Ecological consequences of body size reduction under warming

Body size reduction is a universal response to warming, but its ecological consequences across biological levels, from individuals to ecosystems, remain poorly understood. Most biological processes scale with body size, and warming-induced changes in body size can therefore have important ecological consequences. To understand these consequences, we propose a unifying, hierarchical framework for the ecological impacts of intraspecific body size reductions due to thermal plasticity that explicitly builds on three key pathways: morphological constraints, bioenergetic constraints and surface-to-volume ratio. Using this framework, we synthesize key consequences of warming-induced body size reductions at multiple levels of biological organization. We outline how this trait-based framework can improve our understanding, detection and generalization of the ecological impacts of warming.

Integrating otolith and genetic tools to reveal intraspecific biodiversity in a highly impacted salmon population

Intraspecific biodiversity is vital for species persistence in an increasingly volatile world. By embracing methods that integrate information at different spatiotemporal scales, we can directly monitor and reconstruct changes in intraspecific biodiversity. Here we combined genetics and otolith biochronologies to describe the genotypic and phenotypic diversity of Chinook salmon (Oncorhynchus tshawytscha) in the Yuba River, California, comparing cohorts that experienced a range of hydroclimatic conditions. Yuba River salmon have been heavily impacted by habitat loss and degradation, and large influxes of unmarked hatchery fish each year have led to concern about introgression and uncertainty around the viability of its wild populations, particularly the rarer spring-run salmon. Otolith strontium isotopes showed that Yuba River origin fish represented, on average, 42% (range 7%-73%) of spawners across six return years (2009-2011, 2018-2020), with large interannual variability. The remainder of adult Chinook salmon in the river were primarily strays from the nearby Feather River hatchery, and since 2018 from the Mokelumne River hatchery. Among the Yuba-origin spawners, on average, 30% (range 14%-50%) exhibited the spring-run genotype. The Yuba-origin fish also displayed a variety of outmigration phenotypes that differed in the timing and size at which they left the Yuba river. Early-migrating fry dominated the returns (mean 59%, range 33%-89%), and their contribution rates were negatively correlated with freshwater flows. It is unlikely that fry survival rates are elevated during droughts, suggesting that this trend reflects disproportionately low survival of larger later migrating parr, smolts, and yearlings along the migratory corridor in drier years. Otolith daily increments indicated generally faster growth rates in non-natal habitats, emphasizing the importance of continuing upstream restoration efforts to improve in-river growing conditions. Together, these findings show that, despite a long history of habitat degradation and hatchery introgression, the Yuba River maintains intraspecific biodiversity that should be taken into account in future management, restoration, and reintroduction plans. The finding that genotypic spring-run are reproducing, surviving, and returning to the Yuba River every year suggests that re-establishment of an independent population is possible, although hatchery-wild interactions would need to be carefully considered. Integrating methods is critical to monitor changes in key genetic, physiological, and behavioral traits to assess population viability and resilience.

Tetrapod sperm length evolution in relation to body mass is shaped by multiple trade-offs

Sperm length is highly variable across species and many questions about its variation remain open. Although variation in body mass may affect sperm length evolution through its influence on multiple factors, the extent to which sperm length variation is linked to body mass remains elusive. Here, we use the Pareto multi-task evolution framework to investigate the relationship between sperm length and body mass across tetrapods. We find that tetrapods occupy a triangular Pareto front, indicating that trade-offs shape the evolution of sperm length in relation to body mass. By exploring the factors predicted to influence sperm length evolution, we find that sperm length evolution is mainly driven by sperm competition and clutch size, rather than by genome size. Moreover, the triangular Pareto front is maintained within endotherms, internal fertilizers, mammals and birds, suggesting similar evolutionary trade-offs within tetrapods. Finally, we demonstrate that the Pareto front is robust to phylogenetic dependencies and finite sampling bias. Our findings provide insights into the evolutionary mechanisms driving interspecific sperm length variation and highlight the importance of considering multiple trade-offs in optimizing reproductive traits.

Global patterns and drivers of fish reproductive potential on coral reefs

Fish fecundity scales hyperallometrically with body mass, meaning larger females produce disproportionately more eggs than smaller ones. We explore this relationship beyond the species-level to estimate the "reproductive potential" of 1633 coral reef sites distributed globally. We find that, at the site-level, reproductive potential scales hyperallometrically with assemblage biomass, but with a smaller median exponent than at the species-level. Across all families, modelled reproductive potential is greater in fully protected sites versus fished sites. This difference is most pronounced for the important fisheries family, Serranidae. When comparing a scenario where 30% of sites are randomly fully protected to a current protection scenario, we estimate an increase in the reproductive potential of all families, and particularly for Serranidae. Such results point to the possible ecological benefits of the 30 × 30 global conservation target and showcase management options to promote the sustainability of population replenishment.

Thermal performance curves for aerobic scope and specific dynamic action in a sexually dimorphic piscivore: implications for a warming climate

Digestion can make up a substantial proportion of animal energy budgets, yet our understanding of how it varies with sex, body mass and ration size is limited. A warming climate may have consequences for animal growth and feeding dynamics that will differentially impact individuals in their ability to efficiently acquire and assimilate meals. Many species, such as walleye (Sander vitreus), exhibit sexual size dimorphism (SSD), whereby one sex is larger than the other, suggesting sex differences in energy acquisition and/or expenditure. Here, we present the first thorough estimates of specific dynamic action (SDA) in adult walleye using intermittent-flow respirometry. We fed male (n=14) and female (n=9) walleye two ration sizes, 2% and 4% of individual body mass, over a range of temperatures from 2 to 20°C. SDA was shorter in duration and reached higher peak rates of oxygen consumption with increasing temperature. Peak SDA increased with ration size and decreased with body mass. The proportion of digestible energy lost to SDA (i.e. the SDA coefficient) was consistent at 6% and was unrelated to temperature, body mass, sex or ration size. Our findings suggest that sex has a negligible role in shaping SDA, nor is SDA a contributor to SSD for this species. Standard and maximum metabolic rates were similar between sexes but maximum metabolic rate decreased drastically with body mass. Large fish, which are important for population growth because of reproductive hyperallometry, may therefore face a bioenergetic disadvantage and struggle most to perform optimally in future, warmer waters.

Temporal declines in fecundity: A study of southern Gulf of St. Lawrence Atlantic herring (Clupea harengus) and implications for potential reproductive output

Individuals must reproduce to survive and thrive from generation to generation. In fish, the fecundity of individuals and estimates of total reproductive output are critical for evaluating reproductive success and understanding population dynamics. Estimating fecundity is an onerous task; therefore, many populations lack contemporary estimates of fecundity and size-fecundity relationships. However, reproductive dynamics are not static in time; therefore, it is important to develop contemporary fecundity estimates to better inform conservation and management action. To highlight the importance of contemporary fecundity estimates, we examined the fecundity of southern Gulf of St. Lawrence (sGSL) spring and fall spawning Atlantic herring in 2022, developed size-fecundity models, and compared these to historical fecundity estimates and models. Our results suggest that the average fecundity of sGSL spring and fall herring has undergone a substantial temporal decline of approximately 47% and 58%, respectively, since the 1970s and 1980s. The size-fecundity relationships for fall spawning herring have shifted, with fish of a given size exhibiting lower fecundity in 2022 compared to the 1970s. Alternatively, the size-fecundity relationships for spring spawning herring have remained relatively static. Furthermore, simulations highlighted a substantial reduction in potential reproductive output in 2022 compared to 1970 of approximately 32% and 68% for spring and fall spawners, respectively, based on a fixed number of mature females, which may have negative implications for stock rebuilding. Overall, our study provides support for periodic estimates of fecundity in fish populations to better understand temporal changes in reproductive and population dynamics.

