How to tell apart male and female spotted salamanders (and other Ambystoma)

Spotted Salamander in Pond

So you are outside on a rainy, cold day in late winter, walking around your favorite vernal pool, and you find an Ambystoma salamander. These are the large North American salamanders that often (but not always!) live on land as adults, but migrate to breeding ponds to mate and lay eggs. Once you’ve got one of these salamanders in your had during the breeding season, how can you tell if it is a male or a female?

In an earlier post, I showed how to tell apart male and female wood frogs during the breeding season based on the shape of the front limbs. That method won’t work for spotted salamanders or other Ambystoma; instead you’ve got to look at the cloaca.

The cloaca is the orifice just past the hindlimbs in salamanders. The cloaca serves two main functions: excretion and reproduction. During the breeding season, the cloaca of male Ambystoma are enlarged, while the cloaca of females remain smaller. If you can pick up your spotted salamander and flip it over, you can easily tell its sex. Unfortunately this approach won’t work if you find an Ambystoma during the summer, because the males do not have enlarge cloaca outside of the breeding season.

Salamander Anatomy Cloaca

Female Spotted Salamander Cloaca

Male Spotted Salamander Cloaca

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Flute, Horn, and Treefrog

I was recently contacted by Spencer Arias about using one of my gray treefrog recordings in a piece of music he had composed. Spencer is a member of The New Collaborative, a group of composers who write music based on prompts from their audience submitted through facebook or twitter. The piece Spencer wrote was in response to a prompt of “amphibians.” The use of prompts to give direction for music is a cool idea, and the final piece is fun and interesting to listen to. After listening to it a few times, I was struck by the serendipitous way in which a recording I made one warm summer night in a Michigan pond ended up in a piece of music recorded in New York City and broadcast around the world on youtube.

Composition by Spencer Arias of the New Collaborative:

Video of a calling Gray Treefrog in a Michigan wetland:

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An overdeveloped drive to mate?

Wading around wetlands during the frenzy of amphibian breeding aggregations can reveal fascinating sights and sounds. Male frogs have a wide range of strategies for getting the girl. They might attract a female with song, or lurk quietly trying to sneak in a mating. For some of the male frogs, this will be the only opportunity they have to mate in their entire lives. Consequently, they can get a little overzealous, and errors are made. Males will briefly grab onto other males, but then let go when they hear a specialized “release call” that informs them of their mistake. However, there are some situations where the strong drive to mate combines with the lack of an encounter call with a surprising or even grotesque results.

One such unpleasant outcome is when a male frog amplexes a deceased female. The photo below shows a male wood frog found amplexing a dead female. By the look of it, the female was probably dead for a day or more. Who knows how long the male hung on for!

Sometimes the mix-up is less disgusting, but still interesting. Male frogs will sometimes try to mate with other species of frog, or salamanders. These other species can’t produce the appropriate release call, and so the males just keep hanging on. An example of this is the photo below of a pacific chorus frog trying to mate with a California Newt. I spent six years observing pacific chorus frog breeding aggregations, and it is worth noting that I only saw this frog-on-newt mating a handful of nights. Those nights were always the rainiest nights with the highest densities of frogs. I never saw this behavior cause obvious harm to the newts. However, there may be situations where this can be very bad for the salamander.

Perhaps the most unusual cases are when these two errors – dead animal and wrong species – are combined. I have not yet seen this myself. However, I came across a fascinating example of this on the photo-sharing site flickr. Miha Krofel’s photo below shows a male common toad trying to mate with a dead pike! Click on the photo to go to Miha’s photo stream.

mismatch mating - toad and dead spike

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Estimating amphibian abundance by counting egg masses

One challenge for biologists is estimating how many individuals of a specific species can be found in a given area. There are a number of indirect ways to do this, but many are extremely time-consuming and require capturing and marking individuals. Fortunately, there are some animals whose natural history makes them particularly amenable to estimating population size. Many amphibians lay clusters of eggs; by counting the number of egg clusters, biologists can often indirectly estimate abundance.

The image to the left shows the eggs of two species of salamanders. The bottom egg mass was laid by a spotted salamander (Ambystoma maculatum), while the upper egg mass was laid by a blue-spotted salamander (Ambystoma laterale). Each female will lay multiple egg masses, so counting egg masses does not directly estimate the number of females that bred in a pond. However, counting egg masses can provide estimates of relative abundance, and this information can be important for monitoring amphibian popualtions. For instance, Robert Brodman (2002. The Ohio Journal of Science. 102(5):123-127) estimated the abundance of spotted and Jefferson’s salamanders for over a decade at two ponds in the Cuyahoga Valley National Park, and was able to show that neither species was declining over the course of the study.

Another example of an amphibian laying distinct egg masses is the California Newt (Taricha torosa). Each of the little round balls in the photo below contains around 30 individual embryos. Like the Ambystoma salamanders, female newts lay multiple balls of eggs, so counting the balls of eggs doesn’t give an accurate count of how many females bred in a site.

California Newt Eggs

Pacific chorus frogs (Pseudacris regilla) also lay clutches of multiple eggs, with each clutch containing anywhere from half a dozen eggs, to over 80. As with the salamanders described above, a single female pacific chorus frog may lay multiple clutches of eggs during a single season.

Pacific Chorus Frog Eggs

Wood Frogs’ unique breeding behavior:

In contrast to many other amphibians, wood frogs (Rana sylvatica) have a few unique characteristics of their breeding biology that allows the number of adults to be estimated in a highly accurate fashion. One such characteristic is that they aggregate in tight groups during the breeding season. Even in very large wetlands, adult wood frogs gather together in one or a few spots. These leks may have hundreds or even thousands of male wood frogs calling in an area only a few meters across. The photos to the right and below show one of these aggregations. Take a close look at the image below…. see all the adult wood frogs floating on the surface? Slide your cursor over the image and the individual frogs will be highlighted.

Because wood frogs aggregate, nearly all the eggs are laid in a very small area. This makes it easy to find all the egg masses. However, if wood frogs were like other amphibians, in which females lay multiple separate clutches, our estimate of the number of breeding females would still not be very accurate. Fortunately, wood frogs have another important characteristic of their breeding biology: in most cases, each female wood frog lays a single distinct egg mass. Thus, by counting egg masses, biologists can accurately estimate the number of female wood frogs that laid eggs in a pond. A great paper by Crouch and Paton (2000. Using Egg-Mass Counts to Monitor Wood Frog Populations. Wildlife Society Bulletin 28: 895-901) demonstrated the accuracy of this method. The photo below shows an example. Move your cursor over the image to highlight the individual egg masses.

So here is a little quiz. The photo below shows the eggs taken in a marsh in Michigan in 2009, just after the wood frog breeding season had ended. The eggs were freshly laid. Just after the photo was taken, these egg masses were counted. Take a close look at the photo … how many female wood frogs do you think bred here? After you’ve made your guess, click for the answer

Wood Frog Eggs

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Potter Wasp emerges from mud ball

Potter Wasp emerged from mud ball

Potter wasp mud balls

Back during the summer of 2010 I found a few mud balls attached to some porch furniture. The furniture was going to be cleaned, so I thought I’d save the mud balls to see if anything came out of them. A week later, this Potter Wasp (Eumenes sp.) emerged from one of the mud balls. Presumably the mud ball was full of paralyzed caterpillars, and this wasp spent its larval period eating those caterpillars.

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