Peering into the eyes of different animals, you’ll see some extraordinarily shaped pupils. But why? It turns out that pupil shape is a powerful indicator of what role an animal plays in its ecosystem.
Se te fixas nos ollos de diferentes animais, verás algunhas pupilas con formas extraordinarias. Pero, por que? Pois porque a forma da pupila é un poderoso indicador do papel que un animal ten no seu ecosistema.
Pupils mark the hollow opening in the iris, the eye’s band of pigmented muscle. They’re the portholes through which light enters the eye, where it then strikes the retina and activates light-sensitive cells, setting the process of vision in motion. Pupils are black because most of the light that enters them is absorbed. Their size changes in response to brightness, as well as certain drugs and emotional and mental states— but their basic form varies greatly among species.
As pupilas marcan a abertura do iris, esa zona pigmentada do ollo. Son os ocos polos que a luz entra no ollo, para despois incidir na retina e activar as células fotosensibles, poñendo en marcha o proceso da visión. As pupilas son negras porque absorben a maior parte da luz que entra nelas. O seu tamaño varía segundo a claridade, así como ante certas drogas e estados emocionais e mentais, pero a súa forma básica varía moito entre especies.
House cats, for one, are twilight hunters with vertically elongated pupils. In the dark, these structures expand dramatically, taking in the available light. When it’s bright, they shrink into slits. In fact, cat pupils are so flexible that their maximum area is 135 times greater than their minimum area— whereas our pupils only shrink and expand 15-fold. And because of how the slit pupil takes in light, it creates sharp, vertical contours. When the cat’s brain processes the visuals from each eye, the small but sharp differences between them help the cat judge the precise distance of its target. In fact, many other ambush hunters also have vertically elongated pupils— but mainly those whose eyes are located closer to the ground. This may be because these pupils are especially useful in perceiving objects at the relative short distances these animals tend to hunt.
Así, os gatos domésticos son cazadores nocturnos con pupilas verticais, que se dilatan moito na escuridade, para aproveitar a luz dispoñible, e que se converten en fendas cando hai moita luz. As súas pupilas son tan flexibles, que a súa área máxima é 135 veces maior ca a área mínima, mentres que as nosas só se contraen e se dilatan 15 veces o seu tamaño. E debido á forma en que a pupila vertical recibe a luz crea contornos nítidos e verticais. Cando o cerebro do gato procesa as imaxes de cada ollo, as diferenzas entre elas, pequenas pero nítidas axúdanlle a calcular a distancia exacta ao seu obxectivo. De feito, moitos depredadores de emboscada tamén teñen pupilas verticais, pero sobre todo aqueles que teñen os ollos máis preto do chan. Iso pode deberse a que esas pupilas son especialmente útiles para percibir obxectos nas distancias relativamente curtas en que soen cazar.
The world looks very different from behind the horizontally elongated pupils of many grazing and browsing animals, like goats. These pupils, situated on either side of the head, let horizontal bands of light in that give the goat a near-360-degree view and provide it with sharp, horizontal images. This helps goats detect any disruption to the horizon— alerting them to potential predators— while still enabling them to see ahead and detect obstacles as they make their escape. In fact, goats always keep their pupils aligned with the horizon, rotating their eyeballs in their sockets as they move their heads up and down.
O mundo vese moi diferente tras das pupilas horizontais de moitos animais que pastan e remoen, como as cabras. Esas pupilas, situadas a ambos os lados da cabeza, deixan entrar bandas de luz horizontais, que lle dan á cabra unha visión de case 360 graos e unhas imaxes nítidas e horizontais. Isto axúdalle a detectar calquera cambio no horizonte, alértaa de posibles depredadores, permítelle ver diante dela e detectar obstáculos mentres foxe. De feito, as cabras manteñen sempre as pupilas aliñadas co horizonte, xirando os ollos nas súas órbitas mentres moven a cabeza arriba e abaixo.
Meanwhile, nocturnal geckos have pupils that shrink into slits studded with pinholes in higher light conditions. Each pinhole projects a separate, sharp image onto the geckos retina. Scientists think that comparing these different inputs might help the gecko judge distance without having to move.
Pola súa parte, os geckos nocturnos teñen pupilas que se contraen en fendas con buratos se hai moita luz. Cada burato proxecta unha imaxe separada e nítida na súa retina. Os científicos cren que comparar esa información diferente pódelle axudar ao gecko a calcular a distancia sen ter que moverse.
And while they might have fooled you, mantises and other insects and crustaceans have “pseudopupils.” These aren’t optical structures; they’re optical illusions experienced by the observer. Mantises have compound eyes composed of thousands of light-sensing units. When some are aimed at you, they appear black because they’re absorbing most wavelengths of incoming light— but there’s no actual opening.
E aínda que se cadra enganáronte, as barbantesas e outros insectos e crustáceos teñen “pseudopupilas”, que non son estruturas ópticas, senón ilusións ópticas do observador. As barbantesas teñen ollos compostos por miles de unidades detectoras de luz. Cando te ollan parecen ser negros, porque absorben a maioría das lonxitudes de onda da luz entrante, pero non hai ningunha abertura real.
So, why do we have round pupils? Elongated pupils help sharpen certain dimensions of an animal's vision. But scientists think that, for animals like us with circular pupils, this is a lower priority. Instead of seeing some elements of a scene in extreme focus, we see a larger picture in relative detail, which enables more general skills of observation. This may be especially helpful for foragers looking for food, hunters eyeballing and chasing their prey, and social animals recognizing other faces.
E por que nós temos pupilas redondas? As pupilas alongadas axudan a afinar certas dimensións da visión dun animal. Pero os científicos cren que, para animais coma nós, de pupilas circulares, esa é unha prioridade menor. No canto de ver algúns elementos da escena moi enfocados, vemos unha imaxe máis grande en relativo detalle, o que permite mellores capacidades xerais de observación. Isto pode ser especialmente útil para os buscadores de comida, os cazadores que xiran os ollos perseguindo as súas presas, e os animais sociais que recoñecen outras caras.
As we peer at different pupils, patterns emerge. And yet there are exceptions. For example, Pallas’s cats and mongooses are both small ambush predators, but the Pallas’s cat has round pupils and mongooses have goat-like pupils.
A medida que observamos as distintas pupilas, aparecen patróns. E aínda así hai excepcións. Por exemplo, os gatos de Pallas e as mangostas son pequenos depredadores, pero o gato de Pallas ten pupilas redondas e as mangostas téñenas coma as das cabras.
And we’ve only explored a few pupil shapes. Other animals have crescent- or heart-shaped pupils. And the cuttlefish has perhaps some of the most bizarre: their pupils are circular in the dark, but W-shaped in the light. So, what’s going on here? Well, wouldn’t we all like to know?
E iso que só exploramos unhas poucas pupilas. Outros animais teñen pupilas en forma de media lúa ou de corazón. E o choco ten se cadra unha das máis estrañas: as súas pupilas son circulares na escuridade, pero en forma de W á luz. Por que? Ben, a todos nos gustaría sabelo.