Do Female Frogs Call?

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00:00:13.00 Listen carefully -- can you hear that?
00:00:23.02 Before I went to the jungle of Borneo,
00:00:25.07 nobody had ever recorded this calling behavior before.
00:00:28.15 But before I introduce you to my friend, here,
00:00:31.15 let me take you through the journey
00:00:33.18 of how I made this discovery
00:00:35.08 and what it means for the understanding
00:00:37.10 of mating systems and animal behavior in general.
00:00:41.25 Frogs have evolved amazing structures for sound production.
00:00:45.25 They make call alone or in choruses,
00:00:48.06 but the idea is to attract the female.
00:00:50.09 And the female is listening very carefully
00:00:52.10 to what they have to say.
00:00:54.22 In general, the male calling behavior
00:00:57.13 has two functions.
00:00:59.03 First, they are trying to attract the females,
00:01:01.01 but at the same time
00:01:02.21 they are trying to keep other competitors at bay.
00:01:04.29 If the female is convinced
00:01:08.17 of the attractiveness of the male
00:01:10.19 based on the acoustic characteristics of his call,
00:01:12.21 then she's gonna approach him
00:01:15.00 and mate with him.
00:01:16.21 However, you may think...
00:01:19.12 does the female say something?
00:01:21.04 And the answer is, most of the time, no.
00:01:24.04 The female frogs do not have spontaneous vocal behavior
00:01:28.07 like the males do.
00:01:32.00 Biologists have been fascinated
00:01:34.22 by the differences between females and males
00:01:36.13 since the beginning of time.
00:01:38.06 In the case of frogs,
00:01:39.19 like this couple right here,
00:01:41.14 you may not even know which one is the female
00:01:43.21 and which one is the male.
00:01:45.07 Sometimes you can tell by the size,
00:01:46.26 but there are not traits that are obvious
00:01:49.22 to the naked eye, if you will.
00:01:51.27 In other species, though,
00:01:53.19 males have weapons, like antlers,
00:01:56.08 that they use to combat with other males
00:01:58.15 for access to the females.
00:02:01.01 In other species,
00:02:02.23 males have flashy and colorful feathers
00:02:04.25 that they use for displays
00:02:07.00 that are attractive to the females,
00:02:08.24 and the females may discriminate among the males
00:02:11.06 and choose the most beautiful one.
00:02:15.03 So, in frogs, the answer to,
00:02:17.20 what makes males and females different?,
00:02:20.04 is going to be their voice.
00:02:22.21 Most of the time, if you hear a frog
00:02:26.00 calling in your backyard or in a nearby pond,
00:02:29.24 chances are that it's going to be a male.
00:02:34.17 But at the end, it doesn't matter what they use --
00:02:38.25 antlers, feathers, beautiful songs.
00:02:41.16 If you're gonna think about it
00:02:44.13 as a rule of thumb,
00:02:45.28 males are the ones that display
00:02:47.14 and females are the ones that choose.
00:02:50.06 I'm a herpetologist
00:02:52.04 and I'm interested in amphibians and reptiles.
00:02:54.26 Mostly, I'm interested
00:02:57.03 in the reproductive behavior of frogs.
00:02:59.08 I'm interested in their calling behavior
00:03:00.26 because that's how they get their mates.
00:03:03.07 And I'm also interested in what happens
00:03:05.23 after they get their mates,
00:03:07.10 what happens with the babies,
00:03:09.04 what kinds of strategies they have developed
00:03:12.00 to take care of their offspring.
00:03:13.18 Particularly, I'm fascinated with the larval transport behavior
00:03:17.22 in frogs.
00:03:19.07 Many species of frogs
00:03:21.17 evolved to lay the eggs on land.
00:03:23.27 But this poses a problem of...
00:03:26.06 where is the water for the tadpoles?
00:03:28.14 So, again,
00:03:31.04 these species have evolved this amazing larval transfer behavior
00:03:33.21 where the tadpoles climb on the back of the male,
00:03:36.15 or the mother,
