Exposure to female olfactory cues hastens reproductive ageing and increases mortality when mating in male mice.

Theories of ageing predict that investment in reproduction will trade-off against survival and later-life reproduction. Recent evidence from invertebrates suggests that just perceiving cues of a potential mate's presence can reduce lifespan, particularly in males, and that activation of neuroendocrine reward pathways associated with mating can alleviate these effects. Whether similar effects occur in vertebrates remains untested. We tested whether exposure to olfactory cues from the opposite sex would influence mortality and reproductive senescence in male mice. We observed that males exposed to female olfactory cues from middle- to old age (from 10 to 24 months of age) showed reduced late-life fertility, irrespective of whether they had also been allowed to mate with females earlier in life. Males that were exposed to female odours in conjunction with mating also showed an increased mortality rate across the exposure period, indicating that olfactory cues from females can increase male mortality in some environments. Our results show that exposure to female odours can influence reproductive ageing and mortality in male mice, highlighting that sensory perception of mates may be an important driver of life-history trade-offs in mammals.

Addressing pollination deficits in orchard crops through habitat management for wild pollinators.

There is increasing evidence that farmers in many areas are achieving below maximum yields due to insufficient pollination. Practical and effective approaches are needed to maintain wild pollinator populations within agroecosystems so they can deliver critical pollination services that underpin crop production. We established nesting and wildflower habitat interventions in 24 UK apple orchards and measured effects on flower-visiting insects and the pollination they provide, exploring how this was affected by landscape context. We quantified the extent of pollination deficits and assessed whether the management of wild pollinators can reduce deficits and deliver improved outcomes for growers over 3 years. Wildflower interventions increased solitary bee numbers visiting apple flowers by over 20%, but there was no effect of nesting interventions. Other pollinator groups were influenced by both local and landscape-scale factors, with bumblebees and hoverflies responding to the relative proportion of semi-natural habitat at larger spatial scales (1000 m), while honeybees and other flies responded at 500 m or less. By improving fruit number and quality, pollinators contributed more than £16 k per hectare. However, deficits (where maximum potential was not being reached due to a lack of pollination) were recorded and the extent of these varied across orchards, and from year to year, with a 22% deficit in output in the worst (equivalent to ~£14 k/ha) compared to less than 3% (equivalent to ~£2 k/ha) in the best year. Although no direct effect of our habitat interventions on deficits in gross output was observed, initial fruit set and seed set deficits were reduced by abundant bumblebees, and orchards with a greater abundance of solitary bees saw lower deficits in fruit size. The abundance of pollinators in apple orchards is influenced by different local and landscape factors that interact and vary between years. Consequently, pollination, and the extent of economic output deficits, also vary between orchards and years. We highlight how approaches, including establishing wildflower areas and optimizing the ratio of cropped and non-cropped habitats can increase the abundance of key apple pollinators and improve outcomes for growers.

Characterization Factors to Assess Land Use Impacts on Pollinator Abundance in Life Cycle Assessment.

While wild pollinators play a key role in global food production, their assessment is currently missing from the most commonly used environmental impact assessment method, Life Cycle Assessment (LCA). This is mainly due to constraints in data availability and compatibility with LCA inventories. To target this gap, relative pollinator abundance estimates were obtained with the use of a Delphi assessment, during which 25 experts, covering 16 nationalities and 45 countries of expertise, provided scores for low, typical, and high expected abundance associated with 24 land use categories. Based on these estimates, this study presents a set of globally generic characterization factors (CFs) that allows translating land use into relative impacts to wild pollinator abundance. The associated uncertainty of the CFs is presented along with an illustrative case to demonstrate the applicability in LCA studies. The CFs based on estimates that reached consensus during the Delphi assessment are recommended as readily applicable and allow key differences among land use types to be distinguished. The resulting CFs are proposed as the first step for incorporating pollinator impacts in LCA studies, exemplifying the use of expert elicitation methods as a useful tool to fill data gaps that constrain the characterization of key environmental impacts.

Mating in the absence of fertilization promotes a growth-reproduction versus lifespan trade-off in female mice.

