Consequences For Reproductive Success Research Articles

Long‐term increase in female body condition and its effect on reproduction in two European red‐listed species, Common Pochard (Aythya ferina) and Tufted Duck (Aythya fuligula)

Body condition of breeding females is an important driver of an individual's fitness and the consequent dynamics of populations. Long‐term changes in female body condition are likely to be affected by recent shifts in climatic and environmental conditions that can result in changes to population demography. To help explain the drivers shaping body condition during the incubation period and its consequences for reproductive success, we examined the long‐term pattern in the body condition of breeding females of two declining sympatric diving duck species: Common Pochard Aythya ferina and Tufted Duck Aythya fuligula. We analysed the data obtained from 139 females of Common Pochard and 251 females of Tufted Duck breeding on fishponds in South Bohemia, Czechia, between 2004 and 2020. We calculated the body condition index of females during late incubation based on the residuals from the relationship between body mass and tarsus length and used the incubation stage as an additional predictor of body mass. Body condition of both species did not decline over the 17 years of the study. The effect of winter weather conditions (winter temperature), water transparency (a proxy for food availability) and reproductive investment on body condition was not confirmed. Female body condition positively affected mean egg mass and hatchability in both studied species, i.e. females in better body condition laid larger eggs and hatched eggs with a higher hatching probability. We conclude that the population declines of the studied species are probably not connected to decreasing body condition of breeding females, but other reasons such as change in breeding propensity or offspring survival and recruitment should be considered in future studies.

Diving behavior, foraging strategies, and energetics of female Steller sea lions during early lactation

Lactating Steller sea lions (SSL; Eumetopias jubatus) are income breeders, which balance the energetic cost of provisioning a pup with alternating periods of foraging at sea and nursing onshore during a 12–36 month dependency period. Foraging dives may be benthic or epipelagic, and the diverse diet varies seasonally and geographically. The objective of this study was to use animal-borne video and data recorders (VDRs) to record prey captures and characterize the three-dimensional movements, dive performance, and foraging strategies of female SSL while rearing a pup on Lovushki Island, located in the Kuril Island Archipelago in Far Eastern Russia. Female SSL made short foraging trips (8.7 h) and remained relatively close to the rookery (< 15 km) with an average swim speed of 1.5 m sec−1 and metabolic rate of 3.15 W kg−1, which was 1.8-fold greater than their estimated resting metabolic rate. We identified two types of dives representing shallow (Type 3) and deep (Type 4) benthic foraging, primarily on Atka mackerel (Pleurogrammus monopterygius) at night when they rest on the seafloor. The estimated Field Metabolic Rate (FMR; 2.31 W kg−1) for a mean 31.7 h foraging-nursing cycle was only 1.3-fold greater than their estimated resting metabolic rate, primarily because the females spent 73% of their time onshore nursing the pup. The short foraging trips near the rookery and low FMR indicated abundant prey. On average, female SSL captured 35.4 fish during a foraging trip, which represented an estimated 20.8 kg of prey. This was sufficient to remain in energy balance and provision a pup during early lactation. However, a 10–20% reduction in the size or abundance of prey would result in a 38–76% reduction in milk production, respectively, which would cause reduced growth or death of the pup. These calculations indicate the thin margin for energy balance in SSL during early lactation. Hence, any reduction in the size or abundance of prey could have serious consequences for reproductive success and fitness.

Rapid evolution of a floral trait following acquisition of novel pollinators

Abstract Changes in the pollinator assemblage visiting a plant can have consequences for reproductive success and floral evolution. We studied a recent plant trans‐continental range expansion to test whether the acquisition of new pollinator functional groups can lead to rapid adaptive evolution of flowers. In Digitalis purpurea, we compared flower visitors, floral traits and natural selection between native European populations and those in two Neotropical regions, naturalised after independent introductions. Bumblebees are the main pollinators in native populations while both bumblebees and hummingbirds are important visitors in the new range. We confirmed that the birds are effective pollinators and deposit more pollen grains on stigmas than bumblebees. We found convergent changes in the two new regions towards larger proximal corolla tubes, a floral trait that restricts access to nectar to visitors with long mouthparts. There was a strong positive linear selection for this trait in the introduced populations, particularly on the length of the proximal corolla tube, consistent with the addition of hummingbirds as pollinators. Synthesis. The addition of new pollinators is likely to happen often as humans influence the ranges of plants and pollinators but it is also a common feature in the long‐term evolution of the angiosperms. We show how novel selection followed by very rapid evolutionary change can be an important force behind the extraordinary diversity of flowers.

