Cows painted with zebra-like striping can avoid biting fly attack

The Function of Melanin-Based Colour Polymorphism in Cattle, Sheep and Goats

Natural selection has rarely promoted the evolution of colour polymorphism in wild mammals. However, it is more common in domestic mammals due to artificial selection. For this reason, domestication could provide valuable insights into the mechanisms underlying the evolution of colour diversity. This raises the question of whether the associations between coat colour and other phenotypes in domestic animals are similar to those in free-living animals. Our literature review of cows, goats and sheep suggests that these associations can differ not only between species but also within and between breeds. This pattern holds for all the traits that we considered: morphology, behaviour, physiology, reproduction, milk production and parasitism. The only consistent association we found in the literature was the attraction of flies towards dark-coloured cows. The relationships between same colour morph, cortisol and thermoregulation varied across environments, suggesting a possible condition-dependent expression of multiple traits. We conclude that artificial selection may lead to a different integration of multiple phenotypes compared to animals living in the wild. Therefore, colour variation may not always serve the same functional roles in domestic animals as it does in wild ones.

Impact-absorbing helmet design inspired by walnut texture reaction-diffusion mechanisms

This study investigates the complex textures on walnut shells, which play a vital role in enhancing crashworthiness performance. Despite the challenges in deciphering their functionality and formation, we discovered that these textures can be described by reaction-diffusion equations. These equations capture the shell hardening mechanism and simulate texture formation based on observed lignin diffusion patterns. The texture sample sets, derived from diverse local sampling positions and scopes, were analyzed using a Convolutional Neural Network classification model to determine the most representative texture classes. The parameter combinations from the control equations, integrated with impact risk assessments and personalized needs, informed the design of a protective helmet. Physical and numerical tests confirmed the helmet's impact-absorption capabilities. These insights pave the way for the development of impact-resistant devices, such as bio-armor and shell for automotive parts. STATEMENT OF SIGNIFICANCE: This study investigates the complex textures on walnut shells, which play a vital role in enhancing crashworthiness performance. We discovered that these textures can be described by reaction-diffusion equations, which capture the shell hardening mechanism and simulate texture formation based on observed lignin diffusion patterns. The texture were analyzed using a Convolutional Neural Network classification model to determine the most representative texture classes. The parameter combinations from the control equations, integrated with impact risk assessments and personalized needs, informed the design of a protective helmet. Physical and numerical tests confirmed the helmet's impact-absorption capabilities. These insights pave the way for the development of impact-resistant devices, such as bio-armor and shell for automotive parts.

Zebra stripes induce aberrant motion analysis in flies through aliasing

The function of zebra stripes has long puzzled biologists: contrasted and conspicuous colours are unusual in mammals. The puzzle appears solved: two lines of evidence indicate that they evolved as a protection against biting flies, the geographical coincidence of stripes and exposure to trypanosomiasis in Africa and field experiments showing flies struggling to navigate near zebras. A logical mechanistic explanation would be that stripes interfere with analysis of the optic flow; however, both spatiotemporal aliasing and the aperture effect seem ruled out following recent experiments showing that randomly checked patterns also interfere with the ability of flies to navigate near zebras. No clear mechanistic hypothesis remains. Here, I model from first principles how flies assess their motion relative to stripes, from image forming to motion analysis. I show that, at short distances, flies would consistently misjudge the motion of a striped object and frequently and saliently misjudge the direction of movement of a randomised check pattern. The range of distances at which the model predicts that stripes should impair flies is consistent with observations. The model shows that image formation is subject to spatial aliasing, preventing any form of motion analysis against a striped pattern at medium distances. The motion computation of flies is subject to a second form of aliasing, which, although independent of the temporal resolution of flies, bears conceptual similarities to spatiotemporal aliasing. The findings highlight the necessity of accounting not only for processing and psychology but also for the optics of image formation when taking a perceptual perspective of animal colours and contrasts.

Why don't horseflies land on zebras?

