Effects Of Life-history Traits Research Articles

Lipid Metabolism in Parasitoids and Parasitized Hosts.

Parasitoids have an exceptional lifestyle where juvenile development is spent on or in a single host insect, but the adults are free-living. Unlike parasites, parasitoids kill the host. How parasitoids use such a limiting resource, particularly lipids, can affect chances to survive and reproduce. In part 1, we describe the parasitoid lifestyle, including typical developmental strategies. Lipid metabolism in parasitoids has been of interest to researchers since the 1960s and continues to fascinate ecologists, evolutionists, physiologists, and entomologists alike. One reason of this interest is that the majority of parasitoids do not accumulate triacylglycerols as adults. Early research revealed that some parasitoid larvae mimic the fatty acid composition of the host, which may result from a lack of de novo triacylglycerol synthesis. More recent work has focused on the evolution of lack of adult triacylglycerol accumulation and consequences for life history traits. In part 2 of this chapter, we discuss research efforts on lipid metabolism in parasitoids from the 1960s onwards. Parasitoids are alsomaster manipulators of host physiology, including lipid metabolism, havingevolved a range of mechanisms to affect the release, synthesis, transport, and take-up of lipids from the host. We lay out the effects of parasitism on host physiology in part 3 of this chapter.

Effect of Life-History Traits and Habitat Condition on Genetic Diversity between Invasive and Native Plant Populations

Plant invasions have a huge impact on the health of ecosystems and human well-being. The invasion risk varies with the introduction pathway, the propagule pressure, and the genetic diversity of the founding population. We performed a systematic review and meta-analysis of 30 studies reporting the genetic diversity of 31 plant species in their invasive and native ranges. We evaluated if patterns of genetic diversity differ between ranges and whether these responses are influenced by life-history traits, hybridization, polyploidization, and habitat condition. We found that invasive populations had significantly lower genetic diversity and higher inbreeding than native populations. In fragmented and degraded habitats, the genetic diversity of invaders was lower, but inbreeding was not affected. Polyploid invaders with hybrid capacity also showed lower genetic diversity. Invasive herbs with vegetative propagation were more sensitive to the loss of genetic diversity and had higher levels of inbreeding. Our synthesis showed that the genetic response in the invaded range could result from historical processes, such as founder and bottleneck events. Traits such as selfing are more likely to preserve the signatures of founder events and influence the genetic diversity in invasive populations. Additionally, clonality seems to be the predominant reproduction system in the invaded range.

Effects of life-history traits and network topological characteristics on the robustness of marine food webs

Management targets for biodiversity preservation are shifting from individual species to an ecosystem-wide focus. Indeed, the perturbation analysis of interaction networks, such as food webs, better captures the response of biodiversity to environmental pressures than single-species considerations. Here we propose a framework that examines food web robustness to a given perturbation based on life history traits and the topology of the food web, at different scales: local (species), intermediate (species directly linked together by a trophic interaction), and global (food web). Applying this framework to the Celtic Sea, a historically exploited fishing ground, we showed that the species sensitive to fishing were not the most central (i.e. with many interaction links, estimated based on eigenvector centrality) and that there is no both highly sensitive and exposed species to fishing. We then investigated how the loss of central, sensitive and exposed species to fishing could impact the robustness of the food web. We showed that the food web was the least robust to the simulated loss of species with many predators (i.e. forage species) and most exposed to fishing pressure, indicating that conservation priority could be focused on these species. Estimating species’ sensitivity to fishing was insufficient to predict food web robustness since the simulated removal of the most sensitive species led to a robustness level similar to that of a random removal sequence. Unlike what is often documented, the network appeared relatively robust to the simulated loss of the most central species, due notably to their implication in redundant trophic interactions and the fact that their disappearance increases modularity. This suggests that species-level metrics such as centrality should be completed by analysis at the scale of the whole food web to prioritize species conservation.

