Seasonal Environments Research Articles

Seasonal Effects on the Fecal Microbial Composition of Wild Greater Thick-Tailed Galagos (Otolemur crassicaudatus)

AbstractBacterial communities present in the host digestive tract are important for the breakdown and absorption of nutrients required by the host. Changes in diet and the environment are major factors affecting the composition and diversity of the fecal microbiome. In addition to changes in ambient temperature and rainfall, primates living in seasonal temperate environments also need to adapt to seasonal changes in food resource quantity and quality. However, there is a lack of information about the fecal microbiome in African strepsirrhines relative to other primate taxa. We examined the effects of seasonal dietary and environmental changes on fecal microbial alpha diversity and composition in wild greater thick-tailed galagos (Otolemur crassicaudatus) at Lajuma Research Centre, South Africa. We collected fecal samples and assessed food availability and weather in summer and winter across 1 year and used 16S rRNA next-generation sequencing to characterise the fecal microbiome of 49 animals. We found significant increases in rainfall, ambient temperature, and food availability in summer compared with winter. However, we found no significant changes in body mass or in the overall diversity of bacterial species present in fecal samples between the two seasons. We found significant decreases in the abundance of certain bacterial families in winter, suggesting a change in diet. Our findings suggest that greater thick-tailed galagos can find food resources to maintain their body mass throughout the year. Our insights into the seasonal fecal microbiome of greater thick-tailed galagos add to the growing knowledge and understanding of fecal microbiomes in primates and how they help primates cope with changes to their environments.

Phylogeny and biogeography of the Cryptocaryeae (Lauraceae)

AbstractThe biogeographical history of many lineages within the Lauraceae remains poorly known because of the difficulty of assigning macrofossils to living genera, poor pollen preservation, and the absence of sufficiently resolved or well‐supported phylogenies. Here, we utilize plastid genome sequencing to reinvestigate the phylogenetic and biogeographic history of trees in the tribe Cryptocaryeae, an important component of broad‐leaved forests worldwide, with around 800 species that rely on vertebrate frugivores to disperse their seeds. A new time‐calibrated phylogeny with high support for 176 species was used to infer the biogeographic history and speciation rates based on inferences of BAMM analyses. A monophyletic Cryptocaryeae with Aspidostemon, Beilschmiedia, Cryptocarya, Dahlgrenodendron, and Eusideroxylon clades was confirmed. The five clades of Cryptocaryeae were estimated to share a common ancestor in tropical Africa or Asia in the Early Cretaceous around 123 Ma. The Beilschmiedia and Cryptocarya clades were estimated to have originated in South America around 66 Ma. Extant subclades of the Beilschmiedia clade could colonize Australia by 35 Ma and extant subclades of the Cryptocarya clade could colonize Australia by 42 Ma. Diversification rates of the Beilschmiedia clade accelerated 14 and 12 Ma after its origin and diversification rates of the Cryptocarya clade accelerated 18 Ma after its origin. Over 45% extant Cryptocaryeae species originated in the three periods of accelerated differentiation in the Miocene of Asia and Australia. Long‐distance dispersal has had a major influence on biogeography, with dispersal to Asia likely occurring seven times, Zealandia six times, America three times, Australia three times, Africa twice, and Oceania at least once. Over 70% extant Cryptocaryeae species which diverged before the Quaternary grow in the Southern Hemisphere, while 90% extant Cryptocaryeae species which diverged in the Quaternary grow in the Northern Hemisphere. The Cryptocaryeae originated in and diversified with the first angiosperm‐dominated broad‐leaved evergreen forests, from the Cretaceous to the Paleogene. Long‐distance seed dispersal, probably by birds, although possibly also by flotation, has allowed the tribe to track these forests in space and time, despite a failure to adapt to cold, dry, or highly seasonal environments.

The limits of stress-tolerance for zooplankton resting stages in freshwater ponds.

