Abstract
BackgroundThe African mole-rats (Bathyergidae, Rodentia) are strictly subterranean, congenitally microphthalmic rodents that are hardly ever exposed to environmental light. Because of the lack of an overt behavioural reaction to light, they have long been considered to be blind. However, recent anatomical studies have suggested retention of basic visual capabilities. In this study, we employed behavioural tests to find out if two mole-rat species are able to discriminate between light and dark, if they are able to discriminate colours and, finally, if the presence of light in burrows provokes plugging behaviour, which is assumed to have a primarily anti-predatory function.Methodology/Principal FindingWe used a binary choice test to show that the silvery mole-rat Heliophobius argenteocinereus and the giant mole-rat Fukomys mechowii exhibit a clear photoavoidance response to full-spectrum (“white”), blue and green-yellow light, but no significant reaction to ultraviolet or red light during nest building. The mole-rats thus retain dark/light discrimination capabilities and a capacity to perceive short to medium-wavelength light in the photopic range of intensities. These findings further suggest that the mole-rat S opsin has its absorption maximum in the violet/blue part of the spectrum. The assay did not yield conclusive evidence regarding colour discrimination. To test the putative role of vision in bathyergid anti-predatory behaviour, we examined the reaction of mole-rats to the incidence of light in an artificial burrow system. The presence of light in the burrow effectively induced plugging of the illuminated tunnel.Conclusion/SignificanceOur findings suggest that the photopic vision is conserved and that low acuity residual vision plays an important role in predator avoidance and tunnel maintenance in the African mole-rats.
Highlights
Sensory perception plays a crucial role in animal spatial and temporal orientation, foraging and communication with conspecifics
Photoavoidance response to blue and green light Both species preferred nesting in the dark box and avoided box illuminated by blue (F. mechowii: x2 = 4.8, P = 0.029, N = 17; H. argenteocinereus: x2 = 5.0, P = 0.025, N = 20) and green-yellow light (F. mechowii: x2 = 5.0, P = 0.025, N = 20; H. argenteocinereus: x2 = 5.4, P = 0.020, N = 15) (Fig. 1, third and fourth left bars)
Animals showed a random choice between the dark box and the box illuminated by red light (F. mechowii: x2 = 0.06, P = 0.81, N = 17; H. argenteocinereus: x2 = 0.2, P = 0.65, N = 20; Fig. 1, right bars)
Summary
Sensory perception plays a crucial role in animal spatial and temporal orientation, foraging and communication with conspecifics. In the context of visual ecology, the subterranean niche is arguably the most extreme sensory environment, being deprived of light and all visual cues available above ground. Because it provides shelter from predation and climatic fluctuations, about 250 mammalian species have adopted subterranean lifestyle [3,4,5]. Strictly subterranean mammals are congenitally microphthalmic and possess a severely reduced visual system, the degree of reduction vary substantially among species (for review, see [7,8]). The African mole-rats (Bathyergidae, Rodentia) are strictly subterranean, congenitally microphthalmic rodents that are hardly ever exposed to environmental light. We employed behavioural tests to find out if two mole-rat species are able to discriminate between light and dark, if they are able to discriminate colours and, if the presence of light in burrows provokes plugging behaviour, which is assumed to have a primarily anti-predatory function
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