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Tiny bugs have own personalities despite being clones, scientists say

March 3, 2011
Special to World Science  

Ti­ny green in­sects known as pea aphids have in­di­vid­ual be­hav­ior pat­terns, or “per­sonal­i­ties,” de­spite be­ing clones of one an­oth­er, sci­en­tists say. The re­search­ers found dif­fer­ences in the way each in­di­vid­ual re­sponds to a threat.

The study was part of a “bur­geon­ing” of sci­en­tif­ic in­ter­est in an­i­mal per­son­al­ity varia­t­ion, not­ed the in­ves­ti­ga­tors, with the Uni­vers­ity of Os­nabrueck, Ger­ma­ny. But de­spite this trend, they added, few stud­ies have been done on in­ver­te­brates, or sim­ple an­i­mals with­out back­bones.

The pea aphid, Acyrthosiphon pi­sum, sucks nec­tar from a plant. (Im­age cour­tesy Tsu­to­mu Tsu­ch­ida)


Stud­ies on “clonal in­ver­te­brates,” which are all ge­net­ic­ally iden­ti­cal and would thus be ex­pected to show lim­it­ed dif­fer­ences in be­hav­ior, are “nonex­is­ten­t,” they added, re­port­ing their find­ings in the March 1 on­line is­sue of the jour­nal De­vel­op­men­tal Psy­cho­bi­ol­ogy.

“This is sur­pris­ing giv­en the ob­vi­ous ad­van­tages of us­ing in­ver­te­brates/clones to tack­le the cru­cial ques­tion why such con­sist­ent be­hav­ioral dif­fer­ences ex­ist,” they went on. Per­son­al­ity dif­fer­ences not at­trib­ut­a­ble to genes are gen­er­ally pre­sumed to be due to the en­vi­ron­ment in which an or­gan­ism formed, though there is al­so a grow­ing ap­precia­t­ion of epige­net­ic fac­tors—chem­ical dif­fer­ences that are not ge­net­ic, but that in­flu­ence gene ac­ti­vity.

Pea aphids, sci­entifically named Acyr­tho­si­phon pi­sum, are pale little in­sects ty­pi­cally less than a sixth of an inch (half a cen­ti­me­ter) long that feed on pea plants and their rel­a­tives. A clus­ter of aphids in­fest­ing a giv­en plant is typ­ic­ally a ge­net­ic­ally iden­ti­cal, or clonal, group pro­duced by one moth­er with­out sex, al­though aphids can al­so re­pro­duce sex­u­ally at cer­tain phases.

When a pea aphid is threat­ened by a preda­tor—of which the spe­cies has sev­er­al in­clud­ing wasps and grub­s—it gives off a chem­i­cal alarm sig­nal that alerts near­by aphids. They may re­spond in sev­er­al ways: they can walk away, drop off the plant or seem­ingly ig­nore the sig­nal. The re­search­ers, Wiebke Schuett and col­leagues, found that pea aphids can be di­vid­ed in­to one of three cat­e­gories: con­sist­ent “drop­pers,” con­sist­ent “non-droppers,” and some that be­have un­pre­dict­a­bly.

In ex­pe­ri­ments, “ma­nipula­t­ions of early en­vi­ron­men­tal con­di­tions had lit­tle qual­i­ta­tive im­pact on such pat­terns,” the re­search­ers wrote. Al­though the rea­sons for the dif­fer­ences are un­clear, the find­ings may be im­por­tant for fu­ture stud­ies of per­son­al­ity varia­t­ion and its ev­o­lu­tion­ary and ec­o­log­i­cal con­se­quenc­es, they added.

Re­search­ers seek to un­der­stand how an­i­mals de­vel­op dif­fer­ent “per­sonal­i­ties” in part be­cause they want to un­der­stand how hu­mans do so. An­i­mals are used as mod­el or­gan­isms be­cause they are of­ten sim­pler and eas­i­er to ex­pe­ri­ment on. For in­stance, an­i­mals may be bred dif­fer­ently to ex­am­ine re­sult­ing dif­fer­ences in be­hav­ior, and the early life en­vi­ron­ment of a test an­i­mal can be con­trolled and ex­am­ined.

Stud­ies have found that 20 to 50 per­cent of the varia­t­ion in an­i­mal per­son­al­ity traits is ge­net­ic, ac­cord­ing to re­search­ers with the Neth­er­lands In­sti­tute of Ecol­o­gy and the Max Planck In­sti­tute for Or­nith­ol­o­gy in Ger­ma­ny, who re­viewed the sub­ject for the De­cem­ber is­sue of the jour­nal Phil­o­soph­i­cal Trans­ac­tions of the Roy­al So­ci­e­ty B. 

“De­vel­op­ment and learn­ing” dom­i­nate the rest of this varia­t­ion, they added. But “one of the main ques­tions that still re­mains un­re­solved is why varia­t­ion in per­son­al­ity ex­ists and how this is main­tained… Mo­lec­u­lar ge­net­ic re­search on an­i­mal per­son­al­ity is still in its in­fan­cy.”


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Tiny green insects known as pea aphids have individual behavior patterns, or “personalities,” despite being clones of one another, scientists say. The researchers found differences in the way each individual responds to a threat. The study was part of a “burgeoning” of scientific interest in animal personality variation, noted the investigators, with the University of Osnabrueck, Germany. But despite this trend, they added, few studies have been done on invertebrates, or simple animals without backbones. Studies on “clonal invertebrates,” which are all genetically identical and would thus be expected to show limited differences in behavior, are “nonexistent,” they added, reporting their findings in the March 1 online issue of the journal Developmental Psychobiology. “This is surprising given the obvious advantages of using invertebrates/clones to tackle the crucial question why such consistent behavioral differences exist,” they went on. Personality differences not attributable to genes are generally presumed due to the environment in which an organism developed, although there is also a growing appreciation of epigenetic factors—chemical differences that are not genetic, but that influence gene activity. Pea aphids are green insects, about one sixth of an inch (less than half a centimeter) long that feed on pea plants and their relatives. A cluster of aphids infesting a given plant is typically a genetically identical, or clonal, group produced by one mother without sex, although aphids can also reproduce sexually at certain phases. When a pea aphid is threatened by a predator—of which the species has several including wasps and grubs—it gives off a chemical alarm signal that alerts nearby aphids. They may respond in several ways: they can walk away, drop off the plant or seemingly ignore the signal. The researchers, Wiebke Schuett and colleagues, found that pea aphids can be divided into one of three categories: consistent “droppers,” consistent “non-droppers,” and some that behave unpredictably. In experiments, “manipulations of early environmental conditions had little qualitative impact on such patterns,” the researchers wrote. Although the reasons for the differences are unclear, the findings may be important for future studies of personality variation and its evolutionary and ecological consequences, they added. Researchers seek to understand how animals develop different “personalities” in part because they want to understand how humans do so. Animals are used as model organisms because they are often simpler and easier to experiment on. For instance, animals may be bred differently to examine resulting differences in behavior, and the early life environment of an test animal can be controlled and examined more easily than with a human. Studies have found that 20 to 50 percent of the variation in animal personality traits is genetic, according to researchers with the Netherlands Institute of Ecology and the Max Planck Institute for Ornithology in Germany, who reviewed the subject for the December issue of the journal Philosophical Transactions of the Royal Society B. “Development and learning” dominate the rest of this variation, they added. But “one of the main questions that still remains unresolved is why variation in personality exists and how this is maintained… Molecular genetic research on animal personality is still in its infancy.”