Coevolution between eggs and sperm of insects

Sexual selection is known to play a major role in the evolution of insect sperm size, whereas natural selection is thought to be a major driver of insect egg size. Despite these differing forms of selection operating, it is possible coevolution between male and female gametes can occur owing to their vital interactions during fertilization. We tested egg-sperm coevolution in insects and found that longer sperm correlated to longer and wider eggs. Moreover, the size of the entry point of sperm into insect eggs (micropyles), was positively related to the diameter of sperm, on average being approximately three times the diameter of the sperm. This suggests a function in reducing and channelling sperm entry, but potentially still leaving space for movement. Our work suggests that greater attention needs to be paid to egg-sperm interactions prior to the point of fertilization as they may influence the evolution of gametes.

Shrinking sizes of trout and salamanders are unexplained by climate warming alone

Decreases in body sizes of animals related to recent climate warming can affect population persistence and stability. However, direct observations of average sizes over time and their interrelationships with underlying density-dependent and density-independent processes remain poorly understood owing to the lack of appropriate long-term datasets. We measured body size of two species common to headwater streams in coastal and Cascades ecoregions of the Pacific Northwest of North America over multiple decades, comparing old-growth and managed forests. We found consistent decreases in median length of Coastal Cutthroat Trout Oncorhynchus clarkii clarkii, but a coexisting species, the Coastal Giant Salamander Dicamptodon tenebrosus, appears to be more resilient to size changes over time. Based on observed trends, adult trout have decreased in length by 6-13% over the last 30 years. Length decreased more in larger compared to smaller animals, suggesting that these effects reflect changes in growth trajectories. Results from a model-selection approach that included hydroclimatic and biological information as covariates in one of our study ecoregions demonstrated that stream temperature alone did not explain observed length reductions. Rather, a combination of density-dependent (animal abundances) and local density-independent factors (temperature, habitat, and streamflow) explained observed patterns of size. Continued decreases in size could lead to trophic cascades, biodiversity loss, or in extreme cases, species extirpation. However, the intricate links between density-independent and density-dependent factors in controlling population-level processes in streams need further attention.

Population structure and reproductive indicators of the surubim Pseudoplatystoma punctifer (Siluriformes, Pimelodidae) in the São Miguel River, Amazon basin, Brazil

Fish is an important source of food and income for a significant portion of the Amazonian population, especially those who live along the rivers and lakes in the region. Pseudoplatystoma punctifer (Castelnau, 1855), known as surubim, is a species of Neotropical catfish widely exploited by fisheries and commercially valuable in the Guaporé River basin, Brazil. However, population dynamics are poorly known in the region. To understand the population structure and reproductive biology aspects of the surubim, monthly experimental fisheries were carried out in the São Miguel River, state of Rondônia, Brazil, between August 2020 and July 2021. The captured fish were weighed, and its gonads were removed and weighed for histological analyses (microscopic description) and classification of the maturation stages (macroscopic description). The collected gonads were fixed in 10% buffered formalin, dehydrated, cut into 4-μm-thick sections, and stained with hematoxylin and eosin. A total of 34 individuals were collected (20 females and 14 males), showing positive allometric growth and condition factor from 0.81 to 1.79 for females and males, respectively. Females were larger in size and weight than males. P. punctifer reaches its first maturation at an average length of 68.30 cm, indicating the importance of respecting the minimum capture size as an alternative to ensure the natural stocks of this fishery resource in the region. The results provide support for the establishment of public policies and actions for conservation, management, and regulation of fishing.

Metabolic loads and the costs of metazoan reproduction

Reproduction includes two energy investments-the energy in the offspring and the energy expended to make them. The former is well understood, whereas the latter is unquantified but often assumed to be small. Without understanding both investments, the true energy costs of reproduction are unknown. We present a framework for estimating the total energy costs of reproduction by combining data on the energy content of offspring (direct costs) and the metabolic load of bearing them (indirect costs). We find that direct costs typically represent the smaller fraction of the energy expended on reproduction. Mammals pay the highest reproductive costs (excluding lactation), ~90% of which are indirect. Ectotherms expend less on reproduction overall, and live-bearing ectotherms pay higher indirect costs compared with egg-layers. We show that the energy demands of reproduction exceed standard assumptions.

Per capita sperm metabolism is density dependent

From bacteria to metazoans, higher density populations have lower per capita metabolic rates than lower density populations. The negative covariance between population density and metabolic rate is thought to represent a form of adaptive metabolic plasticity. A relationship between density and metabolism was actually first noted 100 years ago, and was focused on spermatozoa; even then, it was postulated that adaptive plasticity drove this pattern. Since then, contemporary studies of sperm metabolism specifically assume that sperm concentration has no effect on metabolism and that sperm metabolic rates show no adaptive plasticity. We did a systematic review to estimate the relationship between sperm aerobic metabolism and sperm concentration, for 198 estimates spanning 49 species, from protostomes to humans from 88 studies. We found strong evidence that per capita metabolic rates are concentration dependent: both within and among species, sperm have lower metabolisms in dense ejaculates, but increase their metabolism when diluted. On average, a 10-fold decrease in sperm concentration increased per capita metabolic rate by 35%. Metabolic plasticity in sperm appears to be an adaptive response, whereby sperm maximize their chances of encountering eggs.

Effect of prolonged feeding of broodstock diet with increased inclusion of essential n-3 fatty acids on maturing and spawning performance in 3-year-old Atlantic salmon (Salmo salar)

Atlantic salmon (Salmo salar) broodstock recruits are normally fed a specialized diet with a higher content of essential nutrients for a limited time period prior to fasting and transfer to freshwater. Typically, this period lasts for about six months, but may vary among producers. Reduced use of marine ingredients in commercial salmon diets during the last decades has affected the content of essential nutrients, such as n-3 long chained polyunsaturated fatty acids (LC-PUFA), minerals and vitamins. Furthermore, to minimize the risk of losses and implement new breeding achievements faster, breeding companies have shortened the production cycle of broodstock from 4 to 3 years, which may affect the number of fish that are large enough to mature. In the present study, we have extended the broodstock feeding period from 6 to 15 months prior to the freshwater transfer giving a higher content of n-3 LC-PUFA (higher inclusion of marine oils) from February to December (Phase 1), and thereafter a diet with a higher energy content to ensure growth towards the spring and maturation (Phase 2). Four sea cages with approximately 80.000 salmon postsmolt, two sea cages with males and two with females, were given a control diet and an experimental diet. Samples were taken in Phase 1 at start (1.7 kg), mid (3.4 kg) and end Phase 1/start of Phase 2 (8.3 kg), and end of Phase 2 (13.4 kg). The fish were thereafter fasted, and selected fish transferred to landbased freshwater tanks where light and temperature were used to manipulate the spawning time of the fish in two groups (early or late). Due to disease in the facility, measures of egg quality and hatching were only obtained from the early group. During the trial and spawning period, biometrical measurements were recorded, and samples of liver, gonad, fillet and red blood cells (RBC) were collected for fatty acid composition and blood plasma for analysis of lipid and health-related parameters. Samples were also collected for gonadal transcriptomic analysis by microarray and qPCR (end Phase 2) and plasma steroids (end Phase 2, mid maturation and spawning). Males fed the test diet had a larger body size compared to the control group at the end of Phase 2, while no differences were observed between dietary groups for the females. Total mortality in the trial was lower in the test group compared to the control, losses were caused mainly by sea lice treatments, loser fish or cardiomyopathy syndrome (CMS). The dietary LC-PUFA levels in the test diet were reflected in the tissues particularly during Phase 1, but only different in the fillet samples and eggs at the end of Phase 2 and at spawning. Plasma sex steroids content increased at mid maturation and showed lower levels of androgens and estrogens in females fed the test diet compared to the control. At the end of Phase 2, transcriptional analysis showed upregulation of steroidogenic enzymes, although not reflected in changes in plasma steroids in Phase 2, indicating changes to come during maturation. The differences in LC-PUFA content in tissues and plasma steroids did not appear to affect fecundity, sperm quality, egg survival or hatching rate, but the test group had larger eggs compared to the control in the early spawner-group. Prolonged feeding of n-3 LC-PUFA to pre-puberty Atlantic salmon broodstock appears to be important for higher survival in challenging sea cage environments and has an effect on sex steroid production that, together with high energy diet during early maturation, cause the test group to produce larger eggs.

