Evol Ecol Res 6: 147-161 (2004)     Full PDF if your library subscribes.

Regulation of propagule size in the aquatic pseudo-annual Potamogeton pectinatus: are genetic and maternal non-genetic effects additive?

Helen H. Hangelbroek1,2* and Luis Santamaría1

1Department of Plant–Animal Interactions, Netherlands Institute of Ecology (NIOO-KNAW), Rijksstraatweg 6, 3631 AC Nieuwersluis and  2Department of Ecology, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands

Address all correspondence to Helen H. Hangelbroek, Department of Ecology, Evolution and Behavior, University of Minnesota, 1987 Upper Bufurd Circle, 100 Ecology Building, St. Paul, MN 55108, USA.
e-mail: hange001@umn.edu


Genetic and maternal non-genetic effects interact in shaping the phenotype of a particular trait. The strength of the genetic component determines whether selection pressure results in evolutionary changes in the population. The strength of the maternal non-genetic component can affect the pace of selection. In this study, we analysed genetic and maternal propagule size effects on propagule size production in the pondweed Potamogeton pectinatus. In particular, we analysed whether they interact significantly (i.e. whether both effects are additive, synergistic or antagonistic) and how they may influence the outcome of diversifying selection pressures in the field. Fifteen clones differing in the genetically determined size of asexual propagules (tubers) were grown for three asexual generations in a common-garden set-up. The first generation was grown from tubers collected from the field, the second from maternal tubers of comparable size, and the last from both small and large maternal tubers. Maternal tuber size had a large effect on all clones that was independent of their genetically determined tuber size – that is, genetic and maternal non-genetic effects were additive. Path analysis revealed that maternal tuber size affected tuber size and number similarly through its effect on biomass production (vegetative and total tuber production), while the genetic component had a direct effect on tuber size, associated with a trade-off with tuber number. Because the relationship between genetic and maternal non-genetic effects is additive, the outcome of diversifying selection related to tuber predation pressure by Bewick’s swans and sediment heterogeneity will not be affected. However, since the maternal effect is large, variation around optimal sizes is likely to persist in the population, which is consistent with what is found in the field.

Keywords: carry-over effects, fennel pondweed, propagule size, size–number trade-off, tuber size.

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