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Data from: Age, condition and dominance-related sexual ornament size before and during the breeding season in the black grouse Lyrurus tetrix

Male ornaments function as honest cues of male quality in many species and are subject to intra- and intersexual selection. These ornaments are generally studied during peak expression, however their size outside the breeding season may determine ultimate ornament size and costliness, and as such reproductive success. We investigated whether male black grouse Lyrurus tetrix eye comb size was related to age, condition and measures of male dominance before and during the breeding season. Total combined eye comb size began to increase ~70 days before the start of the breeding season. Adult males (aged ≥ 2 years old) had consistently larger eye combs than younger males (1 year old) both before and during the breeding season. Heavier and more dominant adult males (attending the lek more frequently and successfully reproducing) had larger eye combs. For younger males, those that were heavier had larger eye combs. Additionally, males that spent more time on the lek showed increased eye comb size as the breeding season approached. Overall we find that ornament size is positively related to dominance and condition before and during the breeding season. Since dominance is accrued through year-round interactions in many species, the ability to maintain larger signals over prolonged periods,

opencc-zeroDec 2015View details →

Data from: Habitat- and season-specific temperatures affect phenotypic development of hatchling lizards

Embryonic environments influence phenotypic development, but relatively few experiments have explored the effects of natural environmental variation. We incubated eggs of the lizard Anolis sagrei under conditions that mimicked natural spatial and temporal thermal variation to determine their effects on offspring morphology and performance. Incubation temperatures mimicked two microhabitats (open, shade) at two different times of the incubation season (April, July). Egg survival, incubation duration and offspring size were influenced by interactions between habitat- and season-specific nest temperatures, and locomotor performance was influenced primarily by temporal factors. These findings highlight the importance of spatial and temporal environmental variation in generating variation in fitness-related phenotypes.

Data from: Seasonal plasticity in anti-predatory strategies: matching of color and color preference for effective crypsis

Effective anti-predatory strategies typically require matching appearance and behavior in prey, and there are many compelling examples of behavioral repertoires that enhance the effectiveness of morphological defenses. When protective adult morphology is induced by developmental environmental conditions predictive of future predation risk, adult behavior should be adjusted accordingly to maximize predator avoidance. While behavior is typically strongly affected by the adult environment, developmental plasticity in adult behavior — mediated by the same pre-adult environmental cues that affect morphology — could ensure an effective match between anti-predatory morphology and behavior. The coordination of environmentally-induced responses may be especially important in populations exposed to predictable environmental fluctuations (e.g. seasonality). Here, we studied early and late life environmental effects on a suite of traits expected to work together for effective crypsis. We focused on wing color and background color preference in Bicyclus anynana, a model of developmental plasticity that relies on crypsis as a seasonal strategy for predator avoidance. Using a full-factorial design, we disentangled effects of developmental and adult ambient temperature on both appearance and behavior. We showed that developmental conditions affect both adult color and color preference, with temperatures that simulate natural dry season conditions leading to browner butterflies with a perching preference for brown backgrounds. This effect was stronger in females, especially when butterflies were tested at lower ambient temperatures. In contrast to the expectation that motionlessness enhances crypsis, we found no support for our hypothesis that the browner dry-season butterflies would be less active. We argue that the integration of developmental plasticity for morphological and behavioral traits might improve the effectiveness of seasonal anti-predatory strategies.

opencc-zeroDec 2015View details →

Data from: Seasonal changes in starch content in trophopods of Matteuccia struthiopteris

Trophopods are modified stipe bases that function as starch-storage organs in a wide variety of mainly temperate ferns. Ever since they were first observed, the presence of trophopods has been explained by reference to seasonality and they have been assumed to provide nutrition for the rapidly expanding fern leaves in spring. We present the results of an analysis of the annual variation in starch content in Matteuccia struthiopteris (L.) Todaro, cultivated in the Leiden botanical garden. Our results show a distinct seasonal variation in starch content, suggesting that the presence of trophopods is indeed functionally linked to seasonality, but we do not find a decrease in starch content corresponding to the period of leaf expansion that would clearly link the depletion of stored starch to the expansion of new leaves.

