Evolutionary arms race

An evolutionary arms race is when two species (or populations) are so linked that a change in one indirectly causes a change in the other.In the sense that, the selection pressure on the second partner changes, and counters the change in the first partner. It is a metaphor drawn from the so-called arms race between the West and the Soviet Union, after the World War II. Evolutionary arms races are a kind of coevolution.

 Examples 

 Predator-prey 
Predatorprey evolution is the classic example. If a predator gains a new advantage, the prey must answer with a new defense.

Conifers are one example. They grew tall, to some extent out of the reach of sauropod dinosaurs. Dinosaurs grew taller and continued eating the conifers.Bakker, Robert T. 1986. The dinosaur heresies: new theories unlocking the mystery of the dinosaurs and their extinction. Morrow, New York. Chapter 9 When dinosaurs invented flowers. p181 "The warfare between plants and herbivores...".

Gazelles and cheetahs both run very fast, which helps them catch prey. Both have continued to evolve changes which increase their running speed and thus their hunting abilities. This is another example of predator-prey evolution.

The rough-skinned newt and the garter snake interact to impact toxin resistance, according to a well-researched case study. Where the two species live together, the newt produces more toxin, and the snake has evolved to resist it; where they live separately the newt toxin is milder, and the snake has little resistance. The snakes pay a price for their resistance: their digestion and body metabolism is slower than related species. According to one source: "Really resistant snakes have slower crawl speeds than snakes with little or no resistance".Science DailyGarter snake info

 Parasite-host 
Parasitehost evolution is another classic.Price, Peter W. 1980. Parasites. Princeton University Press, Princeton N.J. p34: "The stepwise coevolutionary process results in extreme specialization and complex defense mechanisms". As a host species splits into two, so do its parasites. And when the host immune system defends against the parasites, so they adapt and survive.

 Sexual selection 
Sexual selection can be a kind of evolutionary arms race.

Female mating preferences were responsible for the evolution of male secondary sex characteristics.Andersson M 1994. Sexual selection. Princeton Univ Press, Princeton, NJ. Selection is between males in species where female choice is the pairing method.

Sexual conflict between breeding partners is quite common.Arnqvist G. and Rowe L. 2005. Sexual conflict. Princeton University Press, Princeton New Jersey The basic interests of the male and female can be quite different, and each develops adaptations to get the best 'deal' in terms of offspring. Males: their interest is to mate with a large number of completely faithful females, thus spreading their genes widely in the population. Females: Their interest is to mate with a large number of fit males, thus producing a large number of fit and varied offspring.Schilthuizen, Menno 2001. Frogs, flies and dandelions: the making of species. Oxford University Press, p92. Crudgington H. & Siva-Jothy M.T. 2000. Genital damage, kicking and early death. Nature. 407: 855-856.

 References 

Category:Coevolution
Category:Metaphors referring to nature