Key Life-history Event Research Articles

Self-reported history of breastfeeding in relation to recalled age at menarche in the United States.

Menarche is a key life history event that shapes the female reproductive trajectory and is important to the study of human biology because of the associated epidemiological and social consequences later in life. Our question is whether breastfeeding is associated with the variation in timing of menarche. Using data from a college-aged female student population from Amherst, MA, we examined whether having been breastfed was associated with age at menarche. Of the 340 female participants with information on breastfeeding during infancy, we found that women who were breastfed (n = 286) had an adjusted mean age of menarche of 12.53 years (SE 0.09), while those who were not breastfed (n = 54) had an adjusted mean age of menarche of 12.04 years (SE 0.20; p < 0.03). We propose further research that explores a finer distinction between formula-fed, mixed-fed or predominantly breastfed infants, duration of breastfeeding and age at menarche.

Wearable reproductive trackers: quantifying a key life history event remotely

Advancements in biologging technology allow terabytes of data to be collected that record the location of individuals but also their direction, speed and acceleration. These multi-stream data sets allow researchers to infer movement and behavioural patterns at high spatiotemporal resolutions and in turn quantify fine-scale changes in state along with likely ecological causes and consequences. The scope offered by such data sets is increasing and there is potential to gain unique insights into a suite of ecological and life history phenomena. We use multi-stream data from global positioning system (GPS) and accelerometer (ACC) devices to quantify breeding events remotely in an Arctic breeding goose. From a training set of known breeders we determine the movement and overall dynamic body acceleration patterns indicative of incubation and use these to classify breeding events in individuals with unknown reproductive status. Given that researchers are often constrained by the amount of biologging data they can collect due to device weights, we carry out a sensitivity analysis. Here we explore the relative merits of GPS vs ACC data and how varying the temporal resolution of the data affects the accuracy of classifying incubation for birds. Classifier accuracy deteriorates as the temporal resolution of GPS and ACC are reduced but the reduction in precision (false positive rate) is larger in comparison to recall (false negative rate). Precision fell to 94.5%, whereas recall didn’t fall below 98% over all sampling schedules tested. Our data set could have been reduced by c.95% while maintaining precision and recall > 98%. The GPS-only classifier generally outperformed the ACC-only classifier across all accuracy metrics but both performed worse than the combined GPS and ACC classifier. GPS and ACC data can be used to reconstruct breeding events remotely, allowing unbiased, 24-h monitoring of individuals. Our resampling-based sensitivity analysis of classifier accuracy has important implications with regards to both device design and sampling schedules for study systems, where device size is constrained. It will allow researchers with similar aims to optimize device battery, memory usage and lifespan to maximise the ability to correctly quantify life history events.

Crabs Go With the Flow: Declining Conductivity and Cooler Temperatures Trigger Spawning Migrations for Female Giant Mud Crabs (Scylla serrata) in Subtropical Estuaries

Spawning is a key life history event for aquatic species that can be triggered by environmental signals. For estuarine-dependent species, the timing of such triggers can be important for determining future patterns in recruitment. Here, we used acoustic telemetry to identify the potential drivers of spawning migration in female Giant Mud Crabs (Scylla serrata). Eighty-nine mature female crabs were tagged in two subtropical south-east Australian estuaries, the Clarence River (~ 29.4°S) and Kalang River (~ 30.5°S), during the summer spawning season (November–June) over two years (2018/19 and 2020/21), and their movements were monitored for up to 68 d, alongside high-resolution environmental data. Crabs were considered to have ‘successfully’ migrated if they were detected at the mouth of the estuary, a behaviour exhibited by 52% of tagged crabs. The highest probability of migration was associated with relatively low temperatures (< 22 °C) and when conductivity rapidly declined (< -10 mS cm−1 d−1) following heavy rainfall. Furthermore, migration coincided with larger tides associated with the new and full moon, and following heavy rainfall, which may aid rapid downstream migration. Oceanic detections of 14 crabs (30% of ‘successful’ migrators) showed that once crabs left estuaries they migrated north. These patterns show that variability in environmental triggers for spawning migrations may contribute to interannual variation in spawning patterns, which may in turn impact fisheries productivity in this region.

