Evol Ecol Res 5: 571-587 (2003)     Full PDF if your library subscribes.

Optimal resource allocation explains growth

curve diversity in zebra mussels

Marcin Czarnołęski,¹* Jan Kozłowski,¹ Anna Stańczykowska² and Krzysztof Lewandowski²

¹Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 3, 30-387 Kraków and ²Institute of Biology, University of Podlasie, Prusa 12, 08-110 Siedlce, Poland

Author to whom all correspondence should be addressed.
e-mail: czarn@eko.uj.edu.pl

ABSTRACT

We analysed data on zebra mussels (Dreissena polymorpha) from 19 European populations characterized by diverse production and mortality conditions revealing remarkable spatial differences in the shape of Bertalanffy’s growth curves. An optimization approach to life-history evolution predicts that differences in the pattern of growth reflect shifts in resource allocation maximizing lifetime fitness under different production and mortality rates. We examine the relationships of Dreissena growth curves to the production and mortality rates in the populations, and then compare them with the life-history patterns predicted by a model of optimal resource allocation to growth and reproduction. In accord with the model, Bertalanffy’s growth rate parameter (k) increased and the asymptotic size (L_max) decreased with rising mussel mortality rate. Contrary to expectations, the parameter k rose and the asymptote L_max dropped with the increase in the production rate. The predictive power of the model increased after including consequences of fouling of older mussels by younger conspecifics. We assumed that overgrowth, intensifying with better food conditions in a habitat, alters the size specificity of biomass production and accelerates age-dependent mortality. The assumption is supported by the positive relation of mortality to the production rate index in the empirical data. The results indicate that zebra mussels optimally allocate resources under different mortality and production rates modified by overgrowth. We argue that the noticeable life-history polymorphism in this invasive species may be adaptive.

Keywords: Bertalanffy’s growth curves, Beverton and Holt’s pattern, bioenergetic model, bivalves, body size, Dreissena polymorpha, fouling, growth, life-history evolution, mortality.

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