Coherent long-term body-size responses across all Northwest Atlantic herring populations to warming and environmental change despite contrasting harvest and ecological factors

Body size is a key component of individual fitness and an important factor in the structure and functioning of populations and ecosystems. Disentangling the effects of environmental change, harvest and intra- and inter-specific trophic effects on body size remains challenging for populations in the wild. Herring in the Northwest Atlantic provide a strong basis for evaluating hypotheses related to these drivers given that they have experienced significant warming and harvest over the past century, while also having been exposed to a wide range of other selective constraints across their range. Using data on mean length-at-age 4 for the sixteen principal populations over a period of 53 cohorts (1962-2014), we fitted a series of empirical models for temporal and between-population variation in the response to changes in sea surface temperature. We find evidence for a unified cross-population response in the form of a parabolic function according to which populations in naturally warmer environments have responded more negatively to increasing temperature compared with those in colder locations. Temporal variation in residuals from this function was highly coherent among populations, further suggesting a common response to a large-scale environmental driver. The synchrony observed in this study system, despite strong differences in harvest and ecological histories among populations and over time, clearly indicates a dominant role of environmental change on size-at-age in wild populations, in contrast to commonly reported effects of fishing. This finding has important implications for the management of fisheries as it indicates that a key trait associated with population productivity may be under considerably less short-term management control than currently assumed. Our study, overall, illustrates the need for a comparative approach within species for inferences concerning the many possible effects on body size of natural and anthropogenic drivers in the wild.

Rarity mediates species-specific responses of tropical reef fishes to protection

Marine protected areas (MPAs) are the most widely applied tool for marine biodiversity conservation, yet many gaps remain in our understanding of their species-specific effects, partly because the socio-environmental context and spatial autocorrelation may blur and bias perceived conservation outcomes. Based on a large data set of nearly 3000 marine fish surveys spanning all tropical regions of the world, we build spatially explicit models for 658 fish species to estimate species-specific responses to protection while controlling for the environmental, habitat and socio-economic contexts experienced across their geographic ranges. We show that the species responses are highly variable, with ~40% of fishes not benefitting from protection. When investigating how traits influence species' responses, we find that rare top-predators and small herbivores benefit the most from MPAs while mid-trophic level species benefit to a lesser extent, and rare large herbivores experience adverse effects, indicating potential trophic cascades.

Demographic patterns of walleye (Sander vitreus) reproductive success in a Wisconsin population

Harvest in walleye Sander vitreus fisheries is size-selective and could influence phenotypic traits of spawners; however, contributions of individual spawners to recruitment are unknown. We used parentage analyses using single nucleotide polymorphisms to test whether parental traits were related to the probability of offspring survival in Escanaba Lake, Wisconsin. From 2017 to 2020, 1339 adults and 1138 juveniles were genotyped and 66% of the offspring were assigned to at least one parent. Logistic regression indicated the probability of reproductive success (survival of age-0 to first fall) was positively (but weakly) related to total length and growth rate in females, but not age. No traits analyzed were related to reproductive success for males. Our analysis identified the model with the predictors' growth rate and year for females and the models with year and age and year for males as the most likely models to explain variation in reproductive success. Our findings indicate that interannual variation (i.e., environmental conditions) likely plays a key role in determining the probability of reproductive success in this population and provide limited support that female age, length, and growth rate influence recruitment.

Global warming is projected to lead to increased freshwater growth potential and changes in pace of life in Atlantic salmon Salmo salar

Global warming has been implicated in widespread demographic changes in Atlantic salmon Salmo salar populations, but projections of life-history responses to future climate change are lacking. Here, we first exploit multiple decades of climate and biological data from the Burrishoole catchment in the west of Ireland to model statistical relationships between atmospheric variables, water temperature, and freshwater growth of juvenile Atlantic salmon. We then use this information to project potential changes in juvenile growth and life-history scheduling under three shared socioeconomic pathway and representative concentration pathway scenarios from 1961 to 2100, based on an ensemble of five climate models. Historical water temperatures were well predicted with a recurrent neural network, using observation-based atmospheric forcing data. Length-at-age was in turn also well predicted by cumulative growing degree days calculated from these water temperatures. Most juveniles in the Burrishoole population migrated to sea as 2-year-old smolts, but our future projections indicate that the system should start producing a greater proportion of 1-year-old smolts, as increasingly more juveniles cross a size-based threshold in their first summer for smoltification the following spring. Those failing to cross the size-based threshold will instead become 2-year-old smolts, but at a larger length relative to 2-year-old smolts observed currently, owing to greater overall freshwater growth opportunity. These changes in age- and size-at-seaward migration could have cascading effects on age- and size-at-maturity and reproductive output. Consequently, the seemingly small changes that our results demonstrate have the potential to cause significant shifts in population dynamics over the full life cycle. This workflow is highly applicable across the range of the Atlantic salmon, as well as to other anadromous species, as it uses openly accessible climate data and a length-at-age model with minimal input requirements, fostering improved general understanding of phenotypic and demographic responses to climate change and management implications.

Estimating the relationship between fitness and metabolic rate: which rate should we use?

As physiologists seek to better understand how and why metabolism varies, they have focused on how metabolic rate covaries with fitness-that is, selection. Evolutionary biologists have developed a sophisticated framework for exploring selection, but there are particular challenges associated with estimating selection on metabolic rate owing to its allometric relationship with body mass. Most researchers estimate selection on mass and absolute metabolic rate; or selection on mass and mass-independent metabolic rate (MIMR)-the residuals generated from a nonlinear regression. These approaches are sometimes treated as synonymous: their coefficients are often interpreted in the same way. Here, we show that these approaches are not equivalent because absolute metabolic rate and MIMR are different traits. We also show that it is difficult to make sound biological inferences about selection on absolute metabolic rate because its causal relationship with mass is enigmatic. By contrast, MIMR requires less-desirable statistical practices (i.e. residuals as a predictor), but provides clearer causal pathways. Moreover, we argue that estimates of selection on MIMR have more meaningful interpretations for physiologists interested in the drivers of variation in metabolic allometry. This article is part of the theme issue 'The evolutionary significance of variation in metabolic rates'.

