Somatic Growth Rate Research Articles

Tasas de crecimiento somático de tortuga carey, Eretmochelys imbricata, en el Parque Nacional Natural Gorgona, Colombia, entre 2004 y 2018

La tortuga carey, Eretmochelys imbricata, se encuentra a nivel global en peligro crítico de extinción, y la información demográfica en el Océano Pacífico Oriental es limitada. Por esta razón, esta investigación evalúa las tasas de crecimiento somático en una agregación de individuos inmaduros de tortuga carey empleando el método de captura-marca-recaptura en los arrecifes coralinos de Playa Blanca y la Azufrada en el Parque Nacional Natural Gorgona, Colombia. Entre 2004 y 2018 se realizaron 89 capturas de 49 individuos de tortuga carey. El largo curvo del caparazón promedio (LCC) obtenido fue de 41,6 cm (rango 32-58 cm) y el largo recto del caparazón promedio (LRC) fue de 39,1 cm (rango 30,0-54,1 cm), lo que muestra que estos arrecifes son áreas de forrajeo importantes para individuos inmaduros de esta especie. El índice de condición corporal promedio fue de 1,3 (rango 1,0-1,5). Esto sugiere que las condiciones ambientales mantienen en buen estado la salud de esta agregación. Usando el modelo de crecimiento de von Bertalanffy y estableciendo una talla máxima (L∞) de 63 cm de LCC (donde se obtiene el menor coeficiente de variación), se estimó una k de 0,081 y una tasa anual de crecimiento promedio de 1,5 ± 1,8 cm/año. Esto indica que los individuos en esta agregación estarían alcanzando una LCC de 63 cm entre los 33 y 34 años, talla cercana a la de madurez sexual en la región del Pacífico oriental (aproximadamente 66 cm LCC). Lo anterior ratifica la vulnerabilidad de esta especie debido a las lentas tasas de crecimiento somático y madurez sexual tardía. Se sugiere que los esfuerzos de conservación para esta especie deben ser a largo plazo para procurar su recuperación, en vista de que especies con estas características tienden a expresar tasas de crecimiento poblacional muy bajas.

Improved estimation of age composition by accounting for spatiotemporal variability in somatic growth

Age composition is defined as the proportion of a fish population belonging to each age class and is an informative input to stock assessment models. Variations in somatic growth rates may lead to larger errors in age composition estimates. To reduce this source of error, we compared the performance of four methods for estimating age compositions of a simulated fish population: two methods based on age–length keys (ALK, pooled and annual) and two model-based approaches (generalized additive models (GAMs) and continuation ratio logits (CRLs)). CRL was the most robust and precise method, followed by annual ALKs, particularly when significant growth variability was present. We applied these methods to survey age subsample data for Pacific cod (Gadus macrocephalus) in the eastern Bering Sea, estimating age compositions that were then incorporated in its stock assessment model. The model that included age compositions estimated by CRL displayed the highest consistency with other data in the model. CRL approach has utility for estimating age compositions employed in stock assessment models, especially when substantial variation in somatic growth is present.

Enhancing hybrid Liquidambar somatic seedling production using a temporary immersion bioreactor

Temporary immersion bioreactors can improve hybrid sweetgum somatic embryo conversion and somatic seedling growth rates compared to semisolid medium, significantly improving somatic seedling production efficiency for hybrid sweetgum, an emerging woody biomass crop. Fast-growing hybrid southern hardwood trees should make excellent material for woody biomass production in the Southeastern US, if elite clones can be identified and efficiently propagated. We have enhanced the potential of sweetgum (Liquidambar styraciflua) as a biomass species by generating hybrids between the tree and its Chinese relative, Liquidambar formosana, and propagating the most promising clones via somatic embryogenesis. Some of the hybrid clones have already demonstrated superior biomass productivity compared to elite L. styraciflua trees. However, production of somatic seedlings from these clones remains labor-intensive. Bioreactors, specifically temporary immersion designs, such as the RITA®, have been applied to improve the efficiency of in vitro propagation of a number of woody species. We tested RITA® bioreactors for their potential to improve the production efficiency of high-quality hybrid sweetgum somatic seedlings. In one tested genotype, a RITA® with 50 somatic embryos had about 66% higher conversion frequency (p < 0.05) and produced about 40% more “high-quality” somatic seedlings (p < 0.05) than when somatic embryos were germinated on semisolid medium in GA-7 vessels. In all the genotypes we tested, somatic seedlings produced in RITA® bioreactors had higher survival percentages by the end of acclimatization than somatic seedlings produced on semisolid medium in GA-7 vessels.

