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Scientists study gender size

ZURICH, Switzerland, Jan. 30 (UPI) -- A Swiss-led team of scientists says it may have discovered why males are larger than females in some species and females larger than males in others.

The international team also explored how gender size dimorphism is achieved when it exists -- if males and females grow at the same rate, the larger sex has to extend its growth period. Alternatively, the larger sex can grow faster.

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The 13 researchers from 10 nations investigated the questions using comparative data on 155 species of insects and spiders from seven major groups.

The researchers, led by Wolf Blanckenhorn of the Zoological Museum at the University of Zurich, say they found gender growth rate differences are generally more important than growth period differences in mediating size dimorphism in arthropods.

Of three potential explanations for why female arthropods can grow faster than males, the most intriguing is although generally cheaper to produce small sperm than large eggs, it may be costlier to produce male gonads and genitalia than it is to produce female gonads and genitalia. As a result, males might need more time to mature at larger body sizes, the researchers said.

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The findings appear in the February issue of The American Naturalist.

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