Investment In Eggs Research Articles

The role of metalloproteases in fertilisation in the ascidian Ciona robusta

In the ascidian Ciona robusta (formerly C. intestinalis type A), the mechanism underlying sperm penetration through the egg investment remains unknown. We previously reported that proteins containing both an astacin metalloprotease domain and thrombospondin type 1 repeats are abundant in the sperm surface protein-enriched fraction of C. robusta. Here we investigated the involvement of those proteins in fertilisation. We refined the sequences of astacin metalloproteases, confirmed that five of them are present in the sperm, and labelled them as tunicate astacin and thrombospondin type 1 repeat-containing (Tast) proteins. Fertilisation of C. robusta eggs was potently inhibited by a metalloprotease inhibitor GM6001. The eggs cleaved normally when they were vitelline coat-free or the inhibitor was added after insemination. Furthermore, vitelline coat proteins were degraded after incubation with intact sperm. These results suggest that sperm metalloproteases are indispensable for fertilisation, probably owing to direct or indirect mediation of vitelline-coat digestion during sperm penetration. TALEN-mediated knockout of Tast genes and the presence of GM6001 impaired larval development at the metamorphic stage, suggesting that Tast gene products play a key role in late development.

Variability in egg and jelly-coat size and their contribution to target size for spermatozoa: a review for the Echinodermata

Fertilisation and development in broadcast-spawning marine invertebrates depends on the ability of the egg to attract spermatozoa and provision progeny. Echinoderm eggs have a jelly coat that facilitates sperm–egg collisions. We investigated variation in egg volume and target area for spermatozoa provided by the jelly coat within and between three sea urchin species (Heliocidaris erythrogramma, Heliocidaris tuberculata, Centrostephanus rodgersii), as well as across 22 echinoderm species for which data are available. Egg and jelly-coat size varied within spawns of individual females, between females of a species and between species. The jelly coat increased egg target area by 125–489% for echinoids with planktotrophic development. In general, planktotrophic echinoids (n=16) with larger eggs had thicker jelly coats, as did H. tuberculata females with larger eggs. Variability in egg and jelly-coat size within a species indicates that these traits are prone to maternal effects and may be influenced by factors such as sperm environment and offspring fitness that drive selection on egg investment. The greater variability in jelly-coat size compared with that of the egg has a large potential to affect fertilisation and should be considered in models of fertilisation kinetics. Egg size alone cannot be used as a metric to infer target size for spermatozoa.

Variations of hydra reproductive strategies arising from its modular structure. Two aspects of the modular reproductive effect

Clonal populations in which, after switching to sexual reproduction, simultaneous hermaphrodites may coexist with variable proportions of hermaphrodites functioning only as male or female provide an opportunity to test sex ratio bias and sex investment within a simultaneous hermaphrodite, which are collectively referred to as the modular reproductive effect in this study. An individual-based model (IBM) was used to determine how sex investment and sex ratio bias affect the cnidarian Hydra circumcincta’s fitness. Its clone-mates represent a genet, and after switching to sexual reproduction, they can be simultaneous hermaphrodites, hermaphrodites functioning as females, or hermaphrodites functioning as males, depending on their body size. The results of the model indicated that under low competition among polyps to fertilize eggs, hermaphrodites functioning as females and those functioning as males coexist, with the numerical superiority of the latter being more successful than simultaneous hermaphroditism independently of male-biased allocation of sex functions. When mate competition increases, the coexistence of hermaphrodites functioning as females and those functioning as males with the fundamental sex ratio 1:1 and females able to change their investment in eggs is the most successful. When there is strong mate competition, simultaneous hermaphroditism with strongly female-biased allocation of sex functions is the optimal strategy, except in scenarios with constrained investment in eggs. In such scenarios, various strategies, observed in natural populations of hydras, become successful.

Spring temperature, migration chronology, and nutrient allocation to eggs in three species of arctic-nesting geese: Implications for resilience to climate warming.