Changes in prey, turbidity, and competition reduce somatic growth and cause the collapse of a fish population

AbstractSomatic growth exerts strong control on patterns in the abundance of animal populations via effects on maturation, fecundity, and survival rates of juveniles and adults. In this paper, we quantify abiotic and biotic drivers of rainbow trout growth in the Colorado River, Arizona, USA, and the resulting impact on spatial and temporal variation in abundance. Inferences are based on ~10,000 observations of individual growth rates obtained through an intensive mark–recapture effort conducted over 5 yrs (2012–2016) in a 130‐km long study segment downstream of Glen Canyon Dam. Prey availability, turbidity‐driven feeding efficiency, and intraspecific competition were the dominant drivers of rainbow trout growth. Discharge, water temperature, and solar insulation were also evaluated but had a smaller influence. Mixed‐effect models explained 79–82% of the variability in observed growth rates, with fixed covariate effects explaining 79–87% of the total variation in growth parameters across five reaches and 18 quarterly sampling intervals. Reductions in growth owing in part to a phosphorous‐driven decline in prey availability, led to a substantive loss in mass and poor fish condition. This in turn lowered survival rates and delayed maturation, which led to a rapid decline in abundance and later recruitments. Reductions in feeding efficiency, due to episodic inputs of fine sediment from tributaries, and warmer water temperatures, contributed to reduced growth in downstream reaches, which led to more severe declines in abundance. Somatic growth rates increased following the population collapse due to reduced competition, and in the absence of substantive increases in prey availability. Our study elucidates important linkages between abiotic and biotic factors, somatic growth, and vital rates, and demonstrates how variation in somatic growth influences temporal and spatial patterns in abundance.

The effect of food availability on thermal stress in Daphnia magna: trade-offs among oxidative stress, somatic growth, and reproduction

The effects of food availability on thermal stress in Daphnia magna were investigated for 21 days, with a hypothesis that lower food condition would increase the adverse effect of elevated temperature on D. magna. Under higher food conditions (5 × 105 cells mL−1), elevated temperature (25 °C) did not induce higher oxidative stress (levels of antioxidant enzymes and lipid peroxidation) than reference temperature (20 °C). Thus, reproduction (number of offspring per female) was significantly (p < 0.05) higher at 25 °C compared with that at 20 °C. Under lower food condition (2 × 105 cells mL−1), however, elevated temperature significantly (p < 0.05) induced antioxidant enzyme activity (superoxide dismutase and catalase) and reduced adult somatic growth rate (5–21 days), whereas there was no significant change in reproduction between the two temperature groups. These findings suggest that food availability greatly influences the effect of elevated temperature on D. magna, possibly resulting in a trade-off among oxidative stress defense, somatic growth, and reproduction.

Intrapopulation variability in a functional trait: Susceptibility ofDaphniato limitation by dietary fatty acids

