Capital Breeders Research Articles

Capital and income breeders among herbs: how relative biomass allocation into a storage organ relates to clonal traits, phenology and environmental gradients.

Perennial herbs of seasonal climates invest carbon into belowground storage organs (e.g. rhizomes) to support growth when photosynthetic acquisition cannot cover demands. An alternative explanation interprets storage allocation as surplus carbon that is undeployable for growth when plants are limited by nutrients/water. We analysed relative investments to rhizomes to see to which of these explanations they align, and asked whether they scale with biomass of aboveground organs in individual species and whether clonal growth traits, phenology or environmental conditions explain investment among populations or species. We measured biomass of rhizomes, aboveground stems and leaves in 20 temperate herbaceous perennial species, each at two localities, establishing allometric relationships for pairs of organs. We correlated relative rhizome investment with clonal traits, environmental gradients and phenology, across species. For pairs of organs, biomass typically scales isometrically. Interspecific allocation differences are largely explained by phenology. Neither interspecific nor intraspecific differences were explained by clonal traits or environment. Storage organs of perennial herbs do not comprise deposition of carbon surplus, but receive greater allocation in capital breeders (early-flowering), than among income breeders (late-flowering) relying on acquisition during growing season. Capital and income breeders in plants deserve further examination of benefits/costs.

Age-Related Plasticity Integration in Male Cicadas Tettigetta isshikii: Are Adult Cicadas Capital Breeders?

Labile traits, such as behavioural, physiological traits or body mass, vary within an individual either over time or across environments. Such changes within an individual can be linked across traits, forming within-individual trait correlations. These correlations are particularly expected when ageing causes changes in the expression of multiple traits. Moreover, the direction of these correlations depends on mechanisms that explain age-related changes in each trait, such as physiological deterioration or changes in future fitness expectations. Therefore, assessing within-individual trait correlations offers insights into trait-specific ageing patterns, their integration and age-related reproductive strategies. Here, we tracked individual male cicadas (Tettigetta isshikii) in their natural habitat, repeatedly assessing their plant use (narrow-leafed vs. large-leafed plants), calling activity and body mass. The results revealed that male cicadas lost mass, increased calling activity and a preference for narrow-leafed plants as they aged. This integration of age-related plasticity led to negative within-individual correlations between body mass and behaviours. Considering that adult cicadas consume nutritionally poor xylem sap, the negative within-individual correlations between body mass and risk-taking behaviour suggest that T. isshikii males follow a capital breeding strategy rather than an income breeding strategy. As adult cicadas may use up the energy stored during the nymph stage, an age-related increase in energetically demanding calling activity could cause an age-related decrease in body mass. The terminal investment hypothesis could also explain the age-related increase in calling activity and the preference for narrow-leafed plants. Therefore, we emphasise the importance of individual-level tracking studies in the wild to achieve a comprehensive understanding of the life-history strategies and behavioural ecology of a study animal.

Population changes in a Southern Ocean krill predator point towards regional Antarctic sea ice declines

While foraging, marine predators integrate information about the environment often across wide-ranging oceanic foraging grounds and reflect these in population parameters. One such species, the southern right whale (Eubalaena australis; SRW) has shown alterations to foraging behaviour, declines in body condition, and reduced reproductive rates after 2009 in the South African population. As capital breeders, these changes suggest decreased availability of their main prey at high-latitudes, Antarctic krill (Euphausia superba). This study analysed environmental factors affecting prey availability for this population over the past 40 years, finding a notable southward contraction in sea ice, a 15–30% decline in sea ice concentration, and a more than two-fold increase in primary production metrics after 2008. These environmental conditions are less supportive of Antarctic krill recruitment in known SRW foraging grounds. Additionally, marginal ice zone, sea ice concentration and two primary production metrics were determined to be either regionally significant or marginally significant predictors of calving interval length when analysed using a linear model. Findings highlight the vulnerability of recovering baleen whale populations to climate change and show how capital breeders serve as sentinels of ecosystem changes in regions that are difficult or costly to study.