The macronutrients that Arctic herbivores invest in their offspring are derived from endogenous reserves of fat and protein (capital) that females build prior to the period of investment or from foods they consume concurrently with investment (income). The relative contribution from each source can be influenced by temporal and environmental constraints on a female's ability to forage on Arctic breeding areas. Warming temperatures and advancing Arctic phenology may alter those constraints. From 2011 to 2014, we examined relationships among spring temperature, timing of migration and reproduction, and the sources of nutrients females deposited in eggs for three sympatric species of geese that nested in northern Alaska. Compared to lesser snow geese (Anser caerulescens caerulescens) and greater white-fronted geese (Anser albifrons frontalis), black brant (Branta bernicla nigricans) were more likely to initiate follicle development during migration, resulting in fewer days between their arrival in the Arctic and the onset of incubation and requiring a relatively greater capital investment in eggs. Delaying follicle development until after their arrival in the Arctic provided snow geese and white-fronted geese an opportunity to forage near their nesting area and to deposit exogenous nutrients in eggs. With warmer spring temperatures, brant invested more capital in eggs, but snow geese invested less capital. Brant likely used capital to meet costs associated with earlier onset of follicle development when phenology was advanced, whereas snow geese used capital to compensate for poor foraging conditions during colder Arctic springs. Global warming is likely to reduce the quality of lower latitude marine habitats where brant acquire endogenous reserves and advancing Arctic phenology may increase their reliance on those reserves during reproduction. Near-term warming in northern Alaska may improve foraging conditions and favor the reproductive strategies of some herbivores such as snow geese and white-fronted geese that mainly invest Arctic nutrients in their offspring.

Patterns of variation in eggshell colour of Mountain Bluebirds (Sialia currucoides) provide mixed support for the sexually selected eggshell colour hypothesis

Determining the functional significance of ornamental traits and whether they are shaped by sexual selection requires understanding how they vary among individuals, and their relationship with other measures of quality. Conspicuous eggshell coloration is a trait that may have evolved through sexual selection as a signal of female quality. This hypothesis is based on the possibility that the pigment used to colour blue-green eggs is limited and potentially costly to allocate to eggshells. We investigated the signalling potential of blue-green eggshell colour by quantifying patterns of within- and among-clutch colour variation in Mountain Bluebirds (Sialia currucoides) to determine if pigment was limited and if egg colour traits are intrinsic to individual females. We also explored relationships over two breeding seasons between eggshell colour and other female traits and investment in eggs. Eggshell colour was highly repeatable within clutches for most measures, and relatively consistent between breeding events in different years, indicating that eggshell colour is an intrinsic trait. Eggs in second clutches within a season had less saturated blue-green colour than in first clutches, and within clutches, later-laid eggs were brighter but generally less blue-green in colour than earlier laid eggs, providing evidence of pigment limitation. However, associations between eggshell colour and other female traits and investment in eggs were less clear, and inconsistent among study years. Our findings suggest that there is potential for blue-green egg colour to function as a signal of female quality, but further study is needed to determine if blue-green eggshell colour is a truly informative signal.

Ocean climate and egg investment in the black-legged kittiwake Rissa tridactyla

Ocean climate and egg investment in the black-legged kittiwake Rissa tridactyla

Divergent artificial selection for female reproductive investment has a sexually concordant effect on male reproductive success.

Depending on the genetic architecture of male and female fitness, sex‐specific selection can have negative, positive, or neutral consequences for the opposite sex. Theory predicts that conflict between male and female function may drive the breakdown of intrasexual genetic correlations, allowing sexual dimorphism in sexually antagonistic traits. Reproductive traits are the epitome of this, showing highly differentiated proximate functions between the sexes. Here we use divergent artificial selection lines for female reproductive investment to test how female‐specific selection on a sex‐limited trait affects male reproductive success in a precocial bird, the Japanese quail (Coturnix japonica). We demonstrate that selection for increased egg investment in females positively affects male reproductive success both in competitive and non‐competitive mating situations. This increased reproductive success was linked to a relatively larger left testis in males originating from lines selected for high female reproductive investment. Given that female quail have functional gonads only on their left side, this correlated response indicates that selection has acted on the shared developmental basis of male and female gonads. Our study thereby provides evidence for a positive genetic correlation between key reproductive traits in males and females despite a high degree of sexual dimorphism, and suggests that, in this system, selection on reproductive function is sexually concordant.

Prenatal maternal effects appear to be insensitive to experimental or natural environmental variation

SummaryIn many birds, hatching asynchrony is a common phenomenon, primarily driven by patterns of incubation behaviour. However, experimental results in blue tits (Cyanistes caeruleus) have shown that asynchrony is reduced by intrinsic properties of later eggs that accelerate prenatal development.These intrinsic differences between early and late eggs could be driven by changes in resource availability to females, which are then passively passed onto the egg. Alternatively, it may be due to an anticipatory maternal effect, wherein some signal or resource is actively placed within the egg, which is beneficial to those eggs laid late within the clutch.In order to distinguish between these hypotheses we designed a supplementary feeding experiment, wherein females were provided with food at certain times during the laying phase. This had no discernible effect on development rate, or other egg characteristics, consistent with anticipatory maternal effects.Using a larger dataset we also tested whether natural environmental variation (weather) during egg formation affected maternal investment in eggs. Similarly, egg characteristics were found to be relatively insensitive to the environmental variation, supporting the experimental results.Alay summaryis available for this article.

