Climatic adaptation and hominid evolution: The thermoregulatory imperative

Anthropologists have long recognized the existence among modern humans of geographical variations in body form that parallel climatic gradients, part of more general zoological phenomena commonly referred to as Bergmann's or Allen's “Rules”. These observations have rarely been applied to earlier hominids, in part because fossil skeletons usually are so incomplete that it is difficult to reconstruct body morphology accurately. However, within the past two decades two early hominids have been discovered that preserve enough of the skeleton to allow confident assessment of their body size and shape. Comparison of these specimens—the Australopithecus afarensis A.L. 288-1 (“Lucy”) and the Homo erectus KNM-WT 15000—with others that are less complete make it evident that the evolution of Homo erectus was accompanied by not only a marked increase in body size, but also a similarly dramatic increase in the linearity of body form. That is, relative to their heights, small australopithecines had very broad bodies, whereas large early Homo had narrow bodies. This difference in body form cannot be explained on the basis of obstetric or biomechanical factors, but is consistent with thermoregulatory constraints on body shape. Specifically, to maintain the same ratio of body surface area to body mass, which is an important thermoregulatory mechanism, increases in height should be accompanied by no change in body breadth, which is exactly what is seen in comparisons of A.L. 288-1 and KNM-WT 15000. Conversely, Neandertals living in colder climates had much wider bodies, which are adaptive for heat retention. Differences in limb length proportions between fossil hominids are also consistent with thermoregulatory principles and the geographic variation observed among modern humans. Climatic adaptation during hominid evolution may have wide-ranging implications, not only with regard to interpreting body morphology, but also in relation to ecological scenarios, population movements, and the evolution of the brain.     

Wingstroke frequency of foraging and hovering bumblebees in relation to morphology and temperature

Abstract Wingstroke frequency, morphometries and thoracic temperatures of freely foraging bumblebees were examined in the field at ambient temperatures varying from 10 to 29^oC. Frequency was strongly correlated with morphometric parameters, particularly wing length, but was not correlated with either ambient or thoracic temperature. Magnitudes and scaling of frequency of foraging bees were comparable to values obtained for bees hovering in a closed chamber. These data indicate that frequency is primarily determined by morphometric characteristics which determine lift requirements and do not support the hypothesis that frequency is varied in response to environmental conditions as a means of in-flight thermoregulation.     

On the significance of structural vegetation elements for caterpillar thermoregulation in two peat bog butterflies: Boloria eunomia and B. aquilonaris

Purpose

Temperature profoundly impacts on distribution and habitat-use of organisms. The development of ectothermous caterpillars does not depend on host plant quality only, but also on the availability of suitable thermal conditions. Selection for thermally favorable microclimates (i.e. behavioral thermoregulation) is a primary mechanism of temperature control, and caterpillars can be either (or alternately) temperature conformers (i.e. passively adopting ambient temperature conditions) or thermoregulators (i.e. able to some extent to elevate or decrease their body temperature relative to ambient temperature). Here, we addressed the functional significance of different structural vegetation elements for the behavioral thermoregulation by caterpillars of two butterfly species.

Results

Weather conditions influenced the caterpillar detection probability within host plant patches, indicating that caterpillars can hide and use suitable microclimates provided by vegetation structures to cope with weather variations. This is why we (1) evaluated the heterogeneity in temperature conditions provided by these structures, (2) quantified the influence of ambient temperature and light intensity on caterpillar body temperature, and (3) tested how position on structure, substrate color and exposition influenced caterpillar body temperature. As expected, vegetation structures provided heterogeneous temperature and sun exposition conditions, while caterpillar body temperature was dependent on ambient temperature and light intensity. But body temperature was additionally influenced by the position on vegetation structures, substrate color and exposition.

Conclusions

These results suggest that there is no unique and fixed structure in the vegetation subsuming the best thermal conditions for caterpillars. We argue that a better understanding of the thermal properties of vegetation structures is essential for correctly understanding caterpillar habitat-use and the behavioral mechanisms driving their body thermoregulation. Conceptually this means that thermal conditions should be included in the definition of a species' functional habitat. Practically this may influence the choice of appropriate habitat management for species of conservation concern.     

