Are laboratory studies of life extension misleading us?

[Guest guest]

Interesting NYTimes article on how evolution in laboratory animals may be

affecting the results of study on them, including life extension studies:

Laboratory Life

By OLIVIA JUDSON

Here's a problem: evolution never stops.

Imagine you're a wild fruit fly, of the species Drosophila melanogaster. You're

happily feasting on some yeast that's growing on rotting fruit when, whoomf, you

get sucked into a bottle and taken to a laboratory. From now on, this is your

home.

Life in a bottle — or cage — is different from life in the wild. In nature, for

example, fruit flies reproduce throughout their adult lives. Often, in the

laboratory, they do not: flies grown in bottles may only be allowed to reproduce

for the first five or six days after emerging from the pupa. (Wild flies can

live for more than 80 days.) In nature, flies choose their mates. Often, in the

laboratory, they do not: they are often assigned to one, and that one may be a

close relative. On top of that, the food is different; infectious diseases are

rare; predators are absent.

In short, the pressures of daily life have been transformed — and traits that

were an advantage Out There may no longer be so Inside. Similarly, traits that

would have killed you in the wild may help you get along inside a bottle.

If, for example, older flies are never allowed to reproduce, the ability to lay

eggs later in life becomes irrelevant, so there's nothing to prevent the

appearance of mutations that interfere with that ability. Indeed, if those

mutations increase early fertility, they may even be favored: the most fecund

young flies are likely to leave the most descendants.

Thus, the switch from the wild to the laboratory immediately alters the

evolutionary trajectory of a population — and sure enough, within a few

generations, laboratory-bred life-forms become noticeably different from their

wild cousins.

Exactly what happens depends on how the organisms are kept — different rearing

methods create different evolutionary forces. But in general, laboratory

Drosophila melanogaster evolve shorter lifespans than wild flies; they become

less able to cope with stresses like starvation or desiccation; and their

pattern of fertility changes. As you'd expect, females reared in bottles evolve

to be hugely fecund as young flies but much less so when they are older.

Also as you'd expect, laboratory evolution is not unique to Drosophila

melanogaster. In the wasp Nasonia vitripennis, females descended from a long

line of laboratory wasps evolve to be more prone to promiscuous sexual behavior

than wild wasps. In the Mediterranean fruit fly, Ceratitis capitata,

laboratory-reared females evolve to be less fussy about who they mate with, and

male sexiness changes. Wild female medflies don't find laboratory-reared males

as attractive as they find wild males. Mexican fruit flies, Anastrepha ludens,

have the same problem: laboratory males have evolved in such a way that they are

less popular with wild females.

Mice show a host of changes, too. Compared to their wild relations, laboratory

mice are typically bigger, more docile, reach sexual maturity earlier and die

younger. Some of these changes can appear quickly: one study found that the

ability to reproduce later in life declined within 10 generations of the mice

being bred in the laboratory.

Intriguingly, laboratory mice also have longer telomeres than wild mice.

(Telomeres are the segments of DNA at the ends of chromosomes; they are thought

to play a role in aging and cancer.) Since no one is deliberately breeding mice

for extra-long telomeres, this must arise as some consequence of laboratory

life. But what?

That's not clear. One possibility is that it's due to inbreeding — for lab mice

are often highly inbred. Consistent with this, one study of white-footed mice,

Peromyscus leucopus, found that, when animals were forced to inbreed, telomeres

lengthened substantially in fewer than 30 generations — although why this should

be so is entirely mysterious.

All of which is fascinating. But does it matter?

That depends. For some scientific problems, the fact that laboratory life-forms

evolve substantial differences from their wild relatives is irrelevant. For

others, however, it matters a lot.

Let me give you two examples. Adaptation to the laboratory — or to captivity

more generally — can make it much more difficult for organisms to thrive if they

are later released to the wild. This has important implications for the

conservation of endangered animals and for the control of pests. Captive

breeding programs have been important tools for re-establishing wild populations

of species such as the California condor; but not all programs are successful.

Genetic changes in captivity may be one reason. Similarly, many pest control

programs depend on the " sterile male technique, " whereby males are bred in the

laboratory, sterilized, then released into nature to mate with wild females. For

this to work, the wild females must find the laboratory males attractive.

Changes in mating behavior like the ones I mentioned earlier can, therefore,

quickly reduce the effectiveness of the approach.

A second area where laboratory evolution can be a serious problem is in the

study of subjects like the evolution of aging, and the diseases associated with

it. For example, the study of laboratory populations may give a misleading

impression of how easy it is to extend lifespans: since laboratory organisms

tend to have unnaturally short lifespans, discovering ways to make them live

longer may not be especially informative. We may simply be reversing the

unnatural shortening that we created in the first place, a view supported by the

fact that selection to increase lifespan in laboratory populations often simply

restores it to levels seen in the wild.

Such realizations have led an increasing number of scientists to argue that

long-established laboratory populations are " suspect starting material " for

understanding aging, and that comparisons with wild populations " support the

pessimistic interpretation that laboratory-adapted stocks of rodents may be

particularly inappropriate for the analysis of the genetic and physiological

factors that regulate aging in mammals. "

For some subjects, it's better to go wild.

http://opinionator.blogs.nytimes.com/2010/04/13/laboratory-life/