Trade-offs between growth, reproduction, and lifespan constrain animal life histories, leading to evolutionary diversification of life history cycles in different environments. In female mammals, gestation and lactation are expected to impose the major costs of reproduction, driving reproductive trade-offs, although mating also requires interactions with males that could themselves influence life history. Here we show that a male's presence by itself leads to lifelong alterations in life history in female mice. Housing C57BL/6J female mice with sterilized males early in life led to an increase in body weight, an effect that persisted across life even when females were later allowed to produce pups. We found that those females previously housed with sterile males also showed enhanced late-life offspring production when allowed to reproduce, indicating that earlier mating can influence subsequent fecundity. This effect was the opposite to that seen in females previously housed with intact males, which showed the expected trade-off between early-life and late-life reproduction. However, housing with a sterile male early in life came at a cost to lifespan, which was observed in the absence of females ever undergoing fertilization. Endocrinologically, mating also permanently reduced the concentration of circulating prolactin, a pituitary hormone influencing maternal care. Changes in hormone axes that influence reproduction could therefore help alter life history allocation in response to opposite-sex stimuli. Our results demonstrate that mating itself can increase growth and subsequent fecundity in mammals, and that responses to sexual stimuli could account for some lifespan trade-offs normally attributed to pregnancy and lactation.

Sex differences in adult lifespan and aging rates of mortality across wild mammals.

In human populations, women consistently outlive men, which suggests profound biological foundations for sex differences in survival. Quantifying whether such sex differences are also pervasive in wild mammals is a crucial challenge in both evolutionary biology and biogerontology. Here, we compile demographic data from 134 mammal populations, encompassing 101 species, to show that the female's median lifespan is on average 18.6% longer than that of conspecific males, whereas in humans the female advantage is on average 7.8%. On the contrary, we do not find any consistent sex differences in aging rates. In addition, sex differences in median adult lifespan and aging rates are both highly variable across species. Our analyses suggest that the magnitude of sex differences in mammalian mortality patterns is likely shaped by local environmental conditions in interaction with the sex-specific costs of sexual selection.

Animal pollination increases stability of crop yield across spatial scales.

The benefits of animal pollination to crop yield are well known. In contrast, the effects of animal pollination on the spatial or temporal stability (the opposite of variability) of crop yield remain poorly understood. We use meta-analysis to combine variability information from 215 experimental comparisons between animal-pollinated and wind- or self-pollinated control plants in apple, oilseed rape and faba bean. Animal pollination increased yield stability (by an average of 32% per unit of yield) at between-flower, -plant, -plot and -field scales. Evidence suggests this occurs because yield benefits of animal pollination become progressively constrained closer to the maximum potential yield in a given context, causing clustering. The increase in yield stability with animal pollination is greatest when yield benefits of animal pollination are greatest, indicating that managing crop pollination to increase yield also increases yield stability. These additional pollination benefits have not yet been included in economic assessments but provide further justification for policies to protect pollinators.

Rapid assessment of insect pollination services to inform decision-making.

Pollinator declines have prompted efforts to assess how land-use change affects insect pollinators and pollination services in agricultural landscapes. Yet many tools to measure insect pollination services require substantial landscape-scale data and technical expertise. In expert workshops, 3 straightforward methods (desk-based method, field survey, and empirical manipulation with exclusion experiments) for rapid insect pollination assessment at site scale were developed to provide an adaptable framework that is accessible to nonspecialist with limited resources. These methods were designed for TESSA (Toolkit for Ecosystem Service Site-Based Assessment) and allow comparative assessment of pollination services at a site of conservation interest and in its most plausible alternative state (e.g., converted to agricultural land). We applied the methods at a nature reserve in the United Kingdom to estimate the value of insect pollination services provided by the reserve. The economic value of pollination services provided by the reserve ranged from US$6163 to US$11,546/year. The conversion of the reserve to arable land would provide no insect pollination services and a net annual benefit from insect-pollinated crop production of approximately $1542/year (US$24∙ha-1 ∙year-1 ). The methods had wide applicability and were readily adapted to different insect-pollinated crops: rape (Brassica napus) and beans (Vicia faba) crops. All methods were rapidly employed under a low budget. The relatively less robust methods that required fewer resources yielded higher estimates of annual insect pollination benefit.