Assortative pairing for boldness and consequences for reproductive success in Montagu’s harrier

Abstract Behavioural combination within pairs depending on personality and plasticity might influence reproductive success. However, studies testing this hypothesis are rare, especially in the case of monogamous species with bi-parental care in which the sexes exhibit different behavioural roles. In this study, we investigated the pairing patterns for both boldness and boldness plasticity in Montagu’s harriers (Circus pygargus), a species with sex-specific care, and the consequences for their reproductive success. We measured individual boldness and plasticity for both sexes, and we assessed the pairing pattern in the Montagu’s harrier population for these two traits. We calculated four indices to characterize the behavioural association within pairs: pair boldness, boldness similarity within pairs, pair plasticity and plasticity similarity within pairs. The relationship between the behaviour of the parents and the reproductive success was then tested through these four indices. We found a pattern of assortative pairing based on both boldness and plasticity in the Montagu’s harrier population. Within-pair similarity of plasticity had a significant effect on the reproductive success, which was higher for less similar pairs than for more similar pairs. Our results question the origin of this pairing pattern and suggest that ecological constraint and not sexual selection could be the major driver.

Timing as a sexually selected trait: the right mate at the right moment

Sexual selection favours the expression of traits in one sex that attract members of the opposite sex for mating. The nature of sexually selected traits such as vocalization, colour and ornamentation, their fitness benefits as well as their costs have received ample attention in field and laboratory studies. However, sexually selected traits may not always be expressed: coloration and ornaments often follow a seasonal pattern and behaviours may be displayed only at specific times of the day. Despite the widely recognized differences in the daily and seasonal timing of traits and their consequences for reproductive success, the actions of sexual selection on the temporal organization of traits has received only scant attention. Drawing on selected examples from bird and mammal studies, here we summarize the current evidence for the daily and seasonal timing of traits. We highlight that molecular advances in chronobiology have opened exciting new opportunities for identifying the genetic targets that sexual selection may act on to shape the timing of trait expression. Furthermore, known genetic links between daily and seasonal timing mechanisms lead to the hypothesis that selection on one timescale may simultaneously also affect the other. We emphasize that studies on the timing of sexual displays of both males and females from wild populations will be invaluable for understanding the nature of sexual selection and its potential to act on differences within and between the sexes in timing. Molecular approaches will be important for pinpointing genetic components of biological rhythms that are targeted by sexual selection, and to clarify whether these represent core or peripheral components of endogenous clocks. Finally, we call for a renewed integration of the fields of evolution, behavioural ecology and chronobiology to tackle the exciting question of how sexual selection contributes to the evolution of biological clocks.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Diet Changes in Breeding Herring Gulls (Larus argentatus) in Witless Bay, Newfoundland and Labrador, Canada, over 40 Years

Abstract. The diets of gulls (Laridae) can have consequences for reproductive success, chick growth, and survival, yet there have been no quantitative assessments in eastern Newfoundland since the early 1970s. The diet of Herring Gulls (Larus argentatus) was examined through regurgitated prey items and pellets on Gull Island, Witless Bay, Newfoundland and Labrador, Canada, in 2012, and compared with similar data from 1970–1971. There was a significant shift in Herring Gull diet composition from blue mussels (Mytilus edulis) and capelin (Mallotus villosus) in the 1970s to garbage and Common Murre (Uria aalge) eggs in 2012. Delays in capelin spawning and the large increase in breeding Common Murres on Gull Island are likely factors influencing Herring Gull diet. Garbage, which includes human food scraps as well as plastic debris, now constitutes the single largest diet item for Herring Gulls, corresponding with a global increase in plastic pollution. The consistently low contribution of fisheries discards s...

Disruptive viability selection on a black plumage trait associated with dominance.

