logo

Welcome


AboutZoos, Since 2008





201516Jan19:15

Map­ping snake venom vari­ety reveals unex­pected evo­lu­tion­ary pattern

Infor­ma­tion
pub­lished 16 Jan­u­ary 2015 | mod­i­fied 17 Jan­u­ary 2015
Archived

Venom from an East­ern dia­mond­back rat­tlesnake in the Ever­glades is dis­tinct from the cock­tail of tox­ins deliv­ered by the same species in the Florida pan­han­dle area, some 500 miles away. But no mat­ter where you go in the south­east­ern United States, the venom of the East­ern coral snake is always the same. The results of a large-​scale sur­vey of venom vari­a­tion in the two snake species, pub­lished 8 Jan­u­ary in the jour­nal GENET­ICS, chal­lenge com­mon assump­tions in venom evo­lu­tion research, pro­vide cru­cial infor­ma­tion for rat­tlesnake con­ser­va­tion, and will help coral snake anti-​venom development.

Eastern diamondback rattlesnakevenom collectionEastern coralsnake

Each ven­omous snake species pro­duces a unique venom, a mix­ture of around 50200 toxic pro­teins and pro­tein frag­ments that co-​evolve with the typ­i­cal prey of the snake, such as the smaller rep­tiles eaten by the East­ern coral snake or the rodents pre­ferred by rat­tlesnakes. In this cycle of evo­lu­tion­ary attack and counter-​attack, any genetic vari­ants that enhance venom resis­tance tend to spread through the prey pop­u­la­tion, prompt­ing tweaks to the snake venom recipe that restore its effectiveness.

The result should be dis­tinc­tive local co-​adaptations between preda­tor and prey, as well as con­sid­er­able regional diver­sity in the types and amounts of the dif­fer­ent venom pro­teins. But when Darin Rokyta (Florida State Uni­ver­sity) and his col­leagues col­lected and pro­filed venom from East­ern coral snakes at many sites within Florida, they found no vari­a­tion at all. The mix of pro­teins in coral snake venom from one part of the state was indis­tin­guish­able from that col­lected any­where else. In con­trast, East­ern dia­mond­backs, which live in the same parts of the coun­try as the coral snakes, pro­duce venom with dif­fer­ent ratios of toxic pro­teins in nearly every sub-​population across their range. For exam­ple, two venom com­po­nents, includ­ing one known to cause paral­y­sis in prey, are found at high lev­els in the North­ern­most pop­u­la­tions, and were com­pletely absent in the snakes from Caladesi Island, near Tampa.

We were shocked. This is the first time any­one has looked at venom vari­a­tion at this scale, and every­body has assumed that the co-​evolutionary arms race would cause local pop­u­la­tions to diverge quickly.
« Darin Rokyta, co-​author, Depart­ment of Bio­log­i­cal Sci­ence, Florida State Uni­ver­sity, USA.

Rokyta says there could be sev­eral expla­na­tions for the lack of vari­a­tion in East­ern coral snake venom. For exam­ple, a small pop­u­la­tion of the species might have recently expanded and taken over the entire range, dis­plac­ing other pop­u­la­tions and reduc­ing genetic diver­sity. Or it could reflect a dif­fer­ence in co-​evolutionary dynam­ics between the species and its typ­i­cally rep­til­ian prey, com­pared to the small mam­mals pre­ferred by rat­tlesnakes. The team is now using genetic clues to the pop­u­la­tion his­to­ries of each species to inves­ti­gate pos­si­ble explanations.

The results of the study will be help­ful to researchers devel­op­ing East­ern coral snake anti-​venom. Mak­ing an antivenom requires sam­ples of venom, but if the mix varies sub­stan­tially from place to place, this will affect the drug’s effec­tive­ness and reli­a­bil­ity. For this species, sam­pling from many pop­u­la­tions should not be nec­es­sary. “This tells us it doesn’t mat­ter where we catch these rel­a­tively elu­sive snakes; we can stick to using those loca­tions where they’re easy to find,” Rokyta said.

The vari­a­tion between East­ern dia­mond­back pop­u­la­tions could pro­vide cru­cial infor­ma­tion to author­i­ties man­ag­ing the con­ser­va­tion of this species, which is in decline and under con­sid­er­a­tion for list­ing as threat­ened under the U.S. Endan­gered Species Act. East­ern dia­mond­back rat­tlesnake declines are thought to have been caused by habi­tat loss com­pounded by hunt­ing and per­se­cu­tion by humans. The data from this study can be used for pop­u­la­tion man­age­ment, to ensure the full range of venom sub­types are con­served for the long-​term via­bil­ity of the species.

The received wis­dom was that ven­oms are rapidly-​evolving, but now we know that’s not nec­es­sar­ily the case.” said Mark John­ston, Editor-​in-​Chief of GENET­ICS. “Clearly, venom evo­lu­tion in these two snake species has been shaped by dif­fer­ent forces. The next chal­lenge is to under­stand why.”




(Source: Genet­ics Soci­ety of Amer­ica press release, 08.01.2015)


UN Biodiversity decade
WWF Stop Wildlife Crime
Fight for Flight campaign
End Ivory-funded Terrorism
Support Rewilding Europe
NASA State of Flux

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.
Fol­low me on: