Animal-mediated fertilization in bryophytes – parallel or precursor to insect pollination in angiosperms?

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T1 - Animal-mediated fertilization in bryophytes – parallel or precursor to insect pollination in angiosperms?

AU - Cronberg, Nils

N1 - This is an invited paper published in a special issue of Lindbergia on occasion of the formal retirement of the eminent bryologist Heinjo During, Utrecht University.

PY - 2012

Y1 - 2012

N2 - Bryophytes have until now been absent from all hypotheses regarding the origin of insect pollination of seed plants. The discovery that both springtails and mites are able to transfer sperm in mosses makes it possible to suggest a ’Bryophyte precursor hypothesis of plant pollination’ stating that animal-mediated fertilization in mosses and insect pollination in seed plants is historically linked by homologous or analogous evolution of structures responsible for attraction and reward aimed at a pool of fertilization vectors originally co-evolved with bryophytes and subsequently co-opted by seed plants. The earliest point in time when animal-mediated fertilization of bryophytes, involving springtails and mites, could have arisen is Late Silurian/Early Devonian, ca 280 Myr before the evolutionary radiation of angiosperms. Soil-dwelling microarthropods and wingless insects are assumed to have been the primary vectors transporting sperm in ancient mosses and possibly other groups of bryophytes. These animals may later have secondarily expanded to transfer pollen in gymnosperms and angiosperms, similar to the frequent pollinator shifts observed among angiosperm groups. Several ancestral traits pointed out by recent studies of early angiosperms are in favour of this hypothesis, such as small size of flowers, small and non-sticky pollen, adaptations for growth in moist and shaded habitats close to running water, and weedy growth forms with rapid life-cycles in disturbed habitats. It is also possible to envisage a link from sexual attractants excreted by oogonia in charophyte algae and archegonia in bryophytes to guide sperm, via sugar released to attract insects in pollination drop mechanisms in gymnosperms to more advanced structures specialized for insect attraction such as nectaries and nectar discs in angiosperms.

AB - Bryophytes have until now been absent from all hypotheses regarding the origin of insect pollination of seed plants. The discovery that both springtails and mites are able to transfer sperm in mosses makes it possible to suggest a ’Bryophyte precursor hypothesis of plant pollination’ stating that animal-mediated fertilization in mosses and insect pollination in seed plants is historically linked by homologous or analogous evolution of structures responsible for attraction and reward aimed at a pool of fertilization vectors originally co-evolved with bryophytes and subsequently co-opted by seed plants. The earliest point in time when animal-mediated fertilization of bryophytes, involving springtails and mites, could have arisen is Late Silurian/Early Devonian, ca 280 Myr before the evolutionary radiation of angiosperms. Soil-dwelling microarthropods and wingless insects are assumed to have been the primary vectors transporting sperm in ancient mosses and possibly other groups of bryophytes. These animals may later have secondarily expanded to transfer pollen in gymnosperms and angiosperms, similar to the frequent pollinator shifts observed among angiosperm groups. Several ancestral traits pointed out by recent studies of early angiosperms are in favour of this hypothesis, such as small size of flowers, small and non-sticky pollen, adaptations for growth in moist and shaded habitats close to running water, and weedy growth forms with rapid life-cycles in disturbed habitats. It is also possible to envisage a link from sexual attractants excreted by oogonia in charophyte algae and archegonia in bryophytes to guide sperm, via sugar released to attract insects in pollination drop mechanisms in gymnosperms to more advanced structures specialized for insect attraction such as nectaries and nectar discs in angiosperms.

KW - Bryophyte

KW - pollination biology

KW - fertilization syndrome

KW - angiosperm

KW - pollination drop

KW - springtail

KW - mite

KW - animal-mediated fertilization

KW - evolutionary biology

KW - Bryophyte precursor hypothesis of plant pollination

M3 - Article

VL - 35

SP - 76

EP - 85

JO - Lindbergia

JF - Lindbergia

SN - 0105-0761

ER -