Die sensorische Biologie des Rotfuchses - Hörsinn, Sehsinn, Magnetwahrnehmung

In dieser Studie werden die Sinnessysteme des Rotfuchses behandelt, im Speziellen der Hörsinn, der visuelle Sinn sowie der Magnetsinn. Im ersten Kapitel präsentiere ich ein Verhaltensaudiogramm dreier Rotfüchse. Der Hörbereich des Rotfuchses umfasst 9,84 Oktaven und erstreckt sich von 51 Hz bis 48 kHz. Die absolute Sensitivität (-15 dB SPL bei 4 kHz) ist außergewöhnlich und übertrifft sogar jene der Katze. Ergänzend beschreibe ich die Morphologie des auditorischen Systems des Rotfuchses. Die Beschreibung umfasst die funktionell relevanten Parameter des Außen-, Mittel- und Innenohrs, wie z. B. Abmessungen und Gewichte der Gehörknöchelchen, Flächen der akustischen Membranen, Haarzelldichten sowie die Feinmorphologie der Cochlea. Anschließend zeige ich, dass sich die Sensitivität des auditorischen Systems gut in der Morphologie widerspiegelt und es nur aufgrund der morphologischen Parameter möglich ist, eine recht genaue Vorhersage des Audiogramms zu erstellen. Im zweiten Kapitel stelle ich morphologische Aspekte des visuellen Systems des Rotfuchses vor. Mithilfe von Nissl-Färbungen und Immunhistochemie kartiere ich die retinalen Ganglienzellen und Fotorezeptoren für kurz- (S) und langwelliges (M/L) Licht auf der Retina des Fuchses. Auf dieser Basis berechne ich die Sehschärfe auf 6,3 Zyklen/Grad und die Schalllokalisierungsfähigkeit auf 3-4 Grad, beides innerhalb der Bandbreite anderer Karnivoren liegend. Selbiges gilt für die Verteilung der Zapfen, wobei die M/L-Zapfen einen zentroperipher abfallenden Dichtegradienten aufweisen und die S-Zapfen entlang eines dorsoventralen Gradienten an Dichte zunehmen. Das dritte Kapitel behandelt den Magnetsinn. Für Rotfüchse wurde ein Magnetsinn postuliert, welcher ihnen womöglich bei der Jagd auf Kleinnager zunutze sein könnte. Da der Fuchs beim Jagen hauptsächlich akustische Reize benutzt, wurde ein Einfluss magnetischer Felder auf den Hörsinn hypothetisiert. Aufgrund dessen habe ich die Hörschwelle von Rotfüchsen unter verschiedenen magnetischen Bedingungen getestet, jedoch keinen Hinweis auf einen Einfluss gefunden, weshalb die Hypothese als widerlegt gelten kann. Allerdings konnte ich histologische Befunde sammeln, die für eine Alternativhypothese sprechen, die ein visuell-magnetisches System, analog wie es bei Vögeln vermutet wird, zur Annahme hat: Beim Rotfuchs befindet sich das potentielle Magnetsensormolekül der Vögel, Cryptochrom 1, in den S-Zapfen der Retina. Im abschließenden Teil des letzten Kapitels präsentiere ich die Ergebnisse von Nestbauexperimenten mit Waldmäusen, welche das Vorhandensein eines Magnetsinnes bei diesen Tieren demonstrieren. Weiterhin scheint dieser Magnetsinn durch sehr schwache Radiofrequenzfelder beeinflussbar zu sein – ein Charakteristikum des Radikalpaar-Mechanismus der Magnetwahrnehmung. Dies ist der erste starke Hinweis für das Vorkommen eines derartigen Systems bei einem Säugetier.This study deals with the sensory systems of the red fox, more specifically with audition, vision, and magnetoreception. In the first chapter, I present the behavioural audiograms of three red fox specimens obtained by psychoacoustic procedures. The hearing range of the red fox covers 9.84 octaves ranging from 51 Hz to 48 kHz. The absolute sensitivity (-15 dB SPL at 4 kHz) of the red fox auditory sense is extraordinary, even exceeding that of the domestic cat. Complementary, I describe in detail the morphology of the red fox auditory system, including functionally relevant parameters of the outer, middle and inner ear, such as ossicle measurements and weight, acoustic membrane areas, sensory hair cell densities, and cochlear fine morphology. Subsequently, I demonstrate that the hearing sensitivity of the red fox is well reflected in the measurements and can be predicted with good accuracy on the morphological basis alone. The second chapter is a treatise of some morphological aspects of the visual system of the red fox. By means of Nissl staining and immunohistochemistry, I map the distribution of retinal ganglion cells and short (S) as well as long (M/L) wavelength photoreceptors over the fox retina. Based on the retinal ganglion cell maps the visual acuity of the red fox is assumedly 6.3 cy-cles/degree and the sound localization ability within the range of 3-4 degrees, thus, within the range of other carnivores. The same holds true for the cone distribution, with a centroperipheral decreasing gradient of M/L cones and a dorsoventral increasing density of S cones. The third chapter deals with the sense of magnetoreception. Foxes have been postulated to be magnetosensitive as that might help them during capture of small rodents. As prey capture is mainly auditorily guided, one hypothesis states an influence of magnetic fields on hearing sensitivity. Therefore, I determine the auditory sensitivity of red foxes in different magnetic fields and show that no influence I detectable, making the hypothesis unlikely. However, I show histological evidence in support of an alternative hypothesis which assumes a visual-magnetic system aiding prey capture, similar to the magnetosensitive system in birds: Red foxes, but not rodents, possess the potential magnetosensor of birds, cryptochrome 1 in the S cones of their retina. As an additional part of this chapter I present the results of nest building experiments with wood mice that demonstrates the existence of a magnetic sense and furthermore suggests sensitivity to very weak radiofrequency fields, characteristic for a radical-pair based system of magnetoreception. This is the first strong evidence for such a system in mammals

