Sort by
Infection Causes Trade-Offs between Development and Growth in Larval Amphibians.

AbstractTrade-offs between life history traits are context dependent; they vary depending on environment and life stage. Negative associations between development and growth often characterize larval life stages. Both growth and development consume large parts of the energy budget of young animals. The metabolic rate of animals should reflect differences in growth and developmental rates. Growth and development can also have negative associations with immune function because of their costs. We investigated how intraspecific variation in growth and development affected the metabolism of larval amphibians and whether intraspecific variation in growth, development, and metabolic rate could predict mortality and viral load in larvae infected with ranavirus. We also compared the relationship between growth and development before and after infection with ranavirus. We hypothesized that growth and development would affect metabolism and predicted that each would have a positive correlation with metabolic rate. We further hypothesized that allocation toward growth and development would increase ranavirus susceptibility and therefore predicted that larvae with faster growth, faster development, and higher metabolic rates would be more likely to die from ranavirus and have higher viral loads. Finally, we predicted that growth rate and developmental rate would have a negative association. Intraspecific variation in growth rate and developmental rate did not affect metabolism. Growth rate, developmental rate, and metabolism did not predict mortality from ranavirus or viral load. Larvae infected with ranavirus exhibited a trade-off between developmental rate and growth rate that was absent in uninfected larvae. Our results indicate a cost of ranavirus infection that is potentially due to both the infection-induced anorexia and the cost of infection altering priority rules for resource allocation.

Relevant
Environmental Stress and the Morphology of Daphnia pulex.

AbstractMorphological variation is sometimes used as an indicator of environmental stress in animals. Here, we assessed how multiple morphological traits covaried in Daphnia pulex exposed to five common forms of environmental stress (high temperature, presence of predator cues, high salinity, low food abundance, and low Ca). We measured animal body length, body width, head width, eyespot diameter, and tail spine length along with mass in animals of five different ages (3, 6, 9, 12, and 15 d). There were strong allometric relationships among all morphological traits in reference animals and strong univariate effects of environmental stress on body mass and body length. We found that environmental stressors altered bivariate relationships between select pairwise combinations of morphological traits, with effects being dependent on animal age. Multivariate analyses further revealed high connectivity among body size-related traits but that eyespot diameter and tail spine length were less tightly associated with body size. Animals exposed to natural lake water with and without supplemental food also varied in morphology, with body size differences being suggestive of starvation and other unknown nutritional deficiencies. Yet our results demonstrate that the scaling of body morphological traits of Daphnia pulex is largely invariant with possible context-dependent plasticity in eye size and tail spine lengths. The strong coordination of traits indicates tight molecular coordination of body size during development despite strong and varied environmental stress.

Relevant
Leukocyte Concentrations Are Isometric in Reptiles Unlike in Endotherms.

AbstractHow do large and small reptiles defend against infections, given the consequences of body mass for physiology and disease transmission? Functionally equivalent mammalian and avian granulocytes increased disproportionately with body mass (i.e., scaled hypermetrically), such that large organisms had higher concentrations than expected by a prediction of proportional protection across sizes. However, as these scaling relationships were derived from endothermic animals, they do not necessarily inform the scaling of leukocyte concentration for ectothermic reptiles that have a different physiology and evolutionary history. Here, we asked whether and how lymphocyte and heterophil concentrations relate to body mass among more than 120 reptile species. We compared these relationships to those found in birds and mammals and to existing scaling frameworks (i.e., protecton, complexity, rate of metabolism, or safety factor hypotheses). Both lymphocyte and heterophil concentrations scaled almost isometrically among reptiles. In contrast, functionally equivalent granulocytes scaled hypermetrically and lymphocytes scaled isometrically in birds and mammals. Life history traits were also poor predictors of variation in reptilian heterophil and lymphocyte concentrations. Our results provide insight into differences in immune protection in birds and mammals relative to that in reptiles through a comparative lens. The shape of scaling relationships differs, which should be considered when modeling disease dynamics among these groups.

Relevant
Stopovers Serve Physiological Recovery in Migratory Songbirds.

AbstractMigrating birds perform extreme endurance exercise when flying. This shifts the balance between the production of reactive oxygen species and the antioxidant defense system toward the former, potentially generating oxidative damages. In between migratory flights, birds make stopovers, where besides accumulating fuel (mainly fats), they are assumed to rest and recover from the strenuous flight. We performed a series of studies on both temporarily caged (northern wheatears) and free-flying (northern wheatears and European robins) migrants to investigate whether migrants recover during stopover by decreasing the amount of oxidative lipid damage (malondialdehyde [MDA]) and/or increasing the total nonenzymatic antioxidant capacity (AOX). In caged wheatears, MDA decreased within a single day. These birds were able to simultaneously accumulate considerable amounts of fuel. Also, in the free-flying wheatears, there was a decrease in MDA during stopover; however, this process seemed incompatible with refueling. The reason for this difference could relate to constraints in the wild that are absent in caged birds, such as food limitation/composition and locomotor activity. In the robins, there was a near significant decrease in MDA concentration in relation to how long the birds were already at stopover, suggesting that this species also physiologically recovers during stopover. AOX did not change during stopover in either of the wheatear studies. For the robins, however, uric acid-corrected AOX declined during stopover. Our results show that during stopover, migrating birds rapidly reduce oxidative lipid damage, thereby likely recovering their physiological state. In addition to the commonly accepted function of refueling, stopovers thus probably serve physiological recovery.

Relevant