Short-term dietary changes are reflected in the cerebral content of adult ring-billed gulls

Omega-3 long-chain polyunsaturated fatty acids (n3-LCPUFAs) are produced primarily in aquatic ecosystems and are considered essential nutrients for predators given their structural role in vertebrates' cerebral tissues. Alarmingly, with urbanization, many aquatic animals now rely on anthropogenic foods lacking n3-LCPUFAs. In this study undertaken in Newfoundland (Canada), we tested whether recent or longer term diet explains the cerebral fatty acid composition of ring-billed gulls (Larus delawarensis), a seabird that now thrives in cities. During the breeding season, cerebral levels of n3-LCPUFAs were significantly higher for gulls nesting in a natural habitat and foraging on marine food (mean ± s.d.: 32 ± 1% of total identified fatty acids) than for urban nesters exploiting rubbish (27 ± 1%). Stable isotope analysis of blood and feathers showed that urban and natural nesters shared similar diets in autumn and winter, suggesting that the difference in cerebral n3-LCPUFAs during the breeding season was owing to concomitant and transient differences in diet. We also experimentally manipulated gulls' diets throughout incubation by supplementing them with fish oil rich in n3-LCPUFAs, a caloric control lacking n3-LCPUFAs, or nothing, and found evidence that fish oil increased urban nesters' cerebral n3-LCPUFAs. These complementary analyses provide evidence that the brain of this seabird remains plastic during adulthood and responds to short-term dietary changes.

Captivating Colors, Crucial Roles: Astaxanthin's Antioxidant Impact on Fish Oxidative Stress and Reproductive Performance

Fish, constantly exposed to environmental stressors due to their aquatic habitat and high metabolic rates, are susceptible to oxidative stress. This review examines the interplay between oxidative stress and fish reproduction, emphasizing the potent antioxidant properties of astaxanthin. Our primary objective is to highlight astaxanthin's role in mitigating oxidative stress during critical reproductive stages, leading to improved gamete quality, ovary development, and hormone levels. We also explore its practical applications in aquaculture, including enhanced pigmentation and overall fish health. We conducted a comprehensive literature review, analyzing studies on astaxanthin's antioxidant properties and its impact on fish reproduction. Astaxanthin, a carotenoid pigment, effectively combats reactive oxygen species, inhibiting lipid peroxidation and maintaining membrane integrity. It significantly enhances reproductive success in fish and improves overall fish health in aquaculture settings. This review reveals astaxanthin's multifaceted benefits in fish health and reproduction, offering economic advantages in aquaculture. Future research should delve into species-specific responses, optimal dosages, and the long-term effects of astaxanthin supplementation to inform sustainable aquaculture strategies.

Fitness correlates of blubber oxidative stress and cellular defences in grey seals (Halichoerus grypus): support for the life-history-oxidative stress theory from an animal model of simultaneous lactation and fasting

Life-history-oxidative stress theory predicts that elevated energy costs during reproduction reduce allocation to defences and increase cellular stress, with fitness consequences, particularly when resources are limited. As capital breeders, grey seals are a natural system in which to test this theory. We investigated oxidative damage (malondialdehyde (MDA) concentration) and cellular defences (relative mRNA abundance of heat shock proteins (Hsps) and redox enzymes (REs)) in blubber of wild female grey seals during the lactation fast (n = 17) and summer foraging (n = 13). Transcript abundance of Hsc70 increased, and Nox4, a pro-oxidant enzyme, decreased throughout lactation. Foraging females had higher mRNA abundance of some Hsps and lower RE transcript abundance and MDA concentrations, suggesting they experienced lower oxidative stress than lactating mothers, which diverted resources into pup rearing at the expense of blubber tissue damage. Lactation duration and maternal mass loss rate were both positively related to pup weaning mass. Pups whose mothers had higher blubber glutathione-S-transferase (GST) expression at early lactation gained mass more slowly. Higher glutathione peroxidase (GPx) and lower catalase (CAT) were associated with longer lactation but reduced maternal transfer efficiency and lower pup weaning mass. Cellular stress, and the ability to mount effective cellular defences, could proscribe lactation strategy in grey seal mothers and thus affect pup survival probability. These data support the life-history-oxidative stress hypothesis in a capital breeding mammal and suggest lactation is a period of heightened vulnerability to environmental factors that exacerbate cellular stress. Fitness consequences of stress may thus be accentuated during periods of rapid environmental change.

