Timing Of Life History Events Research Articles

The timing of life history events in the presence of soft disturbances

We study a model for the evolutionarily stable strategy (ESS) used by biological populations for choosing the time of life-history events, such as arrival from migration and breeding. In our model we account for both intra-species competition (early individuals have a competitive advantage) and a disturbance which strikes at a random time, killing a fraction 1−p of the population. Disturbances include spells of bad weather, such as freezing or heavily raining days. It has been shown by Iwasa and Levin (1995) that when the disturbance is so strong that it kills any individual present when it strikes (hard disturbance, p=0), then the ESS is a mixed strategy (individuals choose their arrival date in an interval of possible dates, according to a certain probability distribution). In this case, individuals wait for a certain time and afterwards start arriving (or breeding) every day. In this paper we explore a biologically more realistic situation whereby the disturbance kills only a fraction of the individuals (soft disturbance, p>0). We also remove some technical assumptions which Iwasa and Levin made on the distribution of the disturbance. We prove that the ESS is still a mixed choice of times, however with respect to the case of hard disturbance, a new phenomenon arises: whenever the disturbance is soft, if the competition is sufficiently strong, the waiting time disappears and a fraction of the population arrives at the earliest day possible, while the rest will arrive throughout the whole period during which the disturbance may occur. This means that under strong competition, the payoff of early arrival balances the increased risk of being killed by the disturbance. We study the behaviour of the ESS and of the average fitness of the population, depending on the parameters involved. We also investigate how the population may be affected by climate change: namely the occurrence of more extreme weather events, which may kill a larger fraction of the population, and time shifts of the distribution of the disturbance. We show how the ESS and the average fitness change under the new climate and discuss which is the impact of the new climate on a population that still follows the old strategy. In particular, we show that, at least under some conditions, extreme weather events imply a temporary decrease of the average fitness of the population due to an increased mortality. In addition, if the population adapts to the new climate, the population may have a larger fitness.

The role of host phenology in determining the incidence of an insect sexually transmitted infection

Changes in the timing of life history events within the year alter the degree to which the activity patterns of different species coincide, making the dynamics of interspecific interactions sensitive to the phenology of the interacting parties. For parasites, the availability of suitable hosts to infect represents a crucial determinant of dynamics, and changes in the host (and parasite) phenology may thus alter disease epidemiology and the conditions for disease maintenance. We tested the hypothesis that the incidence of a sexually transmitted mite infection, Coccipolipus hippodamiae, in Adalia bipunctata ladybird beetles in Sweden was determined by host phenology, namely presence/absence of sexual contact between cohorts of the host. We observed that the pattern of mite presence/absence across Swedish A. bipunctata populations was highly reproducible between years, implying a persistent biological/ecological basis underlying the incidence. Further, ladybirds from populations where the mite was absent were able to acquire mites during copulation, develop a mite infection, and transmit infection onward, indicating an ecological (rather than biological) driver of mite incidence. Observations of ladybird phenology in natural populations provided evidence of sexual contact between overwintered and new cohort adults in populations where the mite was present. In contrast, new cohort ladybirds in the two northern Swedish populations where the mite was not present had not had sexual contact with the overwintered generation, creating a ‘hard stop’ to mite transmission. We conclude that variation in host phenology may be an important driver of the incidence of sexually transmitted infections (STIs) by determining the presence/absence of sexual contact between generations. More generally, we hypothesize that sensitivity to variation in host phenology will be highest for parasites like STIs that infect one host species, one host life stage and are directly transmitted on contact between host individuals.

