About the Cover
Cover
Sea star larvae in field collections of plankton from tropical and subtropical areas of the Atlantic Ocean are often observed to reproduce asexually. In this process, called larval cloning, a sequestered region of larval tissue (e.g., part of the pre-oral lobe, an arm, or a bud) dedifferentiates, then redifferentiates, and the clone-either a secondary embryo or a larva-is released.1
The cover depicts a right lateral view of a bipinnaria larva of Luidia sp. (~2.75 mm in length), which was collected from surface waters (~30 m depth) in the Gulf Stream, offshore from Fort Pierce on the east coast of Florida. The larva bears, on its lower right side, a spherical white object-an attached clone developing from a modified posteriolateral larval arm. Though only one is seen here, this type of larva can produce clones from both posteriolateral arms. Each clone will eventually detach from the "parent," becoming an independent larva. The remaining "sickle-shaped," non-cloning larval arms function in feeding and locomotion. The two arms at the upper left extend from the pre-oral lobe, and the mouth is visible toward the right side of the image between the two non-cloning arms. The yellow esophagus (from whence the common name, "golden-throat larva") connects the mouth to the red stomach and tubular intestine. The bright yellow tissue surrounding the digestive system is part of the developing juvenile sea star.
Larval cloning introduces further complexity into the already diverse array of reproductive modes observed in sea stars. Increasing the number of larvae and juveniles produced by a single adult and the duration of an individual's planktonic life may be among the adaptive roles of cloning, thus increasing dispersal capacity and facilitating genetic communication between distant populations and, possibly, transoceanic transport. Sea star larvae are morphologically similar, so field-collected individuals are often difficult to classify on the basis of structure-even to family. This difficulty has been a barrier to further study of larval cloning. But in this issue of The Biological Bulletin (p. 246), K. Emily Knott and her colleagues describe experiments done in the laboratory of Gregory A. Wray that lower the barrier. In brief, by comparing gene sequences from individual field-collected larvae with complementary reference sequences from adults of many different species, cloning larvae can now be identified to genus.
The cloning larva displayed on the cover was collected and photographed by Elizabeth J. Balser, and she and William B. Jaeckle drafted the legend. The cover was designed by Beth Liles (Marine Biological Laboratory).
1Jaeckle, W. B. 1994. Multiple modes of asexual reproduction by tropical and subtropical sea star larvae: an unusual adaptation for genet dispersal and survival. Biol. Bull. 186: 62-71.
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Copyright © 2003 by the Marine Biological Laboratory.
