The relationship between environmental variation and genetic variation in Vibrio populations

Background/Question/Methods

An understanding of the origins of genetic variation is essential for understanding evolutionary processes and for developing conservation strategies which might effectively protect biodiversity. Changes in environmental variables (such as light, temperature or nutrients) are often invoked to explain observed large-scale patterns in diversity. Little experimental work has been done, however, to examine directly the role the environment itself may play in the generation of genetic diversity. In addition, few studies are designed to focus on changes in the variance of environmental variables, which in field situations often change simultaneously with the mean at both large and small scales. Rapidly-evolving organisms such as Vibrio allow for experimental manipulation of environmental conditions in either the lab or the field to study potential evolutionary mechanisms generating diversity. Here, we studied, in situ, the relationship between changes in the mean and the variance of light and temperature on the genetic variation of marine Vibrio populations, inhabiting the intertidal anemone Actinia tenebrosa. Genetic variation at different scales was quantified as multivariate dispersion on the basis of a variety of genetic distance measures. Permutation tests were then used to examine the spatial, temporal and environmental factors significantly influencing genetic variation within a PERMANOVA framework.

Results/Conclusions

Vibrio inhabiting Actinia along a gradient of light and temperature in intertidal caves near Auckland showed significantly greater genetic variation in low and medium light environments when compared to high light environments. These results are consistent with the stability hypothesis. The patterns of differences in genetic variation observed depend, however, on the spatial scale at which populations are being compared. The scale-dependence of these findings emphasizes the importance of field-based studies of population genetics. Appropriate field and lab-based experimental designs are required in order to isolate the effects of light vs temperature, and the effects of changes in their mean vs their variance, on genetic variation.