Data from: Seasonality in the migration and establishment of H3N2 Influenza lineages with epidemic growth and decline

Background: Influenza A/H3N2 has been circulating in humans since 1968, causing considerable morbidity and mortality. Although H3N2 incidence is highly seasonal, how such seasonality contributes to global phylogeographic migration dynamics has not yet been established. In this study, we incorporate time-varying migration rates in a Bayesian MCMC framework. We focus on migration within China and between China and North-America as case studies, then expand the analysis to global communities. Results: Incorporating seasonally varying migration rates improves the modeling of migration in our case studies, and of global influenza population dynamics. In our global model, windows of increased immigration (in migration) map to the seasonal timing of epidemic spread, while windows of increased emigration (out migration) map to epidemic decline. Seasonal patterns also correlate with the probability that local lineages go extinct and fail to contribute to long term viral evolution, as measured through the trunk of the phylogeny. However, the fraction of the trunk in each community was found to be better determined by its overall human population size. Conclusions: Seasonal migration and rapid turnover within regions is sustained by the invasion of 'fertile epidemic grounds' at the end of older epidemics. Thus, the current emphasis on connectivity, including air-travel, should be complemented with a better understanding of the conditions and timing required for successful establishment. This will better our understanding of the seasonal drivers of influenza, improve epidemiological predictions, and improve vaccine updating by identifying strains that not only escape immunity but also have the seasonal opportunity to establish and spread, identified through models which account for migration seasonality. Further work is also needed on additional conditions that contribute to the persistence and long term evolution of influenza within the human population, such as spatial heterogeneity with respect to climate and seasonality.

Data from: Effects of early-season insect herbivory on subsequent pathogen infection and ant abundance on wild cotton (Gossypium hirsutum)

1. Plant induced defences play an important role in mediating interactions between insects and pathogens. Yet, the plant traits underlying these effects, the extended consequences for higher trophic levels (i.e. predators), and the implications for plant growth and reproduction have received little attention. 2. Here we asked whether simulated early insect leaf damage on wild cotton (Gossypium hirsutum) affected subsequent damage by insect leaf chewers and pathogenic fungi, as well as ant abundance. To address the mechanisms behind such effects, we measured plant defensive traits induced by early leaf damage to determine which inducible traits might determine the effects on plant-associates. We also evaluated whether early damage influenced plant growth and flower production, and if such effects were mediated by subsequent insect herbivory or pathogen infection. 3. We show that simulated early leaf damage reduced damage by subsequent leaf-chewing insects, increased plant fungal infections, but did not affect ant abundance. Leaf defensive traits (lignins and pubescence) were significantly induced by early damage and were negatively associated with insect herbivory and infection severity, but did not account for the effects of early leaf damage on either of these subsequent attackers. In addition, ant abundance was not associated with (or accounted for) subsequent herbivory or infection, suggesting they did not confer plant protection. Finally, early leaf damage negatively affected plant growth and flower production and analyses suggested that the effect on the latter was, at least partly, mediated by increased fungal infections. 4. Synthesis: Overall, these findings show that early herbivory determines the outcome of cotton interactions with subsequent attackers, and such effects have an impact on plant growth and flower output.

Data from: Seasonality, alarm pheromone and serotonin: insights on the neurobiology of honeybee defence from winter bees

Honeybees maintain their colony throughout the cold winters, a strategy that enables them to make the most of early spring flowers. During this period, their activity is mostly limited to thermoregulation, while foraging and brood rearing are stopped. Less is known about seasonal changes to the essential task of defending the colony against intruders, which is regulated by the sting alarm pheromone. We studied the stinging responsiveness of winter bees exposed to this scent or a control (solvent). Surprisingly winter bees, while maintaining their responsiveness in control conditions, did not increase stinging frequency in response to the alarm pheromone. This was not due to the bees not perceiving the pheromone, as shown by calcium-imaging of the antennal lobes. Since the alarm pheromone is thought to act through an increase in brain serotonin levels, ultimately causing heightened defensiveness, we checked if serotonin treatments would affect the stinging behaviour of winter bees. Indeed, treated winter bees became more inclined to sting. Thus, we postulate that loss of responsiveness to the sting alarm pheromone is based on a partial or total disruption of the mechanism converting alarm pheromone perception into high serotonin levels in winter bees.

