Abstract Size at the start of life reflects the initial per offspring parental investment—including both the embryo and the nutrients supplied to it. Initial offspring size can vary substantially, both within and among species. Within species, increasing offspring size can enhance growth, reproduction, competitive ability, and reduce susceptibility to predation and starvation later in life, that can ultimately increase fitness. Previous work has suggested that the fitness benefits of larger offspring size may be driven by energy expenditure during development—or how offspring metabolic rate scales with offspring size. Despite the importance of early-life energy expenditure in shaping later life fitness trajectories, consideration of among-species scaling of metabolic rate at the time of birth as a potential source of general metabolic scaling patterns has been overlooked by theory. Here, we review the patterns and processes of energy expenditure at the start of life when mortality is often greatest. We compile existing data on metabolic rate and offspring size for 191 ectotherm species spanning eight phyla and use phylogenetically controlled methods to quantify among-species scaling patterns. Across a 109-fold mass range, we find that offspring metabolic rate scales hypometrically with size, with an overall scaling exponent of 0.66. This exponent varies across ontogenetic stage and feeding activity, but is consistently hypometric, including across environmental temperatures. Despite differences in parental investment, life history and habitat, large-offspring species use relatively less energy as a proportion of size, compared with small-offspring species. Greater residual energy can be used to fuel the next stages of life, particularly in low-resource environments. Based on available evidence, we conclude that, while large knowledge gaps remain, the evolution of offspring size is likely shaped by context-dependent selection acting on correlated traits, including metabolic rates maintaining hypometric scaling, which operates within broader physical constraints.
more »
« less
Size‐dependence of food intake and mortality interact with temperature and seasonality to drive diversity in fish life histories
Understanding how growth and reproduction will adapt to changing environmental conditions is a fundamental question in evolutionary ecology, but predicting the responses of specific taxa is challenging. Analyses of the physiological effects of climate change upon life history evolution rarely consider alternative hypothesized mechanisms, such as size‐dependent foraging and the risk of predation, simultaneously shaping optimal growth patterns. To test for interactions between these mechanisms, we embedded a state‐dependent energetic model in an ecosystem size‐spectrum to ask whether prey availability (foraging) and risk of predation experienced by individual fish can explain observed diversity in life histories of fishes. We found that asymptotic growth emerged from size‐based foraging and reproductive and mortality patterns in the context of ecosystem food web interactions. While more productive ecosystems led to larger body sizes, the effects of temperature on metabolic costs had only small effects on size. To validate our model, we ran it for abiotic scenarios corresponding to the ecological lifestyles of three tuna species, considering environments that included seasonal variation in temperature. We successfully predicted realistic patterns of growth, reproduction, and mortality of all three tuna species. We found that individuals grew larger when environmental conditions varied seasonally, and spawning was restricted to part of the year (corresponding to their migration from temperate to tropical waters). Growing larger was advantageous because foraging and spawning opportunities were seasonally constrained. This mechanism could explain the evolution of gigantism in temperate tunas. Our approach addresses variation in food availability and individual risk as well as metabolic processes and offers a promising approach to understand fish life‐history responses to changing ocean conditions.