Smaller body size under warming is not due to gill-oxygen limitation in a cold-water salmonid

Declining body size in fishes and other aquatic ectotherms associated with anthropogenic climate warming has significant implications for future fisheries yields, stock assessments and aquatic ecosystem stability. One proposed mechanism seeking to explain such body-size reductions, known as the gill oxygen limitation (GOL) hypothesis, has recently been used to model future impacts of climate warming on fisheries but has not been robustly empirically tested. We used brook trout (Salvelinus fontinalis), a fast-growing, cold-water salmonid species of broad economic, conservation and ecological value, to examine the GOL hypothesis in a long-term experiment quantifying effects of temperature on growth, resting metabolic rate (RMR), maximum metabolic rate (MMR) and gill surface area (GSA). Despite significantly reduced growth and body size at an elevated temperature, allometric slopes of GSA were not significantly different than 1.0 and were above those for RMR and MMR at both temperature treatments (15°C and 20°C), contrary to GOL expectations. We also found that the effect of temperature on RMR was time-dependent, contradicting the prediction that heightened temperatures increase metabolic rates and reinforcing the importance of longer-term exposures (e.g. >6 months) to fully understand the influence of acclimation on temperature-metabolic rate relationships. Our results indicate that although oxygen limitation may be important in some aspects of temperature-body size relationships and constraints on metabolic supply may contribute to reduced growth in some cases, it is unlikely that GOL is a universal mechanism explaining temperature-body size relationships in aquatic ectotherms. We suggest future research focus on alternative mechanisms underlying temperature-body size relationships, and that projections of climate change impacts on fisheries yields using models based on GOL assumptions be interpreted with caution.

Does size-selective harvesting erode adaptive potential to thermal stress?

Overharvesting is a serious threat to many fish populations. High mortality and directional selection on body size can cause evolutionary change in exploited populations via selection for a specific phenotype and a potential reduction in phenotypic diversity. Whether the loss of phenotypic diversity that accompanies directional selection impairs response to environmental stress is not known. To address this question, we exposed three zebrafish selection lines to thermal stress. Two lines had experienced directional selection for (1) large and (2) small body size, and one was (3) subject to random removal of individuals with respect to body size (i.e. line with no directional selection). Selection lines were exposed to three temperatures (elevated, 34°C; ambient, 28°C; low, 22°C) to determine the response to an environmental stressor (thermal stress). We assessed differences among selection lines in their life history (growth and reproduction), physiological traits (metabolic rate and critical thermal max) and behaviour (activity and feeding behaviour) when reared at different temperatures. Lines experiencing directional selection (i.e. size selected) showed reduced growth rate and a shift in average phenotype in response to lower or elevated thermal stress compared with fish from the random-selected line. Our data indicate that populations exposed to directional selection can have a more limited capacity to respond to thermal stress compared with fish that experience a comparable reduction in population size (but without directional selection). Future studies should aim to understand the impacts of environmental stressors on natural fish stocks.

Large females connect Atlantic cod spawning sites

The Earth's ecosystems are increasingly deprived of large animals. Global simulations suggest that this downsizing of nature has serious consequences for biosphere functioning. However, the historical loss of large animals means that it is now often impossible to secure empirical data revealing their true ecological importance. We tracked 465 mature Atlantic cod (Gadus morhua) during their winter spawning season and show that large females (up to 114 centimeters in length), which are still found in mid-Norway, were characterized by more complex movement networks compared with smaller females. Large males were sparse but displayed similar movement patterns. Our finding implies that management programs promoting large fish will have positive impacts on population resilience by facilitating the continued use of a diversity of spawning habitats and the connectivity between them.

Marine reserves promote cycles in fish populations on ecological and evolutionary time scales

Marine reserves are considered essential for sustainable fisheries, although their effectiveness compared to traditional fisheries management is debated. The effect of marine reserves is mostly studied on short ecological time scales, whereas fisheries-induced evolution is a well-established consequence of harvesting. Using a size-structured population model for an exploited fish population of which individuals spend their early life stages in a nursery habitat, we show that marine reserves will shift the mode of population regulation from low size-selective survival late in life to low, early-life survival due to strong resource competition. This shift promotes the occurrence of rapid ecological cycles driven by density-dependent recruitment as well as much slower evolutionary cycles driven by selection for the optimal body to leave the nursery grounds, especially with larger marine reserves. The evolutionary changes increase harvesting yields in terms of total biomass but cause disproportionately large decreases in yields of larger, adult fish. Our findings highlight the importance of carefully considering the size of marine reserves and the individual life history of fish when managing eco-evolutionary marine systems to ensure both population persistence as well as stable fisheries yields.

Geographical Variation in Body Size in the Asian Common Toad (Duttaphrynus melanostictus)

The geographic variation in life-history traits of organisms and the mechanisms underlying adaptation are interesting ideas in evolutionary biology. This study investigated age and body size of the Asian common toad (Duttaphrynus melanostictus) among five populations along a geographical gradient. We found that geographical variation in age was non-significant among populations but there was a significant and positive correlation between mean age and body size. Although the body size values at 1043 m are quite different from other sites, after controlling for age effects, there was a significant positive correlation between altitude and body size. Our findings followed the predictions of Bergmann's rule, suggesting that the body size of D. melanostictus is potentially influenced by the low air temperatures at higher altitudes.

Supplemental oxygen does not improve growth but can enhance reproductive capacity of fish

Fish tend to grow faster as the climate warms but attain a smaller adult body size following an earlier age at sexual maturation. Despite the apparent ubiquity of this phenomenon, termed the temperature-size rule (TSR), heated scientific debates have revealed a poor understanding of the underlying mechanisms. At the centre of these debates are prominent but marginally tested hypotheses which implicate some form of 'oxygen limitation' as the proximate cause. Here, we test the role of oxygen limitation in the TSR by rearing juvenile Galaxias maculatus for a full year in current-day (15°C) and forecasted (20°C) summer temperatures while providing half of each temperature group with supplemental oxygen (hyperoxia). True to the TSR, fish in the warm treatments grew faster and reached sexual maturation earlier than their cooler conspecifics. Yet, despite supplemental oxygen significantly increasing maximum oxygen uptake rate, our findings contradict leading hypotheses by showing that the average size at sexual maturation and the adult body size did not differ between normoxia and hyperoxia groups. We did, however, discover that hyperoxia extended the reproductive window, independent of fish size and temperature. We conclude that the intense resource investment in reproduction could expose a bottleneck where oxygen becomes a limiting factor.

Reproductive behavior of Atlantic halibut (Hippoglossus hippoglossus) interpreted from electronic tags

Reproductive timing, location, and behavior are important characteristics that determine marine population dynamics, structure, and resilience to threats, including fishing and climate change. It is challenging to evaluate factors driving variability in these reproductive traits in wild fishes because of the difficulty observing individuals in their natural environments. In the present study, we used high-resolution depth, temperature, and acceleration time series recorded by pop-up satellite archival tags to (1) identify and characterize patterns in depth and acceleration that may be indicative of spawning events in large Atlantic halibut (Hippoglossus hippoglossus), and (2) estimate the effects of individual traits (body size and sex) and environmental factors (location and temperature) on spawning time and frequency. Unique rapid rises observed in the winter depth profiles were interpreted as spawning events. The initiation of the first presumed spawning rise was negatively correlated to water temperature experienced during the prespawning season, suggesting that currently increasing water temperature in the Gulf of St. Lawrence may induce phenological change in halibut spawning time. The number of rises of batch-spawning females was unrelated to female body size. The present study demonstrates how electronic tagging can be used for in-depth characterization of timing, location, and behaviors associated with spawning in a large flatfish species. Such information can inform spatiotemporal management and conservation measures aiming to protect species from directed fishing and by-catch during spawning.