Assessing avian incubation behavior in response to environmental pollution with temperature-humidity loggers

The negative impact of environmental pollution on avian physiology and breeding success is well documented. However, pollution-related behavioral changes during reproduction remain underexplored, despite behavior often being one of the earliest indicators of environmental disturbances and having significant life-history consequences. For example, altered food availability in a polluted environment could potentially perturb the incubation behavior of income breeders. These birds typically alternate between staying in the nest and heating eggs (on-bout) and taking foraging trips (off-bout). In this two-year study (2020 and 2022), we investigated how the incubation behavior of an insectivorous passerine, the pied flycatcher (Ficedula hypoleuca), varied with environmental pollution levels around a Cu-Ni smelter. Additionally, we compared two different metrics – temperature and humidity within the nest – to evaluate their use as indicators of incubation rhythm. We found that temperature- and humidity-based incubation rhythm parameters correlated, but those based on humidity matched better the true incubation behavior documented by simultaneous video recording. This was because the humidity curve showed a more immediate and intensive response to the female's incubation behavior. Birds in the polluted area took slightly more (11%) but shorter (11%) off-bouts, possibly reflecting smaller energetic constraints or better food availability in the polluted area. However, we found no difference in total incubation intensity between polluted and control areas, with F. hypoleuca females incubating their eggs 75% of the daytime in both environments. Hence, incubating females in the polluted area did not allocate more time for gathering their energy reserves than the birds in the control area, and there was also no difference in the hatching success. Our study is the first to use humidity variation to record incubation rhythm, and our results indicate that measuring humidity inside the nest is a promising technique to test and develop further. For example, further studies are needed to test if this method would work in different types of nests. From an environmental protection standpoint, our results also contribute valuable insights to the relatively limited information on pollution-related behavioral changes.

The modified artificial cohort method for three dominant pelagic copepods in the northern North Pacific revealed species-specific differences in the optimum temperature

The most concerning recent ocean changes in temperature issues are known as marine heat waves. Under these conditions, it is important to evaluate the effects of temperature on zooplankton. In this study, we investigated the growth rates of three dominant copepod species (Eucalanus bungii, Metridia pacifica, and Neocalanus plumchrus) in the northern North Pacific under three different temperature conditions (3, 7, and 11°C) using an artificial cohort method. Experimental conditions for 42 hour incubations were set to light intensity and photoperiod corresponding to 50 m depth. The dissolved oxygen solubility after rearing ranged from 69.2% to 102.1%, suggesting sufficient conditions for copepod growth. Chlorophyll a increased in 83% of the experiments, indicating that the food conditions were sufficient for the copepods. The mean proportion of dead specimens evaluated using neutral red was 10.2%, corresponding with the reported values in the field. Thus, it can be concluded that the laboratory-rearing conditions used in this study provided sufficient food, and the only effect evaluated would be that of the three different temperatures. Since the developmental time for each stage is longer than the rearing period, it is important to conduct experiments with a large number of individuals to obtain accurate growth rate results. The specific growth rates of E. bungii and M. pacifica increased with increasing temperature. In contrast, N. plumchrus showed the highest growth rate under moderate water temperature conditions. In terms of weight units (dry, carbon, and nitrogen), the carbon weight-specific growth rates were higher than those of the other two units, a common characteristic of the three species. This reflected lipid accumulation during the late copepodite stages. The interspecies differences in growth rate responses to water temperature reflect species-specific differences in temperature tolerance or the optimum temperature for each species. As E. bungii and M. pacifica reproduce near the surface layer through income breeding, their temperature tolerance or optimum temperature is expected to be high. However, because the reproduction of N. plumchrus occurs in the cold deep layer by using capital breeding, its temperature tolerance and optimum temperature would be lower than those of the former two species.

Productive foraging grounds enhance maternal condition and offspring quality in a capital breeding species.

