Sons Shorten Mother's Lifespan in Preindustrial Families with a High Level of Infant Mortality.

AbstractIn dimorphic vertebrates where males are larger than females, the energetic costs of producing and rearing sons can exceed those of daughters. In humans, differences in maternal energy intake suggest that sons require 10% and 7% more energy than daughters during pregnancy and lactation, respectively. Due to a trade-off between reproduction and somatic maintenance, having sons is expected to have a more pronounced detrimental impact on a mother's lifespan than having daughters. A limitation of previous studies investigating this hypothesis is that the increased mortality cost of having sons was assumed to affect all mothers equally. Using a dataset from a preindustrial Quebec population monitored over two centuries, we found that the number of sons decreased postmenopausal lifespan only in mothers experiencing high infant mortality. Our study highlights the importance of interindividual variation in environmental conditions and maternal health when studying effects of offspring sex on reproductive costs.

Effects of the Herbicide Metolachlor and Pond Drying on Growth and Development of Wood Frog Tadpoles (Lithobates sylvaticus).

Pesticides and climate change are both thought to contribute to the global amphibian decline, yet their combined effects are still poorly understood. Metolachlor is a widespread herbicide applied across North America, but little is known about its effects on amphibians. We used a replicated mesocosm experimental design with different levels of drying (i.e., no drying and medium and rapid drying) and metolachlor concentrations (0, 0.8, 8, and 80 µg/L) to assess their respective and combined effects on wood frog (Lithobates sylvaticus) larvae throughout metamorphosis. Metolachlor had no significant effect on survival and development of tadpoles. However, metolachlor significantly interacted with drying levels to reduce the growth of tadpoles, which was mainly due to a difference detected among metolachlor concentrations under the rapid drying treatment. Drying also directly reduced growth and body mass at metamorphosis. Our results suggest that environmental stressors, such as drying, should be considered in toxicological experiments to provide relevant exposure conditions to pesticides for ephemeral pond species in the context of global climate change. Environ Toxicol Chem 2023;42:1772-1781. © 2023 SETAC.

Environmental and individual determinants of burrow-site microhabitat selection, occupancy, and fidelity in eastern chipmunks living in a pulsed-resource ecosystem.

Background: Habitat selection has major consequences on individual fitness, particularly selection for breeding sites such as nests or burrows. Theory predicts that animals will first use optimal habitats or rearrange their distribution by moving to higher-quality habitats whenever possible, for instance when another resident disperses or dies, or when environmental changes occur. External constraints, such as predation risk or resource abundance, and interindividual differences in age, sex and body condition can lead to variation in animals' perception of habitat quality. Following habitat use by individuals over their lifetime is thus essential to understand the causes of variation in habitat selection within a population. Methods: We used burrow occupancy data collected over eight years to assess burrow-site selection in a population of wild eastern chipmunks (Tamias striatus) relying on pulsed resources. We first compared characteristics of burrow microhabitats with those of equivalent unused plots. We then investigated the factors influencing the frequency of burrow occupation over time, and the individual and environmental causes of annual burrow fidelity decisions. Results: Our results indicate that chipmunks select microhabitats with a greater number of woody debris and greater slopes. Microhabitats of burrows with higher occupancy rates had a lower shrub stratum, were less horizontally opened and their occupants' sex-ratio was skewed towards males. Burrow fidelity was higher in non-mast years and positively related to the occupant's age, microhabitat canopy cover and density of large red maples. Conclusion: The quality of a burrow microhabitat appears to be determined in part by characteristics that favour predation avoidance, but consideration of occupancy and fidelity patterns over several years also highlighted the importance of including individual and contextual factors in habitat selection studies.

The Feast and the Famine: Spring Body Mass Variations and Life History Traits in a Pulse Resource Ecosystem.