00:03:38.11 and they catch a piggyback ride
00:03:41.13 to small bodies of water,
00:03:42.29 where the male, or the female,
00:03:44.21 can deposit them and they can finish
00:03:47.12 their development and become adult frogs.
00:03:50.12 This particular behavior
00:03:52.11 has been observed in many species of poison dart frogs
00:03:54.15 in Central and South America,
00:03:56.13 where I'm from.
00:03:58.00 Scientists have been studying these species for decades.
00:04:00.20 They have been figuring out how they lay the eggs,
00:04:03.22 how they transport the tadpoles,
00:04:05.12 and how do they find the places to deposit the tadpoles?
00:04:10.07 However, if you go to the other side of the world,
00:04:13.03 almost nothing is known
00:04:15.23 about species that have this particular parental care.
00:04:18.18 In fact, there's only two species
00:04:20.29 that so far have been reported
00:04:22.19 to have this parental care behavior.
00:04:24.12 And nothing has been done
00:04:26.17 in terms of figuring out what they do.
00:04:30.15 They may not look like...
00:04:33.06 that colorful, as the poison dart frogs
00:04:34.22 that I showed you before,
00:04:36.07 but I can assure you
00:04:38.01 that they are equally if not more interesting.
00:04:39.19 And in fact, this guy over here
00:04:41.12 became the focus of my research.
00:04:44.12 Let me introduce you to
00:04:46.19 the guardian frog of Borneo, Limnonectes palavanesis.
00:04:48.23 This nocturnal leaf litter frog
00:04:50.24 about an inch long
00:04:52.21 lives exclusively on the island of Borneo.
00:04:55.21 Populations of this species
00:04:58.07 are distributed mainly in the north
00:05:00.04 and the west part of the island,
00:05:01.16 and the first report of larval transport
00:05:04.12 was made in 1986.
00:05:06.27 A couples... a couple of years later,
00:05:09.09 in 1988,
00:05:11.08 the first report of a male guarding the eggs was made.
00:05:13.26 But since then, a little bit over 30 years ago,
00:05:18.14 nothing else has been studied
00:05:20.22 about these species.
00:05:22.20 And it has become a blank slate
00:05:26.09 for me to do research
00:05:28.05 in larval transport behavior.
00:05:29.29 So, when I knew about this,
00:05:32.05 it was an obvious decision for me
00:05:34.08 to go from Connecticut
00:05:36.03 all the way to Borneo
00:05:37.25 to study the parental care behavior of these species.
00:05:40.19 My research took place particularly
00:05:43.08 at the Ulu Temburong National Park
00:05:45.05 in Brunei Darussalam.
00:05:47.01 In the middle of the rainforest,
00:05:49.04 there was a field station that became my home for many months.
00:05:53.01 I put all my equipment on a longboat
00:05:55.22 and I navigated upstream
00:05:58.00 until I reached my field site.
00:06:00.03 And armed with a headlamp and my rubber boots,
00:06:02.12 I set out to find these little frogs.
00:06:05.03 I would look carefully on the forest floor
00:06:07.11 and I would listen very carefully
00:06:09.19 for calling males as well.
00:06:12.23 Many nights, I had to venture into the forest alone,
00:06:15.28 crossing streams,
00:06:17.19 walking long hours,
00:06:19.08 and sometimes things can get very muddy.
00:06:21.28 But all this hard work pays off
00:06:25.01 when you actually can find some frogs.
00:06:29.26 Here, I show you one male of the guardian frog of Borneo
00:06:34.02 taking care of a clutch of eggs.
00:06:36.16 As you can see,
00:06:38.00 they are very good at hiding under the leaf litter,
00:06:40.11 and they can blend very nicely with their environment.
00:06:43.29 So, you can probably imagine
00:06:45.25 that they don't seem particularly happy to be found.
00:06:48.26 During my research,
00:06:51.19 I was able to see that only the males
00:06:54.04 are the ones doing all the parental care behavior
00:06:56.12 of their clutches.
00:06:58.07 They stay with the clutch -- sitting on top or next to it --