In seasonal environments, many organisms evolve strategies such as diapause to survive stressful periods. Understanding the link between habitat stability and diapause strategy can help predict a population's survival in a changing world. Indeed, resting stages may be an important way freshwater organisms can survive periods of drought or freezing, and as the frequency and extent of drought or freezing vary strongly among habitats and are predicted to change with climate change, it raises questions about how organisms cope with, and survive, environmental stress. Using Daphnia magna as a model system, we tested the ability of resting stages from different populations to cope with stress during diapause. The combination of elevated temperatures and wet conditions during diapause shows to prevent hatching altogether. In contrast, hatching is relatively higher after a dry and warm diapause, but declines with rising temperatures, while time to hatch increases. Resting stages produced by populations from summer-dry habitats perform slightly, but consistently, better at higher temperatures and dryness, supporting the local adaptation hypothesis. A higher trehalose content in resting eggs from summer-dry habitat might explain such pattern. Considering that temperatures and summer droughts are projected to increase in upcoming years, it is fundamental to know how resting stages resist stressful conditions so as to predict and protect the ecological functioning of freshwater ecosystems.

Highland and lowland forest birds differ in their feather growth rates: a multispecies test in the southwestern Palaearctic

Mountain birds face numerous challenges caused by altitude‐dependent environmental seasonality. Although elevation gradients may affect bird morphology, migration strategy and/or phenology of seasonal events (breeding and moulting), the life histories of highland compared with lowland birds have been little explored. In this study we compared the growth rate and mass of the tail feathers of six forest passerine species sampled at different elevations in the Iberian Peninsula (north) and the Maghreb (south) to assess potential differences in moult duration and feather quality between highland and lowland bird populations. As timing is crucial in seasonal environments, we also explored seasonal changes in temperature in the different study areas as a proxy for the duration of the optimal temporal windows available in summer for breeding and moulting. In addition, we compared wing configuration between highland and lowland populations, which could reflect differences in their migration strategy (migratory versus sedentary). The results showed that highland birds had less time available for breeding and moulting, longer and more concave wings, and faster feather growth rates than lowland populations, but we found no consistent patterns of variation in feather mass. These results suggest that selection might have favoured an accelerated moult and a more migratory behaviour in highland populations to cope with the reduction in the optimal temporal window as elevation increases. These patterns are similar to those observed in migratory populations moving along latitudinal gradients to breed in highly seasonal northern environments. We therefore hypothesize that elevational gradients at the southern limit of the Palaearctic could be an important driving force promoting variation in feather growth rate and wing configuration, and probably also other avian life‐history characteristics.

Seasonal changes in diet, immune function, and oxidative stress in three passerines inhabiting a Mediterranean climate.

Oxidative status and immune function are energy-demanding traits closely linked to diet composition, particularly resource availability and nutritional value. In seasonal environments, nutrient availability and diet quality fluctuate, potentially influencing these traits. However, limited evidence exists regarding these dietary effects on immune function in seasonal environments. In this study, we employed stable isotope analysis to assess the impact of seasonal changes in niche width and trophic level (i.e., δ15N) on two immune variables (hemolysis and hemagglutination scores) and two oxidative status parameters (lipid peroxidation and total antioxidant capacity) in three passerine species: Zonotrichia capensis (omnivorous), Troglodytes aedon (insectivorous), and Spinus barbatus (granivorous). We found that hemolysis scores varied seasonally in Z. capensis, with higher values in winter compared to summer. Total antioxidant capacity (TAC) also increased during the winter in Z. capensis and S. barbatus. The isotopic niche width for Z. capensis and S. barbatus was smaller in winter than in summer, with the omnivorous species exhibiting a decrease in δ15N. Despite the seasonal shifts in ecological and physiological traits in Z. capensis, we identified no correlation between immune response and TAC with trophic level. In contrast, in the granivorous S. barbatus, the lower trophic level resulted in an increase in TAC without affecting immunity. Our findings revealed that dietary shifts do not uniformly impact oxidative status and immune function across bird species, highlighting species-specific responses to seasonal changes. This underscores the importance of integrating ecological and evolutionary perspectives when examining how diet shapes avian immunity and oxidative balance.

Spatial and seasonal variation in thermal sensitivity within North American bird species.