AbstractPhenotypic plasticity is the most immediate mechanism of adaptative response to environmental change. Studying plastic changes in response to fluctuating environments provides insights into how such adjustments may impact life history traits. Here, we used a 14-year data set of repeated body mass measurements in male eastern chipmunks (Tamias striatus) to assess the extent of plastic changes for this trait in a resource pulse ecosystem. We first determined the magnitude of variation in body mass at the population level in response to the drastic change in food resource availability from American beech tree seeds (Fagus grandifolia). Males that emerged in the spring from winter torpor following a nonmast year had a lower body mass than males emerging after a mast year, but they tended to recover this loss by mid-June. We found significant among-individual variation in spring body mass plasticity (i.e., individual-by-environment interaction). We then investigated the relationships between individual spring body mass plasticity, longevity, and lifetime reproductive success. Interestingly, heavier males lived longer than lighter males, but more plastic males had a lower longevity and lower lifetime reproductive success than less plastic males. The report of such plastic response in a stochastic resource system provides valuable insights into the interplay between the costs and benefits of phenotypic plasticity as an adaptation to environmental fluctuations.

Telomere length positively correlates with pace-of-life in a sex- and cohort-specific way and elongates with age in a wild mammal.

Understanding ageing and the diversity of life histories is a cornerstone in biology. Telomeres, the protecting caps of chromosomes, are thought to be involved in ageing, cancer risks and life-history strategies. They shorten with cell division and age in somatic tissues of most species, possibly limiting lifespan. The resource allocation trade-off hypothesis predicts that short telomeres have thus coevolved with early reproduction, proactive behaviour and reduced lifespan, that is, a fast pace-of-life syndrome (POLS). Conversely, since short telomeres may also reduce the risks of cancer, the anticancer hypothesis advances that they should be associated with slow POLS. Conclusion on which hypothesis best supports the role of telomeres as mediators of life-history strategies is hampered by a lack of study on wild short-lived vertebrates, apart from birds. Using seven years of data on wild Eastern chipmunks Tamias striatus, we highlighted that telomeres elongate with age (n = 204 and n = 20) and do not limit lifespan in this species (n = 51). Furthermore, short telomeres correlated with a slow POLS in a sex-specific way (n = 37). Females with short telomeres had a delayed age at first breeding and a lower fecundity rate than females with long telomeres, while we found no differences in males. Our findings support most predictions adapted from the anticancer hypothesis, but none of those from the resource allocation trade-off hypothesis. Results are in line with an increasing body of evidence suggesting that other evolutionary forces than resource allocation trade-offs shape the diversity of telomere length in adult somatic cells and the relationships between telomere length and life-histories.

Integrating humans into pace-of-life studies: The Big Five personality traits and metabolic rate in young adults.

The pace-of-life syndrome (POLS) predicts that personality and metabolism should be correlated if they function as an integrated unit along a slow-fast continuum. Over the last decade, this conceptual framework has been tested in several empirical studies over a wide array of non-human animal taxa, across multiple personality traits and using standardized measures of metabolism. However, studies associating metabolic rate and personality in humans have been surprisingly scarce. Here, we tested whether there was covariation among personality scores, measured using the Big Five Inventory test, resting metabolic rate (RMR) and preferred walking speed (PWS) in a cohort of young human adults aged between 18 and 27 years old. We found a significant, negative relationship between RMR and Extraversion; less extraverted individuals had a 30% higher RMR than the most extraverted ones. No other personality traits correlated with RMR and none correlated with PWS. The negative correlation between Extraversion and RMR may suggest an allocation energy trade-off between personality and basal metabolism. Our results yielded equivocal support for the POLS and emphasized the need for more research on human to test the generality of this conceptual framework and further assess its validity.

Indirect genetic and environmental effects on behaviors, morphology, and life-history traits in a wild Eastern chipmunk population.

Additive genetic variance in a trait reflects its potential to respond to selection, which is key for adaptive evolution in the wild. Social interactions contribute to this genetic variation through indirect genetic effects-the effect of an individual's genotype on the expression of a trait in a conspecific. However, our understanding of the evolutionary importance of indirect genetic effects in the wild and of their strength relative to direct genetic effects is limited. In this study, we assessed how indirect genetic effects contribute to genetic variation of behavioral, morphological, and life-history traits in a wild Eastern chipmunk population. We also compared the contribution of direct and indirect genetic effects to traits evolvabilities and related these effects to selection strength across traits. We implemented a novel approach integrating the spatial structure of social interactions in quantitative genetic analyses, and supported the reliability of our results with power analyses. We found indirect genetic effects for trappability and relative fecundity, little direct genetic effects in all traits and a large role for direct and indirect permanent environmental effects. Our study highlights the potential evolutionary role of social permanent environmental effects in shaping phenotypes of conspecifics through adaptive phenotypic plasticity.

