disentangling complex phenotype-environment relationships—

Disentangling complex phenotype-Disentangling complex phenotype-environment relationships—environment relationships—

R. Brian LangerhansR. Brian Langerhans11, , Lauren J. ChapmanLauren J. Chapman22, Thomas J. DeWitt, Thomas J. DeWitt33

Diversification of the African cyprinid Diversification of the African cyprinid Barbus neumayeriBarbus neumayeri across water flow and oxygen gradientsacross water flow and oxygen gradients

Funded by EPA STAR and Society of Wetland Scientists (RBL) Funded by EPA STAR and Society of Wetland Scientists (RBL) NSF (IBN0094393 to LJC; DEB0344488 to TJD), Wildlife Conservation Society (LJC).NSF (IBN0094393 to LJC; DEB0344488 to TJD), Wildlife Conservation Society (LJC).

2. Concepts2. ConceptsEnvironmental factors influence phenotypes directly, as well as Environmental factors influence phenotypes directly, as well as indirectly. Indirect effects manifest due to trait correlations and indirectly. Indirect effects manifest due to trait correlations and interactions with other environmental factors. Often phenotype-interactions with other environmental factors. Often phenotype-environment correlations are adaptive. Yet it is reasonable to expect environment correlations are adaptive. Yet it is reasonable to expect adaptation for one environmental factor may constrain or be variously adaptation for one environmental factor may constrain or be variously correlated with other factors, or their phenotypic effects. Such correlated with other factors, or their phenotypic effects. Such intercorrelations make it difficult to interpret simple correlations intercorrelations make it difficult to interpret simple correlations between trait and environment.. For example, one might expect a between trait and environment.. For example, one might expect a relationship between relationship between WF and body shape due to adaptation for and body shape due to adaptation for hydrodynamic efficiency. Ultimately however, the story was more hydrodynamic efficiency. Ultimately however, the story was more complex in our study: we found that, complex in our study: we found that, WF’s direct effect on body shape ’s direct effect on body shape was equally countered by a chain of indirect effects, where increased was equally countered by a chain of indirect effects, where increased WF increased increased DO, leading to decreased gill size, and reduced head , leading to decreased gill size, and reduced head size. This resulted in size. This resulted in no total effect of no total effect of WF on body shape on body shape. .

In the present study (published in J Evol Biol 62:1243-1251), we In the present study (published in J Evol Biol 62:1243-1251), we employed path analysis to examine direct, indirect and total effects of employed path analysis to examine direct, indirect and total effects of WF and and DO on morphological traits of the barb, on morphological traits of the barb, B. neumayeriB. neumayeri. . 3. Methods3. MethodsWe collected fish from nine populations (We collected fish from nine populations (map) that varied in ) that varied in DO and and WF, for which we have monthly data over multiple years). We measured specimen morphology using geometric and monthly data over multiple years). We measured specimen morphology using geometric and traditional morphometrics (traditional morphometrics (picture) and performed path analysis to determine interrelationships ) and performed path analysis to determine interrelationships among environmental and ecomorphological variables.among environmental and ecomorphological variables.

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5. Conclusions5. ConclusionsWF and and DO influenced relative gill size, body shape and caudal fin shape in influenced relative gill size, body shape and caudal fin shape in manners consistent with manners consistent with a prioria priori predictions. Indirect effects were also noted: (1) predictions. Indirect effects were also noted: (1) strong, oppositely signed direct and indirect effects of strong, oppositely signed direct and indirect effects of WF on body shape resulted on body shape resulted in a nonsignificant total effect; (2) in a nonsignificant total effect; (2) DO had no direct effect on body shape, but a had no direct effect on body shape, but a strong total effect via indirect effects on gill size; (3) strong total effect via indirect effects on gill size; (3) WF indirectly influenced gill indirectly influenced gill size via effects on size via effects on DO. Only through examination of multiple environmental . Only through examination of multiple environmental parameters and multiple traits can we hope to understand complex relationships parameters and multiple traits can we hope to understand complex relationships between environment and phenotype.between environment and phenotype.

1. Natural history1. Natural historyThis barb inhabits a range of systems within the This barb inhabits a range of systems within the African African rift lake basins, from dense swamps to from dense swamps to fast flowing rivers, habitats that vary dramatically fast flowing rivers, habitats that vary dramatically in water flow (in water flow (WF) and dissolved oxygen () and dissolved oxygen (DO). ). Because Because DO is generally positively related to is generally positively related to WF, , it can be difficult to separate effects of the two it can be difficult to separate effects of the two variables as they impact aquatic organisms. variables as they impact aquatic organisms. However, in our study system, much of the water However, in our study system, much of the water flows through papyrus swamps that due to heavy flows through papyrus swamps that due to heavy metabolic oxygen demand, can strip oxygen from metabolic oxygen demand, can strip oxygen from even fast flowing water. This effect creates a even fast flowing water. This effect creates a factorial combination of factorial combination of WF and and DO..

Water velocity

U

U

0.72 - 0.78

1.69 1.08 - 0.01

U

0.60

0.95

U

Dissolved oxygen

Gill size

Body shape

Caudal fin shape

11Dept. Biology, Washington University (presently at U. Oklahoma)Dept. Biology, Washington University (presently at U. Oklahoma)22Biology Dept., McGill UniversityBiology Dept., McGill University

33Dept. Wildlife & Fisheries Sciences, Texas A&M UniversityDept. Wildlife & Fisheries Sciences, Texas A&M University

4. Results4. ResultsThe principle body shape variation we found involved a shift from low-The principle body shape variation we found involved a shift from low-bodied, small-headed fish to thebodied, small-headed fish to theopposite morphology (opposite morphology (figure).).

PapyrusPapyrusswamp swamp

Swamp/riverSwamp/riverecotone ecotone

RiverRiver

Barbus neumayeriBarbus neumayeri

When DO is low, my gills grow large,

and I breathe like this.