Rates of parasitism, but not allocation of egg resources, vary among and within hosts of a generalist avian brood parasite.

Brown-headed cowbirds (Molothrus ater) deposit their eggs into the nests of other birds, which then raise the cowbird chick. Female cowbirds thus have limited options for impacting their offspring's development via maternal effects compared to most other passerines. Cowbirds can impact their offspring's phenotype by choosing among potential host nests, and by adjusting egg resources based on host characteristics. To examine whether cowbirds exhibit either or both of these strategies, we investigated rates of cowbird parasitism and egg investment (egg size, yolk-to-albumen ratio, and yolk testosterone and androstenedione) among and within host species in a shrubland bird community. We found that the probability of being parasitized by cowbirds, controlling for host status as a cowbird egg accepter or rejecter and ordinal date, varied significantly among host species, indicating an apparent preference for some hosts. Parasitism rates did not differ with host size, however, and despite variation in cowbird egg size among host species, this variation was not related to host size or cowbird preference. Among host species with eggs that are larger than those of the cowbird, cowbirds were significantly more likely to parasitize nests with relatively smaller eggs, whereas parasitism rates did not vary with relative egg size in host species with smaller eggs. There was no evidence for variation in cowbird egg components among or within host species. Our data indicate that cowbirds discriminate among host nests, but do not appear to adjust the composition of their eggs based on inter- or intraspecific host variation.

The evolution of different maternal investment strategies in two closely related desert vertebrates.

We compared egg size phenotypes and tested several predictions from the optimal egg size (OES) and bet‐hedging theories in two North American desert‐dwelling sister tortoise taxa, Gopherus agassizii and G. morafkai, that inhabit different climate spaces: relatively unpredictable and more predictable climate spaces, respectively. Observed patterns in both species differed from the predictions of OES in several ways. Mean egg size increased with maternal body size in both species. Mean egg size was inversely related to clutch order in G. agassizii, a strategy more consistent with the within‐generation hypothesis arising out of bet‐hedging theory or a constraint in egg investment due to resource availability, and contrary to theories of density dependence, which posit that increasing hatchling competition from later season clutches should drive selection for larger eggs. We provide empirical evidence that one species, G. agassizii, employs a bet‐hedging strategy that is a combination of two different bet‐hedging hypotheses. Additionally, we found some evidence for G. morafkai employing a conservative bet‐hedging strategy. (e.g., lack of intra‐ and interclutch variation in egg size relative to body size). Our novel adaptive hypothesis suggests the possibility that natural selection favors smaller offspring in late‐season clutches because they experience a more benign environment or less energetically challenging environmental conditions (i.e., winter) than early clutch progeny, that emerge under harsher and more energetically challenging environmental conditions (i.e., summer). We also discuss alternative hypotheses of sexually antagonistic selection, which arise from the trade‐offs of son versus daughter production that might have different optima depending on clutch order and variation in temperature‐dependent sex determination (TSD) among clutches. Resolution of these hypotheses will require long‐term data on fitness of sons versus daughters as a function of incubation environment, data as yet unavailable for any species with TSD.

Maternal allocation in eggs when counting on helpers in a cooperatively breeding bird

For cooperatively breeding birds, it has been proposed that breeders should reduce their investment in eggs when they count on helpers, because this can be compensated for by helpers provisioning of nestlings. Data from some species have supported this prediction, but this is not the case in others. It has also been proposed that mothers should not reduce but rather increase investment if the presence of helpers enhances the reproductive value of offspring, a pattern that might also influence egg production as long as helpers are predictable for laying females. Here, we studied maternal expenditure in eggs and clutches in the Iberian magpie, to see whether mothers reduce their expenditure at the egg stage in the presence of helpers. Our results show that investment in clutches varied depending on the year, date in the season and age of the mother, but there were no reductions in maternal expenditure per individual egg when they counted on helpers. On the contrary, a pattern emerged in the opposite direction of more investment in eggs associated with the future presence of helpers at the nestling stage. Our data suggest that the predictability of helpers, along with the type of benefits accrued from the contribution of helpers, may be crucial to understanding the reaction of mothers at egg production.

