Marco A. Lardies

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

SUMMARY 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 Q10). The MR of H. griseus was significantly repeatable (r=0.53) and highly dependent on ambient temperature, and its sensitivity (Q10) 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 individuals 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 Q10 values revealed important interindividual variation, which reflects the existence of intrapopulational variability in the thermal sensitivity of MR. In addition, individual Q10 values were negatively correlated between temperature ranges. This means that crickets having low Q10 at low temperatures, presented high Q10 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.

Impact of medium-term exposure to elevated pCO2 levels on the physiological energetics of the mussel Mytilus chilensis

This study evaluated the impact of medium-term exposure to elevated pCO(2) levels (750-1200 ppm) on the physiological processes of juvenile Mytilus chilensis mussels over a period of 70 d in a mesocosm system. Three equilibration tanks filled with filtered seawater were adjusted to three pCO(2) levels: ~380 (control), ~750 and ~1200 ppm by bubbling air or an air-CO(2) mixture through the water. For the control, atmospheric air (with aprox. 380 ppm CO(2)) was bubbled into the tank; for the 750 and 1200 ppm treatments, dry air and pure CO(2) were blended to each target concentration using mass flow controllers for air and CO(2). No impact on feeding activity was observed at the beginning of the experiment, but a significant reduction in clearance rate was observed after 35 d of exposure to highly acidified seawater. Absorption rate and absorption efficiency were reduced at high pCO(2) levels. In addition, oxygen uptake fell significantly under these conditions, indicating a metabolic depression. These physiological responses of the mussels resulted in a significant reduction of energy available for growth (scope for growth) with important consequences for the aquaculture of this species during medium-term exposure to acid conditions. The results of this study clearly indicate that high pCO(2) levels in the seawater have a negative effect on the health of M. chilensis. Therefore, the predicted acidification of seawater associated with global climate change could be harmful to this ecologically and commercially important mussel.

Latitudinal variation in the reproductive biology of Betaeus truncatus (Decapoda: Alpheidae) along the Chilean coast

Abstract The extensive coast of Chile with its relatively homogeneous water masses favors a wide distribution of marine invertebrates, including the snapping shrimp Betaeus truncatus. We selected one sampling site in northern (Guanaqueros) and two sites in southern Chile (Metri and Putemün) to study latitudinal variation in the reproductive biology of B. truncatus. Monthly samples were collected over a one-year period (1994–95). The smallest ovigerous female was collected in northern Chile, but large-sized females with eggs were obtained principally in southern Chile. Females produced up to 1067 eggs per clutch (Guanaqueros), and average clutch size ranged from 234 (Putemún) to 399 eggs (Guanaqueros). The relationship between fecundity and female size differed significantly between Guanaqueros and the other two southern populations studied. Recently laid eggs in Metri and Putemún were significantly larger than those extruded in northern Chile, and egg volume increased during embryogenesis between 80.8% (Putem ú n) and 184.9% (Metri). Brood mortality was significantly higher in Metri (41.4%) compared to Guanaqueros (20.8%) and Putemün (19.1%). Eggs produced in northern Chile contained the highest percentage of water. Egg dry mass as well as reproductive output increased from north to south. We compare our data with those published for other decapod species, and discuss the observed latitudinal clines.

Egg production in Betaeus emarginatus (H. Milne Edwards, 1837) (Decapoda: Alpheidae): fecundily, reproductive output and chemical composition of eggs

Abstract The major variables concerning clutch size, reproductive output and chemical composition of developing eggs were analyzed in the snapping shrimp Betaeus emarginatus from central-southern Chile. Betaeus emarginatus produced numerous (x=285) and relatively large eggs (x =0.209 mm3, recently-produced embryos), which more than double (116.2%) in volume during embryogenesis. Egg loss was fairly low (11.6%). Water constituted the predominant component of the eggs and increased gradually from 56.5% to 76.1%. Brood masses comprised an average of 8.5% of the female body dry weight, and the reproductive output (RO) was 0.09 (based on dry weight). Due to the apparent lack of information regarding the reproductive biology of snapping shrimps from temperate waters, we compare our data with those of other Alpheidae from tropical and subtropical zones. Our results corroborate the tendency of decreasing RO with increasing latitude.

