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When evolution isn’t so slow and gradual

June 2, 2009
Courtesy University of Chicago Press Journals
and World Science staff

What’s the se­cret to sur­viv­ing dur­ing times of en­vi­ron­men­tal change? Evolve…quickly. A new re­port in the sci­en­tif­ic jour­nal Amer­i­can Nat­u­ral­ist says gup­py popula­t­ions in­tro­duced in­to new habi­tats de­vel­oped new and ad­van­ta­geous traits in just a few years.

Wild guppies. A new re­port says gup­py popula­t­ions in­tro­duced in­to new habi­tats de­vel­oped new and ad­van­ta­geous traits in just a few years. (Im­age cour­tesy Ha­waii DAR)


Evolution occurs when a po­pu­la­tion changes ge­ne­tic­ally because its en­vi­ron­ment is more fa­vor­able to some genes than to others. The ad­vant­ag­eous genes there­fore spread through the po­pu­la­tion be­cause those who have them are able to out­live and out-re­prod­uce their peers.

Sci­en­tists led by Swanne Pam­e­la Gor­don of the Un­ivers­ity of Cal­i­for­nia, Riv­er­side, stud­ied 200 gup­pies that had been tak­en from the Yar­ra Riv­er in Trin­i­dad and in­tro­duced in­to two dif­fer­ent en­vi­ronments in the near­by Da­mier Riv­er, which pre­vi­ously had no gup­pies. One Da­mier en­vi­ronment was predator-free. The oth­er con­tained fish that oc­ca­sion­ally snack on gup­pies.

Eight years af­ter their in­tro­duc­tion, the team re­vis­ited the Da­mier gup­pies to see what adaptive changes they might have pick­ed up in their new en­vi­ronments. 

The re­search­ers found that the fe­males had al­tered their re­pro­duc­tive ef­fort to match their sur­round­ings. In the en­vi­ronment where preda­tors were pre­s­ent, fe­males pro­duced more em­bryos each re­pro­duc­tive cy­cle. This makes sense be­cause where preda­tors abound, one might not get a sec­ond chance to re­pro­duce, Gor­don and col­leagues ar­gued. In less dan­ger­ous wa­ters, fe­males pro­duced few­er em­bryos each time, thus ex­pend­ing few­er re­sources on re­pro­duc­tion.

Fi­nal­ly, the re­search­ers wanted to see if these adaptive changes ac­tu­ally helped the new popula­t­ion to sur­vive. So they took more gup­pies from the Yar­ra, marked them, and put them in the Da­mier along­side the ones that had been there for eight years. They found that the adapted gup­pies had a sig­nif­i­cant sur­viv­al ad­van­tage over the more re­cently in­tro­duced group.

In par­tic­u­lar, ju­ve­niles from the adapted popula­t­ion had a 54 to 59 per­cent in­crease in sur­viv­al rate over those from the newly in­tro­duced group. In the long run, sur­viv­al of ju­ve­niles is cru­cial to the sur­viv­al of the popula­t­ion, the re­search­ers say.

The fact that fit­ness dif­fer­ences were found af­ter only eight years shows just how fast ev­o­lu­tion can work—for short-lived spe­cies an­y­way. “The changes in sur­viv­al in our study may in­i­tially seem en­cour­ag­ing from a con­serva­t­ion per­spec­tive,” the au­thors write. “But it is im­por­tant to re­mem­ber that the elapsed time frame was 13-26 gup­py genera­t­ions. The cur­rent re­sults may there­fore pro­vide lit­tle sol­ace for bi­ol­o­gists and man­agers con­cerned with longer-lived spe­cies.”


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What’s the secret to surviving during times of environmental change? Evolve…quickly. A new report in the scientific journal American Naturalist said guppy populations introduced into new habitats developed new and advantageous traits in just a few years. This is one of only a few studies to look at adaptation and survival in a wild population, the researchers said. Led by Swanne Pamela Gordon of the University of California, Riverside, the scientists studied 200 guppies that had been taken from the Yarra River in Trinidad and introduced into two different environments in the nearby Damier River, which previously had no guppies. One Damier environment was predator-free. The other contained fish that occasionally snack on guppies. Eight years after their introduction, the team revisited the Damier guppies to see what adaptive changes they might have picked up in their new environments. The researchers found that the females had altered their reproductive effort to match their surroundings. In the environment where predators were present, females produced more embryos each reproductive cycle. This makes sense because where predators abound, one might not get a second chance to reproduce, Gordon and colleagues argued. In less dangerous waters, females produced fewer embryos each time, thus expending fewer resources on reproduction. Finally, the researchers wanted to see if these adaptive changes actually helped the new population to survive. So they took more guppies from the Yarra, marked them, and put them in the Damier alongside the ones that had been there for eight years. They found that the adapted guppies had a significant survival advantage over the more recently introduced group. In particular, juveniles from the adapted population had a 54 to 59 percent increase in survival rate over those from the newly introduced group. In the long run, survival of juveniles is crucial to the survival of the population, the researchers say. The fact that fitness differences were found after only eight years shows just how fast evolution can work—for short-lived species anyway. “The changes in survival in our study may initially seem encouraging from a conservation perspective,” the authors write. “But it is important to remember that the elapsed time frame was 13-26 guppy generations. The current results may therefore provide little solace for biologists and managers concerned with longer-lived species.”