Abstract
BackgroundAlthough Nicotiana attenuata is entirely self-compatible, chemical and other floral traits suggest selection for the maintenance of advertisement for moth pollinators.ResultsExperimental exclusions of pollinators from plants with emasculated flowers in natural populations in southern Utah during an outbreak of the hawkmoth Hyles lineata revealed that 24% of the seed set could be attributed to insect pollination, and eliminated wind pollination and apomixis as contributing to seed set. Hence these moths can mediate gene flow when self-pollen is unavailable. To quantify gene flow when self-pollen is available, plants were transformed with two marker genes: hygromycin-B resistance and β-glucuronidase. The utility of these genetic markers to measure gene flow between plants was examined by mixing pollen from plants homozygous for both genes with self-pollen in different ratios and hand-pollinating emasculated flowers of plants growing in a natural population. The proportion of transformed seeds was positively correlated with the amount of transformed pollen applied to stigmas. In glasshouse experiments with the hawkmoth Manduca sexta and experimental arrays of transformed and wild-type plants, pollination mediated by moths accounted for 2.5% of the seed set.ConclusionsEven though moth pollination is rare and highly variable for this largely selfing plant, N. attenuata opportunistically employs a mixed-mating system.
Highlights
Nicotiana attenuata is entirely self-compatible, chemical and other floral traits suggest selection for the maintenance of advertisement for moth pollinators
The wild tobacco Nicotiana attenuata Torrey ex Watson (Solanaceae) represents a model system in chemical ecology and is of particular importance because it has been subject to intensive study in its natural habitat, the Great Basin deserts of North America, as well as under laboratory conditions
Between fires – the intervals average 10 to 30 years and are often greater than a century – the N. attenuata populations survive as a dormant seed bank that germinates in response to smoke-related cues [5]
Summary
Nicotiana attenuata is entirely self-compatible, chemical and other floral traits suggest selection for the maintenance of advertisement for moth pollinators. Between fires – the intervals average 10 to 30 years and are often greater than a century – the N. attenuata populations survive as a dormant seed bank that germinates in response to smoke-related cues [5]. Anthesis usually occurs shortly before the flowers open on the first night, and most seeds set in nature are thought to result from self-pollination. Field experiments have revealed no decrease in seed set or viability from flowers bagged to exclude pollinators compared to uncovered controls, confirming that the species is fully self-compatible ([9]; IT Baldwin, unpublished results). The lack of any apparent inbreeding depression after more than 20 consecutive generations of selfing of six field-collected genotypes (IT Baldwin unpublished results) is consistent with recent population bottlenecks and/or a history of selfing
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