A reciprocal egg-swap experiment reveals sources of variation in developmental success among populations of a desert lizard.

We examined the life history of Blackbanded Darters (Percina nigrofasciata) from two streams in the Choctawhatchee River drainage, Florida, over a three-year study period. Blackbanded Darters from Turkey Creek were longer than fish from Ten Mile Creek; however, size-adjusted clutch and egg sizes were similar between populations. Larger females produced larger clutches, whereas egg size did not vary with female body size. Seasonally, clutch sizes were greater in May than in August. When contrasted with previous studies of Blackbanded Darters in Alabama and Louisiana, the reproductive season of Blackbanded Darters in Florida was unusually long, ceasing for only a few months in late fall. The reproductive season was longer in Turkey Creek than in Ten Mile Creek. Differences in thermal regime among streams may explain differences in life history traits among local and distant populations of Blackbanded Darters. This research, alone and in combination with previous studies of this species, emphasizes two main points. First, it reaffirms that life history studies based on a single locality or conducted at a single point in time may fail to capture the full range of variation in life history traits. Second, it highlights the extensive phenotypic variation found in species with broad geographic ranges. Such species lend themselves to comparative and experimental research on patterns and causes of life history variation. general aim of life history studies is to identify spatial and temporal patterns of variation in life history traits and to understand the underlying causes of variation among populations and species. Life histories represent adaptations to environmental conditions experienced by populations over time (Roff, 1992; Stearns, 1992). Measuring and characterizing variation in life history traits, therefore, enhances our understanding of the selective pressures faced by different populations as well as constraints on their ability to respond adaptively to these pressures. North American darters (Perciformes: Percidae) commonly exhibit spatial and temporal variation in reproductive traits. Body size, duration of spawning season, clutch size, and egg size vary within and among populations for many

Aedes aegypti, the vector for dengue, chikungunya, yellow fever, and Zika, poses a growing global epidemiological risk. Despite extensive research on Ae. aegypti's life history traits and behavior, critical knowledge gaps persist, particularly in integrating these findings across varied experimental contexts. The plasticity of Ae. aegypti's traits throughout its life cycle allows dynamic responses to environmental changes, yet understanding these variations within heterogeneous study designs remains challenging. A critical aspect often overlooked is the impact of using lab-adapted lines of Ae. aegypti, which may have evolved under laboratory conditions, potentially altering their life history traits and behavioral responses compared to wild populations. Therefore, incorporating field-derived populations in experimental designs is essential to capture the natural variability and adaptability of Ae. aegypti. The relationship between larval growing conditions and adult traits and behavior is significantly influenced by the specific context in which mosquitoes are studied. Laboratory conditions may not replicate the ecological complexities faced by wild populations, leading to discrepancies in observed traits and behavior. These discrepancies highlight the need for ecologically relevant experimental conditions, allowing mosquito traits and behavior to reflect field distributions. One effective approach is semi-field studies involving field-collected mosquitoes housed for fewer generations in the lab under ecologically relevant conditions. This growing trend provides researchers with the desired control over experimental conditions while maintaining the genetic diversity of field populations. By focusing on variations in life history traits and behavioral plasticity within these varied contexts, this review highlights the intricate relationship between larval growing conditions and adult traits and behavior. It underscores the significance of transstadial effects and the necessity of adopting study designs and reporting practices that acknowledge plasticity in adult traits and behavior, considering variations due to larval rearing conditions. Embracing such approaches paves the way for a comprehensive understanding of contextual variations in mosquito life history traits and behavior. This integrated perspective enables the synthesis of research findings across laboratory, semi-field, and field-based investigations, which is crucial for devising targeted intervention strategies tailored to specific ecological contexts to combat the health threat posed by this formidable disease vector effectively.