AbstractFunctional traits are measurable characteristics of an organism that have an impact on its fitness. Variation in functional traits between and among species has been suggested to represent the basis for competition and selection, thus allowing for evolution in natural populations.In freshwater ecosystems, the availability of essential polyunsaturated fatty acids (PUFAs), in particular ω3‐ and ω6‐PUFAs, determines the food quality of phytoplankton for the herbivorous zooplanktonDaphnia, an unselective filter feeder. The content of such essential PUFAs in the phytoplankton is thus a functional phytoplankton trait affecting the trophic transfer efficiency and dynamics at the pelagic plant–herbivore interface.In turn, the susceptibility of consumers to become limited by the availability of essential PUFAs is a fitness‐determining trait ofDaphniagenotypes, and variability of this herbivore trait may thus affect the daphnids’ intrapopulation competition. To estimate the intrapopulation variation in susceptibility, we isolated clonal lines ofDaphnia longispinafrom a natural population and compared the strength of their limitation by dietary PUFA availability via standardised laboratory growth assays. We used a liposome supplementation technique to enrich a PUFA‐poor green alga with essential ω3‐ and ω6‐PUFAs and determined juvenile somatic growth rate of differentD. longispinagenotypes as a fitness proxy.As expected,D. longispinagenotypes that coexisted in a natural population differed markedly in their specific patterns of susceptibility to dietary PUFA availability. On average, theD. longispinapopulation was more strongly susceptible to limitations in the availability of the ω6‐PUFA arachidonic acid (20:4ω6) than to limitations in the availability of ω3‐PUFAs α‐linolenic acid (18:3ω3) and eicosapentaenoic acid (20:5ω3).The ability to cope with PUFA limitation is thus a crucial trait that can probably affect intraspecific competition andDaphniapopulation structure. Therefore, we suggest that such intrapopulation variation in susceptibility to absence of dietary PUFAs might be one of the driving forces of natural selection and local adaptation among freshwater zooplankton.

Regional environmental drivers of Kemp’s ridley sea turtle somatic growth variation

Many environmental processes influence animal somatic growth rates. However, elucidating specific drivers of somatic growth variation has been challenging for marine megafauna. Using a 20+ year dataset of somatic growth generated through skeletochronology, we evaluated the relationship between multiple region-wide environmental factors—the Deepwater Horizon (DWH) oil spill, increasing population density, and climate variability—and age- and region-specific Kemp’s ridley sea turtle (Lepidochelys kempii) somatic growth. We observed significant, multi-year reductions in mean oceanic (age 0) and small neritic (age 2–5) juvenile growth rates beginning in 2012 for turtles stranded along the U.S. Gulf of Mexico (GoM) and Atlantic Coasts, which resulted in a reduction in mean size-at-age. We hypothesize that this growth decline is related to long-term deleterious effects of the DWH oil spill on neritic and oceanic food webs in the GoM. Additionally, regional climate indices were strongly correlated with oceanic juvenile growth with a 2-year lag (cross-correlation = –0.57 to 0.60), whereas GoM small neritic juvenile growth was strongly related to population abundance metrics. Generalized additive models that included all examined environmental covariates indicated that the drivers of the 2012 growth rate decline had the strongest effect on Kemp’s ridley growth rates between 1995 and 2015, but that additive or synergistic effects of both climate variability and changing population abundance are likely for certain life stages. Continued collection of sea turtle humeri is needed to further clarify mechanisms underpinning the observed growth patterns given the coincidental timing of changes in environmental parameters examined herein.

Influence of nutrient enrichment on the growth, recruitment and trophic ecology of a highly invasive freshwater fish

The establishment probability of introduced alien fish can be context dependent, varying according to factors including propagule pressure and biotic resistance. The influence of nutrient enrichment on establishment outcomes of alien fishes is uncertain, yet this is a common anthropogenic stressor of many freshwaters. Here, the small-bodied alien topmouth gudgeon Pseudorasbora parva was used in mesocosms to experimentally test how a gradient of nutrient enrichment affected their growth rates, recruitment and trophic ecology. A ‘Control’ represented ambient, mesotrophic conditions, while treatments covered three levels of nutrient enrichment: low (eutrophic), medium (hypertrophic) and high (very hypertrophic). Each mesocosm was seeded with 6 mature P. parva (equal sex ratio) at the start of their reproductive season. After 100 days, length increments of the adult fish were significantly elevated in the low treatment, and these fish had also produced significantly higher numbers of 0+ fish compared to all other treatments. The trophic niche width of the mature fish was substantially higher in the control than the treatments, but this did not appear to confer any advantages to them in somatic growth rate or reproductive output. These results suggest that the nutrient status of receiving waters can have substantial impacts on the outcomes of fish introductions, where eutrophic conditions can assist the rapid population establishment of some alien species.