Proximate and evolutionary sources of variation in offspring energy expenditure in songbirds

AbstractAimUnderstanding variation in offspring energy expenditure is important because energy is critical for growth and development. Weather may exert proximate effects on offspring energy expenditure, but in altricial species these might be masked by parental care and huddling with siblings. Such effects are particularly important to understand given changing global weather patterns, yet studies of wild offspring in the presence of parental care are lacking. Offspring energy expenditure may also vary among species due to evolved responses to environmental selection pressures, requiring studies at both proximate and ultimate levels.LocationUSA, South Africa, Malaysia.Time period2016–2019.Major taxa studiedSongbirds.MethodsWe used the doubly‐labelled water technique to estimate nestling daily energy expenditure of 54 songbird species across three continents. We used Bayesian phylogenetic mixed models to test proximate and evolutionary causes of variation in offspring energy expenditure while accounting for phylogeny and phylogenetic uncertainty.ResultsOffspring energy expenditure increased with more rainfall and colder air temperatures, but decreased among offspring in broods with more siblings. Across species, nestling and adult mortality, but not growth rate, were positively associated with offspring energy use.Main conclusionsWeather had clear proximate effects on offspring energy expenditure and parents were either unable or unwilling to fully offset these effects. However, the decrease in offspring energy use when huddling with more siblings demonstrated a modulating effect of life history traits. For example, high nest predation rates favour reduced parental care and can force offspring to spend more energy coping with environmental conditions. Furthermore, reduced energy expenditure is thought to facilitate increased longevity, which is increasingly realized with lower extrinsic mortality rates, providing an explanation for the positive association between adult mortality and offspring energy expenditure. Ultimately, both proximate and evolutionary influences need to be considered to better understand causes of offspring energetics.

Responses of Manduca sexta larvae to heat waves.

Climate change is increasing the frequency of heat waves and other extreme weather events experienced by organisms. How does the number and developmental timing of heat waves affect survival, growth and development of insects? Do heat waves early in development alter performance later in development? We addressed these questions using experimental heat waves with larvae of the tobacco hornworm, Manduca sexta. The experiments used diurnally fluctuating temperature treatments differing in the number (0-3) and developmental timing (early, middle and/or late in larval development) of heat waves, in which a single heat wave involved three consecutive days with a daily maximum temperature of 42°C. Survival to pupation declined with increasing number of heat waves. Multiple (but not single) heat waves significantly reduced development time and pupal mass; the best models for the data indicated that both the number and developmental timing of heat waves affected performance. In addition, heat waves earlier in development significantly reduced growth and development rates later in larval development. Our results illustrate how the frequency and developmental timing of sublethal heat waves can have important consequences for life history traits in insects.

Fluctuating temperatures extend median lifespan, improve reproduction and reduce growth in turquoise killifish.

In natural populations, individuals experience daily fluctuations in environmental conditions that synchronise endogenous biorhythms. Artificial alterations of environmental fluctuations can have negative consequences for life history traits, including lifespan. In laboratory studies of aging, the role of fluctuating temperature is usually overlooked and we know little of how thermal fluctuation modulates senescence in vertebrates. In this longitudinal study we followed individually-housed turquoise killifish, Nothobranchius furzeri, from two thermal regimes; ecologically relevant diel fluctuations (20 °C - 35 °C) and stable temperature (27.5 °C), and compared their survival, growth and reproduction. Fish experiencing fluctuating temperatures had a longer median lifespan but reached smaller asymptotic body size. Within-treatment variation indicated that extended lifespan in fluctuating temperatures was not causally linked to decreased growth rate or smaller body size, but occurred solely due to the effect of thermal fluctuations. Male body size was positively associated with lifespan in stable temperatures but this relationship was disrupted in fluctuating thermal regimes. Females exposed to fluctuating temperatures effectively compensated egg production for their smaller size. Thus, there was no difference in absolute fecundity between thermal regimes and body-size corrected fecundity was higher in females in fluctuating temperatures. Overall, despite a brief exposure to sub-optimal thermal conditions during fluctuations, fluctuating temperature had a positive effect on survival and reproduction. These results suggest that the expression of life history traits and their associations under stable temperatures are a poor representation of the relationships obtained from ecologically relevant thermal fluctuations.

Females adjust maternal hormone concentration in eggs according to male condition in a burying beetle

In birds and other vertebrates, there is good evidence that females adjust the allocation of hormones in their eggs in response to prenatal environmental conditions, such as food availability or male phenotype, with profound consequences for life history traits of offspring. In insects, there is also evidence that females deposit juvenile hormones (JH) and ecdysteroids (ESH) in their eggs, hormones that play a key role in regulating offspring growth and metamorphosis. However, it is unclear whether females adjust their hormonal deposition in eggs in response to prenatal environmental conditions. Here we address this gap by conducting an experiment on the burying beetle Nicrophorus vespilloides, in which we manipulated the presence of the male parent and the size of the carcass used for breeding at the time of laying. We also tested for effects of the condition (i.e., body mass) of the parents. We then recorded subsequent effects on JH and ESH concentrations in the eggs. We found no evidence for an effect of these prenatal environmental conditions (male presence and carcass size) on hormonal concentration in the eggs. However, we found that females reduced their deposition of JH when mated with heavier males. This finding is consistent with negative differential allocation of maternal hormones in response to variation in the body mass of the male parent. We encourage further work to investigate the role of maternally derived hormones in insect eggs.

