Effects of population size and pollen diversity on reproductive success and offspring size in the narrow endemic Cochlearia bavarica (Brassicaceae)

In small, fragmented populations of self-incompatible plant species. genetic drift and increasingly close relationships between plants may restrict the number of genetically different pollen donors, the availability of compatible mates, and the opportunity for pollen competition and selection These restrictions may reduce the siring success or increase the probability of inbreeding depression in the offspring To test if this was the case, we hand-pollinated maternal plants in small and large populations of the rare, endemic plant Cochlearia bavarica (Brassicaceae) with pollen from one. three, or nine donors from the same population or with little donors from a different population In one additional population of intermediate size, maternal plants were hand-pollinated with ten donors located at a distance of 1, 10, 100. or 1000 in. We then recorded seed and offspring characters Oil average. offspring from small Populations were smaller than normal and fewer survived to maturity. Increasing the number of pollen donors had a positive effect oil reproductive success in small and large populations, but at the highest pollen diversity this occurred at the expense of slightly reduced offspring fitness Because the total amount of transferred pollen was held constant, these effects could not be attributed to increasing pollen load Rather. the increasing pollen diversity may have increased the chances of selecting a particularly good donor for fertilization-an example of a sampling effect of diversity. Pollen from outside a population or from 10-100 in away resulted in higher reproductive success and greater offspring size Effects Of Population size and pollination treatments oil reproductive success and offspring fitness were additive. Apparently, there is no obvious size threshold above which the potential of inbreeding depression call be ignored in C bavarica.