Uticaj temperature i kvaliteta hrane na varijabilnost komponenti adaptivne vrednosti i fiziologiju varenja larvi gubara Lymantria dispar L.

Abstract

Temperatura i kvalitet hrane utiču na performansu larvi gubara, Lymantria dispar L. nezavisno ili u međusobnoj interakciji. Strategije preživljavanja larvi gubara u temperaturno kao i nutritivno heterogenoj sredini obuhvataju različite tipove reverzibilne i ireverzibilne fenotipske plastičnosti, koje preko uticaja na usvajanje i raspodelu resursa utiču na osobine životne istorije i rezistentnost prema ekstremnim uslovima životne sredine. U cilju ispitivanja efekata temperature i kvaliteta hrane, tj. sadržaja proteina i ugljenih hidrata u hrani na komponente adaptivne vrednosti, kao i ekspresiju genetičke varijabilnosti, larve gubara su izložene delovanju tri različite temperature (suboptimalna, optimalna i supraoptimalna) i 4 kombinacije hranljivog sastava dijete, koje su se međusobno razlikovale kako u ukupnom sadržaju proteina i ugljenih hidrata, tako i u njihovom međusobnom odnosu. U istim eksperimentalnim uslovima ispitivana je uloga procesa varenja, odnosno aktivnosti digestivnih enzima u usklađivanju odnosa i količine unetih nutienata sa potrebama organizma na različitim temperaturama. Takođe, ispitan je uticaj nutritivne vrednosti i balansiranosti hrane na senzitivnost gubara prema stresnim temperaturama. Nepovoljne temperature i nizak sadržaj proteina u hrani, kao i disbalans proteina u odnosu na ugljene hidrate, smanjuju performansu larvi gubara. Uticaji temperature i kvaliteta hrane na komponente adaptivne vrednosti: preživljavanje, trajanje razvića, masu i relativnu brzinu rasta, uglavnom su međusobno nezavisni. Pokazano je da povišena temperatura smanjuje preživljavanje i trajanje razvića larvi ali dovodi do povećanja relativne brzine rasta. Nutritivni sastav hrane nije uticao na preživljavanje, ali je nizak sadržaj proteina u hrani dovodio do produžavanja razvića, smanjenja mase i relativne brzine rasta larvi. Relativna brzina rasta larvi je bila manja i pri visokom sadržaju ugljenih hidrata u hrani, dok je smanjenje mase larvi na hrani sa niskim sadržajem proteina bilo veće ako je i sadržaj ugljenih hidrata bio nizak. Ako se larve hrane dijetom sa visokim sadržajem proteina dolazi do smanjenja aktivnosti proteolitičkih enzima, ukupnih proteaza i tripsina, dok se u uslovima niskog sadžaja proteina i visokog sadržaja ugljenih hidrata smanjuje aktivnost karbohidraza, α-amilaze i α-glikozidaze. Temperatura i hrana deluju nezavisno na aktivnost elastaze i tripsina, α-glikozidaze i kiselih fosfataza, dok je za aktivnost ukupnih proteaza, leucin aminopeptidaze, α-amilaze, lipaze i alkalne fosfataze pokazana značajna interakcija temperature i nutritivnog sastava dijete. Promena aktivnosti ukupnih proteaza sa porastom temperature sastoji se u povećanju aktivnosti na nutritivno najsiromašnijoj i smanjivanju aktivnosti na nutritivno najbogatijoj hrani, dok se promena aktivnosti α-amilaze u odgovoru na povećanje temperature sastoji u povećanju aktivnosti na hrani sa niskim sadržajem ugljenih hidrata. Odgovor lipaze i kiselih fosfataza na nizak sadržaj proteina i visok sadržaj ugljenih hidrata u hrani, kao i nutritivno siromašnu hranu sastoji se u povećanju njihove aktivnosti, dok se aktivnost alkalne fosfataze sa porastom temperature povećava i na hrani sa niskim sadržajem proteina i na hrani sa niskim sadržajem ugljenih hidrata. U odgovoru na delovanje temperature, pokazan je „obrnut obrazac“ promene aktivnosti između endo i egzopeptidaze (elastaze i leucin aminopeptidaze), između endo i egzokarbohidraze (-amilaze i -glikozidaze) i između alkalne i kiselih fosfataza, kao i promena fenotipskih korelacija između pojedinih klasa enzima na nepovoljnim temperaturama i suboptimalnom nutritivnom sadržaju hrane. Uticaj temperature i kvaliteta hrane uočava se i na nivou promene ekspresije genetičke varijabilnosti trajanja razvića, kao i preko značajne varijabilnosti fenotipske plastičnosti u odgovoru na delovanje temperature. Na optimalnoj temperaturi dolazi do porasta heritabilnosti mase larvi na nutritivno najsiromašnijoj hrani, dok porast temperature smanjuje heritabilnost mase ako je u hrani nizak sadržaj jednog ili oba nutrijenta. Genetičke korelacije izmedju trajanja razvića i mase larvi u nepovoljnim uslovima životne sredine su negativne, tj. larve koje karakteriše duže larveno razviće istovremeno imaju i manju masu, dok u optimalnim uslovima nisu detektovane značajne korelacije između ovih osobina. Većina genetičkih korelacije između sredina, kako za trajanje razvića, tako i za masu larvi bila je pozitivna, što je očekivan rezultat za vrste generaliste. Sve genetičke korelacije između sredina za trajanje razvića larvi su pozitivne i nisu značajno različite od „1” tako da predstavljaju ograničenje za evoluciju fenotipske plastičnosti. Genetičke korelacije između sredina za masu larvi su pozitivne i značajno različite od „1” i, mada za masu larvi nije ustanovljena varijabilnost fenotipske plastičnosti, evolucija plastičnosti je moguća usled značajnih razlika u heritabilnosti između sredina. Larve gubara mogu „profitirati“ u nepovoljnim uslovima nutritivno siromašne hrane, jer je rezistentost gubara na temperaturni stres procenjena na osnovu vremena preživljavanja, pokazala najveću vrednost u takvim uslovima. Nasuprot tome, ograničavajući faktori preživljavanja su prethodna aklimacija na (konstantno) povišenu temperaturu tokom ranih stupnjeva larvenog razvića i visok sadržaj proteina i ugljenih hidrata u hrani. Suboptimalna temperatura gajenja i hrana koju karakteriše najmanji odnos proteina u odnosu na ugljene hidrate, kao i povećanje temperature gajenja na nutritivno najsiromašnijoj hrani, značajno smanjuju sposobnost larvi gubara da se presvlače na stresnoj temperaturi.