Swordtip squid Uroteuthis edulis is a commercially important species in coastal waters throughout the Northwestern Pacific, including those of Japan and Taiwan. Despite the importance of U. edulis to fisheries, previous studies on the life history traits (growth rate, size at maturity, and fecundity) of its populations in the Northwestern Pacific have been localized and region specific. Thus, we report life history traits of female swordtip squid from the waters off southern Japan and northern Taiwan, to identify seasonal variations within each population, as well as geographical variations between them. Variations in life history traits, including growth rate, mantle length (ML) at maturity, and female reproductive traits (gonadosomatic index, fecundity and egg size), are described and recognized to vary seasonally in both populations. Winter spawners in Japan have the highest growth rate, followed by spring spawners and summer spawners. Spring spawners in Taiwan mature at a younger age than autumn spawners. Geographical variations between populations are reported: fecundity level and egg size of spring spawners in Japan differ from those of spring and autumn spawners in Taiwan, but those of summer spawners in Japan are similar to those of spring and autumn spawners in Taiwan. Data on seasonal and geographical variations in life history traits of U. edulis are useful for effective squid fisheries management.

Variation in life history (LH) traits along the fast-slow continuum (referred to as pace of life, POL) is thought to result from a trade-off between investments in current versus future reproduction. Originally developed for understanding variation in LH strategies at the among-population level, the POL theory has more recently been applied towards understanding variation in LH traits at the within-population level, and further extended to address the covariance of LH traits with additional behavioural and/or physiological traits, referred to as pace-of-life syndromes (POLS). The article by Reale et al. (Philos T Roy Soc B 365:4051–4063, 2010), which synthesized several earlier reviews and opinions on among-individual covariation between LH, behavioural, and physiological traits, and subsequent research testing POLS in a variety of species, have collectively been cited several hundreds of times—a trend that continues. These works have interdisciplinary impact, informing research in life history biology, behavioural and developmental biology, and the social sciences. In this paper, we review the existing theoretical POLS models that provide adaptive explanations for covariances between LH traits and additional behavioural and/or physiological traits while assuming a trade-off between current and future reproduction. We find that the set of relevant models is small. Moreover, models show that covariances between life history traits and behavioural or physiological traits can arise even in the absence of a current-future reproduction trade-off, implying that observing such covariances does not provide a strong indication regarding the process generating POLS. We discuss lessons learned from existing models of POLS, highlight key gaps in the modelling literature, and provide guidelines for better integration between theory and data.

The empirical study of interpopulation variation in life history and other fitness traits has been an important approach to understanding the ecology and evolution of organisms and gaining insight into possible sources of variation. We report a quantitative analysis for variations of five life history traits (larval developmental time, adult body weight, adult lifespan, age at first reproduction, total fecundity) and flight capacity among populations of Epiphyas postvittana originating from four localities in Australia and one in New Zealand. These populations were compared at two temperatures (15° and 25°C) after being maintained under uniform laboratory conditions for 1.5 generations, so that the relative role of genetic divergence and phenotypic plasticity in determining interpopulation variation could be disentangled. Genetic differentiation between populations was shown in all measured traits, with the greatest divergence occurring in developmental time, fecundity and adult body size. However, these traits were highly sensitive to changes in environmental temperatures; and furthermore, significant interactions between population and temperature occurred in all traits except for flight capacity of female moths. Thus, phenotypic plasticity may be another cause of interpopulation variation. The interpopulation variation for some measured traits was apparently related to climatic differences found where the populations originated. Individuals of the populations from the warmer climates tended to develop more slowly at immature stages, producing smaller and less fecund moths but with stronger flight capacity, in comparison to those from the cooler regions. It seems, therefore, that natural populations of E. postvittana have evolved different strategies to cope with local environmental conditions.

