Understanding Evolutionary Impacts of Seasonality: An Introduction to the Symposium

Seasonality is a critically important aspect of environmental variability, and strongly shapes all aspects of life for organisms living in highly seasonal environments. Seasonality has played a key role in generating biodiversity, and has driven the evolution of extreme physiological adaptations and behaviors such as migration and hibernation. Fluctuating selection pressures on survival and fecundity between summer and winter provide a complex selective landscape, which can be met by a combination of three outcomes of adaptive evolution: genetic polymorphism, phenotypic plasticity, and bet-hedging. Here, we have identified four important research questions with the goal of advancing our understanding of evolutionary impacts of seasonality. First, we ask how characteristics of environments and species will determine which adaptive response occurs. Relevant characteristics include costs and limits of plasticity, predictability, and reliability of cues, and grain of environmental variation relative to generation time. A second important question is how phenological shifts will amplify or ameliorate selection on physiological hardiness. Shifts in phenology can preserve the thermal niche despite shifts in climate, but may fail to completely conserve the niche or may even expose life stages to conditions that cause mortality. Considering distinct environmental sensitivities of life history stages will be key to refining models that forecast susceptibility to climate change. Third, we must identify critical physiological phenotypes that underlie seasonal adaptation and work toward understanding the genetic architectures of these responses. These architectures are key for predicting evolutionary responses. Pleiotropic genes that regulate multiple responses to changing seasons may facilitate coordination among functionally related traits, or conversely may constrain the expression of optimal phenotypes. Finally, we must advance our understanding of how changes in seasonal fluctuations are impacting ecological interaction networks. We should move beyond simple dyadic interactions, such as predator prey dynamics, and understand how these interactions scale up to affect ecological interaction networks. As global climate change alters many aspects of seasonal variability, including extreme events and changes in mean conditions, organisms must respond appropriately or go extinct. The outcome of adaptation to seasonality will determine responses to climate change

File of individual observations from published studies

These data were collected from the original publications

Data from: Does selfing or outcrossing promote local adaptation?

The degree to which plants self-fertilize may impact their potential for genetic adaptation. Given that the mating system influences genetic processes within and among populations, the mating system could limit or promote local adaptation. I conducted a literature survey of published reciprocal transplant experiments in plant populations to quantify the effect of mating system on the magnitude of local adaptation. Mating system had no effect on local adaptation. I detected no effect when species were categorized as either self-compatible or self-incompatible or when accounting for environmental differences between source populations. The results suggest that, despite limited genetic variation in selfing species and greater potential for gene flow in outcrossing species, mating system has little influence on adaptation of populations

Data from: Variance and variability, uncovering an underappreciated component of reproductive isolation

Estimating the fitness of line crosses has been a key element in studies of inbreeding depression, hybridization, and speciation. Fitness values are typically compared using differences in the arithmetic mean of a fitness component between types of crosses. One aspect of fitness that is often overlooked is variance in offspring fitness over time. In the majority of studies, ignoring this aspect of fitness is unavoidable because it is impossible to estimate variance in offspring fitness over long time periods. Here, I describe a method of estimating variance in offspring fitness by substituting spatial variation for temporal variation and provide an empirical example. The method is based on Levene's test of homogeneity of variances. It is implemented by quantifying differences in residual variation among cross types. In a previous study, I performed crosses between populations of the annual plant Diodia teres and quantified hybrid fitness. In this study, another component of isolation and heterosis was revealed when considering variance in offspring fitness. When taking into account variance in offspring fitness using geometric mean fitness as the measure of performance, hybrids between populations from different habitats showed less heterosis than when calculating fitness based on arithmetic mean. This study demonstrates that variance in offspring fitness can be an important aspect of fitness that should be measured more frequently

Data from: Genetic divergence for physiological response to temperature between populations of a C3-C4 intermediate annual

Premise of research. Local adaptation ultimately arises as a result of adaptive divergence in phenotypic characters. Within a species, a large portion of the phenotypic traits that confer local adaptation must be physiological characters. Yet few studies consider adaptive divergence in physiological characters or estimate genetic variation within populations for physiological traits that may confer local adaptation. Here I test the hypothesis that there is genetic variation within and between populations of a C3-C4 intermediate for the CO2 compensation point (Γ) and other photosynthetic traits. In addition to local adaptation, population-level variation in photosynthetic characters of C3-C4 intermediates reflects the potential for evolution of more C4-like photosynthesis. Methodology. I chose two populations of Mollugo verticillata, one from a relatively cool climate and one from a warm climate. I quantified variation within and between populations by measuring photosynthetic physiology at 24° and 35°C, temperatures that match the average maximums during the growing season at the populations’ native sites. Pivotal results. I detected little evidence of genetic variation within populations for Γ and carboxylation efficiency, but there was temperature-dependent population variation for Γ, where the population from the cool climate had a lower average Γ at 24°C. Apparent chlorophyll concentration was also greater in this population at both temperatures. Conclusions. The results demonstrate that there has been divergence among populations in Γ. Interestingly, the population from the cooler climate had lower Γ at 24°C. There is little evidence of adaptive evolutionary potential within populations; estimates of broad-sense heritability were not significant even when pooling samples from both populations to increase the overall sample size. Adaptation of more C4-like photosynthesis may proceed through the evolution of other physiological characters not directly related to concentrating carbon

CE_data

Data on Carboxylation efficiency for each maternal family (genotype) at each temperature in each generation of the experiment. Families with an n are from Nicasio and those with an s are from Folsom Lak

varfit-data

The data file of fruit se