Egg size investment in superb fairy-wrens: helper effects are modulated by climate

Natural populations might exhibit resilience to changing climatic conditions if they already show adaptive flexibility in their reproductive strategies. In cooperative breeders, theory predicts that mothers with helpers should provide less care when environmental conditions are favourable, but maintain high investment when conditions are challenging. Here, we test for evidence of climate-mediated flexibility in maternal investment in the cooperatively breeding superb fairy-wren Malurus cyaneus We focus on egg size because in this species egg size influences offspring size, and females reduce egg investment when there are helpers at the nest. We report that females lay larger eggs during dry, hot conditions. However, the effect of temperature is modulated by the presence of helpers: the average egg size of females with helpers is reduced during cooler conditions but increased during hot conditions relative to females without helpers. This appears to reflect plasticity in egg investment rather than among female differences. Analysis of maternal survival suggests that helped females are better able to withstand the costs of breeding in hot conditions than females without helpers. Our study suggests that females can use multiple, independent cues to modulate egg investment flexibly in a variable environment.

Disentangling Genetic and Prenatal Maternal Effects on Offspring Size and Survival.

Organizational processes during prenatal development can have long-term effects on an individual's phenotype. Because these early developmental stages are sensitive to environmental influences, mothers are in a unique position to alter their offspring's phenotype by differentially allocating resources to their developing young. However, such prenatal maternal effects are difficult to disentangle from other forms of parental care, additive genetic effects, and/or other forms of maternal inheritance, hampering our understanding of their evolutionary consequences. Here we used divergent selection lines for high and low prenatal maternal investment and their reciprocal line crosses in a precocial bird-the Japanese quail (Coturnix japonica)-to quantify the relative importance of genes and prenatal maternal effects in shaping offspring phenotype. Maternal but not paternal origin strongly affected offspring body size and survival throughout development. Although the effects of maternal egg investment faded over time, they were large at key life stages. Additionally, there was evidence for other forms of maternal inheritance affecting offspring phenotype at later stages of development. Our study is among the first to successfully disentangle prenatal maternal effects from all other sources of confounding variation and highlights the important role of prenatal maternal provisioning in shaping offspring traits closely linked to fitness.

Maternal investment in fish oocytes and eggs: The molecular cargo and its contributions to fertility and early development

The production of fertile eggs with the capacity to develop into larvae and subsequently into marketable fish is centrally important to the aquaculture industry. This entails not only the programmed production of large numbers of eggs, but also high quality eggs with the potential to support normal development and high survival of offspring to juvenile and later stages of development and growth. Numerous studies highlight the maternal contributions to the development of embryos, including transcripts that regulate cell division and determine oocyte polarity, pattern development during early and late embryonic stages and the transition from maternal to zygotic gene expression and translation. Since most fish embryos develop independently within an enclosed egg envelope, they rely on compounds deposited within the oocytes during their various stages of development. In addition to regulatory nucleic acids (maternal DNA and RNA), these include proteins and other compounds that contribute to the structure and function of the egg envelope and the bulk molecular cargo that will be used as a source of cellular energy and structural components for formation of embryos and larvae. These latter components notably include yolk lipids and proteins deposited during oocyte growth and water acquired at the same time and during cytoplasmic maturation. In this review we highlight recent advances made in revealing the transcripts deposited within the oocyte that contribute to the structural and morphological development of the embryo, and to the regulation of gene expression and translation during oocyte development. Significant advances have been made in revealing the molecular mechanisms of lipid accumulation and metabolism within the oocyte, the intricacies of yolk protein formation via endocytosis of multiple yolk precursor proteins by multiple oocyte receptors, and the complex machinery supporting massive accumulation of water by maturing oocytes of many species. Additionally, many advances have been made in our understanding of the endocrine regulation of all of these processes during oogenesis. We provide here an overview of recent advances in our knowledge on these various aspects of oogenesis and identify several gaps in our knowledge for future studies.

Artificial selection reveals the energetic expense of producing larger eggs.

BackgroundThe amount of resources provided by the mother before birth has important and long-lasting effects on offspring fitness. Despite this, there is a large amount of variation in maternal investment seen in natural populations. Life-history theory predicts that this variation is maintained through a trade-off between the benefits of high maternal investment for the offspring and the costs of high investment for the mother. However, the proximate mechanisms underlying these costs of reproduction are not well understood. Here we used artificial selection for high and low maternal egg investment in a precocial bird, the Japanese quail (Coturnix japonica) to quantify costs of maternal reproductive investment.ResultsWe show that females from the high maternal investment lines had significantly larger reproductive organs, which explained their overall larger body mass, and resulted in a higher resting metabolic rate (RMR). Contrary to our expectations, this increase in metabolic activity did not lead to a higher level of oxidative damage.ConclusionsThis study is the first to provide experimental evidence for metabolic costs of increased per offspring investment.

