The shape of the pupil depends on lifestyle


Fig. 1. A – form pupil: vertical (cat), rounded (lynx), round (men) and horizontal (sheep). B – distribution of 214 species of animals in the form of the pupil and lifestyle (Herbivorous – herbivores, Active – active predators, searching for prey, and Ambush – predators lying in wait to ambush the victim). Drawing from the discussed article in Science Advances

In terrestrial predators attacking from ambush, most common vertical slit pupils, while their victims, herbivores, slit pupil often oriented horizontally. Scientists explain this pattern different purposes of the two groups of animals. Vertical pupil allows predators to see sharper vertically oriented objects, such as their victim, herbivore, on the contrary, it is necessary to survey the wide horizons in time to notice a predator, so their pupils are often adapted to ensure that the horizontal lines are sharply visible.

The pupil regulates the amount of light falling on the retina. In addition to the round pupils, the lumen of which is determined by the circular muscles – sphincter of the pupil, in the nature of frequent slit-shaped pupils are provided with an additional pair of muscles. The range of the slot-like clearance pupil wider than that of a round: the area of ​​the vertical pupil cat can vary 135 times, and the round pupil person – only 15. Therefore, slit pupils useful for animals that are active during the day and at night, a wide range of lighting conditions. After all, the day when the light, the pupil should not miss too much light, and at night it is, on the contrary, should be as wide as possible to the retina fell out, and more so the small number of photons.

But the gap pupil can be oriented in different ways – vertically or horizontally. Scientists from Durham University and California have recently suggested that the orientation of the pupil is not random and depends on the lifestyle of the animal, and the objects in the visual field, which is especially important for him. They compared the shape data 214 pupils terrestrial species to their way of life (Fig. 1). It turned out that the pupils herbivores are mainly oriented horizontally in active predators most common round shape of the pupil, and the predators that lie in wait to ambush the victims, most of the pupils are oriented vertically. The shape of the pupil and depend on the period of daily activity: nocturnal animals often pupils were slotted than round. Regularities found corresponded very stringent levels of significance, so had to understand what the reasons explained by the difference in the shapes of pupils of different groups of animals.

Fig. 2. The depth of field vertical pupil
Fig. 2. Vertical pupil allows the animal to sharply enough to see the vertical contours, located a little closer or farther focal distance. However, horizontal lines, even a little bit far from the focal distance, look much blurred. If the pupil is horizontal, the picture will be the opposite. Drawing from the discussed article in Science Advances
When the eye or the camera focuses on a certain point, the rest of the image becomes blurred. The diameter of the blur circle around a specific point of the visual field depends on the difference between the distance to it and to the point on which the eye is focused, and the diameter of the pupil. If the pupil is not round, the cutting depth of the visible space will be different for different directions. For example, an animal with a vertical pupil will sharply enough to see not only the vertical line on which it is focused, but also vertical lines located farther or nearer the focal length. But to the horizontal contours of a pupil adapted worse and horizontal lines on which the animal itself is not focused will be very blurred (Fig. 2). In animals with a horizontally-oriented slit-shaped pupils is the opposite: they see a sharp horizontal contours, and to perceive vertical objects adapted not so good.

Fig. 2. Vertical pupil allows the animal enough to clearly see the vertical contours, located a little closer or farther focal distance. However, horizontal lines, even a little bit far from the focal distance, look much blurred. If the pupil is horizontal, the picture will be the opposite. Drawing from the discussed article in Science Advances

The benefit of a particular form of the pupil depends on the height at which the animal’s eyes are placed. It is easy to understand, considering the photos taken with different distances from the subject, the closer to the surface of the camera is, the higher the gradient blur that is not in focus (Fig. 3). Therefore, if we compare, for example, a cat and a man, the cat is much more important to correct motion blur, because it is “closer to the ground” than people. For these reasons, scientists have suggested that animals smaller growth slit pupils are more common, and this hypothesis was confirmed when researchers analyzed data on the size of the animals from their sample. Interestingly, birds pupils almost always round, with one exception – at the skimmer vertical slit pupils. This exclusion is suitable for theoretical calculations of researchers because of lifestyle skimmer reminds terrestrial predator of small stature. This bird is flying very low at the surface of the water, preying on fish, so that all concerns about the vagueness of the image on which the face at close range, hold for skimmer.

