The term “fitness” congers images of six-pack abs, yoga poses, and 90’s spandex leotards (for me, anyway). But those images can be misleading when it comes to understanding evolutionary fitness.
Good “fitness” in evolution means “a good fit.” Organisms that fit well in their environmental niche spend less energy just trying to survive; they have more energy left over for reproduction. So fitness is often measured by the number of offspring produced.
A sloth is well camouflaged with its slo-mo movement. Many predators detect prey by movement (if we stick with the 90’s imagery, remember the T.rex in Jurassic Park “can’t see us if we don’t move”). Low metabolism in sloths means very low food requirements. One study measured sloth metabolic rate at 174 kJ (kilajoules) per day. (1) Just for comparison, an average human requires 6000-7000 kJ per day.
- Nagy, KA and GG Montgomery. 1980. Field metabolic rate, water flux, and food consumption in three-toed sloths (Bradypus variegatus). Journal of Mammalogy 61(3)465-472
Australian Water Dragons (Intellagama lasueurii) lounge and bask around pond edges at the University of Queensland, where I saw this handsome fellow. The colorful markings under his chin advertise his masculinity to the local lizard ladies… and to rival males too.
Researchers painted a model Water Dragon (actually a plastic iguana with a few glued-on additions) with either brown markings or red markings. (1) The toy was then introduced among resident Water Dragons to record their response to the intruder. When the toy had brown markings, the real Dragons attacked faster and more often.
Those fancy red and yellow stripes attract mates, but also deter rivals.
- Baird, TA, TD Baird, and R Shine. 2013. Showing Red: Male Coloration Signals Sam-Sex Rivals in an Australian Water Dragon. Herpetologica 69(4) 436-444
Many animals display disruptive coloration, a pattern that visually breaks up the edge of their shape. For example, Mabee’s Salamander (Ambystoma mabeei) wears speckles like frost along its side. And it was an artist who first described this biological phenomenon – Abbott Thayer. (1) His studies of these patterns influenced the use of camouflage in the military.
In a recent fun study, researchers placed graphic squiggle-snakes on a mock-leaf background or plain background. They manipulated the coloration – solid, patterned, or patterned with bold and bright edges to the shapes. The edge-enhancement made the squiggle-snakes more difficult to spot on a leafy background. It also confused the observer about the shape of the snake when it was on a plain background.
- Behrens RR. 2008. Revisiting Abbott Thayer: non-scientific reflections about camouflage in art, war and zoology. Philosophical Transactions of The Royal Society 364(1516) 497-501
- Sharman RJ and PG Lovell. 2019. Edge-enhanced disruptive camouflage impairs shape discrimination. i-Perception 10(5) 1-9
When a predator approaches, options are limited – especially if you’re a tadpole. The woodfrog tadpole (Rana sylvatica) is known to stop swimming and sink to the pond bottom, an action called “freezing behavior.”
In one study, researchers exposed woodfrog embryos to some water from a predator’s tank with or without an injured tadpole (1). When the embryos hatched, the ones that had smelled both the predator and injured relative showed very reduced activity (freezing behavior) if re-exposed to just predator-water.
In mice, freezing behavior is affected by the size and speed of an object. Video showing lab mice exposed to various dots indicates that small, slow objects trigger mice to freeze. When exposed to terrifying large dots, mice take off.
- Mathis, A., M.C.O. Ferrari, N. Windel, F. Messier, and D.P. Chivers. 2008. Learning by embryos and the ghost of predation future. Proc Biol Sci. 275(1651): 2603-2607.
A ring species includes a series of populations set around a large barrier. Each population is a little different from its neighbors, but those differences add up as the distance increases. So, as the populations meet each other on the other side of the barrier, they’ve built up so many differences that they no longer breed. It’s a wonderful example of evolution (parapatric speciation, if you’re interested).
This cutie is the Ensatina salamander which surrounds the San Joaquin valley of California.
It’s a pretty simple process really.
STEP 1: I start with an object (either from life or from one of my photos) and draw a rough sketch in light pencil.
STEP 2: Outline in pen. I keep the lines I like, change the ones I don’t. And add a little more detail. The most fulfilling part of this process is erasing those pencil-sketch lines. The drawing really pops then!
I use Micron pens (waterproof – that’s important!).
STEP3: Add a light wash of watercolor.
Note: one aspect of my process is very unusual. For these little sketches, I use a 5×7″ sketchpad – not watercolor paper (crazy!). The water soaks in fast so I work pretty quickly.
STEP4: Add background.
By the way, I only use 12 colors: the reds (alizarin crimson & windsor red), yellows (new gamboge & aureolin), blues (antwerp & ultramarine), and six colors I just really like (yellow ochre, burnt sienna, cobalt turquoise, sap green, payne’s grey and perylene violet)
STEP5: Layer in another round of color. Intensify some areas, add color details to others, emphasize shadows.
STEP6: Sign, scan, crop, and upload.
Each piece takes 1-4 hours to create, the majority of that is spent on STEP2 (inking).
One very important (and unseen) part of the process is practice. I’ve been learning, trying (messing up), and experimenting for almost 30 years now. While most people think learning how to use watercolors is the key, it’s not. Learning how to draw is the most valuable tool. Once you have that firm foundation, the rest is icing. Enjoy!