Maternal effects of flowering time phenology in Campanula americana

Galloway, L. F., and K. S. Burgess. 2009. Manipulation of flowering time: phenological integration and maternal effects. Ecology 90: 2139-2148. (pdf reprint)
Abstract. – Timing of flowering is central to reproductive success and is currently advancing in many natural populations due to a warmer climate. However, we have little understanding of how earlier initiation of flowering influences subsequent reproductive phenology or the expression of traits in the offspring. To evaluate the consequences of an altered flowering phenology we manipulated cohorts of Campanulastrum americanum , an herb with annual and biennial growth forms, to flower and disperse seeds up to a month earlier, at the same time, and up to a month later than a natural population in two separate years. Relative to the date of first flower, the temporal patterns of flower production, and the timing of fruit maturation and seed dispersal were similar among individuals that initiated flowering over the expanded reproductive season, indicating strong phenological integration of reproductive traits. However, plants that initiated flowering substantially outside the natural window showed a change in the rate of reproduction, with a compressed reproductive schedule for early flowering individuals and an expanded one for late flowering plants. Changes in flowering time had more dramatic effects on the offspring generation. Initiation of flowering two weeks earlier would result in a four-fold increase in the frequency of annual offspring and four weeks earlier a ten-fold increase. The frequency of annuals was less sensitive to modest delays in flowering time but decreased with greater delays in flowering time. Collectively, these results reveal a tightly integrated reproductive phenology that shifts with timing of flowering within generations but may lead to more dramatic responses to climate change between generations.

Burgess, K. S., J. R. Etterson, and L. F. Galloway. 2007. Artificial selection shifts flowering phenology and other correlated traits in an autotetraploid herb. Heredity 99: 641-648. (pdf reprint)
Abstract.– There is mounting evidence that plants are responding to anthropogenic climate change with shifts in flowering phenologies. We conducted a three-generation artificial selection experiment on flowering time in Campanulastrum americanum , an autotetraploid herb, to determine the potential for adaptive evolution of this trait as well as possible costs associated with enhanced or delayed flowering. Divergent selection for earlier and later flowering resulted in a 25-day difference in flowering time. Experiment-wide heritability was 0.31 and 0.23 for the initiation of flowering in early and late lines, respectively. Selection for earlier flowering resulted in significant correlated responses in other traits including smaller size, fewer branches, smaller floral displays, longer fruit maturation times, fewer seeds per fruit and slower seed germination. Results suggest that although flowering time shows the potential to adapt to a changing climate, phenological shifts may be associated with reduced plant fitness due to maladaptive correlated responses.

Galloway, L. F. 2002. The effect of maternal phenology on offspring life history in the herbaceous plant Campanula americana. Journal of Ecology 90: 851-858. (pdf reprint)
Summary
1.  An individual’s phenotype may influence the expression of traits in its offspring. I tested whether maternal flowering phenology influenced offspring germination and thus life history schedule in two populations of Campanula americana. Fall germinating C. americana grow as annuals while individuals that germinate in the spring are biennials.
2.  Under near-natural conditions, early-season flowers produced seeds that were more likely to germinate in the fall than late-season flowers, but spring germination was equally likely for all seeds.
3.  Seed mass (two of three years) and percentage and timing of germination under constant environmental conditions (all three years) did not vary across the reproductive season. External environmental factors are therefore more likely to contribute to seasonal changes in the probability of germinating in the fall than are the characteristics of the seeds.
4.  The frequency of annual offspring varied among maternal plants. The association between the time a flower was open and offspring germination season suggests that evolution of life history schedule may be accomplished by altering maternal flowering phenology.
5.  The association between the time of a flower’s anthesis and its fruit maturation was weaker in two years when water was limiting. Limited water also resulted in earlier seed maturation, and consequently a greater proportion of a population’s seed being produced during the period when fall germination was likely. This, in combination with differences between populations, suggests that the magnitude of maternal phenological effects varies across years and populations.

Return to Galloway lab home page