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(American Journal of Botany. 2009;96:1690-1702.)
doi: 10.3732/ajb.0800315
© 2009 Botanical Society of America, Inc.
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Population Biology

Molecular, morphological, and ecological niche differentiation of sympatric sister oak species, Quercus virginiana and Q. geminata (Fagaceae)1

Jeannine Cavender-Bares2 and Annette Pahlich

Department of Ecology, Evolution, and Behavior; University of Minnesota, St. Paul, Minnesota 55108 USA

ABSTRACT

The genus Quercus (the oaks) is notorious for interspecific hybrization, generating questions about the mechanisms that permit coexistence of closely related species. Two sister oak species, Quercus virginiana and Q. geminata, occur in sympatry in Florida and throughout the southeastern United States. In 11 sites from northern and southeastern regions of Florida, we used a leaf-based morphological index to identify individuals to species. Eleven nuclear microsatellite markers significantly differentiated between the species with a high correspondence between molecular and morphological typing of specimens. Nevertheless, Bayesian clustering analysis indicates interspecific gene flow, and six of 109 individuals had mixed ancestry. The identity of several individuals also was mismatched using molecular markers and morphological characters. In a common environment, the two species performed differently in terms of photosynthetic performance and growth, corresponding to their divergent ecological niches with respect to soil moisture and other edaphic properties. Our data support earlier hypotheses that divergence in flowering time causes assortative mating, allowing these ecologically distinct sister species to occur in sympatry. Limited gene flow that permits ecological differentiation helps to explain the overdispersion of oak species in local communities.

Key Words: Fagaceae • Florida • flowering time • habitat differentiation • morphological variation • nuclear microsatellites • Quercus geminata • Q. virginiana

Received for publication 17 September 2008. Accepted for publication 5 May 2009.

FOOTNOTES

1 The authors thank K. Nixon, A. Gonzalez-Rodriguez, G. May, P. Manos, and N. Deacon for insightful discussions and/or comments on the manuscript. J.C.B. thanks J. Sadle and E. Salisbury for assistance with fieldwork and K. Koehler and E. Warner for other assistance. They thank the Florida Park Service in Districts 2 and 5 for assistance with collection permits. The project was funded by a grant to J.C.B. from the Graduate School Dean’s office, University of Minnesota.

2 Author for correspondence (e-mail: cavender{at}umn.edu)


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