Feeding ecology is an essential component of an organism's life, but foraging comes with risks and energetic costs. Species in which populations exhibit more than one feeding strategy, such as sea turtles, are good systems for investigating how feeding ecology impacts life-history traits, reproduction and carried over effects across generations. Here, we investigated how the feeding ecology of loggerhead sea turtles (Caretta caretta) nesting at the Cabo Verde archipelago correlates with reproductive outputs and offspring quality. We determined the feeding ecology of female turtles before and during the breeding season from stable isotope analysis of carbon and nitrogen and correlated isotopic ratio with female and offspring traits. We found that female turtles feeding at higher trophic positions produced larger clutches. We also found that females with higher δ13C values, typical of productive foraging areas, had greater fat reserves, were less likely to be infected by leech parasites and produced heavier offspring. The offspring of infected mothers with higher δ13C values performed best in crawling and self-righting trials than those of non-infected mothers with higher δ13C values. This study shows adult female loggerheads that exploit productive areas build capital reserves that impact their reproductive success and multiple proxies for offspring quality. Overall, our findings provide valuable insights into the complex interplay between feeding ecology and reproductive success, and reveal the transgenerational carry-over effects of both feeding ecology and health on offspring quality in sea turtles.

Evidence of longitudinal differences in spring migration strategies of an Arctic-nesting goose.

During spring, migratory birds are required to optimally balance energetic costs of migration across heterogeneous landscapes and weather conditions to survive and reproduce successfully. Therefore, an individual's migratory performance may influence reproductive outcomes. Given large-scale changes in land use, climate, and potential carry-over effects, understanding how individuals migrate in relation to breeding outcomes is critical to predicting how future scenarios may affect populations. We used GPS tracking devices on 56 Greater White-fronted Geese (Anser albifrons) during four spring migrations to examine whether migration characteristics influenced breeding propensity and breeding outcome. We found a strong longitudinal difference in arrival to the breeding areas (18 days earlier), pre-nesting duration (90.9% longer), and incubation initiation dates (9 days earlier) between western- and eastern-Arctic breeding regions, with contrasting effects on breeding outcomes, but no migration characteristic strongly influenced breeding outcome. We found that breeding region influenced whether an individual likely pursued a capital or income breeding strategy. Where individuals fell along the capital-income breeding continuum was influenced by longitude, revealing geographic effects of life-history strategy among conspecifics. Factors that govern breeding outcomes likely occur primarily upon arrival to breeding areas or are related to individual quality and previous breeding outcome, and may not be directly tied to migratory decision-making across broad scales.

Resource availability alters breeding strategies in a small mammal community.

Following a resource pulse, animals may finance reproduction by consuming concurrently available resources (income breeding) or by storing resources for future reproduction (capital breeding). Understanding how these reproductive strategies are used is important for determining the ecological mechanisms that structure timing of reproduction and that drive interannual population fluctuations in animals. We gathered a reproductive dataset for five small mammal species over a 12-year period in Northeastern USA during which six masting events of American beech (Fagus grandifolia) and eastern hemlock (Tsuga canadensis) occurred. Masting created alternate years where seeds were either available late (masting year) or early (cached from the previous year) in the breeding season. The small mammal species differed in reliance on seeds and overwintering strategies. We quantified the diet using stable isotopes and recorded reproduction timing, proportion breeding and litter size in females and testes size in males. Timing of seed availability minimally affected litter size but strongly affected proportion breeding and timing of reproduction. During masting years (late seed availability), a higher proportion of females reproduced, with breeding taking place later in the season (lactation timed with peak seed availability), although the delay was restricted in Napaeozapus insignis, an obligate hibernator. After a fall mast, cached seeds were used as capital in the following spring (early seed availability) to support a litter that, depending on the species, occurred 24-79 days sooner than a mast year. No late-season reproduction occurred in years with early seed availability except for Myodes gapperi which produced a second litter, likely financed by fungal consumption. Males also showed strong responses to seed availability, mirroring female reproduction with testes size staying constant in years with late seed availability and sharply decreasing over the breeding season in years with early seed availability. Our results highlight that although photoperiod and temperature broadly set bounds of the breeding season in temperate environments, resource availability influences the reproductive strategies that species use, which in turn alters reproductive timing and can drive large inter-annual population fluctuations. Differences in overwintering strategies and diet may further modulate reproductive timing and output relative to resource pulses.

Anchovy and sardine condition and energy content in the North Aegean Sea (eastern Mediterranean) in relation to their contrasting reproductive strategies.

