Maternal and paternal environmental effects in Campanulastrum americanum

Galloway, L. F., and J. R. Etterson. 2009. Plasticity to canopy shade in a monocarpic herb: within- and between-generation effects. New Phytologist 182: 1003-1012. (reprint here)
Summary.
•  Plants exhibit plasticity in response to their current environment, and in some cases, to that of the previous generation (i.e. maternal effects). However, few studies have evaluated both within- and between-generation plasticities and the extent to which they interact to influence fitness, especially in natural environments.
•  The plasticity of adult traits to two generations of natural differences in light was determined for Campanulastrum americanum, a forest-edge herb that expresses annual and biennial life histories.
•  Plasticity was found to an individual's light environment (within generation) and the maternal light environment (between generations). Responses to ambient light for size traits and timing of flowering were likely passive, whereas apparently adaptive responses were found for light acquisition traits. Maternal light influenced the expression of most adult traits but had the strongest effect when plants were germinated in natural environments.
•  The transgenerational effects of light were consistent with adaptive plasticity for several traits. Plastic within-generation changes in flowering time may also result in adaptive between-generation effects by altering offspring life history schedule. Finally, the results underscore the importance of conducting studies of within- and between-generation plasticity in natural populations, where the environmental context is relevant to that in which the traits evolved .

Galloway, L. F. and J. R. Etterson. 2007. Transgenerational plasticity is adaptive in the wild. Science, 318: 1134-1136. (reprint available on this page)
Abstract. – Plants exhibit adaptive responses to light, but it is not known whether parental plants transmit environmental cues that elicit adaptive responses in offspring. We show that offspring life history (annual versus biennial) is influenced by the maternal light environment (understory versus light gap). This transgenerational plasticity is adaptive when offspring are grown in their maternal light environment, where seeds typically disperse. Projections of population growth show that plants that are appropriately cued for their light environment through maternal effects have 3.4 times greater fitness than otherwise. Transgenerational plasticity has evolved in response to natural variation in light and provides a flexible mechanism by which sedentary organisms cope with heterogeneous environments.

Galloway, L. F. 2005. Maternal effects provide phenotypic adaptation to local environmental conditions. New Phytologist 166: 93-100. (pdf reprint)
Summary. In outcrossing plants seed dispersal is often less than pollen movement. If environmental heterogeneity within a population is greater than the scale of seed dispersal but less than that of pollen movement, an individual's environment will be similar to that of its mother but not necessarily its father. Under these conditions environmental maternal effects may evolve as a plastic source of local adaptation. This idea is illustrated using Campanula americana , an herb found in understory and light-gap habitats. Seed dispersal is limited and therefore offspring typically experience their maternal light environment. Maternal light influences offspring fitness; in the fall twice as many seeds germinated when planted into their maternal light environment. In addition, light-gap plants flower before understory plants. Because early produced seeds germinate in the fall and fall germinating individuals are annuals while spring germinating seeds are biennials, maternal light environment can influence offspring life history. This attention to the ecological context in which maternal effects are expressed provides an understanding of how plastic response to local environments may provide a source of adaptation.

Etterson, J. R. and L. F. Galloway. 2002. The influence of light on paternal plants in Campanula americana (Campanulaceae): pollen characteristics and offspring traits. Am. J. Bot. 89: 1899-1906. (pdf reprint)
Abstract. – Offspring trait expression is determined by the combination of parental genes and parental environments. Although maternal environmental effects have been widely characterized, few studies have focused on paternal environmental effects. To determine whether light availability influences pollen and offspring traits in the woodland herb Campanula americana, we reared clones of 12 genotypes in two light levels. In the parental generation we measured pollen number and size. Plants grown under high light produced more pollen grains per flower than those grown under low light. However, the response was genotype specific; some individuals responded little to changes in light availability while others substantially reduced pollen production. As a consequence, paternity ratios may vary between light environments if more pollen is associated with greater siring success.  We crossed a subset of these plants to produce the offspring generation. The paternal and maternal light environments influenced offspring seed mass, percentage germination, and days to germination, while only maternal light levels influenced later life traits, such as leaf number and size.  Maternal and paternal environmental effects had opposite influences on seed mass, percentage germination and days to germination. Finally, there was no direct relationship between light effects on pollen production and offspring trait expression.

Galloway, L. F. 2001. The effect of maternal and paternal environments on seed characters in the herbaceous plant Campanula americana (Campanulaceae). Am. J. Bot. 88: 832-840. (pdf reprint)
Abstract. – Maternal environments typically influence the phenotype of their offspring. However the affect of the paternal environment or the potential for joint effects of both parental environments on offspring characters is poorly understood. Two populations of Campanula americana, a woodland herb with a variable life history, were used to determine the influence of maternal and paternal light and nutrient environments on offspring seed characters. Families were grown in three levels of light or three levels of nutrients, and crosses were conducted within each environmental gradient to produce seeds with all combinations of maternal and paternal environments. On average, increasing maternal nutrient and light levels increased seed mass and decreased percent germination. The paternal environment affected seed mass, germination time, and percent germination. However, the influence of the paternal environment varied across maternal environments, suggesting that paternal environmental effects should be evaluated in the context of maternal environments. Significant interactions between family and the parental environments for offspring characters suggest that parental environmental effects are genetically variable. In C. americana, the timing of germination determines life history. Therefore parental environmental effects on germination timing, and genetic variation in those parental effects, suggest that parental environments may influence life history evolution in this system.

Galloway, L. F. 2001. Parental environmental effects on life history in the herbaceous plant Campanula americana. Ecology 82: 2781-2789. (pdf reprint)

Abstract. – Although environmental parental effects, especially maternal effects, are well known in plants we have almost no information about their expression in nature. This study explores the influence of maternal and paternal light and nutrient environments on germination characters under natural conditions in the herbaceous plant, Campanula americana. Families were grown in a greenhouse under three levels of light or three levels of nutrients, and crosses were conducted within each environmental gradient to produce seeds with all combinations of maternal and paternal environments. Seeds produced under the controlled environments were planted into the home site of the population and another local site, and germination was monitored over the fall and spring germinating seasons. The paternal light environment influenced percent germination demonstrating that the offspring phenotype may depend on the environment a set of pollen donors is grown in. The effect of maternal nutrient level on percent germination depended on the offspring environment. Percent germination in response to maternal nutrient and paternal light environments varied among families suggesting that these parental environmental effects are genetically variable. Both maternal light and nutrient environments influenced season of germination. Germination season determines life history in C. americana: fall germinating individuals are annuals while spring germinating seed are biennials. Maternal plants grown under low and high light and low nutrient conditions produced more biennial offspring while the remaining maternal environments had an equal frequency of annual and biennial offspring. In C. americana maternal environments influence life history and therefore fitness through their effects on season of germination.

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