Traits used in communication, such as colour signals, are expected to have positive consequences for reproductive success, but their associations with survival are little understood. Previous studies have mainly investigated linear relationships between signals and survival, but both hump‐shaped and U‐shaped relationships can also be predicted, depending on the main costs involved in trait expression. Furthermore, few studies have taken the plasticity of signals into account in viability selection analyses. The relationship between signal expression and survival is of particular interest in melanin‐based traits, because their main costs are still debated. Here, we first determined the main factors explaining variability in a melanin‐based trait linked to dominance: the bib size of a colonial bird, the sociable weaver Philetairus socius. We then used these analyses to obtain a measure representative of the individual mean expression of bib size. Finally, we used capture–recapture models to study how survival varied in relation to bib size. Variation in bib size was strongly affected by year and moderately affected by age, body condition and colony size. In addition, individuals bearing small and large bibs had higher survival than those with intermediate bibs, and this U‐shaped relationship between survival and bib size appeared to be more pronounced in some years than others. These results constitute a rare example of disruptive viability selection, and point towards the potential importance of social costs incurred by the dominance signalling function of badges of status.

Affinity for natal environments by dispersers impacts reproduction and explains geographical structure of a highly mobile bird.

Understanding dispersal and habitat selection behaviours is central to many problems in ecology, evolution and conservation. One factor often hypothesized to influence habitat selection by dispersers is the natal environment experienced by juveniles. Nonetheless, evidence for the effect of natal environment on dispersing, wild vertebrates remains limited. Using 18 years of nesting and mark-resight data across an entire North American geographical range of an endangered bird, the snail kite (Rostrhamus sociabilis), we tested for natal effects on breeding-site selection by dispersers and its consequences for reproductive success and population structure. Dispersing snail kites were more likely to nest in wetlands of the same habitat type (lacustrine or palustrine) as their natal wetland, independent of dispersal distance, but this preference declined with age and if individuals were born during droughts. Importantly, dispersing kites that bred in natal-like habitats had lower nest success and productivity than kites that did not. These behaviours help explain recently described population connectivity and spatial structure across their geographical range and reveal that assortative breeding is occurring, where birds are more likely to breed with individuals born in the same wetland type as their natal habitat. Natal environments can thus have long-term and large-scale effects on populations in nature, even in highly mobile animals.

How to capture breeding Southern Lapwing Vanellus chilensis

he Southern Lapwing (Vanellus chilesnis) is a common bird in Southern America and commonly found in any large open areas, including agriculture and urban. The lapwing is a facultative cooperative breeder and aggressively defends its breeding territory. Thus, the breeding system and their consequences for reproductive success are interesting for evolutionary biology. Capture of the lapwing, however, is difficult. Most studies to date have not captured or individually marked birds even though identifying individuals to examine their roles in the breeding units is essential for understanding group evolution and interactions. Here we describe ways to efficiently capture the Southern Lapwing during the breeding season using mist-nets at night and by taking advantage of their defensive behaviors. Before hatching, nets were placed inside the breeding territories and by strategically walking towards the birds they were guided towards the nets, in which they fell when taking flight. After hatching, we captured the young birds and held them near the nets in which the adults fell when defending them. By using these methods, we captured 78 birds during the 2012 and 2013 breeding seasons. We observed no nest nor territory abandonment after captures. We suggest that our methods are useful in most situations with lapwings and better capture and marking will contribute to developing long-term population monitoring.

Vegetation type variation in marsh habitats: does it affect nest site selection, reproductive success, and maternal investment in Reed Warblers?

Habitat choice may have an important impact on survival and fitness of an individual. Besides an individual’s intrinsic features, such as resource-holding potential, experience, age, and habitat characteristics like habitat heterogeneity may play a role. In line with this, we investigate the importance of vegetation type for habitat choice, reproductive investment, and success within one population of the Reed Warbler (Acrocephalus scirpaceus), a common Palearctic marsh bird that nests in reed (Phragmites australis) and reed mace (Typha spp.) stands. In particular, we want to know whether individuals differ in the use of the nesting habitat and whether choosing a different habitat, namely reed and reed mace, may have consequences for reproductive success and/or reproductive investment. Our results suggest clear differences in vegetation structure between reed and reed mace territories. Reed mace provided denser vegetation for nest sites, and, consequently, breeding density was higher and nest predation lower. Although reproductive success was significantly lower in reed nests, we did not find a directional habitat preference. We also found some indication for size-dependent habitat choice, as bigger males (with longer tarsi) settle in reed mace. Differences in vegetation type could also be observed in regard to maternal investment. Females reproducing in reed mace produced larger and heavier eggs. The results are further discussed in regard to the possibility of sympatric speciation.