Data from: Ecdysteroid hormones link the juvenile environment to alternative adult life histories in a seasonal insect

The conditional expression of alternative life strategies is a widespread feature of animal life and a pivotal adaptation to life in seasonal environments. To optimally match suites of traits to seasonally changing ecological opportunities, animals living in seasonal environments need mechanisms linking information on environmental quality to resource allocation decisions. The butterfly Bicyclus anynana expresses alternative adult life histories in the alternating wet and dry seasons of its habitat as endpoints of divergent developmental pathways triggered by seasonal variation in preadult temperature. Pupal ecdysteroid hormone titers are correlated with the seasonal environment, but whether they play a functional role in coordinating the coupling of adult traits in the alternative life histories is unknown. Here, we show that manipulating pupal ecdysteroid levels is sufficient to mimic in direction and magnitude the shifts in adult reproductive resource allocation normally induced by seasonal temperature. Crucially, this allocation shift is accompanied by changes in ecologically relevant traits, including timing of reproduction, life span, and starvation resistance. Together, our results support a functional role for ecdysteroids during development in mediating strategic reproductive investment decisions in response to predictive indicators of environmental quality. This study provides a physiological mechanism for adaptive developmental plasticity, allowing organisms to cope with variable environments.

opencc-zeroDec 2014View details →

Data from: Seasonal time constraints reduce genetic variation in life history traits along a latitudinal gradient

1. Time constraints cause strong selection on life history traits, because populations need to complete their life cycles within a shorter time. We therefore expect lower genetic variation in these traits in high- than in low-latitude populations, since the former are more time constrained. 2. The aim was to estimate life history traits and their genetic variation in an obligately univoltine damselfly along a latitudinal gradient of 2,730 km. 3. Populations were grown in the laboratory at temperatures and photoperiods simulating those at their place of origin. In a complementary experiment individuals from the same families were grown in constant temperature and photoperiod that mimicked average conditions across the latitude. 4. Development time and size was faster and smaller, respectively, and growth rate was higher at northern latitudes. Additive genetic variance was very low for life history traits and estimates for egg development time and larval growth rate showed significant decreases towards northern latitudes. The expression of genetic effects in life history traits differed considerably when individuals were grown in constant rather than simulated and naturally variable conditions. 5. Our results support strong selection by time constraints. They also highlight the importance of growing organisms in their native environment for correct estimates of genetic variance at their place of origin. Our results also suggest that the evolutionary potential of life history traits is very low at northern compared to southern latitudes, but that changes in climate could alter this pattern.

Data from: It takes two: seasonal variation in sexually dimorphic weaponry results from divergent changes in males and females

Sexually dimorphic weaponry often results from intrasexual selection, and weapon size can vary seasonally when costs of bearing the weapon exceed the benefits outside of the reproductive season. Weapons can also be favored in competition over nonreproductive resources such as food or shelter, and if such nonreproductive competition occurs year‐round, weapons may be less likely to vary seasonally. In snapping shrimp (Alpheus angulosus), both sexes have an enlarged snapping claw (a potentially deadly weapon), and males of many species have larger claws than females, although females are more aggressive. This contrasting sexual dimorphism (larger weaponry in males, higher aggression in females) raises the question of whether weaponry and aggression are favored by the same mechanisms in males and females. We used field data to determine whether either sex shows seasonal variation in claw size such as described above. We found sexual dimorphism increased during the reproductive season due to opposing changes in both male and female claw size. Males had larger claws during the reproductive season than during the nonreproductive season, a pattern consistent with sexual selection. Females, however, had larger claws during the nonreproductive season than during the reproductive season—a previously unknown pattern of variation in weapon size. The observed changes in female weapon size suggest a trade‐off between claw growth and reproduction in the reproductive season, with investment in claw growth primarily in the nonreproductive season. Sexually dimorphic weaponry in snapping shrimp, then, varies seasonally due to sex differences in seasonal patterns of investment in claw growth, suggesting claws may be advantageous for both sexes but in different contexts. Thus, understanding sexual dimorphisms through the lens of one sex yields an incomplete understanding of the factors favoring their evolution.

opencc-zeroDec 2015View details →

Data from: Predicting the evolutionary dynamics of seasonal adaptation to novel climates in Arabidopsis thaliana

Anticipating the effect of climate change on plants requires understanding its evolutionary consequence on traits and genes in complex realistic environments. How seasonal variation has an impact on the dynamics of adaptation in natural populations remains unclear. We simulated adaptation to different climate change scenarios, grounding our analysis in experimental data and explicitly exploring seasonal variation. Seasonal variation dramatically affected the dynamics of adaptation: Marked seasonality led to genetic differentiation within the population to different seasonal periods, whereas low seasonality led to a single population with fast-evolving fitness. Our results suggest the prevalence of phenotypic plasticity across environmental conditions in determining how climate change will shift selection on traits and loci. In this unpredictable context, maintaining broad genomic diversity is critical.

