A Col­lec­tion of News by Moos


Car­ni­vore births in cap­tiv­ity and in the wild occur at the same time of the year

pub­lished 19 May 2018 | mod­i­fied 19 May 2018

Repro­duc­tive sea­son­al­ity is a fixed char­ac­ter­is­tic of a species — Uni­ver­sity of Zurich researchers have now found that car­ni­vores in cap­tiv­ity give birth at the same time of year as their coun­ter­parts in the wild. In some species, the ges­ta­tion period is short­ened in order to pro­vide ideal con­di­tions for the off­spring, while for oth­ers it is extended.

Canadian lynxThe opti­mal time of year for the repro­duc­tion of the lynx is very pre­cise, with the Cana­dian lynx hav­ing the most pro­nounced sea­sonal char­ac­ter­is­tics.
Image: Tier­park Zürich

Many species have a spe­cific mat­ing sea­son when liv­ing in their nat­ural habi­tat. The young ani­mals are usu­ally born in spring when envi­ron­men­tal con­di­tions are opti­mal for their sur­vival, while births at less favourable times such as the start of win­ter are thus avoided. Depend­ing on whether sea­sonal repro­duc­tion is a strong char­ac­ter­is­tic of a species or not, the time period for births will be a longer or a shorter window.

Researchers at the Clinic for Zoo Ani­mals, Exotic Pets and Wildlife at the Uni­ver­sity of Zurich inves­ti­gated the sea­son­al­ity of more than 100 species of car­ni­vores. As it is rather dif­fi­cult to observe births of ani­mals in their nat­ural habi­tat, they eval­u­ated data from 150,000 births that took place in zoos. Zoos con­sis­tently doc­u­ment births and for­ward the infor­ma­tion to the not-​for-​profit organ­i­sa­tion Species360, which col­lects data from zoos all around the world. Their results are pub­lished on 7 May in the Jour­nal Bio­log­i­cal Rhythms.

Sea­son­al­ity is mostly sim­i­lar in zoos and in nature
Until now it was not known whether the sea­son­al­ity of repro­duc­tion in the wild was also main­tained when ani­mals lived in zoos, where the ani­mals have a suf­fi­cient sup­ply of food all year round and can spend the win­ter in heated indoor spaces.

It is sur­pris­ing how closely the zoo data cor­re­lates with that from ani­mals in their nat­ural habitat.

Mar­cus Clauss, Clinic for Zoo Ani­mals, Exotic Pets and Wildlife, Vet­su­isse Fac­ulty, Uni­ver­sity of Zurich, Switzerland

For more than 80% of the species, the time period for births was the same in the zoo as in the wild. “Sea­son­al­ity is an evo­lu­tion­ary fea­ture and thus a fixed char­ac­ter­is­tic of a species – most prob­a­bly through a genet­i­cally deter­mined reac­tion to a sig­nal given by the length of day­light,” adds Clauss. Only a few species – those whose nat­ural habi­tat is in the trop­ics and whose sea­sonal repro­duc­tion is for rea­sons of food avail­abil­ity – start repro­duc­ing all year round when liv­ing in cap­tiv­ity, where food is always plentiful.

Nat­ural habi­tat and repro­duc­tion go together
The car­ni­vores with the most pro­nounced sea­son­al­ity char­ac­ter­is­tics include the red wolf (Canis rufus), the mink (Mustela lutre­ola), the yellow-​throated marten (Martes flav­igula), the wolver­ine (Gulo gulo), the red panda (Ail­u­rus ful­gens), and the Cana­dian lynx (Lynx canaden­sis). The opti­mal time of year for their repro­duc­tion is very pre­cise. In con­trast, repro­duc­tive activ­i­ties of the bush dog (Speothos venati­cus), the jaguar (Pan­thera onca), and the spot­ted hyena (Cro­cuta cro­cuta) are not lim­ited to any par­tic­u­lar time of year. This shows a clear link between the regions which species are native to and their repro­duc­tive behav­iour: The fur­ther a species’ nat­ural habit is from the equa­tor, the more sea­sonal its repro­duc­tive behav­iour will be.

Very short or very long ges­ta­tion peri­ods
The researchers found two fur­ther inter­est­ing pat­terns. Many sea­sonal car­ni­vores have ges­ta­tion peri­ods that are short rel­a­tive to their body size, so that the embryo grows quickly enough between the mat­ing period in fall and the birth date in spring. Oth­ers, how­ever, have extended ges­ta­tion peri­ods so that they give birth at the right time of year. This exten­sion does not occur through a slow­ing down of the embryo growth for exam­ple, but rather through a lim­ited period of dor­mancy dur­ing which the fer­til­ized ovum does not yet get implanted in the womb. “It seems that it is eas­ier for evo­lu­tion­ary processes to speed up the embryo growth than to slow it down,” con­cludes Clauss.

The only excep­tion to this rule is the sea otter (Enhy­dra lutris), the only type of otter to live solely in the ocean. They are native to the coast of Alaska, very far from the equa­tor. Their repro­duc­tive habits should there­fore be sea­sonal – but are any­thing but. The researchers sus­pect that this is prob­a­bly because sea otters eat sea urchins and mus­sels, which are avail­able all year round.

Data from zoos can explain species’ biol­ogy
“It’s fas­ci­nat­ing to see how lit­tle repro­duc­tive sea­son­al­ity is influ­enced by the con­di­tions in a zoo, where enough food is avail­able all year round, and there­fore how the data from zoo ani­mals can be used to describe species’ biol­ogy,” sum­marises Clauss. In domes­tic pets, on the other hand, this con­nec­tion to the wild barely exists any more and their repro­duc­tion is not asso­ci­ated with a spe­cific sea­son. So if you want to see new­born ani­mals, head to the zoo in April or May.

(Source: Uni­ver­sity of Zurich press release, 07.05.2018)

Goal: 7000 tigers in the wild

Tiger range countries map

Tiger map” (CC BY 2.5) by Sander­son et al., 2006.

about zoos and their mis­sion regard­ing breed­ing endan­gered species, nature con­ser­va­tion, bio­di­ver­sity and edu­ca­tion, which of course relates to the evo­lu­tion of species.
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