Data from: Fitness of crop-wild hybrid sunflowers under competitive conditions: implications for crop-to-wild introgression

Understanding the likelihood and extent of introgression of novel alleles
in hybrid zones requires comparison of lifetime fitness of parents and
hybrid progeny. However, fitness differences among cross types can vary
depending on biotic conditions, thereby influencing introgression
patterns. Based on past work, we predicted that increased competition
would enhance introgression between cultivated and wild sunflower
(Helianthus annuus) by reducing fitness advantages of wild plants. To test
this prediction, we established a factorial field experiment in Kansas,
USA where we monitored the fitness of four cross types (Wild, F1, F2, and
BCw hybrids) under different levels of interspecific and intraspecific
competition. Intraspecific manipulations consisted both of density of
competitors and of frequency of crop-wild hybrids. We recorded emergence
of overwintered seeds, survival to reproduction, and numbers of seeds
produced per reproductive plant. We also calculated two compound fitness
measures: seeds produced per emerged seedling and seeds produced per
planted seed. Cross type and intraspecific competition affected emergence
and survival to reproduction, respectively. Further, cross type interacted
with competitive treatments to influence all other fitness traits. More
intense competition treatments, especially related to density of
intraspecific competitors, repeatedly reduced the fitness advantage of
wild plants when considering seeds produced per reproductive plant and per
emerged seedling, and F2 plants often became indistinguishable from the
wilds. Wild fitness remained superior when seedling emergence was also
considered as part of fitness, but the fitness of F2 hybrids relative to
wild plants more than quadrupled with the addition of interspecific
competitors and high densities of intraspecific competitors. Meanwhile,
contrary to prediction, lower hybrid frequency reduced wild fitness
advantage. These results emphasize the importance of taking a full life
cycle perspective. Additionally, due to effects of exogenous selection, a
given hybrid generation may be especially well-suited to hastening
introgression under particular environmental conditions.