ScienceAsia 30 (2004): 75-80 |doi: 10.2306/scienceasia1513-1874.2004.30.075

Effects of Egg Size on Fertilization and Embryonic Development of Sibling Tropical Sea Urchins
(Genus, Echinometra)

Sk. Mustafizur Rahman,^* Tsuyoshi Uehara

ABSTRACT: Egg size has the ability to influence fertilization success and embryonic development in freespawning marine invertebrates. The effects of egg size on fertilization and embryonic development were compared among three sibling species of Echinometra sp. B, Echinometra sp. C, and Echinometra sp. D. Gamete size of Echinometra sp. D is larger than Echinometra sp. B and Echinometra sp. C. Larger eggs of Echinometra sp. D might provide a larger target for sperm and thus, were fertilized at higher rate than smaller Echinometra sp. B and Echinometra sp. C eggs under moderate and limiting sperm concentrations. Developmental time from fertilization to prism stage (embryonic development) in Echinometra sp. B and Echinometra sp. C were comparatively longer than Echinometra sp. D, suggesting that increased allocation of energy reserve in the cytoplasm in larger Echinometra sp. D eggs reduced the developmental period. As Echinometra sp. B, Echinometra sp. C and Echinometra sp. D have diverged from their ancestral species, the differences of the above traits related to egg sizes transcended species differences among them.

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Graduate School of Science and Engineering, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan.

* Corresponding author, E-mail: mustafizku@hotmail.com

Received 10 Sep 2003, Accepted 17 Nov 2003