Responses of wildlife to climate change are typically quantified at the species level, but physiological evidence suggests significant intraspecific variation in thermal sensitivity given adaptation to local environments and plasticity required to adjust to seasonal environments. Spatial and temporal variation in thermal responses may carry important implications for climate change vulnerability; for instance, sensitivity to extreme weather may increase in specific regions or seasons. Here, we leverage high-resolution observational data from eBird to understand regional and seasonal variation in thermal sensitivity for 21 bird species. Across their ranges, most birds demonstrated regional and seasonal variation in both thermal peak and range, or the temperature and range of temperatures when observations peaked. Some birds demonstrated constant thermal peaks or ranges across their geographical distributions, while others varied according to local and current environmental conditions. Across species, birds typically demonstrated either geographical or seasonal adaptation to climate. Local adaptation and phenotypic plasticity are likely important but neglected aspects of organismal responses to climate change.

The change in the biomass allocation to stems and leaves in young plants of Dimorphandra wilsonii under eCO2 may harm this endangered species in native areas

AbstractClimate change is among the main threats to ecosystems, affecting biodiversity and ecosystem services. These changes are associated with increased atmospheric carbon dioxide concentration ([CO2]). This study aimed to investigate how [CO2] influences chlorophyll a fluorescence, vegetative growth, biomass production, and the number of root nodules (NRN) of Dimorphandra wilsonii, a critically endangered species. The study was conducted in six open‐top chambers with two CO2 levels, at elevated [CO2] (eCO2, 717 ± 77 ppm) and at ambient [CO2] (aCO2, 539 ± 42 ppm). We monitored vegetative growth weekly, and at the end of the experiment, we measured chlorophyll a fluorescence and biomass production. Dimorphandra wilsonii plants under eCO2 showed higher (p < 0.05) average leaf dry mass, average leaf area, and lower (p < 0.05) root/shoot ratio than plants under aCO2. The greater aerial biomass allocation contributes to maximizing the photosynthesis performance but could also result in the self‐shading of old basal leaves by new distal leaves on branches. This adjustment could be advantageous in the competition for light; however, it would be a disadvantage for below‐ground resource competition (such as water and nutrients), which could result in decreased drought resistance. Also, this adjustment would be unfavorable to D. wilsonii, which occurs in a seasonal climate environment competing with invasive grasses. Thus, it is possible that climate change scenarios with increases in [CO2] and drought periods could negatively influence the establishment of young plants of D. wilsonii in their natural occurrence area, which could worsen the conservation status of the species.

The phylogenetic reconstruction of the Neotropical cycad genus Ceratozamia (Zamiaceae) reveals disparate patterns of niche evolution

The cycad genus Ceratozamia comprises 40 species from Mexico, Guatemala, Belize, and Honduras, where cycads occur throughout climatically varied montane habitats. Ceratozamia has the potential to reveal the history and processes of species diversification across diverse Neotropical habitats in this region. However, the species relationships within Ceratozamia and the ecological trends during its evolution remain unclear. Here, we aimed to clarify the phylogenetic relationships, the timing of clade and species divergences, and the niche evolution throughout the phylogenetic history of Ceratozamia. Genome-wide DNA sequences were obtained with MIG-seq, and multiple data-filtering steps were used to optimize the dataset used to construct an ultrametric species tree. Divergence times among branches and ancestral niches were estimated. The niche variation among species was evaluated, summarized into two principal components, and their ancestral states were reconstructed to test whether niche shifts among branches can be explained by random processes, under a Brownian Motion model. Ceratozamia comprises three main clades, and most species relationships within the clades were resolved. Ceratozamia has diversified since the Oligocene, with major branching events occurring during the Miocene. This timing is consistent with fossil evidence, the timing estimated for other Neotropical plant groups, and the major geological events that shaped the topographic and climatic variation in Mexico. Patterns of niche evolution in the genus do not accord with the Brownian Motion model. Rather, non-random evolution with shifts towards more seasonal environments at high latitudes, or shifts towards humid or dry environments at low latitudes explain the diversification of Ceratozamia. We present a comprehensive phylogenetic reconstruction for Ceratozamia and identify for the first time the environmental factors involved in clade and species diversification within the genus. This study alleviates the controversies regarding the species relationships in the genus and provides the first evidence that latitude-associated environmental factors may influence processes of niche evolution in cycads.