Geographic variation in the life history of lane snapper Lutjanus synagris, with new insights from the warm edge of its distribution

Research on life-history variations in widely distributed fish species is needed to understand global warming impacts on populations and to improve fisheries management advice. The lane snapper Lutjanus synagris (Linnaeus, 1758) is commercially important to fisheries in the Western Central Atlantic, where spread information on its life-history traits is available. We studied growth, age, reproduction and mortality of lane snapper in the Guatemalan Caribbean, the warmest part of its distribution range, and collated the new information with published data in a latitudinal analysis extending between 18°S and 30°N. Longevity was estimated at 11 years, and von Bertalanffy growth parameters were asymptotic length (Linf) 45.6 and 42.2 cm for females and males, respectively, the growth coefficient (K) was 0.1 year-1 and the theoretical age at zero length (t0 ) was -4.4 years. Lane snapper grew slowest in April, prior to the rainy season, and at the onset of the reproductive season, which lasted from May to October. Fifty percent of female and male lane snappers matured at 23 and 17 cm, corresponding to 3.5 and 2.4 years of age respectively. A regional multivariate analysis found seawater temperature to be an important driver of life-history variation. Lane snapper lifespan was shorter at the warm edge of its distribution range, and maximum size and peak reproductive investment were negatively related to sea surface temperature. The trade-offs in lane snapper life-history traits and phenology likely enhance its fitness to differing environments. Interpolation from the present regional estimates to less-studied regions of the Caribbean is useful for preliminary understanding of reaction norms and harvest potentials.

The evolution of aging and lifespan

Aging is a nearly inescapable trait among organisms yet lifespan varies tremendously across different species and spans several orders of magnitude in vertebrates alone. This vast phenotypic diversity is driven by distinct evolutionary trajectories and tradeoffs that are reflected in patterns of diversification and constraint in organismal genomes. Age-specific impacts of selection also shape allele frequencies in populations, thus impacting disease susceptibility and environment-specific mortality risk. Further, the mutational processes that spawn this genetic diversity in both germline and somatic cells are strongly influenced by age and life history. We discuss recent advances in our understanding of the evolution of aging and lifespan at organismal, population, and cellular scales, and highlight outstanding questions that remain unanswered.

A new flexible model for maintenance and feeding expenses that improves description of individual growth in insects

Metabolic theories in ecology interpret ecological patterns at different levels through the lens of metabolism, typically applying allometric scaling to describe energy use. This requires a sound theory for individual metabolism. Common mechanistic growth models, such as 'von Bertalanffy', 'dynamic energy budgets' and the 'ontogenetic growth model' lack some potentially important aspects, especially regarding regulation of somatic maintenance. We develop a model for ontogenetic growth of animals, applicable to ad libitum and food limited conditions, based on an energy balance that expresses growth as the net result of assimilation and metabolic costs for maintenance, feeding and food processing. The most important contribution is the division of maintenance into a 'non-negotiable' and a 'negotiable' part, potentially resulting in hyperallometric scaling of maintenance and downregulated maintenance under food restriction. The model can also account for effects of body composition and type of growth at the cellular level. Common mechanistic growth models often fail to fully capture growth of insects. However, our model was able to capture empirical growth patterns observed in house crickets.

Teleost genomic repeat landscapes in light of diversification rates and ecology

Repetitive DNA make up a considerable fraction of most eukaryotic genomes. In fish, transposable element (TE) activity has coincided with rapid species diversification. Here, we annotated the repetitive content in 100 genome assemblies, covering the major branches of the diverse lineage of teleost fish. We investigated if TE content correlates with family level net diversification rates and found support for a weak negative correlation. Further, we demonstrated that TE proportion correlates with genome size, but not to the proportion of short tandem repeats (STRs), which implies independent evolutionary paths. Marine and freshwater fish had large differences in STR content, with the most extreme propagation detected in the genomes of codfish species and Atlantic herring. Such a high density of STRs is likely to increase the mutational load, which we propose could be counterbalanced by high fecundity as seen in codfishes and herring.

Fertilization Mode Covaries with Body Size

AbstractThe evolution of internal fertilization has occurred repeatedly and independently across the tree of life. As it has evolved, internal fertilization has reshaped sexual selection and the covariances among sexual traits, such as testes size, and gamete traits. But it is unclear whether fertilization mode also shows evolutionary associations with traits other than primary sex traits. Theory predicts that fertilization mode and body size should covary, but formal tests with phylogenetic control are lacking. We used a phylogenetically controlled approach to test the covariance between fertilization mode and adult body size (while accounting for latitude, offspring size, and offspring developmental mode) among 1,232 species of marine invertebrates from three phyla. Within all phyla, external fertilizers are consistently larger than internal fertilizers: the consequences of fertilization mode extend to traits that are only indirectly related to reproduction. We suspect that other traits may also coevolve with fertilization mode in ways that remain unexplored.

Increased offspring provisioning by large female fish and consequences for reproductive efficiency

Contemporary fisheries research and management have highlighted the need to protect size and age structures of fish populations. Many studies particularly emphasize a disproportionate contribution of populations' largest, oldest female fish to population-level recruitment through maternal effects: non-genetic effects of females on performance of their offspring including through energetic provisioning of eggs. Our study synthesized the effects of increasing female size on offspring performance using a meta-analysis approach. In a stepwise fashion, we conducted three separate meta-analyses to estimate the broad-scale patterns of maternal effects in fish. We synthesized relationships between female size and egg size, egg size and offspring size, and egg size and offspring survival. We tested maternal effects across numerous taxonomic orders and system types including freshwater, diadromous, and saltwater species. We also compared the effects of increasing egg size on offspring performance at different experimental durations. These three meta-analyses all supported the paradigm that larger females render individual benefits to offspring performance. However, females have finite gonadal energy and space for egg provisioning and must trade off between egg size and fecundity. For the largest females to contribute disproportionately to population recruitment (relative to their gonadal investment), they must utilize their gonadal investment more efficiently than their smaller conspecifics. Using example studies in published literature, we demonstrated how established maternal effects on egg provisioning do not necessarily support greater reproductive efficiency in larger females. Therefore, while larger females do produce larger eggs, which promote offspring growth and survival, we concluded these benefits may not always outweigh relative fecundity costs of larger eggs.

Variability in the energy reserves of swordfish (Xiphias gladius) of the southeastern Pacific Ocean: A temporal and intra-individual perspective

The temporal dynamics of energy reserves are associated with the physiological processes (i.e., reproduction) in marine fishes, in which storage organs play a key role for efficient energy investment. We evaluated the temporal (i.e., seasons) and intra-individual (i.e., organs) dynamics of adult female swordfish (Xiphias gladius) during its feeding period off the Chilean coast in the southeastern Pacific Ocean (SEPO). The biochemical composition (i.e., lipids, proteins, and glucose), energy content and fatty acid profile of the muscle, liver and gonad were evaluated during the austral autumn, winter, and spring. Our results showed principally an intra-individual effect in both the muscle and liver in the autumn and spring. Herein, a trend of higher amounts of lipids and total energy were found in the muscle, while the liver showed greater protein and glucose contents. Consequently, the muscle showed a higher saturated, monounsaturated, and polyunsaturated fatty acid contents than the liver. Although the gonad showed no significant temporal effect in the lipids and proteins contents, an increasing trend of each biochemical constituent, fatty acid group and gonadosomatic index were found from autumn to winter. Consistently, the glucose and total energy content as well Fulton's condition factor were significantly higher in winter. These findings reflect the spatial-temporal physiological dynamic of swordfish based on the storage of energy reserves in different organs during its feeding period. In this way, the products obtained from swordfish could have an added value depending on the season and capture zone, which could benefit the exploitation and regulation measures of this resource under an ecological approach of conservation and sustainability in the SEPO.

