Pollination, breeding system, and genetic structure in two sympatric Delphinium (Ranunculaceae) species

Citation
Cf. Williams et al., Pollination, breeding system, and genetic structure in two sympatric Delphinium (Ranunculaceae) species, AM J BOTANY, 88(9), 2001, pp. 1623-1633
Citations number
64
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Plant Sciences
Journal title
AMERICAN JOURNAL OF BOTANY
ISSN journal
0002-9122 → ACNP
Volume
88
Issue
9
Year of publication
2001
Pages
1623 - 1633
Database
ISI
SICI code
0002-9122(200109)88:9<1623:PBSAGS>2.0.ZU;2-S
Abstract
Two sympatric Delphinium species, D. barbeyi and D. nuttallianum, are ecolo gically and morphologically similar. However, D. barbeyi has multiple, larg e inflorescences while D. nuttallianum has a single, small inflorescence. T hese differences in floral display should result in greater intraplant poll en transfer in D. barbeyi, leading to higher rates of self-pollination thro ugh geitonogamy. Reduced gene flow by pollen should in turn produce greater population differentiation among populations of D. barbeyi relative to D. nuttallianum. We tested these predictions by comparing pollinator behavior, breeding systems, outcrossing rates, and population genetic structure of s ympatric populations of the two species in Colorado. Bumble bee and humming bird pollinators visit more flowers and inflorescences per foraging bout in D. barbeyi than in D. nuttallianum. The species differed in breeding syste m; D. barbeyi produced more seeds by autogamy (9 vs. 2%) than D. nuttallian um and suffered no reduction in seed set in hand-self vs. outcross pollinat ions, in contrast to a 41% decline in D. nuttallianum. The outcrossing rate in one D. barbeyi population was 55%, but ranged from 87 to 97% in four D. nuttallianum populations. Genetic differentiation among population subdivi sions estimated by hierarchical F statistics was > 10 times greater in D. b arbeyi (<(<theta>)over cap> = 0.055-0.126) than D. nuttallianum (<(<theta>) over cap> = 0.004-0.009) at spatial scales ranging from metres to 3.5 km. S patial autocorrelation analysis also indicated more pronounced local geneti c structure in D. barbeyi than D. nuttallianum populations. Fixation indice s (F-IS) of D. barbeyi adults were much lower than expected based on mating system equilibrium and suggest that differences in the degree of self-comp atibility and/or the timing of postpollination selection/inbreeding depress ion between the two species further contribute to the genetic differences b etween them.