The lizard Psammodromus algirus (Squamata: Lacertidae) is darker at high altitudes

Altitudinal gradients offer a good opportunity to study organisms' adaptations to clinal environmental variables. Regarding altitude, the most influential variables on organisms are temperature and ultraviolet (UV) solar radiation, the first decreasing and the second increasing with altitude. Both variables affect ectotherms' biology, as ectotherms depend on environmental temperature for thermoregulation, frequently being heliotherms. Here, we studied dorsal coloration in the lizard Psammodromus algirus (Linnaeus, 1758) along a wide altitudinal gradient (2200 m) in Sierra Nevada (south‐east Spain). We hypothesize that the skin will be darker with altitude, i.e. in environments with lower temperatures and higher UV radiation intensity. Results show that individual dorsal colorations became darker at high altitude. We propose two non‐mutually exclusive explanations for this result: (1) darker dorsal surface would favour faster warming at high altitudes, where temperature is lower, and (2) darker dorsal surface would protect against UV radiation, stronger at high altitudes. We found significant relationships between both temperature and UV radiation and population dorsal darkness, giving mixed support for the two explanations. Moreover, dorsal hue was positively correlated with substrate hue, suggesting that hue evolved to maximize crypsis. Our study therefore suggests that geographical variation in dorsal coloration in this lizard is adaptive, and darkness coloration might have evolved in response to adverse conditions (low temperature and high UV radiation) at high altitudes. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 132–141.     

Selective bird predation on the peppered moth: the last experiment of Michael Majerus

Colour variation in the peppered moth Biston betularia was long accepted to be under strong natural selection. Melanics were believed to be fitter than pale morphs because of lower predation at daytime resting sites on dark, sooty bark. Melanics became common during the industrial revolution, but since 1970 there has been a rapid reversal, assumed to have been caused by predators selecting against melanics resting on today's less sooty bark. Recently, these classical explanations of melanism were attacked, and there has been general scepticism about birds as selective agents. Experiments and observations were accordingly carried out by Michael Majerus to address perceived weaknesses of earlier work. Unfortunately, he did not live to publish the results, which are analysed and presented here by the authors. Majerus released 4864 moths in his six-year experiment, the largest ever attempted for any similar study. There was strong differential bird predation against melanic peppered moths. Daily selection against melanics (s ≈ 0.1) was sufficient in magnitude and direction to explain the recent rapid decline of melanism in post-industrial Britain. These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.     

Thermobiological effects of temperature‐induced color variations in Aglais urticae (Lepidoptera,Nymphalidae)

Coloration of animals is important for camouflage, for social behavior, or for physiological fitness. This study investigates the color variation in adults of Aglais urticae obtained on subjecting some pre‐imaginal stages to different temperature conditions and their thermobiological consequences. To investigate the evolutionary–ecological interactions of temperature and pigmentation in butterflies, caterpillars, and pupae of the small tortoiseshell, Aglais urticae (Lepidoptera, Nymphalidae), larvae from Central Europe and Scandinavia were reared at temperatures between 7 and 34°C in the laboratory or in the field. After emergence, the intensity of pigmentation of the imagines and their increase in body temperature under defined full‐spectrum light irradiation were quantified by image analysis and thermal imaging. At constant conditions, ambient rearing temperature and pigmentation intensity of imagines were negatively and linearly correlated in Central European butterflies, regardless of whether the pupal stage alone or, additionally, the last period of the larval stage was exposed to these conditions: low temperatures induced darker coloration and high temperatures led to lighter individuals. A thermal pulse of a few days alone at the beginning of pupal dormancy led to a similar, albeit weakened, effect. Caterpillars of the Scandinavian subspecies A. urticae polaris, whose pupal dormancy took place under Central European field conditions, developed into strongly pigmented imagines. The thermobiological relevance of more intense pigmentation was shown by significantly higher absorption of light, and thus stronger increased body temperature after 5 min of defined illumination, but this difference ceased after 15 min. Our results show that phenotypic plasticity in wing coloration is adaptive since temperature‐induced developmental changes provide thermobiological benefit in adult butterflies. We propose that, in subpolar latitudes, darker coloration likely has a selection advantage favoring individuals with reaction norms gradually shifted to stronger pigmented phenotypes, possibly leading to the establishment of a pigmentation cline.     