00:07:01.20 until the eggs are ready to hatch.
00:07:03.24 And when this happens,
00:07:05.15 the tadpoles break out of the egg capsule,
00:07:07.20 climb on the back of the male,
00:07:09.11 and when all of them are ready to go,
00:07:11.11 the male starts a journey,
00:07:13.08 finding small pools of water
00:07:16.12 where they can grow and finish their development.
00:07:21.00 Males that are taking care of the eggs
00:07:23.07 or transporting tadpoles
00:07:25.01 do not produce any calls.
00:07:26.16 So, if I wanted to know how these males
00:07:29.00 are attracting females,
00:07:30.24 I needed to find the males
00:07:32.28 that are not on parental duties.
00:07:34.20 In general, the males stayed on top of the leaf litter
00:07:38.01 and called to attract females to their location.
00:07:41.22 This call is very loud
00:07:44.03 and can be heard from very far away.
00:07:50.19 So, whenever I heard that sound,
00:07:52.15 I would make a beeline for it
00:07:54.27 because I knew a male was waiting for me, to be recorded.
00:07:58.20 I recorded many males like this,
00:08:01.00 and I wanted to get as many males as possible.
00:08:04.00 And it was in one of these many nights
00:08:06.12 recording a male
00:08:08.14 when I heard a sound that I wasn't particularly familiar with.
00:08:12.02 And I didn't know where it was
00:08:13.26 or what it was.
00:08:17.16 Remember our friend from the beginning?
00:08:20.19 So, this is a frog that belongs
00:08:23.05 to the species of the guardian frog.
00:08:25.19 And if this is the male calling...
00:08:30.06 so, what is this?
00:08:32.28 After careful observation,
00:08:35.03 I noticed that this is actually a female calling.
00:08:38.20 This is a very particular,
00:08:41.21 unique behavior in frogs,
00:08:44.01 because females do not produce spontaneous calls.
00:08:47.26 It is very interesting
00:08:51.14 that nobody had ever recorded this behavior before,
00:08:53.24 because females... even though...
00:08:57.04 have a very short and soft call,
00:08:59.08 they are calling.
00:09:00.26 And one of the reasons why I think
00:09:03.04 nobody had ever reported this before
00:09:04.24 is because scientists for the longest time
00:09:07.15 thought that only male frogs
00:09:09.16 were capable of producing sounds.
00:09:12.21 So, having a [female] calling
00:09:15.27 started creating a lot of questions in my head
00:09:18.27 about what's happening in these species.
00:09:21.03 In general, in species that have male parental care,
00:09:24.10 unique traits of the females,
00:09:28.09 like, in this case, female calling behavior,
00:09:30.07 are usually associated
00:09:32.18 with a mating system that is called sex role reversal.
00:09:35.04 So, we know that the guardian frog
00:09:38.19 has male parental care,
00:09:40.10 and then you have this female calling behavior.
00:09:42.21 These two things together
00:09:45.06 are key for the occurrence of this mating system.
00:09:48.08 So, could it be that the guardian frog of Borneo
00:09:51.18 is a sex role reversed species?
00:09:55.15 But before I answer this question,
00:09:57.00 let me tell you a little bit more in detail
00:09:59.17 what a sex role reversed species is.
00:10:02.18 In these species,
00:10:05.00 the males are the ones providing all the parental care,
00:10:09.08 and the females exhibit traits
00:10:11.12 that are normally only associated with the males.
00:10:13.16 In addition, the females are going to use those traits
00:10:18.03 to display more vigorously
00:10:20.09 than the males do.
00:10:21.22 And also, the females that are ready to mate
00:10:25.25 are going to be more abundant
00:10:27.15 than the males that are ready to mate.
00:10:30.23 Because this is going to create a shortage of males
00:10:33.27 available for mating,
00:10:35.12 this is going to create the possibility
00:10:37.23 of female-female competition.
