Why Sexual Reproduction?

Monday, January 19, 2009
By Student
photo by Diego Fontaneto

photo by Diego Fontaneto

by Stephen

In a nut shell, sexual reproduction increases genetic variation and allows organisms to evolve in changing environments by pairing beneficial traits together which would in turn get passed on to subsequent generations and to do away with harmful variations.  Asexual reproducing organisms create exact replicas and in theory would be unable to adapt to changing environments.

Yet this article has shown that the bdelloid rotifer which produces asexually has adapted to several separate environments.  Bdelloid rotifers are small animals that are around .05nm in length that reproduce asexually by means of parthenogenesis.  Parthenogenesis is the development of the female egg without fertilization from the male sperm.

Bdelloid rotifers have survived for over 100 million years and make up 380 distinct entities.  This challenges the ideas of scientists that sexual reproduction is essential for long term success and diversity.

To test if bdelloid rotifers evolve and branch into distinct entities, scientists created an ancestral tree that mapped the evolutionary changes.  They did this by measuring the trophi (jaw sizes) of the rotifers and analyzing mitochondrial cytochrome oxidase and nuclear 28S ribosomal DNA sequences.

The results showed that bdelloid rotifers are monophyletic which means that all the descendents come from a common ancestor.  By analyzing the evolutionary tree, researchers showed genetic clusters which “represent independently evolving entities.”  This means that the asexually reproducing bdelloid rotifer evolves!

The researchers argue, this study “refutes the idea that sex is necessary for diversification into evolutionary species.”

Do you think there are other organisms like the bdelloid rotifer that have yet to be discovered?   Do you think that these separate “entities” should be classified as species?  Can you find any other asexually reproducing organisms that have branched to form new species?

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