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
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.
Around 5000 species of mammals inhabit the Earth today, and almost all make their own Vitamin C from simple sugar. Your dog doesn’t need orange juice to live a scurvy-free life.
Human ancestors, and most other primates, lost the genetic ability to perform this impressive biochemical feat around 61 million years ago . How did they/we survive?
Short answer – don’t know (yet). It’s accepted that these primate ancestors were insectivores. Insects, in general, do not contain high levels of Vitamin C . But, insects do like hanging around flowers, fruits, and leaves. An insect could be noshing on some C-rich fruit (insects do require Vitamin C for development and reproduction) when the primate ate it. Or the primate could accidentally eat plant material while aiming for the insect.
What about other Vitamin C deficient mammals – Guinea pigs and bats? Guinea pigs… and fruit bats… certainly get plenty of Vitamin C in their diet. What about insect-eating bats? Well, maybe they aren’t as Vitamin C inept as we thought . And, we deficients may be able to survive on less Vitamin C and/or recycle the little we do ingest .
- Lachapelle M.Y. and G. Drouin. 2011. Inactivation dates of the human and guinea pig vitamin C genes. Genetica 139:199–207.
- Kourimska L. and A. Adamkova. 2016. Nutritional and sensory quality of edible insects. NSF Journal. 4:22-26.
- Troadec, M. and J. Kaplan. 2018. Some vertebrates go with the GLO. Cell. 132(6)921-922.
With all the beautiful berries available now, I’ve been seeing more fruit flies hanging around the kitchen. Annoying? Yes. Ruining my strawberries? Nope. Fruit flies lay their eggs on damaged or rotting fruit. So they’re only interested in the pieces that are going bad. I’m ok with that.
But consider a fruit fly who lays her eggs on fresh fruit. She’d have the agricultural community freaking out. Just imagine the risk to berry crops. Actually, you don’t have to imagine because scientists have already done the calculations for you: it’s potentially $2.6 billion of risk (1).
Evolution has already dealt this stunning set of cards to Drosophila suzukii, the spotted-wing drosophila (2). The females have an ovipositor (the anatomical structure that deposits eggs) that looks like a serrated knife. Unlike the common fruit fly in your house, this species’ egg-laying parts can cut through the skins of raspberries, strawberries, blueberries, cherries, and grapes.
Want to learn more about the spotted-wing drosophila? IFAS at the University of Florida has a great info page on the little beastie (with horrifically gorgeous pictures, by Martin Hauser, of that ovipositor – if you haven’t seen fruit fly genitalia yet, you are missing out).
p.s. Thanks to Dr. Nadia Singh for introducing me to Drosophila suzukii.
- Walsh, Douglas, M. Bolda, R. Goodhue, A. Dreves, J. Lee, D. Bruck, V. Walton, S. O’Neal, F. Zalom. 2011. Drosophila suzukii (Diptera: Drosophilidae): Invasive Pest of Ripening Soft Fruit Expanding its Geographic Range and Damage Potential. Journal of Integrated Pest Management. 2(1): G1-7.
- Atallah, L. Teixeira, R. Salazar, G. Zaragoza, A. Kopp. 2014. The making of a pest: the evolution of a fruit-penetrating ovipositor in Drosophila suzukii and related species. Proceedings of the Royal Society B: Biological Sciences, 281 (1781)