What are trade-offs and why do they exist?

Before I delve into the several insane examples of animals with intriguing tradeoffs, I feel it is important to introduce some of the main concepts I will be exploring on my blog. We’ll start with the obvious question: What is a trade-off? Agrawal, Conner and Rasmann (2010) define it as being “...Any case in which fitness cannot be maximized because of competing demands on the organism.”In the language of evolutionary biology, the term fitness is defined as being “The extent to which an individual contributes genes to future generations” (Freeman & Herron 2014), that is, the ability for it to survive and reproduce. There have been, and continue to be, several studies that investigate the trade-offs that limit the adaptive potential of organisms (Agrawal, Conner and Rasmann 2010). There are life history trade-offs (life history traits are defined as “...the traits that affect an organism’s schedule of reproduction and survival” (TB1). In these cases there are costs associated with frequency of reproduction, number of offspring and investment in parental care” (Reece et al. 2011). There are also adaptations that cause the loss of optimised defence mechanisms against predators, and in fact sometimes make them more obvious and prone to getting eaten.

Sounds like hard work. So why do trade-offs exist? Why doesn’t natural selection act upon organisms until they reach a perfect form? Well there is a hypothetic organism termed the “Darwinian demon,” which has the ability to simultaneously maximise all aspects of its fitness by reproducing directly after being born, producing infinite amounts of offspring and living forever (Law, 1979). This would occur in nature if the evolution of species was unconstrained, which is not the case. Natural selection cannot and does not operate in a way that leads to perfection by optimising all traits at the same time. It instead operates on a “better than” basis, which enables the organism to suit its current environment and withstand selective pressures. This can be observed in the many ‘imperfections’ that organisms have adapted over time, in an unconscious quest to balance traits that enable them to better be able to survive and reproduce (Reece et al. 2011).

A male peacock displaying. Photographer: Chris Jacobs

Although we see flaws in nature’s design of these organisms, there has to be a reason why they still exist. For example, the colourful display of a peacock’s feathers to attract peahens may be costly in the sense that it doesn’t really aid him in camouflage or escape from predators, however the reproductive advantage it creates must outweigh the cost. This is another concept known as sexual selection (Reece et al. 2011) and will be talked about in my subsequent blogs.

 References:

1. Agrawal, A. A., Conner, J.K., & Rasmann, S., 2010, ‘Tradeoff s and Negative Correlations in Evolutionary Ecology’, Evolution since Darwin, vol. 1, no. 150, pp. 243-268
2. Freeman, S., Herron, J.C., 2014, Evolutionary Analysis, Pearson Education Limited, Edinburgh.
3. Law, R. 1979, ‘Optimal Life Histories Under Age-Specific Predation,’ The American Naturalist,  Vol. 114, No. 3, pp.399-417
4. Reece, J.B., Meyers, N., Urry, L.A., Cain, M.L., Wasserman, S.A., Minorsky, P.V., Jackson, R.B & Cookie, B.N. 2011, Campbell Biology, 9^th Edition, Pearson Education, Australia
5. http://www.science-explained.com/blog/2013/08/30/insect-rodeo/ (16^th March 2014)