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Interspecific pollen competition as a reproductive barrier between sympatric species of Helianthus (Asteraceae)
Author(s) -
Rieseberg Loren H.,
Desrochers Andrée M.,
Youn Sue J.
Publication year - 1995
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1995.tb15672.x
Subject(s) - pollen , biology , intraspecific competition , interspecific competition , helianthus annuus , botany , helianthus , achene , introgression , pollen tube , sunflower , pollination , ecology , horticulture , genetics , gene
Artificial crosses between Helianthus annuus and H. petiolaris using 1:9, 1:1, and 9:1 mixtures of intraspecific: interspecific pollen were conducted to determine the role of interspecific pollen competition as a reproductive barrier in Helianthus. Of 1,245 achenes analyzed from the pollen competition experiments, only 49 were hybrids. The number of hybrids observed was significantly less than expectations for all three pollen mixtures, regardless of the identity of maternal parent ( P < 0.01). Stigma age and pollen ratio had no significant impact on hybrid frequency. However, hybrids were significantly more frequent with H. annuus than with H. petiolaris as the maternal parent ( P < 0.01). Analysis of pollen tube growth rates revealed no differences in the rate of growth of intraspecific vs. interspecific pollen. Likewise, pollinations with either intraspecific or interspecific pollen or with different pollen ratios did not affect the percentage of filled achenes. Thus, the mechanism responsible for selective fertilization by intraspecific pollen in mixed pollen loads remains unclear. Nonetheless, these findings suggest that interspecific pollen competition plays an important role in controlling the formation of hybrids between H. annuus and H. petiolaris and may partially account for patterns or differential cytoplasmic vs. nuclear introgression in Helianthus.