Orchid bees in the fast lane

STRI/DICYT To test a controversial theory about what sets the pace of life, scientists worked at the Smithsonian Tropical Research Institute (STRI) in Panama to compare metabolism and membrane lipid composition of 22 species of orchid bees of different sizes. Their findings support a theory that the cell membranes of animals in the fast lane—that have high metabolic rates—are different from the cell membranes of animals with a slower pace of life, at least in the proportion of the fatty acids they contain.

Membranes define the borders of animal cells and anchor proteins that pump materials in and out and produce energy. The membrane pacemaker hypothesis holds that animals that have higher metabolic rates have a higher proportion of polyunsaturated fatty acids in their membranes.

If you google membrane pacemaker hypothesis, one of the first hits is a page about fighting aging in humans. The hypothesis has far-reaching implications and metabolism may be an important clue when it comes to explaining how aging works in all animals, including humans. So far, the hypothesis has been tested in animals from albatrosses to oysters. But comparing the membranes of very different animals is like comparing proverbial apples and oranges. They are different in so many ways that it’s not surprising that their membranes are also different.

Smithsonian staff scientist Dave Roubik is the world’s expert on orchid bees. “Because we know how to collect orchid bees and we already know how they are related, it was easy to test this hypothesis in 22 closely related species that varied 16 fold in body size and 2'5 fold in metabolic rate while hovering,” Roubik said. “This is also the first time that the hypothesis has been tested in insects.”

Male bees spend most of their time gathering scents in pouches on their hind legs. Roubik baits the bees by placing pieces of blotter paper impregnated with natural essential oils. When males come to collect, it’s easy to capture and identify them.

The team from the University of Ottawa in Canada, the University of California, Santa Barbara and STRI discovered a direct association between fatty acid composition of the bees’ membranes and their hovering metabolic rate, supporting the hypothesis that membrane composition, along with other factors that include body size and phylogeny, conspire to “set the pace of life.” Their findings are published in the Feb. 4 edition of the Proceedings of the Royal Society B.