more » « less- NSF-PAR ID:
- 10489898
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Evolutionary Applications
- Volume:
- 17
- Issue:
- 2
- ISSN:
- 1752-4571
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)There is increasing recognition that low dissolved oxygen (DO) and low pH conditions co-occur in many coastal and open ocean environments. Within temperate ecosystems, these conditions not only develop seasonally as temperatures rise and metabolic rates accelerate, but can also display strong diurnal variability, especially in shallow systems where photosynthetic rates ameliorate hypoxia and acidification by day. Despite the widespread, global co-occurrence of low pH and low DO and the likelihood that these conditions may negatively impact marine life, very few studies have actually assessed the extent to which the combination of both stressors elicits additive, synergistic or antagonistic effects in marine organisms. We review the evidence from published factorial experiments that used static and/or fluctuating pH and DO levels to examine different traits (e.g. survival, growth, metabolism), life stages and species across a broad taxonomic spectrum. Additive negative effects of combined low pH and low DO appear to be most common; however, synergistic negative effects have also been observed. Neither the occurrence nor the strength of these synergistic impacts is currently predictable, and therefore, the true threat of concurrent acidification and hypoxia to marine food webs and fisheries is still not fully understood. Addressing this knowledge gap will require an expansion of multi-stressor approaches in experimental and field studies, and the development of a predictive framework. In consideration of marine policy, we note that DO criteria in coastal waters have been developed without consideration of concurrent pH levels. Given the persistence of concurrent low pH–low DO conditions in estuaries and the increased mortality experienced by fish and bivalves under concurrent acidification and hypoxia compared with hypoxia alone, we conclude that such DO criteria may leave coastal fisheries more vulnerable to population reductions than previously anticipated.more » « less
-
Abstract Atlantic bluefin tuna (ABT) (Thunnus thynnus) travel long distances to spawn in oligotrophic regions of the Gulf of Mexico (GoM) which suggests these regions offer some unique benefit to offspring survival. To better understand how larval survival varies within the GoM a spatially explicit, Lagrangian, individual-based model was developed that simulates dispersal and mortality of ABT early life stages within realistic predator and prey fields during the spawning periods from 1993 to 2012. The model estimates that starvation is the largest cumulative source of mortality associated with an early critical period. However, elevated predation on older larvae is identified as the main factor limiting survival to late postflexion. As a result, first-feeding larvae have higher survival on the shelf where food is abundant, whereas older larvae have higher survival in the open ocean with fewer predators, making the shelf break an optimal spawning area. The modeling framework developed in this study explicitly simulates both physical and biological factors that impact larval survival and hence could be used to support ecosystem based management efforts for ABT under current and future climate conditions.more » « less
-
more » « less
Abstract The growth of any organism depends on habitat conditions, food availability, and their seasonal interactions. Yet in the vast literature on Pacific salmon (
Oncorhynchus ), the seasonal interaction between habitat conditions and food availability has received relatively little attention. We examined juvenileOncorhynchus mykiss rearing, physical habitat, and resource phenologies in two Mediterranean coastal streams—one perennial, cool, and shaded and the other intermittent, seasonally warm, and sunny. We used a bioenergetic model to investigate the timing and magnitude of growth potential for drift‐foragingO. mykiss during the spring and summer in both systems. Growth potential peaked at least 2 months earlier in the intermittent stream than in the perennial stream. By early summer (June), growth potential had declined in the intermittent stream, whereas growth rates were peaking in the perennial stream. However, the mid‐July lipid content of juvenileO. mykiss in the intermittent stream was nearly twice that of fish in the perennial stream. By late summer (August), foraging profitability declined in both streams, as abiotic conditions in the intermittent stream approached lethal. In contrast, the perennial stream maintained suitable abiotic conditions even though the growth rate was low. We suggest that the divergent resource phenologies and seasonal mortality risks experienced by anadromousO. mykiss rearing in these streams could drive diversification of traits governing size, age, and timing of outmigration. -
more » « less
Abstract Most fishing is inherently size‐selective, in that fishers preferentially select a subset of the population for harvest based on economic incentives associated with different‐sized fish. Size‐selective fishing influences the targeted population and fishery performance in multiple ways, including changing the reproductive capacity of the target population and altering fishery yield. Understanding how social–ecological variability, including size selectivity, affects target species populations is critical for fisheries management to optimize the benefits of fisheries and the ecological impacts on target populations. In this study, we used yield per recruit, spawning stock biomass per recruit, and length‐based spawning potential ratio models to explore how a range of size selectivity scenarios affect fishery and population productivity for Mexican chocolate clams,
Megapitaria squalida , in Loreto, Baja California Sur, Mexico. We found that alternate slot limits result in trade‐offs between fishery yield and reproductive productivity of the target population. A more restrictive slot limit reduced the proportion of the population available to harvest, resulting in higher reproductive capacity of the population, compared to a less restrictive slot limit, conditional on the rate of fishing mortality. In the long run, a more restrictive slot limit will likely lead to a higher number of recruits, larger stock size, and higher long‐term fishery yield relative to a less restrictive scenario. Our findings highlight that how people fish matters, perhaps as much as the quantity of fish harvested; size‐selective fishing that aligns with the life history of target populations and stakeholders’ goals is critical to sustaining fisheries and the valuable food and livelihoods they provide.