Species-specific responses to ocean acidification should account for local adaptation and adaptive plasticity

Global stressors, such as ocean acidification, constitute a rapidly emerging and significant problem for marine organisms, ecosystem functioning and services. The coastal ecosystems of the Humboldt Current System (HCS) off Chile harbour a broad physical–chemical latitudinal and temporal gradient with considerable patchiness in local oceanographic conditions. This heterogeneity may, in turn, modulate the specific tolerances of organisms to climate stress in species with populations distributed along this environmental gradient. Negative response ratios are observed in species models (mussels, gastropods and planktonic copepods) exposed to changes in the partial pressure of CO2 (pCO2) far from the average and extreme pCO2 levels experienced in their native habitats. This variability in response between populations reveals the potential role of local adaptation and/or adaptive phenotypic plasticity in increasing resilience of species to environmental change. The growing use of standard ocean acidification scenarios and treatment levels in experimental protocols brings with it a danger that inter-population differences are confounded by the varying environmental conditions naturally experienced by different populations. Here, we propose the use of a simple index taking into account the natural pCO2 variability, for a better interpretation of the potential consequences of ocean acidification on species inhabiting variable coastal ecosystems. Using scenarios that take into account the natural variability will allow understanding of the limits to plasticity across organismal traits, populations and species.

Variation in Thermal Sensitivity and Thermal Tolerances in an Invasive Species across a Climatic Gradient: Lessons from the Land Snail Cornu aspersum

The ability of organisms to perform at different temperatures could be described by a continuous nonlinear reaction norm (i.e., thermal performance curve, TPC), in which the phenotypic trait value varies as a function of temperature. Almost any shift in the parameters of this performance curve could highlight the direct effect of temperature on organism fitness, providing a powerful framework for testing thermal adaptation hypotheses. Inter-and intraspecific differences in this performance curve are also reflected in thermal tolerances limits (e.g., critical and lethal limits), influencing the biogeographic patterns of species’ distribution. Within this context, here we investigated the intraspecific variation in thermal sensitivities and thermal tolerances in three populations of the invasive snail Cornu aspersum across a geographical gradient, characterized by different climatic conditions. Thus, we examined population differentiation in the TPCs, thermal-coma recovery times, expression of heat-shock proteins and standard metabolic rate (i.e., energetic costs of physiological differentiation). We tested two competing hypotheses regarding thermal adaptation (the “hotter is better” and the generalist-specialist trade-offs). Our results show that the differences in thermal sensitivity among populations of C. aspersum follow a latitudinal pattern, which is likely the result of a combination of thermodynamic constraints (“hotter is better”) and thermal adaptations to their local environments (generalist-specialist trade-offs). This finding is also consistent with some thermal tolerance indices such as the Heat-Shock Protein Response and the recovery time from chill-coma. However, mixed responses in the evaluated traits suggest that thermal adaptation in this species is not complete, as we were not able to detect any differences in neither energetic costs of physiological differentiation among populations, nor in the heat-coma recovery.

Effects of environmental variables on burial depth of two infaunal bivalves inhabiting a tidal flat in southern Chile

The annual pattern of burial depth in natural populations of the infaunal bivalves Tagelus dombeii (Tellinacea) and Venus antiqua (Veneracea) is described in relation to annual food availability in both the water column and the sediment and abiotic factors (temperature and salinity) at Coihuin tidal flat, in southern Chile. A field experiment in which burial depth was measured in situ each month (over 14 months), with the aid of a fixed-length nylon thread attached to the shell. For T. dombeii the results showed a significant increase in burial depth with increasing bivalve size and syphon weight. Tagelus dombeii had a mean burial depth of 17·5 cm, which was three times more than in V. antiqua (5·30 cm). The burial depth dynamics for both species displayed a strong correlation with food availability in the water column. Approximately 60% of the variability in burial depth in T. dombeii and V. antiqua was explained by concentration of chlorophyll- a in the water column. Food concentration on the sediment surface did not effect burial depth, i.e. deposit feeding seems to be of minor significance in either species.

