Microplastics can trigger evolutionary changes

Microplas­tics are enter­ing the envi­ron­ment in ever greater con­cen­tra­tions and decom­pose only very slow­ly. The plas­tic par­ti­cles, which are up to five mil­lime­ters in size, are dis­persed by water and wind. Microplas­tics have now been detect­ed in all ecosys­tems, from the deep sea to high alpine glac­i­ers. Although there is increas­ing evi­dence that the inges­tion of microplas­tics — depend­ing on size, quan­ti­ty and com­po­si­tion — could be harm­ful to organ­isms, the degree of dan­ger has not yet been con­clu­sive­ly determined.

That microplas­tics can also trig­ger evo­lu­tion­ary changes has now been shown for the first time by an inter­na­tion­al team of sci­en­tists* from the LOEWE Cen­ter for Trans­la­tion­al Bio­di­ver­si­ty Genomics (TBG), the Senck­en­berg Bio­di­ver­si­ty and Cli­mate Research Cen­ter Frank­furt (SBiK‑F) and the Eston­ian Nation­al Lab­o­ra­to­ry of Chem­istry and Physics. Their genom­ic study was pub­lished in the jour­nal Chemos­phere. Accord­ing to the study, the inges­tion of microplas­tic par­ti­cles trig­gers an evo­lu­tion­ary adap­ta­tion in the Chi­rono­mus ripar­ius mosquito.

In an exper­i­ment span­ning sev­er­al gen­er­a­tions of mos­qui­toes, they were exposed to a con­cen­tra­tion of microplas­tics sim­i­lar to that found in the envi­ron­ment. This ini­tial­ly showed a loss of fit­ness in the form of death rates of up to 50 per­cent. Sub­se­quent­ly, how­ev­er, an inter­est­ing devel­op­ment set in: With­in three gen­er­a­tions, the mos­qui­toes adapt­ed to the uptake of the pol­lu­tant, so that there was no longer any dif­fer­ence to the con­trol group in terms of sur­vival rates. At the same time, how­ev­er, changes were reg­is­tered in their entire genome that could be inter­pret­ed as the rea­son for this incred­i­bly rapid adap­ta­tion. In par­tic­u­lar, those genes that play a role in com­bat­ing inflam­ma­tion and oxida­tive stress — a sub­stance imbal­ance in cells that impairs repair and detox­i­fi­ca­tion func­tions — showed signs of evo­lu­tion­ary adaptation.

“Even though twitch­bugs were able to adapt very quick­ly to microplas­tics, this is only par­tial­ly good news. Because this may not reflect the sit­u­a­tion in nat­ur­al pop­u­la­tions and ecosys­tems. Many dif­fer­ent fac­tors need to be tak­en into account for this to happen.”

- Dr. Hali­na Binde Doria, study author

For one, she said, the exper­i­men­tal sit­u­a­tion may not show all the neg­a­tive effects of microplas­tics on sur­vival or repro­duc­tion rates, in short, evo­lu­tion­ary fit­ness. For exam­ple, the inges­tion of microplas­tic par­ti­cles direct­ly or indi­rect­ly affects nutri­ent uptake in the gut and could have neg­a­tive effects dur­ing nutri­ent-poor peri­ods, such as win­ter. Also, adap­ta­tion to microplas­tics could over­ride impor­tant oth­er adap­ta­tions, such as con­trol of muta­tion rates. In addi­tion, he said, it is known that not all species can adapt as quick­ly as twitch­bugs. On these, microplas­tics would have harm­ful effects in the longer term.

Study leader Prof. Markus Pfen­ninger, also work­ing at the LOEWE Cen­ter TBG and the SBiK‑F as well as at the Johannes Guten­berg Uni­ver­si­ty Mainz, sum­ma­rizes: “Our study shows that microplas­tics in the envi­ron­ment have the poten­tial to for­ev­er alter the evo­lu­tion­ary devel­op­ment of species exposed to them. Even if there appear to be no imme­di­ate harm­ful effects, microplas­tics pose a hith­er­to under­es­ti­mat­ed threat to all ecosys­tems. We now want to fur­ther explore the genom­ic respons­es of twitch­bugs to microplas­tics as an exam­ple, as their rapid repro­duc­tive rate, ease of main­te­nance in the lab, and avail­able ref­er­ence genome make them well suit­ed for these analyses.”