Spatial and temporal variation in sugar availability for insect parasitoids in agricultural fields and consequences for reproductive success

Our ability to improve biological control of insect pests depends on our understanding of factors that limit the reproductive success of their natural enemies in the field. Pest control by parasitoids in agricultural fields can be compromised by the availability of sugar resources. We studied sugar availability for Anagrus parasitoids that parasitize the eggs of leafhopper pests (genus Erythroneura) in vineyards in northern California. Laboratory assays indicated that parasitoids survive less than a day on average without feeding, and ∼3days when supplied with honey. We captured foraging parasitoids in five unsprayed vineyards in northern California and applied a simple chemical test to assay the presence of sugar in their abdomen. Parasitoid abundance decreased throughout the day (08:00–16:00h), suggesting that many parasitoids survive less than a day in the field. The proportion of feeding (sugar-positive) individuals was generally low (∼10% on average); it varied among field sites and decreased as the season progressed (from July to October). Parasitoids captured in the afternoon were more often found with sugar in their guts compared to those captured in the morning hours. This may be explained by a direct positive effect of sugar on parasitoid survival, but may also result from longer-lived parasitoids simply having more time to locate scarce sugar resources. The egg loads of female parasitoids were negatively related to sugar availability, suggesting that sugar increases oviposition success, although we could not rule out a causal role for other site-date specific factors. Overall, our results suggest that Anagrus parasitoids in vineyards may be limited by sugar availability, and that adding sugar resources such as flowering cover crops, especially towards the end of the season, could potentially improve their efficacy as biological control agents. However, this is only likely to be successful in combination with the elimination of other factors that compromise parasitoid success.

Morph-dependent resource acquisition and fitness in a polymorphic bird

Understanding genetic colour polymorphism has proved a major challenge, both in terms of the underlying genetic mechanisms and the evolutionarily forces maintaining such genetic variation. In this context, genetic differences in aggression or competitive-related traits may covary with the expression of alternative phenotypes, and affect the evolutionary stability and maintenance of colour polymorphisms. Genetic red and black head-colour morphs of the Gouldian finch (Erythrura gouldiae) co-occur in temporally and geographically stable frequencies in sympatric populations. Gouldian finches are obligate cavity-nesters with highly specific preferences for nest-site morphometry that directly affect reproductive success. Because intra- and interspecific competition for high quality nest-sites is prevalent, and fitness is directly related to nest-site quality, we investigated the relative access (and consequences for reproductive success) of alternative morphs to this critical limiting resource in the wild. Red males defended higher quality nest-sites, and overcame greater levels of nest-site competition against conspecifics and superior heterospecific competitors than black males. Red-headed males also produced more fledglings (especially with red-headed females) than black-headed males, independent of nest-site quality. Finally, the independent (positive) effect of nest-site quality on reproductive success was confirmed. Such competitive asymmetries are important to relative selection among coexisting morphs, and are likely to contribute to the maintenance of alternative sympatric colour-morphs in wild populations.

Carry-over effects of winter climate on spring arrival date and reproductive success in an endangered migratory bird, Kirtland's Warbler (Setophaga kirtlandii)

ABSTRACT. Understanding how animals will adapt to climate change requires understanding how climate variables influence their biology year round, and how events in different seasons interact. Migratory birds may be especially vulnerable because of the wide range of geographic areas that they depend on throughout the annual cycle. We examined the potential effects of non-breeding season climate change on the breeding biology of Kirtland's Warbler (Setophaga kirtlandii, formerly Dendroica kirtlandii), an endangered songbird that breeds in the Northern Lower Peninsula of Michigan and winters in the Bahamas. Our objectives were to determine whether spring arrival dates on the breeding grounds correlate with late winter rainfall in non-breeding areas and whether this has consequences for reproductive success. We used data on spring arrival dates and number of fledglings per year, sampling many individuals across multiple years, to show that males arrive on breeding grounds later following drier winters. There ...

The relationship between personality and plasticity in tree swallow aggression and the consequences for reproductive success

Both personality and plasticity can influence fitness, but few studies have investigated these two sources of individual variation simultaneously for the same behaviour. The individual quality hypothesis proposes that individuals with high personality scores will also be better able to respond to the changes in the environment (i.e. have a high degree of plasticity). Alternatively, the ‘compensatory’ hypothesis proposes that personality and plasticity are negatively correlated, because only individuals with low personality scores need to be able to rapidly adjust to environmental conditions. To examine these two hypotheses, we investigated the overall level of aggressiveness (personality) in nest defence, the ability of individuals to adjust this behaviour to respond to changes in temperature (plasticity), and their consequences for reproductive success in male and female tree swallows, Tachycineta bicolor. Using linear mixed effect models with individual as a random effect, we found that consistent differences between individuals explained approximately 55% of variation in aggressiveness and that more aggressive individuals were better able to adjust to variation in temperature, providing support for the individual quality hypothesis. However, although more aggressive males tended to fledge a higher number of young, the degree of plasticity only conferred a reproductive advantage for nonaggressive males, providing support for the compensatory hypothesis. For females, neither personality, nor plasticity was a good predictor of reproductive success. Our results suggest that personality and plasticity in aggressiveness are important components of individual variation but that the fitness advantages of each are context dependent.

