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To investigate the potential benefits of the catadromous thinlip grey mullet (Chelon ramada Risso, 1827) migration to freshwater, the total lipid content and fatty acid (FA) profile of female’s muscle and gonads caught in both the estuary and river were analyzed. The freshwater contingent presented a higher body condition, greater muscle gross energy, and larger gonads with higher lipid reserves. These animals showed a muscle profile rich in C16:1n-7 and lower LC-PUFA that contrast with the higher relative amount of C18:1n-9, n-3 FA, and unsaturated LC-PUFA, such as C18 and C20 FA found in the estuarine contingent. The gonads of both contingents showed a constant and high relative amount of polyunsaturated FAs (PUFA, 37%). However, in terms of essential fatty acids (EFAs), the estuarine contingent had a higher relative amount of C18:2n-6, C20:4n-6, C20:5n-3, and C22:6n-3. On the other hand, the freshwater contingent showed a higher relative amount of n-3 FA precursors, namely C18:3n-3, and a still low relative amount of C22:6n-3. This suggests a mismatch between the metabolic omega-3 pathway and the physiological maturity stages, similar to a phenomenon of dormancy. In this sense, not all these individuals may reproduce annually, and the later stages of gonad development will require supplementary energy derived from feeding at the estuary. Thus, freshwater migration may promote a reproductive strategy enabling adults to take advantage of the warm and food-rich summer/autumn period, adjust spawning and juvenile appearance, and reduce the population’s exposure to habitat changes and/or stochastic events.

Objective This paper highlights the complexity of marine fish spawner–recruit systems and how they vary across species and ecosystems while providing a universal terminology and framework to evaluate fish reproduction. We emphasize the gonadal development important to assess maturity, fecundity, where and when fish spawn, and transition and sex assignment in protogynous species. Methods We review and compare reproductive traits in warmwater and coldwater fishes. Reproductive phases for both sexes and protogynous species are defined and histological micrographs presented. New methods are developed to assess maturity; spawning seasonality; peak spawning; and, for protogynous species, sex assignment. Result Protogyny, extended spawning seasons, and indeterminate fecundity are more common in warmwater than coldwater systems. The following reproductive phases are defined as immature, transitional (sex change), early developing (the first stage of entrainment in the reproductive cycle), late developing (stages needed to complete maturational competence), spawning, regressing (spawning season termination), and regenerating (fish that are mature but outside of the spawning season). A method to assess the certainty of maturity assignment based on reproductive phase and the age and size range sampled is presented, as are best practices to estimate size and age at maturity. To remove the subjectivity from current methods to estimate spawning seasonality, we present a new quantitative method to identify the core spawning season and peak spawning months. Conclusion A species’ ability to adapt to fishing and climate change varies with their reproductive strategy. Improving our understanding of fish reproduction necessitates standardizing methodology and terminology. Impact statement We demonstrate the complexity of fish reproductive strategies and how reproductive traits are species‐specific and differ between warmwater and coldwater systems, affecting population productivity. We present a unified framework and terminology to describe fish reproduction and new methods to assess key reproductive parameters.

Aurelia aurita s.l. scyphistomae are capable of developing different asexual modes for propagation and thus present a multi-mode reproductive strategy. The reproduction rates and the reproductive strategy they adopt depend on a combination of various environmental parameters. We investigated the A. aurita s.l. polyp-to-polyp reproduction strategy and population growth in relation to polyp density. Our results confirmed that density-dependent factors control population growth of A. aurita s.l. scyphistomae in three different ways: (1) decreasing the polyp reproduction rate, (2) triggering the production of motile bud-like tissue particles and (3) inducing the detachment of developed scyphistomae. Whereas the decrease in the reproduction rate reduces the number of recruits, the motile particles and the detachment of scyphistomae contribute to minimizing density-dependent effects by allowing reproductive products and scyphistomae to drift away. Thus, not only are the negative effects of intraspecific competition for space and food diminished but also the potential colonization of new substrates, and further increase in scyphistoma density is favoured on larger spatial scales. The potential capability to switch its polyp-to-polyp reproduction strategy in response to environmental clues and population density may give Aurelia high adaptability in the temperate coastal waters where they commonly live and where they may be exposed to wide-ranging and fluctuating environmental variables that affect their survival and longevity. Considering these features, as well as the wide tolerance of Aurelia scyphistomae (and medusae) to environmental parameters, it is not surprising that the species/lineages of Aurelia are cosmopolitan and exhibit the most frequent bloom events worldwide.

