Hatching controlled by the circatidal clock, and the role of the medulla terminalis in the optic peduncle of the eyestalk, in an estuarine crab Sesarma haematocheir

Masayuki Saigusa

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Abstract

Embryos attached to the female crab Sesarma haematocheir hatch synchronously within 1 h. Hatching is also synchronized near the time of the expected nocturnal high tide. These events are governed by a single circatidal clock (or pacemaker) in the female crab. The present study examined the role of the optic peduncle of the eyestalk on hatching and hatching synchrony. Surgery was performed either from the tip of the eyestalk [to remove the region of the optic peduncle from the compound eye-retina complex to the medulla interna (MI)] or from a small triangle 'window' opened on the eyestalk exoskeleton [to create lesions on the medulla terminalis (MT) of the optic peduncle]. Neither hatching nor hatching synchrony was affected by removal of the region of the optic peduncle from the compound eye-retina complex to the MI: the circatidal rhythm also remained. Removal of the MI probably caused damage to the sinus gland and the bundle of axons running from the sinus gland to the X organ. Nevertheless, maintenance of highly synchronized hatching indicates that the X organ-sinus gland system is not related to hatching. Hatching and hatching synchrony were not affected by dorsal-half cuts of the MT: the timing of hatching was not affected either. By contrast, transverse and ventral-half cuts of the MT caused severe damage to most females; hatching of many females was suppressed, while hatching of some females was either periodic, at intervals of approximately 24h, or arrhythmic for a few days. The bundle of neuronal axons is tangled in the MT, and the axons inducing hatching pass through the ventral half of the MT. Complete incision of these axon bundles may have suppressed hatching. Incomplete incision of the axon bundle or partial damage to the neurons may have caused periodic or arrhythmic patterns of hatching. There are two possible roles for MT in hatching. One possibility is that neurons in the MT only induce hatching under the control of the circatidal pacemaker located in a site somewhere other than the optic peduncle. Another possibility is that the circatidal pacemaker is actually present in the MT. The second possibility seems more plausible. Each embryo has a special 48-49.5h developmental program for hatching. This program could be initiated by the circatidal pacemaker in the female, and hatching synchrony may also be enhanced by the same pacemaker.

Original languageEnglish
Pages (from-to)3487-3504
Number of pages18
JournalJournal of Experimental Biology
Volume205
Issue number22
Publication statusPublished - Nov 1 2002

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Keywords

  • Circatidal pacemaker
  • Estuarine crab
  • Eyestalk
  • Gentle-release behavior
  • Hatching synchrony
  • Medulla terminalis
  • Neuronal pathway
  • Optic peduncle
  • Sesarma haematocheir
  • Vigorous-release behavior

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science

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