The Lizard Log

The Langkilde Lab in Action

When Do Siblings Become Food?

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Continuing with our undergraduate blogging we are featuring Aaron Jacobs, a junior majoring in the Vertebrate and Physiology option of Biology and minoring in Psychology.  During his time here at Penn State he has been on the executive board for Camp Kesem, an organization that provides camps for children who have been affected by a parent’s cancer.  He is a resident assistant, a teaching assistant for Biology 230W and president of a campus organization called Cancer Outreach.  He is planning on furthering his education after Penn State by going to medical school with the hopes of becoming a surgeon. Aaron’s blog post is below:

I have been working on various projects in the Langkilde Lab for almost three semesters, and one of those projects has been published recently.  This publication started with an observation I made one day while caring for the lab’s lizard colony. I was feeding and maintaining the  housing bins of our fence lizards (Sceloporus undulatus), when I noticed that a lizard was missing. Sceloporus is a highly studied genus of lizards, commonly known as spiny lizards, and it includes some of the most common lizards in the United States. Sceloporus undulatus, the Eastern Fence Lizard, is found throughout the eastern U.S., and is the subject of a lot of research in our lab. After a brief check to make sure that this disappearance wasn’t a bookkeeping error, I realized that the lizard that was missing was still in the housing bin, but was just in the stomach of one of the other lizards.

Cannibalism is a rare occurrence in reptiles, but this situation represented an even rarer event. This wasn’t just an act of cannibalism; it was an act of siblicide.  It turned out that the two lizards, the eater and the eaten, weren’t just the same species, but were family; they were hatched from the same clutch of eggs.  This act of siblicide is a rare occurrence and the first ever documented in the genus Sceloporus. Siblicide in general is probably rare because it reduces the fitness of an organism’s genes.  By eating a sibling, which shares genes with an individual, the chance of that individual’s genes to get passed on is decreased. For more information about some hypotheses regarding this rare occurrence see our recently published paper.

The cannibalized Sceloporus undulatus lizard (right fecal pellet) and one of his siblings (left).

The cannibalized Sceloporus undulatus lizard (right fecal pellet) and one of his siblings (left).

Cannibalism is not unknown in Sceloporus, and may occur for many reasons. One reason for cannibalism is the fact that Sceloporus species are opportunistic feeders and, due to size disparities, will eat fellow conspecifics because the smaller lizards make easy prey.  The supply of food also plays a role in determining if a species will undergo cannibalistic behaviors.  If food resources are low, lizards will consume fellow lizards due to it being more beneficial to consume a conspecific than to perish and have no chance of passing on your genes. The density of adults to juveniles plays a role in cannibalistic events as well: the more adults that are near juveniles the higher the chance that the larger lizards will eat the smaller juveniles.  The last proposed hypothesis for why cannibalistic events occur is the distance to the nesting sites where oviposition occurs.  S. undulatus seem to pick nesting sites based on the temperature and moisture levels. The farther the distance from adult territories to a nesting site, the more time the juveniles have before coming in contact with adult lizards, which provides them with more time to grow larger and avoid cannibalism.

Cannibalistic events show a positive relationship with size disparity and adult/juvenile density (a) . Cannibalistic events show a negative relationship with food availability and distance to oviposition (b) .

Cannibalistic events show a positive relationship with size disparity and adult/juvenile density (a). Cannibalistic events show a negative relationship with food availability and distance to oviposition (b).

Publishing a note on this observation was a way of documenting an extremely rare occurrence in captivity and in the wild.  This project has provided data for further experiments to build from and, due to the rarity of such an event, it has given us knowledge as to how this species and possibly others interact. Siblicide does occur, as this shows, and the reasons why an organism might engage in an act with negative consequences for fitness should be further investigated.  Potentially, some species may not distinguish between siblings and unrelated lizards.

This ended up being a fascinating project, and I was glad to be a part of it. I was able to contribute to this note by collecting data, providing input on possible reasons for such an occurrence and researching other papers on cannibalism in lizards, and specifically looking for examples of siblibide that have already been published. By being a part of this note, I gained inside knowledge of how the process of publishing works, from the sending of the paper to the publisher, receiving a revised copy, resending and so forth.  It is a long process and I now feel that I have gained a better understanding of research and have knowledge that I can apply to future publications.

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