The term phenology is derived from the Greek word phaino meaning to show or to appear. Hence, phenology is defined as the study of the seasonal timing of life cycle events. For plants the seasonal timing of such events can be critical to survival and reproduction. In agriculture the most common failure of introduced crops is the inability to adjust to the seasons imposed by the new, environment (68). In the past few years, interest in the ecology and evolution of timing of life cycle events has grown. Here we review the literature on phenological patterns of germination, flowering, and fruiting (including dispersal).The phenological pattern of any life cycle event can be quantitatively defined as a statistical distribution characterized by such parameters as time of occurrence (onset, mean, mode), duration (range), synchrony (variance), and skewness. For each life cycle event we discuss each parameter for which data are available. Because parameters at one level can contribute to parameters at higher levels, parameters are sometimes related. For example, the degree of synchrony within and among individuals can determine duration at the population level. Therefore, we discuss phenological patterns at the levels of individuals, populations, species, and communities. Also, we use the word phenology in its strict sense of seasonal timing within years; and we address variation among years only when it pertains to the discussion of within-year patterns.The purpose of this review is to present hypotheses about possible evolutionary causes and consequences of different phenological patterns and to discuss the evidence for each hypothesis. We also briefly summarize information about the environmental and genetic controls of timing because these are the proximate factors that can influence the evolution of phenological patterns. We divide our review into four sections. The first three address germination, flowering, and fruiting separately. Each section covers possible selective factors, proximate environmental cues, and genetic determinants of different phenological parameters. The last section focuses on the relationships of germination, flowering, and fruiting, to the whole life cycle of the plant. Here we address possible ecological and evolutionary constraints that may direct the evolution of all life cycle events.Space prevents an exhaustive literature review, particularly of descriptive studies, so we mention representative studies and reviews that provide the reader access to additional literature. We do not address phenological patterns of leaf production (43,146) or the specific methodologies for collecting and analyzing phenological data (151, 194, 20 1). GERMINATIONThe seedling stage is the most vulnerable time in the life cycle of a plant (10 1). Mortality is often severe because small seedlings have minimal capacity for homeostatic responses or physiological retrenchment in the face of unfavorable abiotic or biotic conditions (10). Therefore, the timing of germination should be under strong selection to occu...

Lacey, E. P. (1996) Parental effects in Plantago lanceolata. L. I. A growth chamber experiment to examine pre-and post-zygotic temperature effects. Evolution 50(2): 865-878. In spite of the potential evolutionary importance of parental effects, many aspects of these effects remain inadequately explained. This paper explores both their causes and potential consequences for the evolution of life-history traits in plants. In a growth chamber experiment, I manipulated the pre-and postzygotic temperatures of both parents of controlled crosses of Plantago lanceolata. All offspring traits were affected by parental temperature. On average, low parental temperature increased seed weight, reduced germination and offspring growth rate, and accelerated onset of reproduction by 7%, 50%, 5%, and 47%, respectively, when compared to the effects of high parental temperature. Both pre-and postzygotic parental temperatures (i.e., prior to fertilization vs. during fertilization and seed set, respectively) influenced offspring traits but not always in the same direction. In all cases, however, the postzygotic effect was stronger. The prezygotic effects were more often transmitted paternally than maternally. Growth and onset of reproduction were influenced both directly by parental temperature as well as indirectly via the effects of parental temperature on seed weight and germination. Significant interactions between parental genotypes and prezygotic temperature treatment (G × E interactions) show that genotypes differ in their intergenerational responses to temperature with respect to germination and growth. The data suggest that temperature is involved in both genetically based and environmentally induced parental effects and that parental temperature may accelerate the rate of evolutionary change in flowering time in natural populations of P. lanceolata. The environmentally induced temperature effects, as mediated through G × (prezygotic) E interactions are not likely to affect the rate or direction of evolutionary change in the traits examined because postzygotic temperature effects greatly exceed prezygotic effects. Key words: Germination, growth, life-history evolution, maternal effects, onset of reproduction, parental effects, paternal effects, Plantago lanceolata, pre-and postzygotic effects, seed weight, temperature Article:Parents can influence the phenotypes of their offspring beyond their direct chromosomal contributions. In many circumstances, the parental environment may transcend the generational barrier to alter the phenotypic expression of fitness traits in offspring (see reviews of plants, Rowe