Diversidad y Conservación de Gasterópodos Subterráneos de Agua Dulce en los Estados Unidos y en México Resumen Las declinaciones de los polinizadores han impulsado los esfuerzos por evaluar cómo el cambio del uso de suelo afecta a los insectos polinizadores y los servicios de polinización en los paisajes agrícolas. Aun así, muchas de las herramientas para medir los servicios de los insectos polinizadores requieren datos sustanciales a escala de paisaje y el conocimiento de expertos. Desarrollamos tres métodos sencillos (método de gabinete, censo de campo y manipulación empírica con experimentos de exclusión) durante algunos talleres de expertos para la evaluación rápida de la polinización por insectos a escala de sitio con el objetivo de proporcionar un marco de trabajo adaptable y accesible para quienes no son especialistas y cuentan con recursos limitados. Estos métodos fueron diseñados para TESSA (Toolkit for Ecosystem Service Site-Based Assessment, en inglés) y permiten la evaluación comparativa de los servicios de polinización en los sitios de interés para la conservación y su estado alternativo más plausible (p. ej.: convertido a suelo agrícola). Aplicamos los métodos en una reserva natural del Reino Unido para estimar el valor de los servicios de polinización por insectos que proporciona la reserva. El valor económico de los servicios de polinización que proporciona la reserva varió desde US$6,163 a US$11,546 al año-1 . La conversión de la reserva a suelo arable no proporcionaría servicios de polinización por insectos, pero sí un beneficio anual neto a partir de la producción de cultivos polinizados por insectos de aproximadamente $1,542 al año-1 (US$24 ha-1 año-1 ). Los métodos tuvieron una aplicabilidad generalizada y estaban ya adaptados a los diferentes cultivos polinizados por insectos: cultivos de colza (Brassica napus) y habas (Vicia faba). Todos los métodos pudieron usarse con bajo presupuesto. Los métodos relativamente menos robustos que requirieron menos recursos produjeron estimados más elevados del beneficio anual de la polinización por insectos.

Establishment and management of wildflower areas for insect pollinators in commercial orchards.

Sown wildflower areas are increasingly recommended as an agri-environmental intervention measure, but evidence for their success is limited to particular insect groups or hampered by the challenges of establishing seed mixes and maintaining flower abundance over time. We conducted a replicated experiment to establish wildflower areas to support insect pollinators in apple orchards. Over three years, and across 23 commercial UK orchards with and without sown wildflowers, we conducted 828 transect surveys across various non-crop habitats. We found that the abundance of flower-visiting solitary bees, bumblebees, honeybees, and beetles was increased in sown wildflower areas, compared with existing non-crop habitats in control orchards, from the second year following floral establishment. Abundance of hoverflies and other non-syrphid flies was increased in wildflower areas from the first year. Beyond the effect of wildflower areas, solitary bee abundance was also positively related to levels of floral cover in other local habitats within orchards, but neither local nor wider landscape-scale context affected abundance of other studied insect taxa within study orchards. There was a change in plant community composition on the sown wildflower areas between years, and in patterns of flowering within and between years, showing a succession from unsown weedy species towards a dominance of sown species over time. We discuss how the successful establishment of sown wildflower areas and delivery of benefits for different insect taxa relies on appropriate and reactive management practices as a key component of any such agri-environment scheme.

Wild insect diversity increases inter-annual stability in global crop pollinator communities.

While an increasing number of studies indicate that the range, diversity and abundance of many wild pollinators has declined, the global area of pollinator-dependent crops has significantly increased over the last few decades. Crop pollination studies to date have mainly focused on either identifying different guilds pollinating various crops, or on factors driving spatial changes and turnover observed in these communities. The mechanisms driving temporal stability for ecosystem functioning and services, however, remain poorly understood. Our study quantifies temporal variability observed in crop pollinators in 21 different crops across multiple years at a global scale. Using data from 43 studies from six continents, we show that (i) higher pollinator diversity confers greater inter-annual stability in pollinator communities, (ii) temporal variation observed in pollinator abundance is primarily driven by the three-most dominant species, and (iii) crops in tropical regions demonstrate higher inter-annual variability in pollinator species richness than crops in temperate regions. We highlight the importance of recognizing wild pollinator diversity in agricultural landscapes to stabilize pollinator persistence across years to protect both biodiversity and crop pollination services. Short-term agricultural management practices aimed at dominant species for stabilizing pollination services need to be considered alongside longer term conservation goals focussed on maintaining and facilitating biodiversity to confer ecological stability.

Opportunities to reduce pollination deficits and address production shortfalls in an important insect-pollinated crop.