00:10:40.22 Species like the seahorses and pipefish,
00:10:45.25 and a handful of birds,
00:10:49.07 have been reported to have sex role reversal.
00:10:52.12 This has also been observed in insects.
00:10:56.22 But so far,
00:10:58.23 it has never been reported in frogs.
00:11:04.20 If the guardian frog of Borneo
00:11:07.05 is a sex role reversed species,
00:11:08.23 we would expect that several aspects
00:11:10.15 -- if not all of them --
00:11:12.20 of the natural history of the species
00:11:14.16 match the conditions for sex role reversal to occur.
00:11:18.09 So far, we know that
00:11:21.17 males provide all the parental care,
00:11:23.11 taking care of the eggs
00:11:25.06 and transporting the tadpoles to small bodies of water.
00:11:28.07 And I have discovered that the females
00:11:31.11 exhibit this spontaneous female calling,
00:11:33.12 which you would normally only associate
00:11:35.25 with male frogs.
00:11:37.14 So, this begs for the other questions:
00:11:39.16 do females display more vigorously than the males?
00:11:42.12 And are the females more abundant than them?
00:11:45.02 And ultimately,
00:11:47.05 do they compete against each other for mating opportunities?
00:11:52.18 The fact that the females call spontaneously
00:11:54.19 was a stroke of luck,
00:11:57.25 because it allows me to compare
00:12:00.12 the calling rate of males and the calling rate of females.
00:12:03.00 The calling rate is defined
00:12:05.19 as the number of times a frog,
00:12:07.07 in this case,
00:12:08.27 produces a call within a given period of time.
00:12:10.22 So, throughout the night,
00:12:13.06 I will record how many times a female
00:12:15.23 produced a call within an hour
00:12:17.19 and how many times a male
00:12:19.20 produced a call within an hour,
00:12:21.11 and I did this throughout the night
00:12:23.05 for many different individuals.
00:12:24.29 In this figure we have in the x axis the time,
00:12:28.04 and the y axis is showing us the calling rate.
00:12:31.00 This is the calling rate of the males.
00:12:35.09 If we compare this with the calling rate of the females,
00:12:38.06 we can see that even though there's a lot of variation
00:12:41.07 throughout the night,
00:12:43.03 the females on average call way more than the males do.
00:12:46.24 Males call once every 10 minutes
00:12:49.17 while the females do it 30 times every 10 minutes.
00:12:55.08 These data allow me to check off this condition
00:12:59.19 that the females display more vigorously than the males.
00:13:05.12 For our next question,
00:13:07.10 I wanted to see how many males
00:13:09.11 were available for mating
00:13:10.29 and how many females were available for mating.
00:13:14.15 Males of the guardian frog
00:13:16.03 are widely dispersed throughout the forest.
00:13:19.05 Now, we know that the males
00:13:20.27 don't call that often,
00:13:22.08 but when they do,
00:13:23.24 they are attracting females to their location.
00:13:26.23 I observed how females
00:13:29.06 venture through the forest
00:13:31.05 homing in on the call of these males.
00:13:33.09 And I observed that sometimes
00:13:36.11 two, three, and, in a few exceptional cases,
00:13:39.10 four females would gather around a specific male
00:13:41.23 and start calling spontaneously,
00:13:43.19 as if serenading him.
00:13:45.06 These females form these particular aggregations
00:13:48.22 that have never been observed in another species of frog.
00:13:52.12 I found that almost 50% of the time,
00:13:57.17 every time you encounter a male calling,
00:13:59.19 he was gonna have two or more females around him.
00:14:03.20 So, if you compare how many males
00:14:06.12 that are calling... are available for mating
00:14:09.01 and how many females,
00:14:11.17 you can see that females are more abundant than the males.
00:14:14.01 This is evidence
00:14:17.02 that is concordant
00:14:19.16 with the criteria of females being more abundant