Adaptive phenotypic plasticity in thermally sensitive traits, that is, thermal acclimation, generally increases with increasing latitude and altitude. The presumed explanation is that high-latitude/altitude organisms have evolved greater acclimation ability because of exposure to greater temperature fluctuations. Using a conceptual model of the thermal environment during the reproductive season, we tested this hypothesis against an alternative that plasticity is greater because of increased exposure to specific temperatures that strongly select for thermal acclimation. We examined geographic variation in floral reflectance/color plasticity among 29 European populations of a widespread perennial herb, Plantago lanceolata. Individuals partially thermoregulate reproduction through temperature-sensitive plasticity in floral reflectance/color. Plasticity was positively correlated with latitude and altitude. Path analyses support the hypothesis that the thermal environment mediates these geographic effects. Plasticity declined as seasonal temperature range increased, and it increased as duration of the growing season shortened and as the proportion of time exposed to temperatures favoring thermoregulation increased. Data provide evidence that floral reflectance/color plasticity is adaptive and that it has evolved in response not to the magnitude of temperature variation during the reproductive season but rather to the relative exposure to low temperatures, which favor thermoregulation.

Abstract:Understanding the roles of age and size in the timing of first reproduction or flowering in plants has become a goal for those investigating the evolution of life cycle patterns in general. Here I review the studies that are helping to clarify these roles, and indicate some directions for future research. Article:In plants, the critical life cycle phases are embryo development on the maternal parent, seed growth (or dormancy) independent of the parent, vegetative growth and reproduction ( Fig. I ). Each phase is characterized by a particular rate of resource acquisition and pattern of resource allocation, e.g. to vegetative versus reproductive structures. The time of transition from one phase to the next marks the time when one set of phasespecific acquisition and allocation patterns switches to another set. A plant's zygotic life begins at fertilization. Its vegetative life begins at germination.Time of transition from vegetative growth to reproduction (time of first flowering) has recently received much attention from evolutionary ecologists. This interest began in earnest in the early 1970s at the time that Harper and White published a paper on the demography of plants, which showed that age at first reproduction is delayed as 'lifespan' (really, vegetative life-span) lengthens (Fig. 2). The correlation was clear; the causes of the correlation, however, were not. Because plants often grow indeterminately, vegetative age and size can be strongly correlated. Thus, is time of first reproduction deter-mined by age or size? Size-dependencySize is a good predictor of the onset of flowering in short-lived (mostly biennial) monocarps 2-6 , long-lived monocarps 7-9 , polycarps with long-lived monocarpic ramets 9,10 , other polycarps 11 , and monocarps that sometimes become polycarpic 12 . Size-dependency of onset of reproduction, however, varies greatly among species.Annuals are notably absent from this list. Natural populations of many annuals, even of wild progenitors of crop species, show great variation in the density and size at which they flower 13,14 . In many of these plants, flowering is initiated by an external environmental cue like photoperiod, and individuals respond to the cue independently of size (and independently of density, which strongly determines size).Three factors have probably led to this size-independent behavior in annuals. First, the length of the growing season is usually unpredictable, whether the limiting environmental variable be drought, heat, cold, etc. Second, the quality of the growing season often varies. Third, and most important, annuals by definition lack the ability to survive the period between growing seasons; what is predictable is their death within a year after germination. For all these reasons selection should strongly reduce size-dependency, i.e. reduce the threshold size for flowering such that it seldom determines onset of flowering. This reduction ensures that some seed is set every season, irrespective of the length and quality of the season. Variable seed ...

A reciprocal transplant experiment was conducted to examine several aspects of life—history variation in Daucus carota along its latitudinal range in eastern North America. Seeds collected from natural populations at 36°, 42°, and 45° N were sown onto plots at each of the three latitudes. Marked seedlings were followed for 3 yr to examine (1) genetic and environmental components of variation in growth, survival, and year of reproduction; (2) size and age at time of reproduction; and (3) the roles that density— and age—dependent selection may play in producing the variation in age of reproduction. Mean age of reproduction increased clinally from south to north but showed no pattern of variation among different—aged populations within the same latitude. The clinal variation has likely arisen since the introduction of D. carota into North America in the 17th century and has developed independently of any role that growth rate plays in determining age of reproduction. Density influences age of reproduction both directly and indirectly by affecting plant size. Age—specific survival varied strongly over plot latitude but not among populations planted in the same latitude. The ratio of percent germination and survival of 1—yr—olds to percent survival of 2—yr—olds was °3:1, 0.2:1, and 0.15:1 for plots at 36°, 42°, and 45° N, respectively. The experiment suggests that latitudinal variation in age—specific mortality patterns is helping to maintain clinal variation in age of reproduction. Density—independent factors contribute more strongly to age—specific mortality than do density—dependent factors. Age classes are based on times of peak flowering rather than on times of growing seasons. Such intervals allow for better evolutionary interpretation of demographic data.