Dietary flavonoids enhance conspicuousness of a melanin‐based trait in male blackcaps but not of the female homologous trait or of sexually monochromatic traits

Signalling theory predicts that signals should fulfil three fundamental requirements: high detectability, discriminability and, most importantly, reliability. Melanins are the most common pigments in animals. Correlations between genotypic and phenotypic qualities of the sender and size and morph of melanin‐based traits are known, but it is contentious whether melanin‐based colouration may signal any quality. We examined the effect of supplementing blackcaps (Sylvia atricapilla) with flavonoids, potent plant antioxidants, on plumage colouration. We demonstrate that melanin‐based colour can fulfil all requirements of signals of phenotypic condition. As predicted by sexual selection theory, flavonoid supplementation influenced only the sexually dichromatic black cap of males, whereas the female homologous trait and the sexually monochromatic back colouration remained unaffected. Using avian vision models we show that birds can estimate male flavonoid intake from colouration of males’ black cap. Because flavonoid ingestion can increase immune responsiveness in blackcaps, melanin head colouration may signal environmentally determined immune condition.     

Garotenoids and colouration of poplar hawkmoth caterpillars (Laothoe populi)

Carotcnoids and chlorophylls a and b were extracted from final instar caterpillars of the poplar hawkmoth ( Laothoe populi ) and the eyed hawkmoth ( Smerinthus ocellata ), as well as from their food plants. Both species of caterpillar absorb the two chlorophylls and the carotenoids lutein, cis -lutein and β-carotene in the gut and deposit lutein and cis -lutein in the integument. It is the lutein, together with pterobilin, that is largely responsible for the colour of the insect: yellow-green poplar hawkmoth caterpillars have more lutein in the integument than dull green ones which in turn have more than white ones. Yellow-green and dull green caterpillars both sequester lutein and cis -lutein in the gut wall, but the yellow-greens translocate more of these pigments to the integument than the dull greens. The white caterpillars absorb very little lutein and cis -lutein into the gut, and so they have much less also in the integument. The mechanism by which the reflected light perceived by the caterpillar is translated into differential absorption of pigment by the gut and deposition in the integument is not known.     

Green colouration of cocoons in Antheraea yamamai (Lepidoptera: Saturniidae): light-induced production of blue bilin in the larval haemolymph

When the larvae of a saturniid silkmoth, Antheraea yamamai, are maintained under high intensity light (5000 lux), they produce green cocoons whereas the cocoons produced under light of low intensity (e.g., 50 lux) or in darkness are yellow. The green colour of the cocoon is due to the presence of a blue bilin pigment in combination with yellow pigment, and light stimulates the accumulation of blue bilin. In the present study, we show that two blue bilins, with similar characteristics to the sarpedobilin in the green cocoon, can be induced in larval haemolymph both in vivo and in vitro. In both conditions, the amount of these bilins increased with increasing intensity or duration of light exposure. Induction also occurred at 0 degrees C. In contrast, the chromophore of the constitutive biliprotein of the haemolymph did not change depending on light conditions. Size fractionation of the haemolymph indicates that the precursor of the blue bilins induced by light is bound to a protein with a molecular mass of 5000 Da or more. Thus, in these insects, the blue bilin responsible for green colouration is facultative under photochemical stimulation.     

Age, Growth, and Sexual Development in the Self-fertilizing Hermaphroditic Fish Rivulus marmoratus

We studied age, growth, and sexual development in the early life intervals of the self-fertilizing mangrove killi-fish, Rivulus marmoratus. Newly hatched (day 0) individuals had sagittal otoliths of 60m radius, with about 30 increments. Sequential sampling until about day 60 after hatching yielded otoliths with the number of increments outside the 60m radius equal to the daily age of the fish. Alizarin complexone marking of otoliths also confirmed the increments were daily, and demonstrated the applicability of this technique to field studies for capture-mark-recapture, or age and growth estimates. Individuals fed a restricted amount of food formed fewer daily otolith growth increments than fish fed to satiation each day. Using histological analysis for identifying gonad morphogenesis, we found no correlation between gonadal development and external appearance (caudal ocellus, orange fin colouration) in young fish of known ages. The caudal ocellus was not present until 9mm total length, and developed thereafter. Of 136 individuals examined, fish less than 17.2mm total length (TL, n = 124) were females. Testicular tissue first appeared among individuals 17–18mm TL (n = 3), while some individuals greater than 18mm TL (n = 8) were functional hermaphrodites. The single male in our study was relatively of small body size (9.6mm, day 37) with a distinct caudal ocellus, indicating that it is presumably a primary male.     

Phylogenetic comparative analysis supports aposematic colouration–body size association in millipede assassins (Hemiptera: Reduviidae: Ectrichodiinae)

The diversity of colour patterns and its importance in interactions with the environment make colouration in animals an intriguing research focus. Aposematic colouration is positively correlated with body size in certain groups of animals, suggesting that warning colours are more effective or that crypsis is harder to achieve in larger animals. Surprisingly, this relationship has not been recovered in studies investigating insects, which may have been confounded by a focus on aposematic taxa that are also gregarious. Millipede assassin bugs (Hemiptera: Reduviidae: Ectrichodiinae) comprise species with cryptic and aposematic colour patterns across a range of body sizes, are typically solitary as adults and are thus an excellent model for investigating a possible association between colouration and body size. Here, we use a comprehensive phylogeny for Ectrichodiinae, ancestral state reconstruction of colouration, and phylogenetic comparative methods to test for a colouration–body size association. The ancestor of Ectrichodiinae is reconstructed as cryptically coloured, with multiple subsequent transitions between aposematic and cryptic colouration. Aposematic colouration is positively associated with male body length and supports the hypothesis that selection on Ectrichodiinae body size may influence evolutionary transitions between aposematic and cryptic colouration or alternatively that selection for aposematic colouration influences body size evolution.     