00:14:21.08 than the males.
00:14:23.11 For our next question,
00:14:25.15 do females compete among them for mating opportunities?,
00:14:28.05 I'm gonna have to leave you with a cliffhanger that...
00:14:30.27 maybe.
00:14:33.14 During my time in the forest,
00:14:35.02 I never observed females competing physically
00:14:37.03 for the calling male,
00:14:38.25 but competition can take place in many different ways.
00:14:41.14 Because the females call, and call so vigorously,
00:14:44.22 there is the potential for acoustic competition.
00:14:47.17 And there's also the potential
00:14:50.01 for the male to discriminate
00:14:51.22 among two different females,
00:14:53.13 behaving as the choosy sex.
00:14:55.12 If these two things happen in these species,
00:14:58.14 this would provide further evidence
00:15:00.15 that this species is actually sex role reversed.
00:15:03.18 And I hope to answer these and other questions
00:15:07.03 with my future research,
00:15:08.19 trying to determine if females
00:15:11.00 react to a simulated competitor
00:15:13.21 with playback experiments,
00:15:15.20 and I would also like to see if males
00:15:17.23 have preferences for acoustic characteristics
00:15:20.15 of the female calls,
00:15:22.02 and if they can discriminate
00:15:24.12 and choose between two females.
00:15:30.05 So far, my research has laid the groundwork
00:15:34.00 for these species to be the first case of sex role reversal in frogs
00:15:39.04 and to be the first frog to actually join
00:15:42.04 this iconic group of species
00:15:44.01 that have sex role reversal.
00:15:49.00 Studying these systems
00:15:51.06 that go against what we actually think is conventional
00:15:54.25 challenges our understanding
00:15:57.05 of how animal systems work.
00:15:59.21 This little frog has been around for many years,
00:16:02.14 and nobody had studied it,
00:16:04.24 and it took one person
00:16:06.29 to take the time and to make careful observations
00:16:09.17 about this behavior
00:16:11.12 to discover what they have to tell us.
00:16:14.05 I want to call the attention to the importance
00:16:16.27 of doing natural history studies
00:16:18.23 and behavioral studies,
00:16:20.16 because there is so much more that we have to learn
00:16:22.27 and so much more to discover.
00:16:25.06 So, for now,
00:16:27.19 I hope that in the meanwhile
00:16:29.24 you keep your ears open,
00:16:32.00 because there may be a frog or a bird,
00:16:33.23 or maybe another creature
00:16:35.24 that you didn't even know produces a sound,
00:16:38.21 that is just waiting to make its voice heard.

This Talk

Speaker: Johana Goyes-Vallejos

Audience:

Educators of H. School / Intro Undergrad
Student
Educators of Adv. Undergrad / Grad
Researcher
Educators

Recorded: May 2018

Talk Overview

In frog species, typically male frogs call, while females stay silent. Dr. Johana Goyes-Vallejos shows that in the smooth guardian frog of Borneo (Limnonectes palavanensis) this is not the case and that female frogs call, too, producing spontaneous vocalizations to attract males. Dr. Goyes-Vallejos’ discovery that female frogs call suggests that L. palavanensis exhibits a reversal in calling behavior and possibly a sex-role-reversed mating system, which would be the first ever observed in a frog species.

This talk is part of the Young Scientist Seminars, a video series produced that features young scientists giving talks about their research and discoveries.

Speaker Bio

Johana Goyes-Vallejos

Johana Goyes Vallejos received her bachelor’s degree in Biology from Universidad del Valle, in Cali, Colombia. For her Ph.D., she joined the lab of Dr. Kentwood Wells in the Ecology and Evolutionary Biology Department at the University of Connecticut. Johana’s research interests include sexual selection and amphibian mating systems (frogs and toads), with a particular… Continue Reading