Variation in life history traits is directly linked to individual fitness. This interplay is complicated by environmental perturbations in an unpredictable habitat. To maximise fitness, individuals react to environmental changes by reallocating resources between maintenance, growth and reproduction. Disentangling these factors is complicated as traits are interlinked by trade-offs between current reproduction and future survival and reproduction. This study provides first estimates of life history traits and trade-offs of a tropical apex predator, the Galapagos sea lion (Zalophus wollebaeki), in an unpredictable habitat, the Galapagos archipelago. Thirteen years of individual data on birth mass, early growth and offspring, and environmental data allowed the examination of factors influencing reproductive performance of adult females and calculation of pupping rates. Females became primiparous between ages 4 and 9. Neither oceanographic nor body condition in the females’ first year of life influenced age at primiparity. Age at primiparity had no effect on a female’s birth rate, on average one pup every 2 years. Sex of a pup did not influence the subsequent inter-birth interval, but first-year pup survival lengthened it. Until age 6, females showed lower birth rate (< 0.40). Fecundity was higher between age 6 and 14 (birth rate 0.40–0.48). We could not detect an influence of inter-annually differing oceanographic conditions on pupping rates. Female Galapagos sea lions appear to deal with variation in early-life history traits and environmental unpredictability by a low but stable reproductive output modified only by the trade-off between current and future reproduction. Life history traits and trade-offs have been examined in many species in temperate regions and in seasonal but predictable tropical habitats. However, they have rarely been investigated in long-lived species in tropical but unpredictable habitats, where the interplay between life history traits, individual fitness and population demography may be more complex. Our long-term dataset for Galapagos sea lion females, a tropical apex predator, shows that the trade-off between current and future reproduction figures prominently in their life history. However, they produce a low, but stable reproductive output largely unaffected by variation in early life history traits and largely independent of environmental unpredictability.

Allocation decisions depend on an organism's condition which can change with age. Two opposite changes in life-history traits are predicted in the presence of senescence: either an increase in breeding performance in late age associated with terminal investment or a decrease due to either life-history trade-offs between current breeding and future survival or decreased efficiency at old age. Age variation in several life-history traits has been detected in a number of species, and demographic performances of individuals in a given year are influenced by their reproductive state the previous year. Few studies have, however, examined state-dependent variation in life-history traits with aging, and they focused mainly on a dichotomy of successful versus failed breeding and non-breeding birds. Using a 50-year dataset on the long-lived quasi-biennial breeding wandering albatross, we investigated variations in life-history traits with aging according to a gradient of states corresponding to potential costs of reproduction the previous year (in ascending order): non-breeding birds staying at sea or present at breeding grounds, breeding birds that failed early, late or were successful. We used multistate models to study survival and decompose reproduction into four components (probabilities of return, breeding, hatching, and fledging), while accounting for imperfect detection. Our results suggest the possible existence of two strategies in the population: strict biennial breeders that exhibited almost no reproductive senescence and quasi-biennial breeders that showed an increased breeding frequency with a strong and moderate senescence on hatching and fledging probabilities, respectively. The patterns observed on survival were contrary to our predictions, suggesting an influence of individual quality rather than trade-offs between reproduction and survival at late ages. This work represents a step further into understanding the evolutionary ecology of senescence and its relationship with costs of reproduction at the population level. It paves the way for individual-based studies that could show the importance of intra-population heterogeneity in those processes.

Despite the importance of maternally selected nests in shaping offspring phenotypes, our understanding of how the nest environment affects embryonic development and offspring traits of most non-avian reptiles is rather limited largely due to the logistical difficulty in locating their nests. To identify the relative contributions of environmental (temporal [seasonal] and spatial [nest-site]) and intrinsic (clutch) factors on embryonic development and offspring traits, we conducted a cross-fostering experiment by swapping eggs between maternally-selected nests of the toad-headed agama (Phrynocephalus przewalskii) in the field. We found that nest environment explained a large proportion of variation in incubation duration, hatching success, and offspring size and growth. In contrast, clutch only explained a small proportion of variation in these embryonic and offspring traits. More significantly, compared with spatial effects, seasonal effects explained more phenotypic variation in both embryonic development and offspring traits. Eggs laid early in the nesting season had longer incubation durations and produced smaller hatchlings with higher post-hatching growth rates than did later-laid eggs. Consequently, hatchlings from early-laid eggs reached larger body sizes prior to winter. In addition, we found that female toad-headed agama did not select nests specific to reaction norms of their own offspring because hatchlings from original or translocated nests had similar phenotypic traits. Overall, our study demonstrates the importance of seasonal variation in nest environments in determining embryonic development and offspring phenotypes, which has not been widely appreciated at least in non-avian reptiles.

