Grapheme-colour synaesthesia improves detection of embedded shapes,but without pre-attentive ‘pop-out’ of synaesthetic colour

For people with synaesthesia letters and numbers may evoke experiences of colour. It has been previously demonstrated that these synaesthetes may be better at detecting a triangle made of 2s among a background of 5s if they perceive 5 and 2 as having different synaesthetic colours. However, other studies using this task (or tasks based on the same principle) have failed to replicate the effect or have suggested alternative explanations of the effect. In this study, we repeat the original study on a larger group of synaesthetes (n = 36) and include, for the first time, an assessment of their self-reported colour experiences. We show that synaesthetes do have a general advantage over controls on this task. However, many synaesthetes report no colour experiences at all during the task. Synaesthetes who do report colour typically experience around one third of the graphemes in the display as coloured. This is more consistent with theories of synaesthesia in which spatial attention needs to be deployed to graphemes for conscious colour experiences to emerge than the interpretation based on ‘pop-out’.     

The seven ways eukaryotes produce repeated colour motifs on external tissues

The external tissues of numerous eukaryote species show repeated colour patterns, usually characterized by units that are present at least twice on the body. These dotted, striped or more complex phenotypes carry out crucial biological functions, such as partner recognition, aposematism or camouflage. Very diverse mechanisms explaining the formation of repeated colour patterns in eukaryotes have been identified and described, and it is timely to review this field from an evolutionary and developmental biology perspective. We propose a novel classification consisting of seven families of primary mechanisms: Turing(-like), cellular automaton, multi-induction, physical cracking, random, neuromuscular and printing. In addition, we report six pattern modifiers, acting synergistically with these primary mechanisms to enhance the spectrum of repeated colour patterns. We discuss the limitations of our classification in light of currently unexplored extant diversity. As repeated colour patterns require both the production of a repetitive structure and colouration, we also discuss the nature of the links between these two processes. A more complete understanding of the formation of repeated colour patterns in eukaryotes will require (i) a deeper exploration of biological diversity, tackling the issue of pattern elaboration during the development of non-model taxa, and (ii) exploring some of the most promising ways to discover new families of mechanisms. Good starting points include evaluating the role of mechanisms known to produce non-repeated colour patterns and that of mechanisms responsible for repeated spatial patterns lacking colouration.     

Detectability matters: conspicuous nestling mouth colours make prey transfer easier for parents in a cavity nesting bird

An often underappreciated function of signals is to notify receivers of the presence and position of senders. The colours that ornament the mouthparts of nestling birds, for example, have been hypothesized to evolve via selective pressure generated by parents'' inability to efficiently detect and feed nestlings without such visually conspicuous targets. This proposed mechanism has primarily been evaluated with comparative studies and experimental tests for parental allocation bias, leaving untested the central assumption of this detectability hypothesis, that provisioning offspring is a visually challenging task for avian parents and conspicuous mouths help. To test this assumption, I manipulated the mouths of nestling house sparrows to appear minimally and maximally conspicuous, and quantified prey transfer difficulty as the total duration of a feeding event and the number of transfer attempts required. Prey transfer to inconspicuous nestlings was, as predicted, more difficult. While this suggests that detectability constraints could shape nestling mouth colour evolution, even minimally conspicuous nestlings were not prohibitively difficult for parents to feed, indicating that a more nuanced explanation for interspecific diversity in this trait is needed.     

Effect of production system before the finishing period on carcass,meat and fat qualities of beef

Twenty Gascon young bulls that had been reared either in intensive conditions (INT) (n=10) with early weaning at 3 to 4 months, or in a traditional extensive (EXT) system (n=10) with weaning at 7 months, were subjected to the same conditions during the 145-day finishing period. Production system before the finishing period did not affect conformation, dressing percentage or morphology of the carcass; nevertheless, tissue composition differed somewhat between the two groups. Display had a stronger effect on meat colour than did production system. Percentage of myoglobin was highest in INT (P⩽0.001), although meat texture and sensory quality did not differ between rearing conditions. EXT animals had darker, more yellow fat, a higher percentage of n-3 fatty acids (P⩽0.001), a lower percentage of saturated fatty acids (P⩽0.05) and a lower n-6/n-3 index (P⩽0.001) than did the INT-reared animals. Production system before the fattening period might modify some of the characteristics of commercial beef, especially those associated with fat.     

Intensity of mouth coloration in Blackcap Sylvia atricapilla nestlings affects food distribution among siblings but not provisioning of the whole brood

Among various begging stimuli, mouth coloration has received increasing attention in recent years, and previous research has demonstrated that mouths of nestling Canaries Serinus canaria get redder with the extent of food deprivation and that parents preferentially feed nestlings of redder gapes. This study assesses whether the intensity of red mouth colour in nestling Blackcaps Sylvia atricapilla is a signal in parent–offspring communication. This is one of the few species with a naturally red gape in which the function of mouth redness has been tested. Three predictions were experimentally tested: (1) reddening the gape of a single nestling within a brood increases its provisioning in relation to other siblings; (2) reddening the gapes of all nestlings within a brood increases parental feeding rate; and (3) food deprivation increases nestling mouth redness. The effect of nestling quality on mouth redness was also assessed. The intensity of gape coloration affected food distribution, but in a way opposite to that expected: an increase in mouth redness of the nestling caused reduced feeding by parents. However, reddening the gapes of all nestlings had no effect on provisioning of the whole brood, suggesting that Blackcap parents use different cues for provisioning particular nestlings and the whole brood. Intensity of mouth redness in Blackcap nestlings was not affected either by food deprivation or by nestling quality in terms of mass and rank in the nest.     