Dietary pollutants induce oxidative stress, altering maternal antioxidant provisioning and reproductive output in the temperate sea urchin Evechinus chloroticus

Evidence is growing to suggest that the capacity to withstand oxidative stress may play an important role in shaping life-history trade-offs, although little is known on the relationship in broadcast spawning marine invertebrates. In this group, variation in gamete quantity and quality are important drivers of offspring survival and successful recruitment. Therefore the provisioning of eggs with antioxidants may be an important driver of life history strategies because they play a critical role in preventing damage from reactive oxygen species to macromolecules. In this study, a suite of oxidative stress biomarkers was measured in the gonads and eggs of the sea urchin Evechinus chloroticus exposed to polycyclic aromatic hydrocarbons (PAHs). Links between oxidative stress markers and core components of fitness including fecundity, gamete quality and maternal transfer of antioxidants were assessed. Experimental induction of oxidative stress was achieved via exposure to a mix of four PAHs over a 21-day period. In PAH exposed individuals, we observed a significant upregulation of the antioxidant defence and detoxification enzymes SOD, CAT, GR, GPx and GST, as well as a greater pool of the non-enzymatic antioxidant glutathione in gonad tissue and eggs. In contrast, glutathione redox status was not affected by PAH exposure, with the percentage of reduced glutathione remaining at approximately 80% in both gonad tissue and released eggs. PAH-exposed adults experienced greater than three- and five-fold increases in oxidative protein and lipid damage, respectively, in gonad tissue. In contrast, eggs maintained low levels of damage, not differing from baseline levels found in eggs released from PAH-naïve mothers. PAH exposure also resulted in a 2-fold reduction in fecundity of reproductively mature females but no significant alteration to egg diameter. Although PAH-exposed females released fewer eggs, successful fertilisation of those eggs was slightly enhanced with average rates ranging from 90–99% in comparison to 76–90% in control eggs. Early-stage offspring reflected maternal antioxidant status with populations derived from PAH-exposed mothers demonstrating significantly higher antioxidant levels than those derived from PAH-naïve mothers. This maternally inherited protection enhanced the capacity of embryos to minimise oxidative damage to lipids and proteins during early development but, despite this, did not reduce the proportion of morphological abnormalities in the population. Overall, these findings indicate that when faced with short-term contaminant stress E. chloroticus has the capacity to trade high reproductive output during a spawning event for a greater antioxidant investment in eggs. However, this production of potentially more resilient offspring did not translate to a fitness gain, at least for the early larval stages in the present experimental conditions.

In search of genetic constraints limiting the evolution of egg size: direct and correlated responses to artificial selection on a prenatal maternal effector.

Maternal effects are an important force in nature, but the evolutionary dynamics of the traits that cause them are not well understood. Egg size is known to be a key mediator of prenatal maternal effects with an established genetic basis. In contrast to theoretical expectations for fitness-related traits, there is a large amount of additive genetic variation in egg size observed in natural populations. One possible mechanism for the maintenance of this variation is through genetic constraints caused by a shared genetic basis among traits. Here we created replicated, divergent selection lines for maternal egg investment in Japanese quail (Coturnix japonica) to quantify the role of genetic constraints in the evolution of egg size. We found that egg size responds rapidly to selection, accompanied by a strong response in all egg components. Initially, we observed a correlated response in body size, but this response declined over time, showing that egg size and body size can evolve independently. Furthermore, no correlated response in fecundity (measured as the proportion of days on which a female laid an egg) was observed. However, the response to selection was asymmetrical, with egg size plateauing after one generation of selection in the high but not the low investment lines. We attribute this pattern to the presence of genetic asymmetries, caused by directional dominance or unequal allele frequencies. Such asymmetries may contribute to the evolutionary stasis in egg size observed in natural populations, despite a positive association between egg size and fitness.

