Examining the community-level influence of local adaptation in an invasive habitat-forming bryozoan

Background/Question/Methods

In a world undergoing drastic environmental changes, understanding the ecological and evolutionary processes shaping species diversity across environments has become a major issue for ecologists. For foundation species, genetic diversity and local adaptations may have direct or indirect effects on community diversity. Here we use a fouling invertebrate that serves as a foundation species for other invertebrates to address two questions: (1) Is there evidence of local adaptation to different regions of California? (2) If so, does local adaptation influence the diversity of the surrounding community? We focus on Watersipora subtorquata, an invasive bryozoan (colonial animal) that invaded southern California around 1980; it has since spread across the coastline, providing a suitable model for understanding the feedbacks between facilitation and community structure. To determine whether Watersipora exhibits local adaptation, I performed a reciprocal transplant experiment with settlement tiles (n=160) at four sites in the extremes of California’s four isotherms. We conducted biweekly photo sampling to measure several traits of Watersipora. After three months, the tiles were collected, and the change in colony mass was used as an estimate of fitness and a measure of local adaptation. To determine the effects on community diversity, we also assessed the mobile and sessile species diversity on and around Watersipora.

Results/Conclusions

Reciprocal transplants provided evidence of Watesripora’s local adaptation. The fitness of Watersipora colonies in each region was dependent on the site of origin of the colony. Additionally, the fitness of each clone had a significant effect on the diversity of the associated invertebrate community. In addition to genotype, latitude had a significant effect on species diversity. The effect of Watersipora on species diversity was largely dependent on colony structural heterogeneity. While Watersipora has been found to serve as a non-toxic recruitment surface on the hulls of ships using anti-fouling paints, it does not seem to be a preferred substratum for sessile organisms under natural conditions. The dynamics of Watersipora are particularly interesting because in addition to being a widespread introduced species, it also functions as a foundation species, providing secondary habitat and settlement substrate to the community. Our results suggest that understanding the extent to which local diversity variation and adaptation reflect eco-evolutionary feedbacks will be crucial for determining the forces ultimately affecting community structure.