Evolutionary ecology of insect growth: from geographic patterns to biochemical trade-offs
Date
2017-12-20
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Abstract
Senimaani pole selge, miks on iga putukaliik just sellise kehasuurusega, nagu me teda näeme looduses. Suurem kehasuurus on kasulik, kuna suurematel emastel on enam järglaseid. Samas peab suurest kehast olema ka mingit kahju, muidu toimuks evolutsioonis kehasuuruse pidev suurenemine. Erinevate geograafiliste populatsioonide võrdlemisest võib olla abi mõistmaks, kuidas looduslik valik kehasuurust mõjutab. Kui kuskil on isendid samast liigist suuremad, võime seostada seda erinevust keskkonnaga. Võime ka uurida, mil moel putukad suuremaks kasvavad ja seeläbi jõuda jälile, miks nad seda teevad, aga mujal jällegi ei tee.
TÜ entomoloogid kasvatasid Lõuna- ja Põhja-Euroopast (41°N-65°N) pärit kuue ööliblikaliigi röövikuid laboris termokambrites. Katsete eesmärgiks oli võrdlevalt hinnata eri laiuskraadidelt pärit sama liiki putukate geneetilist varieeruvust elukäigutunnustes ja immuunsuses.
Üllatuslikult leiti, et Lõuna-ja Põhja-Euroopast pärit isendid kasvad ühtemoodi, vaatamata suuremale kehasuurusele lõunas. Lõunapoolsed liblikad saavutasid suurema kehasuuruse pikema arenguajaga. Samas mida kauem arenetakse, seda pikemat aega ollakse eksponeeritud (lindudepoolsele) kisklussurvele, mistõttu väheneb võimalus jõuda nukkumiseni. See võiks olla üks suurema kehasuuruse kulusid.
Putukate kehasurus ja arengukestus sõltub ka temperatuurist. Töös leiti, et temperatuur mõjutab liigikaaslaseid samamoodi: geneetilist varieeruvust temperatuuride mõjudega hakkama saamiseks on vähe. Putukad ei pruugi seetõttu kiiresti kohastuda muutuvate keskkonnatingimustega. Samas leiti populatsioonidevahelisi erinevusi immuunsuses: põhjapool näib immuunvõime olevat tugevam. Seda ehk seetõttu, et seal on olnud suurem vajadus võidelda bakteriaalsete nakkustega
Up until now there is no clear explanation why every insect species has an exact body size in nature. Larger body size is more beneficial, as larger females produce more offspring. At the same time, larger body size must have its costs, because otherwise we would witness unlimited increase in body size in the course of evolution. Comparing different geographical regions may be a way how to determine the effect of natural selection on body size. If at some areas the same species has larger individuals, we can connect body size with respective environments. We can also study how insects acquire larger body size, and as a result learn why larger body size is attained in some but not in other areas. Entomologists from university of Tartu reared six moth species originating from south and north Europe (41°N-65°N) in environmental chambers. The goal was to determine genetic variability in life history traits and immunity using same insect species from different latitudes. Surprisingly, individuals from south and north Europe grew at the same pace, despite all southern individuals being larger, and larger size was attained by longer development. Longer development denotes increased risk of being eaten before reaching pupal stage by (avian) predators. This probably is the cost of larger body size. Insect body size and development was affected also by temperature. We found that within species most individuals are affected the same way: there is lack of variability in dealing with temperature effects. As a result, insects might not evolve quickly, if environmental conditions change. In contrary, we found some among-population differences in immunity: northern individuals are more immune. Possibly because in the north insects may have the need to fight off more bacterial infections compared to their southern conspecifics.
Up until now there is no clear explanation why every insect species has an exact body size in nature. Larger body size is more beneficial, as larger females produce more offspring. At the same time, larger body size must have its costs, because otherwise we would witness unlimited increase in body size in the course of evolution. Comparing different geographical regions may be a way how to determine the effect of natural selection on body size. If at some areas the same species has larger individuals, we can connect body size with respective environments. We can also study how insects acquire larger body size, and as a result learn why larger body size is attained in some but not in other areas. Entomologists from university of Tartu reared six moth species originating from south and north Europe (41°N-65°N) in environmental chambers. The goal was to determine genetic variability in life history traits and immunity using same insect species from different latitudes. Surprisingly, individuals from south and north Europe grew at the same pace, despite all southern individuals being larger, and larger size was attained by longer development. Longer development denotes increased risk of being eaten before reaching pupal stage by (avian) predators. This probably is the cost of larger body size. Insect body size and development was affected also by temperature. We found that within species most individuals are affected the same way: there is lack of variability in dealing with temperature effects. As a result, insects might not evolve quickly, if environmental conditions change. In contrary, we found some among-population differences in immunity: northern individuals are more immune. Possibly because in the north insects may have the need to fight off more bacterial infections compared to their southern conspecifics.
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Keywords
putukad, vastsed, kasvukiirus, evolutsiooniline ökoloogia, insects, grubs, growth rate, evolutionary ecology