Adaptation of timing of life history traits and population dynamic responses to climate change in spatially structured populations

Changes in the seasonal timing of life history events are documented effects of climate change. We used a general model to study how dispersal and competitive interactions affect eco-evolutionary responses to changes in the temporal distribution of resources over the season. Specifically, we modeled adaptation of the timing of reproduction and population dynamic responses in two competing populations that disperse between two habitats characterized by an early and late resource peak. We investigated three scenarios of environmental change: (1) food peaks advance in both habitats, (2) in the late habitat only and (3) in the early habitat only. At low dispersal rates the evolutionarily stable timing of reproduction closely matched the local resource peak and the environmental change typically caused population decline. Larger dispersal rates rendered less intuitive eco-evolutionary population responses. First, dispersal caused mismatch between evolutionarily stable timing of reproduction and local resource peaks and as a result, reproductive output for subpopulations could increase as well as decrease when resource availability underwent temporal shifts. Second, population responses were contingent on competition between populations. This could accelerate population declines and cause extinctions or even reverse population trends from negative to positive compared to the low dispersal case. When dispersal rate was large and the early resource peak was advanced available niche space was reduced. Hence, even when a population survived the environmental change and obtained positive equilibrium population density, subsequent adaptation of competing populations could drive it to extinction due to convergent evolution and competitive exclusion. These results shed new light on the role of competition and dispersal for the evolution of timing of life history events and provide guidelines for understanding short and long-term population response to climate change.

The effects of severe flooding on native masu salmon and nonnative rainbow trout in the Atsuta River, Hokkaido, Japan

Debris flow has potentially pronounced effects on streams and fish populations. In August 2010, a severe flood, which was coupled with wide-ranging landslides and massive debris flows, occurred in the Atsuta River. In this study, we evaluated the effects of floods on salmonid populations by examining the abundance and density of masu salmon Oncorhynchus masou and rainbow trout O. mykiss in the Atsuta River and comparing these values in the post-flood period to those in the pre-flood period. The estimated abundance and density of masu salmon did not change between the pre- and post-flood periods. In contrast, the density of adult (age-1and older) rainbow trout decreased dramatically. Although the density of age-0 rainbow trout decreased after the floods, there was no significant difference between the pre- and post-flood values. These results suggest that the effects of severe floods differ among species and these differences may be attributed to differences between masu salmon and rainbow trout in the timing of life-history events, such as fry emergence and spawning.

When phenology matters: age–size truncation alters population response to trophic mismatch

Climate-induced shifts in the timing of life-history events are a worldwide phenomenon, and these shifts can de-synchronize species interactions such as predator–prey relationships. In order to understand the ecological implications of altered seasonality, we need to consider how shifts in phenology interact with other agents of environmental change such as exploitation and disease spread, which commonly act to erode the demographic structure of wild populations. Using long-term observational data on the phenology and dynamics of a model predator–prey system (fish and zooplankton in Windermere, UK), we show that age–size truncation of the predator population alters the consequences of phenological mismatch for offspring survival and population abundance. Specifically, age–size truncation reduces intraspecific density regulation due to competition and cannibalism, and thereby amplifies the population sensitivity to climate-induced predator–prey asynchrony, which increases variability in predator abundance. High population variability poses major ecological and economic challenges as it can diminish sustainable harvest rates and increase the risk of population collapse. Our results stress the importance of maintaining within-population age–size diversity in order to buffer populations against phenological asynchrony, and highlight the need to consider interactive effects of environmental impacts if we are to understand and project complex ecological outcomes.

Phenological shifts and the fate of mutualisms.

Climate change is altering the timing of life history events in a wide array of species, many of which are involved in mutualistic interactions. Because many mutualisms can form only if partner species are able to locate each other in time, differential phenological shifts are likely to influence their strength, duration and outcome. At the extreme, climate change-driven shifts in phenology may result in phenological mismatch: the partial or complete loss of temporal overlap of mutualistic species. We have a growing understanding of how, when, and why phenological change can alter one type of mutualism-pollination. However, as we show here, there has been a surprising lack of attention to other types of mutualism. We generate a set of predictions about the characteristics that may predispose mutualisms in general to phenological mismatches. We focus not on the consequences of such mismatches but rather on the likelihood that mismatches will develop. We explore the influence of three key characteristics of mutualism: 1) intimacy, 2) seasonality and duration, and 3) obligacy and specificity. We predict that the following characteristics of mutualism may increase the likelihood of phenological mismatch: 1) a non-symbiotic life history in which co-dispersal is absent; 2) brief, seasonal interactions; and 3) facultative, generalized interactions. We then review the limited available data in light of our a priori predictions and point to mutualisms that are more and less likely to be at risk of becoming phenologically mismatched, emphasizing the need for research on mutualisms other than plant-pollinator interactions. Future studies should explicitly focus on mutualism characteristics to determine whether and how changing phenologies will affect mutualistic interactions.