Low-light dependence of the magnetic field effect on cryptochromes: Possible relevance to plant ecology

Various responses to static magnetic fields (MF) have been reported in plants, and it has been suggested that the geomagnetic field influences plant physiology. Accordingly, diverse mechanisms have been proposed to mediate MF effects in plants. The currently most probable sensor candidates are cryptochromes (Cry) which are sensitive to submillitesla MF. Here, we propose a quantitative approach of the MF effect on Cry depending on light intensity, and try to link it to a possible functional role for magnetic sensitivity in plants. Based on a theoretical evaluation and on a review of relevant data on Arabidopsis thaliana Cry 1, we point out that the MF effect on the signaling state of Cry, as well as the possible consequences of that effect on certain phenotypes (growth in particular) showparallel dependences on light intensity, being most prominent at lowlight levels. Based on these findings, we propose that Cry magnetosensitivity in plants could represent an ecological adaptation which regulates the amount of Cry signaling state under low light conditions. That hypothesis would preferentially be tested by studying sensitive and specific endpoints, such as the expression of clock proteins that are downregulated by Cry, but under light intensities lower than those used so far. Finally, we highlight that the low-light dependence of the MF effect described here could also apply to light-dependent functions of animal Cry, in particular magnetoreception which, from the present evaluation, would be based on the magnetic sensitivity of the photoreduction reaction, like in plants.SCOPUS: ar.jSCOPUS: er.jinfo:eu-repo/semantics/publishe

Effect of exposure to extremely low frequency magnetic fields on melatonin levels in calves is seasonally dependent

The question of health effects of extremely low frequency (50/60 Hz) magnetic fields (ELFMF) has been widely discussed, but the mechanisms of interaction of these fields with biological systems for intensities relevant to human and animal exposure are still under question. The melatonin (MLT) hypothesis suggests that exposure to ELFMF might decrease MLT production thereby promoting cancerogenesis. So far, most studies of MLT secretion under exposure to ELFMF reported negative or inconsistent results. Here, we measured salivary MLT in 1-2 months old cattle calves exposed to 50 Hz-MF in the hundreds of nT-range. We found an inhibitory effect of the ELFMF upon MLT secretion in winter (in accordance with the MLT hypothesis). In contrast, in summer, MLT concentration was increased by ELFMF exposure (contrary to the MLT hypothesis). The inhibitory effect in winter was much stronger than the positive effect in summer. We hypothesize that this season-dependent effect upon MLT synthesis might by mediated by an effect of ELFMF upon the serotonin metabolism and conclude that future tests of ELFMF effects should also measure serotonin levels and consider association with the seasonal effects (photoperiod or temperature) during the exposure.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Cryptochrome 1 in retinal cone photoreceptors suggests a novel functional role in mammals