Dietary niche and growth rate of the nonnative tubenose goby (Proterorhinus semilunaris) in the Lake Superior basin

The tubenose goby (Proterorhinus semilunaris) entered the Great Lakes in the 1990s via ballast water, but remains poorly studied within North America, making it difficult to predict its effects on native ecosystems. Dietary breadth and somatic growth rate have important ramifications for survival, competitiveness, and dispersal ability of a fish species, and thereby its ecological impact. We studied diet and growth of age-0 tubenose goby within the St. Louis River, a tributary to Lake Superior that contains the largest population within the Lake Superior basin. We sampled tubenose gobies from shallow, vegetated habitats during summer and fall. Stomach contents were identified and weighed to measure fullness and dietary breadth between seasons and several locations. We aged fish based on otolith daily increments to model somatic growth. Diet was dominated by isopods and amphipods, and dietary breadth was low and not significantly different between locations and seasons. Tubenose goby diet strongly overlapped with that of tadpole madtom (Noturus gyrinus), a native, demersal species. We tested several candidate growth models; the Gompertz growth function was the most parsimonious model among those examined. The model demonstrates that tubenose goby obtains a small maximum size and is short-lived. We conclude that tubenose goby presents a unique risk to the Great Lakes and other freshwater bodies because their life history is typical of invasive species, their diet overlaps with native fish, and because they occupy shallow, vegetated habitat which functions as both nursery and foraging habitat for many native fishes.

Native drivers of fish life history traits are lost during the invasion process.

Rapid adaptation to global change can counter vulnerability of species to population declines and extinction. Theoretically, under such circumstances both genetic variation and phenotypic plasticity can maintain population fitness, but empirical support for this is currently limited. Here, we aim to characterize the role of environmental and genetic diversity, and their prior evolutionary history (via haplogroup profiles) in shaping patterns of life history traits during biological invasion. Data were derived from both genetic and life history traits including a morphological analysis of 29 native and invasive populations of topmouth gudgeon Pseudorasbora parva coupled with climatic variables from each location. General additive models were constructed to explain distribution of somatic growth rate (SGR) data across native and invasive ranges, with model selection performed using Akaike's information criteria. Genetic and environmental drivers that structured the life history of populations in their native range were less influential in their invasive populations. For some vertebrates at least, fitness‐related trait shifts do not seem to be dependent on the level of genetic diversity or haplogroup makeup of the initial introduced propagule, nor of the availability of local environmental conditions being similar to those experienced in their native range. As long as local conditions are not beyond the species physiological threshold, its local establishment and invasive potential are likely to be determined by local drivers, such as density‐dependent effects linked to resource availability or to local biotic resistance.

Spatiotemporal analysis of the daily growth traits of the prerecruits of a small pelagic fish in response to environmental drivers

AbstractA comparative analysis of daily growth patterns was carried out for prerecruits (PR) of Engraulis ringens, collected from spring to summer (2015–2016) in northern (18º25'S–24º40'S) and southern nursery areas (32º40'S–41º00'S) off the Chilean coast. Prerecruits ranged from 2.2 to 7.3 cm TL (4.27 ± 0.88) and from 27 to 102 days (54.68 ± 15.92) of age and were hatched mainly in spring 2015. Growth traits were addressed through otolith microstructure analysis to determine the increment width profiles (IW), back‐calculated growth rates (BIGR), and overall absolute growth rates (AGR), whereas the Chl–a and sea‐surface temperature (SST) variations were assessed by analyzing satellite and field‐based data. The IWs (5.42 ± 1.94 µm versus 1.02 ± 0.37 µm), BIGRs (1.02 ± 0.37 versus 0.72 ± 0.26 mm·day−1), and AGRs (0.93 ± 0.15 versus 0.62 ± 0.08 mm·day−1) were significantly higher in the northern than in the southern stocks. The SST ranged from 17°C to 23°C (19.42 ± 1.45) and from 12°C to 18°C (14.81 ± 1.31) and varied significantly between stocks and months, whereas the higher concentration of Chl–α (~8 mg/m3), occurred close to the shallow coastal areas irrespective of stocks. A parabolic relationship between the recent otolith growth rates (ROGR) (as a proxy of recent daily somatic growth rates) and SST recorded at the date of capture estimated a maximum ROGR of 13.4 µm·day−1 at 18°C. These results demonstrated that water temperature seemed to be an important daily growth controller for early juveniles of E. ringens in the Humboldt Current System and that the field‐based growth–temperature relationship obtained will contribute to future potential bioenergetics models for this important forage species.

