Biology subjects

Malkemper, E. P.

Publications and source records attributed to Malkemper, E. P..

5 recordsLinked to original sources

bioRxiv2026

Light-independent and pulsing-sensitive magnetic compass responses in planarians

Many animals can sense the Earth's magnetic field and use it for orientation. However, the mechanism underlying magnetoreception has not been identified, partially due to the lack of reproducible and genetically tractable model systems. Here, we establish a directional assay for planaria to test their responses to different magnetic fields. Girardia dorotocephala showed a preferred magnetic directionality in the horizontal plane in an Earth-strength magnetic field in the absence of visible light, which shifted if the azimuth was rotated and was absent when the magnetic field was cancelled. This directional preference differed between labs. Furthermore, the directional response was affected by a short but strong magnetic pulse, resulting in a random distribution. The effect of the pulse was temporary, with directional preferences recovering over several days. Taken together, these data are consistent with a magnetoreception mechanism in planarians that functions independently of light and relies on permanently magnetised material, such as single-domain magnetite. As planarians are genetically tractable and well-established, they are a promising invertebrate model organism that might offer insights into the mechanisms underlying magnetoreception in animals.

animal behavior and cognition↗

bioRxiv2026

Multimodal imaging reveals no evidence for magnetite-based magnetoreceptors in the mole-rat eye

Magnetoreception, the ability to perceive the geomagnetic field, is widespread across animals. The underlying sensory mechanism remains elusive, but a long-standing hypothesis proposes single-domain magnetite linked to mechanosensitive ion channels. The Ansells mole-rat (Fukomys anselli) is a subterranean rodent with a magnetic sense, and published behavioral and histological data are consistent with magnetite-based magnetoreceptors in the cornea or retina. Here, we systematically screened for magnetite in the mole-rat eye, combining iron detection via enhanced Prussian blue staining and synchrotron X-ray fluorescence microscopy (XFM) with magnetic detection via MRI quantitative susceptibility mapping (MRI-QSM) and quantum-diamond microscopy (QDM). This revealed only a few iron particles in the retina and cornea, which predominantly overlapped with titanium or chromium, indicating a non-biogenic origin. XFM showed iron-enriched lines in the cornea, but these did not show ferrimagnetic signals. Focusing on other ocular tissues, MRI-QSM revealed the highest susceptibility in the ciliary body, where iron-rich pigmented cells were identified. A TEM-screen, however, failed to detect single-domain magnetite particles in these cells. We conclude that our high-sensitivity multimodal screen provides no evidence for magnetite-based magnetoreceptors in the mole-rat eye, suggesting that mole-rat magnetoreceptors either do not reside in the eye or are based on different physical principles.

neuroscience↗

bioRxiv2025

Neuronal recordings in head-fixed and freely-moving mole-rats

Mole-rats are subterranean rodents that have evolved remarkable sensory adaptations to life in underground tunnel systems, yet their neural mechanisms remain largely unexplored. Here, we present a protocol for in vivo electrophysiological recordings in awake, head-fixed, and freely moving African mole-rats (Fukomys anselli/micklemi), overcoming unique challenges of studying the neurobiology of subterranean species. For example, we find that mole-rat brain physiology impacts survival after surgeries, with higher carbon dioxide concentrations required for recovery compared to other rodents, likely due to a mutation in the chloride-potassium symporter KCC2. Having addressed the challenges, we used tetrodes and Neuropixels probes to record single-unit activity and local field potentials (LFP) across several cortical and subcortical regions for several weeks. We observed single units responsive to auditory and visual stimuli in the superior colliculus, and hippocampal recordings in freely moving mole-rats revealed prominent theta rhythms at frequencies lower than those observed in any other rodent species to date. Finally, we performed integrated three-dimensional and two-dimensional probe-track analysis within the same brain using tissue clearing, light sheet imaging, rehydration, and vibratome sectioning, and we present a newly developed stereotaxic brain atlas for implantation and histological alignment. The established methodology will guide future studies in comparative rodent neurobiology, providing further insights into neurobiological adaptations to subterranean environments. Given their phylogenetic and ecological similarities, we expect our protocols to be transferable to other subterranean species, including the widely studied naked mole-rat (Heterocephalus glaber). HighlightsO_LIProtocols for chronic and acute electrode implantations in mole-rats C_LIO_LIStereotaxic brain atlas for the Ansells mole-rat (https://doi.org/10.17617/3.UNDKRO) C_LIO_LINeuropixels and tetrode single-unit recordings in head-fixed and freely moving mole-rats C_LIO_LIIntegrated 3D (tissue clearing) and 2D (histology) probe-track analysis within the same brain C_LIO_LIDiscovery of low-frequency hippocampal theta rhythm in Ansells mole-rats C_LI

neuroscience↗

bioRxiv2021

Comparing two circular distributions: advice for effective implementation of statistical procedures in biology

Many biological variables, often involving timings of events or directions, are recorded on a circular rather than linear scale, and need different statistical treatment for that reason. A common question that is asked of such circular data involves comparison between two groups or treatments: Are the populations from which the two samples drawn differently distributed around the circle? For example, we might ask whether the distribution of directions from which a stalking predator approaches its prey differs between sunny and cloudy conditions; or whether the time of day of mating attempts differs between lab mice subject to one of two hormone treatments. An array of statistical approaches to these questions have been developed. We compared 18 of these (by simulation) in terms of both abilities to control type I error rate near the nominal value, and statistical power. We found that only eight tests offered good control of type I error in all our test situations. Of these eight, we are able to identify Watsons U2 test and MANOVA based on trigonometric functions of the data as offering the best power in the overwhelming majority of our test circumstances. There was often little to choose between these tests in terms of power, and no situation where either of the remaining six tests offered substantially better power than either of these. Hence, we recommend the routine use of either Watsons U2 test or MANOVA when comparing two samples of circular data.

animal behavior and cognition↗

bioRxiv2020

Eyes are essential for magnetoreception in a mammal

Several groups of mammals use the Earths magnetic field for orientation, but their magnetosensory organ remains unknown. The Ansells mole-rat (Fukomys anselli) is a subterranean rodent with innate magnetic orientation behavior. Previous studies proposed that its magnetoreceptors are located in the eye. To test this hypothesis, we assessed magnetic orientation in enucleated mole-rats. Initially, we demonstrate that enucleation of mole-rats does not lead to changes in routine behaviors. We then studied magnetic compass orientation by employing a well-established nest building assay. To ensure that directional responses were based on magnetic parameters, we tested animals under four magnetic field alignments. In line with previous studies, control animals exhibited a significant preference to build nests in magnetic south-east. In contrast, enucleated mole-rats built nests in random magnetic orientations, suggesting an impairment of their magnetic sense. The results provide robust support for the hypothesis that mole-rats perceive magnetic fields with their minute eyes.

animal behavior and cognition↗