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Lizard Mates

Lizard Mates Photo Credit: Clipart.com

The life of a lizard seems pretty simple—find a nice, sunny rock to sit on, find a decent mate to have babies with. Now, a new study shows that for the descriptively named side-blotched lizard, these two pursuits are intimately connected. You'll hear about it in this Science Update.


Transcript

Lizard love. I'm Bob Hirshon and this is Science Update.

In the animal world, the big, hunky guy usually gets the girl. But it turns out that female lizards prefer the males with the best real estate.

That's according to a study conducted by UCLA researcher Ryan Calsbeek and his colleagues.

Calsbeek:

One of the things that we were interested in at the beginning was whether females were interested in males for the males themselves, or for the resources that they provided to females. And so, since the normal situation in nature is for large males to control the best resources, we had to uncouple those experimentally.

They did that by moving rocks from the territories of big, beefy lizards to the territories of smaller, wimpier ones. Good rocks are important because they provide shelter from enemies and places for sunning, which is critical for the cold-blooded lizards.

Calsbeek:

What we saw as a result of those manipulations was that females moved away from the big males, their original choice of mate, and settled with these smaller males on the high-quality territories.

But big guys weren't left completely out in the cold. Most females mated both with their primary partner and with a larger lizard down the block. Calsbeek says this strategy gives females the best chance for having healthy babies. For the American Association for the Advancement of Science, I'm Bob Hirshon.


Making Sense of the Research

It's not surprising that the female lizards usually prefer larger, healthier-looking males with impressive territories. And since male lizards fight for their territory, the big guys generally end up with both the prime real estate and the female attention. The goal of this experiment was to uncouple the size of the lizard from the size of the territory. In other words, the researchers asked the question: if a female had to pick one or the other, which would they find more important?

As the story suggests, the answer isn't simple. Generally, the females set up camp on the best territories, even when puny males were in charge. And the high-quality territories themselves had some direct benefits: the females on them laid larger eggs, and laid their eggs sooner, which were both associated with highly fit offspring. But the females still ran off for trysts with larger males who were stranded in less desirable territories. In fact, this kind of promiscuity is not unusual in side-blotched lizards: about 80% of females have offspring by multiple males in a single clutch of eggs.

It turns out there are some benefits to trading off. Females' bodies can actually sort sperm from multiple fathers, and they tend to produce sons from eggs fertilized by larger males and daughters from the eggs fertilized by smaller males. This is a win-win situation, because male lizards fathered by large males tend to be large themselves, and therefore more "fit," but female lizards fathered by large males tend to lay their eggs at the wrong time. So, by mating with several males and mixing and matching their sperm, the female is able to produce highly fit sons and daughters in the same brood. This study shows that in the world of animal mating, what may seem like a simple choice may in fact be very complex.

Now try and answer these questions:

  1. What was the purpose of this experiment?
  2. What were the findings?
  3. Why did the female lizards continue to mate with both smaller and larger males?
  4. Based on this study, what kinds of mating behaviors would you expect females to exhibit under normal conditions?

For Educators

The San Diego Natural History Museum's Field Guide offers this page on side-blotched lizards.

In PBS' online activity The Mating Game, contestants try and find the best mate for various animals, and learn about different mating strategies in the process.


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