Tuesday, January 22, 2008

reproductive strategies in angiosperms   posted by chairmanK @ 1/22/2008 04:48:00 AM

Botanists reported the discovery of a species of palm tree in Madagascar which sprouts a giant inflorescence (images from the BBC and National Geographic). In the New York Times:
"It's spectacular," said Mijoro Rakotoarinivo of the Royal Botanical Gardens in Madagascar. "It does not flower for maybe 100 years and can be mistaken for other types of palm. But then a large shoot grows out of the top and starts to spread, a bit like a Christmas tree." Those branches then become covered in hundreds of tiny white flowers that ooze with nectar, attracting insects and birds.

But the effort of flowering and fruiting depletes the tree so much, said John Dransfield, a botanist and the author of the study, that within a few months it collapses and dies. The palm tree, which grows to 66 feet, is found only in a remote region in the northwest of the country. Puzzling Mr. Dransfield is how botanists had missed such a "whopping palm" until now, adding that there appear to be only about 100 in existence. He suggests that the tree has been quietly living and dramatically dying in Madagascar for 80 million years.

The peer-reviewed paper which describes this species (Tahina spectabilis) appeared in the Botanical Journal of the Linnean Society (available by subscription from Blackwell-Synergy). Disappointingly, the supposedly newsworthy lifecycle of this species is not mentioned at all in the paper! According to the paper, Tahina spectabilis was first spotted by a local family in August 2005; at the time of this first visit, the tree had not sprouted its inflorescence, and so it was mistaken for a different species. The same family revisited in September 2006, at which time they observed the towering "Christmas tree" inflorescence. Thus, the confirmed lower bound on the flowering time of this plant is only 1 year. So why does one of the authors speculate on a 100-year flowering time when speaking to the news media? (Are there any botanists here who know?)

Regardless, this discovery is a good launching point for thinking about the evolutionary biology of sexual reproduction. Tahina spectabilis grows 4-10 meters tall - and sprouts an inflorescence that is 4 meters long! What evolutionary process could lead to such an expensive reproductive investment? How would one characterize this species in terms of r/K selection theory? Botanists have long been interested in the fitness trade-offs of different inflorescence patterns. Now, with the current tools of molecular biology, experiments in model species such as Arabidopsis promise to uncover the genetics of inflorescence. When we think about the sexual phenotypes of animals, we usually focus on mating and sociality; unfortunately, such behaviors are difficult to quantify. Plants don't have behavioral repertoires, but they do have elaborate sexual hardware. Phenotypic variation in hardware is relatively easy to quantify; one can perform time-lapse imaging of a plant over its entire development to track the spatial arrangement of the flowers, number of branch points, duration of infructescence, etc. And such variation in hardware can be directly, mechanistically related to genetic variation in the underlying developmental programs.