Aim Variation of life history traits along spatial gradients is poorly understood in invasive species and particularly in freshwater fish. We aimed to examine life history variation in a highly invasive fish (Gambusia holbrooki) along latitudinal and upstream–downstream river gradients and to assess the effects of age on this variation. We hypothesized similar responses in populations inhabiting environments more favourable to this species (lower latitudes and lower reaches of rivers).Location European rivers from southern Spain to southern France.Methods We sampled mosquitofish from the lowest reaches of ten river basins along 6° of latitude in the Mediterranean region and seven sites along the upstream–downstream gradient in three of the rivers. We examined abundance, population structure, size‐at‐age and other life history traits along these gradients.Results As hypothesized, lower reaches and lower latitudes both resulted in higher reproductive effort and lower body condition of mosquitofish. However, these patterns explained low per cent variation, were nonlinear and strongly depended on fish age. Independently of fish size, age groups differed in reproductive effort, in the gonadal weight–size relationship and its variation along spatial gradients. Mean size‐at‐age (or overall body size) did not vary with latitude (so the intra‐specific version of Bergmann’s rule or its converse does not apply) and in contrast increased upstream in rivers.Main conclusions Our findings suggest that for life history traits of freshwater organisms, river longitudinal variation plays a role as important as climate, with often differential effects. Our results also illustrate the poor knowledge of spatial variation of many life history traits, which precludes the understanding and prediction of biological invasions in a rapidly changing world.

Variation in population density and life history traits were studied in six white-tailed prairie dog (Cynomys leucurus) populations in Wyoming using mark – recapture techniques. All life history traits (except juvenile sex ratios) and population density exhibited significant variation within towns between years and among towns in the same year. Temporal and spatial habitat variation significantly affects juvenile body mass but not adult body mass, which, in turn, results in the observed variation in life history traits. We conclude that white-tailed prairie dogs are dynamic reproducers and that their population age distributions are neither stable nor stationary. Use of life tables to study life history patterns of this species or of similar species would be inappropriate because of a failure to meet a basic assumption of life table models.

:The classical approach for investigating latitudinal variations in life history tactics of ectotherms is to determine if there are significant correlations between the traits of a given species and latitude. However, as temperature does not vary linearly with latitude, the latter parameter may only be a gross index of local climatic conditions. The objective of this paper is to present how we used Litynski’s (1984) climate classification to investigate latitudinal variations in life history traits of the white sucker (Catostomus commersoni). Data from the literature (44 lakes) and from sampling done on 18 lakes of the Laurentian Shield (Québec, Canada) were used to compare different approaches to predict geographical variations in life history traits. The results showed that variation in life history traits of the white sucker documented over the geographical extent of the study area was better explained by considering the numerical classification of climates, based on mean annual temperature, annual precipitation and an index of continentality, rather than by simple linear regression with latitude or mean annual temperature; longevity and age at maturity of males and females were significantly higher in northern populations while maximum length, length at maturity of males and females, and growth were significantly higher in southern populations. Our results suggest that it may be better to use functional climatic variables, instead of the more usual ones, such as latitude and mean annual air temperature, to study geographical variations in the life history of ectotherms.

