Evidence for local outbreeding depression in the Mediterranean island endemic Anchusa crispa Viv. (Boraginaceae)

In this study we examined the relative effects of inbreeding and outbreeding on offspring fitness over two generations in Anchusa crispa Viv., a rare species which on Corsica (France) occurs in small populations composed of patches of few individuals. Self- and outcross-pollinations were carried out in a single population and F-1 progeny grown to flowering. Plants grown from selfing and outcrossing were then selfed or outcrossed to produce F-2 individuals in four combinations of pollination treatments over two generations, i.e. self + self, self + outcross, outcross + self and outcross + outcross. In the F-1 generation, selfed progeny had a significantly greater number of cymes per plant than outcrossed progeny (P = 0.006). Plants from two generations of selfing had fewer seeds per fruit (P = 0.06) but a significantly greater survival rate (P < 0.001) and a greater number of cymes (P = 0.06) than those from two generations of outcrossing. Selfed F-2 from outcrossed F-1 had a significantly greater number of cymes (P < 0.01) than outcrossed F-2 from outcrossed F-1. In the comparison between selfed and outcrossed F-2 from selfed F-1 the former had a significantly greater survival rate (P < 0.001), but the latter significantly more flowers per cyme (P < 0.05). Together, these results indicate that outbreeding depression may occur on a very local scale within populations of this rare endemic species, with important implications for the conservation of rare plants.