Polyploidy and body size variation in a natural population of the rotifer Euchlanis dilatata

Abstract

Polyploidy has been reported in many plant species and in some animal species (reviewed by Lewis, 1980 and Suomalainen et al., 1987, respectively). A common consequence of polyploidy in plants is an increase in size (Lewis, 1980; Tal, 1980; Levin, 1983). In animals, most of the studies supporting this generalization are based on comparisons of body sizes of individuals from different populations. In this case, body size variation may reflect environmental differences to which populations of different ploidy are adapted. Very few comparisons of sympatric diploid and polyploid individuals are available either to support or counter this generalization. In Artemia parthenogenetica, pentaploids are larger than sympatric diploids (Wang, 1988). However. in the unisexual fish Poeciliopsis monachu-lucida triploids usually grow more slowly and have a smaller body size than sympatric diploids (Schultz, 1982). In rotifers, interpopulation variation in body size among geographically or temporally separated populations may have a genetic basis (King and Serra, 1980; Yufera, 1982; Serra and Miracle, 1983; She11 and Carrillo, 1984). Morales ( 1987) surveyed lakes in the Sierra Nevada, Spain, and found considerable body size variation in Euchlunis dilatata among the lakes. Morales-Baquero (1988) quantified this variation morphometrically for E. d&tutu from 70 populations. He reported body sizes ranging from 177 pm-340 pm in length and from 125 pm-270 pm in width. He concluded that interlake variation was a more important determinant of body size than intralake factors and hypothesized that these differences might have a genetic basis. The genetic basis underlying body size variation has not previously been investigated in any rotifer. One of us (EJW) noted substantial intrapopulational body size variation in E. dilatata collected from Devils Lake (Lincoln County, Oregon), with animals of two distinct body sizes found during 12 months of intensive sampling. Animals with the