AOBPreview originally published online on February 6, 2009
Annals of Botany 2009 103(6):941-950; doi:10.1093/aob/mcp014
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Pollen-tube growth rates in Collinsia heterophylla (Plantaginaceae): one-donor crosses reveal heritability but no effect on sporophytic-offspring fitness
1 Department of Biology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
2 Department of Plant Ecology and Systematics, Lund University, Ecology Building, 223 62 Lund, Sweden
3 Department of Ecology and Evolution, Plant Ecology, Uppsala University, Villavägen 14, 752 36 Uppsala, Sweden
4 Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, USA
5 School of Biological Sciences, University of Portsmouth, King Henry Building, Portsmouth, PO1 2DY, UK
* For correspondence. E-mail asa.lankinen{at}ekol.lu.se
Received: 22 September 2008 Returned for revision: 6 November 2008 Accepted: 18 December 2008 Published electronically: 6 February 2009
Background and Aims: Evolutionary change in response to natural selection will occur only if a trait confers a selective advantage and there is heritable variation. Positive connections between pollen traits and fitness have been found, but few studies of heritability have been conducted, and they have yielded conflicting results. To understand better the evolutionary significance of pollen competition and its potential role in sexual selection, the heritability of pollen tube-growth rate and the relationship between this trait and sporophytic offspring fitness were investigated in Collinsia heterophylla.
Methods: Because the question being asked was if female function benefited from obtaining genetically superior fathers by enhancing pollen competition, one-donor (per flower) crosses were used in order to exclude confounding effects of post-fertilization competition/allocation caused by multiple paternity. Each recipient plant was crossed with an average of five pollen donors. Pollen-tube growth rate and sporophytic traits were measured in both generations.
Key Results: Pollen-tube growth rate in vitro differed among donors, and the differences were correlated with in vivo growth rate averaged over two to four maternal plants. Pollen-tube growth rate showed significant narrow-sense heritability and evolvability in a father–offspring regression. However, this pollen trait did not correlate significantly with sporophytic-offspring fitness.
Conclusions: These results suggest that pollen-tube growth rate can respond to selection via male function. The data presented here do not provide any support for the hypothesis that intense pollen competition enhances maternal plant fitness through increased paternity by higher-quality sporophytic fathers, although this advantage cannot be ruled out. These data are, however, consistent with the hypothesis that pollen competition is itself selectively advantageous, through both male and female function, by reducing the genetic load among successful gametophytic fathers (pollen), and reducing inbreeding depression associated with self–pollination in plants with mix-mating systems.
Key words: Collinsia heterophylla, evolvability, female fitness, good genes, heritability, male fitness, mixed-mating system, Plantaginaceae, pollen competition, sexual selection
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