Mate choice is one of the most well-studied aspects of evolution. To prove that they’re worth the effort, animals will do just about anything. They dance, prance, sing, bellow, and fight for attention. When you look around the animal kingdom, the wild results of mate choice boldly stand out, from the impractically beautiful tails of peacocks to the ostentatious antlers of elk and deer. With so much focus placed on quality, you might assume that every species has their own complex way of conveying their worth, and that all of the females of the world are finicky creatures.
But not so for the female strawberry poison dart frog — when she’s ready to mate, she doesn’t pick the strongest or the brightest guy around. She just goes for the closest.
This came as a shock to Ivonne Meuche and her colleagues from the University of Veterinary Medicine in Hannover, Germany. Strawberry poison dart frogs are some of the most colorful animals on the planet. There are more than a dozen color morphs, from the bright red they’re named for to vibrant blues and greens. When the mating season arrives, male frogs gather in these large groups called leks to vie for female attention. In other lekking species, these large displays sort the men from the boys in the minds of the females, with the most impressive singers/dancers/etc winning the most matings. It is believed that these large groups give the males a chance to prove their top-notch genes or parenting skills. So the scientists wanted to know what drives mate choice in these colorful frogs. Does their bold coloration play a role? Or, like in other species of frogs and toads, does size matter most?
Listen to a male call:
To test female choice, the team played male calls that varied in pitch and rate made by frogs of different sizes and shapes, and watched to see which the females picked. The female frogs didn’t choose based on any of those factors, though. “We did not find female preferences for certain call properties or physical properties,” the authors explain. “Our data suggest that in our study population, female strawberry poison frogs use a mate sampling tactic that could be defined as “accept the closest calling male”.” When it comes to convincing a female strawberry poison dart frog, a male doesn’t have to be the strongest or the handsomest. He just has to be the first she gets to.
The scientists believe this very non-choosy behavior is a result of the reproductive biology of these colorful little frogs. They found that when a female is ready to lay eggs, she has a short time frame in which to do so. Females that don’t mate in that window end up laying unfertilized eggs, thus squandering their body’s efforts to reproduce. Since time is of the essence, the best choice available for these girls is to take what they can get, for even a lesser quality mate is better than no mate at all.
The authors do note that their study has limitations. Populations of strawberry poison dart frogs vary a lot in the natural world in many ways that the team was unable to test. For example, the proportion of males to females or potential egg-laying sites might shift how females behave. Other studies have found that when there are more females than males, as was true in this study, that the pressure to be picky relaxes. So, further research, in the lab and in the wild, are needed to determine if this species has multiple tactics for choosing mates, or if the closest male always wins out.
But, at least in their study population, the team is confident in their results. And it makes sense — the cost of searching for a better mate is high for these bright little females, so it’s not worth their time to be picky. “High egg mortality as well as the risk of losing the whole clutch by laying unfertilised eggs and the probably low benefits of intensive mate sampling support our assumption that acceptance of the closest calling male represents an optimal mate sampling tactic in female strawberry poison frogs,” they write. The longer these frogs wait to mate, the more likely they are to fail altogether. So why not just pick any guy and hope for the best?
Citation: Meuche I., Brusa O., Linsenmair K.E., Keller A. & Pröhl H. (2013). Only distance matters — non-choosy females in a poison frog population, Frontiers in Zoology, 10 (1) 29. DOI: 10.1186/1742-9994-10-29