Non-linear effects on the population performance of Bighead Carp under different maturation schedules

Bighead Carp currently threatens to invade the Laurentian Great Lakes from the Mississippi River, but the novel climatic conditions it will encounter by expanding northwards could affect its population performance. Bighead Carp in colder climates exhibits slower growth and matures later, with later maturation typically leading to larger adult size and increased fecundity and survival. Accordingly, the life-history strategies of Bighead Carp at its northern range limits could differ from those observed in its current invaded range. To explore how population performance could differ across changing environmental conditions, we used a stage- and age-based matrix population model parameterized with values reported for Bighead Carp populations around the world. The model was used to evaluate how different ages of maturity and their resulting impacts to body size, survival, and fecundity could impact rates of population growth and establishment. Age of maturity had a non-linear effect on population growth, with maturation at intermediate ages (4-6 years) resulting in better performance. However, performance differed less between maturation ages when fecundity was allowed to increase disproportionately with body size. Greater population growth at younger ages of maturity suggest that invasion at lower latitudes could enable establishment in fewer years due to faster rates of development in warmer temperatures. Across all maturation schedules, population growth was most sensitive to the recruitment of age-1 individuals and least sensitive to adult survival, and vital rates overall varied more in their contribution to population growth at younger ages of maturity. Thus, understanding the factors that control age-1 recruitment would inform projections of population performance for Bighead Carp in the Laurentian Great Lakes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10530-023-03126-z.

Copepod life history evolution under high- and low-food regimes

Copepods play a critical role in the carbon cycle of the planet - they mediate the sequestration of carbon into the deep ocean and are the trophic link between phytoplankton and marine food webs. Global change stressors that decrease copepod productivity create the potential for catastrophic positive feedback loops. Accordingly, a growing list of studies examine the evolutionary capacity of copepods to adapt to the two primary stressors associated with global change: warmer temperatures and lower pH. But the evolutionary capacity of copepods to adapt to changing food regimes, the third major stressor associated with global change, remains unknown. We used experimental evolution to explore how a 10-fold difference in food availability affects life history evolution in the copepod, Tisbe sp. over 2 years, and spanning 30+ generations. Different food regimes evoked evolutionary responses across the entire copepod life history: we observed evolution in body size, size-fecundity relationships and offspring investment strategies. Our results suggest that changes to food regimes reshape life histories and that cryptic evolution in traits such as body size is likely. We demonstrate that evolution in response to changes in ocean productivity will alter consumer life histories and may distort trophic links in marine foodchains. Evolution in response to changing phytoplankton productivity may alter the efficacy of the global carbon pump in ways that have not been anticipated until now.

Sex-specific transgenerational plasticity: developmental temperatures of mothers and fathers have different effects on sons and daughters

Each parent can influence offspring phenotype via provisioning of the zygote or sex-specific DNA methylation. Transgenerational plasticity may therefore depend on the environmental conditions experienced by each parent. We tested this hypothesis by conducting a fully factorial experiment across three generations of guppies (Poecilia reticulata), determining the effects of warm (28°C) and cold (21°C) thermal backgrounds of mothers and fathers on mass and length, and thermal performance (sustained and sprint swimming speeds, citrate synthase and lactate dehydrogenase activities; 18, 24, 28, 32 and 36°C test temperatures) of sons and daughters. Offspring sex was significant for all traits except for sprint speed. Warmer mothers produced sons and daughters with reduced mass and length, and warmer fathers produced shorter sons. Sustained swimming speed (Ucrit) of male offspring was greatest when both parents were raised at 28°C, and warmer fathers produced daughters with greater Ucrit. Similarly, warmer fathers produced sons and daughters with greater metabolic capacity. We show that the thermal variation experienced by parents can modify offspring phenotype, and that predicting the impacts of environmental change on populations would require knowledge of the thermal background of each mother and father, particularly where sexes are spatially segregated.

Inferring the ecology of north-Pacific albacore tuna from catch-and-effort data

Catch-and-effort data are among the primary sources of information for assessing the status of terrestrial wildlife and fish. In fishery science, elaborate stock-assessment models are fitted to such data in order to estimate fish-population sizes and guide management decisions. Given the importance of catch-and-effort data, we scoured a comprehensive dataset pertaining to albacore tuna (Thunnus alalunga) in the north Pacific Ocean for novel ecological information content about this commercially valuable species. Specifically, we used unsupervised learning based on finite mixture modelling to reveal that the north Pacific albacore-tuna stock can be divided into four pseudo-cohorts. We discovered that smaller body mass pseudo-cohorts inhabit relatively high-subtropical to temperate-latitudes, with hotspots off the coast of Japan. Larger body mass pseudo-cohorts inhabit lower-tropical to subtropical-latitudes, with hotspots in the western and central north Pacific. These results offer evidence that albacore tuna prefer different habitats depending on their body mass, and point to long-term migratory routes for the species that the current tagging technology is unlikely to capture in full. We discuss the implications of the results for data-driven modelling of albacore tuna in the north Pacific, as well as the management of the north Pacific albacore-tuna fishery.

Validation of a microwave energy meter to non-lethally estimate energetic reserves in adult sturgeon

Whole-body (WB) energetic reserves influence fish survival, growth, and reproduction but are typically quantified using lethal methods (i.e. proximate analyses) or interpreted through body condition indices. Energetic reserves can impact population dynamics through influences on growth rates, age-at-first-reproductive-maturity, and spawning periodicity at the individual-fish level, especially in long-lived sturgeon species. Therefore, a non-lethal tool to track the energetic reserves of endangered sturgeon populations could inform adaptive management and further our understanding of the sturgeon's biology. The Distell Fatmeter is a microwave energy meter that has been validated to non-lethally estimate energetic reserves in some fish species, but never successfully for sturgeon. Here, stepwise linear regressions were applied to test commonly monitored body metrics and Fatmeter measurements at nine different anatomical sites on captive adult pallid sturgeon (Scaphirhynchus albus; total length of 790-1015 mm; WB lipid of 13.9-33.3%) compared with WB lipid and energy content determined by proximate analyses. Fatmeter measurements alone explained approximately 70% of the variation in WB energetic reserves, which outperformed models considering body metrics alone by a margin of approximately 20%. The top-ranked models based on AICc score (second-order Akaike Information Criterion) included a combination of body metrics and Fatmeter measurements and accounted for up to 76% of the variation in WB lipid and energy. We recommend the incorporation of Fatmeter measurements at a single site located dorsally to the lateral scutes at the posterior end of the fish above the pelvic fins (U-P) into conservation monitoring programs for adult pallid sturgeon (total length [TL] ≥ 790 mm; fork length [FL] ≥ 715 mm) and the cautious application of Fatmeter measurements for sturgeon between 435 and 790 mm TL (375-715 mm FL). Measurements at this U-P site combined with body mass explained approximately 75% of the variation in WB lipid and energy.

The effect of temperature and dietary energy content on female maturation and egg nutritional content in Atlantic salmon

The environment experienced by a female influences reproductive traits in many species of fish. Environmental factors such as temperature and diet are not only important mediators of female maturation and reproduction but also of egg traits and offspring fitness through maternal provisioning. In this study, we use 3-year-old tank-reared Atlantic salmon from two Finnish populations to investigate the effect of temperature and diet on maturation and egg traits. We show that a temperature difference of 2°C is sufficient to delay maturation in female Atlantic salmon whereas a 22% reduction in dietary energy content had no effect on maturation. Diet did not influence the body size, condition or fecundity of the mature females or the size or protein content of the eggs. However, a higher energy diet increased egg lipid content. Neither female body size nor condition were associated with egg size or fat/protein composition. Our results indicate that female salmon that have a poorer diet in terms of energy content may have a reproductive disadvantage due to the lower energy provisioning of eggs. This disadvantage has the potential to translate into fitness consequences for their offspring.

