GENOTYPE ENVIRONMENT INTERACTIONS AND RELATIVE CLONAL FITNESS IN A MARINE BRYOZOAN

1. Several hypotheses for the adaptive basis of sex assume that genotypic fitness varies according to location in a spatially or temporally heterogeneous environment. This study aimed to measure genotype-environment interactions in fitness-related traits, and to compare locality and time as sources of interaction. 2. Clones of the bryozoan Celleporella hyalina were artificially propagated to give cohorts of genetically identical colonies which were reared in the field under three different water flow treatments, and over two seasonal periods. 3. The total number of zooids per colony, and the number of gonozooids alone, were both used as indices of clonal performance, measured at the end of each seasonal experiment. 4. By both zooid scores, clones varied greatly in mean performance, and thus in fitness. Correlations between fitness ranking in different environments were mostly positive, but many clones did show large shifts in rank order between environments. In autumn-winter some clones were of consistently high or low fitness in all three flow treatments, despite large treatment differences in mean zooid productivity. 5. Seasonal differences had a greater effect on fitness ranking than flow regime. This pattern was more pronounced when gonozooid number was used as the index of performance. 6. Disparities in clonal performance were reduced in the least productive environments. These conditions caused a greater reduction in performance in genotypes of high average fitness. 7. The performance of an individual clone within an environment was not always constant. In spring-summer, replicate colonies often differed considerably in growth rate, even when growing closely adjacent to each other. 8. The results illustrate the need for precise definitions of fitness, and for further experimental work to determine the niche breadth of individual clones and thus the relative intensity of competition within and between genotypes.