Tioga Pass and Lee Vining
In Press. Differential performance of reciprocal hybrids in multiple
environments. Journal of Ecology.
to Penstemon Research Topics:
to Additional Research Topics:
influencing plant community composition
ecology at Carrizo Plain National Monument
Local ecology and geographic range limits
related taxa may be maintained as distinct species by endogenous isolation
in the form of genomic incompatibilities and by exogenous isolation in
the form of environmental factors. To understand the relative importance
of endogenous and exogenous factors, we performed hand-pollinations and
reciprocal transplant experiments in a natural plant hybrid zone.
We measured reproductive isolation by making crosses between two parent
species of Penstemon and naturally occurring hybrids. Inclusion of reciprocal
hybrid crosses allowed us to determine whether fitness components differed
depending on the identity of the mother, as would be expected if cytoplasmic
genes were involved.
Hybrid performance was evaluated in the greenhouse and in a reciprocal
transplant experiment in the field. We measured fruit set, seed set, seed
weight, time required for fruits to mature, and seedling growth for potted
plants. To test for exogenous isolation, we planted pure parents, reciprocal
F1 hybrids, and later generation hybrids in a reciprocal transplant experiment,
and measured survival.
On average, hybrids had fitness equal to or greater than parents in all
environments, including the greenhouse and all field gardens, indicating
a lack of endogenous isolation. Parent species and reciprocal F1 hybrids
differed in many of the traits that were measured. In each field garden,
the hybrid with the native cytoplasm had a higher survival rate, suggesting
local adaptation to different elevations.
Exogenous factors that differ along elevational gradients can be more
important than intrinsic genetic incompatibilities in determining the
fitness of plant hybrids. Our results illustrate the importance of studying
hybrid performance in multiple environments and in generating reciprocal
hybrids to effectively test for isolating mechanisms in natural hybrid