The neutrophil to lymphocyte ratio indexes individual variation in the behavioural stress response of wild roe deer across fluctuating environmental conditions

Understanding how wild animals adapt to perturbations and their consequences for life history traits and population dynamics is a current focus of attention in ecology and conservation biology. Here, we analysed variation in the neutrophil to lymphocyte ratio (N:L ratio), a proxy of stress level, in wild roe deer Capreolus capreolus from three populations experiencing markedly different environmental conditions. We first assessed whether among-individual differences in the N:L ratio were consistent over time and across environmental contexts. We then investigated how both individual characteristics (behaviour at capture, age, sex, body mass), and environmental context (habitat and year quality) were linked to this indicator of stress level. We found moderate, but consistent, repeatability of the N:L ratio in all three populations, indicating stable among-individual differences in the way individuals cope physiologically with varying environmental conditions. In addition, we found a weak, but consistent, association between the N:L ratio and behaviour at capture in two of the three populations. Finally, the N:L ratio also varied in relation to temporal changes in environmental conditions. In particular, individuals had, on average, higher levels of stress in poor-quality years in two of the three populations. We discuss our results in relation to the coping styles framework. Due to global change, natural populations are increasingly faced with unpredictable fluctuations of their environment. The stress response, via the release of glucocorticoids, is a key mechanism that enables individuals to cope with these variations. However, all individuals do not necessarily cope with life threatening and/or stressful situations in the same way, but as yet, the major drivers underlying variation in stress level remain unclear. We showed that the N:L ratio, reflecting baseline stress level, was repeatable and influenced by both individual and environmental factors. In particular, variation in the N:L ratio was linked to the quality of the year in terms of resource availability and, to a lesser extent, to the individual’s behaviour at capture. Our study demonstrates that both environmental context and individual characteristics drive variation in the N:L ratio in a wild vertebrate population.

Metabolic and behavioral responses of predators to prey nutrient content

Predators feed on a diversity of prey that can vary widely in nutrient content. While prey nutrient content is known to have important consequences for life history traits, less is known about how it affects physiology and behavior. The purpose of this study was to test how diet affected the physiology and behavior of the wolf spider Hogna carolinensis. We hypothesized that higher protein intake would result in a lower metabolic rate due to less energy intake. Further, we also expected the high protein group to exhibit increased activity levels and aggression in an attempt to increase energy intake. Spiders were maintained on three different treatment diets in order to simulate prey with differing macronutrient composition: high protein, intermediate, and high lipid. Spider respiration was measured to quantify the baseline metabolic rate (SMR), digestive metabolic rate (SDA), and active metabolic rate (AMR). We found no significant effect of diet on metabolic rates. However, the SDA coefficient (i.e. digestive cost relative to prey content) was higher in the high protein group, meaning that this group metabolized a greater portion of their prey during digestion and had a lower net energy intake from prey. In our behavioral assays, spiders in the high protein group were significantly more active and attacked prey more quickly in their first trial. Our results demonstrate that diet had relatively little effect on predator metabolism but more of an effect on behavior. These findings suggest that diet regulation should be analyzed by studying multiple responses together, including metabolism and behavior, to gain a more comprehensive understanding of the effects of diet on organism performance and fitness.

How do migratory fish populations respond to barrier removal in spawning and nursery grounds?

Connection between critical habitats is an important consideration in efforts to restore native and socio-economically important fish species or control the spread of invasive species. However, differences in fish life history might influence the effectiveness of restoration and management actions. In addition, the strength of connection among spatially separate subpopulations could affect the response of the overall population to a local environmental change. In this study, we modeled the response of migratory fish populations with different homing rates, straying distances, and reproductive modes (iteroparity and semelparity) to changes in the carrying capacity of spawning/nursery grounds in a lake-stream system. Increasing the carrying capacity of one spawning/nursery ground could increase the abundance of the local subpopulation and overall population, but both short-term (i.e., abundance change in the first 20 years) and long-term (i.e., equilibrium abundance) responses varied with life history traits. Furthermore, the abundance of some subpopulations might decrease because of the movement of straying adults toward more productive spawning/nursery grounds. In general, straying distance influenced the short-term response and spatial pattern of the population while homing rate influenced the equilibrium abundance. This study revealed the effect of life history traits on population response to restoration actions, which may be crucial for managers in charge of multi-species management, such as enhancing native fishes while controlling invasive species.

