No Correlation Between Pollen Fertility and Viability: Differential Measures of Male Gametophytic Fitness in Cannabis sativa L.

Pollen grains are male gametophytes, an ephemeral haploid generation of plants, commonly engaging in competition for a limited supply of ovules. Since differential male fertility may influence the direction and pace of population evolution, the relative fitness of pollen is regularly estimated as either pollen viability, the proportion of pollen containing intact cytoplasms and regenerative nuclei, or pollen fertility, the frequency of pollen germinating under standardized conditions. Here, we estimated the relative fitness of pollen in a dioecious, wind-pollinated model system, Cannabis sativa, by characterizing pollen fertility and viability from multiple sires. Pollen fertility quickly declined within two weeks of anther dehiscence, and pollen stored under freezer conditions did not germinate regardless of storage time. In contrast, pollen viability declined slowly and persisted longer than the lifetime of a sporophyte plant under both room temperature and freezer conditions. Pollen samples that underwent both fertility and viability analysis displayed no significant correlation, implying researchers cannot predict pollen fertility from pollen viability, nor infer male gametophytic fitness from a single measure. Our work demonstrates two approaches to measure proxies of male fitness in C. sativa, and identifies new questions around what are valuable estimates of male fitness in plants.