Forage species with high biomass, such as anchovies and sardines, play a key role in pelagic ecosystems and make up a significant proportion of the world's capture fisheries production. In recent years, condition indices have gained interest as significant indicators for assessing the effects of environmental and human pressures on these species and the quality of their habitats. In the present study, we examined, for the first time in the North Aegean Sea (eastern Mediterranean), the year-round variation in somatic and gonadal condition, energy density, and percentage of lipid content of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). Energy density was measured with bomb calorimetry and percentage lipid content with the fatmeter, a portable electronic device. Finally, the monthly changes in gonadal and energetic condition were examined in relation to the annual cycle of temperature and mesozooplankton biomass, simulated by the implementation of a coupled hydrodynamic-biogeochemical model (POM-ERSEM). There was a strong relationship between fish energy density (kJ g-1) and percentage dry weight. Furthermore, the mean monthly energy density and fatmeter measurements were strongly correlated, especially in sardine. Overall, the monthly changes in energetic condition were indicative of the species' different strategies for energy acquisition and allocation to reproduction (capital vs. income breeding): sardine exhibited low energy density and percentage lipid content during the winter spawning period (November-March) and markedly higher energetic condition from spring to autumn (April-October). Anchovy spawning period, as inferred from gonadal condition, lasted from April to September, i.e., during the warm period of the year but its energy density and percentage lipid content did not exhibit any seasonal changes and were markedly lower than in sardine from April to October. Finally, the simulated mesozooplankton biomass was higher from January to July, which corresponded to the second half of the spawning season for sardine, but first half of the spawning season for anchovy.

Migratory movements of fin whales from the Gulf of St. Lawrence challenge our understanding of the Northwest Atlantic stock structure

Fin whales, Balenoptera physalus, are capital breeders, having the potential to separate breeding and feeding both spatially and temporally. Fin whales occur throughout the Northwest Atlantic, but stock structure and seasonal movements remain unclear. By deploying satellite transmitters on 28 individuals, we examine movement patterns within and beyond the Gulf of St. Lawrence (GSL), Canada, and challenge the current understanding of stock structure. Eight individuals left the GSL in autumn, with five tags persisting into January. Migration patterns of these whales showed considerable variation in timing and trajectory, with movements extending south to 24°N, and thus beyond the assumed distribution limit of the species in the Northwest Atlantic. A rapid return to the Scotian Shelf or Gulf of Maine was observed from several whales after incursions in southern waters, suggesting that fin whales in the Northwest Atlantic may not have a common winter destination that fits the definition of a breeding ground. Area-restricted search (ARS) behavior dominated fin whale activities during summer (92%) and fall (72%), with persistence into the winter (56%); ARS occurred at multiple locations in the GSL, Scotian Shelf and Shelf edge, and near seamounts of the North Atlantic, having characteristics consistent with foraging areas.

UPAYA MENINGKATKAN PERTUMBUHAN TERNAK KELINCI DI DASAN KARANG ANYAR DESA SIKUR LOMBOK TIMUR

Service to the community in the village of Karang Anyar Sikur Village, East Lombok, aims to improve knowledge breeders skill especially breeders rabbit that is in through making and giving quality feed. The population and growth of rabbits in Karang Anyar Sikur Village, East Lombok is relatively low compared to other villages in East Lombok, this is due to the lack of knowledge about the management of feeding rabbits, including the quality and quantity of feed provided. The implementation of the activity is carried out gradually, starting from the survey location, setting the time for implementation, making the brochure/leaf, and watching the video about the cultivation of the rabbit and the evaluation stage. By achieving the goal of this activity, it is expected that the community, especially the pet group, will be able to make formulas for the rabbit's food from the materials that are available at the location, with the content of the nutrition, according to the needs of the rabbit, and the provision of good food, so that it can increase the growth of the rabbit Income breeders rabbit.

