The Language of Love: Breeding Behavior in Reptiles and Amphibians – March 2013

By Erin Lane

Part II: Scintillating Scents

When it comes to the senses, we humans are dominated by our eyesight.  Sound, touch, smell, and taste all fall into place as well to create a dynamic set of tools to experience the surrounding world.  What we sometimes forget is that not all animals experience the world the same way that we do.  For some, like many frogs and toads, sound is key when it comes to communication.  For others, touch, or tactile communication, is by far the most important sense, while still others depend on taste and smell to figure out the world.

Last month we left off talking about how animals use sound to attract mates.  This month, we will be discussing how your pets use chemical cues to communicate.

Smelling and tasting

You have no doubt seen a snake flick its tongue in and out in rapid succession.  Sometimes it is in response to food, being handled, or being placed in a new environment.  What the snake is doing is grabbing up chemicals floating in the air to be examined.  Sometimes people refer to this as ‘tasting’ the air, and they aren’t that far off.  Smell and taste rely on the same mechanisms to analyze chemicals in the environment.  In both instances, chemicals from the environment (e.g., from food, scents, pheromones) bind with specialized receptors that are interpreted as a particular smell or taste.  So, when a snake is ‘tasting’ the air, they are more or less smelling andtasting.

This False Water Cobra is checking out the camera!

You have probably also seen this behavior in lizards as well.  This is especially noticeable in tegus and monitors, whose long forked tongues flick in and out much like that of a snake.  However, it is also prevalent in other lizards, such as bearded dragons.  When you put two dragons together for the first time, you will likely see one or both of them tasting the other with the tip of their tongue.  This is likely a way to determine who the other dragon is—male or female, healthy or not, a good mate or a bad one.

The benefit of chemicals is that they can continue to be an effective form of communication, even after the animal that produced them has left the vicinity.  Chemicals can linger in an environment, laid down in excrement, body oils, musk, or other specialized exudates.  While we see scent marking all the time in mammals (think of your cat rubbing its chin on you, or your dog urinating while on a walk), we don’t usually think of reptiles as doing much scent marking.  However, much research would suggest otherwise.  There is evidence in some reptile species that individuals can even differentiate between a desirable and an undesirable mate just by using chemical cues.

Sniffing out a winner

In the animal world, males are typically the ones doing the chasing.  Females in most species have evolutionary incentive to choose the best mate available, or to accept the male that has outcompeted others for access to her.  In other words, in most mating systems, males have more impressing to do, and females have more choosing.  Females and males alike use chemical cues, among others, to detect and distinguish between good mates.  For females, this usually means finding the best male available.

For example, female Iberian rock lizards (Lacerta monticola) can distinguish between males with symmetrical and asymmetrical femoral pores using just the scent of a male on a cotton swab1, 2.  Now what do femoral pores have to do with love?  Good question.  Femoral pores are the large tubular scale-like bumps found along the under side of the upper thigh on many lizard species. They exude a waxy substance, and seem to be primarily used by males to lay down scent.  This scent likely says a lot about the quality of the male, like whether he eats well, or is sexually mature.  Symmetry is often a sign of overall health and good development.  Female Iberian rock lizards can therefore differentiate between males that are objectively higher and lower quality, possibly helping them to choose a good mate.

Here you can clearly see the femoral pores present on this male Bearded Dragon.

The scent of a female

Males also use chemical cues to find receptive females.  Male southern water skinks (Eulamprus heatwolei) have been shown to differentiate between the scents of females that are more and less receptive to mating3.  When given a choice between three hides scented with a large receptive female, a smaller unreceptive female, or no scent, males tended to choose the hide that   smelled like a large sexually receptive female.  While males are usually not as picky as females when it comes to finding a mate, they still need to determine where they will be most wanted.  It takes energy to court a female, and would be wasted on one that has no interest in mating.

Playing the pond

Such discrimination of scents has also been found in turtles.  Both male and female Spanish terrapins (Mauremys leprosa) show a preference for pools of water that formerly contained different sizes of other Spanish terrapins4.  Females showed a preference for water scented by large males, and males preferred water scented by females that had better immune response (i.e., healthier).’

Males also had preferred water that had chemicals from relatively smaller males than water that had contained relatively larger ones.  It is not surprising that females preferred chemicals left by males that were larger, as large body size has been found to be a good fitness indicator and a trait preferred by females across many taxa.

This male Bearded Dragon is interested in mating, but the female just wants to eat grass!

It is also interesting that males were attracted to the chemicals left by females that were likely healthier, or at least had a better immune system.  As stated earlier, while males aren’t usually as picky, they often do show some preference for females that are more likely to want to copulate, or are able to produce offspring.  Males also showed a tendency to avoid water formerly occupied by bigger males, and to prefer water formerly occupied by smaller males.  This makes sense when we remember that females like bigger males.  If you are the biggest male terrapin around, you probably won’t have a hard time attracting all the females in the pond.

In conclusion

Chemical communication is found throughout the animal world.  Many reptiles use their sense of smell and taste to find food or mates, or even to avoid competition.  It can be an effective means of leaving a message for others to smell or taste, or a way to advertise your own attractiveness.  However, chemicals are not the only means by which reptiles find love.  Next month we will be discussing how our ectothermic pets attract each other via visual signals.