Cryptochromes are a ubiquitous group of blue-light absorbing flavoproteins that in the mammalian retina have an important role in the circadian clock. In birds, cryptochrome 1a (Cry1a), localized in the UV/violet-sensitive S1 cone photoreceptors, is proposed to be the retinal receptor molecule of the light-dependent magnetic compass. The retinal localization of mammalian Cry1, homologue to avian Cry1a, is unknown and it is open whether mammalian Cry1 is also involved in magnetic field sensing. To constrain the possible role of retinal Cry1, we immunohistochemically analysed 90 mammalian species across 48 families in 16 orders, using an antiserum against the Cry1 C-terminus that in birds labels only the photo-activated conformation. In the Carnivora families Canidae, Mustelidae and Ursidae and in some Primates, Cry1 was consistently labeled in the outer segment of the shortwave-sensitive S1 cones. This finding would be compatible with a magnetoreceptive function of Cry1 in these taxa. In all other taxa, Cry1 was not detected by the antiserum that likely also in mammals labels the photo-activated conformation, although Western blots showed Cry1 in mouse retinal cell nuclei. We speculate that in the mouse and the other negative-tested mammals Cry1 is involved in circadian functions as a non-light-responsive protein

Author correction: Cryptochrome 1 in retinal cone photoreceptors suggests a novel functional role in mammals

Correction to: Scientific Reports https://doi.org/10.1038/srep21848, published online 22 February 2016 This Article contains an error. Among the studied species, the orangutan was erroneously specified as Bornean orangutan Pongo pygmaeus. In fact, the studied individual was a Sumatran orangutan Pongo abelii

Non-Breeding Eusocial Mole-Rats Produce Viable Sperm—Spermiogram and Functional Testicular Morphology of Fukomys anselli

Ansell’s mole-rats (Fukomys anselli) are subterranean rodents living in families composed of about 20 members with a single breeding pair and their non-breeding offspring. Most of them remain with their parents for their lifetime and help to maintain and defend the natal burrow system, forage, and care for younger siblings. Since incest avoidance is based on individual recognition (and not on social suppression) we expect that non-breeders produce viable sperm spontaneously. We compared the sperm of breeding and non-breeding males, obtained by electroejaculation and found no significant differences in sperm parameters between both groups. Here, we used electroejaculation to obtain semen for the first time in a subterranean mammal. Spermiogram analysis revealed no significant differences in sperm parameters between breeders and non-breeders. We found significantly larger testes (measured on autopsies and on living animals per ultrasonography) of breeders compared to non-breeders (with body mass having a significant effect). There were no marked histological differences between breeding and non-breeding males, and the relative area occupied by Leydig cells and seminiferous tubules on histological sections, respectively, was not significantly different between both groups. The seminiferous epithelium and to a lesser degree the interstitial testicular tissue are characterized by lesions (vacuolar degenerations), however, this feature does not hinder fertilization even in advanced stages of life. The continuous production of viable sperm also in sexually abstinent non-breeders might be best understood in light of the mating and social system of Fukomys anselli, and the potential to found a new family following an unpredictable and rare encounter with an unfamiliar female (“provoked or induced dispersal”). Apparently, the non-breeders do not reproduce because they do not copulate but not because they would be physiologically infertile. The significantly increased testes volume of breeding males (compared to non-breeders) is in agreement with previously found higher testosterone levels of breeders

Reproductive males have larger testes compared to non-reproductive males.

<p>Absolute testes volume (mm³) relative to body mass (g) for breeders (filled circles) compared to non-breeders (open circles) of Ansell’s mole-rats (<i>Fukomys anselli</i>).</p

Normal morphology of Ansell’s mole-rat sperm.

<p>The samples were obtained by electroejaculation (light microscopy, magnification 600x, oil immersion, eosin & nigrosin staining).</p

Main parameters (mean, SD given in parenthesis) of male reproductive characteristics measured in Ansell’s mole-rats.

<p>Volumes estimated for the right and left testis of each male were averaged to obtain mean absolute and relative testes volumes, respectively. *The minimum age at the time of testis measurement was estimated for two specimens since they were caught in the field in Lusaka, Zambia.</p

Light microscopy (x200) of histological testicular sections (8μm thickness) of three Ansell's mole-rats.

<p>A. young non-reproductive (age: 22 months), B. old non-reproductive (age: 8.7 years), C. reproductive male (age: 9.8 years). The germinal epithelium of the seminiferous tubules and to a lesser degree the interstitial testicular tissue of all individuals were characterized by lesions (vacuolar degenerations) exemplarily indicated by black arrowheads.</p