Net carbon uptake has increased through warming-induced changes in temperate forest phenology

The timing of life-history events has a strong impact on ecosystems. Now, analysis of the phenology of temperate forests in the eastern US indicates that in the case of an earlier spring and a later autumn, carbon uptake (photosynthesis) increases considerably more than carbon release (respiration).

When not to have another baby: An evolutionary approach to low fertility

AbstractBACKGROUNDIn this paper, I explain the theoretical foundations of fertility from the perspective of evolutionary demography and evolutionary anthropology.OBJECTIVEMy goal in this paper is to provide examples of how evolutionary demography is generating and testing new hypotheses about human fertility and parental behaviour.METHODSTo illustrate the paradigm of low fertility, I present several evolutionary explanations for reduced fertility, or no fertility at all. The explanations I cite are drawn from studies on child maltreatment, homosexual preference, post-demographic transition low fertility, and late-life low fertility (menopause), as these are phenomena that appear to challenge evolutionary approaches.CONCLUSIONSI find that the sophisticated tools of behavioural ecology and evolutionary anthropology and demography can do more than simply explain high fertility, and are currently being used to generate and test new hypotheses about fertility, including hypotheses that address the issue of low fertility.1. An introduction to evolutionary demographyEvolutionary demography (or the application of evolutionary theory to human demographic behaviour) rests on the assumption that all organisms are designed by natural selection. As evolutionary theory is an overarching theory that explains how all living things look, develop, and behave, it is not surprising that it is relevant to understanding human fertility. Natural selection is assumed to act on physiological and decision-making processes in such a way that these processes maximise inclusive fitness in the environment in which they evolved. Inclusive fitness is a measure of the number of relatives an individual produces, weighted according to how closely related they are to the individual by direct descent (Hamilton 1964).In this paper, I outline some recent developments in the application of evolutionary theory to human demography. Rather than reviewing the entire field, which is very large, I will illustrate this approach by tackling what might be considered the most challenging question raised in the discipline: namely, what is the evolutionary basis for the failure of some people to reproduce? A simplistic analysis might suggest that humans (and indeed any species) should, subject to constraints, be evolved try to reproduce at the maximum possible rate. I will examine how evolutionary demographers and biologists have explained three contexts in which humans either do not reproduce, or do so far less than is theoretically possible: homosexuality, menopause, and the demographic transition. I will conclude by responding to some of the theoretical issues the other contributors to this volume are also addressing.Biologists generally define evolutionary demography as the application of life history theory to population processes. Having worked in both the biological and the social sciences, I often switch between the two different vocabularies of the social and biological sciences. One difference between these scientific disciplines is that the phenomenon that demographers call fertility (the number of births, which is the definition I use), biologists call fecundity. The two fields are similar in many respects. Life history theory is a well-developed sub-discipline of evolutionary ecology which is explicitly concerned with the timing of life history events (growth, reproduction, maintenance, and death) under natural selection. The timing and the scheduling of births in order to maximise fitness (in the Darwinian sense) can in theory be calculated for any given environment and any given set of environmental constraints. In examining the timing of births, researchers often try to understand both the behavioural and the physiological determinants of fertility (e.g., menopause). Parental investment is viewed as a life history trait that is determined in part by considerations regarding the quantity versus the quality of offspring. …