Stripes deter horseflies (tabanids) from landing on zebras and, while several mechanisms have been proposed, these hypotheses have yet to be tested satisfactorily. Here, we investigated three possible visual mechanisms that could impede successful tabanid landings (aliasing, contrast and polarization) but additionally explored pattern element size employing video footage of horseflies around differently patterned coats placed on domestic horses. We found that horseflies are averse to landing on highly but not on lightly contrasting stripes printed on horse coats. We could find no evidence for horseflies being attracted to coats that better reflected polarized light. Horseflies were somewhat less attracted to regular than to irregular check patterns, but this effect was not large enough to support the hypothesis of disrupting optic flow through aliasing. More likely it is due to attraction towards larger dark patches present in the irregular check patterns, an idea bolstered by comparing landings to the size of dark patterns present on the different coats. Our working hypothesis for the principal anti-parasite features of zebra pelage are that their stripes are sharply outlined and thin because these features specifically eliminate the occurrence of large monochrome dark patches that are highly attractive to horseflies at close distances.

Blood-seeking horseflies prefer vessel-imitating temperature gradients on host-mimicking targets: Experimental corroboration of a new explanation of the visual unattractiveness of zebras to tabanids

Several hypotheses tried to explain the advantages of zebra stripes. According to the most recent explanation, since the borderlines of sunlit white and black stripes can hamper thermal vessel detection by blood-seeking female horseflies, striped host animals are unattractive to these parasites which prefer hosts with a homogeneous coat, on which the temperature gradients above blood vessels can be detected more easily. This hypothesis has been tested in a field experiment with horseflies walking on a grey barrel with thin black stripes which were slightly warmer than their grey surroundings in sunshine, while in shade both areas had practically the same temperature. To eliminate the multiple (optical and thermal) cues of this test target, we repeated this experiment with improved test surfaces: we attracted horseflies by water- or host-imitating homogeneous black test surfaces, beneath which a heatable wire ran. When heated, this invisible and mechanically impalpable wire imitated thermally the slightly warmer subsurface blood vessels, otherwise it was thermally imperceptible. We measured the times spent by landed and walking horseflies on the test surface parts with and without underlying heated or unheated wire. We found that walking female and male horseflies had no preference for any (wired or wireless) area of the water-imitating horizontal plane test surface on the ground, independent of the temperature (heated or unheated) of the underlying wire. These horseflies looked for water, rather than a host. On the other hand, in the case of host-imitating test surfaces, female horseflies preferred the thin surface regions above the wire only if it was heated and thus warmer than its surroundings. This behaviour can be explained exclusively with the higher temperature of the wire given the lack of other sensorial cues. Our results prove the thermal vessel recognition of female horseflies and support the idea that sunlit zebra stripes impede the thermal detection of a host's vessels by blood-seeking horseflies, the consequence of which is the visual (non-thermal) unattractiveness of zebras to horseflies.

Sunlit zebra stripes may confuse the thermal perception of blood vessels causing the visual unattractiveness of zebras to horseflies

Multiple hypotheses have been proposed for possible functions of zebra stripes. The most thoroughly experimentally supported advantage of zebra stripes is their visual unattractiveness to horseflies (tabanids) and tsetse flies. We propose here a plausible hypothesis why biting horseflies avoid host animals with striped pelages: in sunshine the temperature gradients of the skin above the slightly warmer blood vessels are difficult to distinguish from the temperature gradients induced by the hairs at the borderlines of warmer black and cooler white stripes. To test this hypothesis, we performed a field experiment with tabanids walking on a host-imitating grey test target with vessel-mimicking thin black stripes which were slightly warmer than their grey surroundings in sunshine, while under shady conditions both areas had practically the same temperature as demonstrated by thermography. We found that horseflies spend more time walking on thin black stripes than surrounding grey areas as expected by chance, but only when the substrate is sunlit. This is because the black stripes are warmer than the surrounding grey areas in the sun, but not in the shade. This is consistent with the flies' well-documented attraction to warmer temperatures and provides indirect support for the proposed hypothesis. The frequent false vessel locations at the numerous black-white borderlines, the subsequent painful bitings with unsuccessful blood-sucking attempts and the host's fly-repellent reactions enhance considerably the chance that horseflies cannot evade host responses and are swatted by them. To eliminate this risk, a good evolutionary strategy was the avoidance of striped (and spotted) host animals.