Global drivers of population density in terrestrial vertebrates

AbstractAimAlthough the effects of life history traits on population density have been investigated widely, how spatial environmental variation influences population density for a large range of organisms and at a broad spatial scale is poorly known. Filling this knowledge gap is crucial for global species management and conservation planning and to understand the potential impact of environmental changes on multiple species.LocationGlobal.Time periodPresent.Major taxa studiedTerrestrial amphibians, reptiles, birds and mammals.MethodsWe collected population density estimates for a range of terrestrial vertebrates, including 364 estimates for amphibians, 850 for reptiles, 5,667 for birds and 7,651 for mammals. We contrasted the importance of life history traits and environmental predictors using mixed models and tested different hypotheses to explain the variation in population density for the four groups. We assessed the predictive accuracy of models through cross‐validation and mapped the partial response of vertebrate population density to environmental variables globally.ResultsAmphibians were more abundant in wet areas with high productivity levels, whereas reptiles showed relatively higher densities in arid areas with low productivity and stable temperatures. The density of birds and mammals was typically high in temperate wet areas with intermediate levels of productivity. The models showed good predictive abilities, with pseudo‐R2ranging between 0.68 (birds) and 0.83 (reptiles).Main conclusionsTraits determine most of the variation in population density across species, whereas environmental conditions explain the intraspecific variation across populations. Species traits, resource availability and climatic stability have a different influence on the population density of the four groups. These models can be used to predict the average species population density over large areas and be used to explore macroecological patterns and inform conservation analyses.

Lumpy species coexistence arises robustly in fluctuating resource environments

The effect of life-history traits on resource competition outcomes is well understood in the context of a constant resource supply. However, almost all natural systems are subject to fluctuations of resources driven by cyclical processes such as seasonality and tidal hydrology. To understand community composition, it is therefore imperative to study the impact of resource fluctuations on interspecies competition. We adapted a well-established resource-competition model to show that fluctuations in inflow concentrations of two limiting resources lead to the survival of species in clumps along the trait axis, consistent with observations of "lumpy coexistence" [Scheffer M, van Nes EH (2006) Proc Natl Acad Sci USA 103:6230-6235]. A complex dynamic pattern in the available ambient resources arose very early in the self-organization process and dictated the locations of clumps along the trait axis by creating niches that promoted the growth of species with specific traits. This dynamic pattern emerged as the combined result of fluctuations in the inflow of resources and their consumption by the most competitive species that accumulated the bulk of biomass early in assemblage organization. Clumps emerged robustly across a range of periodicities, phase differences, and amplitudes. Given the ubiquity in the real world of asynchronous fluctuations of limiting resources, our findings imply that assemblage organization in clumps should be a common feature in nature.

Seed mass of angiosperm woody plants better explained by life history traits than climate across China

Seed mass is a basic trait in studies of functional ecology. Examining how seed mass is affected by biotic and abiotic factors could improve our understanding of ecological strategies in plants. Here we examined the relationships of seed mass with 13 climate variables and seven life history traits, and partitioned the relative effects of life history traits vs. climate, based on seed mass data for 1265 woody angiosperm species in China. Our results showed that seed mass decreased with latitude, and most climate variables were positively correlated with seed mass. Geographic seed mass pattern was affected by both energy and water availability in the growing season, but the effect of energy availability was more important. Seed mass was also significantly related to other traits such as growth form, fruit type, dispersal mode, breeding system, leaf habit, fruit development time, and minimum juvenile period, with growth form and dispersal mode being the most closely related traits. Our results showed that climate explained much less variation in seed mass than life history traits, and that phylogeny played an important role in shaping the large-scale patterns of seed mass.

Pollination Mode and Mating System Explain Patterns in Genetic Differentiation in Neotropical Plants.