Pollinators face multiple pressures and there is evidence of populations in decline. As demand for insect-pollinated crops increases, crop production is threatened by shortfalls in pollination services. Understanding the extent of current yield deficits due to pollination and identifying opportunities to protect or improve crop yield and quality through pollination management is therefore of international importance. To explore the extent of "pollination deficits," where maximum yield is not being achieved due to insufficient pollination, we used an extensive dataset on a globally important crop, apples. We quantified how these deficits vary between orchards and countries and we compared "pollinator dependence" across different apple varieties. We found evidence of pollination deficits and, in some cases, risks of overpollination were even apparent for which fruit quality could be reduced by too much pollination. In almost all regions studied we found some orchards performing significantly better than others in terms of avoiding a pollination deficit and crop yield shortfalls due to suboptimal pollination. This represents an opportunity to improve production through better pollinator and crop management. Our findings also demonstrated that pollinator dependence varies considerably between apple varieties in terms of fruit number and fruit quality. We propose that assessments of pollination service and deficits in crops can be used to quantify supply and demand for pollinators and help to target local management to address deficits although crop variety has a strong influence on the role of pollinators.

Neonicotinoid pesticide exposure impairs crop pollination services provided by bumblebees.

Recent concern over global pollinator declines has led to considerable research on the effects of pesticides on bees. Although pesticides are typically not encountered at lethal levels in the field, there is growing evidence indicating that exposure to field-realistic levels can have sublethal effects on bees, affecting their foraging behaviour, homing ability and reproductive success. Bees are essential for the pollination of a wide variety of crops and the majority of wild flowering plants, but until now research on pesticide effects has been limited to direct effects on bees themselves and not on the pollination services they provide. Here we show the first evidence to our knowledge that pesticide exposure can reduce the pollination services bumblebees deliver to apples, a crop of global economic importance. Bumblebee colonies exposed to a neonicotinoid pesticide provided lower visitation rates to apple trees and collected pollen less often. Most importantly, these pesticide-exposed colonies produced apples containing fewer seeds, demonstrating a reduced delivery of pollination services. Our results also indicate that reduced pollination service delivery is not due to pesticide-induced changes in individual bee behaviour, but most likely due to effects at the colony level. These findings show that pesticide exposure can impair the ability of bees to provide pollination services, with important implications for both the sustained delivery of stable crop yields and the functioning of natural ecosystems.

The interplay of landscape composition and configuration: new pathways to manage functional biodiversity and agroecosystem services across Europe.

Managing agricultural landscapes to support biodiversity and ecosystem services is a key aim of a sustainable agriculture. However, how the spatial arrangement of crop fields and other habitats in landscapes impacts arthropods and their functions is poorly known. Synthesising data from 49 studies (1515 landscapes) across Europe, we examined effects of landscape composition (% habitats) and configuration (edge density) on arthropods in fields and their margins, pest control, pollination and yields. Configuration effects interacted with the proportions of crop and non-crop habitats, and species' dietary, dispersal and overwintering traits led to contrasting responses to landscape variables. Overall, however, in landscapes with high edge density, 70% of pollinator and 44% of natural enemy species reached highest abundances and pollination and pest control improved 1.7- and 1.4-fold respectively. Arable-dominated landscapes with high edge densities achieved high yields. This suggests that enhancing edge density in European agroecosystems can promote functional biodiversity and yield-enhancing ecosystem services.

Non-bee insects are important contributors to global crop pollination.

Wild and managed bees are well documented as effective pollinators of global crops of economic importance. However, the contributions by pollinators other than bees have been little explored despite their potential to contribute to crop production and stability in the face of environmental change. Non-bee pollinators include flies, beetles, moths, butterflies, wasps, ants, birds, and bats, among others. Here we focus on non-bee insects and synthesize 39 field studies from five continents that directly measured the crop pollination services provided by non-bees, honey bees, and other bees to compare the relative contributions of these taxa. Non-bees performed 25-50% of the total number of flower visits. Although non-bees were less effective pollinators than bees per flower visit, they made more visits; thus these two factors compensated for each other, resulting in pollination services rendered by non-bees that were similar to those provided by bees. In the subset of studies that measured fruit set, fruit set increased with non-bee insect visits independently of bee visitation rates, indicating that non-bee insects provide a unique benefit that is not provided by bees. We also show that non-bee insects are not as reliant as bees on the presence of remnant natural or seminatural habitat in the surrounding landscape. These results strongly suggest that non-bee insect pollinators play a significant role in global crop production and respond differently than bees to landscape structure, probably making their crop pollination services more robust to changes in land use. Non-bee insects provide a valuable service and provide potential insurance against bee population declines.

