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Adaptations for nocturnal vision in insect apposition eyes

Greiner, Birgit LU (2005)
Abstract (Swedish)
Popular Abstract in Swedish

Hur kan nattaktiva insekter se i mörker med fel sorts ögon?



Majoriteten av alla dagaktiva insekter har en sorts facettöga som kallas appositionsöga. Appositionsögon är anpassade till ett liv med god tillgång på ljus ? nattaktiva djur har därför i princip alltid andra sorters ögon (superpositionsögon). Anledningen till att appositionsögon fungerar bäst på dagen är att de har små linser vilket gör dem mycket okänsliga och opålitliga i mörker. I avhandlingens introduktion behandlar jag insekternas synsinne och anledningen till att vissa ändå använder dåligt anpassade ögon för nattseende. Men det är bara i en enda insekt, ett väldigt speciellt nattaktivt bi, som hittills alla... (More)
Popular Abstract in Swedish

Hur kan nattaktiva insekter se i mörker med fel sorts ögon?



Majoriteten av alla dagaktiva insekter har en sorts facettöga som kallas appositionsöga. Appositionsögon är anpassade till ett liv med god tillgång på ljus ? nattaktiva djur har därför i princip alltid andra sorters ögon (superpositionsögon). Anledningen till att appositionsögon fungerar bäst på dagen är att de har små linser vilket gör dem mycket okänsliga och opålitliga i mörker. I avhandlingens introduktion behandlar jag insekternas synsinne och anledningen till att vissa ändå använder dåligt anpassade ögon för nattseende. Men det är bara i en enda insekt, ett väldigt speciellt nattaktivt bi, som hittills alla aspekter undersökts ? såväl beteende som optiska och neurala anpassningar och teorin bakom det hela.



De flesta bin i världen är dagaktiva och har appositionsögon. Ändå finns det bin i Panama som flyger runt på natten. Teoretiska beräkningar visar att dessa bin inte borde kunna se någonting så fort det börjar skymma, men Panamabina flyger från sitt bo (ett 5 mm stort hål i en liten pinne), genom grenar och lövverk i djungeln, letar reda på nektargömmor långt borta från sitt hem och hittar sedan tillbaka till boet utan att flyga vilse. Dessutom, som visas i första artikeln, kan de även urskilja och använda landmärken för att orientera i mörker. Men hur klarar de det med sina okänsliga appositionsögon?



Den andra och tredje artikeln visar att appositionsögon hos nattaktiva bin och getingar har specifika optiska och anatomiska anpassningar som gör dem 30 gånger ljuskänsligare än deras dagaktiva släktingar. Mest effektivt är otroligt stora ljuskänsliga fotoreceptorer som absorberar ljus från en mycket bredare infallsvinkel än i ett normalt appositionsöga. En känslighetsförbättring på 30 gånger är inte att förakta, men inte tillräcklig om man tänker på att ljusintensitetsskillnaden är 100 millioner gånger mellan dag och natt. Därför undrade jag vilka andra möjliga anpassningar som måste finnas.



Enligt vår teoretiska modell (artikel VI), skulle nattaktiva bin använda sig av fotonsummering (i rum och tid) för att kunna se i svag belysning. Om Panamabina summerar signaler från flera facetter kan de få tillräckligt med ljus för att även kunna se under natten. Som jag visar i artiklarna IV & V, finns det stora, sidoförgrenade celler i den optiska delen av deras hjärna. Alla förgreningarna är mycket större jämfört med motsvarande celler i dagaktiva bin ? en tendens som finns också i andra insektgrupper ? och täcker en stor yta av 10-18 facetter. Vår modell förutsäger detta, vilket förstärker hypotesen att dessa celler förmedlar spatiell fotonsummering.



I min avhandling visar jag att nattaktiva insekter med appositionsögon har utvecklat specifika optiska och neurala anpassningar vilka möjliggör för dem att vara aktiva under natten i en tryggare miljö med förminskad konkurrens. (Less)
Abstract
Due to our own preference for bright light, we tend to forget that many insects are active in very dim light. The reasons for nocturnal activity are most easily seen in tropical areas of the world, where animals face severe competition for food and nocturnal insects are able to forage in a climate of reduced competition and predation.



Generally nocturnal insects possess superposition compound eyes. This eye design is truly optimized for dim light as photons can be gathered through large apertures comprised of hundreds of lenses. In apposition eyes, on the other hand, the aperture consists of a single lens resulting in a poor photon catch and unreliable vision in dim light. Apposition eyes are therefore typically found in... (More)
Due to our own preference for bright light, we tend to forget that many insects are active in very dim light. The reasons for nocturnal activity are most easily seen in tropical areas of the world, where animals face severe competition for food and nocturnal insects are able to forage in a climate of reduced competition and predation.



Generally nocturnal insects possess superposition compound eyes. This eye design is truly optimized for dim light as photons can be gathered through large apertures comprised of hundreds of lenses. In apposition eyes, on the other hand, the aperture consists of a single lens resulting in a poor photon catch and unreliable vision in dim light. Apposition eyes are therefore typically found in day-active insects and according to theoretical calculations should render bees blind by mid dusk.