Fig. 3. Simulated view of a plane for animals of different heights (0.6, 0.2 and 0.1 m). Left greatest height, the right – the smallest. The closer to the ground located the eye of the animal, the more blurred look objects do not fall into focus. Drawing from the discussed article in Science Advances

Why the eyes of predators attacking from ambush, better able to see the vertical line, and their eyes herbivorous victims, on the contrary, are set to horizontal contours? One can only assume that the predator is more important to see the victim (which is more like a vertically oriented object), and the victim, on the contrary, it is necessary to survey the wide horizons, which must be clearly visible to her in time to notice the threat. In addition, the victim need to determine the direction of where to go, and you need only predator chasing the victim, and the surrounding open spaces is not very interested.

Various forms of the pupil several times independently during evolution occurred. It turns out that some form of pupil in animals with different ways of life – this is an example of convergent evolution, when the useful life sign parallel develops in organisms other than the closest groups.

Kids Games accelerate the development of motor skills at the cost of slowing growth

Fig. 1. In addition to accelerating the development of motor skills in Assamese macaques games can provide other advantages – for example, to train the communication skills or the ability to make quick decisions in unexpected situations. Image source

The more time a young Assamese macaques spend on the games, the more quickly develop their motor skills, but the slower they grow. These observations suggest that the animals can spend time playing, even if it will have to sacrifice for the sake of the resources needed for growth. This behavior could be fixed only if the benefits of skills development that helps the game is very high.

During games, spend time not only people, but also many animals – primates, felines, dolphins, crows, small rodents. It is believed that playing only those animals that have enough resources to more utilitarian needs – nutrition, growth, protection of the territory. However, new data from the German naturalist, said that playing in some animals may be located closer to the base of the pyramid of values. Young mountain monkeys, or Assamese macaques, for example, often prefer to save on growth and spending power in the game. This distribution of scarce resources may be justified, because the game speed up the development of motor skills in these monkeys.

Although it is often said that the games help develop motor skills, this idea has not yet been accurately proven. Only circumstantial evidence was – for example, the coincidence of the peaks with the peaks of the gaming activity synapse formation in the motor cortex in several animal species. And if we talk about examples of animals that have long played and in which motor skills are well developed, the cause and effect here can be swapped – no motor skills are developed through games and play more than those who have the ability. To distinguish between these two options, it is necessary to observe the animals with his early childhood. Then you can learn and how to develop his skills, and how they can be associated with a love of games.

Such observation of cubs Assamese macaques in the wild habitats conducted by German researchers from the University of Göttingen Georg-August for two years. Scientists interested in not only the potential benefits of the games, but also their “cost” for the animals. Game – it is an activity that brings tangible benefits here and now, so that in a first approximation, it can be regarded simply as a waste of energy.

The researchers wanted to test whether the animals to play not only in the “fed” the times when there is enough food. Therefore, in the vicinity of the habitat study group monkeys are evaluated further and the number of fruits, which are eaten by monkeys. And in order to determine whether the growth of young macaques waste of effort to the game, the researchers several times a month were evaluated for their size photos. All study was delivered in a way that researchers have minimal impact on the natural way of living apes and just follow the life of animals from the side.

Scientists have recorded in detail how to spend time 17 young Assamese macaques. He was important to estimate the proportion of time that each of the young dedicates games, and find out exactly what is the game – single or group, with objects or locomotor (catch-up, or a pile-small) – and how these games are active (running whether participants go or sit on the ground). This latter aspect was important to assess to account for differences in energy costs on different types of games. To assess the potential benefits of the games, the researchers identified 17 motor skills (such as running or jumping from branch to branch) and recorded when one of the young for the first time applied a particular skill. It was assumed that the game may affect how quickly young macaques will acquire motor skills.

The study proved that the growth rate is inversely proportional to young rhesus time which they spent in active games (Fig. 2). The largest proportion of time spent in games – 12.2% – in line with slower growth at 30%. To play longer, animals refused not the search for and consumption of food, and from the rest. Therefore, a delay in the growth can not be attributed to a lack of supply of those animals who are too addicted to games; growth slowed down because of the expenditure of energy on the game itself.