Seasonal energetics: are insects constrained by energy during dormancy?

In seasonal environments, many animals, including insects, enter dormancy, where they are limited to a fixed energy budget. The inability to replenish energetic stores during these periods suggests insects should be constrained by pre-dormancy energy stores. Over the last century, the community of researchers working on survival during dormancy has operated under the strong assumption that energy limitation is a key fitness trait driving the evolution of seasonal strategies. That is, energy use has to be minimized during dormancy because insects otherwise run out of energy and die during dormancy, or are left with too little energy to complete development, reproductive maturation or other costly post-dormancy processes such as dispersal or nest building. But if energy is so strongly constrained during dormancy, how can some insects - even within the same species and population - be dormant in very warm environments or show prolonged dormancy for many successive years? In this Commentary, we discuss major assumptions regarding dormancy energetics and outline cases where insects appear to align with our assumptions and where they do not. We then highlight several research directions that could help link organismal energy use with landscape-level changes. Overall, the optimal energetic strategy during dormancy might not be to simply minimize metabolic rate, but instead to maintain a level that matches the demands of the specific life-history strategy. Given the influence of temperature on energy use rates of insects in winter, understanding dormancy energetic strategies is critical in order to determine the potential impacts of climate change on insects in seasonal environments.

Phenotypic plasticity of male calls in two populations of the katydid Neoconocephalus triops (Insecta: Tettigoniidae)

The ability to respond to environmental changes plays a crucial role for coping with environmental stressors related to climate change. Substantial changes in environmental conditions can overcome developmental homeostasis, exposing cryptic genetic variation. The katydid Neoconocephalus triops is a tropical species that extended its range to the more seasonal environment of North America where it has two reproductive generations per year. The harsher winter conditions required adults to diapause which resulted in substantially different mating calls of the diapausing winter animals compared to the non-overwintering summer animals in northern Florida. The summer call corresponds to that of tropical populations, whereas the winter call represents the alternative call phenotype. We quantified call plasticity in a tropical (Puerto Rico) and a temperate population of N. triops (Florida) that differ in experiencing winter conditions in their geographic regions. We hypothesized that the plastic call traits, i.e., double-pulse rate and call structure, are regulated independently. Further, we hypothesized that phenotypic plasticity of double-pulse rate results in quantitative changes, whereas that of call structure in qualitative changes. We varied the photoperiod and duration of diapause during male juvenile and adult development during rearing and analyzed the double-pulse rate and call structure of the animals. Double-pulse rate changed in a quantitative fashion in both populations and significant changes appeared at different developmental points, i.e., the double-pulse rate slowed down during juvenile development in Florida, whereas during adult diapause in Puerto Rico. In the Florida population, both the number of males producing and the proportion of total call time covered by the alternative call structure (= continuous calls) increased with duration spent in diapause. In the Puerto Rico population, expression of the alternative call structure was extremely rare. Our results suggest that the expression of both pulse rate and call structure was quantitative and not categorical. Our systematic variation of environmental variables demonstrated a wide range of phenotypic variation that can be induced during development. Our study highlights the evolutionary potential of hidden genetic variation and phenotypic plasticity when confronted with rapidly changing environments and their potential role in providing variation necessary for communication systems to evolve.

Towards an integrated understanding of dietary phenotypes.

Diet and nutrition comprise a complex, multi-faceted interface between animal biology and food environments. With accumulating information on the many facets of this association arises a need for systems-based approaches that integrate dietary components and their links with ecology, feeding, post-ingestive processes and the functional and ecological consequences of these interactions. We briefly show how a modelling approach, nutritional geometry, has used the experimental control afforded in laboratory studies to begin to unravel these links. Laboratory studies, however, have limited ability to establish whether and how the feeding and physiological mechanisms interface with realistic ecological environments. We next provide an overview of observational field studies of free-ranging primates that have examined this, producing largely correlative data suggesting that similar feeding mechanisms operate in the wild as in the laboratory. Significant challenges remain, however, in establishing causal links between feeding, resource variation and physiological processes in the wild. We end with a more detailed account of two studies of temperate primates that have capitalized on the discrete variation provided by seasonal environments to strengthen causal inference in field studies and link patterns of intake to dynamics of nutrient processing. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Historical Assembly of Andean Tree Communities.

