Preliminary observations on the effect of light and temperature on the hatching success and rate of Lepidurus arcticus eggs

Abstract

Dormancy, which arrests development, is a well-known survival strategy among animals living in the Arctic to overcome harsh periods. It is not clear if the dormant state in notostracans is controlled endogenously (diapause) or exogenously (quiescence). For Lepidurus arcticus, it is unknown how it responds to the photoperiod entrainment, if it has a biological clock and if it has a rhythmic expression of the clock genes. We studied the hatching success of resting eggs at four constant temperatures (5, 10, 15 and 25 °C) and under different illumination regimes [continuous light (LL) and continuous dark (DD)]. It was assumed that light and temperature are both important triggers, with temperature having the most pronounced effect. In our experiment, hatching occurred only at 5 and 10 °C, while we did not observe hatching at 15 and 25 °C. The highest percentage of eggs hatched was at 10 °C in LL (60%); the lowest was at 5 °C in DD (18%). The percentages hatched at 5 °C in LL (24%) and at 10 °C in DD (26%) were similar. Our results indicate that both temperature and light had a significant and interacting effect on hatching in L. arcticus, with temperature being the dominant factor controlling the process. This suggests that changes in temperature affecting the Arctic may significantly impact phenology of this key species in the region. Given that no hatching was observed at 15 °C or above, the persistence of this species may be at risk in areas were arctic lakes are expected to warm to such levels during the summer months.

KEY WORDS:

• biological rhythms
• dormancy
• hatching
• Notostraca, Arctic

ACKNOWLEDGEMENTS

This work was supported by a number of public institutions: Consiglio Nazionale delle Ricerche, Sapienza University of Rome, Confucio Institute – Sapienza University of Rome, 6°Comunità Montana del Velino. Further support was provided by private companies: G.S.A. srl in the person of Giancarlo Colangeli, OPTEK Inc. USA, Millennium Datawere srl Rivalta Scrivia-Italia and Silco srl Torino. Thanks to the staff of CNR D.T.A. and Kings Bay Marine Laboratory for their assistance and Steve Coulson for his useful advices. Thanks to Italian Arctic Data Center and Mauro Mazzola for the atmospheric data.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Svalbard Science Forum, Arctic Field Grant 2015 [ES539220] (V. Pasquali) and Sapienza University of Rome, Starting Grant 2017 (E. Calizza).