Form, function

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 AM University
When DO is low, my gills grow large, and I
breathe like this.
Diversification of the African cyprinid Barbus
neumayeri 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
Barbus neumayeri
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, WFs 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 621243-1251), 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).