Drosophila ,which played a significant role in understanding many complex biological process is well on the way of solving another major puzzle. Species of Drosophila lay eggs outside in the environment , which develops and transforms into first instar larvae in about 24 hours time. UC San Diego biologists have discovered a species from the islands of Seychelles, often lay larvae instead of eggs. Understanding the development of this species might provide us with some clues how animals switch from laying eggs to live birth ?

Currently we have complete genome sequence data of 12 species of Drosophila and the species which lays larvae directly is one among them. Studying the genes which are differentially expressed might help us understand why females of this species, and not others, can retain their fertilized eggs until they are ready to hatch. Eggs laid by this species takes only around 2 hours to hatch when compared to 24 hours for other species.The Seychelles flies also lay larger eggs — nearly double the average volumes found for the other species — and their ovaries have fewer threadlike structures called ovarioles in which insect eggs mature before fertilization.

Authors think that Live birth could result from changes to the male reproductive strategy as well. Proteins found in the semen of the well-known lab fruit fly, Drosophila melanogaster, stimulate egg laying in the female. A modification of these signals could be responsible for the switch.One other fly , Drosophila yakuba, also occasionally laid larvae instead of eggs, and their eggs also hatched fairly quickly, most in under 14 hours.

These results are published in journal of evolutionary biology.

Reference:

T. A. Markow, S. Beall, L. M. Matzkin.
Egg size, embryonic development time and ovoviviparity in Drosophila species. Journal of Evolutionary Biology, 2008; DOI: 10.1111/j.1420-9101.2008.01649.x

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