From

Evolutionary Ecology Research, 1999, 1: 111–128

© 1999 Gary G. Mittelbach

Variation in feeding morphology between pumpkinseed

populations: Phenotypic plasticity or evolution?

Gary G. Mittelbach,1* Craig W. Osenberg2 and Peter C. Wainwright3‡

These results show that the natural variation in

pharyngeal morphology between these populations of pumpkinseeds is primarily the result of a

plastic response to the environment, rather than a response to selection driven by the environmental

differences.
Thus, although our results provide no evidence of a genetic basis for variation in functional

morphology, the observed phenotypic plasticity represents an important mechanism

that can mould a fish’s morphology to the resource base of a lake. Ultimately, this would be

most adaptive if reduced crushing morphology resulted in the more efficient use of softbodied

prey. To date, we have no evidence for such a trade-off in pumpkinseed, although

work on its sister species, the redear sunfish, has shown that such a trade-off exists (Huckins,

1997; see also Ehlinger, 1990; Schluter, 1995; Robinson et al., 1996, for other examples

of trade-offs).

Robinson et al. (1993) collected pumpkinseeds from the shallow littoral zone

and from rocky outcrops in the open water of Paradox Lake, NY, and found that individuals

from these two areas differed in diet. Pumpkinseeds from rocky outcrops feed on

zooplankton and snails, while those in the littoral zone feed on snails and other bentic

invertebrates. Individuals from the two areas also differed in body shape, gill-raker width

and pectoral fin length. In a common-garden type experiment, Robinson and Wilson (1996)

found that phenotypic plasticity and genetic differentiation accounted for 53 and 14%,

respectively, of the variation in body shape. Therefore, like our study, phenotypic plasticity

was the major factor accounting for morphological variation among pumpkinseeds,

although genetic differentiation also appeared to contribute significantly to the Paradox

Lake polymorphism.

ALSO

Ehlinger, T.J. 1990. Phenotype-limited feeding efficiency and habitat choice in bluegill: Individual

differences and trophic polymorphism. Ecology, 71: 886–896.



Ehlinger, T.J. and Wilson, D.S. 1988. Complex foraging polymorphism in bluegill sunfish. Proc. Natl.

Acad. Sci., 85: 1878–1882.



Lauder, G.V. 1983a. Functional and morphological bases of trophic specialization in sunfishes

(Teleostei, Centrarchidae). J. Morph., 178: 1–21.



Mittelbach, G.G., Osenberg, C.W. and Wainwright, P.C. 1992. Variation in resource abundance

affects diet and feeding morphology in the pumpkinseed sunfish (Lepomis gibbosus). Oecologia,

90: 8–13.



Wainwright, P.C., Lauder, G.V., Osenberg, C.W. and Mittelbach, G.G. 1991b. The functional basis

of intraspecific trophic diversification in sunfishes. In The Unity of Evolutionary Biology (E.C.

Dudley, ed.), pp. 515–528. Portland, OR: Dioscorides Press.



Wainwright, P.C., Lauder, G.V., Osenberg, C.W. and Mittelbach, G.G. 1991b. The functional basis

of intraspecific trophic diversification in sunfishes. In The Unity of Evolutionary Biology (E.C.

Dudley, ed.), pp. 515–528. Portland, OR: Dioscorides Press.