When we study animals (or any organism really), we as scientists have a tendency to think of them as little replicates of each other. In one sense, this is a productive way of thinking: we need to group our organisms to allow us to analyze them. The most basic unit of biological grouping is the species, a group of organisms that share a common gene pool. When we look in a guide book to help us identify an organism we’ve found, we often see one picture or diagram which represents an idealized individual (perhaps even a Platonic form!) of that species; it has all of the important marks that can be used to identify an individual of that species and rarely shows any extraneous details. If the species of interest happens to be sexually dimorphic, we might even get two pictures, one of each sex!
An example of the “idealized” animals shown in a guidebook (in this case, my well-used copy of Reptiles and Amphibians of Eastern/Central North America, by Conant and Collins)
Of course, as scientists, we can also designate different categories within a species (males vs. females, adults vs. juveniles, etc.) and look for differences between them in whatever characteristics we are studying. But the real world of organisms is far messier than the placing of our individual organisms into these mental bins. Many of the animals we encounter have very unique traits, or phenotypes, as a result of their real-world experiences; I’ve highlighted some examples from our field work below:
A basic fact of life for reptiles is the periodic shedding of their skin or ecdysis. We often encounter lizards in various stages of ecdysis; some of them look fairly amusing or just untidy as they carry around large quantities of dry and fluffy skin before it has completely rubbed off. When we care for lizards that are shedding their skin, we make sure to keep them well hydrated and mist them daily to ensure that they don’t have any problems shedding.
Two examples of Eastern fence lizards that are in the process of shedding their skins. The lizard on the left has just started to shed in the armpits, while the male lizard on the right has only his belly left to shed (you can see the blue patches peeking out from behind the old skin).
When snakes shed their skins, they also shed the protective scales over their eyes, called eye caps. However, as these scales begin to separate from the skin underneath, a snake’s eyes can become milky or cloudy. Not surprisingly, this impairs the snake’s vision and can result in them being more twitchy, bitey, or aggressive. In this case, the shedding state of an individual can influence its behavior. In other animals, such as birds, molting (shedding feathers) is known to have an effect on stress levels and can also influence behavior. When using an animal like this for research, it may be important to note this individual level variation.
A Corn snake (Pantherophis guttatus) getting ready to shed. While its eyes are milky, this fellow was quite docile and happy to pose for a few pics.
One herpetological fact that many people are familiar with is that many species of lizards can “lose their tails.” This doesn’t mean that the lizard has misplaced a part of itself but rather that its tail will detach from its body if grabbed by a predator (or, in many cases, if handled too roughly by a human). Lizard tails are adapted to break on their own (i.e. they are not “ripped off”) and do so quickly and with little loss of blood, a process called autotomy. The “lost” tail, which is often brightly colored or boldly patterned, may proceed to wiggle around, distracting the predator (which may get a tasty tail snack), while the lizard itself makes its getaway. While losing a tail is costly for a lizard, as it represents a large loss of stored energy, it is certainly better than being eaten! We often find lizards that have lost part of their tails and are in the process of regrowing them. Most of the time, this process goes along without a hitch; after a few months, the lizard will have regrown its tail and replenished the energy lost to the predator. Sometimes, however, things go differently:
This eastern fence lizard seems to have had an incomplete, or messy, break. While this lizard isn’t in any danger, it’s unlikely its tail will ever completely regrow.
This fence lizard lost the tip of its tail but something has gone awry with the regrowth process.
Sometimes when a tail grows back, things go a bit strangely. This anole was probably attacked by a predator (maybe a bird or snake) as we can see a series of small injuries along the length of its tail. The tail was broken at the tip (bottom of picture) and likely partially broken and healed at a midpoint. However, this partial break, in addition to healing the original tail, also grew an “extra” tail, resulting in a split tail, or bifurcation.
This Green Anole (Anolis carolinensis), now has an extra-fancy double tail.
We may also see other examples of predation in a populations such as healed wounds and/or missing limbs. Nature really is red in tooth and claw!
Lizards like this guy are invariably called “Stumpy” and are not uncommon (we have two this year!). Interestingly, both Stumpys are large, healthy males that seem to suffer no ill-effects from missing their hands/feet.
Fence lizards are amazing survivors. This male probably took a hit from a bird of prey or other predator but healed up and was back out looking for ladies.
Looking at the incidences of broken tails, scars, and other signs off attack can be valuable data; they can give us information about the predation pressure experienced by lizards in a certain population. In a sense, we’re seeing the ghosts of predators past. Not surprisingly, we often see these signs more in male lizards than females. Male lizards are more conspicuous, being more brightly colored and perching in high, open spaces. They probably choose these sites to facilitate surveillance of their territories and to aid in advertising their attractive blue chin and chest patches to any females that might be nearby. However, this behavior is risky business, as these signals to other lizards are likely to be intercepted by other organisms in the area. Our experience is that males are often much easier to find and catch (sometimes they will even do pushups at us or attack our nooses instead of running away while we are trying to catch them!). Thus, it’s no surprise that these show-offs might be tempting targets for any predators in their area.
We also see some individuals whose abnormal appearances/phenotypes are likely due to genetic or developmental issues. For instance, the lizard shown below only had four toes on each of his left feet, and some of those toes were missing pieces or malformed. The lack of the usual number of toes (five) is like due to some developmental issue and is generally rare (we only find 1 or 2 lizards/year showing similar conditions). However, we often find fence lizards, especially males, with missing toes. These toes can also give us information about the environments experienced by our lizards. They are likely lost in male-male combat when males defend their territories from intruders or compete for access to females. We have also seen males missing toes (and even feet!) due to damage from fires, and in colder areas, lizards may lose toes due to harsh winters and frostbite.
This lizard has a malformed left foot with only four toes.
His back left foot also only had four toes, but some of these are missing (as are some on his right foot; not shown). These are likely due to male-male combat.
I hope you’ve enjoyed seeing how each lizard (and other organism) we might come across is an individual with a unique background. While we may not be able to research some of these traits (it’s hard to analyze things that are rare or unique), I think it’s important to remember that organisms have individual histories. Sometimes these little differences can provide us with useful data, but I also find it fascinating to see the amazing variation in the natural world. Not knowing what you’ll find when you catch the next lizard, flip the next rock, or catch the next insect is part of what makes being a scientist one of the coolest jobs I can think of!
The Lizard Log 