Patterns of species diversity have been associated with changes in climate across latitude and elevation. However, the ecological and evolutionary mechanisms underlying these relationships are still actively debated. Here, we present a complementary view of the well-known tropical niche conservatism (TNC) hypothesis, termed the multiple zones of origin (MZO) hypothesis, to explore mechanisms underlying latitudinal and elevational gradients of phylogenetic diversity in tree communities. The TNC hypothesis posits that most lineages originate in warmer, wetter, and less seasonal environments in the tropics and rarely colonize colder, drier, and more seasonal environments outside of the tropical lowlands, leading to higher phylogenetic diversity at lower latitudes and elevations. In contrast, the MZO hypothesis posits that lineages also originate in temperate environments and readily colonize similar environments in the tropical highlands, leading to lower phylogenetic diversity at lower latitudes and elevations. We tested these phylogenetic predictions using a combination of computer simulations and empirical analyses of tree communities in 245 forest plots located in six countries across the tropical and subtropical Andes. We estimated the phylogenetic diversity for each plot and regressed it against elevation and latitude. Our simulated and empirical results provide strong support for the MZO hypothesis. Phylogenetic diversity among co-occurring tree species increased with both latitude and elevation, suggesting an important influence on the historical dispersal of lineages with temperate origins into the tropical highlands. The mixing of different floras was likely favored by the formation of climatically suitable corridors for plant migration due to the Andean uplift. Accounting for the evolutionary history of plant communities helps to advance our knowledge of the drivers of tree community assembly along complex climatic gradients, and thus their likely responses to modern anthropogenic climate change.

The role of seasonality in shaping the interactions of honeybees with other taxa.

The Eltonian niche of a species is defined as its set of interactions with other taxa. How this set varies with biotic, abiotic and human influences is a core question of modern ecology. In seasonal environments, the realized Eltonian niche is likely to vary due to periodic changes in the occurrence and abundance of interaction partners and changes in species behavior and preferences. Also, human management decisions may leave strong imprints on species interactions. To compare the impact of seasonality to that of management effects, honeybees provide an excellent model system. Based on DNA traces of interaction partners archived in honey, we can infer honeybee interactions with floral resources and microbes in the surrounding habitats, their hives, and themselves. Here, we resolved seasonal and management-based impacts on honeybee interactions by sampling beehives repeatedly during the honey-storing period of honeybees in Finland. We then use a genome-skimming approach to identify the taxonomic contents of the DNA in the samples. To compare the effects of the season to the effects of location, management, and the colony itself in shaping honeybee interactions, we used joint species distribution modeling. We found that honeybee interactions with other taxa varied greatly among taxonomic and functional groups. Against a backdrop of wide variation in the interactions documented in the DNA content of honey from bees from different hives, regions, and beekeepers, the imprint of the season remained relatively small. Overall, a honey-based approach offers unique insights into seasonal variation in the identity and abundance of interaction partners among honeybees. During the summer, the availability and use of different interaction partners changed substantially, but hive- and taxon-specific patterns were largely idiosyncratic as modified by hive management. Thus, the beekeeper and colony identity are as important determinants of the honeybee's realized Eltonian niche as is seasonality.

Night work, season and alertness as occupational safety hazards in the Arctic: protocol for the Noralert observational crossover study among Norwegian process operators

IntroductionThe objective of this study is to determine the effects of night work, Arctic seasonal factors and cold working environments on human functions relevant to safety. The study aims to...

