Saturday, October 29, 2011
Wikipedia) shows the Azores archipelago outlined in red. The Azores are a chain of nine volcanic islands positioned near the middle of the North Atlantic, nearly 2,500 miles east of North America's Atlantic coast. Colonized by sea-going Portuguese explorers in the 15th century, the Azores are home to some 240,000 people.
And, oddly enough, citrine forktails. Some authorities think that these forktails arrived recently, perhaps at the tail end of the 19th century. How did such a seemingly fragile, weak flyer manage to cross over two thousand miles of rough North Atlantic waters? Probably impossible to say with certainty, but several other species of tiny odonates - including other Ischnura forktails - are well known island colonizers. It seems likely that these insects are capable of getting swept up in storm cells and can survive lengthy if unintended aerial journeys to new lands.
But the tale of the Azores' citrine forktails gets much stranger. Researchers began intensive studies of this disjunct forktail population about twenty years ago, and quickly realized that all of the animals were female! It turns out that Azorean citrine forktails reproduce entirely by parthenogenesis, which is a type of asexual reproduction. Many species of animals are known to reproduce by parthenogenesis, and the various mechanisms by which this works are complicated. Thelytokous parthenogenesis is the term for the forktail's reproductive strategy. Suffice to say that embryonic growth and development is possible without direct contribution of sperm from males.
I hope that thelytokous parthenogenesis does not find its way into Homo sapiens.