Lizz Rice – Australian Science

Multi-Coloured Vision

Lizz Rice — Fri, 15 Aug 2014 00:15:14 +0000

Colour is our eye’s interpretation of light reflecting off objects. The different colours we see are different wavelengths of light. Colour-specific photoreceptors in the retina of our eyes, cones, translate the wavelengths into what we see as colour.

Humans generally have three types of cone to do this. One responds to shorter waves of light (we see these as blues), one responds to longer waves of light (reds) and one responds to the middle lengths (greens). The cones work together to see other colours, such as purple.

The three cone system is called trichromatic vision, but most other mammals, like dogs and cats, only have two types of cones. This is known as dichromatic vision.

Some people only have dichromatic vision too. We call this colour blindness, somewhat misleadingly, as dichromats still have plenty of colours available to them.

Rather, they struggle to make out some colours. They can be defined asprotanopes (total lack of red cones), deuteranopes (lack of green cones) or tritanopes (lack of blue cones).

There is also another group of people called anomalous trichromats, who have all three cones but make odd judgements compared with the rest of us. The peak sensitivity of one of their cones shifts along the spectrum, so they need more or less of the wavelength to achieve the colour. For instance, people with deuteranomaly (the most common) find their green cone sensitivity shifts towards the red part of the spectrum, so they need fewer long waves of light to see red.

It is rare to be born a tritanope, but around 8% of men and 0.5% of womenare affected by red or green colour blindness.

It is so much more common in men because the gene responsible is carried on the X chromosome. Women (XX) are likely to have a normal copy to override the mutated gene, whereas men (XY), with only one X chromosome, have no other choice.

It is also possible to acquire colour vision defects through problems like disease and injury.

The visual world of the colour blind not only becomes less rich, but simple tasks like detecting sunburn, or determining ripe fruit becomes a struggle. Jay Neitz’s slideshow shows what living in a colour blind world might be like.

There are advantages to dichromacy. Researchers have identified 15 shades of khaki that those with normal vision found almost impossible to tell apart, but those with deuteranomaly were able to easily distinguish.

Their ability to discern camouflage may have provided an evolutionary benefit because a reduction in colour signals makes the differences in texture and brightness more apparent. This would explain why it is so prevalent in society.

But they lack the ability to, say, spot a cherry on a cherry tree, which is possibly why we evolved trichromacy in the first place.

Our world has been designed for trichromatics and living with colour deficiency can be detrimental to many areas of life: education, where colour-coding is extensively used, or pursuing careers, for example, as a firefighter, electrician or pilot.

In the future it may be possible to use gene therapy to correct colour blindness. The idea has already been successfully applied to monkeys.

Adult squirrel monkeys (Saimirisciureus) with red-green colour blindness were trained to touch the location of a coloured patch among grey dots. After treatment that added the missing visual pigment gene, the monkeys passed the test with flying colours.

The success of these nervous systems to respond to a new sensory input indicates that, contrary to popular belief, the capacity for development does not end.

It is not known how the human brain would respond to a new colour channel. Though there was no psychological distress observed in monkeys, the internal experience cannot be discerned. Safety also must be ensured before it can be considered for human use.

There may be another way.

Neil Harbisson hears colours. He is the wearer of an “eyeborg

Cite this article:
Rice L (2014-08-15 00:15:14). Multi-Coloured Vision. Australian Science. Retrieved: May 03, 2024, from http://australianscience.com.au/biology/multi-coloured-vision/

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The Health of the Honey Bee

Lizz Rice — Tue, 15 Jul 2014 00:15:33 +0000

The delicate state of the European honeybee (Apismellifera) can be traced back to 2006, when the mysterious Colony Collapse Disorder (CCD) began wiping them out. Adult honey bees went missing from their hives, and no bodies were to be found. Since, apiaries have struggled – the US reports a yearly loss of about 30% – leaving the future of the honey bee in a precarious position.

It is thought the sudden collapse is caused by a number of factors working together in synergy, pounding bee’s immunity so they are no longer as resilient as they used to be.

Exposure to pesticides has been afiercely debated and much publicised culprit. A group of neurotoxicants called neonicotinoids have been found to create an increased susceptibility to gut pathogens in honeybees. They have also been found to affect bee behaviour, learning and memory,crucial for them to forage, find their way home and relate the information to the colony.
Much of this research has been performed in the laboratory, however, and it is questionable how well the findings can be applied outside of it. In this environment, bees exhibit differences in their physiology and stress levels, and studies tend to expose them to an unrealistic level of neonicotinoids.

How much pesticides open the door to other threats is uncertain. Without improved field testing it is difficult to assess the amount of exposure honey bees are actually receiving and their reaction to the combinations and accumulations of pesticide smothered crops.

The EU has frozen the use of neonicotinoids while a more accurate estimate of risks is developed.

Despite not being native to Australia, the honey bee is well established, where feral colonies and hives managed by beekeepers are spread over most of the country.

Neonicotinoids remain in extensive use in Australia. The Australian Pesticides and Veterinary Medicines Authority (APVMA) in 2013 concluded that these pesticides were less of a risk compared with those before.

As beekeepers move away from the chemical-free sources of nectar and pollen found in native scrub and forest and into agricultural and horticultural pollination, there is a commensurate increase in exposure to agricultural chemicals.

This means more rigorous testing of pesticides needs to be done, with improved labelling, regulation and guidance of products used in agriculture.

Changes in land use, where flowering meadows and weeds have given way to agriculturally intense monocultures, mean that bee’s natural foraging habitats are disappearing.

One study has analysed honey bee’s foraging preferences so as to establish which areas would cause them least amount of disruption. Their great foraging range and sensitive response to forage quality means they can be used as bioindicators to monitor large areas and inform environmental management.

Pollen quality and diversity has a major influence on bee’s health and their ability to cope with pathogens, pesticides and parasites such as Varroa destructor.

Varroa destructor is considered to be one of thedriving forces behind colony loss.The lifespan of adult workers in affected broods are reduced,so they cannot survive winter long enough to produce the next generation (Dooremalen etal, 2012).

Varroahas spread all over the world with devastating effect, although whether it attacks immunity or it is the mite’s feeding activity that causes such problems is not yet clear. Of all the major honey producing countries, only Australia remains mite-free.

Australia hosts a large number of feral honey bees due to a warm climate and plants rich in nectar. This high reliance on feral bee pollination means the impact of Varroa could be great, as Australia does not have the resources to offset the effects.

Casey Cooper, president of the New South Wales Apiarist Association, stresses the importance of not letting Varroa get here in the first place.

By increasing biosecurity, pests and diseases like Varroa mite are kept out of the country. Biosecurity includesmeasures such as port surveillance, where hives are kept at all ports and areas and monitored regularly.

Australia is not reporting the huge losses that other countries are. Cooper, however, argues that his organisation has seen a 30% decrease in hives for registered beekeepers since 2006. He believes there is a looming food security crisis related to the decline of honeybees.

Ian Zadow, Chairman of the Australian Honey Bee Industry Council, estimated that “one in three mouthfuls of food we eat relies on the honey bee for pollination of that food.

Cite this article:
Rice L (2014-07-15 00:15:33). The Health of the Honey Bee. Australian Science. Retrieved: May 03, 2024, from http://australianscience.com.au/biology/health-honey-bee/

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