通過轉錄組和行為分析 研究Periophthalmus modestus（廣東彈塗魚）的潮汐振盪

Abstract

棲息在潮間帶的生物，不僅需要應對每天24小時的亮暗變化，還需適應潮汐的漲落。潮汐使鹽度、水位、溫度等多種環境條件的變化有12.4小時的週期性波動。因此，對於這些生物而言，擁有內生性潮汐時鐘可能有助於它們適應外界環境的節律性變化，從而增強其適應能力和生存機會。目前，關於潮汐節律的研究主要集中在無脊椎動物，如甲殼類動物、軟體動物和昆蟲。然而，脊椎動物是否也具備潮汐節律，以及潮汐節律在脊椎動物中的組成尚不明確。因此，我們選用廣東彈塗魚（Periophthalmus modestus）作為實驗動物，在實驗室中模擬不同的人工亮暗和潮汐週期，以研究脊椎動物在潮汐環境下的行為表現。研究發現，在沒有光線的情況下，彈塗魚的活動時間和停留的位置遵循13小時的潮汐週期。然而，在沒有潮汐線索的條件下，彈塗魚的活動時間遵循24小時的亮暗週期，而其對於停留位置的選擇則呈現出接近13小時的節律性。此外，當沒有光線及潮汐刺激時，彈塗魚同時表現出近似日夜及潮汐的週期性行為。我們的結果指出，內生性生理時鐘能調控彈塗魚的行為，促使其能同時適應外界的24小時和13小時週期性刺激。因此，我們提出彈塗魚可能擁有兩個內生性生理時鐘：一個隨亮暗週期表現晝夜節律，另一表現潮汐週期的時鐘為一組兩個的時鐘，兩個時鐘產生兩個反相的節律以此生成潮汐週期。同時，彈塗魚的晝夜節律基因呈現出約24小時的晝夜節律。這些晝夜節律基因並未產生潮汐節律。因此，我們推測有另一套不同於晝夜節律基因的系統負責潮汐時鐘的運作。

Intertidal organisms face not only exposure to 24 hours light-dark cycle but also changes in tide, which generates a 12.4-hour cycle fluctuation of salinity, water level, temperature, and many additional environmental conditions. Thus, for organisms living in the tidal zone, having a tidally endogenous clock may help an individual face the rhythmic changes in external conditions and enhance it fitness and survival. Current research of the circatidal rhythm primarily focuses on invertebrates such as crustaceans, mollusks, and insects. However, whether circatidal rhythm also exists in intertidal vertebrates and the genetic components of the tidal clock in vertebrates remains unclear. Thus, we used mudskipper Periophthalmus modestus as a model to study the tidally affected behaviors of vertebrate animals in the lab with different artificial light-dark and tidal cycles. We found that under the tidal cycle without light cues, the locomotor activity and preference of habituation location of P. modestus followed a 13-hour tidal cycle. However, without tidal cues, the locomotor activity of P. modestus followed a 24-hour light-dark cycle, while their preference of habituation location showed a rhythmicity of close to 13 hours. In addition, in the absence of light and tidal cues, mudskippers exhibit behaviors with both approximately circadian and circatidal rhythms. Together, our results suggest that the endogenous clock could control the behaviors of P. modestus to follow both the external 24-hour and 13-hour cyclic cues. Therefore, we proposed that P. modestus may have two endogenous clocks: one is a circadian clock to track light cycles, the other one is two circatidal clocks in anti-phase to track tidal cycles. Meanwhile, circadian genes exhibit a circadian period in P. modestus. In fact, these circadian genes did not show a tidal period. Therefore, we guess that a different system from circadian genes is responsible for the circatidal clock.