Disentangling complex phenotype-environment relationships—

1. R. Brian Langerhans1, Lauren J. Chapman2, Thomas J. DeWitt3 Disentangling complex phenotype-environment relationships— 1Dept. Biology, Washington University (presently at U. Oklahoma) 2Biology Dept., McGill University 3Dept. Wildlife & Fisheries Sciences, Texas A&M University When DO is low, my gills grow large, and I breathe like this. Diversification of the African cyprinid Barbusneumayeri across water flow and oxygen gradients 4. Results The principle body shape variation we found involved a shift from low-bodied, small-headed fish to the opposite morphology (figure). 1. Natural history This barb inhabits a range of systems within the African rift lake basins, from dense swamps to fast flowing rivers, habitats that vary dramatically in water flow (WF) and dissolved oxygen (DO). Because DO is generally positively related to WF, it can be difficult to separate effects of the two variables as they impact aquatic organisms. However, in our study system, much of the water flows through papyrus swamps that due to heavy metabolic oxygen demand, can strip oxygen from even fast flowing water. This effect creates a factorial combination of WF and DO. Player: U - 0.78 0.72 Water velocity Dissolved oxygen Gill size Barbusneumayeri U - 0.01 1.69 1.08 2. Concepts Environmental factors influence phenotypes directly, as well as indirectly. Indirect effects manifest due to trait correlations and interactions with other environmental factors. Often phenotype-environment correlations are adaptive. Yet it is reasonable to expect adaptation for one environmental factor may constrain or be variously correlated with other factors, or their phenotypic effects. Such intercorrelations make it difficult to interpret simple correlations between trait and environment.. For example, one might expect a relationship between WF and body shape due to adaptation for hydrodynamic efficiency. Ultimately however, the story was more complex in our study: we found that, WF’s direct effect on body shape was equally countered by a chain of indirect effects, where increased WF increased DO, leading to decreased gill size, and reduced head size. This resulted in no total effect of WF on body shape. In the present study (published in J Evol Biol 62:1243-1251), we employed path analysis to examine direct, indirect and total effects of WF and DO on morphological traits of the barb, B. neumayeri. Body shape 0.60 U 0.95 Path model & results Caudal fin shape U 5. Conclusions WF and DO influenced relative gill size, body shape and caudal fin shape in manners consistent with a priori predictions. Indirect effects were also noted: (1) strong, oppositely signed direct and indirect effects of WF on body shape resulted in a nonsignificant total effect; (2) DO had no direct effect on body shape, but a strong total effect via indirect effects on gill size; (3) WF indirectly influenced gill size via effects on DO. Only through examination of multiple environmental parameters and multiple traits can we hope to understand complex relationships between environment and phenotype. 3. Methods We collected fish from nine populations (map) that varied in DO and WF, for which we have monthly data over multiple years). We measured specimen morphology using geometric and traditional morphometrics (picture) and performed path analysis to determine interrelationships among environmental and ecomorphological variables. River Papyrus swamp Swamp/river ecotone Funded by EPA STAR and Society of Wetland Scientists (RBL) NSF (IBN0094393 to LJC; DEB0344488 to TJD), Wildlife Conservation Society (LJC).