Ontogenetic Shifts in Oxygen Uptake in Common Mudskipper (Periophthalmus kalolo) and its Role in Microhabitat Selection

Aims: The common mudskipper, Periophthalmus kalolo is a tropical, amphibious fish that utilizes both air and water as a respiratory medium. Adult oxygen uptake in water and air is well studied, but requirements of post-metamorphosed fish are virtually unknown. Our study quantifies how ontogenetic shifts across mudskipper life stage affects microhabitat choice.&#x0D; Study Design: metabolic rates in air and water were estimated for common mudskippers with mass values from 0.03 to 28.9 grams. Fish in each media were divided into 5 standard length classes (≤ 2.00, 2.01-4.00, 4.01-6.00, 6.01-8.00, ≥ 8.01 cm). Oxygen consumption for each class was calculated as the mean individual oxygen consumption for the group.&#x0D; Place and Duration of Study: Hoga Research Laboratory, Wakatobi National Park, Sulawesi, Indonesia, between June 14 and August 26, 2005.&#x0D; Methodology: Gilson manometry, and flow-through respirometery was used to determine respective aerial and aquatic oxygen uptake values for common mudskippers.&#x0D; Results: Mudskipper lengths varied by an order of magnitude (1.0 to 10.3 cm) and mass varied by three orders of magnitude (0.03 to 17.3 g). Mass-adjusted aerial metabolic rates of fish 2.00 cm or less in length, consumed up to ten times more oxygen than larger fish. whereas, aerial consumption values for size classes 2.01 cm and above did not differ significantly from each other (ANOVA: F4,112 = 40.29, P &lt; 0.0001; SNK, α = 0.05).&#x0D; Metabolic rates of submerged fish fell into two statistically distinct subsets. mudskippers with lengths of 4.00 cm or less had significantly higher metabolic rates than fish in remaining size classes; however, mean oxygen uptake values of fish within subsets did not differ significantly (ANOVA: F4,87 = 6.89, P &lt; 0.0001; SNK, α = 0.05). When oxygen consumption values at each size class were compared, only the smallest mudskipper size class (£ 2.00 cm) differed significantly between air and water (t-test: df = 34, t = 3.44, P &lt; 0.0001). Mudskippers 2 cm in standard length or smaller consumed over seven times more oxygen in air than water. All other size classes had similar rates of oxygen uptake in air and water and air:water oxygen uptake ratios fell to approximately 1:1.&#x0D; Conclusions: (1) Common mudskippers select different mangal habitats based on developmental life stage. (2) Small, post-metamorphosed fish &lt;2 mm in standard length, prefer cool shaded mangal areas, whereas, larger mudskippers utilize sun-exposed zones.&#x0D; (3) Post-metamorphosed fish, consume 10X more oxygen than all other size groups, confirming that juveniles are well suited to aerial respiration oxygen shortly after hatching. (4) Emerged post-metamorphosed fish exploit cooler, wetter pool habitats, thereby ameliorating problems of desiccation, excretion, and/or predation. (5) Ontogenetic shifts are a key life-history event in P. kalolo that promotes wider mangrove habitat use, and plays an important role in establishing common mudskipper as a key mangal species.

Variation of social strategies within and between individual black-tailed prairie dogs (Cynomys ludovicianus) during the reproductive season

