribution of wind and water pollination; (2) examine the pollen of wind- and water-pollinated plants; (3) examine the mechanisms of wind and water pollination; and (4) describe pollination syndromes for wind and water pollination. Terminology
The terminology of abiotic pollination depends largely on the location of pollen transfer (Table 1). Delpino (as presented in Delpino and Ascherson 1871) recognized that pollen transfer could take place without animals and divided abiotic pollination into wind (anemophily) and water pollination (hydrophily)
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J. D . Ackerman: Abiotic pollen and pollination
Table 1. Abiotic pollination mechanisms in plants may occur through aerial and aquatic vectors, but the latter is restricted to the angiosperms (adapted from Ackerman 1995) Environment Fluid
Agent or Mechanism of Pollination
(A) Aerial 1) Animal Vector 2) Wind (Anemophily) 3) Apomixis (B) Aqu
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