Phenotypic plasticity represents an elegant adaptive response of individuals to a change in their environment. Bluehead wrasses (Thalassoma bifasciatum) exhibit astonishing sexual plasticity, including female-to-male sex change and discrete male morphs that differ strikingly in behavior, morphology, and gonadal investment. Using RNA-seq transcriptome profiling, we examined the genes and physiological pathways underlying flexible behavioral and gonadal differences among female, dominant (bourgeois) male, and female-mimic (sneaker) male blueheads. For the first time in any organism, we find that female mimicry by sneaker males has a transcriptional signature in both the brain and the gonad. Sneaker males shared striking similarity in neural gene expression with females, supporting the idea that males with alternative reproductive phenotypes have “female-like brains.” Sneaker males also overexpressed neuroplasticity genes, suggesting that their opportunistic reproductive strategy requires a heightened capacity for neuroplasticity. Bourgeois males overexpressed genes associated with socio-sexual behaviors (e.g., isotocin), but also neuroprotective genes and biomarkers of oxidative stress and aging, indicating a hitherto unexplored cost to these males of attaining the reproductively privileged position at the top of the social hierarchy. Our novel comparison of testicular transcriptomes in a fish with male sexual polymorphism associates greater gonadal investment by sneaker males with overexpression of genes involved in cell proliferation and sperm quality control. We propose that morphological female-mimicry by sneaker male teleosts entails pervasive downregulation of androgenesis genes, consistent with low androgen production in males lacking well-developed secondary sexual characters.

How reproductive strategies contribute to patterns of senescence in natural populations remains contentious. We studied reproductive senescence in the dimorphic white-throated sparrow, an excellent species for exploring this issue. Within both sexes the morphs use distinct reproductive strategies, and disassortative pairing by morph results in pair types with distinct parental systems. White morph birds are more colorful and aggressive than tan counterparts, and white males compete for extrapair matings, whereas tan males are more parental. Tan males and white females share parental care equally, whereas white males provide little parental support to tan females. We found morph-specific patterns of reproductive senescence in both sexes. White males exhibited greater reproductive senescence than tan males. This result likely reflects the difficulty of sustaining a highly competitive reproductive strategy as aging progresses rather than high physiological costs of competitiveness, since white males were also long-lived. Moreover, morph was not consistently related to reproductive senescence across the sexes, arguing against especially high costs of the traits associated with white morph identity. Rather, tan females exhibited earlier reproductive senescence than white females and were short-lived, perhaps reflecting the challenges of unsupported motherhood. Results underscore the importance of social dynamics in determining patterns of reproductive senescence.

Reproductive strategies, whether sexual or asexual, are critical aspects of introduction success and spread for non-indigenous species. The Western Pacific Diadumene lineata (Verrill, 1869), the world’s most widely distributed sea anemone due to numerous introductions, is believed to reproduce only by asexual means outside of its home range. Over the past 100 years, no populations with both males and females have been reported to co-occur outside of its native Japan. We report the first discovery of sympatric reproductive male (sperm-bearing) and female (egg-bearing) D. lineata in Coos Bay, Oregon, USA, confirmed by histological analysis. Given that only single gender introduced populations have been reported elsewhere, the presence of both genders in this US Pacific Northwest bay may be linked to high and continuous propagule pressure resulting from a history of intensive lumber and timber shipping directly between Japan and Coos Bay. Novel modern-day introductions of this species, in which reproductive traits previously only associated with native populations are manifested, could influence the future invasion success and spread of this species.