Warm developmental temperatures induce non-adaptive plasticity in the intrasexually selected colouration of a dragonfly

1. When the breeding environment fluctuates across generations, reproductive traits may evolve plasticity that optimises the balance between survival and mating success for the prevailing environment. 2. For sexually selected colouration, this balance can depend on environmental temperatures. Accordingly, breeding colouration often co-varies with temperature through space and time. However, whether such traits exhibit plasticity in response to environmental temperatures is poorly understood. 3. In the present study, a dragonfly (Pachydiplax longipennis) was reared under ambient or experimentally warmed conditions and tested for plasticity in its intrasexually selected wing colouration. Although wing colouration improves male territorial success, these advantages are smaller under warmer conditions than cooler conditions. It was therefore predicted that males reared under the ambient thermal conditions of the study site (Cleveland, Ohio) would develop more wing colouration than those reared under experimentally warmed conditions. 4. Contrary to this prediction, males reared in warm larval temperatures produced more wing colouration. Thus, although the secondary sexual colouration of this species displays some thermal plasticity, it does not appear to be adaptive relative to the known thermal variation of intrasexual selection in this population. 5. Given that the environment often determines the strength and direction of sexual selection, future studies should consider the potential for non-adaptive, and even maladaptive, developmental plasticity in the sexually selected traits of insects.     

Polymorphic Müllerian mimicry and interactions with thermal melanism in ladybirds and a soldier beetle: a hypothesis

It is argued that groups of similarly coloured species of coccinellids are Müllerian mimicry rings. This is based on a synthesis of the literature about the nature of their biology and aposematic colour patterns, their highly developed chemical defence and the responses of bird predators to them. The system of multiple mimicry ‘rings’ is illustrated for the Dutch coccinellid fauna. Some polymorphic species, including Adalia, exhibit red forms and black melanic forms which are apparently components of different putative mimicry rings. A similar reasoning is put forward with regard to the orange and the black forms of the soldier beetle Cuntharis livida. Hypotheses involving spatial variation in comimics, as have been developed to account for some other cases of polymorphic Miillerian mimicry, predict that sympatric polymorphic species exhibiting similar sets of phenotypes will show parallels in their geographical variation. This is tested for A. bipunctata and A. decempunctata in The Netherlands. On this local scale there is no parallel variation; A. bipunctata exhibits marked geographical differentiation whereas A. decempunctata shows a general uniformity in morph frequency. Observations on their population biology show that only in A. bipunctata is there a major spring period of adult reproduction on shrubs exposed to direct sunshine. Previous work has demonstrated an influence of thermal melanism in this period of the life cycle. It is suggested that local responses in species such as A. bipunctata may reflect a partial ‘escape’ from stabilizing aposematic selection. The basis of a steep cline found in C. livida, which opposes one in A. bipunctata, is unknown and unlikely to be related to mimicry. There is some evidence that the polymorphism is influenced by non-random mating. When species and communities of coccinellids are considered on a wide geographical scale many observations about their colour patterns and spatial variation, especially those of Dobzhansky, support an interaction between selection favouring mimetic resemblance and forms of climatic selection, especially thermal melanism. The polymorphism in Adalia is discussed in relation to a system of multiple mimicry rings and to Thompson's recent theoretical treatment of the maintenance of some polymorphisms for warning coloration by a balance between aposematic and apostatic selection. This becomes more tenable in coccinellids because of evidence that bird predators show a variable response to them. Frequency-independent selection arising from thermal melanism can provide the basis of spatial variation in equilibrium points. An alternative to such a hypothesis is one in which differences in unpalatability between species of coccinellids are emphasized (after experiments of Pasteels and colleagues). Some less unpalatable species such as Adalia may have responded to periods of prolonged disruptive selection acting in a frequency-dependent way to promote polymorphic mimicry associated with different modal colour patterns and intermediate in nature between classical Batesian and Müllerian mimicry. The likely occurrence of a supergene controlling polymorphism in some coccinellids is consistent with such an explanation.