Thermal melanism in ectotherms

Temperature has dramatic evolutionary fitness consequences and is therefore a major factor determining the geographic distribution and abundance of ectotherms. However, the role that age might have on insect thermal tolerance is often overlooked in studies of behaviour, ecology, physiology and evolutionary biology. Here, we review the evidence for ontogenetic and ageing effects on traits of high- and low-temperature tolerance in insects and show that these effects are typically pronounced for most taxa in which data are available. We therefore argue that basal thermal tolerance and acclimation responses (i.e. phenotypic plasticity) are strongly influenced by age and/or ontogeny and may confound studies of temperature responses if unaccounted for. We outline three alternative hypotheses which can be distinguished to propose why development affects thermal tolerance in insects. At present no studies have been undertaken to directly address these options. The implications of these age-related changes in thermal biology are discussed and, most significantly, suggest that the temperature tolerance of insects should be defined within the age-demographics of a particular population or species. Although we conclude that age is a source of variation that should be carefully controlled for in thermal biology, we also suggest that it can be used as a valuable tool for testing evolutionary theories of ageing and the cellular and genetic basis of thermal tolerance.

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Insect thermal tolerance: what is the role of ontogeny, ageing and senescence?

During the past decade, melanins and melanogenesis have attracted growing interest for a broad range of biomedical and technological applications. The burst of polydopamine-based multifunctional coatings in materials science is just one example, and the list may be expanded to include melanin thin films for organic electronics and bioelectronics, drug delivery systems, functional nanoparticles and biointerfaces, sunscreens, environmental remediation devices. Despite considerable advances, applied research on melanins and melanogenesis is still far from being mature. A closer intersectoral interaction between research centers is essential to raise the interests and increase the awareness of the biomedical, biomaterials science and hi-tech sectors of the manifold opportunities offered by pigment cells and related metabolic pathways. Starting from a survey of biological roles and functions, the present review aims at providing an interdisciplinary perspective of melanin pigments and related pathway with a view to showing how it is possible to translate current knowledge about physical and chemical properties and control mechanisms into new bioinspired solutions for biomedical, dermocosmetic, and technological applications.

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Melanins and melanogenesis: from pigment cells to human health and technological applications.

Widespread recognition of the importance of biological studies at large spatial and temporal scales, particularly in the face of many of the most pressing issues facing humanity, has fueled the argument that there is a need to reinvigorate such studies in phys- iological ecology through the establishment of a macrophysiology. Following a period when the fields of ecology and physiological ecol- ogy had been regarded as largely synonymous, studies of this kind were relatively commonplace in the first half of the twentieth century. However, such large-scale work subsequently became rather scarce as physiological studies concentrated on the biochemical and mo- lecular mechanisms underlying the capacities and tolerances of spe- cies. In some sense, macrophysiology is thus an attempt at a con- ceptual reunification. In this article, we provide a conceptual framework for the continued development of macrophysiology. We subdivide this framework into three major components: the estab- lishment of macrophysiological patterns, determining the form of those patterns (the very general ways in which they are shaped), and understanding the mechanisms that give rise to them. We suggest ways in which each of these components could be developed usefully.

Synthesis Macrophysiology: A Conceptual Reunification

Widespread recognition of the importance of biological studies at large spatial and temporal scales, particularly in the face of many of the most pressing issues facing humanity, has fueled the argument that there is a need to reinvigorate such studies in physiological ecology through the establishment of a macrophysiology. Following a period when the fields of ecology and physiological ecology had been regarded as largely synonymous, studies of this kind were relatively commonplace in the first half of the twentieth century. However, such large-scale work subsequently became rather scarce as physiological studies concentrated on the biochemical and molecular mechanisms underlying the capacities and tolerances of species. In some sense, macrophysiology is thus an attempt at a conceptual reunification. In this article, we provide a conceptual framework for the continued development of macrophysiology. We subdivide this framework into three major components: the establishment of macrophysiological patterns, determining the form of those patterns (the very general ways in which they are shaped), and understanding the mechanisms that give rise to them. We suggest ways in which each of these components could be developed usefully.

/pdf/macrophysiology-a-conceptual-reunification-53g0uh7mk8.pdf

Macrophysiology: A Conceptual Reunification

Preferred body temperatures (T
 sel) of ectotherms are important for ecological and evolutionary studies. In lizards, the measurement of T
 sel is controversial for several reasons, generally related to hypotheses addressing how T
 sel may evolve in the wild. Although seldom explicitly tested, evolutionary hypotheses of adaptation to local climate require that T
 sel meets the conditions of natural selection, which include repeatability, heritability and a link to fitness. Here, we investigated repeatability (τ, intra-class correlation coefficient) of T
 sel at several time-scales using four Cordylid species from heterogeneous thermal habitats. Although there was significant inter-individual variation within days (P   0.05). Repeatability was low in all species investigated (from 0 to 0.482) when compared against other estimates of repeatability of T
 sel in the literature. Irrespective of how T
 sel was calculated, it showed inconsistent and variable temporal effects across species. Furthermore, repeatability of T
 sel did not change with acclimation to laboratory conditions. These data have implications for understanding the evolution of thermoregulation in these and other ectotherms.

/pdf/low-repeatability-of-preferred-body-temperature-in-four-u8k35nuqba.pdf

Low repeatability of preferred body temperature in four species of Cordylid lizards: Temporal variation and implications for adaptive significance

Whether melanism plays a significant role in thermoregulation has been a persistent question in studies of thermal biology of ectotherms. This review provides a synthesis of the thermal melanism hypothesis which states that dark individuals (i.e. lower skin reflectance) are at an advantage under conditions of low temperature since they heat up faster than light individuals at a given level of solar radiation. Although skin color is an important trait in the thermal biology of ectotherms, it has rarely been explored in non-insect models. We draw on the available literature to assess the validity of four key assumptions that underlie this hypothesis. Ample support was found for the assumption that melanistic diurnal species inhabit cooler areas than lighter species and that melanism results in greater fitness in cold climates. By contrast, little direct support could be found for the assumption that there is a consistent melanism–body size tradeoff. Finally, the assumption that color, thermal physiology and behavior are coadapted has some support but requires further investigation. Overall, the functional, molecular and adaptive mechanisms of thermal melanism await further study. r 2007 Elsevier Ltd. All rights reserved.

Susana Clusella Trullas

Papers

Thermal melanism in ectotherms

Low repeatability of preferred body temperature in four species of Cordylid lizards: Temporal variation and implications for adaptive significance

Mini review Thermal melanism in ectotherms