Sociality describes the tendency for members of a species to associate in a group based on social attraction. To balance the trade-offs of sociality, the fitness consequences (and therefore proclivity towards being social) should be expected to vary across individuals and within the same individual, across time. We used social network analysis to evaluate the causes and consequences of within- and between-individual variation in sociality in a wild population of black-tailed prairie dogs (Cynomys ludovicianus) during the reproductive season. We hypothesised that individuals would adjust their behaviours based on a key life-history event: reproduction. We assessed this variation by comparing differences in social behaviour between individuals in different life history stages and within individuals across the reproductive season. We predicted breeding females would increase their agonistic interactions to protect their offspring from infanticide during reproduction, while non-reproductive individuals would increase their affiliative interactions to maintain stability in their social network and increase their indirect fitness. We found that the number of social interactions decreased after reproduction for all individuals. Breeding females did not increase their agonistic interactions compared to other groups, but instead had overall decreased social interactions during reproduction, which corresponded with increased fitness. For non-breeding females, an increase of affiliative social interactions correlated with increased indirect fitness as we predicted. Our multiple-level, temporally structured analyses revealed under-realised complexities regarding within- and between-individual variation in social interactions, suggesting reproductive status dictates different social strategies to optimise fitness. Social living with conspecifics confers a range of costs and benefits, the trade-offs of which are expected to change based on life history. Therefore, individuals should modulate their sociality across life history transitions to optimise fitness. Reproductive status is known to affect socio-behavioural decisions across taxa. We used a highly social species, black-tailed prairie dogs, to investigate variation in social structure across the reproductive season, and understand both the causes and consequences of individual variation in social structure. Prairie dogs offered easily observable, dynamic social behaviours and quantifiable fitness consequences to truly demonstrate acute social change. Our results suggest that there is variation of social interactions not only within individuals over time, but also between reproductive groups in the same time period. Our analyses suggest that social variation has important consequences for fitness and should further stimulate study of temporally based analyses of social behaviour.

Territory acquisition mediates the influence of predators and climate on juvenile red squirrel survival.

Juvenile survival to first breeding is a key life-history stage for all taxa. Survival through this period can be particularly challenging when it coincides with harsh environmental conditions such as a winter climate or food scarcity, leading to highly variable cohort survival. However, the small size and dispersive nature of juveniles generally make studying their survival more difficult. In territorial species, a key life-history event is the acquisition of a territory. A territory is expected to enhance survival, but how it does so is not often identified. We tested how the timing of territory acquisition influenced the winter survival of juvenile North American red squirrels Tamiasciurus hudsonicus, hereafter red squirrels, and how the timing of this event mediated the sources of mortality. We hypothesized that securing a territory prior to when food resources become available would reduce juvenile susceptibility to predation and climatic factors overwinter. Using 27years of data on the survival of individually marked juvenile red squirrels, we tested how the timing of territory acquisition influenced survival, whether the population density of red squirrel predators and mean temperature overwinter were related to individual survival probability, and if territory ownership mediated these effects. Juvenile red squirrel survival was lower in the years of high predator abundance and in colder winters. Autumn territory owners were less susceptible to lynx Lynx canadensis and possibly mustelid Mustela and Martes spp., predation. Autumn territory owners had lower survival in colder winters, but surprisingly non-owners had higher survival in cold winters. Our results show how the timing of a life-history event like territory acquisition can directly affect survival and also mediate the effects of biotic and abiotic factors later in life. This engenders a better understanding of the fitness consequences of the timing of key life-history events.

Mating precedes selective immune priming which is maintained throughout bumblebee queen diapause

BackgroundUnderstanding the mechanisms by which organisms adapt to unfavourable conditions is a fundamental question in ecology and evolutionary biology. One such mechanism is diapause, a period of dormancy typically found in nematodes, fish, crustaceans and insects. This state is a key life-history event characterised by arrested development, suppressed metabolism and increased stress tolerance and allows an organism to avoid prolonged periods of harsh and inhospitable environmental conditions. For some species, diapause is preceded by mating which can have a profound effect on female behaviour, physiology and key biological processes, including immunity. However, our understanding of how mating impacts long-term immunity and whether these effects persist throughout diapause is currently limited. To address this, we explored molecular changes in the haemolymph of the ecologically important pollinator, the buff-tailed bumblebee Bombus terrestris. B. terrestris queens mate prior to entering diapause, a non-feeding period of arrested development that can last 6–9 months. Using mass-spectrometry-based proteomics, we quantified changes in the pre-diapause queen haemolymph after mating, as well as the subsequent protein expression of mated queens during and post-diapause.ResultsOur analysis identified distinct proteome profiles associated with diapause preparation, maintenance and termination. More specifically, mating pre-diapause was followed by an increase in the abundance of antimicrobial peptides, key effectors of the immune system. Furthermore, we identified the elevated abundance of these proteins to be maintained throughout diapause. This finding was in contrast to the general reduction observed in immune proteins during diapause suggestive of selective immune priming and expression during diapause. Diapause also affected the expression of proteins involved in cuticular maintenance, olfaction, as well as proteins of unknown function, which may have roles in diapause regulation.ConclusionsOur results provide clear molecular evidence for the consequences and benefits of mating at the immune level as it precedes the selective increased abundance of antimicrobial peptides that are sustained throughout diapause. In addition, our results provide novel insights into the molecular mechanisms by which bumblebees prepare for, survive, and recover from diapause, insights that may have implications for our general understanding of these processes in other insect groups.