Combined effects of agrochemicals and ecosystem services on crop yield across Europe.

Simultaneously enhancing ecosystem services provided by biodiversity below and above ground is recommended to reduce dependence on chemical pesticides and mineral fertilisers in agriculture. However, consequences for crop yield have been poorly evaluated. Above ground, increased landscape complexity is assumed to enhance biological pest control, whereas below ground, soil organic carbon is a proxy for several yield-supporting services. In a field experiment replicated in 114 fields across Europe, we found that fertilisation had the strongest positive effect on yield, but hindered simultaneous harnessing of below- and above-ground ecosystem services. We furthermore show that enhancing natural enemies and pest control through increasing landscape complexity can prove disappointing in fields with low soil services or in intensively cropped regions. Thus, understanding ecological interdependences between land use, ecosystem services and yield is necessary to promote more environmentally friendly farming by identifying situations where ecosystem services are maximised and agrochemical inputs can be reduced.

Sex differences in telomeres and lifespan in Soay sheep: From the beginning to the end.

There is tremendous diversity in ageing rates and lifespan not only among taxa but within species, and particularly between the sexes. Women often live longer than men, and considerable research on this topic has revealed some of the potential biological, psychological and cultural causes of sex differences in human ageing and lifespan. However, sex differences in lifespan are widespread in nonhuman animals suggesting biology plays a prominent role in variation in ageing and lifespan. Recently, evolutionary biologists have borrowed techniques from biomedicine to identify whether similar mechanisms causing or contributing to variation in ageing and lifespan in humans and laboratory animals also operate in wild animals. Telomeres are repetitive noncoding DNA sequences capping the ends of chromosomes that are important for chromosomal stability but that can shorten during normal cell division and exposure to stress. Telomere shortening is hypothesized to directly contribute to the ageing process as once telomeres shorten to some length, the cells stop dividing and die. Men tend to have shorter telomeres and faster rates of telomere attrition with age than women, suggesting one possible biological cause of sex differences in lifespan. In this issue of Molecular Ecology, Watson et al. () show that telomere lengths in wild Soay sheep are similar between females and males near the beginning of life but quickly diverge with age because males but not females showed reduced telomere lengths at older ages. The authors further show that some of the observed sex difference in telomere lengths in old age may be due to male investment in horn growth earlier in life, suggesting that sexually dimorphic allocation to traits involved in sexual selection might underlie sex differences in telomere attrition. This study provides a rare example of how biological mechanisms potentially contributing to sex differences in lifespan in humans may also operate in free-living animals. However, future studies using a longitudinal approach are necessary to confirm these observations and identify the ultimate and proximate causes of any sex differences in telomere lengths. Collaborations between evolutionary biologists and gerontologists are especially needed to identify whether telomere lengths have a causal role in ageing, particularly in natural conditions, and whether this directly contributes to sex differences in lifespan.

Superoxide dismutase deficiency impairs olfactory sexual signaling and alters bioenergetic function in mice.

Oxidative stress (an overproduction of reactive oxygen species in relation to defense mechanisms) may restrict investment in life history traits, such as growth, reproduction, lifespan, and the production of sexual signals to attract mates. The constraint on sexual signaling by oxidative stress is of particular interest because it has been proposed as a mechanism ensuring that only good-quality males produce the most attractive sexual signals. Despite these predictions, evidence supporting this theory is, at best, equivocal. We used a superoxide dismutase knockout mouse to demonstrate that oxidative stress directly impairs investment in morphological (preputial glands) and molecular (major urinary proteins) components of olfactory signaling essential for mate attraction. By maintaining males in a much more competitive environment than usual for mouse laboratory experiments, we also revealed a range of phenotypes of superoxide dismutase deficiency not observed in previous studies of this mouse model. This range included impaired bioenergetic function, which was undetectable in the control environment of this study. We urge further examination of model organisms in seminatural conditions and more competitive laboratory environments, as important phenotypes can be exposed under these more demanding conditions.

Oxidative stress as a cost of reproduction: beyond the simplistic trade-off model.

