Zagledajući u oči različitih životinja, vidjet ćete nebične oblike zjenica. Ali zašto? Ispostavlja se da je oblik zjenice moćan pokazatelj kakvu ulogu životinja igra u svom ekosistemu.
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.
Zjenice predstavljaju šupalj otvor u irisu, snop pigmentovanih mišića oka. To su otvori kroz koje svjetlo prolazi do oka, gdje potom pogađa retinu i aktivira ćelije osjetljive na svjetlost, pokrećući proces vizije. Zjenice su crne jer većina svjetlosti koja ulazi unutar njih bude upijena. Njihova veličina se mijenja ovisno o svjetlosti, kao i zbog određenih droga, emocionalnih i mentalnih stanja— ali njihov osnovni oblik uveliko varira među vrstama.
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.
Kućne mačke su lovci tokom sumraka s vertikalno izduženim zjenicama. U tami, ovi oblici se šire drastično upijajući dostupnu svjetlost. Kada je svijetlo, one se skupljaju u proreze. Mačje zenice su tako fleksibilne da je njihova maksimalna veličina 135 puta veća od njihove minimalne veličine— dok se naše zjenice smanje i rašire samo petnaestorostruko. Zbog načina na koji zjenice oblika proreza upijaju svjetlost, stvaraju se oštre, vertikalne konture. Kada mozak mačke procesuira vizuelni prikaz iz očiju, male ali oštre razlike između njih pomažu mački da odredi tačnu udaljenost njene mete. Štaviše, mnogi drugi grabežljivci također imaju vertikalno izdužene zjenice— ali uglavnom oni čije su oči locirane bliže tlu. Može biti zbog toga što su ove zjenice naročito korisne u opažanju predmeta na relativno kratkim udaljenostima na kojima ove životinje love.
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.
Svijet izgleda veoma drugačije iza horizontalno izduženih zjenica mnogih životinja koje pasu i brste, poput koza. Ove zjenice, koje se nalaze s obje strane glave, puštaju horizontalne svjetlosne zrake koje pružaju kozama pogled od 360 stepeni i omogućavaju oštre, horizontalne slike. Ovo pomaže kozama da uoče svaku nepravilnost na horizontu— upozoravajući ih na potencijalne predatore dok idalje imaju mogućnost vidjeti ispred i detektovati prepreke dok bježe. Štaviše, koze uvijek drže svoje zjenice u ravni sa horizontom, rotirajući očne jabučice u očnim dupljama dok pomjeraju glavu gore-dolje.
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.
U međuvremenu, noćni gušteri imaju zjenice koje se smanje u proreze ispunjene otvorima na bolje osvijetljenim mjestima. Svaki otvor projektuje odvojenu, oštru sliku u mrežnicu guštera. Naučnici smatraju da bi poređenje ovih različitih unosa moglo pomoći gušteru da odredi udaljenost bez pomjeranja.
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.
I dok su vas možda prevarili, bogomoljke i drugi insekti i rakovi imaju ″pseudo-zjenice.″ One nisu optičke strukture; one us optičke iluzije koje doživljava posmatrač. Bogomoljke imaju složene oči sastavljene iz hiljadu fotorecepcionih jedinica. Kada su neke uperene u vas, izgledaju crne jer upijaju većinu talasne dužine dolazećeg svjetla ali nema stvarnog otvora.
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.
Ali zašto onda mi imamo okrugle zjenice? Izdužene zjenice pomažu izoštriti određene dimenzije životinjskog vida. Ali naučnici misle da za životinje kakve smo mi sa kružnim zjenicama, da je to niži prioritet. Umjesto da vidimo neke elemente scene u ekstremnom fokusu, mi vidimo veću sliku relativno detaljno, koja nam omogućava više općih vještina posmatranja. Ovo može biti naročito od pomoći za tragače hrane, lovce koji vrebaju i jure svoj plijen, i za društvene životinje koje prepoznavaju druga lica.
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.
Dok posmatramo različite zjenice, pojavljuju se uzorci. Ipak postoje izuzeci. Naprimjer, Pallasove mačke i mungosi su mali predatori iz sjene, ali Pallasova mačka ima okrugle zjenice a mungosi zjenice poput kozjih.
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 samo smo istražili nekoliko oblika zjenica. Druge životinje imaju zjenice u obliku polumjeseca ili srca. A sipa ima možda neke od najbizarnijih: njihove zjenice su okrugle u mraku, ali oblika duplog V na svjetlosti. Dakle, šta se ovdje događa? Pa, zar ne bismo svi to željeli znati?
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?