Fig. 2. Linkage growth rate (vertical axis) and the percentage of time spent in games (horizontal axis). Data is given as a percentage deviation from the mean. Fig. discussion of the article in Science Advances

The more time young macaques were performed and playing games were more active, the faster they develop new motor skills. And because the skills that researchers have identified, appeared in the animals after they started to play, it can be concluded that it is active games caused the accelerated development of the skills of those who have played a lot, and not vice versa.

Young males performed in games longer than the female, and as a result, motor skills develop faster than males. At the same time, behind males from females in growth, reaching adult body size an average of five months later. The representatives of the Old World monkey family, to which the studied species of monkeys, females can not invest so much in the game forces the males, as the rate of growth and maturation of females depends their reproductive success. For males this relationship is not the same, so they can afford to invest in the rapid development of motor skills. It can help the male to take a privileged position in the community and eventually affect his fertility.

It is interesting that Young did not stop playing, even in difficult times, when the fruit was scarce, although lack of food further slowed their growth. It turns out that the game among young macaques – important article of energy costs and that the animals do not play only when they have enough resources. And when all the power is not enough, even the animals sacrificed growth rate for the game. This behavior could be fixed only if the game in the end turn out to be beneficial for the animals. In addition to accelerating the development of motor skills, which is especially important for males Old World monkey, games can provide other advantages – for example, to train the communication skills or the ability to make quick decisions in unexpected situations. Interestingly, these skills may be more important than the rate of growth not only in humans but also in Old World monkey monkeys.

Childhood primates very long. Often write that it is necessary for the development of the brain and the acquisition of complex skills, but until now it was not clear why these processes should be associated with such a slow growth. Recent data suggest a mechanism that can bind develop important skills at the speed of growth: through games – expensive but great fun.

Analogs contemporary moles, otters and primates existed in the Jurassic period

Fig. 1. Three Jurassic animal – like a squirrel, tree shrews or lemur Agilodocodon, digging krotopodobny Docofossor and waterfowl, like an otter or beaver Castorocauda – demonstrate the diversity of morphology and ways of life of early mammals. Drawing one of the authors of one of the items discussed, April Isch Neander from the University of Chicago, from a site

Fossil remains of two primitive mammals found in the mid- and late Jurassic deposits of northeastern China, showed that the Jurassic beasts were more diverse than previously thought. One of the new species led a burrowing lifestyle and remotely resembled a mole; the second lived in the trees and looked like a modern squirrel or tree shrews. Both species belong to dokodontam – a dead-end branch of the basal mammals consisting in a more distant relationship with placental and marsupial than the platypus and echidna. Apparently, many adaptations, such as the reduction of the lumbar ribs, and phalanges have evolved independently in the different groups of mammals based on the same genetic mechanisms.

It was once thought that almost all Mesozoic mammals were small, inconspicuous and monotonous, like shrews. However, the findings of the last decades, many of which were made in China, denied this view. “Elements” talked about some of these discoveries, including the amazing waterfowl “bobrohvoste» Castorocauda from the group dokodontov (Docodonta), which resembled an otter Borba and both could eat fish (see ref. At the end of the news).

Chinese and American paleontologists reported in the latest issue of the journal Science just two remarkable finds made in the north-east of China. The findings showed that the ecological and morphological diversity of Jurassic mammals were even higher than previously thought.

Both new kind as mentioned above bobrohvost refer to dokodontam. This group, according to many experts, is one of the deadlock (who left no living descendants) basal branches, separated from the common trunk mammal before, the latter divided into the ancestors of modern monotremes (platypus, echidna) and terievyh (marsupials and placental) . However, there are others, including radically different versions of the classification of mammals and their ancestors (see .: MF Ivakhnenko. The problem of transition Theromorpha – Mammalia).

The first of two newly discovered animals called Docofossor brachydactylus, meaning “digging shirokopaly dokodont.” His bones were found in Late Jurassic deposits, Hebei Province (Fig. 2).

