Tropical birds are relatively long-lived and produce few offspring, which develop slowly and mature relatively late in life, the slow end of the life-history axis, whereas temperate birds lie at the opposite end of this continuum. We tested the hypothesis that tropical birds have evolved a reduced basal metabolic rate (BMR). We measured BMR of 69 species of tropical birds, the largest data set amassed on metabolic rates of tropical birds, and compared these measurements with 59 estimates of BMR for temperate birds. Our analyses included conventional least squares regression, regressions based on phylogenetic independent contrasts, and a comparison of BMR of 13 phylogenetically matched pairs, one species from the tropics and one from northerly temperate areas. Our triptych showed that tropical birds had a reduced BMR, compelling evidence for a connection between the life history of tropical birds and a slow pace of life. Further, tropical migrants breeding in temperate habitats had a lower BMR than did temperate residents, suggesting that these migrants have physiological traits consistent with a slow pace of life. In addition, we determined that tropical birds had a lower cold-induced peak metabolic rate and thermogenic metabolic scope than temperate species, a finding that is consistent with the hypothesis that their environment has not selected for high levels of thermogenesis, or alternatively, that a slow pace of life may be incompatible with high thermogenic capacity. We conclude that physiological function correlates with the suite of life-history traits.basal metabolic rate ͉ life history ͉ peak metabolic rate ͉ tropics ͉ migration L ife-history traits, such as clutch size, age at maturity, rate of growth of offspring, and longevity tend to cluster in ecological space such that species with long lives produce small numbers of offspring that develop slowly and mature relatively late in life (1-3). At the opposite end of this ''slow-fast'' continuum, organisms have low survival rates coupled with large numbers of offspring that develop rapidly and reach sexual maturity at an early age. Among some species, life-history traits also covary with rate of energy expenditure, the pace of life, such that animals with high rates of reproduction have high energy expenditure, and vice versa (4, 5). Support for the connectivity between life history, especially survivorship, and rate of living comes from studies on fruit flies Drosophila (6), houseflies Musca domestica (7), and nematode worms Caenorhabditis elegans (8), as well as meta-analyses on mammals (2, 9, 10). Although less attention has been given to relationships between life history and metabolism in birds, Trevelyan et al. (11) did show an association between resting metabolic rate in birds and their maximum life span.With small clutches (12-14), slower growth as nestlings (15), long periods when fledglings are dependent on parents (16, 17), and higher rates of adult survival than temperate counterparts (15,(18)(19)(20), tropical birds fall along the slow en...

Mutations in patatin-like phospholipase domain-containing 1 (PNPLA1) cause autosomal recessive congenital ichthyosis, but the mechanism involved remains unclear. Here we show that PNPLA1, an enzyme expressed in differentiated keratinocytes, plays a crucial role in the biosynthesis of ω-O-acylceramide, a lipid component essential for skin barrier. Global or keratinocyte-specific Pnpla1-deficient neonates die due to epidermal permeability barrier defects with severe transepidermal water loss, decreased intercellular lipid lamellae in the stratum corneum, and aberrant keratinocyte differentiation. In Pnpla1−/− epidermis, unique linoleate-containing lipids including acylceramides, acylglucosylceramides and (O-acyl)-ω-hydroxy fatty acids are almost absent with reciprocal increases in their putative precursors, indicating that PNPLA1 catalyses the ω-O-esterification with linoleic acid to form acylceramides. Moreover, acylceramide supplementation partially rescues the altered differentiation of Pnpla1−/− keratinocytes. Our findings provide valuable insight into the skin barrier formation and ichthyosis development, and may contribute to novel therapeutic strategies for treatment of epidermal barrier defects.

Summary This review covers the background to discovery of the two key lipoxygenases (LOX) involved in epidermal barrier function, 12R-LOX and eLOX3, and our current views on their functioning. In the outer epidermis, their consecutive actions oxidize linoleic acid esterified in ω-hydroxy-ceramide to a hepoxilin-related derivative. The relevant background to hepoxilin and trioxilin biochemistry is briefly reviewed. We outline the evidence that linoleate in the ceramide is the natural substrate of the two LOX enzymes and our proposal for its importance in construction of the epidermal water barrier. Our hypothesis is that the oxidation promotes hydrolysis of the oxidized linoleate moiety from the ceramide. The resulting free ω-hydroxyl of the ω-hydroxyceramide is covalently bound to proteins on the surface of the corneocytes to form the corneocyte lipid envelope, a key barrier component. Understanding the role of the LOX enzymes and their hepoxilin products should provide rational approaches to ameliorative therapy for a number of the congenital ichthyoses involving compromised barrier function.

Studies of basal metabolic rate (BMR), the minimum metabolic rate of postabsorptive, inactive endotherms while in their rest phase and thermal neutral zone, have contributed significantly to our understanding of animal energetics. Besides body mass, the main determinant of BMR, researchers have invoked diet and phylogenetic history as important factors that influence BMR, although their relative importance has been controversial. For 58 species within the Carnivora, we tested the hypothesis that BMR is correlated with home range size, a proxy for level of activity, and diet, using conventional least squares regression (CLSR) and regression based on phylogenetic independent contrasts (PIC). Results showed that BMR of Carnivora was positively correlated with home range size after controlling for body mass, regardless of the statistical method employed. We also found that diet and mass-adjusted home range size were correlated. When we simultaneously tested the effect of diet and mass-adjusted home range on mass-adjusted BMR, home range size was insignificant because of its colinearity with diet. Then we eliminated home range size from our model, and diet proved to be significant with both CLSR and PIC. We concluded that species that eat meat have larger home ranges and higher BMR than species that eat vegetable matter. To advance our understanding of the potential mechanisms that might explain our results, we propose the "muscle performance hypothesis," which suggests that selection for different muscle fiber types can account for the differences in BMR observed between meat eaters and vegetarian species within the Carnivora.

·SC·dry·mass in Ohio), and a lower percentage of cholesterol (4.1±3.6% in Saudi Arabia; 5.4±2.5% in Ohio) in their SC.Although CWL was lower in sparrows from Arabia, and lipid composition of their SC differed, we could not detect differences between rates of water loss through non-living skin attached to glass vials (46.0±15.7·mg·H 2 O·cm -2 ·day -1 for sparrows in Saudi Arabia; 45.8±27.2·mg·H 2 O·cm -2 ·day -1 for sparrows in Ohio). These results suggest that biological control mechanisms interact with layers of lipids in the stratum corneum to adjust CWL to the environment.