Does egg dispersal occur via the ocean in the stick insect Megacrania tsudai (Phasmida: Phasmatidae)?
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Although insects expand their distribution by various ways, generally only the adult phase has been taken into consideration in research on dispersal. In Megacrania tsudai, it has been proposed that eggs are dispersed through seawater. To test this hypothesis, eggs were treated under normal condition (NC) on wet cotton swabs, and marine condition (MC), floating on salt water for 30, 60, 90, and 365 days. In addition, eggs in the NC and MC treatment groups were dissected every 10 days to verify the developmental stage. The hatching rates in the NC and MC treatment groups were not significantly different among the five treatment groups. However, the egg period, time from laying to hatching, in the MC treatment group was significantly longer than that in any other treatment groups. The egg period was lengthened when the floating period on seawater was longer. The time of the start of egg development was similar in the NC and MC treatment groups, but the developmental speed was slower in the MC treatment group. These results support that M. tsudai can expand its distribution by dispersing its eggs through seawater, probably thanks to specific characteristics of eggs that allow their survival when they float in the sea.
KeywordsEgg period Hatching rate Megacrania tsudai Salinity tolerance Seawater dispersal
We appreciate Takeshi Sasaki of The University Museum (Fujukan), University of the Ryukyus for his valuable advices and support of this research. We also thank Yuki Yamakoshi, Keita Nakamura, and Hiromu Tanimoto for their help and two reviewers for their valuable comments. This study was partly supported by the ‘International Research Hub Project for Climate Change and Coral Reef/Island Dynamics’ from the University of the Ryukyus and The KAIGIN Environment Fund—managed by THE OKINAWA KAIHO BANK, LTD.
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