Nevertheless, the tropical bee Megalopta genalis and the wasp Apoica pallens have managed the transition to a nocturnal lifestyle while retaining their highly unsuitable apposition eye design. Far from being blind, these bees and wasps forage at extremely low light intensities. Moreover, M. genalis is the first insect shown to use landmark navigation at light intensities less than starlight. How do their apposition eyes permit such complex visual behaviour in so little light?



Optical adaptations can significantly enhance sensitivity in apposition eyes. In bees and wasps, the major effect comes from their extremely wide photoreceptors, which are able to trap light reaching the eye from a large visual angle. These optical adaptations lead to a 30-fold increase in sensitivity compared to diurnal bees and wasps. This however is not sufficient for the 8 log units difference in light intensity between day and night.



Our hypothesis is that neural adaptations in the form of spatial and temporal summation must be involved. By means of spatial summation the eyes could sum signals from large groups of visual units (ommatidia), in order to improve sensitivity at the cost of coarser spatial resolution. In nocturnal bees, spatial summation could be mediated via their wide laterally-spreading first-order interneurons (L-fibres) present in the first optic ganglion (lamina). These L-fibres have significantly larger dendritic fields than equivalent neurons in diurnal bees and the potential to sum photons from up to 18 visual units. Theoretical modelling further supports this hypothesis, as the optimal dendritic field size predicted by the model agrees well with the anatomical data. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof. Meinertzhagen, Ian A., Life Sciences Centre, Dalhousie University, Halifax, Canada.
organization
publishing date
type
Thesis
publication status
published
subject
keywords
temporal and spatial summation, optical and neural adaptations, theoretical modelling., Djurs anatomi och morfologi, Zoologi, dim light, vision, landmark navigation, nocturnal bees and wasps, Zoology, Animal anatomy, animal morphology
pages
140 pages
publisher
Lund Unversity, Department of Cell and Organism Biology
defense location
Högtidssalen, Zoologihuset, Helgonav. 3, Lund
defense date
2005-12-16 10:00
ISBN
91-85067-22-9
language
English
LU publication?
yes
id
97598f0d-109f-424e-97d5-8aa872e25362 (old id 545724)
date added to LUP
2007-09-04 15:48:37
date last changed
2016-09-19 08:45:12
@phdthesis{97598f0d-109f-424e-97d5-8aa872e25362,
  abstract     = {Due to our own preference for bright light, we tend to forget that many insects are active in very dim light. The reasons for nocturnal activity are most easily seen in tropical areas of the world, where animals face severe competition for food and nocturnal insects are able to forage in a climate of reduced competition and predation.<br/><br>
<br/><br>
Generally nocturnal insects possess superposition compound eyes. This eye design is truly optimized for dim light as photons can be gathered through large apertures comprised of hundreds of lenses. In apposition eyes, on the other hand, the aperture consists of a single lens resulting in a poor photon catch and unreliable vision in dim light. Apposition eyes are therefore typically found in day-active insects and according to theoretical calculations should render bees blind by mid dusk.<br/><br>
<br/><br>
Nevertheless, the tropical bee Megalopta genalis and the wasp Apoica pallens have managed the transition to a nocturnal lifestyle while retaining their highly unsuitable apposition eye design. Far from being blind, these bees and wasps forage at extremely low light intensities. Moreover, M. genalis is the first insect shown to use landmark navigation at light intensities less than starlight. How do their apposition eyes permit such complex visual behaviour in so little light?<br/><br>
<br/><br>
Optical adaptations can significantly enhance sensitivity in apposition eyes. In bees and wasps, the major effect comes from their extremely wide photoreceptors, which are able to trap light reaching the eye from a large visual angle. These optical adaptations lead to a 30-fold increase in sensitivity compared to diurnal bees and wasps. This however is not sufficient for the 8 log units difference in light intensity between day and night.<br/><br>
<br/><br>
Our hypothesis is that neural adaptations in the form of spatial and temporal summation must be involved. By means of spatial summation the eyes could sum signals from large groups of visual units (ommatidia), in order to improve sensitivity at the cost of coarser spatial resolution. In nocturnal bees, spatial summation could be mediated via their wide laterally-spreading first-order interneurons (L-fibres) present in the first optic ganglion (lamina). These L-fibres have significantly larger dendritic fields than equivalent neurons in diurnal bees and the potential to sum photons from up to 18 visual units. Theoretical modelling further supports this hypothesis, as the optimal dendritic field size predicted by the model agrees well with the anatomical data.},
  author       = {Greiner, Birgit},
  isbn         = {91-85067-22-9},
  keyword      = {temporal and spatial summation,optical and neural adaptations,theoretical modelling.,Djurs anatomi och morfologi,Zoologi,dim light,vision,landmark navigation,nocturnal bees and wasps,Zoology,Animal anatomy,animal morphology},
  language     = {eng},
  pages        = {140},
  publisher    = {Lund Unversity, Department of Cell and Organism Biology},
  school       = {Lund University},
  title        = {Adaptations for nocturnal vision in insect apposition eyes},
  year         = {2005},
}