Data from: Seasonality in communication and collective decision-making in ants

The ability of animals to adjust their behaviour according to seasonal changes in their ecology is crucial for their fitness. Eusocial insects display strong collective behavioural seasonality, yet the mechanisms underlying such changes are poorly understood. We show that nest preference by emigrating Temnothorax albipennis ant colonies is influenced by a season-specific modulatory pheromone that may help tune decision-making according to seasonal constraints. The modulatory pheromone triggers aversion towards low-quality nests and enhances colony cohesion in summer and autumn, but not after overwintering—in agreement with reports that field colonies split in spring and reunite in summer. Interestingly, we show that the pheromone acts by downgrading the perceived value of marked nests by informed and naive individuals. This contrasts with theories of collective intelligence, stating that accurate collective decision-making requires independent evaluation of options by individuals. The violation of independence highlighted here was accordingly shown to increase error rate during emigrations. However, this is counterbalanced by enhanced cohesion and the transmission of valuable information through the colony. Our results support recent claims that optimal decisions are not necessarily those that maximize accuracy. Other criteria—such as cohesion or reward rate—may be more relevant in animal decision-making.

opencc-zeroDec 2016View details →

Data from: Seasonal variation in the biocontrol efficiency of bacterial wilt is driven by temperature-mediated changes in bacterial competitive interactions

1. Microbe-based biocontrol applications hold the potential to become an efficient way to control plant pathogen disease outbreaks in the future. However, their efficiency is still very variable, which could be due to their sensitivity to the abiotic environmental conditions. 2. Here we assessed how environmental temperature variation correlates with the Ralstonia pickettii, an endophytic bacterial biocontrol agent, ability to suppress Ralstonia solanacearum pathogen during different tomato crop seasons in China. 3. We found that the pathogen suppression was highest when the seasonal mean temperatures were around 20 °C and rapidly decreased with increasing mean crop season temperatures. Interestingly, low levels of disease incidence did not correlate with low pathogen or high biocontrol agent absolute densities. Instead, the biocontrol to pathogen density ratio was more important predictor of disease incidence levels between different crop season. To understand this mechanistically, we measured the growth and strength of competition between the biocontrol agent and the pathogen over a naturally occurring temperature gradient in vitro. We found that the biocontrol strain grew relatively faster at low, and the pathogen at high temperature ranges, and that similar to field experiments, pathogen suppression peaked at 20° C. 4. Together our results suggest that temperature-mediated changes in the strength of bacterial competition could potentially explain the variable R. solanacearum biocontrol outcomes between different crop seasons in China. 5. Synthesis and applications. Bacterial strains that can retain their functionality regardless of the environmental conditions (i.e. have flat reaction norms), could be good candidate species for developing more consistent biocontrol applications.

Data from: Seasonal drivers of understorey temperature buffering in temperate deciduous forests across Europe

Aim: Forest understory microclimates are often buffered against extreme heat or cold, with important implications for the organisms living in these environments. We quantified seasonal effects of understory microclimate predictors describing canopy structure, canopy composition and topography (i.e. local factors), as well as forest patch size and distance to coast (i.e. landscape factors). Location: Temperate forests in Europe Time period: 2017-2018 Major taxa studied: Woody plants Methods: We combined data from a microclimate sensor network with weather station records to calculate the difference – or offset – between temperatures measured inside and outside forests. We used regression analysis to study the effects of local and landscape factors on the seasonal offset of minimum, mean and maximum temperatures. Results: Maximum temperature during summer was on average cooler by 2.1 °C and minimum temperature during winter and spring were 0.4 °C and 0.9 °C warmer inside than outside forests. The local canopy cover was a strong non-linear driver of the maximum temperature offset during summer, and we found increased cooling beneath tree species that cast the deepest shade. Seasonal offsets of minimum temperature were mainly regulated by landscape and topographic features, such as the distance to coast and topographic position. Main conclusions: Forest organisms experience less severe temperature extremes than suggested by currently available macroclimate data, so climate-species relationships and species' responses to anthropogenic global warming cannot be modelled accurately in forests using macroclimate data alone. Changes in canopy cover and composition will strongly modulate warming of maximum temperatures in forest understories, with important implications for understanding responses of forest biodiversity and functioning to the combined threats of land-use change and climate change. Our predictive models are generally applicable across lowland temperate deciduous forests, providing ecologically important microclimate data for forest understories.