Integrating Mortality Risk and the Adaptiveness of Hibernation.

Low mortality rate is often associated with slow life history, and so far, has mainly been assessed through examinations of specific adaptations and lifestyles that limit mortality risk. However, the organization of activity time budgets also needs to be considered, since some activities and the time afforded for performing them may expose animals to higher mortality risks such as increased predation and/or increased metabolic stress. We examined the extent of activity time budgets contribution to explaining variation in life history traits in mammals. We specifically focused on hibernating species because of their marked seasonal cycle of activity/inactivity associated with very different mortality risks. Hibernation is considered a seasonal adaptation to prolonged periods of food shortage and cold. This inactivity period may also reduce both extrinsic and intrinsic mortality risks, by decreasing exposure to predators and drastically reducing metabolic rate. In turn, reduction in mortality may explain why hibernators have slower life history traits than non-hibernators of the same size. Using phylogenetically controlled models, we tested the hypothesis that longevity was positively correlated with the hibernation season duration (the time spent between immergence and emergence from the hibernaculum or den) across 82 different mammalian species. We found that longevity increased significantly with hibernation season duration, an effect that was particularly strong in small hibernators (<1.5 kg) especially for bats. These results confirm that hibernation not only allows mammals to survive periods of energy scarcity, but further suggest that activity time budgets may be selected to reduce mortality risks according to life history pace.

Individual and environmental determinants of Cuterebra bot fly parasitism in the eastern chipmunk (Tamias striatus).

Understanding the interactions between parasites, hosts, and their shared environment is central to ecology. Variation in infestation prevalence may be the result of varying environmental and population characteristics; however, variations in parasitism may also depend on individual characteristics that influence both the exposure and susceptibility to parasites. Using 12 years of data from a population of wild eastern chipmunks relying on pulsed food resources, we investigated the determinants of bot fly parasitism at both the population and individual level. We assessed the relationship between infestation prevalence and weather conditions, population size and food abundance. Then, we assessed the relationship between infestation intensity and chipmunk behavior, sex, age, body mass and food abundance. Precipitation, temperature and population size were positively related to infestation prevalence, while beech masts were negatively related to infestation prevalence, highlighting the importance of local environmental conditions on hosts and parasites. We also found that the influence of activity and exploration on infestation intensity varied according to sex in adults. More active and faster exploring males had more parasites compared to females, suggesting that reproductive behaviors may influence parasite exposure. For juveniles, infestation intensity was greater when juveniles emerged in the spring as opposed to fall, possibly because spring emergence is synchronized with the peak of bot fly eggs in the environment, low food availability and longer activity period. Our results suggest that the environmental, population and host characteristics that are advantageous for reproduction and resource acquisition may come at the cost of increasing parasitism.

Epigenetic anticipation for food and reproduction.

Physiological changes in anticipation of cyclic environmental events are common for the persistence of populations in fluctuating environments (e.g. seasons). However, dealing with sporadic resources such as the intermittent production of seed masting trees may be challenging unless reliable cues also make them predictable. To be adaptive, the anticipation of such episodic events would have to trigger the corresponding physiological response. Epigenetic modifications could result in such physiological anticipatory responses to future changes. The eastern chipmunk (Tamias striatus) is known to adjust its reproductive activity to match juvenile weaning with peak seed availability of masting trees, which are essential for their survival. We therefore expected that epigenetic changes would be linked to spring reproductive initiation in anticipation for beech seed availability in fall. We correlated the variation of DNA methylation profiles of 114 adult chipmunks captured in May with beech seeds abundance in September, over 4 years, for three distinct populations, as well as individuals sampled twice during reproductive and non-reproductive years. The significant correlation between spring epigenetic variation and the amount of food in the fall confirmed the phenotypic flexibility of individuals according to environmental fluctuations. Altogether, these results underlined the key role of epigenetic processes in anticipatory responses enabling organisms to persist in fluctuating environments.

Consumption of red maple in anticipation of beech mast-seeding drives reproduction in eastern chipmunks.

