Insect egg size and shape are influenced by how and where the egg is laid, but not by the body size or rate of development of the insect, according to a paper published online this week in Nature.
Cassandra Extavour, Samuel Church and colleagues found that insect eggs were a compelling system in which to test various evolutionary theories related to size. Insect eggs are diverse, but can be compared across distant lineages using quantitative traits. The authors compiled a database of more than 10,000 descriptions of insect eggs from published scientific research. The list included more than 6,700 species, 526 families, and every currently described insect and non-insect hexapod order. The eggs range in volume across eight orders of magnitude: the largest is the blueberry-sized egg of the Earth-borer beetle (Bolboleaus hiaticollis) and the smallest is too small to be seen by the human eye.
The authors tested previous hypotheses about evolutionary trade-offs with developmental time, body size, or the presumed ‘cost’ of egg shells. By comparing insect egg size and shape, they found that these theories do not hold. Although the authors showed that developmental time is not linked to egg size, they suggest that other features of development - such as cell number and distribution - may scale in predictable ways across the different egg sizes. Finally, the authors provide evidence that shifts to incubation in aquatic environments were linked to the evolution of smaller eggs, and that shifts to parasitic incubation were linked to smaller, more asymmetric eggs.
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