The difference a day makes: Breeding remodels hearing, hormones and behavior in female Cope's gray treefrogs (Hyla chrysoscelis)

In seasonal breeders, there are behavioral, endocrine, and neural adaptations that promote the sexual receptivity of females and tune their sensory systems to detect and discriminate among advertising males and to successfully copulate. What happens immediately after this key life history event is unclear, but this transitional moment offers a window into the mechanisms that remodel sexual phenotypes. In this study of wild female Cope's gray treefrogs (Hyla chrysoscelis), we tested the hypothesis that oviposition results in a suite of coordinated changes in the sexual phenotype. Specifically, we predicted that sexual receptivity and discrimination behaviors would decline along with circulating concentrations of steroid hormones (corticosterone, estradiol, testosterone) and auditory sensitivity to the acoustic frequencies emphasized in male advertisement calls. We conducted these trait measurements before and after oviposition (ca. 24-h period). There was a 100% decrease in behavioral responsiveness after oviposition, and the concentrations of all three steroids plummeted during this brief window of time, especially testosterone. Moreover, higher concentrations of corticosterone—an important component of the endocrine stress response—were associated with longer response latencies, suggesting that adrenal hormones should be considered in future studies on the hormonal basis of mate choice. Counter to our prediction, auditory sensitivity increased following oviposition, and the amplitude of the auditory brainstem response was influenced by concentrations of estradiol. In pre-oviposition females auditory sensitivity diminished with increasing estradiol concentrations, while sensitivity increased with increasing estradiol concentrations in post-oviposition females, suggesting non-linear estrogenic modulation of peripheral auditory neural recruitment. Overall, our results indicate that there is considerable remodeling of behavioral output following oviposition that co-occurs with changes in both endocrine and sensory physiology.

Phenological Diversity of Salmon Smolt Migration Timing within a Large Watershed

AbstractAlthough there is growing concern that climate change might drive phenological mismatches between predators and prey, it is possible that within‐ and among‐species phenological variation provides resilience against such a mismatch. One key life history event that may be vulnerable to climate‐induced mismatch is the seaward migration of juvenile salmon relative to the spring bloom of their marine zooplankton prey. Here, we quantified phenological diversity of out‐migration timing among salmon populations within a large watershed and its implications for climate mismatches with marine zooplankton. Specifically, we sampled juvenile Sockeye Salmon Oncorhynchus nerka throughout the spring and early summer in the estuary of the Skeena River, a vast watershed with numerous locally adapted salmon populations that support commercial, recreational, and First Nations fisheries, and we used genetic stock identification to link the fish to their population of origin. We found that Sockeye Salmon were migrating through the estuary for more than 50 d, with peak emigration for different populations varying by over 5 weeks. The out‐migration timing of specific populations was related to geographic factors, including elevation of the rearing lake and the river distance between individual rearing lakes and the estuary, with different populations arriving 1.5 d later for every 100 m of elevation or 3 d later for every 100 km of river distance. Concurrent with sampling, we quantified the estuarine prey of juvenile Sockeye Salmon; zooplankton species composition and abundance varied throughout the smolt migration period, and the different salmon populations encountered different prey abundances upon ocean entry. Together, these results indicate underappreciated phenological diversity in this harvested metapopulation, which may contribute to response diversity and metapopulation‐level resilience to climate change.