Understanding the determinants of reproduction is a central question in evolutionary ecology. In pulsed-resource environments, the reproduction and population dynamics of seed consumers are driven by pulsed production of seeds by trees or mast-seeding. In Southern Québec, eastern chipmunks Tamias striatus exclusively reproduce during the summer before and the spring after a mast-seeding event of American beech. They thus seem to anticipate beech mast by reproducing during early summer, so that juveniles can emerge at the time of maximum beechnut abundance during late summer. However, the cues allowing chipmunks to anticipate beech mast remain unknown, and the existence of the anticipation process itself has been questioned. To tackle those issues, we investigated the links between the nutritional ecology and reproduction of adult chipmunks and compared their spring diet in mast- versus post-mast years. We monitored female reproductive status (N = 446), analysed cheek pouch contents at capture (n = 3,761 captures) and recorded seed production by deciduous trees on three different sites in Mont-Sutton from 2006 to 2018. Results revealed a systematic shift in chipmunk diet towards red maple seeds in springs preceding a beech mast, with red maple seeds composing more than 77% of chipmunk diet. However, red maple consumption was unrelated to red maple production, but was related to beech seed production in the upcoming fall. We also found that red maple consumption best predicted the proportion of females in summer oestrus. Our results confirm that chipmunks anticipate beech mast-seeding and highlight a key role of red maple consumption in that anticipation. Results also suggest that red maple seeds may contain nutrients or secondary plant components essential to sustain or trigger the summer reproduction in chipmunks, which allow them to remain synchronized with pulsed productions of both red maple and beech and improve their fitness.

Social selection acts on behavior and body mass but does not contribute to the total selection differential in eastern chipmunks.

Through social interactions, phenotypes of conspecifics can affect an individual's fitness, resulting in social selection. Social selection is assumed to represent a strong and dynamic evolutionary force that can act with or in opposition to natural selection. Few studies, however, have estimated social selection and its contribution to total selection in the wild. We estimated natural and social selection gradients on exploration, docility, and body mass, and their contribution to selection differentials, in a wild eastern chipmunk population (Tamias striatus). We applied trait-based multiple regression models derived from classical phenotypic selection analyses, which allowed us to include several social partners (i.e., neighbors). We detected social selection gradients on female docility and male body mass, indicating that female with docile neighbors and males with large neighbors had lower fitness. In both sexes, social selection gradients varied with the season. However, we found no phenotypic assortment or disassortment for the studied traits. Social selection gradients, therefore, did not contribute to total selection differentials, and natural selection alone could drive phenotypic changes. Evaluating the factors that drive the evolution of the covariance between interacting phenotypes is necessary to understand the role of social selection as an evolutionary force.

Spatio-temporal variation in oxidative status regulation in a small mammal.

Life-history allocation trade-offs are dynamic over time and space according to the ecological and demographical context. Fluctuations in food availability can affect physiological trade-offs like oxidative status regulation, reflecting the balance between pro-oxidant production and antioxidant capacity. Monitoring the spatio-temporal stability of oxidative status in natural settings may help understanding its importance in ecological and evolutionary processes. However, few studies have yet conducted such procedures in wild populations. Here, we monitored individual oxidative status in a wild eastern chipmunk (Tamias striatus) population across the 2017 summer active period and over three study sites. Oxidative damage (MDA: Malondialdehyde levels) and non-enzymatic antioxidant levels (FRAP: Ferric reducing antioxidant power and HASC: Hypochlorous acid shock capacity) were quantified across time and space using assays optimized for small blood volumes. Our results showed an increase in oxidative damage mirrored by a decrease in FRAP throughout the season. We also found different antioxidant levels among our three study sites for both markers. Our results also revealed the effects of sex and body mass on oxidative status. Early in the active season, females and individuals with a greater body mass had higher oxidative damage. Males had higher HASC levels than females throughout the summer. This study shows that oxidative status regulation is a dynamic process that requires a detailed spatial and temporal monitoring to yield a complete picture of possible trade-offs between pro-oxidant production and antioxidant capacity.

Using Geographic Distance as a Potential Proxy for Help in the Assessment of the Grandmother Hypothesis.