Shrinking body size and climate warming: Many freshwater salmonids do not follow the rule

Declining body size is believed to be a universal response to climate warming and has been documented in numerous studies of marine and anadromous fishes. The Salmonidae are a family of coldwater fishes considered to be among the most sensitive species to climate warming; however, whether the shrinking body size response holds true for freshwater salmonids has yet to be examined at a broad spatial scale. We compiled observations of individual fish lengths from long-term surveys across the Northern Hemisphere for 12 species of freshwater salmonids and used linear mixed models to test for spatial and temporal trends in body size (fish length) spanning recent decades. Contrary to expectations, we found a significant increase in length overall but with high variability in trends among populations and species. More than two-thirds of the populations we examined increased in length over time. Secondary regressions revealed larger-bodied populations are experiencing greater increases in length than smaller-bodied populations. Mean water temperature was weakly predictive of changes in body length but overall minimal influences of environmental variables suggest that it is difficult to predict an organism's response to changing temperatures by solely looking at climatic factors. Our results suggest that declining body size is not universal, and the response of fishes to climate change may be largely influenced by local factors. It is important to know that we cannot assume the effects of climate change are predictable and negative at a large spatial scale.

Life history optimisation drives latitudinal gradients and responses to global change in marine fishes

Within many species, and particularly fish, fecundity does not scale with mass linearly; instead, it scales disproportionately. Disproportionate intraspecific size-reproduction relationships contradict most theories of biological growth and present challenges for the management of biological systems. Yet the drivers of reproductive scaling remain obscure and systematic predictors of how and why reproduction scaling varies are lacking. Here, we parameterise life history optimisation model to predict global patterns in the life histories of marine fishes. Our model predict latitudinal trends in life histories: Polar fish should reproduce at a later age and show steeper reproductive scaling than tropical fish. We tested and confirmed these predictions using a new, global dataset of marine fish life histories, demonstrating that the risks of mortality shape maturation and reproductive scaling. Our model also predicts that global warming will profoundly reshape fish life histories, favouring earlier reproduction, smaller body sizes, and lower mass-specific reproductive outputs, with worrying consequences for population persistence.

Enhancement of zebrafish sperm production via a large body-sized surrogate with germ cell transplantation

Zebrafish (Danio rerio) is a commonly-used vertebrate model species for many research areas. However, its low milt volume limits effective cryopreservation of sperm from a single individual and often precludes dividing a single semen sample to conduct multiple downstream procedures such as genomic DNA/RNA extraction and in-vitro fertilization. Here, we apply germ stem cell transplantation to increase zebrafish sperm production in a closely related larger species from the same subfamily, giant danio Devario aequipinnatus. The endogenous germ cell of the host is depleted by dead-end morpholino antisense oligonucleotide. Histology of the sterile gonad and quantitative PCR of gonadal tissue reveals all sterile giant danio develop the male phenotype. Spermatogonial cells of Tg(ddx4:egfp) transgenic zebrafish are transplanted into sterile giant danio larvae, and 22% of recipients (germline chimera) produce donor-derived sperm at sexual maturation. The germline chimera produce approximately three-fold the volume of sperm and 10-fold the spermatozoon concentration of the donor. The donor-derived sperm is functional and gives rise to viable progeny upon fertilization of donor oocytes. We show that the issue of low milt volume can be effectively addressed by employing a larger surrogate parent.

Declines in body size of sockeye salmon associated with increased competition in the ocean

Declining body sizes have been documented for several species of Pacific salmon; however, whether size declines are caused mainly by ocean warming or other ecological factors, and whether they result primarily from trends in age at maturation or changing growth rates remain poorly understood. We quantified changes in mean body size and contributions from shifting size-at-age and age structure of mature sockeye salmon returning to Bristol Bay, Alaska, over the past 60 years. Mean length declined by 3%, corresponding to a 10% decline in mean body mass, since the early 1960s, though much of this decline occurred since the early 2000s. Changes in size-at-age were the dominant cause of body size declines and were more consistent than trends in age structure among the major rivers that flow into Bristol Bay. Annual variation in size-at-age was largely explained by competition among Bristol Bay sockeye salmon and interspecific competition with other salmon in the North Pacific Ocean. Warm winters were associated with better growth of sockeye salmon, whereas warm summers were associated with reduced growth. Our findings point to competition at sea as the main driver of sockeye salmon size declines, and emphasize the trade-off between fish abundance and body size.

Long-term variability in spawning stock age structure influences climate-recruitment link for Barents Sea cod

Fish populations may spawn a vast number of offspring, while only a small and highly variable fraction of a new cohort survives long enough to enter into the fisheries as recruits. It is intuitive that the size and state of the spawning stock, the adult part of the fish population, is important for recruitment. Additionally, environmental conditions can greatly influence survival through vulnerable early life stages until recruitment. To understand what regulates recruitment, an essential part of fish population dynamics, it is thus necessary to explain the impact of fluctuations in both spawning stock and environment, including interactions. Here, we examine if the connection between the environment and recruitment is affected by the state of the spawning stock, including biomass, mean age and age diversity. Specifically, we re-evaluate the hypothesis stating that recruitment from a spawning stock dominated by young fish and few age classes is more vulnerable to environmental fluctuations. We expand upon earlier work on the Barents Sea stock of Atlantic cod, now with data series extended in time both backwards and forwards to cover the period 1922-2019. While our findings are correlative and cannot prove a specific cause and effect mechanism, they support earlier work and strengthen the evidence for the hypothesis above. Furthermore, this study supports that advice to fisheries management should include considerations of environmental status.

Optimal energy allocation trade-off driven by size-dependent physiological and demographic responses to warming

Body size-dependent physiological effects of temperature influence individual growth, reproduction, and survival, which govern animal population responses to global warming. Considerable knowledge has been established on how such effects can affect population growth and size structure, but less is known of their potential role in temperature-driven adaptation in life-history traits. In this study, we ask how warming affects the optimal allocation of energy between growth and reproduction and disentangle the underlying fitness trade-offs. To this end, we develop a novel dynamic energy budget integral projection model (DEB-IPM), linking individuals' size- and temperature-dependent consumption and maintenance via somatic growth, reproduction, and size-dependent energy allocation to emergent population responses. At the population level, we calculate the long-term population growth rate (fitness) and stable size structure emerging from demographic processes. Applying the model to an example of pike (Esox lucius), we find that optimal energy allocation to growth decreases with warming. Furthermore, we demonstrate how growth, fecundity, and survival contribute to this change in optimal allocation. Higher energy allocation to somatic growth at low temperatures increases fitness through survival of small individuals and through the reproduction of larger individuals. In contrast, at high temperatures, increased allocation to reproduction is favored because warming induces faster somatic growth of small individuals and increased fecundity but reduced growth and higher mortality of larger individuals. Reduced optimum allocation to growth leads to further reductions in body size and an increasingly truncated population size structure with warming. Our study demonstrates how, by incorporating general physiological mechanisms driving the temperature dependence of life-history traits, the DEB-IPM framework is useful for investigating the adaptation of size-structured organisms to warming.

