Boy or Girl?: A Climate-Fated Adventure In Lizards

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Niveoscincus ocellatus (Photo credit)

Ever caught yourself wondering what it might be like if you could know the sex of your future children? Several methods allow for this to be determined with modest accuracy in the late stages of a human pregnancy, but what about early pregnancy? Before pregnancy? In other animals?

Sometimes the answers to these questions can be predicted based on the context in which they are asked. For example, I came across this article this article a few months ago, and would like to share its findings (full paper here; additional source). Essentially, the researchers found that climate, combined with genetics, was a main determinant of what sex-determining system emerged in a species of lizard.

But isn't sex in vertebrates determined by chromosomes? Not always. For instance, in many (not all) reptiles, sex is influenced by environmental factors, often temperature (i.e., temperature-dependent sex determination, or TSD). But how would a knowledge of TSD help you predict the sex your offspring? Well consider the example offered by our study in question.

In these experiments, an international cohort of herpetologists collected and observed female Spotted Skinks, Niveoscincus ocellatus from two types of habitats in Tasmania: highland and lowland. The habitats differ in altitude and therefore atmospheric oxygen, UV irradiation, moisture, and temperature, among others. Female N. ocellatus from the lowland habitat, when raised in a lab setting, varied in the ratios of male/female lizards based on the amount of sunlight they were exposed to (4 hr or 10 hr; sunlight functioning as a natural variable in temperature, UV irradiation, and light). Surprisingly, although the same species, female N. ocellatus from the highland habitat did not demonstrate this discrepency between sunlight exposure times.

What does this mean? The authors of this paper predict that in N. ocellatus, the lowland-dwelling lizards are more likely to give birth to female lizards than male lizards when temperature is higher. Lowland female lizards born earlier (as a result of warm temperatures earlier in the year) have a reproductive advantage over lowland female lizards born earlier in the year. Neither highland lizards or male lowland lizards experience a similar boost from being born earlier (resulting in more females in lowland species in warmer years). For the highland lizards, the overall temperature is colder and there is not a significant reproductive advantage to being born earlier in the year. Additionally, the paper revealed a possible mechanism for species divergence (i.e., cladogenesis) - that of environmentally-sensitive evolution of sex-determination systems.

Remember our question about predicting the sex of future offspring?  The authors also suggest that if the warming trend continues in the species' habitat, more females will be expected. Hypothetically, lowland N. ocellatus mothers can plan on more female offspring in their future (assuming it remains an evolutionary stable strategy for the species). Greeting card companies for newborns take note!

It a Gril! (via Cake Wrecks)

Male Green Frogs in Suburban Habitats Sometimes Develop Eggs

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Interesting video of the now:


I hope you enjoyed that. I post it not only because of the interesting topic, but the simple manner by which a complex process is described. As I look into graduate school more and more, I'll probably be posting videos similar in feel to this one. This is simply because visiting research lab websites exposes me to, well, lab research.

Reptile Communal Nesting

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Check out this cool article about normally-solitary reptiles laying eggs in communal nests.

Communal nesting!? What's that, Alex? For one, it has traditionally been thought of as a non-reptilian behavior. Communal nesting is simply the laying of eggs by a female animal into the nest of a conspecific (same species) animal. This behavior is different than cooperative breeding, which could be thought of as a "daycare system" - individuals care for the young of other individuals, even at the expense of their own breeding abilities.

A quote that summarizes the opinions of the authors on why communal nesting occurs in some reptiles:

Building a nest can be hard work for reptiles. Some female lizards, for example, may spend days digging a hole deep enough to deposit eggs. During those days, she is not doing other important things such as finding food. She is also more vulnerable to predators. Females can avoid these costs by simply laying eggs in a nest that someone else has gone to the trouble to build.

The model, the authors argue, could be advantageous in an evolutionary sense. It is common sense to note that anything that reduce an animal's required level of energy expenditure to successfully pass on genetic material is good for the species in the long-run. This argument does NOT always hold true; however, that's the common sense approach. It is still true that parental care is not the norm in most described species behaviors THUS FAR, but read on...

While searching around for the topic, I found another well-cited article summarizing review articles (articles that synthesize scientific literature) which argues that communal nesting is probably much more common in reptilian species than first thought. If you read through the article, you note how little is known about nests in most species of reptiles. In fact, for most named species, nests have never even been reported in the scientific literature! Just another opportunity to grab your hiking boots and go outside!

Review - "Origin of Species"

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You know the spiel.

Charles Darwin sailed the seas aboard the HMS Beagle on an historic journey. The face of science was forever changed when he and Alfred Wallace independently developed their theories of evolution by natural selection. However, with the publication of 'Origin,' Darwin got the foot in the door necessary to inseparably tie his name with the theory of evolution.

First things first: this book is important.

Now that that's out of the way, how does it read? 'Origin' is difficult. You can hear Darwin stretching his arms out wide and grasping for the perfect way to explain the incompleteness of the fossil record, evolution by natural selection, or what have you. On the whole, you can only read 'Origin' ten, rarely more than twenty, pages at a time.

'Origin' is, of course, entirely historical by now. Reading 'Origin,' the reader knows that Darwin had no knowledge of basic Mendelian genetics and can be impressed with his analysis of certain patterns.

I recommend this book to someone looking for something to think about (with sufficient free time), any student of biology etc., or anyone who feels they have an understanding of the scientific theory of evolution.

Overall: 4/5 (hard to read, but thought-provoking)