We studied genetic diversity and differentiation patterns in Neotropical plants to address effects of life history traits (LHT) and ecological attributes based on an exhaustive literature survey. We used generalized linear mixed models (GLMMs) to test the effects as fixed and random factors of growth form, pollination and dispersal modes, mating and breeding systems, geographical range and habitat on patterns of genetic diversity (HS, HeS, π and h), inbreeding coefficient (FIS), allelic richness (AR) and differentiation among populations (FST) for both nuclear and chloroplast genomes. In addition, we used phylogenetic generalized least squares (pGLS) to account for phylogenetic independence on predictor variables and verify the robustness of the results from significant GLMMs. In general, GLMM revealed more significant relationships among LHTs and genetic patterns than pGLS. After accounting for phylogenetic independence (i.e., using pGLS), FST for nuclear microsatellites was significantly related to pollination mode, mating system and habitat. Plants specifically with outcrossing mating system had lower FST. Moreover, AR was significantly related to pollination mode and geographical range and HeS for nuclear dominant markers was significantly related to habitat. Our findings showed that different results might be retrieved when phylogenetic non-independence is taken into account and that LHTs and ecological attributes affect substantially the genetic pattern in Neotropical plants, hence may drive key evolutionary processes in plants.

Variation in total and volatile carbon concentration among the major tree species of the boreal forest

Understanding variation in carbon (C) concentration of live trees is essential for quantifying forest C stocks and validating forest C accounting models. Previous studies in boreal forests have assumed 50% C concentration or focused on species-specific C concentration estimation based on samples taken mostly from stemwood tissue of large trees. Yet, little is known about differences in C concentration between woody tissues or among trees of different sizes nor about the effects of life-history traits, such as shade tolerance and the role of volatile C on total C concentration in live trees. In this study, we examined variation in total and volatile C concentration in bark and stemwood tissues for trees of different sizes for six major North American boreal tree species. We found that bark had significantly higher total C and volatile C concentrations than stemwood and that both total C and volatile C concentration significantly varied among tree species. The average total C concentrations were 56.2% in the bark and 50.5% in the stemwood, and the average volatile C concentration were 5.8% and 3.0% for bark and stemwood, respectively. Furthermore, total C and volatile C concentration in stemwood and bark of almost all shade-intolerant species increased with tree size, whereas those of shade-tolerant species showed negative or neutral size-associated change. Our results show that volatile C concentration is a key driver of variation in total C concentration and highlights the importance of considering variation in C concentration when quantifying forest C stocks, which has important consequences for predicting future global C emissions scenarios.

A novel methodology for the rapid assessment of waterbird vulnerability to disturbance

A methodology for rapidly assessing the vulnerability of waterbirds to disturbance was tested at Sabaki estuary, Kenya. Three variables were employed to measure the responses of 15 species: (1) bird density, (2) minimum distance of birds from a stationary disturbance and (3) recovery times following a moving disturbance. Spatial response metrics (1) and (2) were regressed against expected species densities (in the absence of disturbance). Normalised mean residuals then described species-specific deviations from the average spatial response to disturbance. A hypothetical model was constructed, whereby species were placed on a spatial response gradient and overlaid by the recovery metric (3). Greater Flamingo Phoenicopterus roseus, Lesser Flamingo Phoeniconaias minor, African Spoonbill Platalea alba and Terek Sandpiper Xenus cinereus exhibited the strongest avoidance responses. The two spatial metrics (1 and 2) achieved concordance for 73% of species, and all three metrics gave similar results for six of seven species at the extremes of the spatial response gradient. Non-concordance between response metrics is likely an effect of life-history traits (e.g. territoriality). Our results support the use of relative spatial response metrics (1 and 2) for robust and rapid identification of waterbird species that are most responsive and, by virtue, vulnerable to the effects of disturbance on tropical estuaries.

Significant genetic structure despite high vagility revealed through mitochondrial phylogeography of an Australian freshwater turtle (Chelodina longicollis)

Restriction to the freshwater environment plays a dominant role in the population genetic structure of freshwater fauna. In taxa with adaptations for terrestriality, however, the restrictions on dispersal imposed by drainage divides may be overcome. We investigate the mitochondrial phylogeographic structure of the eastern long-necked turtle (Chelodina longicollis), a widespread Australian freshwater obligate with strong overland dispersa\l capacity and specific adaptations to terrestriality. We predict that such characteristics make this freshwater species a strong candidate to test how life-history traits can drive gene flow and interbasin connectivity, overriding the constraining effects imposed by hydrological boundaries. Contrary to expectations, and similar to low-vagility freshwater vertebrates, we found two ancient mitochondrial haplogroups with clear east–west geographic partitioning either side of the Great Dividing Range. Each haplogroup is characterised by complex genetic structure, demographically stable subpopulations, and signals of isolation by distance. This pattern is overlaid with signatures of recent gene flow, likely facilitated by late Pleistocene and ongoing anthropogenic landscape change. We demonstrate that the divergent effects of landscape history can overwhelm the homogenising effects of life-history traits that connect populations, even in a highly vagile species.