The idea that oxidative stress may underpin life history trade-offs has become extremely popular. However, experimental support for the concept has proved equivocal. It has recently been suggested that this might be because of flaws in the design of existing studies. Here, we explore the background to the oxidative stress hypothesis and highlight some of the complexities in testing it. We conclude that the approach recently suggested to be least useful in this context (comparing reproducing to non-reproducing animals) may in fact be the most powerful. Moreover, suggested alternative approaches of limiting food supply or manipulating litter sizes have many complexities and problems. We suggest some useful alternative approaches that have not been previously advocated, particularly the study of individuals reproducing at greater parity later in life. Finally, the measures of oxidative stress and tissues that are analysed influence the experimental outcome. This suggests our conceptual model of the trade-off is currently too simplistic, and that studies based on single or limited numbers of assays, or restricted to single tissues, whether they support or refute the theory, should be interpreted with great caution.

Diversification of the eutherian placenta is associated with changes in the pace of life.

Few mammalian organs vary as dramatically among species as the placenta. This variation is remarkable considering that the placenta's primary function--transfer of nutrients and waste between mother and offspring--does not differ among species. Evolutionary changes in placental morphology remain poorly understood, with suggestions that parent-offspring conflict or evolutionary changes in life history might drive placental evolution. Here we demonstrate that life history differences among eutherian mammals are associated with major transitions in maternofetal interdigitation and placental invasiveness. We show that the repeated evolution of villous interdigitation is associated with reduced offspring production early in life and an increased lifespan. Further changes in placental morphology that reestablish a larger surface area are also associated with a change back to greater offspring production. After controlling for these differences in interdigitation, we also show that the least invasive placental type is associated with a fast pace of life. We predict that selection for a faster pace of life intensifies parent-offspring conflict, and that the repeated evolution of less-invasive placental structures might have allowed mothers to wrest back control of gestation from the fetus and alter their relative allocation to offspring production across life.

A genetic reduction in antioxidant function causes elevated aggression in mice.

Male-male aggression can have a large influence on access to mates, particularly in highly territorial animals such as mice. It has been suggested that males with impaired antioxidant defence and a consequential increased susceptibility to oxidative stress may have a reduced ability to invest in aggressive behaviours, which could limit their mating opportunities and reproductive success. Oxidative stress occurs as a result of an uncontrolled over-production of reactive oxygen species (ROS) in relation to defence mechanisms (such as antioxidants), and can cause damage to a variety of different cellular components. Impairments in specific aspects of antioxidant defence, leading to oxidative stress, can limit investment in some reproductive traits in males, such as sperm quality and the production of sexual signals to attract mates. However, a direct effect of impaired antioxidant defence on aggressive behaviour has not, to our knowledge, been reported. In this study, we demonstrate that mice with experimentally elevated sensitivity to oxidative stress (through inhibition of copper-zinc superoxide dismutase, Sod1) actually show the opposite response to previous predictions. Males completely deficient in SOD1 are more aggressive than both wild-type males and males that express 50% of this antioxidant enzyme. They are also faster to attack another male. The cause of this increased aggression is unknown, but this result highlights that aggressive behaviour in mice is not highly constrained by inhibited Sod1 expression, in contrast to other reproductive traits known to be impaired in this mouse model.

Experimental evidence that litter size imposes an oxidative challenge to offspring.

The post-natal environment in which young develop can substantially impact development, adult phenotype and fitness. In wild mice, competition among litter-mates affects development rate and adult behaviour. We manipulated post-natal litter size in a cross-fostering design to investigate the effects of enlarged and reduced litter sizes on sexual signalling, oxidative stress and the links between them. Oxidative stress causes somatic damage that can limit reproductive success and lifespan, and is predicted to mediate investment in life-history traits, including sexual signals. We predicted that litter enlargement would cause an increase in potential oxidative stress, inhibit growth and reduce sexual signalling in male mice. Males reared in enlarged litters were smaller at weaning and, despite rapid growth immediately after weaning, remained smaller at 10 weeks of age than those reared in smaller litters. Females from enlarged litters were consistently smaller throughout post-weaning development and showed no increase in growth rate compared with females from reduced litters. In enlarged litters, protein thiol concentration was lower at weaning in the liver and kidneys, with this trend continuing at 10 weeks of age in the kidneys only. Aconitase enzyme activity was also lower in mice from enlarged litters at weaning and 10 weeks of age in the kidneys. Male mice from enlarged litters scent marked more frequently and had larger preputial glands than those from reduced litters, indicating greater sexual signalling investment irrespective of this increased oxidative challenge. The results of this study are the first to reveal oxidative costs of developmental stress in small mammals.