The effects of chemical warfare agent Clark I on the life histories and stable isotopes composition of Daphnia magna

Chemical warfare agents (CWA) dumped worldwide in all types of aquatic reservoirs pose a potential environmental hazard. Leakage of CWAs from eroding containers at dumping sites had been observed, and their presence in the tissues of aquatic animals was confirmed. However, the ecological effects of CWA have not yet been studied. In standardized laboratory bioassays, we tested if sublethal concentration of Clark I, an arsenic based CWA, can affect life histories (somatic growth rate, fecundity, size at maturity), population growth rate and stable isotope signatures of a keystone crustacean grazer Daphnia magna. We found that the life histories and fitness of daphnids reared in the presence of Clark I differed from those reared in Clark-free conditions. The effects were observed when Clark I concentrations were no less than 5 μg×L−1. With increasing concentrations of the tested CWA, all of the tested parameters decreased linearly. The finding indicates that even sublethal concentrations of Clark I can affect crustacean populations, which should be taken into account when assessing the environmental risks of this particular CWA. We found intraspecific diversity in susceptibility to Clark I, with some clones being significantly less vulnerable than others. We also found that in the presence of Clark I, the ratio of heavy and light isotopes of nitrogen in the bodies of daphnids was affected – daphnids exhibited δ15N enrichment with increasing concentrations of this CWA. The isotopic composition of carbon was not affected by the presence of Clark I. The nitrogen isotopic signature may be used as an indicator of stress in zooplankton exposed to the presence of toxic xenobiotics.

Dopamine mediates life-history responses to food abundance in Daphnia

Expression of adaptive reaction norms of life-history traits to spatio-temporal variation in food availability is crucial for individual fitness. Yet little is known about the neural signalling mechanisms underlying these reaction norms. Previous studies suggest a role for the dopamine system in regulating behavioural and morphological responses to food across a wide range of taxa. We tested whether this neural signalling system also regulates life-history reaction norms by exposing the zooplankton Daphnia magna to both dopamine and the dopamine reuptake inhibitor bupropion, an antidepressant that enters aquatic environments via various pathways. We recorded a range of life-history traits across two food levels. Both treatments induced changes to the life-history reaction norm slopes. These were due to the effects of the treatments being more pronounced at restricted food ration, where controls had lower somatic growth rates, higher age and larger size at maturation. This translated into a higher population growth rate (r) of dopamine and bupropion treatments when food was restricted. Our findings show that the dopamine system is an important regulatory mechanism underlying life-history trait responses to food abundance and that bupropion can strongly influence the life history of aquatic species such as D. magna. We discuss why D. magna do not evolve towards higher endogenous dopamine levels despite the apparent fitness benefits.

Competitive abilities and distribution ranges of four asexual Daphnia pulex lineages and Daphnia mitsukuri in Eurasian continental islands

AbstractDaphnia pulex and D. mitsukuri are morphologically similar and distributed in small lowland Japanese lakes. Daphnia pulex in Japan reproduces by obligate parthenogenesis and is composed of four different lineages (JPN1–JPN4) with North American origins. Although this species is found throughout Japan, JPN1 has the largest distribution range, followed by JPN2. Daphnia mitsukuri is a putatively endemic species that is now rarely found in Japan. Since Daphnia share the same algal food, the difference in distribution ranges among the four asexual D. pulex lineages and D. mitsukuri may be caused by exploitative competition for algal food. To examine this possibility, we measured the threshold food concentration (TFC) at zero‐net growth rate and the food concentration required for 50% of the individuals to survive (FC50). In addition, we examined the effects of temperature on the somatic growth rate (SGR) and the mortality rates of four asexual D. pulex lineages and D. mitsukuri. The experiments showed that TFC was lowest in D. pulex JPN1 and highest in D. mitsukuri, supporting the idea that the largest distribution range of JPN1 is due to its superiority in inter‐lineage competition, and that the distribution area of D. mitsukuri is reduced through exploitative competition with D. pulex. However, although JPN2 was found in relatively large areas, it had higher TFC than JPN3 and JPN4, which appear in very limited areas. These results clearly showed that the difference in distribution ranges among D. pulex lineages are not necessarily determined by their competitive superiority alone.