Follicular complex may predict reproductive tactics in siluriform fishes

In this study, we evaluated the morphology and morphometry of the layers that make up the follicular complex surrounding mature oocytes in the six fish species Auchenipterichthys longimanus, Ageneiosus ucayalensis, Hypophthalmus marginatus, Baryancistrus xanthellus, Panaqolus tankei and Peckoltia oligospila, belonging to the order Siluriformes, which inhabit the Amazon basin. On the basis of the morphology and thickness of the layers of the follicular complex, the species were divided into two groups: 1- A. longimanus, A. Ucayalensis and H. marginatus and 2 - B. xanthellus, P. tankei and P. oligospila. The total thickness of the layers that make up the follicular complex showed a difference between type III and IV oocytes for all species of each group. Differences in the theca layer, follicular cells and zona radiata between species and between groups were submitted to statistical analysis. Morphologically, group 1 showed columnar follicular cells and thin zona radiata. Meanwhile, group 2 displayed a layer of cuboidal-shaped follicular cells layer and thicker zona radiata. These differences may be related to the environment and reproductive behaviors, as group 1 migrates without parental care and has eggs that are generally smaller and abundant. While group 2, represented by loricariidae, inhabit lotic environments, have reproductive tactics of parental care and eggs that are generally large and in small numbers. Therefore, we can infer that the follicular complex in mature oocytes can predict the reproductive tactics of the species.

Social status influences relationships between hormones and oxidative stress in a cichlid fish

An individual's social environment can have widespread effects on their physiology, including effects on oxidative stress and hormone levels. Many studies have suggested that variation in oxidative stress experienced by individuals of different social statuses might be due to endocrine differences, however, few studies have evaluated this hypothesis. Here, we assessed whether a suite of markers associated with oxidative stress in different tissues (blood/plasma, liver, and gonads) had social status-specific relationships with circulating testosterone or cortisol levels in males of a cichlid fish, Astatotilapia burtoni. Across all fish, blood DNA damage (a global marker of oxidative stress) and gonadal synthesis of reactive oxygen species [as indicated by NADPH-oxidase (NOX) activity] were lower when testosterone was high. However, high DNA damage in both the blood and gonads was associated with high cortisol in subordinates, but low cortisol in dominants. Additionally, high cortisol was associated with greater production of reactive oxygen species (greater NOX activity) in both the gonads (dominants only) and liver (dominants and subordinates). In general, high testosterone was associated with lower oxidative stress across both social statuses, whereas high cortisol was associated with lower oxidative stress in dominants and higher oxidative stress in subordinates. Taken together, our results show that differences in the social environment can lead to contrasting relationships between hormones and oxidative stress.

Mothers modify the cost of reproduction by dynamic changes in antioxidant function and filial cannibalism

Investment in current reproduction may negatively influence subsequent fitness. Oxidative stress has been proposed as a potential mediator of this trade-off between current and future reproductive success. However, evidence of reproduction causing oxidative stress is limited, possibly owing to compensatory mechanisms that counteract oxidative insults. Here we test the idea that organisms protect against oxidative challenges through a dynamic interaction between behavioural and physiological adjustments at different stages of reproduction. To test this idea, we manipulated maternal care in the mouthbrooding cichlid fish Astatotilapia burtoni by allowing females to continue care (brooders) or by preventing care (non-brooders). We found that brooders depleted the pool of antioxidants as brood care progressed; however, we only observed increased oxidative DNA damage at the early stage of care relative to non-brooders, possibly owing to upregulated antioxidant protection during later stages of care. Most brooders adjusted parental investment by consuming some of their offspring during mouthbrooding. Intriguingly, the level of filial cannibalism was positively related to liver antioxidant function. These changes in antioxidant function and filial cannibalism allow parents to manage the cost of reproduction and are important for our understanding of how oxidative stress mediates life-history trade-offs.

