When it\u2019s time to mate, female eastern gray tree frogs venture at night toward the pond, where they are bombarded by a chorus of hundreds of male frogs singing with pulsed \u201cchirps\u201d that differ in pitch, duration, volume and repetition. The collective serenade goes on for hours, though individual males take breaks.<\/p>\n
\u201cMale calling has been described as the most energetically challenging behavior of any vertebrate,\u201d said Gerlinde Ho\u0308bel, \u201cand the competition is stiff. Males pay attention to what other males are doing, and they push themselves as far as they can.\u201d<\/p>\n
With so much variation to choose from, how does a female decide which she\u2019ll respond to? The question would be impossible to study in a natural setting because of the sheer volume calls and their traits, said Ho\u0308bel, an associate professor of biological sciences at 51ÁÔÆæ.<\/p>\n
Instead, Ho\u0308bel and her students bring frogs they\u2019ve caught to an environment specifically designed for tree frog romance in the lab. Inside what looks like a large walk-in freezer in Lapham Hall is a simulated setting, dubbed the \u201cfrog arena.\u201d<\/p>\n
Here, Ho\u0308bel and her lab members are teasing apart what the different types of vocalizations might mean and using the arena to investigate an assortment of questions about frog communication, including female preferences to calls.<\/p>\n
The stakes couldn\u2019t be higher: Most females will mate only once in their lives, while many males will not find a mate at all. So answers to mating behavior questions have evolutionary implications, Ho\u0308bel said.<\/p>\n
It\u2019s the females who often drive sexual selection, a preference by one sex for certain characteristics in those of the other sex, she said.<\/p>\n
\u201cMuch of the amazing mating diversity we see in nature \u2013 like songs, plumage color and dances \u2013 are the outcome of sexual selection by female choice. Sexual selection is one of the main drivers of biological diversity.\u201d<\/p>\n
Conditions inside the frog arena can be controlled to mimic the pond. The temperature is kept at 68 degrees, and a nightlight provides just enough light. The walls are covered in acoustic foam, which prevents the sound distortions that occur indoors.<\/p>\n
In a circular clearing on the floor, the researchers have placed small speakers around the circumference. In the center, they confine a female frog in a pod and then leave the chamber. In some of their experiments, they will expose the female to two different male calls, and then remotely lift the lid and free her to pursue her choice.<\/p>\n
\u201cIn theory, the females will go faster toward what they consider the most sexy,\u201d said doctoral student Olivia Feagles. \u201cIf the call is really ugly to them, maybe they wander around a little and wait for other options.\u201d<\/p>\n
Thanks to a camera and an infrared light in the arena, researchers on the outside can watch without disturbing the females, who don\u2019t see infrared light.<\/p>\n
The only missing pieces are the actual male frogs.<\/p>\n
Instead, male calls have been recorded in the field and used to program computer-generated reproductions played in the arena.<\/p>\n
\u201cThis way, we can not only manipulate the frog calls,\u201d Ho\u0308bel said, \u201cbut also other environmental features like chorus densities by adding more speakers, or predator cues by playing predator sounds.\u201d<\/p>\n
Each season the lab members will run about 1,000 or more trials in the arena. This year, they gathered a bumper crop of female frogs from their natural habitat at the 51ÁÔÆæ Field Station near Saukville, where Ho\u0308bel\u2019s lab operates a second frog arena.<\/p>\n
During a recent arena experiment, doctoral student Kane Stratman narrated the action from his computer screen. \u201cThe male call she was thinking about just took a break,\u201d he reported. \u201cAnd there\u2019s a more attractive male call over there that just started up. The hypothesis is she should not wait around very long to go for it.\u201d<\/p>\n
After years of experimentation, the researchers know this species likes longer, faster calls on average. But there are plenty of females who like short or intermediate-length calls, Stratman said.<\/p>\n
Decoding the mating communication may reveal why all the calls aren\u2019t the same, he said. A more mixed bag of female preferences in the population could mean that a larger range of males will have a chance of mating, leading to a maintenance of variation in male calls.<\/p>\n
For each female they test, the lab members graph the time she takes to make a choice with the length of her chosen call. Some show a steep curve indicating a strong preference. On others, the curve is more shallow, which means she has a preferred call, but she\u2019s tolerant of those that are not a perfect match.<\/p>\n
This tool is helping Feagles correlate the individual preferences of the females with the characteristics of the males they ultimately chose.<\/p>\n
Feagles also is investigating how choosy each female is, by repeatedly lengthening the perceived distance of the call and recording how far the female is willing to travel for the more attractive call. A less finicky female is more likely to choose to mate with an ugly call that is conveniently nearby rather than searching for a more attractive call across the pond.<\/p>\n
Memory is also a consideration, Stratman said. Another question he is exploring using the arena is to determine how long a female can remember where she heard a really attractive call before she settles for an \u201caverage-Joe call\u201d that\u2019s closer to her.<\/p>\n
It\u2019s about balancing preferences with opportunities, Ho\u0308bel said.<\/p>\n
\u201cMate choice is a complex affair, and females have to balance what they want \u2013 preference \u2013 and how much they want it \u2013 choosiness \u2013 with the conditions they encounter at the pond.\u201d<\/p>\n
By Laura Otto<\/strong>, University Relations<\/small><\/p>\n","protected":false},"excerpt":{"rendered":" When it\u2019s time to mate, female eastern gray tree frogs venture at night toward the pond, where they are bombarded by a chorus of hundreds of male frogs singing with pulsed \u201cchirps\u201d that differ in pitch, duration, volume and repetition. …<\/p>\n","protected":false},"author":28112,"featured_media":16664,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":"","uwm_wg_additional_authors":[]},"categories":[1715],"tags":[1860],"class_list":["post-16652","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-in-focus-2021","tag-october"],"yoast_head":"\n