Life-history theory predicts that selection could favor the decoupling of somatic and reproductive senescence if post-reproductive lifespan (PRLS) provides additional indirect fitness benefits [1, 2]. The grandmother hypothesis proposes that prolonged PRLS evolved because post-reproductive grandmothers gain inclusive fitness benefits by helping their daughters and grandchildren [3, 4]. Because most historical human data do not report direct evidence of help, we hypothesized that geographic distance between individuals may be inversely related to their capacity to help. Using an exceptionally detailed dataset of pre-industrial French settlers in the St. Lawrence Valley during the 17th and 18th centuries, we assessed the potential for grandmothers to improve their inclusive fitness by helping their descendants, and we evaluated how this effect varied with geographic distance, ranging between 0 and 325 km, while accounting for potential familial genetic and environmental effects [5-9]. Grandmothers (F0) who were alive allowed their daughters (F1) to increase their number of offspring (F2) born by 2.1 and to increase their number of offspring surviving to 15 years of age by 1.1 compared to when grandmothers were dead. However, the age at first reproduction was not influenced by the life status (alive or dead) of grandmothers. As geographic distance increased, the number of offspring born and lifetime reproductive success decreased, while the age at first reproduction increased, despite the grandmother being alive in these analyses. Our study suggests that geographic proximity has the potential to modulate inclusive fitness, supporting the grandmother hypothesis, and to contribute to our understanding of the evolution of PRLS.

Development of small blood volume assays for the measurement of oxidative stress markers in mammals.

Measuring oxidative stress has become increasingly valuable in ecological studies, especially when different markers are measured on the same individual. However, many of the current methods lack sensitivity for analysis of low blood volume samples, which represent a challenge for longitudinal field studies of small organisms. Small blood volumes can usually only be analysed by using a single assay, therefore providing limited information on individual's oxidative profile. In this study, we used blood collected from a population of wild eastern chipmunks (Tamias striatus) and modified methods presented in the literature to improve analytical selectivity and sensitivity required for small blood volumes. Specifically, we proposed a modified malondialdehyde (MDA) analysis protocol by HPLC and also optimized both the uric acid independent ferric reducing antioxidant power (FRAP) and hypochlorous acid shock capacity (HASC) assays. Development of the three modified methods was achieved with a sensitivity and repeatability that meets standards of field ecology while allowing measurement of all three assays in duplicate using less than 60 µL of plasma. Availability of these tests using small blood volumes will provide ecologists with a more comprehensive portrait of an individual's oxidative profile and a better understanding of its determinants and interactions with the environment.

Eco-evolutionary dynamics in a contemporary human population.

Recent studies of the joint dynamics of ecological and evolutionary processes show that changes in genotype or phenotype distributions can affect population, community and ecosystem processes. Such eco-evolutionary dynamics are likely to occur in modern humans and may influence population dynamics. Here, we study contributions to population growth from detailed genealogical records of a contemporary human population. We show that evolutionary changes in women's age at first reproduction can affect population growth: 15.9% of variation in individual contribution to population growth over 108 years is explained by mean age at first reproduction and at least one-third of this variation (6.1%) is attributed to the genetic basis of this trait, which showed an evolutionary response to selection during the period studied. Our study suggests that eco-evolutionary processes have modulated the growth of contemporary human populations.

Association between Floods and Acute Cardiovascular Diseases: A Population-Based Cohort Study Using a Geographic Information System Approach.

BACKGROUND: Floods represent a serious threat to human health beyond the immediate risk of drowning. There is few data on the potential link between floods and direct consequences on health such as on cardiovascular health. This study aimed to explore the impact of one of the worst floods in the history of Quebec, Canada on acute cardiovascular diseases (CVD). METHODS: A cohort study with a time series design with multiple control groups was built with the adult population identified in the Quebec Integrated Chronic Disease Surveillance System. A geographic information system approach was used to define the study areas. Logistic regressions were performed to compare the occurrence of CVD between groups. RESULTS: The results showed a 25%-27% increase in the odds in the flooded population in spring 2011 when compared with the population in the same area in springs 2010 and 2012. Besides, an increase up to 69% was observed in individuals with a medical history of CVD. CONCLUSION: Despite interesting results, the association was not statistically significant. A possible explanation to this result can be that the population affected by the flood was probably too small to provide the statistical power to answer the question, and leaves open a substantial possibility for a real and large effect.