Shifts in risk sensitivity and resource availability alter fat stores for a large mammal following extreme winter conditions

Abstract For species that inhabit environments where resource availability may be unpredictable, balance of resource allocation to life‐history traits can have heightened consequences for survival, reproduction, and ultimately, fitness. Acquisition and allocation of energy to maintenance, capital gain and reproduction should be in tune with the landscape an animal inhabits—environmental severity, food availability and population size all influence the resources animals have and dictate the ways they should be allocated. In seasonal environments, animals that experience periods of extreme resource limitation (e.g. harsh winters) may favour allocation of resources to body reserves to secure their survival at the cost of reproduction (i.e. risk averse). In contrast, the same accumulation of body reserves may not be necessary to survive in relatively benign landscapes where instead, allocation to reproduction is favoured (i.e. risk prone). According to the theory of risk‐sensitive allocation of resources, when animals are exposed to unprecedented or life‐threatening conditions, they may shift resource allocation to favour building capital over allocation in reproduction to preempt against encountering another life‐threatening event in the future. Using data from a long‐term project on a highly site‐faithful and long‐lived species, mule deer (Odocoileus hemionus), we evaluated how a life‐threatening winter and the associated changes in resource availability resulting from a population reduction influenced how animals acquired and allocated energy to survival (i.e. fat accumulation). Per capita precipitation, and the associated reduction in population abundance after the severe winter, had a positive influence of accrual of fat over summer. After the extreme physiological stress of a hard winter, deer starting spring with low body reserves accumulated 2.8 percentage points more fat over summer compared with before the experience of a bad winter and had an increased probability of recruiting fewer offspring. Fat stores can interact with environment, life history and behaviour to influence survival during periods of resource scarcity. For a long‐lived herbivore, we documented shifts in risk tolerance associated with fat accrual in preparation for winter, supporting the notion that risk‐sensitive allocation of resources may be plastic—an essential adaptation for animals to cope with rapidly changing landscapes. Read the free Plain Language Summary for this article on the Journal blog.

The evolution of enclosed nesting in passerines is shaped by competition, energetic costs, and predation threat

Abstract Many avian species breed in enclosed nests that may provide better protection against predation and climatic conditions compared to open nests and are generally associated with larger clutch sizes and slower offspring growth. Here we show that different enclosed nesting strategies are each linked to behaviors with very different costs and benefits on a macroevolutionary scale. Using a detailed dataset of nest structure and location from the order Passeriformes, we employed phylogenetic comparative methods to evaluate (1) how predation, competition, design complexity, and energetic costs have shaped evolutionary transitions between different nesting strategies, and (2) whether these strategies also have distinct relationships with life-history traits. We find that flexible strategies (i.e., nesting in both open and enclosed sites) as well as energetically demanding strategies are evolutionarily unstable, indicating the presence of underlying ecological tradeoffs between antipredator protections, construction costs, and competition. We confirm that species with enclosed nests have larger clutch sizes and longer development and nestling periods compared to open nesters, but only species that construct enclosed nests rather than compete for preexisting cavities spend more time incubating and are concentrated in the tropics. Flexible strategies prevail in seasonal environments and are linked to larger clutches—but not longer development—compared to nesting in the open. Overall, our results suggest that predation, competition, and energetic costs affect the evolution of nesting strategies, but via distinct pathways, and that caution is warranted when generalizing about the functions of enclosed nest designs in birds.

Does early spring arrival lead to early nesting in a migratory shorebird? Insights from remote tracking

Advancing breeding phenology is a commonly observed response to climate warming among bird species, potentially in response to shifts in the phenology of key resources. However, for migratory birds breeding at high latitudes, their capacity to breed earlier may be constrained by the time available between arrival on the breeding grounds and nesting, especially for later‐arriving individuals. This may have consequences for productivity, as early laying is often linked to higher breeding success, particularly in such seasonal environments. We investigated how migratory arrival timing influences subsequent timing of breeding, in particular whether the time between arrival and laying (arrival–laying gap) varies with arrival date, and if later‐arriving individuals are able to catch up with early‐arriving conspecifics. We tracked individual Icelandic Black‐tailed Godwit Limosa limosa islandica with GPS and PTT tags for one to two complete breeding seasons between 2013 and 2022. After arrival in Iceland, most Godwits visited their breeding territory within 5 days, though this interval was longer for earlier‐arriving birds. The total gap between arrival and laying was also longer for earlier‐arriving birds, such that laying date did not vary significantly with arrival date. These results suggest that, despite individual consistency in migratory phenology, subsequent timing of nesting is probably influenced by other factors, such as mate arrival timing and/or annual variation in environmental conditions. Regular pre‐nesting visits to the breeding territory may indicate that Godwits are able to monitor such factors closely and to nest early when conditions allow, but a larger sample of individuals and years is needed to assess whether early‐arriving individuals contribute disproportionately to population‐level advances in breeding phenology. Widespread tracking with high temporal and spatial resolution helps improve our understanding of phenological variation during the breeding season and its consequences for productivity and variation in juvenile phenology.

