News tips from the May/June issue of Physiological and Biochemical Zoology

(Press-News.org) MAY/JUNE PBZ TIPSHEET

Giant Hummingbirds: Running a little hot, but not on empty What keeps an asexual fish species from taking over? Small sea birds: Holding heat, rather than cranking up the furnace

For the complete table of contents for the May/June issue, go to journals.uchicago.edu/pbz.

Giant Hummingbirds: Running a little hot, but not on empty

Scientists have long thought that the giant hummingbird (Patagona gigas) was just about as big as a hummingbird could get. They're nearly twice the size of the next largest species, and it was assumed that the energy needed for hovering flight would take the giants close to the upper metabolic limits for an animal that size. Not so, according to a study led by María José Fernández of the University of California, Berkeley, and the Pontificia Universidad Católica de Chile. Fernández and her colleagues measured the amount of energy burned by giant hummingbirds when hovering and at rest. They also assessed the total amount of energy that the birds use in a day. The research found that giant hummingbirds do use more energy for their body size than smaller hummingbirds do, but they were still well below what is thought to be the upper metabolic limit. The finding suggests that metabolism is not necessarily the constraining factor in the evolution of hummingbird body size.

María José Fernández, Robert Dudley, and Francisco Bozinovic, "Comparative Energetics of the Giant Hummingbird (Patagona gigas).

What keeps an asexual fish species from taking over?

When a red-bellied dace and a finescale dace (freshwater fish in the carp and minnow family) mate with each other, they produce a hybrid with a very special ability: it can reproduce asexually. This asexual hybrid should have a tremendous evolutionary advantage over its sexually reproducing forefathers. In sexual populations, two individuals need to get together to reproduce, but in asexual populations every individual can reproduce on its own, giving asexuals twice the reproductive potential. Theoretically, the asexual advantage should enable the hybrids to outcompete sexual dace living in the same pond. But in reality that doesn't happen. Sexual and asexual dace are known to live side-by-side. So why doesn't the hybrid dace take over? According to a study by researchers from the University of British Columbia, it's because the hybrids aren't as healthy. Using swimming speed as a proxy for overall health, the researchers found that hybrids performed worse than at least one of the parent species in a series of speed tests. The results suggest that at minimum, the hybrid has no physiological performance advantage over the sexual species, and is probably at something of a disadvantage. The lower physiological performance may counteract the hybrids' reproductive advantage, preventing them from taking over. The results offer one possible explanation for why sexual reproduction has stayed dominant in vertebrates.

Jonathan A. Mee, Colin J. Brauner, and Eric B. Taylor, "Repeat Swimming Performance and Its Implications for Inferring the Relative Fitness of Asexual Hybrid Dace (Pisces: Phoxinus) and Their Sexually Reproducing Parental Species."

Small sea birds hold heat rather than cranking up the furnace

A new study offers some clues about how small aquatic birds survive in extremely cold climates. Staying warm is hard work for aquatic birds. Heat loss is around twenty times greater in water than in air, so aquatic birds have to increase their resting metabolism to generate heat on the water. Heat loss is an even greater issue for small birds, so it was assumed that small birds would have to increase their metabolism in water even more than large birds do. But according to a study by researchers at the University of Wyoming, that's not always the case. The researchers studied the metabolism of Cassin's auklets, a small sea bird found throughout the Northern Pacific Ocean. They found that auklets do increase their metabolism on the water, but not as much proportionately as some larger birds do. In fact, ducks, auks, cormorants, and small penguins responded quite differently to air and water temperatures, perhaps reflecting very different demands during evolutionary history.

Samantha E. Richman and James R. Lovvorn, "Effects of Air and Water Temperatures on Resting Metabolism of Auklets and Other Diving Birds."

### Published by the University of Chicago Press, Physiological and Biochemical Zoology has presented current research in environmental, adaptational, and comparative physiology and biochemistry since 1928. The journal publishes the results of original investigations in animal physiology and biochemistry at all levels of organization, from the molecular to the organismic, focusing on adaptations to the environment.