The slipper lobster Scyllarus arctus is an important fishery resource in Galicia (NW Iberian Peninsula), with a large reduction of its populations in recent decades in the North-east Atlantic and Mediterranean, but only limited information on its reproduction. This study provides an analysis of the reproductive potential of this scyllarid during two breeding cycles (2008 and 2009) in the NE Atlantic (43°20′N 8°50′W). We studied several reproductive traits (fecundity, brood weight, egg weight and volume) in broods with eggs both in an early and late embryonic stage, in relation to female size and temporal variations. Total output (fecundity and weight) and egg weight were closely linked to maternal size, and this relationship remained in broods with late-stage eggs. In relation to temporal variations, our data revealed an important seasonal variability in fecundity and egg weight, showing an inverse pattern in the reproductive strategy in the first two seasons of the reproductive period, with a maximum egg weight in winter (December–February) and a maximum number of eggs produced in spring (April–May). A predictive model for realized fecundity was developed: log (FE) = 0.064 + 2.907 log (length)−0.018 Month2 + 0.174 Month, which accounted for over 90% of variation in the total data.

Holothuria leucospilota and Stichopus chloronotus are among the most widespread tropical sea cucumber species usually harvested for food and medicine in Asian countries, for which natural stocks have collapsed worldwide. Both species can reproduce sexually and asexually, and a better understanding of their reproductive strategy can provide useful information for conservation purposes. To describe the genetic structure and diversity of sympatric populations from these species in space and time, individuals were sampled over different sites and seasons in Reunion Island (Southwestern Indian Ocean). They were genotyped using 24 and 9 specific microsatellite markers for H. leucospilota and S. chloronotus, respectively. Multi-locus genotypes (MLG) and lineages (MLL) were identified, and analyses of population structure were performed among sites and seasons. No repeated MLG nor MLL were found for H. leucospilota, demonstrating the absence of asexual reproduction. Populations of H. leucospilota were not genetically differentiated, acting as a metapopulation, with larval exchanges within the reef. Contrarily, repeated MLGs were found for S. chloronotus and all populations were genetically differentiated. Asexual reproduction seems to reach a high level for this species (mean clonal richness = 0.24). For both species, genetic structure was stable through seasons. Thus, these sympatric fissiparous sea cucumber species use two different strategies of reproduction, which may allow them to reduce interspecific competition.

The income-capital breeding model was developed to explain birth seasonality and reproductive strategies in female animals in relation to the abundance of food energy in the environment. An income breeder uses currently available energy and acts so as to maximize either maternal survival or weanling survival, depending on the relationship between timing of births and abundance of food energy. A capital breeder stores energy reserves for future reproductive use. Here we examined energetic influences on reproductive seasonality in a population of female white-faced capuchins ( Cebus capucinus ) living in a seasonal dry forest in Costa Rica. Our objectives were to determine: 1) the degree of fruiting seasonality in capuchin food trees and 2) the temporal relationship between capuchin births/conceptions and fruit abundance. Our sample included 25 yr of birth data ( N  = 100 births), 4 yr of capuchin fruit tree phenology data, and 18 mo of ovarian hormone data, which we used to calculate gestation lengths and estimate conception dates. Using circular statistics, we found that the mean peak in fruit abundance occurs in June, and that this population of capuchins reproduces seasonally, with 44% of births occurring within a 3-mo period (May to July, mean month = May). We propose that white-faced capuchins can be generally classified as income breeders that maximize maternal survival instead of weanling survival and that they time infant births such that the most energy expensive period of reproduction, mid-to-late lactation, occurs during the mean peak in fruit abundance.

Maintenance of health and the production of offspring are competing processes that can result in tradeoffs. As vertebrates invest substantial resources in their immune system, it is crucial to understand the interactions between immunity and reproductive strategies. In the lizard Zootoca vivipara, females have condition- and context-dependent mating strategies. We predicted that, if the risk of infection is higher for polyandrous females, then polyandrous females should invest more in immune system while monandrous females should invest more in reproduction. In order to test our prediction, we captured 62 gravid females of known age in a natural population; we kept them until parturition to access to their offspring. Then, using microsatellite marker-based paternity analyses within litters, we determine the mating strategy of females (monandrous or polyandrous). Females were also challenged with PHA to estimate their inflammatory response. Our results show that polyandrous females have a higher PHA response than the monandrous females, and that monandrous females produce more males and more juveniles of better body condition than polyandrous females. The relationship between mating behaviour and immune function may have consequences for females and may shape the evolution of mating systems.