Prey Use and Selection in Relation to Reproduction by Peregrine Falcons Breeding along the Yukon River, Canada

Some raptors are considered to be generalist predators and switch among different species of prey according to their availability in the environment. In contrast, other raptor species are specialists with narrow dietary niche widths, selecting only one or a few types of prey; reproductive success in these species is often closely related to variability in abundance of preferred prey species. Determining whether raptors are generalist or specialist predators is important for understanding the degree to which fluctuations in their population sizes are influenced by individual responses to changes in prey availability. We assessed diet components based on prey remains collected at nest ledges to determine whether Peregrine Falcons breeding along the Yukon River in northern Canada were specialist feeders or, conversely, whether they took prey according to its relative abundance. We also examined whether the use of certain types of prey had consequences for reproductive success. Compositional analyses showed that peregrines exhibited nonrandom prey selection, with shorebirds, jays and thrushes, and waterbirds being used more than expected based on their abundance, whereas sparrows and other small passerines were used significantly less than expected. Similarly, medium-sized prey was selected by peregrines, but small (<50 g) and large (>1000 g) prey were used significantly less than expected. Pairs occupying territories in which the diet included large numbers of waterbirds, and few sparrows and small passerines, fledged more young. Although prey >1000 g were among the least selected by pairs in our study population, pairs that used these larger prey species fledged more offspring. These patterns may relate directly to the contribution of female parents to provisioning. Females that are able to capture large prey items may deliver larger amounts of biomass to their nests and, as a consequence, may have high reproductive output. We conclude that Peregrine Falcons in the Yukon are selective predators and that some of the variation in reproductive rates in this population may be attributed to variation in the types of prey available to and utilized by individual pairs.

Food availability at birth limited reproductive success in historical humans

Environmental conditions in early life can profoundly affect individual development and have consequences for reproductive success. Limited food availability may be one of the reasons for this, but direct evidence linking variation in early-life nutrition to reproductive performance in adulthood in natural populations is sparse. We combined historical agricultural data with detailed demographic church records to investigate the effect of food availability around the time of birth on the reproductive success of 927 men and women born in 18th-century Finland. Our study population exhibits natural mortality and fertility rates typical of many preindustrial societies, and individuals experienced differing access to resources due to social stratification. We found that among both men and women born into landless families (i.e., with low access to resources), marital prospects, probability of reproduction, and offspring viability were all positively related to local crop yield during the birth year. Such effects were generally absent among those born into landowning families. Among landless individuals born when yields of the two main crops, rye and barley, were both below median, only 50% of adult males and 55% of adult females gained any reproductive success in their lifetime, whereas 97% and 95% of those born when both yields were above the median did so. Our results suggest that maternal investment in offspring in prenatal or early postnatal life may have profound implications for the evolutionary fitness of human offspring, particularly among those for which resources are more limiting. Our study adds support to the idea that early nutrition can limit reproductive success in natural animal populations, and provides the most direct evidence to date that this process applies to humans.

FLC: A key regulator of flowering time in Arabidopsis

The timing of floral transition has significant consequences for reproductive success in plants. The molecular genetic dissection of flowering time control in Arabidopsis identified an integrated network of pathways that quantitatively control this developmental switch. A central player in this process is the FLOWERING LOCUS C gene (FLC), which blocks flowering by inhibiting the genes required to switch the meristem from vegetative to floral development. Three systems (the FRIGIDA gene, vernalization, and the autonomous pathway) all influence the state of FLC. Last years many new genes have been identified that regulate FLC expression, and most of them are involved in the modification of FLC chromatin. This review focuses on recent insights in FLC regulation.

