Aquatic insect ecophysiological traits reveal phylogenetically based differences in dissolved cadmium susceptibility

doi:10.1073/pnas.0801686105

Aquatic insect ecophysiological traits reveal phylogenetically based differences in dissolved cadmium susceptibility

*Department of Environmental and Molecular Toxicology, Campus Box 7633, North Carolina State University, Raleigh, NC 27604;
^‡Water Resources Division, U.S. Geological Survey, 345 Middlefield Road, MS 465, Menlo Park, CA 94025; and
^§Department of Biology, University of California, Riverside, CA 92521

Edited by George N. Somero, Stanford University, Pacific Grove, CA, and approved April 28, 2008 (received for review February 20, 2008)

Abstract

We used a phylogenetically based comparative approach to evaluate the potential for physiological studies to reveal patterns of diversity in traits related to susceptibility to an environmental stressor, the trace metal cadmium (Cd). Physiological traits related to Cd bioaccumulation, compartmentalization, and ultimately susceptibility were measured in 21 aquatic insect species representing the orders Ephemeroptera, Plecoptera, and Trichoptera. We mapped these experimentally derived physiological traits onto a phylogeny and quantified the tendency for related species to be similar (phylogenetic signal). All traits related to Cd bioaccumulation and susceptibility exhibited statistically significant phylogenetic signal, although the signal strength varied among traits. Conventional and phylogenetically based regression models were compared, revealing great variability within orders but consistent, strong differences among insect families. Uptake and elimination rate constants were positively correlated among species, but only when effects of body size and phylogeny were incorporated in the analysis. Together, uptake and elimination rates predicted dramatic Cd bioaccumulation differences among species that agreed with field-based measurements. We discovered a potential tradeoff between the ability to eliminate Cd and the ability to detoxify it across species, particularly mayflies. The best-fit regression models were driven by phylogenetic parameters (especially differences among families) rather than functional traits, suggesting that it may eventually be possible to predict a taxon's physiological performance based on its phylogenetic position, provided adequate physiological information is available for close relatives. There appears to be great potential for evolutionary physiological approaches to augment our understanding of insect responses to environmental stressors in nature.

Footnotes

^†To whom correspondence should be addressed. E-mail: david_buchwalter{at}ncsu.edu
Author contributions: D.B.B. and S.N.L. designed research; D.B.B., D.J.C., C.A.M., and L.X. performed research; D.B.B. and T.G. analyzed data; and D.B.B. and T.G. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0801686105/DCSupplemental.