Southern Ocean humpback whale trophic ecology. I. Combining multiple stable isotope methods elucidates diet, trophic position and foraging areas

Southern Ocean humpback whales Megaptera novaeangliae are capital breeders, breeding in the warm tropics/subtropics in the winter and migrating to nutrient-rich Antarctic feeding grounds in the summer. The classic feeding model is for the species to fast while migrating and breeding, surviving on blubber energy stores. Whilst northern hemisphere humpback whales are generalists, southern hemisphere counterparts are perceived as krill specialists, but for many populations, uncertainties remain regarding their diet and preferred feeding locations. This study used bulk and compound-specific stable isotope analyses and isoscape-based feeding location assignments to assess the diet, trophic ecology and likely feeding areas of humpback whales sampled in the Ross Sea region and around the Balleny Islands. Sampled whales had a mixed diet of plankton, krill and fish, similar to the diet of northern hemisphere humpback whales. Proportions of fish consumed varied but were often high (2-60%), thus challenging the widely held paradigm of Southern Ocean humpback whales being exclusive krill feeders. These whales had lower 15N values and trophic position estimates than their northern hemisphere counterparts, likely due to lower Southern Ocean baseline 15N surface water values and a lower percentage consumption of fish, respectively. Most whales fed in the Ross Sea shelf/slope and Balleny Islands high-productivity regions, but some isotopically distinct whales (mostly males) fed at higher trophic levels either around the Balleny Islands and frontal upwelling areas to the north, or en route to Antarctica in temperate waters off southern Australia and New Zealand. These results support other observations of humpback whales feeding during migration, highlighting the species’ dietary plasticity, which may increase their foraging and breeding success and provide them with greater resilience to anthropogenically mediated ecological change. This study highlights the importance of combining in situ field data with regional-scale isoscapes to reliably assess trophic structure and animal feeding locations, and to better inform ecosystem conservation and management of marine protected areas.

Shift from income breeding to capital breeding with latitude in the invasive Asian shore crab Hemigrapsus sanguineus

Organisms vary in the timing of energy acquisition and use for reproduction. Thus, breeding strategies exist on a continuum, from capital breeding to income breeding. Capital breeders acquire and store energy for breeding before the start of the reproductive season, while income breeders finance reproduction using energy acquired during the reproductive season. Latitude and its associated environmental drivers are expected to heavily influence breeding strategy, potentially leading to latitudinal variation in breeding strategies within a single species. We examined the breeding strategy of the Asian shore crab Hemigrapsus sanguineus at five sites spanning nearly 10° of latitude across its invaded United States range. We hypothesized that the primary breeding strategy of this species would shift from income breeding to capital breeding as latitude increases. We found that though this species’ breeding strategy is dominated by capital breeding throughout much of the range, income breeding increases in importance at lower latitudes. This latitudinal pattern is likely heavily influenced by the duration of the foraging and breeding seasons, which also vary with latitude. We also found that reproductive characteristics at the northern and southern edges of the invaded range were consistent with continued range expansion. We suggest that the reproductive flexibility of the Asian shore crab is a key facilitator of its continued invasion success. Our results highlight the influence of latitude on the breeding strategy of a species and emphasize the need for further research regarding the ecological importance and implications of flexibility in breeding strategies within species.

Future climate-induced distribution shifts in a sexually dimorphic key predator of the Southern Ocean.

The response to climate change in highly dimorphic species can be hindered by differences between sexes in habitat preferences and movement patterns. The Antarctic fur seal, Arctocephalus gazella, is the most abundant pinniped in the Southern Hemisphere, and one of the main consumers of Antarctic krill, Euphausia superba, in the Southern Ocean. However, the populations breeding in the Atlantic Southern Ocean are decreasing, partly due to global warming. Male and female Antarctic fur seals differ greatly in body size and foraging ecology, and little is known about their sex-specific responses to climate change. We used satellite tracking data and Earth System Models to predict changes in habitat suitability for male and female Antarctic fur seals from the Western Antarctic Peninsula under different climate change scenarios. Under the most extreme scenario (SSP5-8.5; global average temperature +4.4°C projected by 2100), suitable habitat patches will shift southward during the non-breeding season, leading to a minor overall habitat loss. The impact will be more pronounced for females than for males. The reduction of winter foraging grounds might decrease the survival of post-weaned females, reducing recruitment and jeopardizing population viability. During the breeding season, when males fast on land, suitable foraging grounds for females off the South Shetland Islands will remain largely unmodified, and new ones will emerge in the Bellingshausen Sea. As Antarctic fur seals are income breeders, the foraging grounds of females should be reasonably close to the breeding colony. As a result, the new suitable foraging grounds will be useful for females only if nearby beaches currently covered by sea ice emerge by the end of the century. Furthermore, the colonization of these new, ice-free breeding locations might be limited by strong female philopatry. These results should be considered when managing the fisheries of Antarctic krill in the Southern Ocean.

