UNA REGIONALIZZAZIONE DELLE CAPACITÀ VISIVE NELL’OCCHIO COMPOSTO DI TALITRUS SALTATOR (CRUSTACEA, AMPHIPODA)

49° Congresso della Società Italiana di Biologia Marina Cesenatico (FC), 4-8 giugno 2018

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AUTORI: A. CIOFINI, L. MERCATELLI, D. JAFRANCESCO, A. UGOLINI, T. HARIYAMA TITOLO: A REGIONALIZATION OF THE VISUAL CAPABILITIES WITHIN THE COMPOUND EYE OF TALITRUS SALTATOR (CRUSTACEA, AMPHIPODA)?

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Nome e Cognome Alice CIOFINI e-mail: alice.ciofini@unifi.it

Autore che paga la quota di iscrizione al Congresso Nome e Cognome Alberto Ugolini

e-mail: alberto.ugolini@unifi.it

Autore che presenta il lavoro al Congresso Nome e Cognome Alice CIOFINI

e-mail: alice.ciofini@unifi.it

Si ricorda a tutti gli Autori che la partecipazione al congresso è vincolata al pagamento della quota di iscrizione dei singoli partecipant

49° Congresso della Società Italiana di Biologia Marina Cesenatico (FC), 4-8 giugno 2018

A. CIOFINI, L. MERCATELLI1, D. JAFRANCESCO1, A. UGOLINI, T. HARIYAMA2 Dipartimento di Biologia, Università di Firenze, Via Romana, 17 - 50125 Firenze, Italia.

alice.ciofini@unifi.it

1_{Istituto Nazionale di Ottica Applicata CNR, Largo E. Fermi, 6 - 50125 Firenze, Italia.} 2_{Department of Biology, Hamamatsu University School of Medicine, 1-20-1, Handayama, Higashi-Ku,}

Hamamatsu 431-3192, Japan.

A REGIONALIZATION OF THE VISUAL CAPABILITIES

WITHIN THE COMPOUND EYE OF TALITRUS SALTATOR

(CRUSTACEA, AMPHIPODA)?

UNA REGIONALIZZAZIONE DELLE CAPACITÀ VISIVE NELL’OCCHIO COMPOSTO DI TALITRUS SALTATOR (CRUSTACEA, AMPHIPODA)?

Abstract – The proper perception of celestial orienting factors is fundamental for the zonal recovery of the

supralittoral amphipod Talitrus saltator (Crustacea, Amphipoda). Here, we test the existence of the regionalization of its visual capabilities within its compound eye. Indeed, we show that the dorsal area plays a main role in the detection of skylight cues and we point out putative morphological adaptions of the ommatidia located in this region.

Key-words: celestial orientation behaviour, compound eye, Talitrus saltator.

Introduction - In its zonal recovery along the sea-land axis of sandy shores, the

supralittoral amphipod Talitrus saltator (Montagu, 1808) is well known to rely on several celestial cues, such as the sun, the moon and the luminance pattern of the sky (see Pardi and Ercolini, 1986; Ugolini et al., 2009). However, the perception of a skylight factor in the UV-blue wavelengths range (λ<450 nm) is fundamental for the proper use of the celestial orienting references by this species (Ugolini et al., 1996). Recent studies (Ugolini et al., 2010) have pointed out the existence within its compound eye of discrete photoreceptors sensitive to different ranges of light (UV-blue and green, respectively). Since other arthropods exhibit a typical spatial distribution of their visual pigments with UV-blue sensitive cells mainly located in the dorsal region of their eye (Duelli and Wehner, 1973; Wehner and Strasser, 1985), we investigated the eventual regionalization of the visual capabilities in T. saltator.