爬行动物胚胎的行为热调节

行为热调节是外温动物体温调节的主要方式。传统观点认为行为热调节仅存在于胚后阶段,然而近年来研究表明爬行动物胚胎具备行为热调节能力。本文回顾了爬行动物胚胎行为热调节的发现和研究进展,探讨了胚胎行为热调节的生态适应意义,分析了胚胎如何感知温度以完成行为热调节,指出了该领域的未来研究方向。     

Hominine morphology, climatic determinism and an alternative hypothesis

Climatic determinism is an established hypothesis to explain phenotypic selection of hominine physique. Adaptations to heat and cold stress are, however, probably physiological rather than morphological. This paper advances an alternative hypothesis which relegates the influence of the climate to an indirect role only. Athletes select themselves into events for which their physiques are appropriate. ‘Field eventers’ are, in Sheldon's terminology, mesomorphic and ectopenic (muscular and lacking in linearity). ‘Track eventers’ other than sprinters, have balanced physiques and are ectomorphic (linear). Distance runners are usually small and walkers tall. All are endopenic (lacking in the fat component). The physique of the northern (Inuit and Gurkhas) and southern (Bantu and San) study populations had morphological affinities with the physiques of the field and track eveters respectively. Northern populations, hunting megafauna over hilly terrain and sometimes through snow, need physiques of strength in body and leg. Southern populations, running down medium-size game, need the physique of distance runners. The physique of these contemporary populations may therefore be explained in terms of adaptations to the recent demands of hunting a particular range of fauna in a given physicogeographical environment. The pleomorphism and relative endomorphy of the White subjects can be explained by the relative sedentism associated with the adoption of agriculture. The hypothesis also explains the extreme physiques of Pygmies and Nilotics. The thermoregulatory and the alternative ‘task demand’ hypotheses, however, are not incompatible. The small size of the San hunter, for example, whilst having an undoubted biomechanical advantage, will assist rather than hinder thermoregulation.     

The behavioural thermal preference of the common triplefin (Forsterygion lapillum) tracks aerobic scope optima at the upper thermal limit of its distribution

Ocean temperatures are rising and fish are redistributing themselves poleward and into deeper waters to retain a favourable thermal environment (11 and 30). To investigate whether biogeographical shifts might occur through behavioural redistribution into optimal environments, we examined whether a common triplefin species (Forsterygion lapillum) would behaviourally select (i.e. track) a temperature that matches its physiological optimum under laboratory conditions. F. lapillum were acclimated to 15, 18 or 21 °C for at least 4 weeks, after which various rates of oxygen consumption (MO₂) were measured using automated respirometry and their behavioural thermal preferenda assessed using an electronic shuttle choice tank. Aerobic metabolic scope (resolved as the difference between maximal and maintenance MO₂) did not differ across all thermal treatments (i.e. specimens acclimated to 15, 18 or 21 °C) revealing that F. lapillum is a eurythermal species with a range of optimal physiological performance that closely matches the environmental conditions they are exposed to. A comparably wide range of behavioural preference would perhaps be expected but all three acclimation groups showed a surprisingly narrow behavioural preference range of 20–21 °C. The results therefore suggest that, irrespective of acclimation, eurythermal species may have a tendency to select optimal temperatures at the upper limit of their thermal distribution range. The results are discussed in the context of the ecology and the expected response of F. lapillum to future thermal change.     

Foraging energetics of arctic cormorants and the evolution of diving birds

Efficient body insulation is assumed to have enabled birds and mammals to colonize polar aquatic ecosystems. We challenge this concept by comparing the bioenergetics of cormorants ( Phalacrocorax carbo ) living in temperate and arctic conditions. We show that although these birds have limited insulation, they maintain high body temperature (42.3 °C) when diving in cold water (1–10 °C). Their energy demand at these times is extremely high (up to 60 W kg⁻¹). Free-living cormorants wintering in Greenland (water temperature −1 °C) profoundly alter their foraging activity, thus minimizing time spent in water and the associated high thermoregulatory costs. They then meet their daily food demand within a single intense dive bout (lasting 9 min on average). Their substantial energy requirements are balanced by the highest predatory efficiency so far recorded for aquatic predators. We postulate that similar behavioural patterns allowed early diving birds (Cretaceous) to colonize cold coastal areas before they evolved efficient insulation.