Phenotypic plasticity in life-history characteristics of invasive blue catfish, Ictalurus furcatus

Blue catfish, Ictalurus furcatus, are an invasive species in the Chesapeake Bay region, where they negatively impact native species of ecological, economic and cultural value. Management of blue catfish is, however, hindered by a lack of information on their population dynamics. We studied decadal changes in growth and body condition and made inferences about maturity schedules of blue catfish in two Chesapeake Bay subestuaries (James and York rivers). Specifically, we quantified the dynamic responses of these populations to biotic and abiotic characteristics experienced by fish during two stages of invasion (1998−2000 or “early” period and 2015−2017 or “recent” period). In general, somatic growth rate, body condition and reproductive allocation were greater in the early, less dense populations, which also exhibited larger mean size-at-maturity. We observed sexual dimorphism in growth patterns where males reached larger asymptotic sizes than females in both rivers. Such sex-specific and density-dependent responses in life-history characteristics provide information critical for the development of quantitative models and deployment of effective management plans. Our results highlight the need for management plans to consider dynamic feedback mechanisms: efforts to decrease population density may diminish the negative impacts of blue catfish on native species, but this will be offset by increased growth rates and higher reproductive output.

Hurricane Frequency and Intensity May Decrease Dispersal of Kemp’s Ridley Sea Turtle Hatchlings in the Gulf of Mexico

Environmental variability can be an important factor in the population dynamics of many species. In marine systems, for instance, whether environmental conditions facilitate or impede the movements of juvenile animals to nursery habitat can have a large influence on subsequent population abundance. Both subtle differences in the position of oceanographic features (such as meandering currents) and major disturbances (such as hurricanes) can greatly alter dispersal outcomes. Here, we use an ocean circulation model to explore seasonal and annual variation in the dispersal of post-hatchling Kemp’s ridley sea turtles (Lepidochelys kempii). We simulated the transport of 24 cohorts of young Kemp’s ridley dispersing from three main nesting areas in the western Gulf of Mexico to describe variability in transport during the main hatching season and across years. We examined whether differences in transport distance among Kemp’s ridley cohorts could be explained by hurricane events. We found that years with high numbers of hurricanes corresponded to shorter dispersal distances within the first six months. Our findings suggest that differences in dispersal among sites and the impact due to hurricanes could influence the survivorship and somatic growth rates of turtles from different nesting sites and hatching cohorts. Considering such factors in future population assessments may aid in predicting how the potential for increasing tropical storms, a phenomenon linked to climate change, could affect Kemp’s ridley and other populations of sea turtles in the Atlantic.

Regional Variation in Kemp’s Ridley Sea Turtle Diet Composition and Its Potential Relationship With Somatic Growth

Reptile growth is influenced by many ecological processes that can cumulatively give rise to divergent somatic growth rates within spatially structured populations. As somatic growth variation can strongly influence a species’ population dynamics, identifying proximate drivers can be critical to the conservation and management of protected species. Kemp’s ridley sea turtles (Lepidochelys kempii) exhibit spatial variation in both diet composition and growth, but whether components of this variation are linked has not been evaluated. Through an integration of skeletochronological and stable isotope analyses of stranded turtle humerus bones we characterized regional variation in Kemp’s ridley diet composition and potential relationships with somatic growth rates. Turtles were divided among five regions within the U.S. Gulf of Mexico (GoM) and Atlantic Coast based on location of stranding, and humerus bones were sampled for stable carbon (δ13C) and nitrogen (δ15N) isotope ratios. These data were combined with region-specific prey stable isotope data sourced from the primary literature into Bayesian stable isotope mixing models (MixSIAR) to estimate the proportional contribution of five prey groups (crustaceans, bivalves, gastropods, fish, macroalgae/seagrass) to Kemp’s ridley diets. Our analysis revealed strong regional differences in mixing model-derived diet composition estimates that closely tracked published records of Kemp’s ridley diet. Invertebrates generally comprised the largest proportion (43.5–97.7 %) of turtle diets. However, we also observed high proportional contributions of fish (42.6–43.1 %) to western GoM turtle diets and macroalgae/seagrass (42.4–47.8 %), or isotopically similar prey resources (e.g., tunicates), to eastern GoM turtle diets. Growth rates were poorly correlated with δ15N values—a proxy for trophic level—and diet composition estimates, suggesting that diet composition alone may not explain the regional differences in somatic growth observed in this species. This study highlights the value of complementary skeletal and isotopic analyses to understanding regional diet variation in sea turtles as well as the importance of continued collection of isotopic data for both sea turtles and their prey. These results also help fill critical knowledge gaps pertaining to the relationship between sea turtle foraging ecology and somatic growth dynamics, a topic of high importance to sea turtle conservation and management.