Evidence for reproductive senescence across ray-finned fishes: A review

The origin, incidence, and consequences of reproductive senescence vary greatly across the tree of life. In vertebrates, research on reproductive senescence has been mainly focused on mammals and birds, demonstrating that its variation is largely linked to critical life history traits, such as growth patterns, juvenile, and adult mortality, and reproductive strategy. Fishes represent half of the vertebrate taxonomic diversity and display remarkable variation in life history. Based on a thorough literature review, we summarize current evidence on reproductive senescence in ray-finned fishes (Actinopterygii). While survival and physiological senescence are acknowledged in fish, their potential age-related reproductive decline has often been disregarded due to the prevalence of indeterminate growth. We demonstrate that age-related reproductive decline is reported across fish phylogeny, environments, and traits. An important point of our review is that the incidence of reproductive senescence in a species depends on both the number of studies for that species and the coverage of its maximum lifespan by the study. Reproductive senescence was documented for one-third of the studied fish species, with females suffering an age-related decline in reproductive traits less often than males or both parents combined. Neither parental care nor migratory strategy corresponded with the occurrence of reproductive senescence in fish. The traits that were affected by reproductive senescence most often were sex-specific, with pre-mating and mating categories of traits declining in females and sperm quality and quantity in males. We also demonstrate that reproductive senescence can be buffered by indeterminate growth. We provide rich evidence of reproductive senescence across ray-finned fishes, but we highlight the need for better data on age-related reproduction in fishes.

Energy acquisition strategy for reproduction in a semelparous squid

Background

Energy demand for reproduction leads to a wide diversity of foraging and life-history strategy among wild animals, linking to a common objective to maximize reproductive success. Semelparous squid species in particular can use up to 50% of the total energy intake for reproduction. However, the energy acquisition strategy for reproduction is still a controversial issue regarding whether the squid shift in diet ontogenetically. Here we used Argentinean shortfin squid (Illex argentinus) as a case study to investigate the strategy of energy acquisition for reproduction, by analyzing energy density of the squid’s reproductive tissues including ovary, nidamental glands and oviduct eggs, and stable isotopes and fatty acids of the squid’s ovary.

Results

The reproductive energy (the sum of the energy accumulated in ovary, nidamental glands and oviduct eggs) increased significantly with maturation. The ovary nitrogen stable isotopes (δ15N) showed a significant increase with maturation, but the increase by maturity stage was not equal to the typical enrichment of about 3‰ per trophic level. Isotopic niche width showed an increasing trend with maturation, and isotopic niche space exhibited greater overlap at advanced maturity stages. The relative amounts of 16:0, 20:5n3 and 20:4n6 in the ovary, tracing for carnivores and top predators, increased after the onset of maturation. The overall fatty acid profiles of the ovary showed significant differences among maturity stages, but obvious overlaps were found for mature squids. Mixed-effects model results revealed that reproductive energy was positively correlated with δ15N values. The reproductive energy was also positively related to the relative amounts of 18:0 and 20:4n6, respectively tracing for herbivores and top predators.

Conclusions

Our results validate that the squid shifts to feed on higher trophic prey for reproduction as energy demand increases once maturation commences. However, the squid does not shift feeding habits at a trophic level but instead broadens prey spectrum, coupled with increasing intake of higher trophic prey items, to meet the energy demand for reproduction. Such energy acquisition strategy may be selected by the squid to maximize reproductive success by balancing energy intake and expenditure from foraging, warranting future studies that aim to clarify such strategy for reproduction among semelparous species.

Energy utilization during ovarian development of the cichlid fish Oreochromis mossambicus (Peters) inhabiting a perennial lentic water body in Bangalore, India

Mozambique tilapia Oreochromis mossambicus (Peters) is an invasive fish and a continuous breeder in inland waters of India. Present investigation highlights the distinct developmental stages of developing ovary and associated changes in the energy content. This investigation helps to understand the allocation of energy for development of eggs, prespawn and also oral brooding by the female. Although it is a continuous breeder, based on size of the ovary, number of eggs, their size and energy content, immature, early maturing, developing, prespawning and spawning stages are clearly noticed. Egg diameter during development of ovary varied between 0.31 mm (immature) and 2.21 mm (spawning). Energy content of ovary from immature to spawning stage ranged from 20.7515 kJ g^-1 dry ovary to 31.1560 kJ g^-1 dry ovary. Nearly 28.73% of energy content of ovary is expended for spawning. Similarly, yolk-sac fry utilized nearly 25.85% of energy of the fertilized egg for its development. Energy content of ovary of mouth-brooding female averaged 22.9528 kJ g^-1 dry ovary, which is comparable to energy content of early maturing stage of ovary (24.5558 kJ g^-1 dry ovary). A strong correlation between body weight and energy content of the developing ovary (P < 0.01), and between ovary weight and energy content of ovary (P < 0.01), was evident. During mouth-brooding, the fish continues to allocate energy to its developing ovary. Energy investment by the fish is the result of simultaneous processes associated with gonadal and somatic energy. As body size growth and gonadal development are interconnected, information on energy utilization by an iteroparous mouth-brooding fish could provide the pattern of energy allocation during ovarian developmental phase. Further details of energy utilization, as explained in this paper, could be used as one of the factors to predict the efficiency of fish production.

Genetic decline and recovery of a demographically rebuilt fishery species

The demographic history of a population is important for conservation and evolution, but this history is unknown for many populations. Methods that use genomic data have been developed to infer demography, but they can be challenging to implement and interpret, particularly for large populations. Thus, understanding if and when genetic estimates of demography correspond to true population history is important for assessing the performance of these genetic methods. Here, we used double-digest restriction-site associated DNA (ddRAD) sequencing data from archived collections of larval summer flounder (Paralichthys dentatus, n = 279) from three cohorts (1994-1995, 1997-1998 and 2008-2009) along the U.S. East coast to examine how contemporary effective population size and genetic diversity responded to changes in abundance in a natural population. Despite little to no detectable change in genetic diversity, coalescent-based demographic modelling from site frequency spectra revealed that summer flounder effective population size declined dramatically in the early 1980s. The timing and direction of change corresponded well with the observed decline in spawning stock census abundance in the late 1980s from independent fish surveys. Census abundance subsequently recovered and achieved the prebottleneck size. Effective population size also grew following the bottleneck. Our results for summer flounder demonstrate that genetic sampling and site frequency spectra can be useful for detecting population dynamics, even in species with large effective sizes.

Seasonal variation in cuckoldry rates in the socially monogamous cichlid fish Variabilichromis moorii

Mating patterns in animal populations can respond to environmental conditions and consequently vary across time. To examine this variation in nature, studies must include temporal replicates from the same population. Here, we report temporal variation in genetic parentage in the socially monogamous cichlid Variabilichromis moorii from Lake Tanganyika, using samples of broods and their brood-tending parents that were collected across five field trips from the same study population. The sampled broods were either spawned during the dry season (three field trips) or during the rainy season (two trips). In all seasons, we detected substantial rates of extra-pair paternity, which were ascribed to cuckoldry by bachelor males. Paternity shares of brood-tending males were consistently higher, and the numbers of sires per brood were consistently lower, in broods that were spawned in the dry seasons compared to broods from the rainy seasons. In contrast, the strength of size-assortative pairing in our V. moorii population did not vary temporally. Seasonal fluctuations in environmental conditions, such as water turbidity, are proposed as a mechanism behind variable cuckolder pressure. Our data demonstrate the utility of long-term monitoring to improve our understanding of animal mating patterns.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10750-022-05042-0.