A recent local sweep at thePHYAlocus in the Northern European Spiterstulen population ofArabidopsis lyrata

Northern and central European Arabidopsis lyrata ssp. petraea populations are locally adapted to prevailing climatic conditions through differences in timing of life history events. The timing of flowering and, in perennials, the timing of growth cessation influence fitness. Phytochrome A may have an important role in regulating these life history traits as it perceives changes in daylength. We asked whether PHYA has contributed to local adaptation to the northern conditions in A. l. petraea. To search for signals of directional selection at the PHYA locus, we resequenced PHYA and 9 short fragments around PHYA from a 57-kb region from a German (Plech) and a Norwegian (Spiterstulen) population and compared patterns of differentiation and diversity to a set of 19 reference loci around the genome. First, we found that the populations were highly differentiated: there were three nonsynonymous fixed differences at the PHYA locus, which was in stark contrast with the total four fixed differences in the 19 reference loci. Compatible with a sweep hypothesis, variation was almost completely removed from the 9.4-kb region around PHYA in the northern Spiterstulen population. The overall level of linkage disequilibrium (LD) was higher in Spiterstulen, but there was no LD across the PHYA locus in the population, which is also a known consequence of a selective sweep. The sweep has likely occurred after the last glacial maximum, which suggests that it has contributed to adaptation to the northern conditions.

Progress towards an interdisciplinary science of plant phenology: building predictions across space, time and species diversity

Climate change has brought renewed interest in the study of plant phenology - the timing of life history events. Data on shifting phenologies with warming have accumulated rapidly, yet research has been comparatively slow to explain the diversity of phenological responses observed across latitudes, growing seasons and species. Here, we outline recent efforts to synthesize perspectives on plant phenology across the fields of ecology, climate science and evolution. We highlight three major axes that vary among these disciplines: relative focus on abiotic versus biotic drivers of phenology, on plastic versus genetic drivers of intraspecific variation, and on cross-species versus autecological approaches. Recent interdisciplinary efforts, building on data covering diverse species and climate space, have found a greater role of temperature in controlling phenology at higher latitudes and for early-flowering species in temperate systems. These efforts have also made progress in understanding the tremendous diversity of responses across species by incorporating evolutionary relatedness, and linking phenological flexibility to invasions and plant performance. Future research with a focus on data collection in areas outside the temperate mid-latitudes and across species' ranges, alongside better integration of how risk and investment shape plant phenology, offers promise for further progress.

On the ecology of Calanus finmarchicus in the Subarctic North Atlantic: A comparison of population dynamics and environmental conditions in areas of the Labrador Sea-Labrador/Newfoundland Shelf and Norwegian Sea Atlantic and Coastal Waters

The Norwegian Sea is generally warmer than the Labrador Sea because it is influenced more by Atlantic Water inflows from the south, whereas the latter receives relatively larger inputs of Arctic Water from the north. Despite its more northerly location, the spring bloom generally starts earlier in the Norwegian Sea. Within each of the two seas, however, there are regional and interannual differences in temperature and the timing of the spring bloom. The responses of Calanus finmarchicus populations to these differences in environmental conditions include differences in physical characteristics (e.g. female size), physiological rates (egg production rates) and seasonal cycles of abundance. Females are generally larger in the Labrador Sea and have higher egg production rates for a given chlorophyll concentration than do those in the Norwegian Sea. Within and among areas in both seas, as temperatures increase and spring blooms tend to occur earlier, C. finmarchicus start to reproduce earlier, the new generation develops faster, and in some areas a second generation ensues. In areas where near surface temperatures are relatively high in summer and/or where phytoplankton growth rates are relatively low in summer or autumn, reproduction and development cease, and C. finmarchicus desert the surface layers for their overwintering depths. This occurs in the Norwegian Sea in summer and in the central Labrador Sea in autumn. By contrast, in areas where near surface temperatures remain cool in summer and where phytoplankton growth persists through the autumn, reproduction and development can continue through summer and autumn, probably until winter vertical mixing prevents phytoplankton growth. This occurs on the southern Newfoundland Shelf. Even in areas where the growth season is prolonged, however, a proportion of the first generation, and probably subsequent generations, descends to overwinter. If the size of the overwintering population is used as an index of net productivity, then for equivalent regions in the Norwegian Sea and Labrador Sea (the areas of each most affected by Atlantic inflow), the differences in ambient temperatures and bloom dynamics apparently have little impact. With global warming, as temperatures in the Norwegian and Labrador Seas increase up to a certain threshold, the timing of life history events for C. finmarchicus will likely be advanced and the number of generations produced per year could increase. The time spent in the near surface layers will probably decrease, however, while the overall effect on population size may not be large. Once the temperature threshold for unfavourable survival of C. finmarchicus has been exceeded, the distribution range for C. finmarchicus will likely contract northwards, with important consequences for dependent species in the affected regions.