Integrating life history traits and forest structure to evaluate the vulnerability of rainforest birds along gradients of deforestation and fragmentation in eastern Australia

The management of rainforest ecosystems for multi-species conservation must assess the impacts of habitat degradation at different spatial scales as well as determine which species are vulnerable to landscape change. Our research objectives were to (1) evaluate the effects of life history traits on the patch occupancy and vulnerability of rainforest birds, (2) determine the relative effects of stand, landscape and patch structure on species richness, and (3) evaluate the relative contributions of deforestation and fragmentation to species richness. We collected presence–absence data for 29 bird species in 46 rainforest patches in South East Queensland, Australia. We used a multi-species occupancy model that accounted for incomplete detection to evaluate hypotheses for occupancy and species richness. Avian occupancy was strongly influenced by life history traits, including population density, foraging behavior, dispersal strategy, clutch size, body mass and diet. Sedentary species with low population sizes, low clutch sizes, large body sizes and insectivorous diets, such as the ground-dwelling Albert’s Lyrebird (Menura alberti) and canopy-dwelling Paradise Riflebird (Ptiloris paradiseus), were the most vulnerable to landscape change. After accounting for life history, the positive effect of stand basal area was the best predictor of species richness followed by the positive effects of rainforest and dry eucalypt forest in the landscape, with less support for the positive effect of patch size and negative effect of patch isolation. Deforestation was more detrimental to the bird community than rainforest fragmentation. Conservation actions that retain high stand basal area, promote unmodified landscape mosaics and maintain moderate patch sizes near large rainforest tracts are expected to be effective strategies for managing the rainforest bird community. Landscape conservation strategies to minimize habitat loss are expected to be more effective than managing the configuration of rainforest patches.

Demographic Diversity and Sustainable Fisheries

Fish species are diverse. For example, some exhibit early maturation while others delay maturation, some adopt semelparous reproductive strategies while others are iteroparous, and some are long-lived and others short-lived. The diversity is likely to have profound effects on fish population dynamics, which in turn has implications for fisheries management. In this study, a simple density-dependent stage-structured population model was used to investigate the effect of life history traits on sustainable yield, population resilience, and the coefficient of variation (CV) of the adult abundance. The study showed that semelparous fish can produce very high sustainable yields, near or above 50% of the carrying capacity, whereas long-lived iteroparous fish can produce very low sustainable yields, which are often much less than 10% of the carrying capacity. The difference is not because of different levels of sustainable fishing mortality rate, but because of difference in the sensitivity of the equilibrium abundance to fishing mortality. On the other hand, the resilience of fish stocks increases from delayed maturation to early maturation strategies but remains almost unchanged from semelparous to long-lived iteroparous. The CV of the adult abundance increases with increased fishing mortality, not because more individuals are recruited into the adult stage (as previous speculated), but because the mean abundance is more sensitive to fishing mortality than its standard deviation. The magnitudes of these effects vary depending on the life history strategies of the fish species involved. It is evident that any past high yield of long-lived iteroparous fish is a transient yield level, and future commercial fisheries should focus more on fish that are short-lived (including semelparous species) with high compensatory capacity.

Effects of life-history traits on parasitism in a monogamous mammal, the eastern rock sengi (Elephantulus myurus)

The distribution of parasites is often characterised by substantial aggregation with a small proportion of hosts harbouring the majority of parasites. This pattern can be generated by abiotic and biotic factors that affect hosts and determine host exposure and susceptibility to parasites. Climate factors can change a host's investment in life-history traits (e.g. growth, reproduction) generating temporal patterns of parasite aggregation. Similarly, host age may affect such investment. Furthermore, sex-biased parasitism is common among vertebrates and has been linked to sexual dimorphism in morphology, behaviour and physiology. Studies exploring sex-biased parasitism have been almost exclusively conducted on polygynous species where dimorphic traits are often correlated. We investigated the effects of season and life-history traits on tick loads of the monogamous eastern rock sengi (Elephantulus myurus). We found larger tick burdens during the non-breeding season possibly as a result of energetic constraints and/or climate effects on the tick. Reproductive investment resulted in increased larval abundance for females but not males and may be linked to sex-specific life-history strategies. The costs of reproduction could also explain the observed age effect with yearling individuals harbouring lower larval burdens than adults. Although adult males had the greatest larval tick loads, host sex appears to play a minor role in generating the observed parasite heterogeneities. Our study suggests that reproductive investment plays a major role for parasite patterns in the study species.