Fig. 2. Docofossor brachydactylus: general view of the findings (A), the portrayal of what remains of the skull (B), and the reconstruction of the skeleton (S). The image of the article under discussion Zhe-Xi Luo et al. in Science

Dokofossor – mammal a length of about 9 cm (from nose to base of tail) and weighing 13-17 In the structure of the skull and teeth are, on the one hand, primitive features characteristic of other mammalian basal (mammaliaform, mammaliaformes), on the other – specific features characteristic of modern burrowing animals such as marsupial moles and golden mole. The most convincing evidence in favor of digging lifestyle revealed in the structure of the limbs. Paws dokofossora – a specialized foot underground dweller. In particular, his fingers are made up of only two phalanges (instead of three, as in most ancient and modern mammals), and the terminal phalanx enlarged, expanded like a shovel, and a special projection at the base prevents the terminal phalanges folded back. All this – typical signs of burrowing animals. For example, reducing the number of phalanges is typical for modern golden mole, fingers that look like fingers dokofossora (Fig. 3). This is a typical example of a parallel evolution, i.e. forming an independent similar adaptations in different groups of animals, in this case – at basal mammals (dokodontov) and placenta.

Fig. 3. Evolutionary Tree dokodontov (A), the reconstruction of wood dokodonta Agilodocodon (B), its paw (C), floating dokodont Castorocauda (D), newfound digging dokodont Docofossor (E). Right (F) – comparison of the proportions of the phalanges in mammals living in trees (arboreal), do not live in trees all the time, but it’s good climbing (scansorial), land-based (terrestrial), burrowing (fossorial) and underground inhabitants (subterranean). Shown fingers following animals (top to bottom): flying lemurs (Cynocephalus), lemur (Lemur), Agilodocodon, opossum (Didelphis), hedgehog (Erinaceus), a viper (Tachyglossus), Docofossor (BMNH131735), golden mole (Chrysochloris). The image of the article under discussion Qing-Jin Meng et al. in Science

The authors suggest that the basis for such convergence are common genetic mechanisms responsible for regulation of the limb development in embryos of terrestrial vertebrates. At the golden mole in the course of embryonic development in the future fingers formed the beginnings of the three phalanges, but then two of them (the proximal and middle) merge. In mice and humans the same phenotype (merger phalanges) sometimes occurs because of the disruption of the gene regulatory cascades that control tab of the joint between the phalanges. Among the regulators involved in this process include proteins BMP2 (bone morphogenetic protein 2), GDF5 (growth and differentiation factor 5) and several others. These regulators are likely to manage the development of fingers and Jurassic mammals, and similar variations in their work caused by mutations that lead to a similar phenotype changes – for example, to merge the phalanges.

Likewise, it explains the parallel evolution of another important feature – lumbar ribs and lumbar spine. Modern mammals lumbar vertebrae ribs there, and lumbar spine morphology clearly different from the breast-carrying ribs. Loss of lumbar ribs and separation of the lumbar considered an adaptation associated with increased mobility and flexibility of the back of the body and the intensification of respiration. According to the fossil record, in different groups of early mammals reduction of lumbar ribs (partial or complete) occurred in parallel and independently.

New findings have shown that this is true for dokodontov. In dokofossora, Castorocauda and other dokodontov has lumbar ribs, the size of which gradually decreases as it approaches the sacrum. It seems, the original (ancestral) condition tag for dokodontov and all mammals. However, the second newly discovered dokodonta, agilodokodona (See below.) Lumbar ribs No lumbar clearly distinguished from breast. This implies that the evolutionary lineage dokodontov, as in the other groups of early mammalian occurred independent reduction lumbar ribs.

The reason lumbar ribs easily lost, and sometimes may appear again, presumably lies in the fact that the genetic regulatory cascade manage bookmarks of ribs in embryogenesis, the same for all mammals. A key role is played by genes Hox9, Hox10, Myf5, Myf6 and others. Changes in the work of a small number of genes may be sufficient for a radical change in phenotype. For example, you can get the mouse embryos developed lumbar ribs, if you turn off all three copies of the gene Hox10 (see .: New fossil discovery sheds light on the early evolution of mammals, “Elements”, 17.03.2007).

The second ancient mammals, called Agilodocodon scansorius («agile dokodont climbing”), found in the Middle Jurassic of Inner Mongolia (Fig. 4). This dokodont was also small (14 cm from nose to tail, the weight of 27-40 g). Judging by the structure of the spine and extremities, agilodokodon was well adapted to climbing trees. In particular, the proportion of his fingers point to the arboreal (Fig. 3). All other known dokodonty were either ground or floating (bobrohvost), or, as we now know, digging. T