Materials and methods - We tested the celestial orientation of freshly collected adult

individuals with discrete regions of their eyes (the dorsal 1/3 area and the ventral 2/3 area respectively) obscured by black enamel. Intact animals were released as controls. Each group was composed of 30 individuals. Experiments were carried out in a confined environment (see Ugolini and Macchi, 1988 for a description of the apparatus) by placing gelatine filters above the device. In particular, we used a grey (transmittance =23.5%) and a blue (transmittance =73%, λmax=450 nm) filter. Tests

were conducted both in conditions of sun visible and with its vision blocked. Data were analysed following the methods proposed by Batschelet (1981) for circular distributions. Furthermore, we assessed the anatomical structure of the ommatidia occurring in the eye of T. saltator. Semi-thin (1 μm thick) sections were cut along the dorso-ventral axis of the eye, stained with blue toluidine and observed by light microscope. We then realized 3D reconstruction of ommatidia by aligning and volume-rendering photos taken from each section.

49° Congresso della Società Italiana di Biologia Marina Cesenatico (FC), 4-8 giugno 2018

Results - Our behavioural investigations showed that each group of individuals

released performed a mean orientation in good agreement with the expected direction. However, in any cases, animals with the dorsal portion of their eyes obscured exhibited a major difficulty in performing directional choices than the other lots of individuals tested. Furthermore, morphological investigations and 3D reconstructions of the ommatidial structure revealed that ommatidia located in the dorsal area are typically straight, whereas those occurring in the rest of the eye exhibit a bent shape.

Conclusions - This work suggests a regionalization of the visual capabilities in T. saltator. In fact, behavioural investigations, although not providing evidence for the

spatial distribution of the visual pigments within the compound eye of this species, indicate that ommatidia located in the dorsal region play a main role in the proper perception of celestial cues by this species. The anatomical differences revealed in the ommatidial structure between the dorsal region and the rest of the eye support this hypothesis, since they suggest specific adaptions of the dorsal ommatidia with respect those occurring elsewhere. Since highly specialized ommatidia located in the dorsal rim of the eye (DRA) are involved in the perception of polarized light by many species of arthropods (see Labhart and Meyer, 1999), our results do not exclude that the correct detection of the celestial orienting factors by T. saltator is in fact mediated by the pattern of polarization of the sky.

References

BATSCHELET E. (1981) - Circular statistic in biology. Academy press, London: 371 pp.

DUELLI P., WEHNER R. (1973) - The spectral sensitivity of polarized light orientation in

Cataglyphis bicolor (Formicidae, Hymenoptera). J. Comp. Phys. A, 86: 37-53.

LABHART T., MEYER E.P. (1999) - Detectors for polarized light in insects: a survey of ommatidial specializations in the dorsal rim area of the compound eye. Micr. Res. Techn., 47: 368-379.

PARDI L., ERCOLINI A. (1986) - Zonal recovery mechanism in talitrid crustaceans. Boll. Zool., 53: 139-160.

UGOLINI A., MACCHI T. (1988) - Learned component in the solar orientation of Talitrus saltator Montagu (Amphipoda: Talitridae). J. Exp. Mar. Biol. Ecol., 121: 79-87.

UGOLINI A., GALANTI G., BORGIOLI G., MERCATELLI L., HARIYAMA T. (2010) -Photoresponses of the compound eyes of the sandhopper Talitrus saltator (Crustacea, Amphipoda) in the ultraviolet-blue range. Biol. Bull., 219: 72-79.

UGOLINI A., GALANTI G., MERCATELLI L. (2009) - Difference in skylight intensity is a new celestial cue for sandhopper orientation (Amphipoda Talitridae). Anim. Behav., 77: 170-175.

UGOLINI A., GALANTI G., MERCATELLI L. (2013) - Do sandhoppers use the skylight polarization as a compass cue? Anim. Behav., 86: 427-434.

UGOLINI A., VIGNALI B., CASTELLINI C., LINDSTROM M. (1996) - Zonal orientation and spectral filtering in Talitrus saltator (Amphipoda, Talitridae). J. Mar. Biol. Assoc. UK, 76: 377-389. WEHNER R., STRASSER S. (1985) - The pool area of the honeybee’s eye: behavioural evidences.

Phys. Ent., 10: 337-349.