Data from: Density-mediated carry-over effects explain variation in breeding output across time in a seasonal population

In seasonal environments, where density dependence can operate throughout the annual cycle, vital rates are typically considered to be a function of the number of individuals at the beginning of each season. However, variation in density in the previous season could also cause surviving individuals to be in poor physiological condition, which could carry over to influence individual success in the following season. We examine this hypothesis using replicated populations of Drosophila melanogaster, the common fruitfly, over 23 non-overlapping generations with distinct breeding and non-breeding seasons. We found that the density at the beginning of the non-breeding season negatively affected the fresh weight of individuals that survived the non-breeding season and resulted in a 25% decrease in per capita breeding output among those that survived to the next season to breed. At the population level, per capita breeding output was best explained by a model that incorporated density at the beginning of the previous non-breeding season (carry-over effect, COE) and density at the beginning of the breeding season. Our results support the idea that density-mediated COEs are critical for understanding population dynamics in seasonal environments.

Data from: Nutrient-specific compensation for seasonal cold stress in a free-ranging temperate colobine monkey

1. Homeostatic responses of animals to environmentally-induced changes in nutrient requirements provide a powerful basis for predictive ecological models, and yet such responses are virtually unstudied in the wild. 2. We tested for macronutrient-specific compensatory feeding responses by free-ranging golden snub-nosed monkeys (Rhinopithecus roxellana) inhabiting high altitude temperate forests where they experience a substantial difference in ambient temperature in cold winters vs. warmer springs. The monkeys had free access to natural foods throughout the year, and to ensure that any seasonal differences in nutrient intake were due to homeostatic compensation and not constraints on food availability, we studied the monkeys during periods in which they were provisioned with the same amount of supplementary foods in winter and spring. 3. Thermoregulatory energy costs in winter and spring were calculated using partitional calorimetric estimations of convective and radiative heat loss obtained from thermal imaging of free-ranging monkeys in situ. Daily nutrient intakes were measured using continuous focal follows (average 6.9 h/day) of free-ranging individuals (27 in spring and 28 in winter). 4. We used a nutritional geometry framework to integrate these data and test three predictions: i. In order to remain thermoneutral (balance heat loss with heat expenditure), golden snub-nosed monkeys decrease daily energy consumption during the spring compared to winter, ii. Decreased energy intake is accomplished specifically by reducing intake of the primary energetic nutrients, carbohydrate and lipid, relative to protein, and iii. The seasonal reduction in ingested fat and carbohydrate calories will quantitatively match the reduction in thermoregulatory costs in spring compared with winter. 5. Our results showed that energy intake in spring was reduced to almost half (55%) of that in winter. As predicted, this was achieved by specifically reducing fat and carbohydrate consumption with protein intake unchanged, by a quantity (326 kJ/mbm) that almost exactly matched the seasonal difference in the daily energetic costs of thermoregulation (329 kJ/mbm). 6. This is the first study to test for a match between nutrient-specific homeostatic compensation and environmentally-induced perturbations in nutrient requirements in free-ranging animals, and underpins the potential for the homeostasis framework to provide predictive power to ecological models.

Data from: Faster migration in autumn than in spring: seasonal migration patterns and non-breeding distribution of Icelandic Whimbrels Numenius phaeopus islandicus

Migration is fundamental in the life of many birds and entails significant energetic and time investments. Given the importance of arrival time in the breeding area and the relatively short period available to reproduce (particularly at high latitudes), it is expected that birds reduce spring migration duration to a greater extent than autumn migration, assuming that pressure to arrive into the wintering area might be relaxed. This has previously been shown for several avian groups, but recent evidence from four tracked Icelandic Whimbrels (Numenius phaeopus islandicus), a long distance migratory wader, suggests that this subspecies tends to migrate faster in autumn than in spring. Here, we (1) investigate differences in seasonal migration duration, migration speed and ground speed of Whimbrels using 56 migrations from 19 individuals tracked with geolocators and (2) map the migration routes, wintering and stopover areas for this population. Tracking methods only provide temporal information on the migration period between departure and arrival. However, migration starts with the fuelling that takes place ahead of departure. Here we estimate the period of first fuelling using published fuel deposition rates and thus explore migration speed using tracking data. We found that migration duration was shorter in autumn than in spring. Migration speed was higher in autumn, with all individuals undertaking a direct flight to the wintering areas, while in spring most made a stopover. Wind patterns could drive Whimbrels to stop in spring, but be more favourable during autumn migration and allow a direct flight. Additionally, the stopover might allow the appraisal of weather conditions closer to the breeding areas and/or improve body condition in order to arrive at the breeding sites with reserves.