Field estimates of parentage reveal sexually antagonistic selection on body size in a population of Anolis lizards.

Sexual dimorphism evolves when selection favors different phenotypic optima between the sexes. Such sexually antagonistic selection creates intralocus sexual conflict when traits are genetically correlated between the sexes and have sex-specific optima. Brown anoles are highly sexually dimorphic: Males are on average 30% longer than females and 150% heavier in our study population. Viability selection on body size is known to be sexually antagonistic, and directional selection favors large male size whereas stabilizing selection constrains females to remain small. We build on previous studies of viability selection by measuring sexually antagonistic selection using reproductive components of fitness over three generations in a natural population of brown anoles. We estimated the number of offspring produced by an individual that survived to sexual maturity (termed RSV), a measure of individual fitness that includes aspects of both individual reproductive success and offspring survival. We found directional selection on male body size, consistent with previous studies of viability selection. However, selection on female body size varied among years, and included periods of positive directional selection, quadratic stabilizing selection, and no selection. Selection acts differently in the sexes based on both survival and reproduction and sexual conflict appears to be a persistent force in this species.

Proximity and emergency department use: Multilevel analysis using administrative data from patients with cardiovascular risk factors.

OBJECTIVE: To determine if geographic proximity to an emergency department (ED) is related to ED use in a metropolitan population of patients with cardiovascular risk factors. DESIGN: Population-based, retrospective cohort study. SETTING: The census metropolitan area of Montreal, Que. PARTICIPANTS: Cohort of 99 400 patients with diabetes, hypertension, or dyslipidemia in 2007 without a history of cardiovascular disease. Each patient was spatially referred to 1 of 5857 dissemination areas (DAs). MAIN OUTCOME MEASURES: Annual number of visits to an ED with respect to the distance between the centroid of a patient's DA and the closest ED, controlling for age, sex, comorbidities, and neighbourhood immigration, social, and material characteristics. Multilevel logistic and negative binomial regressions were used to determine if the proximity to the closest ED was related to ED use, frequent ED use (≥ 4 visits in a year), and number of ED visits. RESULTS: A total of 25 889 (26.0%) patients in the cohort visited an ED at least once during a 1-year period, among which 4563 (4.6%) were frequent users with at least 4 visits. These frequent users were responsible for 28 249 (45.5%) of all 62 021 visits to EDs. The distance between a DA and its closest ED was significantly and negatively correlated with ED use (P < .001), even after controlling for confounding variables. Patients living in a DA close to an ED were also more likely to be frequent users, but the extent of use among them (range from 4 to 82 ED visits) was not related to the distance to the closest ED. CONCLUSION: These results suggest that patients at risk of cardiovascular disease living in a metropolitan area are more likely to seek a medical encounter at the ED if they live closer to it.

Homeostatic dysregulation proceeds in parallel in multiple physiological systems.

An increasing number of aging researchers believes that multi-system physiological dysregulation may be a key biological mechanism of aging, but evidence of this has been sparse. Here, we used biomarker data on nearly 33, 000 individuals from four large datasets to test for the presence of multi-system dysregulation. We grouped 37 biomarkers into six a priori groupings representing physiological systems (lipids, immune, oxygen transport, liver function, vitamins, and electrolytes), then calculated dysregulation scores for each system in each individual using statistical distance. Correlations among dysregulation levels across systems were generally weak but significant. Comparison of these results to dysregulation in arbitrary 'systems' generated by random grouping of biomarkers showed that a priori knowledge effectively distinguished the true systems in which dysregulation proceeds most independently. In other words, correlations among dysregulation levels were higher using arbitrary systems, indicating that only a priori systems identified distinct dysregulation processes. Additionally, dysregulation of most systems increased with age and significantly predicted multiple health outcomes including mortality, frailty, diabetes, heart disease, and number of chronic diseases. The six systems differed in how well their dysregulation scores predicted health outcomes and age. These findings present the first unequivocal demonstration of integrated multi-system physiological dysregulation during aging, demonstrating that physiological dysregulation proceeds neither as a single global process nor as a completely independent process in different systems, but rather as a set of system-specific processes likely linked through weak feedback effects. These processes--probably many more than the six measured here--are implicated in aging.