Lunar-Rhythmic Molting in Laboratory Populations of the Noble Crayfish Astacus astacus (Crustacea, Astacidea): An Experimental Analysis

Robert Franke,Gabriele Hoerstgen-Schwark

doi:10.1371/journal.pone.0068653

Abstract

Juvenile noble crayfish, Astacusastacus (Crustacea, Astacidea) in the second year of age were kept in the laboratory for a twelve-month period under continuing “summer conditions” (LD 16:8, 19°C). Molting processes in this population could be synchronized by artificial moonlight cycles. Peaks of exuviations occurred at “new moons”. Males showed a slightly higher degree of synchronization than females. A phase-shift of the artificial lunar cycle in relation to the natural cycle resulted in a corresponding shift of the molting cycle. This clearly demonstrates that changes in the nocturnal light regime provide the primary external information for the lunar-monthly molting rhythm. There is a first indication that lunar photic stimuli do not act directly but as a zeitgeber which entrains an endogenous molting rhythm to the lunar cycle. Moreover, the results of the long-term experiments suggest that the hibernal resting period of A . astacus in the field (no molts between October and April) may also involve some endogenous programming. Continuing artificial summer conditions can delay but not completely suppress this resting period. The adaptive significance of the phenomena and how the findings may be applied to improve the management of crowded crayfish stocks are discussed.

Highlights

IntroductionMolting is often coupled to distinct phases of geophysical cycles
Molts can be coupled with environmental cycles of shorter periodicities such as the lunar-monthly cycle, the semi-lunar cycle of spring-neap tides, the daily cycle, and the tidal cycle
When coupled to particular phases of environmental cycles, processes which are arrhythmic at the individual level or even occur only once in an individual’s life time can display a marked rhythm at the level of the population. This applies to the observed molting rhythm in A. astacus which manifests only at the population level

Summary

Introduction

Molting is often coupled to distinct phases of geophysical cycles. Seasonal synchrony of molting is well known for crustaceans of higher latitudes. Molts can be coupled with environmental cycles of shorter periodicities such as the lunar-monthly cycle, the semi-lunar cycle of spring-neap tides, the daily cycle, and the tidal cycle. This has been reported for a number of marine crustaceans [2,3,4,5,6,7,8,9] and some insects [10,11]. The adaptive significance of these phenomena as well as the underlying mechanisms are only little understood

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Conclusion