Asymmetrical Gene Flow in a Hybrid Zone of Hawaiian Schiedea (Caryophyllaceae) Species with Contrasting Mating Systems

Asymmetrical gene flow, which has frequently been documented in naturally occurring hybrid zones, can result from various genetic and demographic factors. Understanding these factors is important for determining the ecological conditions that permitted hybridization and the evolutionary potential inherent in hybrids. Here, we characterized morphological, nuclear, and chloroplast variation in a putative hybrid zone between Schiedea menziesii and S. salicaria, endemic Hawaiian species with contrasting breeding systems. Schiedea menziesii is hermaphroditic with moderate selfing; S. salicaria is gynodioecious and wind-pollinated, with partially selfing hermaphrodites and largely outcrossed females. We tested three hypotheses: 1) putative hybrids were derived from natural crosses between S. menziesii and S. salicaria, 2) gene flow via pollen is unidirectional from S. salicaria to S. menziesii and 3) in the hybrid zone, traits associated with wind pollination would be favored as a result of pollen-swamping by S. salicaria. Schiedea menziesii and S. salicaria have distinct morphologies and chloroplast genomes but are less differentiated at the nuclear loci. Hybrids are most similar to S. menziesii at chloroplast loci, exhibit nuclear allele frequencies in common with both parental species, and resemble S. salicaria in pollen production and pollen size, traits important to wind pollination. Additionally, unlike S. menziesii, the hybrid zone contains many females, suggesting that the nuclear gene responsible for male sterility in S. salicaria has been transferred to hybrid plants. Continued selection of nuclear genes in the hybrid zone may result in a population that resembles S. salicaria, but retains chloroplast lineage(s) of S. menziesii

Studies in the Genus Bidens. I

Volume: 56Start Page: 490End Page: 49

North Shore

With the rapid encroachment of city and town upon the outlying districts about Chicago, and the consequent despoilation of the native flora, it has seemed to the writer advisable to undertake a careful study of a certain restricted area, while there is yet an opportunity, and to place these results on record. For several reasons, Skokie marsh was deemed most worth of study. During the past few years the so-called "North Shore" towns situated in the vicinity of the marsh have grown at a phenomenal rate. Much land but recently used in farming is now occupied bypublished or submitted for publicationis peer reviewe

Notes on varieties of Bidens connata and a hybrid with B. cernua

Volume: 67Start Page: 59End Page: 6

Further notes on the distribution of Bidens connate vars. pinnata and gracilipes

Volume: 64Start Page: 23End Page: 2

Studies in the Genus Bidens. II

Volume: 59Start Page: 301End Page: 31