Reproductive strategy of the invasive sharpbelly,Hemiculter leucisculus(Basilewsky 1855), in Erhai Lake, China

This study describes the reproductive strategy of the sharpbelly Hemiculter leucisculus, an invasive and dominant species in Erhai Lake in China with the goal of understanding how reproductive strategy contributes to its environmental adaptability and invasive potential. Specimens (n = 3583) were collected monthly or bimonthly from July 2009 to June 2011 (min: 114-Feb, max: 883-Aug), using gill nets (inner/outer mesh = 30/110 mm, stretched mesh). Gonads were removed, weighed and preserved for further (histological) analyses. Oocyte size-frequency distribution was continuous and had advanced vitellogenic oocytes with postovulatory follicles present in spawning females, both suggesting that sharpbelly is a multiple spawner with adhesive eggs. Spawning extended from April to September, with the peak period from May to August. Standard lengths (SL, cm) at minimal observed maturity/L50/L99.9 values were 4.6/5.6/10.5 for females and 5.1/5.5/7.5 cm for males, respectively. Females were over-represented (P < 0.01) in SL-classes over 9 cm and males completely absent from the 13 to 19 cm SL-classes. Overall sex ratio was highly significantly (P < 0.01) biased towards females (♀ = 1518, ♂ = 685, ♀/♂ = 2.21), however this was reversed in the spawning stock (8.3–16 cm, ♀ = 58, ♂ = 142, ♂/♀ = 2.45, P < 0.01). Batch spawning, a long spawning period, high male investment in reproduction and adhesive eggs all represent local adaptations in reproductive strategy that, along with other environmental factors, contribute to the invasion success of sharpbelly in Erhai.

Paternal attractiveness and the effects of differential allocation of parental investment

The differential allocation hypothesis (DAH) predicts that an individual should vary its reproductive investment according to the attractiveness of its mate. A recently revised version of the DAH makes explicit that investment can be positive, i.e. higher for the offspring of attractive males which should be of higher quality, or negative, i.e. higher for offspring of unattractive males, for example compensating for inheriting poor paternal genes. Moreover, investment can be made by the father and the mother. Here, we tested whether experimental manipulation of male attractiveness affected parental investment at different reproductive stages and thus influenced fitness-related traits in offspring. In two aviaries, all male zebra finches, Taeniopygia guttata, were given red leg rings to increase attractiveness and in two aviaries all males received green leg rings to decrease attractiveness. This controlled for assortative mating between treatments. Ring colour was merely an experimental manipulation of male attractiveness, not paternal quality, so we might expect additional investment to elevate offspring quality. Eggs were cross-fostered between and within treatments to allow differentiation of effects of investment in eggs and nestlings. Clutch and brood sizes were standardized. Both positive and negative investment were observed: Eggs from red-ringed fathers had higher yolk to albumen ratios than eggs from green-ringed fathers. Nestlings from eggs laid and incubated by parents in the red-ringed group had higher hatching masses than those in the green-ringed group. Both parents in the green-ringed group fed nestlings more frequently than red-ringed parents. Offspring performance was influenced by the treatment of both foster and biological parents, but combined effects of these different investment patterns on fitness-related traits were ambiguous. Male attractiveness appeared to affect patterns of reproductive investment but not consistently across all forms of reproductive investment suggesting that the costs and benefits of differential allocation vary among individuals and across contexts.

Oxidative stress during courtship affects male and female reproductive effort differentially in a wild bird with biparental care.

Oxidative stress has been suggested as one of the physiological mechanisms modulating reproductive effort, including investment in mate choice. Here, we evaluated whether oxidative stress influences breeding decisions by acting as a cost of or constraint on reproduction in the brown booby (Sula leucogaster), a long-lived seabird with prolonged biparental care. We found that during courtship, levels of lipid peroxidation (LP) of males and females were positively associated with gular skin color, a trait presumably used in mate choice, while levels of reactive oxygen species (ROS) were higher as laying approached and in early breeding pairs. Evidence of a constraining effect of oxidative stress for females was suggested by the fact that females with higher ROS during courtship laid smaller first eggs and had chicks with lower rates of body mass gain, and higher female LP was associated with lower offspring attendance time. No evidence of an oxidative cost of parental effort was found; from courtship to parental care, levels of ROS in males and females decreased, and changes in LP levels were non-significant. Finally, using a cross-fostering experiment we found that offspring ROS was unrelated to rearing and genetic parents' ROS. Interestingly, offspring LP was positively associated with the LP during courtship of both the rearing parents and the genetic father, suggesting that offspring LP might have both a genetic and an environmental component. Hence, in the brown booby, oxidative stress may be a cost of investment in reproductive traits before egg laying and constrain females' investment in eggs and parental care.