Floral colour variation of Nicotiana glauca in native and non-native ranges: Testing the role of pollinators' perception and abiotic factors

• Invasive plants displaying disparate pollination environments and abiotic conditions in native and non-native ranges provide ideal systems to test the role of different ecological factors driving flower colour variation.
• We quantified corolla reflectance of the ornithophilous South American Nicotiana glauca in native populations, where plants are pollinated by hummingbirds, and in populations from two invaded regions: South Africa, where plants are pollinated by sunbirds, and the Balearic island of Mallorca, where plants reproduce by selfing. Using visual modelling we examined how corolla reflectance could be perceived by floral visitors present in each region. Through Mantel tests we assessed a possible association between flower colour and different abiotic factors.
• Corolla reflectance variation (mainly along medium to long wavelengths, i.e. human green-yellow to red colours) was greater among studied regions than within them. Flower colour was more similar between South America and South Africa, which share birds as pollinators. Within invaded regions, corolla reflectance variation was lower in South Africa, where populations could not be distinguished from each other by sunbirds, than in Spain, where populations could be distinguished from each other by their occasional visitors. Differences in corolla colour among populations were partially associated with differences in temperature.
• Our findings suggest that shifts in flower colour of N. glauca across native and invaded ranges could be shaped by changes in both pollination environment and climatic factors. This is the first study on plant invasions considering visual perception of different pollinators and abiotic drivers of flower colour variation.

     

Eye colour in juvenile Atlantic salmon: effects of social status, aggression and foraging success

Status-based differences in sclera colour in small groups of juvenile Atlantic salmon Salmo salar , held in a semi-natural environment over a 20 day period, became obvious 3 days after the start of the study and persisted for the 20 days. Dominant fish had pale sclera, and this pattern was very stable over the experimental period. In contrast, the sclera colour of subordinate fish (ranks 2–5) fluctuated from day to day. Median sclera colour offish ranked 4–5 darkened on days they received more aggression, and sclera of rank 2 fish were lighter on days on which they initiated more attacks. Changes in sclera colour of fish ranked 2–4 were more frequent during feeding periods than non-feeding periods. This study confirms that the relationship between eye colour and status described in tanks is also seen in more natural environments, and also that colour change in juvenile salmonids is a complex response to local events.     

The role of vision in the host plant-finding behaviour of the Hessian fly

Abstract. After mating, female Hessian flies, Mayetiola destructor (Say), sit for several hours before taking flight and exhibiting host-finding behaviours. Observation of these behaviours indicated that females used both chemical and visual cues to find oviposition sites, and that visual cues from plants consisted of both spectral (colour) and spatial information. Females oriented to and were stimulated to land on targets reflecting wavelengths in the region of 530-560nm (either alone or in combination with UV) but were inhibited by wavelengths from 400 to 500 nm. This spectral discrimination was probably mediated by photoreceptors located in the medio-frontal zone of the compound eyes. The spatial patterning of targets also influenced orientation during flight; targets with vertical rather than horizontal contour lengths and a higher density of vertical contour lengths were approached and landed on more frequently.     

Colourful stripes send mixed messages to safe and risky partners in a diffuse cleaning mutualism

The steps by which neutral, random and/or negative biological interactions evolve into mutualistic ones remain poorly understood. Here, we study Elacatinus gobies and the ‘client’ fishes they clean. Colourful stripes are common to mutualist cleaners and noncleaning sister species. Blue stripes are unique to cleaners and are more conspicuous to predators than are basal yellow or green stripes. In turn, we focused on the role of colour as a potentially specialized signal. We show that cleaners may possess a chemical defence and demonstrate that stripes are sufficient to elicit client posing behaviour and to deter attack, corroborating the putative role of chemistry. Analysis of previously published records shows that yellow cleaners interact with predatory clients less often compared to green and blue cleaners. Our results highlight evolution from predator resistance to advertising with conspicuous signals. Similar trajectories, via recognizable signals to risky partners, may be common in other diffuse mutualisms.     

Linkage between genes for coat colour and for blood plasma esterase in dogs

A study on linkage in dogs has been made on the basis of comparable studies in other mammal species. In a breeding experiment one dog was mated to 14 bitches. The dog was heterozygous for the plasma esterase locus (Es-1) and the extension locus (E) for coat colour. The 14 bitches, homozygous for both loci, produced a total of 96 offspring. The recombination distance between the loci is calculated to be 34.4 +/- 4.8 cM. The basis for homology between species for the two loci has been discussed.