Social dominance and reproduction result in increased integration of oxidative state in males of an African cichlid fish

Oxidative stress is a potential cost of social dominance and reproduction, which could mediate life history trade-offs between current and future reproductive fitness. However, the evidence for an oxidative cost of social dominance and reproduction is mixed, in part because organisms have efficient protective mechanisms that can counteract oxidative insults. Further, previous studies have shown that different aspects of oxidative balance, including oxidative damage and antioxidant function, vary dramatically between tissue types, yet few studies have investigated oxidative cost in terms of interconnectedness and coordination within the system. Here, we tested whether dominant and subordinate males of the cichlid Astatotilapia burtoni differ in integration of different components of oxidative stress. We assessed 7 markers of oxidative stress, which included both oxidative damage and antioxidant function in various tissue types (total of 14 measurements). Across all oxidative stress measurements, we found more co-regulated clusters in dominant males, suggesting that components of oxidative state are more functionally integrated in dominant males than they are in subordinate males. We discuss how a high degree of functional integration reflects increased robustness or efficiency of the system (e.g. increased effectiveness of antioxidant machinery in reducing oxidative damage), but we also highlight potential costs (e.g. activation of cytoprotective mechanisms may have unwanted pleiotropic effects). Overall, our results suggest that quantifying the extent of functional integration across different components of oxidative stress could reveal insights into the oxidative cost of important life history events.

Individual experience as a key to success for the cuckoo catfish brood parasitism

Brood parasites are involved in coevolutionary arms races with their hosts, whereby adaptations of one partner elicit the rapid evolution of counter-adaptations in the other partner. Hosts can also mitigate fitness costs of brood parasitism by learning from individual or social experience. In brood parasites, however, the role of learning can be obscured by their stealthy behaviour. Cuckoo catfish (Synodontis multipunctatus) parasitise clutches of mouthbrooding cichlids in Lake Tanganyika and are the only non-avian obligate brood parasites among vertebrates. We experimentally demonstrate that cuckoo catfish greatly enhance their efficiency in parasitising their hosts as they learn to overcome host defences. With increasing experience, cuckoo catfish increased their parasitism success by greater efficiency through improved timing and coordination of intrusions of host spawnings. Hence, within the coevolutionary arms races, brood parasites learn to overcome host defences during their lifetime.

The importance of learning for brood parasites is explored using cuckoo catfish. The catfish increase their parasitism success as they gain experience, mainly by improving their social coordination and timing of intrusions to cichlid host spawnings.

The oxidative cost of helping and its minimization in a cooperative breeder

Cooperative actions are beneficial to the group, but presumably costly to the individual co-operators. In cooperatively breeding species, helping to raise young is thought to involve important energetic costs, which could lead to elevated exposure to reactive oxygen species, resulting in oxidative stress. However, identifying such costs can be difficult if individuals adjust their investment in helping in relation to environmental conditions or their own physiological condition. Experimental approaches are therefore required to quantify the costs of helping but, to date, these have been infrequent. Here, we combined correlational and experimental data to investigate the oxidative cost of helping-at-the-nest and how this affects helping decisions in wild sociable weavers Philetairus socius, a colonial cooperatively breeding bird. At the correlational level, we found that the probability of helping was influenced by the interaction of an individual’s oxidative state and age: compared to younger birds, older individuals were more likely to help when they had higher oxidative damage, and the opposite trend was found for younger individuals. After experimentally increasing the energetic cost of flight, manipulated helpers in breeding colonies decreased nestling feeding rates and incurred an increase in oxidative damage, which was not present in manipulated helpers in non-breeding colonies. This indicates that individuals decreased their helping behavior to minimize the associated costs. These results suggest that oxidative stress can influence helping decisions and underlie a trade-off between cooperation and self-maintenance, which is central to understanding when helping might take place in this and other species.

