Tidal and diel orchestration of behaviour and gene expression in an intertidal mollusc

Abstract

Intertidal inhabitants are exposed to the 24-hour solar day, and the 12.4 hour rising and falling of the tides. One or both of these cycles govern intertidal organisms’ behaviour and physiology, yet little is known about the molecular clockworks of tidal rhythmicity. Here, we show that the limpet Cellana rota exhibits robust tidally rhythmic behaviour and gene expression. We assembled a de-novo transcriptome, identifying novel tidal, along with known circadian clock genes. Surprisingly, most of the putative circadian clock genes, lack a typical rhythmicity. We identified numerous tidally rhythmic genes and pathways commonly associated with the circadian clock. We show that not only is the behaviour of an intertidal organism in tune with the tides, but so too are many of its genes and pathways. These findings highlight the plasticity of biological timekeeping in nature, strengthening the growing notion that the role of ‘canonical’ circadian clock genes may be more fluid than previously thought, as exhibited in an organism which has evolved in an environment where tidal oscillations are the dominant driving force.

Bivalve mollusc circadian clock genes can run at tidal frequency

“…In coastal and subtidal field conditions, the oyster C. gigas expresses bimodal valve behaviour with a strong tidal pattern modulated by a daily rhythm. This bimodal phenotype has often been described in intertidal organisms, such as insects, crustaceans [4] and molluscs, such as the gastropod Cellana rota [33], but less for organisms settled in the subtidal zone of the littoral, excepted in the horseshoe crab Limulus polyphemus [34]. These results that oyster behaviour exhibits both tidal and daily rhythms were validated by previous 1 year studies at the same field location [25,35].…”

12-h clock regulation of genetic information flow by XBP1s

“…We originally hypothesized that the mammalian 12-h clock evolved from the circatidal clock of coastal and estuarine animals that modulates their behavior in tune with the ebb and flow of the tides with an approximately 12.4-h period [1,6], which were also shown to be driven by a dedicated circatidal pacemaker distinct from the circadian clock [43][44][45][46][47]. To seek further support for our hypothesis, we analyzed 2 recently published time series RNA-Seq datasets of 2 marine animals exhibiting a circatidal clock, aposymbiotic sea anemone Aiptasia diaphaha [48] and the limpet Cellana rota [10]. In both cases, we found a large overlap of 12-h cycling transcripts between mouse and these two tidal species (Fig 7A-7C, S6A-S6C Fig, and S15 Table).…”

“…The main line of evidences supporting the existence of a cell-autonomous mammalian 12-h clock include (1) the presence of intact hepatic 12-h rhythms of gene expression in circadianclock-deficient mice in vivo under free-running conditions [1,6]; (2) the detection of cell-autonomous 12-h rhythms of gene expression in mouse embryonic fibroblasts (MEFs) in a Bmal1-independent manner [1,6]; (3) that similar genes are regulated in a 12-h rhythmic manner in different organisms, indicating evolutionary conservation of these 12-h mechanisms [1]; and (4) that genes exhibiting 12-h rhythms arose much earlier during evolution than circadian genes [1,6,8]. It is hypothesized that circatidal clock mechanisms would have developed before the divergence of the major animal clades, existing in a common ancestor, occupying bodies of water in which tidal cycles would have been as ecologically important-if not more so-than the circadian cycle [8][9][10].…”

Sequences of Circadian Clock Proteins in the Nudibranch Molluscs Hermissenda crassicornis, Melibe leonina, and Tritonia diomedea

“…As described above, these molecular clocks are quite similar operationally, but they differ in the proteins used for negative feedback and how light input is transmitted to the clock. While circadian genes have been identified in some species in the other major protostome lineage, Lophotrochozoa (Zantke et al, 2013; Bao et al, 2017; Perrigault and Tran, 2017; Schnytzer et al, 2018), we do not yet fully understand the molecular mechanisms underlying clocks in lophotrochozoans as a group. Further elucidating the molecular basis of circadian clocks in this clade may shed light on the evolution of circadian clocks.…”

“…However, despite strong interest in gastropod circadian rhythms, and the advantages of this group of animals for investigating the neuronal bases of behaviors, there has been very little progress in identifying circadian genes in gastropods, with the exception of the transcript for period in Bulla gouldiana (Constance et al, 2002), the basic helix-loop-helix (bHLH)-containing proteins BMAL1 and CLOCK in Biomphalaria glabrata, Lottia gigantea , and Patella vulgate (Bao et al, 2017), and some automated annotations on GenBank at the National Center for Biotechnology Information (NCBI, Bethesda, MD). Furthermore, after submission of this paper, Schnytzer et al (2018) published a study reporting on the transcript sequences for most of the core circadian clock genes in the limpet Cellana rota .…”