This book is an up-to-date and comprehensive account of research on avian reproduction. It develops two unique themes: the consideration of female avian reproductive physiology and ecology, and an emphasis on individual variation in life-history traits. The book investigates the physiological, metabolic, energetic, and hormonal mechanisms that underpin individual variation in the key female-specific reproductive traits and the trade-offs between these traits that determine variation in fitness. The core of the book deals with the avian reproductive cycle, from seasonal gonadal development, through egg laying and incubation, to chick rearing. Reproduction is considered in the context of the annual cycle and through an individual's entire life history. The book focuses on timing of breeding, clutch size, egg size and egg quality, and parental care. It also provides a primer on female reproductive physiology and considers trade-offs and carryover effects between reproduction and other life-history stages. Each chapter describes individual variation in the trait of interest and the evolutionary context for trait variation. The book argues that there is only a rudimentary, and in some cases nonexistent, understanding of the physiological mechanisms that underpin individual variation in the major reproductive life-history traits, and that research efforts should refocus on these key unresolved problems by incorporating detailed physiological studies into existing long-term population studies, generating a new synthesis of physiology, ecology, and evolutionary biology.

A controversy exists in the Pacific Northwest of the United States between logging of old-growth coniferous forests and conservation of Northern Spotted Owl (Strix occidentalis caurina) populations. This species has a strong association with old-growth forests that also have economic value as timber. Research questions relevant to conservation of this species include how temporal trends in Northern Spotted Owl populations are influenced and how spatial configuration of old-growth forests affects these populations. To address these questions, we studied a population of marked Northern Spotted Owls on 95 territories in northwestern California from 1985 through 1994. We examined the magnitude of temporal and spatial variation in life history traits (survival, reproductive output, and recruitment), the effects of climate and landscape characteristics on temporal and spatial variation in these traits, respectively, and how this variation affected aspects of population dynamics. We used a components-of-variation analysis to partition sampling from process variation, and a model selection approach to estimate life history traits using capture–recapture and random-effects models. Climate explained most of the temporal variation in life history traits. Annual survival varied the least over time, whereas recruitment rate varied the most, suggesting a “bet-hedging” life history strategy for the owl. A forecast of annual rates of population change (λ), estimated from life history traits, suggested that Northern Spotted Owl populations may change solely due to climate influences, even with unchanging habitat conditions. In terms of spatial variation, annual survival on territories was positively associated both with amounts of interior old-growth forest and with length of edge between those forests and other vegetation types. Reproductive output was negatively associated with interior forest, but positively associated with edge between mature and old-growth conifer forest and other vegetation types. A gradient existed in territory-specific estimates of fitness derived from these life history estimates. This gradient suggested that a mosaic of older forest interspersed with other vegetation types promoted high fitness in Northern Spotted Owls. Habitat quality, as defined by fitness, appeared to buffer variation in annual survival but did not buffer reproductive output. We postulated that the magnitude of λ was determined by habitat quality, whereas variation of λ was influenced by recruitment and reproductive output. As habitat quality declines, variation in λ should become more pronounced.

Understanding how genetic variation in the Tree Swallow (Tachycineta bicolor) is geographically structured is informative because this broadly distributed North American bird is increasingly used as a model for studies of mating systems, life-history traits, and physiology. We explored patterns of phylogeographic differentiation across the Tree Swallow's breeding range by using nine microsatellite loci and a mitochondrial DNA sequence marker. Contrary to this species' high population-level variation in life-history traits and other ecologically important characteristics, we found no genetic structuring across the majority of its distribution, spanning Tennessee, New York, and Alaska, but we found that birds from California form a distinct yet subtly differentiated genetic cluster. The Tree Swallow can be characterized as a species with both continent-wide genetic panmixia and slight differentiation at one edge of its breeding distribution. This pattern of genetic variation has implications for understanding the underlying basis of geographic variation in this species' life history and other phenotypic traits.

Life history variation among geographically close populations of the toad-headed lizard (Phrynocephalus przewalskii): Exploring environmental and physiological associations