Does Absence Matter?

This paper examines the effects of three different types of father absence on the timing of life history events among women in rural Bangladesh. Age at marriage and age at first birth are compared across women who experienced different father presence/absence conditions as children. Survival analyses show that daughters of fathers who divorced their mothers or deserted their families have consistently younger ages at marriage and first birth than other women. In contrast, daughters whose fathers were labor migrants have consistently older ages at marriage and first birth. Daughters whose fathers died when they were children show older ages at marriage and first birth than women with divorced/deserted fathers and women with fathers present. These effects may be mediated by high socioeconomic status and high levels of parental investment among the children of labor migrants, and a combination of low investment, high psychosocial stress, and low alloparental investment among women with divorced/deserted fathers. Our findings are most consistent with the Child Development Theory model of female life history strategies, though the Paternal Investment and Psychosocial Acceleration models also help explain differences between women in low paternal investment situations (e.g., father divorced/abandoned vs. father dead). Father absence in and of itself seems to have little effect on the life history strategies of Bangladeshi women once key reasons for or correlates of absence are controlled, and none of the models is a good predictor of why women with deceased fathers have delayed life histories compared with women whose fathers are present.

Growth and size-dependent loss of newly settled bivalves in two distant regions of the Wadden Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 472:141-154 (2013) - DOI: https://doi.org/10.3354/meps10011 Growth and size-dependent loss of newly settled bivalves in two distant regions of the Wadden Sea Henrike Andresen1,*, Ine Dorresteijn1, Jaap van der Meer1,2 1Royal Netherlands Institute for Sea Research (NIOZ), Den Burg (Texel) 1790 AB, The Netherlands 2Department of Theoretical Biology, Free University, Amsterdam 1081 HV, The Netherlands *Email: henrikea@gmx.de ABSTRACT: Individual growth and the timing of life history events determine the course of individual body sizes. Hence, these factors can influence size-dependent species interactions, such as predation. In the Wadden Sea, predation by crustaceans plays an important role in the survival of pre-recruit bivalves. To investigate growth rates and size-dependent loss in 2 distant regions of the Wadden Sea, in situ marking with the fluorochrome calcein was combined with cage experiments. Through marking, we obtained, for the first time, size-increment data for the fragile newly settled juveniles of the species Macoma balthica and Cerastoderma edule in the field. Growth and size-selective mortality were analysed separately, whereas hitherto both have usually been inferred from size distributions at this life stage. Fluorescent marking also revealed that growth rates were very variable among individuals. Growth was temporarily higher at Texel than at Sylt in both species. In combination with the exclosure experiments and the sampling of predators and migrating bivalves, selective loss of smaller individuals was detected in both regions and was related to predation pressure. Climate influences on phenology have potentially strong effects on species interactions, altering survival and thus recruitment and population dynamics. KEY WORDS: Individual marking · Predator-exclusion experiments · Benthic invertebrates · Soft‑bottom intertidal · Early life history · Post-settlement mortality · Fluorescent dye · Bivalvia Full text in pdf format PreviousNextCite this article as: Andresen H, Dorresteijn I, van der Meer J (2013) Growth and size-dependent loss of newly settled bivalves in two distant regions of the Wadden Sea. Mar Ecol Prog Ser 472:141-154. https://doi.org/10.3354/meps10011 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 472. Online publication date: January 09, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Early life environment, life history and risk of endometrial cancer

