Notes from a Common Garden Experiment

The cages in which females are individually housed during the common garden experiment. Each cage has a bamboo perch and a plant in potting soil where the lizard can lay her eggs.

We are in the midst of a common garden experiment in which we’ve taken gravid Anolis carolinensis females from morphologically differentiated populations in the wild and returned with them to the lab where we are collecting eggs to incubate and hatch. We’d eventually like to know whether the offspring of these females maintain the differentiation observed in the wild under common growth conditions. If yes, this is good evidence that the differences we’ve observed are a result of genetic changes among populations, rather than phenotypic plasticity during development and growth. A few notes from this ongoing experiment follow.

We brought back 69 females on August 1 2011, and we’ve been checking for eggs 2 to 3 times per week. As of September 6, we had collected 61 eggs. Most females have produced one egg, a few two, and the rest none. Egg laying rates were higher earlier in the experiment (maxing out at 12 eggs per search during the second week of August) but we’re still collecting 3 to 4 eggs per search even now, a month later.

An egg. The female buried it beneath the potted plant, which was removed during the search. The egg is approximately one centimeter long. Females bury their eggs in the dirt, which helps prevent egg desiccation.

Generally, anoles have a distinct reproductive season. For A. carolinensis, the reproductive season wraps up in late summer / early fall. Accordingly, we’ve found a dozen or so unfertilized eggs laid the cage carpet (rather than buried in the soil), which is normal for females approaching the end of their reproductive season. These eggs are small, yellow, and often don’t have a discernible shell. Occasionally, however, we find an egg laid on the cage carpet that looks like a normal, fertilized, fully-shelled egg. By the time we discover these eggs, they are often desiccated beyond repair.

A desiccated egg found on the cage carpet.

As laying a healthy egg outside of the soil seems like a strange action for a female to take, my question for the anole world is: “Are these eggs actually fertilized?” Have any of you anole breeders out there rescued carpet-laid eggs prior to desiccation and successfully hatched lizards from them?

Presently, all the eggs are in the incubator. Incubation times last from 4-5 weeks depending on the species, so we are expecting our first hatchlings very soon!

Eggs in individual petrie dishes on an incubator rack.

About Yoel Stuart

I am interested in whether, how, and why ecology shapes evolution (and evolution shapes ecology) through time, with an emphasis on microevolutionary pattern and process, adaptation, and field experiments. I completed my Ph.D. on Anolis lizards in the Department of Organismic and Evolutionary Biology at Harvard University. I am currently a post-doctoral researcher at the University of Texas, Austin studying threespine stickleback. They're not anoles, but they're cool too.

9 thoughts on “Notes from a Common Garden Experiment

  1. My impression is that many of these ‘carpet-laid eggs’ are indeed fertile and salvageable. Over the course of a three-year anole breeding effort at Washington University, we successfully hatched several dozen eggs that were laid outside of their potted plants. The key is to find them quickly (within a few hours) and to make sure that they are re-hydrated promptly. Not surprisingly, mortality was higher among these eggs than those laid in soil, but it is possible to hatch them.

  2. Eggs laid outside of your soil cups can definitely be fertile and might hatch if caught prior to desiccating. We’re also in the midst of a large anole breeding experiment here in Rochester. Anthony Geneva’s experiment with Anolis distichus is producing around 45 eggs per week from a ~150 female colony. All of his females are being housed with males, and all of their offspring were presumably sired in captivity rather than resulting from mating in the wild (we’ll assess this directly with microsatellites at the end of the experiment). We surpassed 800 total eggs for the season yesterday. I think we already have 300+ hatchlings, with lots more on the way! We should post more on this soon because some of our techniques are quite different from those used at Harvard (we use large yogurt cups filled with vermiculite for egg laying, incubate eggs in vermiculite filled deli cups, and raise hatchlings in new custom built acrylic cages).

  3. As Rich mentioned, we’re in the midst of a massive breeding experiment here. We’ve been working on our protocol for the last few years, but I think we’ve had a few “key innovations” that have made big projects manageable, and increased the productivity and success of our colony.

    I think the most important thing we added to our protocol are those yogurt cups Rich mentioned. Females seem to feel very secure in them, and I think the reduced stress contributes to to more animals laying well-developed eggs. Furthermore, it’s at lot easier to maintain a suitable microclimate in them, so eggs can remain viable for a week or more until we can find them. For similar reasons, females are compelled to lay eggs in them. Vermiculite is a lot softer material for females the nest in as well. Part of the problem you’re having could be they can’t penetrate the soil to a point their satisfied with.

  4. @ Paul: How did you re-hyrdrate the eggs? Did you put them in really moist vermiculite?

    @ Wes/Rich: These aren’t the elusive gray dewlapped A. carolinensis. The populations come from my spoil island work, which suggests that A. carolinensis on islands with A. sagrei have larger toepads with more lamellae, compared to A. carolinensis on islands without A. sagrei.

    @ Dan/Rich: Please do post your breeding colony details! It’d be great to know what your lab is up to and how to make our breeding experiments more successful!

  5. @ Yoel: Yes, we re-hydrated eggs by placing in very wet vermiculite for a couple days, and then transferring to moist vermiculite. (Eggs left in wet vermiculite for extended periods can swell too much and damage the embryos). Great suggestion by the Glor lab to skip the soil and offer vermiculite directly to the females!

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