Costs of Horn Fly (Diptera: Muscidae) Control for Cow-calf Producers in Tennessee and Texas, 2016

Tennessee and Texas cow-calf producers were surveyed to assess their 2016 expenses for horn fly control methods. Cattle producers who were members of the Texas and Southwestern Cattle Raisers Association and Tennessee cattle producers who have participated in the Tennessee Agricultural Enhancement Program participated in the survey. Average horn fly management costs in Tennessee and Texas were $9.50/head and $12.40/head, respectively. An ordinary least squares regression and quantile regression were estimated to examine how horn fly costs are influenced by producer and farm demographics, seasonality of horn flies, producer horn fly perceptions, and management practices. When controlling for these variables, Tennessee and Texas cattle producers did not spend significantly different amounts on horn fly control methods. Horn fly costs were associated with producer and farm demographics, producer perceptions of horn flies, and management practices. For example, results indicate that horn fly management costs vary depending on a producer's level of education and income. Having Angus cattle and larger herd sizes were associated with lower costs per head spent on horn fly management. Producers who did not consider horn flies to be a problem until greater quantities of flies were present on the animal spent 15% less per head on managing horn flies. In terms of horn fly control methods, feedthrough insecticides increased horn fly costs the most, followed by using ear tags. This is the first known research to estimate horn fly management costs among cattle producers.

Genetic parameters and genomic regions associated with horn fly resistance in organic Holstein cattle

Horn flies (Haematobia irritans [L.]) contribute to major economic losses of pastured cattle operations, particularly in organic herds because of limitations on control methods that can be used. The objectives of this research were to determine if resistance to horn flies is a heritable trait in organic Holstein cattle, determine associations with yield traits, and to detect genomic regions associated with fly infestation. Observations of fly load were recorded from 1,667 pastured Holstein cows, of which 640 were genotyped, on 13 organic dairies across the United States. Fly load score was determined using a 0 to 4 scale based on fly coverage from chine to loin on one side of the body, with 0 indicating few to no flies and 4 indicating high infestation. The scoring system was validated by counting flies from photographs taken at the time of scoring from 252 cows. To mitigate the effect of our data structure on potential selection bias effects on genetic parameter estimates, survival to subsequent lactations of scored animals and herd-mates that had been culled before the trial was accounted for as the trait stayability. Genetic parameters were estimated using single-step genomic analysis with 3-trait mixed models that included fly score, stayability, and a third phenotype. Model effects differed by variable, but fixed effects generally included a contemporary group, scorer, parity, and stage of lactation; random effects included animal, permanent environment, and residual error. A genome-wide association study was performed by decomposing estimated breeding values into marker effects to detect significant genomic regions associated with fly score. The rank correlation between the subjective fly score and the objective count was 0.79. The average heritability of fly score (± standard error) estimated across multiple models was 0.25 ± 0.04 when a known Holstein maternal grandsire was required and 0.19 ± 0.03 when only a known Holstein sire was required. Genetic correlation estimates with yield traits were moderately positive, but a greater fly load was associated with reduced yield after accounting for genetic merit. Lower fly loads were associated with white coat coloration; a significant genomic region on Bos taurus autosome 6 was identified that contains the gene KIT, which was the most plausible candidate gene for fly resistance because of its role in coat pattern and coloration. The magnitude of heritable variation in fly infestation is similar to other traits included in selection programs, suggesting that producers can select for resistance to horn flies.

Highlights of Veterinary Entomology, 2019

Research in the field of veterinary entomology is dominated by studies concerning arthropods that affect animal health. In 2019, this research primarily addressed the overwhelming industry need to manage detrimental species such as biting flies and ticks and the ongoing problems caused by insecticide/acaricide resistance evolution in these pests. Research also included evidence supporting the need for the conservation of beneficial species, such as biological control organisms. Many studies in a variety of pest systems have demonstrated the potential detrimental effects of insecticide use on nontarget organisms, and those of veterinary importance are no exception. An emphasis also was placed on research regarding alternative management strategies for veterinary pests. The presentation herein provides a descriptive summary of selected research that contributed greatly to the body of knowledge regarding arthropods of veterinary importance. This included several studies that will pave the way towards more effective veterinary pest management in an effort to improve animal health and welfare and, therefore, the sustainability of animal agriculture.