Endometrial cancer risk is influenced by reproductive behaviours, including parity and breastfeeding, and timing of life history events such as age at menarche and menopause. One potential mechanism by which altered reproductive strategies may influence endometrial cancer risk is through exposure to reproductive hormones. Current theory suggests that high lifetime exposure to oestrogen, unopposed by progesterone, increases endometrial cancer risk; here we suggest that progesterone deficiency itself may also play a significant role. Additionally, given that reproductive profile variables are themselves influenced by early childhood conditions, we hypothesise that endometrial cancer risk may be influenced by the childhood psychosocial environment as mediated through changes to adolescent and adult reproductive behaviours and hormone exposures. Investigating reproductive cancers, including endometrial cancer, using a life history approach may help to increase understanding of why these cancers occur and potentially help implementation of early detection and screening processes in the future.

What is soundscape ecology? An introduction and overview of an emerging new science

We summarize the foundational elements of a new area of research we call soundscape ecology. The study of sound in landscapes is based on an understanding of how sound, from various sources—biological, geophysical and anthropogenic—can be used to understand coupled natural-human dynamics across different spatial and temporal scales. Useful terms, such as soundscapes, biophony, geophony and anthrophony, are introduced and defined. The intellectual foundations of soundscape ecology are described—those of spatial ecology, bioacoustics, urban environmental acoustics and acoustic ecology. We argue that soundscape ecology differs from the humanities driven focus of acoustic ecology although soundscape ecology will likely need its rich vocabulary and conservation ethic. An integrative framework is presented that describes how climate, land transformations, biodiversity patterns, timing of life history events and human activities create the dynamic soundscape. We also summarize what is currently known about factors that control temporal soundscape dynamics and variability across spatial gradients. Several different phonic interactions (e.g., how anthrophony affects biophony) are also described. Soundscape ecology tools that will be needed are also discussed along with the several ways in which soundscapes need to be managed. This summary article helps frame the other more application-oriented papers that appear in this special issue.

Exploring mechanisms linking temperature increase and larval phenology: The importance of variance effects

In temperate environments, many animals and plants show seasonal peaks of abundance. Rising temperatures due to climate change could affect the timing of these peaks with important consequences for populations of organisms positioned higher in the food web. If the peak of consumer species shifts with respect to the resources a trophic mismatch occurs by which many individuals of a population of consumers may not encounter the food source. I show that increased temperatures can lead to trophic mismatch through an alteration of the variance of the abundance distributions of consumers or resources over time; such change would reduce the overlap between the temporal distribution of consumers and resources. This occurs through: (1) a non-linear effect of temperature on the developmental rates; and (2) variations in the shape of the temperature curve during the year. These effects should be widespread among different kinds of organisms. Temperature increase may therefore have consequences for trophic mismatch through the combined effect of differential shifts in the average timing of life history events and through the reduction in the spread or variance of these events.

The roles of the immune system in Women's reproduction: Evolutionary constraints and life history trade‐offs

