Patterns of Mean Nuclear DNA Content in Microseris douglasii (Asteraceae) Populations

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Abstract
We measured DNA content of 210 plants of Microseris douglasii collected between 1980 and 1982 representing 10 populations. One major site, Parkfield-Coalinga, had a mixture of plants with a low to high DNA content in 1977, the last year of a major California drought. Collections in 1980-1982 showed an increase in mean DNA content and a reduction in variation. No differences in DNA content were detected among plants growing in different microsite habitats. Since 1978-1982 were years of generally abundant rainfall, these results are compatible with the hypothesis that increased moisture availability may be conducive to selection for higher DNA amounts. At a second site, Jolon, temporal shifts were observed from low DNA amount in the drought year of 1962 to high DNA values in 1973, and back to low DNA content in 1977. All plants of the general collections of 1980-1982 had low DNA amounts. Some high-DNA plants were detected by selectively sampling for extremely robust growth forms. The population, therefore, contained a mixture of DNA content biotypes and had not increased in mean DNA content during the improved moisture regime of 1978-1982. At a third major site, Middletown, mean DNA content was high in 1977 and decreased in 1980 and 1981. Except for one very small population, all plants growing on serpentine outcrops with poorly developed soil had low DNA. In sites where populations traversed serpentine and heavy clay substrates, all plants had similar DNA. Plants of six relatively high DNA content biotypes were grown under severely stressed growth-chamber conditions. The mean DNA content of progeny of stressed plants of each biotype was only slightly (av. = 0.8%) lower than, and the variance was similar to, that of controls.