Effect of photoperiod and light intensity on learning ability and memory formation of the pond snail Lymnaea stagnalis
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ORIGINAL PAPER
Effect of photoperiod and light intensity on learning ability and memory formation of the pond snail Lymnaea stagnalis Ahmed A. A. Hussein1,2,3 · El‑Sayed Baz1 · Janine Mariën2 · Menerva M. Tadros3 · Nahla S. El‑Shenawy1 · Joris M. Koene2 Received: 28 May 2020 / Accepted: 6 October 2020 © The Author(s) 2020
Abstract Natural light is regarded as a key regulator of biological systems and typically serves as a Zeitgeber for biological rhythms. As a natural abiotic factor, it is recognized to regulate multiple behavioral and physiological processes in animals. Disruption of the natural light regime due to light pollution may result in significant effects on animal learning and memory development. Here, we investigated whether sensitivity to various photoperiods or light intensities had an impact on intermediate-term memory (ITM) and long-term memory (LTM) formation in the pond snail Lymnaea stagnalis. We also investigated the change in the gene expression level of molluscan insulin-related peptide II (MIP II) is response to the given light treatments. The results show that the best light condition for proper LTM formation is exposure to a short day (8 h light) and low light intensity (1 and 10 lx). Moreover, the more extreme light conditions (16 h and 24 h light) prevent the formation of both ITM and LTM. We found no change in MIP II expression in any of the light treatments, which may indicate that MIP II is not directly involved in the operant conditioning used here, even though it is known to be involved in learning. The finding that snails did not learn in complete darkness indicates that light is a necessary factor for proper learning and memory formation. Furthermore, dim light enhances both ITM and LTM formation, which suggests that there is an optimum since both no light and too bright light prevented learning and memory. Our findings suggest that the upsurge of artificial day length and/ or night light intensity may also negatively impact memory consolidation in the wild. Keywords Conditioning · Gastropod · Light intensity · Memory · MIP II · Mollusk · Photoperiod
Introduction As an abiotic factor, natural light is regarded as a key regulator of biological systems and generally acts as a Zeitgeber for biological rhythms (Bradshaw and Holzapfel 2010). One of the most common environmental cycles is the day-night cycle which can differ across the seasons depending on the latitude. Even though natural light is not constant, but varies * Ahmed A. A. Hussein [email protected] * El‑Sayed Baz [email protected] 1
Department of Zoology, Faculty of Science, Suez Canal University, Ismailia, Egypt
2
Department of Ecological Science, Faculty of Science, Vrije Universiteit, Amsterdam, The Netherlands
3
Malacology Lab, Theodor Bilharz Research Institute (TBRI), Giza, Egypt
over time in terms of photoperiods and light intensity, this provides sufficient information for entraining biological rhythms (Gorman et al. 2005). Nevertheless, in recent years it has become c
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