Life history theory posits that, as long as survival is assured, finite resources are available for reproduction, maintenance, and growth/storage. To maximize lifetime reproductive success, resources are subject to trade-offs both within individuals and between current and future investment. For women, reproducing is costly and time-consuming; the bulk of available resources must be allocated to reproduction at the expense of more flexible systems like immune function. When reproducing women contract infectious diseases, the resources required for immune activation can fundamentally shift the patterns of resource allocation. Adding to the complexity of the reproductive-immune trade-offs in women are the pleiotropic effects of many immune factors, which were modified to serve key roles in mammalian reproduction. In this review, we explore the complex intersections between immune function and female reproduction to situate proximate immunological processes within a life history framework. After a brief overview of the immune system, we discuss some important physiological roles of immune factors in women's reproduction and the conflicts that may arise when these factors must play dual roles. We then discuss the influence of reproductive-immune trade-offs on the patterning of lifetime reproductive success: (1) the effect of immune activation/infectious disease on the timing of life history events; (2) the role of the immune system, immune activation, and infectious disease on resource allocation within individual reproductive events, particularly pregnancy; and (3) the role of the immune system in shaping the offspring's patterns of future life history trade-offs. We close with a discussion of future directions in reproductive immunology for anthropologists.

Life Expectancy and the Timing of Life History Events in Developing Countries

Life history theory predicts that greater extrinsic mortality will lead to earlier and higher fertility. To test this prediction, I examine the relationship between life expectancy at birth and several proxies for life history traits (ages at first sex and first marriage, total fertility rate, and ideal number of children), measured for both men and women. Data on sexual behaviors come from the Demographic and Health Surveys (DHS). Two separate samples are analyzed: a cross-sectional sample of 62 countries and a panel sample that includes multiple cross-sectional panels from 48 countries. Multivariate regression analysis is used to control for potential confounding variables. The results provide only partial support for the predictions, with greater support among women than men. However, the prediction is not supported in sub-Saharan African countries, most likely owing to the nonequilibrium conditions observed in sub-Saharan Africa with respect to life expectancy. The applicability of the model to understanding HIV/AIDS risk behaviors is discussed.

Anuran life history plasticity: Variable practice in determining the end-point of larval development

AbstractPlasticity in the timing of life history events and their impact on individual fitness, particularly the timing of and size at metamorphosis in animals with complex life cycles such as anuran amphibians, has long been of interest to ecologists. For different studies on life history plasticity to be comparable, there must be clearly defined and commonly agreed transition points, but it is unclear how consistently this is being performed in studies using anuran amphibians. In a review of 157 published studies, I found considerable variation in defining the end point of the larval phase. While a slight majority used the emergence of the forelimbs as the conclusion of the larval phase, some used a period within the developmental phase of metamorphic climax and others used the resorption of the tail. Studies included in this review, that assessed the same life history variable at two different developmental stages, reported some differences in results depending on which developmental stage was used. Recent evidence also shows that metamorphic climax is itself a period which can vary with environmental conditions, but, even in studies that included part or all of metamorphic climax in the larval phase, the treatment of individuals during metamorphic climax was not reported. Therefore, I argue that life history studies on anuran amphibians should distinguish the following phases: larval, metamorphic climax, juvenile, adult; that the end of the larval phase is best defined in ecological studies by forelimb emergence and that conditions under which individuals undergo metamorphic climax should be fully described.

Indirect effects of FRIGIDA: floral trait (co)variances are altered by seasonally variable abiotic factors associated with flowering time

Reproductive timing is a critical life-history event that could influence the (co)variation of traits developing later in ontogeny by regulating exposure to seasonally variable factors. In a field experiment with Arabidopsis thaliana, we explore whether allelic variation at a flowering-time gene of major effect (FRIGIDA) affects (co)variation of floral traits by regulating exposure to photoperiod, temperature, and moisture levels. We detect a positive latitudinal cline in floral organ size among plants with putatively functional FRI alleles. Statistically controlling for bolting day removes the cline, suggesting that seasonal abiotic variation affects floral morphology. Both photoperiod and precipitation at bolting correlate positively with the length of petals, stamens, and pistils. Additionally, floral (co)variances differ significantly across FRI backgrounds, such that the sign of some floral-trait correlations reverses. Subsequent experimental manipulations of photoperiod and water availability demonstrate direct effects of these abiotic factors on floral traits. In sum, these results highlight how the timing of life-history events can affect the expression of traits developing later in ontogeny, and provide some of the first empirical evidence for the effects of major genes on evolutionary potential.