Seasonal variation in glucose and insulin is modulated by food and temperature conditions in a hibernating primate.

Feast-fast cycles allow animals to live in seasonal environments by promoting fat storage when food is plentiful and lipolysis when food is scarce. Fat-storing hibernators have mastered this cycle over a circannual schedule, by undergoing extreme fattening to stockpile fuel for the ensuing hibernation season. Insulin is intrinsic to carbohydrate and lipid metabolism and is central to regulating feast-fast cycles in mammalian hibernators. Here, we examine glucose and insulin dynamics across the feast-fast cycle in fat-tailed dwarf lemurs, the only obligate hibernator among primates. Unlike cold-adapted hibernators, dwarf lemurs inhabit tropical forests in Madagascar and hibernate under various temperature conditions. Using the captive colony at the Duke Lemur Center, we determined fasting glucose and insulin, and glucose tolerance, in dwarf lemurs across seasons. During the lean season, we maintained dwarf lemurs under stable warm, stable cold, or fluctuating ambient temperatures that variably included food provisioning or deprivation. Overall, we find that dwarf lemurs can show signatures of reversible, lean-season insulin resistance. During the fattening season prior to hibernation, dwarf lemurs had low glucose, insulin, and HOMA-IR despite consuming high-sugar diets. In the active season after hibernation, glucose, insulin, HOMA-IR, and glucose tolerance all increased, highlighting the metabolic processes at play during periods of weight gain versus weight loss. During the lean season, glucose remained low, but insulin and HOMA-IR increased, particularly in animals kept under warm conditions with daily food. Moreover, these lemurs had the greatest glucose intolerance in our study and had average HOMA-IR values consistent with insulin resistance (5.49), while those without food under cold (1.95) or fluctuating (1.17) temperatures did not. Remarkably low insulin in dwarf lemurs under fluctuating temperatures raises new questions about lipid metabolism when animals can passively warm and cool rather than undergo sporadic arousals. Our results underscore that seasonal changes in insulin and glucose tolerance are likely hallmarks of hibernating mammals. Because dwarf lemurs can hibernate under a range of conditions in captivity, they are an emerging model for primate metabolic flexibility with implications for human health.

Spring temperature drives phenotypic selection on plasticity of flowering time.

In seasonal environments, a high responsiveness of development to increasing temperatures in spring can infer benefits in terms of a longer growing season, but also costs in terms of an increased risk of facing unfavourable weather conditions. Still, we know little about how climatic conditions influence the optimal plastic response. Using 22 years of field observations for the perennial forest herb Lathyrus vernus, we assessed phenotypic selection on among-individual variation in reaction norms of flowering time to spring temperature, and examined if among-year variation in selection on plasticity was associated with spring temperature conditions. We found significant among-individual variation in mean flowering time and flowering time plasticity, and that plants that flowered earlier also had a more plastic flowering time. Selection favoured individuals with an earlier mean flowering time and a lower thermal plasticity of flowering time. Less plastic individuals were more strongly favoured in colder springs, indicating that spring temperature influenced optimal flowering time plasticity. Our results show how selection on plasticity can be linked to climatic conditions, and illustrate how we can understand and predict evolutionary responses of organisms to changing environmental conditions.

Periodic Trajectories for HIV Dynamics in a Seasonal Environment With a General Incidence Rate

In this paper, we propose a five-dimensional nonlinear system of differential equations for the human immunodeficiency virus (HIV) including the B-cell functions with a general nonlinear incidence rate. The compartment of infected cells was subdivided into three classes representing the latently infected cells, the short-lived productively infected cells, and the long-lived productively infected cells. The basic reproduction number was established, and the local and global stability of the equilibria of the model were studied. A sensitivity analysis with respect to the model parameters was undertaken. Finally, some numerical simulations are presented to illustrate the theoretical findings.