Environmental refuges increase performance of juvenile mussels Mytilus chilensis: Implications for mussel seedling and farming strategies.

Estuarine ecosystems are characterized by a wide physical-chemical variation that in the context of global change scenarios may be exacerbated in the future. The fitness of resident organisms is expected to be influenced by such variation and, hence, its study is a priority. Some of that variation relates to water vertical stratification, which may create "environmental refuges" or distinct layers of water with conditions favoring the fitness of some individuals and species. This study explored the performance of juvenile mussels (M. chilensis) settled in two distinctive water depths (1 m and 4 m) of the Reloncaví fjord (southern Chile) by conducting a reciprocal transplants experiment. Salinity, saturation state and the contents of CO3 in seawater were among the factors that best explained the differences between the two layers. In such environmental conditions, the mussel traits that responded to such variation were growth and calcification rates, with significantly higher values at 4 m deep, whereas the opposite, increased metabolic stress, was higher in mussels raised and transplanted to the surface waters (1 m). Such differences support the notion of an environmental refuge, where species like mussels can find better growth conditions and achieve higher performance levels. These results are relevant considering the importance of M. chilensis as a shellfish resource for aquaculture and a habitat forming species. In addition, these results shed light on the variable responses exhibited by estuarine organisms to small-scale changes in the characteristics of the water column, which in turn will help to better understand the responses of the organisms to the projected scenarios of climate global change.

Role of temperature and carbonate system variability on a host-parasite system: Implications for the gigantism hypothesis.

Biological interactions and environmental constraints alter life-history traits, modifying organismal performances. Trematode parasites often impact their hosts by inducing parasitic castration, frequently correlated with increased body size in the host (i.e., gigantism hypothesis), which is postulated to reflect the re-allocation of energy released by the reduction in the reproductive process. In this study, we compared the effect of a trematode species on shell size and morphology in adult individuals of the intertidal mussels Perumytilus purpuratus (>20 mm) collected from two local populations of contrasting environmental regimes experienced in central-southern Chile. Our field data indicates that in both study locations, parasitized mussels evidenced higher body sizes (shell length, total weight and volume) as compared with non-parasitized. In addition, parasitized mussels from the southern location evidenced thinner shells than non-parasitized ones and those collected from central Chile, suggesting geographical variation in shell carbonate precipitation across intertidal habitats of the Chilean coast. In laboratory conditions, mussels collected from a local population in central Chile were exposed to two temperature treatments (12 and 18 °C). Parasitized mussels showed higher growth rates than non-parasitized, regardless of the seawater temperature treatments. However, the metabolic rate was not influenced by the parasite condition or the temperature treatments. Our field and laboratory results support the parasite-induced gigantism hypothesis, and suggest that both the thermal environment and geographic location explain only a portion of the increased body size, while the parasitic condition is the most plausible factor modulating the outcome of this host-parasite interaction.

The energetic physiology of juvenile mussels, Mytilus chilensis (Hupe): The prevalent role of salinity under current and predicted pCO2 scenarios.

As a result of human activities, climate forecasts predict changes in the oceans pCO2 and salinity levels with unknown impacts on marine organisms. As a consequence, an increasing number of studies have begun to address the individual influence of pCO2 and salinity but much remains to be done to understand their combined effects on the physiology and ecology of marine species. Our study addressed this knowledge gap by measuring the influence of current and predicted levels of pCO2 (380 and 1200 ppm, respectively) and salinity (20, 25 and 30 psµ) on the energetic physiology of juvenile mussels (Mytilus chilensis) from the south-eastern Pacific region. Our results indicate that a reduced salinity caused a significant reduction in clearance rate, absorption efficiency and scope for growth of this species. Meanwhile, an increase in pCO2 levels caused a reduction in excretion rates and interacted significantly with salinity in the rate of oxygen uptake measured in the mussel. These results suggest that potential changes in salinity might have a direct role on the physiology of M. chilensis. The effect of pCO2, although less prevalent among the variables measured here, did interact with salinity and is also likely to alter the physiology of this species. Given the ecological and economic importance of M. chilensis, we call for further studies exploring the influence of pCO2 across a wider range of salinities.

Intertidal pool fish Girella laevifrons (Kyphosidae) shown strong physiological homeostasis but shy personality: The cost of living in hypercapnic habitats.

Tide pools habitats are naturally exposed to a high degree of environmental variability. The consequences of living in these extreme habitats are not well established. In particular, little it is known about of the effects of hypercanic seawater (i.e. high pCO2 levels) on marine vertebrates such as intertidal pool fish. The aim of this study was to evaluate the effects of increased pCO2 on the physiology and behavior in juveniles of the intertidal pool fish Girella laevifrons. Two nominal pCO2 concentrations (400 and 1600µatm) were used. We found that exposure to hypercapnic conditions did not affect oxygen consumption and absorption efficiency. However, the lateralization and boldness behavior was significantly disrupted in high pCO2 conditions. In general, a predator-risk cost of boldness is assumed, thus the increased occurrence of shy personality in juvenile fishes may result in a change in the balance of this biological interaction, with significant ecological consequences.

Heritability of progeny size in a terrestrial isopod: transgenerational environmental effects on a life history trait.

Maternal effects, the environment that mothers provide to their offspring, their provision of nutrients and the environment that offspring of the same clutch share, have come to be recognized as an important influence on offspring fitness. In addition, in invertebrates, maternal effects and common environment may change according to a mother's diet. We tested for the changes in quantitative genetic parameters in a half-sib design where mothers were fed diets varying in nutrient content. Surprisingly, we found that not only maternal and common environmental variance changed with experimental diets but also there were significant changes in narrow-sense heritabilities, with corresponding h(2) values of 0.61 (high protein), 0.08 (high carbohydrate) and 0.001 (equal carbohydrate:protein). Our results show how an environmentally driven evolutionary process could occur in nature, since the response to selection could change dramatically according to the composition of the diet that females are ingesting.

Intrapopulational variation in the standard metabolic rate of insects: repeatability, thermal dependence and sensitivity (Q10) of oxygen consumption in a cricket.

Studies focusing on physiological variation among individuals, and its possible evolutionary consequences, are scarce. A trait can only be a target of natural selection if it is consistent over time, that is, a trait must be repeatable. In ectotherms it has been suggested that standard metabolic rate (MR) is related to Darwinian fitness, since it reflects energy usage and expenditure. The metabolic rate of the cricket Hophlosphyrum griseus was determined at three ambient temperatures. Repeatability of MR was estimated by product-moment correlation on residuals of body mass, as well as the thermal sensitivity of MR on an individual basis (individual Q(10)). The MR of H. griseus was significantly repeatable (r=0.53) and highly dependent on ambient temperature, and its sensitivity (Q(10)) was dependent on the temperature range. Our estimation of MR repeatability was high in comparison to published studies in vertebrates. Ours is the second report of repeatability (i.e. consistency over time of an individual's performance ranking within a population) of any aspect of energy metabolism in an insect, and also the first study to report significant repeatability of MR. Individual Q(10) values revealed important interindividual variation, which reflects the existence of intrapopulational variability in the thermal sensitivity of MR. In addition, individual Q(10) values were negatively correlated between temperature ranges. This means that crickets having low Q(10) at low temperatures, presented high Q(10) at high temperatures, and vice versa. Our results suggest that MR could be of selective value in insects, showing consistency over time and intrapopulational variability in its thermal dependence. Nevertheless, its heritability remains to be determined.