Geographic variation in thermal physiological performance of the intertidal crab Petrolisthes violaceus along a latitudinal gradient

Environmental temperature has profound effects on the biological performance and biogeographical distribution of ectothermic species. Variation of this abiotic factor across geographic gradients is expected to produce physiological differentiation and local adaptation of natural populations depending on their thermal tolerances and physiological sensitivities. Here, we studied geographic variation in whole-organism thermal physiology of seven populations of the porcelain crab Petrolisthes violaceus across a latitudinal gradient of 3000 km, characterized by a cline of thermal conditions. Our study found that populations of P. violaceus show no differences in the limits of their thermal performance curves and demonstrate a negative correlation of their optimal temperatures with latitude. Additionally, our findings show that high-latitude populations of P. violaceus exhibit broader thermal tolerances, which is consistent with the climatic variability hypothesis. Interestingly, under a future scenario of warming oceans, the thermal safety margins of P. violaceus indicate that lower latitude populations can physiologically tolerate the ocean-warming scenarios projected by the IPCC for the end of the twenty-first century.

Shifts in shell mineralogy and metabolism of Concholepas concholepas juveniles along the Chilean coast

Along the west coast of South America, from the tropical zone to the Patagonian waters, there is a significant latitudinal gradient in seawater temperature, salinity and carbonate chemistry. These physical–chemical changes in seawater induce morphological and physiological responses in calcifying organisms, which may alter their energy budget and calcification processes. In this study, we study the organism energy maintenance (i.e. metabolic rate) and mineralogical composition of the shell of the juvenile marine snails Concholepas concholepas (Gastropoda: Muricidae), collected from benthic populations located ~2000km apart, varies across geographic regions along the Chilean coast. We found that in juvenile snails, the calcite:aragonite ratio in the pallial shell margin (i.e. newly deposited shell) increase significantly from northern to southern populations and this increase in calcite precipitation in the shell of juveniles snails was associated with a decrease in oxygen consumption rates in these populations. Our result suggests that calcite secretion may be favoured when metabolic rates are lowered, as this carbonate mineral phase might be less energetically costly for the organism to precipitate. This result is discussed in relation to the natural process such as coastal upwelling and freshwater inputs that promote geographic variation in levels of pH and carbonate saturation state in seawater along the Chilean coast.

Diet-induced developmental plasticity in life histories and energy metabolism in a beetle

La plasticidad fenotipica adaptativa ha sido reconocida como una estrategia importante por el cual los organismos maximizan su adecuacion biologica en ambientes variables y la cual varia a lo largo del desarrollo. En los organismos la plasticidad fenotipica generalmente se refiere a como los diferentes tipos de rasgos pueden estar conectados con una relacion alometrica, la cual varia a lo largo del desarrollo. Una disociacion entre los distintos estadios ontogeneticos debiese representar un nulo efecto del ambiente experimentado durante la ontogenia temprana en la expresion de los rasgos de los individuos adultos. La calidad del alimento influencia la sobrevivencia, desarrollo y reproduccion en la mayoria de los artropodos herbivoros. En este estudio examinamos los efectos de la cantidad de proteina en la dieta sobre los rasgos fisiologicos y de historia de vida en el escarabajo Tenebrio molitor a traves de toda la ontogenia. Con larvas recien eclosionadas se establecieron cuatro tratamientos experimentales: Baja Proteina (LP), Control Baja Proteina (LPC), Alta Proteina (HP) y Control Alta Proteina (HPC). Los individuos fueron mantenidos en la misma dieta o transferidos a la dieta opuesta en el estadio de pupa y mantenidos durante todo el periodo de adulto. Contrario a lo esperado, la duracion del ciclo de vida, tasa de crecimiento larval y masa corporal en T. molitor fue similar entre los distintos tratamientos. Ademas, se econtraron compromisos individuales entre la dieta ambiental (contenido rico o pobre de proteina) durante la fase larval y el numero de huevos de hembras adultas. Las larvas alimentadas en una dieta con deficiencia en proteina exhibieron una tasa respiratoria significativamente mayor que larvas alimentadas en una dieta rica en proteinas. La alimentacion compensatoria podria estar actuando en las larvas de T. molitor indicando diferencias en el metabolismo pero no en la tasa de crecimiento, masa corporal y las caracteristicas del ciclo de vida. Nuestros resultados demuestran plasticidad fenotipica de los rasgos metabolicos y de historia de vida en T. molitor y como esta cambia en relacion a la dieta y como estos cambios pueden tener efectos significativos sobre la adecuacion biologica de la progenie y de la hembra.