Integration of physiology, behaviour and life history traits: personality and pace of life in a marine gastropod

Attempts to unravel the proximate and ultimate causes of individual behavioural and life history variation have often pointed to predicted correlations between behavioural, physiological and life history traits, forming pace-of-life syndromes (POLS). The POLS hypothesis predicts that high levels of production (growth, fecundity) require high levels of foraging effort and risk taking, supported by high metabolism. Despite tremendous interest in this topic, the POLS hypothesis still has limited empirical support, which has led to calls for more stringent empirical tests of the hypothesis and its assumptions. To that end, we examined the associations between risk-taking behaviour (boldness), resting metabolic rate (RMR) and somatic growth rate in a marine gastropod, Littoraria irrorata, under controlled laboratory conditions using a longitudinal repeated measures design. After accounting for the effects of sex, size and time (trial number), a multivariate mixed model revealed that bolder individuals had higher RMR, and grew faster, whereas RMR and growth were not strongly correlated. Further, if individuals were bolder than their average on a given day, then their RMR was also higher. Our study represents rare and compelling support for the POLS hypothesis, simultaneously studying its three key components (behaviour, energetics and life history), the success of which we attribute to careful control, concurrent sampling of each trait, and rigorous analysis of the among- and within-individual patterns of variation and covariance.

Multigenerational plasticity of Daphnia magna under thermal stress across ten generations.

The effects of increasing temperature owing to thermal discharge and global warming on zooplanktons such as Daphnia magna are a growing concern. The purpose of this study was to evaluate the effects of elevated temperature (25°C) on oxidative stress responses, growth, and reproduction of D. magna across 10 generations. The number of offspring per female at 21d was significantly increased and the rate of adult somatic growth (5-21d) was decreased in the F0 generation at 25°C compared with those at the reference temperature 20°C. However, the F3 generation showed the lowest number of offspring and the highest adult somatic growth rate and oxidative stress responses (5d) at 25°C. Moreover, all life-history traits seemed to recover to the levels of the control group from the F6 generation at 20°C. These findings suggest that D. magna under continuous thermal stress exhibits non-adaptive responses in the early generations (F0-F3) and changes to adaptive responses in the later generations (F6-F9). However, the underlying epigenetic mechanism should be identified in the future.

A Bayesian state-space model for seasonal growth of terrestrial vertebrates

The rate of somatic growth determines when individuals transition between life stages, which along with survival and reproduction, are principal factors governing the rate of population change. For short-lived species that inhabit seasonally dynamic environments, accounting for fluctuations in somatic growth is necessary to make reliable inferences about population dynamics. We describe a Bayesian, state-space formulation of a von Bertalanffy growth model that integrates a sinusoidal model to allow for seasonal fluctuations in growth while also accounting for individual heterogeneity and measurement error. We use this model to describe post-metamorphic growth of canyon treefrogs, Hyla arenicolor, based on capture-recapture data from 404 individuals over a two-year period. For simulated data where we assumed growth varies seasonally, our model provides unbiased estimates of growth rate, mean asymptotic length, standard deviation of individual asymptotic lengths, and date of maximum growth. For field data from canyon treefrogs, we found strong evidence of seasonal variation in growth, with maximum growth during the summer monsoon season. Growth rate of females was 19 % lower than males, although on average, females reached asymptotic lengths that were 15 % greater than males. Ignoring systematic intra-annual variation in growth can bias inferences about population dynamics, particularly for fast-growing species that reproduce more than once per year or inhabit environments with strong seasonal signals. We present a straightforward approach for using repeated length measurements from individuals of unknown age to estimate growth while accounting for seasonality and individual heterogeneity, which are sources of variation common in many vertebrate populations.