Agüera A et al. (2015), Parameter Estimations of Dynamic Energy Budget ...

ECB-ART-44293

PLoS One 2015 Jan 01;1010:e0140078. doi: 10.1371/journal.pone.0140078.

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Parameter Estimations of Dynamic Energy Budget (DEB) Model over the Life History of a Key Antarctic Species: The Antarctic Sea Star Odontaster validus Koehler, 1906.

Agüera A , Collard M , Jossart Q , Moreau C , Danis B .

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Marine organisms in Antarctica are adapted to an extreme ecosystem including extremely stable temperatures and strong seasonality due to changes in day length. It is now largely accepted that Southern Ocean organisms are particularly vulnerable to global warming with some regions already being challenged by a rapid increase of temperature. Climate change affects both the physical and biotic components of marine ecosystems and will have an impact on the distribution and population dynamics of Antarctic marine organisms. To predict and assess the effect of climate change on marine ecosystems a more comprehensive knowledge of the life history and physiology of key species is urgently needed. In this study we estimate the Dynamic Energy Budget (DEB) model parameters for key benthic Antarctic species the sea star Odontaster validus using available information from literature and experiments. The DEB theory is unique in capturing the metabolic processes of an organism through its entire life cycle as a function of temperature and food availability. The DEB model allows for the inclusion of the different life history stages, and thus, becomes a tool that can be used to model lifetime feeding, growth, reproduction, and their responses to changes in biotic and abiotic conditions. The DEB model presented here includes the estimation of reproduction handling rules for the development of simultaneous oocyte cohorts within the gonad. Additionally it links the DEB model reserves to the pyloric caeca an organ whose function has long been ascribed to energy storage. Model parameters described a slowed down metabolism of long living animals that mature slowly. O. validus has a large reserve that-matching low maintenance costs- allow withstanding long periods of starvation. Gonad development is continuous and individual cohorts developed within the gonads grow in biomass following a power function of the age of the cohort. The DEB model developed here for O. validus allowed us to increase our knowledge on the ecophysiology of this species, providing new insights on the role of food availability and temperature on its life cycle and reproduction strategy.

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Genes referenced: impact LOC100887844 LOC115925415

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	Fig 1. Schematic representation of the standard DEB model [18].Arrows represent energy fluxes (J d-1) that drive the dynamics of the four state variables (boxes). Energy enters the organism as food (X), is assimilated at a rate of pË™A into reserves (E). The mobilization rate (pË™C), regulates the energy leaving the reserve to cover somatic maintenance (pË™M), structural growth (pË™G), maturity maintenance (pË™J), maturation (pË™R) (immature individuals) and reproduction (pË™R) (mature individuals). Îº is the proportion of the mobilized energy diverted to pË™M and pË™G, while the rest is used for pË™J and pË™R.
	Fig 2. Schematic representation of the reproduction buffer handling rules for Odontaster validus.Arrows represent energy fluxes (J d-1). After paying for maturity costs pË™R is stored in the reproduction buffer E R that is continuously being mobilized to develop the gonads. The gonads contain two different cohorts of oocytes, each one receiving energy at a rate given by pË™Yn, however cohort 1 is 365 days older than cohort 0 and pË™Yn depends on t (age). Îº R is the reproduction efficiency and represent the energy dissipated as the buffer is transformed into eggs.
	Fig 3. Temperature sensitivity.Dots are the scaled values of observed oxygen consumption rates. The line represents the adjusted Arrhenius function (parameters are in Table 1).
	Fig 4. DEB model output with the data on post-metamorphic individuals used for parameter estimation.A. Length-weight relationship, dots are data from laboratory experiments, fed ad libitum (Pearse et al. unpublished data), diamonds are values from McMurdo station at the same time of the year [23]. B. Proportional growth rate by day according to size. Dots are data from laboratory experiments, animals fed ad libitum [23]. C. Maximum gonad weight according to size. Dots are observed data from laboratory experiments, animals fed ad libitum (Pearse et al. unpublished data). Maximum gonad size is reached before reproduction takes places around June in McMurdo [12]. D. Pyloric caeca weight according to size. Dots are observed data from laboratory experiments after being fed ad libitum for more than a year (Pearse et al. unpublished data). MRE is the mean absolute relative error.
	Fig 5. Oxygen consumption according to temperature.Dots are observed values for several individuals averaging 7.2 g wet weight [27]. The line represent DEB model predictions using the estimated values from Table 1. MRE is the mean absolute relative error.
	Fig 6. DEB model output with data on pre-metamorphic individuals used for parameter estimation.A. Larval growth in length according to age. Dots are observations in the laboratory [29]. Food was available in excess and the animals fed once they were able to do so. B. Loss of dry weight from fertilization, data from [37]. In this case there was no food available during the whole experiment. MRE is the mean absolute relative error.
	Fig 7. Gametogenesis.A. Proportional weight of one cohort of oocytes as it develop during two years and are released during reproduction. Dots were yielded from field observations made by Pearse [12]. The line is the DEB model output considering E R handling rules. B. Development of successive cohorts in time, each cohort grows following Eq (3).
	Fig 8. Weight according to age of O. validus, representing the contributions of the reproduction buffer, the reserves and the structure to the total weight.A. Considering the conditions in the laboratory ad libitum feeding. B. Considering the food conditions estimated for McMurdo. For both graphs a constant temperature of 271.5 K was considered.
	Fig 9. Pyloric Index (pyloric caeca weight / (total weightâ€“gonad weight)) increment after the change in food availability (from the field to the laboratory).Points shows observed PI in the field at the moment of recollection (day 0) and the PI from individuals sampled in the laboratory experiment during the first year. Error bars are standard deviations. White line (mean) and shaded area (95% 95% confidence interval) are DEB model output for the PI, considering the DEB reserve dynamics after a change in food resources (S1 Appendix) applied to the animals used to obtain PI at day 0. Solid line: PI in the lab considering the reserves are in equilibrium with the available food (0.30, f = 1). Dashed line: PI for the available food estimated by the model for McMurdo (0.25, f f = 0.8).
	Fig 10. Gonadosomatic Index (GSI).A. Animals kept in the laboratory and fed ad libitum. B. Animals at the food level estimated for McMurdo. Points are mean and 95% confidence interval of laboratory and field observations respectively [25]. Line (mean) and shaded areas (95% confidence interval) are DEB model output applying the reproduction buffer handling rules to a 100 individuals with the same mean weight and SD than the ones used in the observations.

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