Biological and ecological traits rather than geography control mercury (Hg) in scutes of marine turtles from the Southwest Atlantic

The use of sentinel species in monitoring programs for toxic metals such as mercury (Hg) is essential to understand these pollutants' impact on the environment. For this purpose, it is essential to use organisms that have a lifespan compatible with the residence time of Hg in the oceans, and preferably with a wide geographical distribution, such as sea turtles. Here, we assess the regional variability of Hg concentrations using carapace scutes of four sea turtle species along the foraging and spawning area in the northeast coastline of Brazil. Mercury concentrations in samples showed no relationship with the environmental Hg levels (obtained from literature). Rather, Hg concentrations varied according to species-specific biological, and ecological traits. Characteristics such as the ontogenetic shift in the diet of Chelonia mydas, capital breeding in females, depth of foraging in oceanic waters, and selectivity of food items, such as in Eretmochelys imbricata, significantly influenced Hg concentrations.

Allosuckling in southern right whale calves

Allosuckling, the suckling of milk from a non-biological mother, occurs in some species of mammals. Allosuckling has not been quantified in baleen whale calves; therefore, we examine allosuckling in southern right whales (SRWs; Eubalaena australis) off Australia. SRWs are listed as Endangered under the Australian Environment Protection and Biodiversity Conservation Act as their numbers remain below the estimated historical abundance. On a small aggregation area, where there were three mother–calf pairs present, we aimed to quantify the proportion of time that calves allosuckled relative to the time spent filial suckling. To achieve this, we conducted unmanned aerial vehicle focal follows on mother–calf pairs and video recorded all interactions among pairs (n = 22 interactions, 3 h total observation time). During interactions, allosuckling occurred in seven interactions, and filial nursing occurred in 11 interactions. One of the calves performed allosuckling, and it was the largest calf with the largest mother. The calf allosuckled from both of the non-biological mothers present. The average proportion of time allosuckling per interaction was 4% (95% CI = ± 0.01, range = 0–0.25), whilst filial nursing for the same calf was 8% (95% CI = ± 0.02, range = 0–0.37). It is important to understand the frequency of allosuckling, and to quantify the energetic benefits for allosuckling calves and the energetic cost incurred by targeted non-biological mothers. This is particularly pertinent for capital breeders who do not replenish lost energy reserves until they migrate to their feeding grounds.

Combining bioenergetics and movement models to improve understanding of the population consequences of disturbance

We developed dynamic bioenergetics models to investigate how behavioural responses to anthropogenic disturbance events might affect the population dynamics of three marine mammal species (harbour porpoise, grey seal and harbour seal) with contrasting life‐history traits (capital versus income breeders) and movement behaviour (resident versus nomadic). We used these models to analyse how individual vital rates were affected by differences in the probability of disturbance and the duration of any behavioural response, while taking account of uncertainty in the model parameters and heterogeneity in behaviour. The outputs of individual movement models and telemetry data were then used to determine how the probability of exposure might vary among species, individuals, and geographical locations. We then demonstrate how these estimated probabilities of exposure can be translated into probabilities of disturbance. For illustrative purposes, we modelled the potential effects of a temporary decrease in energy assimilation associated with a series of disturbance events that might realistically occur during the construction of an offshore windfarm. Offspring starvation mortality was the vital rate that was most affected by these disturbance events. Monitoring of rate should be considered as standard practice so that populations responses can be detected as early as possible. Predicted effects on individual vital rates depended on the species' movement behaviour and the likely density of animals where the modelled construction activity was assumed to take place. The magnitude of these effects also depended critically on the assumed duration of the reduction in energy assimilation. No direct estimates of this variable are currently available, but we suggest some ways in which it could be estimated. The described approach could be extended to other species and activities, given sufficient information to parameterise the component models. However, we emphasise the need to account for among‐individual heterogeneities and uncertainties in the values of the many model parameters.