Carotenoid-based plumage pigmentation and concentration as a function of sex and habitat type in the Yellow-breasted Boubou Laniarius atroflavus

The study of avian integumentary colouration can offer insight into dietary and metabolic processes as well as fitness in focal species. Yet, we know relatively less about the system of feather colouration in African birds in comparison to Europe, North America and the neotropics. In this study, we biochemically characterised and quantified the pigmentary basis for breast plumage colouration in the Yellow-breasted Boubou Laniarius atroflavus, a little-known Afromontane species restricted to the Nigerian–Cameroon Highlands. We also measured differences in carotenoid concentration and feather reflectance between sexes, and between birds inhabiting edge and riparian habitats. Six carotenoid pigments were recovered from the yellow feathers – canary xanthophyll A and B, a cis isomer of each, isoastaxanthin and an unidentified carotenoid. We determined that the yellow colour of the breast feathers is carotenoid-based, with the greater proportion as canary xanthophylls. The presence of the ketocarotenoid, isoastaxanthin, provides the basis for further studies into red, orange and yellow coloured congenerics. Males appeared to have higher feather pigment concentrations than females, and birds resident in the edge habitat appeared to have slightly higher feather pigment concentrations than those in the degraded riparian habitat. There was little indication of differences in feather reflectance between sexes and habitat types. However, low samples size restricted further differentiation. There is also the need for further studies on the dietary and metabolic pathways of feather colouration to better understand how ecological variation may shape pigment uptake, transport, synthesis and deposition in feathers.     

Adaptive plasticity in wing melanisation of a montane butterfly across a Himalayan elevational gradient

1. Traits that are significant to the thermal ecology of temperate or montane species are expected to prominently co-vary with the thermal environment experienced by an organism. The Himalayan Pieris canidia butterfly exhibits considerable variation in wing melanisation. We investigated: (i) whether variation in wing melanisation and (ii) activity period of this montane butterfly was influenced by the seasonally and elevationally changing thermal landscape.
2. We discovered that wing melanisation varied across elevation, seasons, sex, and wing surfaces, with the variation strongly structured in space and time: colder seasons and higher elevations produced more melanic individuals. Notably, melanisation did not vary uniformly across all wing surfaces: (i) melanisation of the ventral hindwing co-varied much more prominently with elevation, but (ii) melanisation on all other surfaces varied with seasonal changes in the thermal environment.
3. Observed wing surface-specific patterns indicated thermoregulatory function for this variation in melanisation. Such wing surface-specific responses to seasonal and elevational variation in temperature have rarely been reported in montane insects.
4. Moreover, daily and seasonal thermal cycles were found to strongly influence activity periods of this species, suggesting the potential limits to wing melanisation plasticity.
5. Overall, these results showed that the seasonal and elevational gradients in temperature influence the thermal phenotype as well as activity periods of this Himalayan butterfly. It will be critical to study the phenotypic evolution of such montane insects in response to the ongoing climate change, which is already showing significant signs in this iconic mountain range.

     

Evidence for aposematism in the plant bug Lopidea nigridea Uhler (Hemiptera: Miridae: Orthotylinae)

The biology of the plant bug Lopidea nigridea is described, with particular focus on whether this red and black species can be considered aposematic. Lopidea individuals were rejected after attack in 92 of 112 feeding trials involving three of their five most common arthropod predator species. Compared to another syntopic plant bug species, L. nigridea is aggregated in distribution, and individuals are sedentary in their basic daily habits. These life-history features, coupled with the ability to survive most attacks by arthropod predators in the feeding trials, suggest that L. nigridea is protected to some degree by an aposematic defence. How L. nigridea may acquire its distastefulness is discussed, with special attention to host plant relations in L. nigridea and in the genus Lopidea as a whole.     

Adaptive divergence within and between ecotypes of the terrestrial garter snake, Thamnophis elegans, assessed with F(ST)-Q(ST) comparisons

Populations of the terrestrial garter snake (Thamnophis elegans) around Eagle Lake in California exhibit dramatic ecotypic differentiation in life history, colouration and morphology across distances as small as a few kilometres. We assayed the role of selection in ecotypic differentiation in T. elegans using F(ST)-Q(ST) analysis and identified selective agents using direct and indirect observations. We extended the conventional implementation of the F(ST)-Q(ST) approach by using three-level analyses of genetic and phenotypic variance to assess the role of selection in differentiating populations both within and between ecotypes. These results suggest that selection has driven differentiation between as well as within ecotypes, and in the presence of moderate to high gene flow. Our findings are discussed in the context of previous correlational selection analyses which revealed stabilizing and correlational selection for some of the traits examined.     

Tail colour signals performance in blue tit nestlings

Indirect sexual selection arises when reproductive individuals choose their mates based on heritable ornaments that are genetically correlated to fitness. Evidence for genetic associations between ornamental colouration and fitness remains scarce. In this study, we investigate the quantitative genetic relationship between different aspects of tail structural colouration (brightness, hue and UV chroma) and performance (cell‐mediated immunity, body mass and wing length) in blue tit (Cyanistes caeruleus) nestlings. In line with previous studies, we find low heritability for structural colouration and moderate heritability for performance measures. Multivariate animal models show positive genetic correlations between the three measures of performance, indicating quantitative genetic variation for overall performance, and tail brightness and UV chroma, two genetically independent colour measures, are genetically correlated with performance (positively and negatively, respectively). Our results suggest that mate choice based on independent aspects of tail colouration can have fitness payoffs in blue tits and provide support for the indirect benefits hypothesis. However, low heritability of tail structural colouration implies that indirect sexual selection on mate choice for this ornament will be a weak evolutionary force.