Seed production from hand outcrosses and natural pollination.--Hand outcrossed
flowers produced 16% more seeds than naturally pollinated flowers (Table 3).
By transplanting metamorphs back to the field in 2009, I was also able to show that for those offspring that were able to complete metamorphosis, selfing resulted in decreased survival and reproductive fitness compared to outcrossed
controls (Table 4).
In both species, outcrossed
seeds are heavier, have higher germination frequency, higher growth rate, and lower risk of early seedling death than selfed seeds.
where [w.sub.s] and [w.sub.o] are the mean fitnesses of inbred and outcrossed
progeny calculated from the eight maternal sibmeans of each crosstype, respectively (cf.
Collectively, these findings suggest that outcrossed
pollen provided by pollinators is essential to maximize H.
They found only one positive (outcrossed
) kernel each in plots at the 100-, 150-, and 200-m distances, and none at greater distances (300 and 400 m).
On the other hand, progeny produced by selfing are usually inferior to outcrossed
progeny due to inbreeding depression (Darwin 1876, Charlesworth and Charlesworth 1987, Husband and Schemske 1996).
Nonetheless, given a sufficiently high selective advantage for the stabilized derivatives, the process becomes feasible even in outcrossed
We used the ratio between selfed produced progeny (fruits and seeds) and the value for outcrossed
produced progeny to estimate inbreeding depression (Charlesworth & Charlesworth, 1987): [delta] = 1 - ([w.sub.s]/[w.sub.x]) where [w.sub.s] is the average fitness of selfed progeny and [w.sub.x] is the average fitness of outbred progeny.
For example, Griffen (1987) found that 10 winter wheat cultivars in New Zealand had outcrossing rates between 0.14 and 3.95% at a distance of 15 cm, while Martin (1990) in Kansas found that 12 winter wheat varieties outcrossed
0.1 to 5.6% over 30 cm.
Since pollinators usually spend [less than]30 s on an inflorescence, we estimate that natural populations of the study species are highly outcrossed
. The fraction of the pollen load carried over from flower to flower was found to be 0.67 in O.
The average estimated outcrossing rate of the whole population is t = 0.6; however, few individuals of the population (0.4-13.0%, fluctuating on a yearly basis) are male sterile and fully outcrossed
(del Castillo 1994).