Quantitative genetics and the persistence of environmental effects in clonally propagated organisms.

Phenotype is often viewed as a product of genes and the environment in which these genes are expressed. However, numerous studies have shown that environment can cause lasting changes in phenotype that can be passed from one generation to the next, much as genes are transmitted. In clonally propagated organisms, persistence of environmental effects has been observed in a range of plant and animal species, but has rarely been the object of study. We measured the persistence and magnitude of environmental effects on phenotype over three clonal generations in the arctic sedge Eriophorum vaginatum. We found that the environment in which tillers developed had large effects on their later performance (parental effects) and that these effects were in part independent of the size of tillers. The magnitude and persistence of environmental effects did not differ between environmental treatments or among genotypes. However, after 52 weeks of growth and two rounds of clonal propagation, grandparental treatment effects were not significant. We describe methods that can be used in quantitative genetics studies of clonal organisms to reduce bias in estimates of genotypic and environmental variance and argue that the persistence of environmental effects in clonal plant material has ecological and evolutionary consequences similar to those described for maternal environmental effects in sexual organisms.

Maternal sex and mate relatedness affect offspring quality in the gynodioecious Silene acaulis.

In gynodioecious species, females sacrifice fitness by not producing pollen, and hence must have a fitness advantage over hermaphrodites. Because females are obligately outcrossed, they may derive a fitness advantage by avoiding selfing and inbreeding depression. However, both sexes are capable of biparental inbreeding, and there are currently few estimates of the independent effects of maternal sex and multiple levels of inbreeding on female advantage. To test these hypotheses, females and hermaphrodites from six Alaskan populations of Silene acaulis were crossed with pollen from self (hermaphrodites only), a sibling, a random plant within the same population, and a plant from a different population. Germination, survivorship and early growth revealed inbreeding depression for selfs and higher germination but reduced growth in sib-crosses, relative to outcrosses. Independent of mate relatedness, females germinated more seeds that grew faster than offspring from hermaphrodites. This indicates that inbreeding depression as well as maternal sex can influence breeding system evolution. The effect of maternal sex may be explained by higher performance of female genotypes and a greater abundance of female genotypes among the offspring of female mothers.

Allozyme and morphological variation in two subspecies of Dryas octopetala (Rosaceae)in Alaska.

The Alaskan endemic shrub Dryas octopetala ssp. alaskensis and its circumpolar conspecific ssp. octopetala are adapted to closely adjacent habitats in alpine areas of Alaska. These alpine areas form geographically disjunct "islands" among which there are limited opportunities for gene flow. Allozyme electrophoresis and a common garden experiment were used to examine genetic variation between subspecies and among disjunct populations of each subspecies. Overall, allozyme variation in D. octopetala is low with little differentiation among populations or between subspecies. Morphological differences, however, are greater between subspecies than among populations within subspecies. Divergence for a few morphological and life-history characters has apparently occurred in response to strong selection, but without divergence at allozyme loci. The ancestors of both subspecies of D. octopetala in Alaska were isolated during the Pleistocene in the glacial refugia of Alaska and Yukon, which may explain low overall variation. Dryas. o. alaskensis is thought to be a Pleistocene derivative of ssp. octopetala, which may account for the low allozyme divergence between subspecies. Recent restriction to alpine areas may explain the low differentiation among disjunct populations.