Transient estrogen exposure from birth affects uterine expression of developmental markers in neonatal gilts with lasting consequences in pregnant adults

Disruption of estrogen-sensitive, estrogen receptor (ER)-dependent events during porcine uterine development between birth (postnatal day=PND 0) and PND 14 affects patterns of uterine morphoregulatory gene expression in the neonate with lasting consequences for reproductive success. Uterine capacity for conceptus support is reduced in pregnant adult gilts exposed to estradiol valerate (EV) for 14 days from birth. Objectives here were to determine effects of EV exposure from birth through PND 13 on neonatal uterine and adult endometrial markers of growth, patterning, and remodeling. Targets included the relaxin receptor (RXFP1), estrogen receptor-alpha (ESR1) and vascular endothelial growth factor (VEGFA), morphoregulatory markers HOXA10 and WNT7A, and the matrix metalloproteinases (MMP)2 and MMP9. Gilts were treated daily with EV (50 microg/kg body weight per day, i.m.) or corn oil vehicle from birth through PND 13. Uteri were obtained from neonates on PND 14 and from adults on pregnancy day 12 (PxD 12). In neonates, EV exposure from birth increased uterine RXFP1 gene expression, and both ESR1 and VEGFA proteins. At PxD 12, endometrial RXFP1 mRNA remained elevated, while ESR1 protein was reduced. Early EV treatment decreased neonatal uterine WNT7A, but increased HOXA10 expression. WNT7A expression was reduced in EV-treated adults. Transient EV exposure increased MMP9 transcripts at PND 14, whereas both latent and active MMP9 activity was increased due to early EV treatment in adults on PxD 12. Results support the hypothesis that transient, estrogen-induced disruption of porcine uterine development from birth alters early programming events that lead to functional consequences in the adult.

Fishery‐induced demographic changes in the timing of spawning: consequences for reproductive success*

AbstractDemography can have a significant effect on reproductive timing and the magnitude of such an effect can be comparable to environmentally induced variability. This effect arises because the individuals of many fish species spawn progressively earlier within a season and may produce more egg batches over a longer period as they get older, thus extending their lifetime spawning duration. Inter‐annual variation in spawning time is a critical factor in reproductive success because it affects the early environmental conditions experienced by progeny and the period they have to complete phases of development. By reducing the average lifetime spawning duration within a fish stock, fishing pressure could be increasing the variability in reproductive success and reducing long‐term stock reproductive potential. Empirical estimates of selection on birth date, from experiments and using otolith microstructure, demonstrate that there is considerable variation in selection on birth date both within a spawning season and between years. The few multi‐year studies that have linked egg production with the survival of progeny to the juvenile stage further highlight the uncertainty that adults face in timing their spawning to optimize offspring survival. The production of many small batches of eggs over a long period of time within a season and over a lifetime is therefore likely to decrease variance and increase mean progeny survival. Quantifying this effect of demography on variability in survival requires a focus on lifetime reproductive success rather than year specific relationships between recruitment and stock reproductive potential. Modelling approaches are suggested that can better quantify the likely impact of changing spawning times on year‐class strength and lifetime reproductive potential. The evidence presented strengthens the need to avoid fishing severely age truncated fish stocks.

Chronic Hypoxia Impairs Gamete Maturation in Atlantic Croaker Induced by Progestins through Nongenomic Mechanisms Resulting in Reduced Reproductive Success

Recent studies have shown that chronic hypoxia exposure impairs reproduction in fish by interfering with endocrine function, although the mechanisms of endocrine disruption remain unclear. The effects of chronic exposure (4 or 10 weeks) to hypoxia (dissolved oxygen, DO: 1.7 mg L(-1)) on gamete maturation and its endocrine control, as well as the consequences for reproductive success, were investigated in Atlantic croaker (Micropogonias undulatus). Circulating levels of the progestin hormone that induces gamete maturation, 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S), were significantly decreased in croaker of both sexes chronically exposed to hypoxia and were associated with impairment of oocyte meiotic maturation and sperm motility. Interestingly, expression of the novel membrane receptor mediating these nongenomic 20beta-S actions, membrane progestin receptor alpha (mPRalpha), was significantly decreased on oocyte and sperm plasma membranes of hypoxia-exposed fish. Hypoxia-induced impairment of gamete maturation was accompanied with a dramatic decline in the percent fertilized eggs in a spawning trial. Moreover, the fertilized eggs from hypoxia-exposed donors displayed decreased hatching success and larval survival. The results suggestthat nongenomic progestin signaling controlling the final stages of the reproductive cycle in fish is impaired under hypoxic conditions.