Works Cited:

1 López, Muñoz, & Martín (2002)

Martín & López (2000)

Head, Keogh, & Doughty (2005)

Ibanez, Lopez, and Martin (2012)

The Language of Love: Breeding Behavior in Reptiles and Amphibians – January 2013

By Erin Lane

Introduction

For most of the country, it’s the middle of winter.  Cold storms are moving through, the thermostat is turned up on the furnace, and going out in anything less than a parka is out of the question.  Your herps, however, are likely blissfully unaware—either because they are basking in their own temperature controlled enclosure, or because they are sleeping it out until the Spring.  This doesn’t mean though that they aren’t getting prepared for breeding season.  As your temps start to warm up here in the next month, your pets will be undergoing physiological changes that will prepare them for breeding season.

Whether you have snakes or frogs, monitors or turtles, most of their wild counterparts have a well defined period of time when the conditions are just right for procreating.  In the tropics, this may be the start of the rainy season.  For creatures living in the temperate zones (which is most of the U.S.), this means the beginning of warmer days and milder weather.

This is also the time that most of our pet reptiles and amphibians begin to gear up as well.  The means of communicating the readiness to breed is different from species to species, but there are some common types of communication when advertising love.  As we get ready for springtime here at the Reptile Times, we will be discussing the many ways in which our ectothermic (aka ‘cold blooded’) animals attract and choose mates.

Green Tree Frogs like this one are found throughout the East Coast of the US

Part I: Auditory Announcements

Although we initially rely pretty heavily on appearance when attracting or finding a mate, many species would find all of this primping and grooming a waste of time.  For most anurans (frogs and toads), the voice is often the most important tool to attract a mate.  But why?  What is the benefit of vocal communication, and how can that help to find a suitable partner?

Well, think about the areas in the world that have the highest densities of anurans.  These are wet places with dense vegetation, such as rain forests.  Even if you have good eyesight, it won’t help you to find other small, cryptically colored frogs hiding out under leaves and in small pools of water.  With so much thick foliage, it won’t do much good to see well.

Chorus Frogs, like this one, get their name from the distinctive calls they are known for making

Picky listeners

Sound, on the other hand, carries far, even when visual barriers are present.  Having a strong voice means that you can be heard over a greater distance, thereby increasing the number of listeners (and potential mates).  As for most animals, it is the males that do the majority of calling.  Females tend to be choosy since they typically have a very limited number of reproductive opportunities in a given season.  Making eggs is taxing, and, depending on the species, they may only have one opportunity to have their eggs fertilized.  In that case, finding a mate becomes a choice that could be the difference between their genes getting successfully passed on to the next generation, or not at all.  If the chosen male doesn’t pass on good strong genes to your offspring, they may not live long enough to have offspring of their own.

Males, on the other hand, typically have a very different take.  Where females are all about quality, males are all about quantity.  Unlike females that produce large, energetically costly eggs, males make millions of small, energy efficient sperm.  In most cases, the number of females they can breed with is dependant primarily on how many they can convince.  So when it comes to attracting a mate, males are usually the ones with the tougher job.

Size matters

You have likely heard the saying “appearances can be deceiving,” but it’s hard in the animal world to disguise a voice.  Vocalizations, or calls, are usually closely tied with the size of the animal making them.  For example, a small frog can’t make a deep call, just like a snare drum will never sound as big and deep as a base drum (think of an American bull frog versus a chorus frog).  It’s all about the size of the instrument, and it’s hard, if not impossible, to alter a call enough to trick a discerning ear.

But why is being bigger important?  It isn’t always, but being bigger usually means that the male is older, has more access to food, or both.  If a male lived long enough to become big and can make a nice booming call, it likely has good genes that have allowed it to find food and escape predators.

Standing out in the crowd

Often times, males stay put and call while the females seek out the one they wish to breed with.  In some species, the males form a lek, which is essentially a gathering place where they can show off for females.  The females come to the lekking spot, and can suss out which male would be best to breed with.  In some cases, the mere act of being able to participate in the lek is the only qualification a male needs to attract a mate.  Males that live long enough to make it there every season are usually those that are higher quality, and therefore suitable for a choosy female.  In other species, females will find vocalizing males from a distance, led on by the sound of their call.  Only males that have strong, attractive calls will be sought after, meaning that males with less attractive ones will be left singing to themselves.

An important point to make here is that every species will have its own particular call structure and/or frequency.  Ideally, females will only be attracted to the call of their own species.  If they weren’t, it would be a waste of their time, and they wouldn’t be likely to reproduce.  They are tuned in, so to speak, to the vocalizations of their own kind, and discern between calls that are within certain acoustic parameters.  Some of them within those parameters just happen to be more or less attractive.

This is an important element in vocal communication because of possible interference from other species.  In your mind, go to that lush rain forest with all of those frogs.  Think of how many species there are, and how that might sound.  Pretty confusing, for an animal that is relying on sound to find a mate.  Animals need to be able to ‘filter out’ the sounds of other species, and focus in on those of their own.  Not an easy task for us, perhaps, but one that comes naturally to even the most inconspicuous little frog.

This little Chorus Frog was caught in a surprise spring snowfall – he hopped away to sing another day!

Curtain call

As the country begins to thaw out in the next few months, we will start to see our reptiles and amphibians perk up, and get into breeding mode.  This is the time of year that is often most rewarding to serious herp breeders and casual hobbyists alike.  Your pets begin to wake up, eat more, and, often times, start looking for a mate.  The way they do so depends on the species, and it can make for truly interesting behavior.

Although we rely heavily on sight when finding a potential mate, many animals use other senses to discern a good partner.  For frogs and toads, it’s all about the voice.  A call that sounds out over the rest is sometimes the most enticing attraction for a female, making it a male’s most important asset.  However, sound is not the only way that animals communicate and find mates.  Next month we will be discussing how some species use chemical cues to find and attract each other.  In the mean time, keep an ear out for local frogs and toads as they get ready to sing their hearts out in search of springtime partners.