Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [39]
Scientists have a number of theories about how genetic variation is maintained in populations, ranging from the simple notion that selection may not have had a chance to weed out loser genes in some cases, to elaborate ideas about interactions among the genes that happen to be linked together on the same chromosome. Many of these explanations apply to the maintenance of different personalities, too, particularly the idea that advantages and disadvantages trade off against each other. Take the spider femme fatales, for example. Being exceptionally eager to snag a passing fly means that you are more likely to survive another day, which is obviously favored by natural selection: you get moved up a notch on the "likely to live long enough to have babies" scale. But being too rapacious in your treatment of a potential mate might mean lower likelihood of getting enough sperm to fertilize your eggs, which tips the balance in the other direction. On the other hand, a more suave approach to mates may be irretrievably associated with a more lackadaisical feeding style. Each personality type has its pluses and minuses under different circumstances, and they can all coexist because they each make trade-offs in different ways.
Of course, having a particular set of personality characteristics doesn't necessarily mean giving something up. Some individuals are just all-around winners, and if a behavior is advantageous all the time, then the individual exhibiting it makes out like a bandit and never pays the price. Being particularly active, for example, might mean that an animal finds more food, is more likely to be chosen as a mate, and is first in line for shelter when a storm threatens. Although our Puritanical sides may argue that everything has its price, sometimes that price is negligible. In cases where a trade-off within an individual doesn't exist, one might expect that selection would favor those lucky few, and variation might indeed decrease in the population.
Alternatively, having a particular personality type may be advantageous if your environment is not very predictable. Andy Sihlikens it to investing in the stock market; if you don't have any information on what is going to happen, it may be better to keep your money where it is than try to play the market, a particularly prescient point in today's economy. For an animal, being predator-wary all the time can be a good strategy when the actual likelihood of being eaten is unknown, a kind of better-nervous-than-sorry attitude. If on the other hand one can be reasonably sure that predators aren't lurking, then one can let oneself go a bit more, as it were, and act one way under some circumstances, and another way under others.
Yet another way that behavioral variation can be maintained is by having the success of some types depend on how common other types are in a population. If a group of, say, water striders is mainly composed of lethargic, cautious individuals, then being a fast-moving brave strider will be advantageous as long as the reckless types are rare, because the rare ones can dart in and grab food while everyone else is just gathering their thoughts. Once the fast movers reproduce and rise in abundance, however, the slower bugs can in turn do well, perhaps because their type is less likely to be nabbed by a predatory spider. Then the slow individuals do better, and so on; both types can persist over time, even if their relative numbers fluctuate.
Similarly, several researchers, most notably Judy Stamps at the University of California at Davis, suggest that personality trade-offs can have repercussions for how fast an animal