Habitat selection by threatened burrowing spiders (Araneae: Atypidae, Eresidae) of central Europe: evidence base for conservation management

Habitat selection in sedentary, long-lived burrowing spiders is a key life-history event that directly affects their reproductive success. In this study, we analyzed the role of the chemical and physical properties of soil in habitat selection by threatened temperate burrowing spiders. We examined 296 burrows of three Atypus spp. and three Eresus spp. at 68 sites in Czechia. We found that the study species were associated with soils that have high or very high cation exchange capacity, which allows the presence of a stable and humid microclimate in their burrows. We found that specific bedrock types can be used as predictors of the presence of particular study species. All Eresus spp. avoided compacted soils. However, when present in soils with very low penetration resistance, they were limited to sites with high soil cohesion. The burrows of all study species were located at well-drained sites. The study species seemed to be selective for a steppe-like character of their microhabitat but not necessarily for its southward orientation. We found the study species even at sites where steppes were present in the early 1950s and that underwent later afforestation but not extensive landscaping or plowing. What types of disturbances can be sustained by the study species and how long it takes the decreased populations to recover after, e.g., trampling associated with grazing, remain to be investigated.

Queen control of a key life-history event in a eusocial insect

In eusocial insects, inclusive fitness theory predicts potential queen-worker conflict over the timing of events in colony life history. Whether queens or workers control the timing of these events is poorly understood. In the bumble-bee Bombus terrestris, queens exhibit a 'switch point' in which they switch from laying diploid eggs yielding females (workers and new queens) to laying haploid eggs yielding males. By rearing foundress queens whose worker offspring were removed as pupae and sexing their eggs using microsatellite genotyping, we found that queens kept in the complete absence of adult workers still exhibit a switch point. Moreover, the timing of their switch points relative to the start of egg-laying did not differ significantly from that of queens allowed to produce normal colonies. The finding that bumble-bee queens can express the switch point in the absence of workers experimentally demonstrates queen control of a key life-history event in eusocial insects. In addition, we found no evidence that workers affect the timing of the switch point either directly or indirectly via providing cues to queens, suggesting that workers do not fully express their interests in queen-worker conflicts over colony life history.

DIFFERENTIAL AGING OF BITE AND JUMP PERFORMANCE IN VIRGIN AND MATED TELEOGRYLLUS COMMODUS CRICKETS

Evolutionary theories of aging state that the force of natural selection declines with age, resulting in trait senescence. However, sexual selection theory predicts that costly traits that signal mate value should increase in expression as survival prospects decline. Mortality rates and fertility tend to show strong signatures of senescence, whereas sexual signaling traits increase with age, but how the expression of traits such as whole-organism performance measures that are subject to both sexual and nonsexual selection should change with age is unclear. We examined the effects of both a key life-history event (mating) and diet quality (male and female optimal diets) on aging in two whole-organism performance traits (bite force and jump take-off velocity) in male and female Teleogryllus commodus crickets. We found no evidence for diet effects on any of the measured traits. Aging effects were more evident in females than in males for both jumping and biting, and constitute a mix of senescence and terminal investment patterns depending on sex/mating class. Sex and mating therefore have important implications for resource allocation to performance traits, and hence for aging of those traits, and interactions between these two factors can result in complex changes in trait expression over individual lifetimes.

The trade-off between growth rate and locomotor performance varies with perceived time until breeding

Environmental circumstances can cause changes in early growth patterns that subsequently affect the adult phenotype. Here we investigated how different growth trajectories affected subsequent locomotor performance, and how such effects were influenced by the perceived time until the key life-history event of reproduction. Using juvenile three-spined sticklebacks Gasterosteus aculeatus, we show that a brief period of manipulated temperature in early life (independent of food supply) caused effects on skeletal growth trajectory not only during the manipulation itself, but also during a subsequent compensatory phase. The outcome of these changes was that fish in all treatment groups reached the same average size by sexual maturity, despite having different growth patterns. However, their growth trajectory had impacts on both pre-breeding swimming endurance and its decline over the course of the breeding season, such that swimming ability was negatively correlated with skeletal growth rate during the compensation period. We also show for the first time that 'negative compensation' (i.e. a decelerating growth trajectory) led to an improved swimming performance compared with steadily growing controls. Replicate experiments and photoperiod manipulations, moreover, revealed that the effects of growth rate on subsequent swimming performance were greater when the perceived time until the breeding season was shorter. These results show that the costs of accelerated or decelerated growth can last well beyond the time over which growth rates differ, and are affected by the time available until an approaching life history event such as reproduction, possibly because of the time available to repair the damage.