Expression of clock genes tracks daily and tidal time in brains of intertidal crustaceans Eurydice pulchra and Parhyale hawaiensis

May 9, 2025Current biology : CB

Daily and tidal rhythms of clock gene activity in the brains of two intertidal crustaceans

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Abstract

Around 60 clusters of putative 'clock' cells were identified in the brains of intertidal crustaceans E. pulchra and P. hawaiensis.

Circadian clock genes per and cry2 showed daily expression rhythms in specific cell groups of E. pulchra under light:dark cycles.
The timeless gene exhibited 12-hour rhythmic expression in different cell groups, indicating a possible circatidal rhythm.
Laboratory-reared P. hawaiensis displayed circadian expression of per and cry2 in some cells after exposure to tidal agitation.
Dorsal-lateral cells in P. hawaiensis showed strong 12-hour rhythms of per and cry2, aligned with tidal agitation rather than light cycles.
In P. hawaiensis without tidal agitation, daily rhythms of per and cry2 were present in some cells, while dorsal-lateral cells lacked rhythmicity.

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Intertidal organisms, such as the crustaceans Eurydice pulchra and Parhyale hawaiensis, express daily and tidal rhythms of physiology and behavior to adapt to their temporally complex environments. Although the molecular-genetic basis of the circadian clocks driving daily rhythms in terrestrial animals is well understood, the nature of the circatidal clocks driving tidal rhythms remains a mystery. Using in situ hybridization, we identified discrete clusters of ∼60 putative "clock" cells co-expressing canonical circadian clock genes across the protocerebrum of E. pulchra and P. hawaiensis brains. In field-collected, tidally rhythmic E. pulchra sampled under a light:dark (LD) cycle, the expression of period (per) and cryptochrome 2 (cry2) exhibited daily rhythms in particular cell groups, whereas timeless (tim) showed 12-h rhythms in others. In tidally rhythmic laboratory-reared P. hawaiensis, previously entrained to 12.4-h cycles of agitation under LD and sampled under continuous darkness, several cell groups (e.g., medioposterior cells) exhibited circadian expression of per and cry2. In contrast, dorsal-lateral cells in the protocerebrum exhibited robust ∼12-h, i.e., circatidal, rhythms of per and cry2, phased to the prior tidal agitation but not the prior LD. In P. hawaiensis exhibiting daily behavior under LD without tidal agitation, robust daily rhythms of per and cry2 expression were evident in medioposterior and other cells, whereas expression in dorsal-lateral cells was not rhythmic, underlining their essentially tidal periodicity. These results implicate canonical circadian molecules in circatidal timekeeping and reveal conserved brain networks as potential neural substrates for the generation of daily and tidal rhythms appropriate to intertidal habitats.

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Expression of clock genes tracks daily and tidal time in brains of intertidal crustaceans Eurydice pulchra and Parhyale hawaiensis

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