The Language of Love, part 2
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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 and tasting.
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.
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.
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.
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.
1 López, Muñoz, & Martín (2002)
2 Martín & López (2000)
3 Head, Keogh, & Doughty (2005)
4 Ibanez, Lopez, and Martin (2012)