Abstract
Pollination patterns determine the reproductive neighborhood size of plants, the connectivity of populations, and the impacts of habitat fragmentation. We characterized pollination in three populations of Quercus macrocarpa occurring in a highly altered landscape in northeastern Illinois to determine whether isolated remnant stands were reproductively isolated. • We used microsatellites to genotype all adults and 787 acorns from two isolated savanna remnants and a stand in an old-growth forest. One isolated remnant occurred in a highly urbanized/industrialized landscape, and one occurred in an agricultural landscape. Parentage assignment was used to assess pollen-mediated gene flow. • Pollen donors from outside the study sites accounted for between 46% and 53% of paternities and did not differ significantly among sites, indicating that similar high levels of gene flow occurred at all three sites. Within stands, the mean pollination distance ranged from 42 to 70 meters, and when accounting for outside pollinations, mean pollination distances were well over 100 meters. Genetic diversity of incoming pollen was extremely high in all three stands. The number of effective pollen donors, N(ep), calculated from paternity assignment was higher than that estimated by an indirect correlated paternity approach. • Our findings indicate that extremely isolated stands of oaks are unlikely to be genetically and reproductively isolated, and remnant stands may contribute to maintaining genetic connectivity in highly modified landscapes.
Highlights
Premise of the study: Pollination patterns determine the reproductive neighborhood size of plants, the connectivity of populations, and the impacts of habitat fragmentation
The total exclusionary power calculated by CERVUS for paternity assignment was 0.999 for Burnham Prairie, 0.997 for Goose Lake Prairie, and 0.998 for Cranberry Slough
Parentage analysis suggests that extremely isolated patches of Q. macrocarpa receive large amounts of pollen from distant sources, with males outside the stands fathering more than half the progeny at both Burnham Prairie and Goose Lake Prairie
Summary
Premise of the study: Pollination patterns determine the reproductive neighborhood size of plants, the connectivity of populations, and the impacts of habitat fragmentation. We characterized pollination in three populations of Quercus macrocarpa occurring in a highly altered landscape in northeastern Illinois to determine whether isolated remnant stands were reproductively isolated. Patterns of pollen- and seed-mediated gene flow may be inferred indirectly by measuring population genetic structure (Berg and Hamrick, 1995; Bacles et al, 2004; Boys et al, 2005). This approach is limited, in that it provides only an estimate of historical levels of gene flow, and it generally does not partition gene flow into that effected by seeds and by pollen unless maternal and paternal markers are available. Given that many plant populations have been subject to very recent and drastic alterations of habitat, elucidating ongoing
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