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Free keywords:
local adaptation; inbreeding; outcrossing depression; germination; fitness
Abstract:
Gene combinations conferring local fitness may be destroyed
by mating with individuals that are adapted to a different
environment. This form of outbreeding depression provides an evolutionary
incentive for self-fertilization. We show that the yeast Saccharomyces
paradoxus tends to self-fertilize when it is well adapted
to its local environment but tends to outcross when it is poorly
adapted. This behavior could preserve combinations of genes when
they are beneficial and break them up when they are not, thereby
helping adaptation. Haploid spores must germinate before mating,
and we found that fitter spores had higher rates of germination across
a 24-hour period, increasing the probability that they mate with
germinated spores from the same meiotic tetrad. The ability of yeast
spores to detect local conditions before germinating and mating suggests
the novel possibility that these gametes directly sense their own
adaptation and plastically adjust their breeding strategy accordingly.
