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For birds, predation linked to faster aging

May 1, 2014
Courtesy of the Max Planck In­sti­tute for Or­nith­ol­o­gy
and World Science staff

Bird spe­cies that suf­fer from more preda­t­ion tend to age faster, a new study finds. That sup­ports an old the­o­ry in­tend­ed to ex­plain why an­i­mals have such widely var­y­ing life­spans, sci­ent­ists claim.

The re­search­ers could­n’t say wheth­er the find­ings might help ex­plain hu­man life­span as well. But it seems to hold “at least in birds, where the nec­es­sary da­ta are avail­a­ble for many spe­cies”—some 1,400 of them, whose longe­vi­ties vary by some 25-fold, ac­cord­ing to a state­ment from the Max Planck In­sti­tute for Or­nith­ol­o­gy in Seewiesen, Germany, where the study was con­ducted.

A water thick-knee (Burhinus vermiculatus) de­fends its nest ag­ainst a mon­i­tor liz­ard. (© MPI for Orni­tho­logy See­wies­en/ Wolf­gang Goy­mann)


“We were able to con­firm” the the­o­ry “on a broad geo­graph­i­cal scale,” said Mi­hai Valcu, a co-author of the stu­dy, pub­lished on­line April 25 in the jour­nal Ecog­ra­phy.

Some fish, tur­tles or even in­ver­te­brates can live to hun­dreds of years, while the ne­on pyg­my gob­y—a small fish—reaches ripe old age at only 60 days. In birds, par­rots such as the Sulfur-crested cock­a­too can live to over 100 years, while the small Al­len’s hum­ming­bird tops out at just four.

The clas­si­cal “evo­lu­tion ary the­o­ry of age­ing,” pro­posed by ev­o­lu­tion­ary bi­ol­o­gist George C. Wil­liams over 50 years ago, claims shorter life­spans will af­flict adult an­i­mals that suf­fer high preda­t­ion, ex­po­sure to par­a­sites and oth­er ran­domly oc­cur­ring events.

One way to look at why, is that na­ture or ev­o­lu­tion won’t both­er ex­pend­ing much “ef­fort” to ex­tend the life­span of crea­tures that will probably die young an­y­way. Of course, that’s not the real rea­son, as ev­o­lu­tion is­n’t con­sid­ered a con­scious pro­cess. Ev­o­lu­tion oc­curs when in­di­vid­u­als have more off­spring than oth­ers as a re­sult of hav­ing more “favora­ble” genes. This lets them spread their favora­ble genes through the popula­t­ion, so that grad­u­al­ly, whole spe­cies change. The way those genes arise in the first place is just as any new genes do: muta­t­ion.

So the ag­ing the­o­ry can be ex­pressed like this: if a spe­cies suf­fers high preda­t­ion or rates of paras­itic at­tack, most in­di­vid­u­als will al­ready be killed be­fore the rare muta­t­ions that cause health­i­er age­ing can make an ev­o­lu­tion­ary dif­fer­ence.

Mi­hai Valcu and Bart Kem­pe­naers from the in­sti­tute used a large da­tabase on es­ti­mates of max­i­mum life-span of bird spe­cies. Us­ing a com­plex sta­tis­ti­cal anal­y­sis they found that max­i­mum longe­vity goes down as the num­ber of pred­a­tor spe­cies with­in the same ar­ea goes up. The rela­t­ion­ship held when oth­er life his­to­ry traits known to in­flu­ence longe­vity, such as size and clutch size, were tak­en in­to ac­count. It al­so held no mat­ter how the anal­y­sis was done: at the spe­cies lev­el, at a fin­er re­gion­al scale (groups of spe­cies with­in a cer­tain ar­e­a) or even when com­par­ing en­tire “biore­gions,” they said.


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Bird species that suffer from more predation tend to age faster, a new study finds—supporting an old theory intended to explain why animals have such widely varying lifespans. The researchers couldn’t say whether the findings might help explain human lifespan as well. But it seems to hold “at least in birds, where the necessary data are available for many species”—some 1,400 of them, whose longevities vary by some 25-fold, according to a statement from the Max Planck Institute for Ornithology in Seewiesen, Germany, where the study was conducted. “We were able to confirm” the theory “on a broad geographical scale,” said Mihai Valcu, a co-author of the study, published online April 25 in the journal Ecography. Some fish, turtles or even invertebrates can live to hundreds of years, while the neon pygmy goby—a small fish—reaches ripe old age at only 60 days. In birds, parrots such as the Sulfur-crested cockatoo can live to over 100 years, while the small Allen’s hummingbird tops out at just four. The classical “evolutionary theory of ageing,” proposed by evolutionary biologist George C. Williams over 50 years ago, claims shorter lifespans will afflict adult animals that suffer high predation, exposure to parasites and other randomly occurring events. One way to look at why, is that nature or evolution won’t bother expending much “effort” to extend the lifespan of creatures that will probably die young anyway. Of course, that’s not the real reason, as evolution isn’t considered a conscious process. It occurs automatically when individuals have more offspring than others as a result of having more “favorable” genes. This lets them spread their favorable genes through the population, so that gradually, whole species change. The way those genes arise in the first place is just as any new genes do: mutation. So the aging theory can be expressed like this: if a species suffers high predation or rates of parastic attack, most individuals will already be killed before the rare mutations that cause healthier ageing can make an evolutionary difference. Mihai Valcu and Bart Kempenaers from the institute used a large database on estimates of maximum life-span of bird species. Using a complex statistical analysis they found that maximum longevity goes down as the number of predator species within the same area goes up. The relationship held when other life history traits known to influence longevity, such as size and clutch size, were taken into account. It also held no matter how the analysis was done: at the species level, at a finer regional scale (groups of species within a certain area) or even when comparing entire “bioregions,” they added.