The influence of diet on gut microbiome and body mass dynamics in a capital-breeding migratory bird.

Gut-associated microbial communities are known to play a vital role in the health and fitness of their hosts. Though studies investigating the factors associated with among-individual variation in microbiome structure in wild animal species are increasing, knowledge of this variation at the individual level is scarce, despite the clear link between microbiome and nutritional status uncovered in humans and model organisms. Here, we combine detailed observational data on life history and foraging preference with 16S rRNA profiling of the faecal microbiome to investigate the relationship between diet, microbiome stability and rates of body mass gain in a migratory capital-breeding bird, the light-bellied Brent goose (Branta bernicla hrota). Our findings suggest that generalist feeders have microbiomes that are intermediate in diversity and composition between two foraging specialisms, and also show higher within-individual plasticity. We also suggest a link between foraging phenotype and the rates of mass gain during the spring staging of a capital breeder. This study offers rare insight into individual-level temporal dynamics of the gut microbiome of a wild host. Further work is needed to uncover the functional link between individual dietary choices, gut microbiome structure and stability, and the implications this has for the reproductive success of this capital breeder.

Life History Parameters to Inform Pattern of Prenatal Investment in Marine Mammals

Marine mammals are a diverse group of aquatic animals that exhibit wide variation in body size, living conditions, breeding habitat, social behaviour and phylogeny. Although case studies about prenatal investment in cetaceans and pinnipeds have been investigated, comparative studies across different marine mammal taxonomic groups have not yet been conducted systematically. Here, six life history parameters from 75 marine mammal species were collected based on a meta-analysis of the existing literature, and prenatal investment patterns for different taxonomic groups were explored using an unsupervised artificial neural network of a self-organizing map (SOM). Most marine mammal species can be clearly divided into two clusters of small-bodied taxa (small-bodied toothed whales, pinnipeds) and large-bodied taxa (baleen whales, sperm whales and beaked whales, large-bodied toothed whales) based on their distribution within SOM feature maps. Gestation periods and breeding intervals are significantly shorter in pinnipeds than in small-bodied toothed dolphins despite being similar in body size, indicating their adaption to birthing and nursing on land or ice floes. Specific deep-dive feeding behaviour seems to have no impact on the prenatal investment of beaked whales and sperm whales, as these species exhibit a similar capital breeding strategy to baleen whales. Medium-bodied sirenians adopt an intermediate strategy between small-bodied and large-bodied toothed whales, suggesting their prenatal investment strategy is not affected by herbivorous habits. Overall, our results support the body-size hypothesis and breeding-substrate hypothesis and indicate that prenatal investment strategies of marine mammals are possibly not influenced by feeding habits or social behaviour. We suggest that effective conservation measures for small-bodied toothed whales and pinnipeds should prioritize the protection of habitats and minimize human disturbance, whereas conservation measures for large-bodied whales and beaked whales should focus on strategies to prevent substantial declines in population size.

Reproductive tactics, birth timing and the risk-resource trade-off in an income breeder.

In variable environments, habitats that are rich in resources often carry a higher risk of predation. As a result, natural selection should favour individuals that balance allocation of time to foraging versus avoiding predation through an optimal decision-making process that maximizes fitness. The behavioural trade-off between resource acquisition and risk avoidance is expected to be particularly acute during gestation and lactation, when the energetic demands of reproduction peak. Here, we investigated how reproductive female roe deer adjust their foraging activity and habitat use during the birth period to manage this trade-off compared with non-reproductive juveniles, and how parturition date constrains individual tactics of risk-resource management. Activity of reproductive females more than doubled immediately following parturition, when energy demand is highest. Furthermore, compared with non-reproductive juveniles, they increased their exposure to risk by using open habitat more during daytime and ranging closer to roads. However, these post-partum modifications in behaviour were particularly pronounced in late-parturient females who adopted a more risk-prone tactic, presumably to compensate for the growth handicap of their late-born offspring. In income breeders, individuals that give birth late may be constrained to trade risk avoidance for foraging during peak allocation to reproduction, with probable consequences for individual fitness.