Mosquito repellence induced by tarsal contact with hydrophobic liquids

Mosquito legs have a unique highly water-repellent surface structure. While being beneficial to mosquitoes, the water-repellence of the tarsi enhances the wettability of hydrophobic substances such as oils. This high wettability induces strong attraction forces on a mosquito’s legs (up to 87% of the mosquito’s weight) towards the oil. We studied the landing behaviour of mosquitoes on oil-coated surfaces and observed that the mosquito contact time was reduced compared to that on hydrophilic-liquid-coated surfaces, suggesting that the oil coating induces an escape response. The observed escape behaviour occurred consistently with several hydrophobic liquids, including silicone oil, which is used globally in personal care products. As the repellent effect is similar to multiple hydrophobic substances, it is likely to be mechanically stimulated owing to the physical properties of the hydrophobic liquids and not due to chemical interactions. On human skin, the contact time was sufficiently short to prevent mosquitoes from starting to blood-feed. The secretion of Hippopotamus amphibius, which has physical properties similar to those of low-viscosity silicone oil, also triggered an escape response, suggesting that it acts as a natural mosquito repellent. Our results are beneficial to develop new, safe, and effective mosquito-repellent technologies.

Zebra stripes, tabanid biting flies and the aperture effect

Of all hypotheses advanced for why zebras have stripes, avoidance of biting fly attack receives by far the most support, yet the mechanisms by which stripes thwart landings are not yet understood. A logical and popular hypothesis is that stripes interfere with optic flow patterns needed by flying insects to execute controlled landings. This could occur through disrupting the radial symmetry of optic flow via the aperture effect (i.e. generation of false motion cues by straight edges), or through spatio-temporal aliasing (i.e. misregistration of repeated features) of evenly spaced stripes. By recording and reconstructing tabanid fly behaviour around horses wearing differently patterned rugs, we could tease out these hypotheses using realistic target stimuli. We found that flies avoided landing on, flew faster near, and did not approach as close to striped and checked rugs compared to grey. Our observations that flies avoided checked patterns in a similar way to stripes refutes the hypothesis that stripes disrupt optic flow via the aperture effect, which critically demands parallel striped patterns. Our data narrow the menu of fly-equid visual interactions that form the basis for the extraordinary colouration of zebras.

A Historical Review of Management Options Used against the Stable Fly (Diptera: Muscidae)

The stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), remains a significant economic pest globally in situations where intensive animal production or horticultural production provide a suitable developmental medium. Stable flies have been recorded as pests of livestock and humans since the late 1800s to early 1900s. Over 100 years of research has seen numerous methodologies used to control this fly, in particular to protect cattle from flies to minimise production losses. Reduced milk production in dairy cows and decreased weight gain in beef cattle account for losses in the US alone of > $2000 million annually. Rural lifestyles and recreation are also seriously affected. Progress has been made on many control strategies against stable fly over a range of chemical, biological, physical and cultural options. This paper reviews management options from both a historical and a technical perspective for controlling this pest. These include the use of different classes of insecticides applied to affected animals as toxicants or repellents (livestock and humans), as well as to substrates where stable fly larvae develop. Arthropod predators of stable flies are listed, from which potential biological control agents (e.g., wasps, mites, and beetles) are identified. Biopesticides (e.g., fungi, bacteria and plant-derived products) are also discussed along with Integrated Pest Management (IPM) against stable flies for several animal industries. A review of cultural and physical management options including trapping, trap types and methodologies, farm hygiene, scheduled sanitation, physical barriers to fly emergence, livestock protection and amendments added to animal manures and bedding are covered. This paper presents a comprehensive review of all management options used against stable flies from both a historical and a technical perspective for use by any entomologist, livestock producer or horticulturalist with an interest in reducing the negative impact of this pest fly.

Coloration in Mammals

Mammalian colors and color patterns are some of the most diverse and conspicuous traits found in nature and have been widely studied from genetic/developmental and evolutionary perspectives. In this review we first discuss the proximate causes underlying variation in pigment type (i.e., color) and pigment distribution (i.e., color pattern) and highlight both processes as having a distinct developmental basis. Then, using multiple examples, we discuss ultimate factors that have driven the evolution of coloration differences in mammals, which include background matching, intra- and interspecific signaling, and physiological influences. Throughout, we outline bridges between developmental and functional investigatory approaches that help broaden knowledge of mammals' memorable external appearances, and we point out areas for future interdisciplinary research.

Correction: Cows painted with zebra-like striping can avoid biting fly attack

[This corrects the article DOI: 10.1371/journal.pone.0223447.].