A good man is hard to find -- and for female Galapagos iguanas, the search for the sexiest mate is so exhausting that it may actually threaten their ability to survive, according to a study published Wednesday.
Female iguanas on the equatorial island of Santa Fe spend about a month checking out the available males, some of whom maintain almost constant displays of masculine prowess. But visiting the males carries a cost: any time a suitor gets too close, a female must back away to avoid mating before she's ready.
For the study, published in the online journal PLoS One, researchers spent three months watching iguanas play the dating game. When a female approaches a male's territory, he will open his jaw wide, bob his head and sidle toward her. If she doesn't back away, he'll attempt to grab her by the neck.
The males are patient -- they won't pursue a female who retreats -- but it nonetheless takes significant effort for the females to keep walking away.
Although males' territories, or leks, have no food or other resources, they do offer some measure of protection from smaller, less desirable males, who prowl the outskirts of the leks and may force copulation on females.
"Females are pretty much on territories all the time that they're not foraging," said lead author Maren Vitousek, a graduate student in ecology at Princeton University.
The scientists implanted small data recorders in the female iguanas to monitor their energy costs. The devices recorded heart rate and body temperature every three seconds.
Combining this data with observations of mating behavior, the researchers determined that females could "lose up to 20% of their body weight" avoiding sexual encounters that they weren't ready for, Vitousek said.
Females that hung out near the biggest, strongest males -- thus gaining the best genes for their offspring -- lost even more energy because those males approached them more often.