Fasting ameliorates oxidative stress: A review of physiological strategies across life history events in wild vertebrates

Fasting is a component of many species' life history due to environmental factors or behavioral patterns that limit access to food. Despite metabolic and physiological challenges associated with these life history stages, fasting-adapted wild vertebrates exhibit few if any signs of oxidative stress, suggesting that fasting promotes redox homeostasis. Here we review mammalian, avian, reptilian, amphibian, and piscine examples of animals undergoing fasting during prolonged metabolic suppression (e.g. hibernation and estivation) or energetically demanding processes (e.g. migration and breeding) to better understand the mechanisms underlying fasting tolerance in wild vertebrates. These studies largely show beneficial effects of fasting on redox balance via limited oxidative damage. Though some species exhibit signs of oxidative stress due to energetically or metabolically extreme processes, fasting wild vertebrates largely buffer themselves from the negative consequences of oxidative damage through specific strategies such as elevating antioxidants, selectively maintaining redox balance in critical tissues, or modifying behavioral patterns. We conclude with suggestions for future research to better elucidate the protective effects of fasting on oxidative stress as well as disentangle the impacts from other life history stages. Further research in these areas will facilitate our understanding of the mechanisms wild vertebrates use to mitigate the negative impacts associated with metabolically-extreme life history stages as well as potential translation into therapeutic interventions in non-fasting-adapted species including humans.

The costs of being a good dad: egg-carrying and clutch size impair locomotor performance in male midwife toads (Alytes obstetricans)

Parental care is widespread across the animal kingdom. Parental behaviours are beneficial by increasing offspring survival but induce significant costs to the parents. Because parental care is far more common in females, the associated reproductive costs have been largely studied in this sex. Although male parental care is likely to involve significant costs, it has been markedly less well investigated. We studied the costs of egg-carrying on locomotor performance in an amphibian species (Alytes obstetricans) with male parental care. We examined complementary parameters including hopping performance, righting response, hindleg muscle response to egg burden, and homing time in males carrying or not carrying eggs. We found that carrying males showed altered locomotor performance for most traits. In addition, alteration of performance was closely related to relative clutch size. Clutch desertion occurred in smaller individuals carrying larger relative clutch mass, and performance after desertion was similar to that of non-reproductive individuals. Overall, our study demonstrates that carrying eggs significantly alters male mobility and that performance–clutch size trade-offs are relevant in understanding the evolution of paternal care.

Seasonal factors driving biochemical biomarkers in two fish species from a subtropical reservoir in southern Brazil: An integrated approach

Reservoirs are lentic man-made waterbodies resulting from river damming processes. Pollutants coming from adjacent areas can accumulate in the water and sediment of these modified freshwater environments. Fish are often found in reservoirs occupying several trophic niches. Biochemical biomarkers are early warning signals of environmental disturbance to an organism. It is essential to understand how pollutants, abiotic variables and biochemical biomarker responses behave throughout the seasons to implement biomonitoring programs. Loricariichthys anus and Geophagus brasiliensis were collected, and abiotic variables were seasonally measured for one year, at six sampling sites in Passo Real reservoir, in a subtropical region of Southern Brazil. Biochemical biomarkers were analyzed in four tissues of both fish species, as well as metal and pesticide concentrations in the reservoir's water and sediment. Redundancy analysis (RDA) was carried out to find the temporal relationship between biomarkers and environmental variables. RDA has clearly shown the separation of seasons for both species. Azoxystrobin, simazine and propoxur were the pesticides mostly contributing to the variation, whereas metals had lesser contribution to it. Seasonality appears to be the main factor explaining biomarkers' variability. PERMANOVA has confirmed the effect of temperature and dissolved oxygen on biomarkers of both fish species. Thus, it is hard to differentiate if the fluctuation in biomarkers' responses only reflects the normal state of organisms or it is a biological consequence from negative effects of fish exposure to several types of pollution (sewage, pesticides, and fertilizers) entering this aquatic system. In this study, to circumvent the seasonality issue on biomonitoring, the analysis of biomarkers on these fish should not be carried out in organs directly affected by temperature (such as liver and gills), or during reproduction periods (mainly in Spring).