Temperature and food quality affect the performance of gypsy moth larvae Lymantria dispar L. independently or in an interaction with each other. Survival strategies of gypsy moth larvae in temperature and nutritionally heterogeneous environments include various types of reversible and irreversible phenotypic plasticity, which due to the effect of uptake and distribution of resources affect the life-history traits and resistance to extreme environmental conditions. In order to investigate the direct and interactive effects of temperature and food quality on fitness components, as well as the expression of genetic variation, gypsy moth larvae were exposed to three different temperatures (suboptimal, optimal and supraoptimal) and 4 sets of nutrient composition of the diet, which differed in protein and carbohydrate content. Under the same experimental conditions, the role of digestion and digestive enzyme activity in adjusting nutrient quantity and ratio with organism needs at different temperatures was investigated. Also, it was investigated the effect of nutritional value of the food on sensitivity of gypsy moth larvae to stressful temperatures. An adverse temperature and low protein content in food, as well as an imbalance of protein compared to carbohydrates, reduced performance of gypsy moth larvae. Effects of temperature and food quality on fitness components - survival, developmental time, larval weight and relative growth rate were mainly independent. It has been shown that elevated temperature reduces survival and duration of development, but leads to an increase of the relative growth rate. Nutritional composition of food had no effect on survival, but the low protein content led to prolonged developmental time, reduced larval weight and relative growth rate of gypsy moth larvae. The relative growth rate of larvae was lower if carbohydrate content in food was high, while larval weight reduction was greater if protein content was low and the carbohydrate content was high. Diet with high protein content led to the decrease in specific activities of total protease and trypsin, while low protein and high carbohydrate diet decreased specific activities of carbohydrases, α-amylase and α-glucosidase of larvae. Temperature and food independently influenced activity of elastase and trypsin, α- glucosidase and acid phosphatase, while total protease, leucine aminopeptidase, lipase and alkaline phosphatase activities were significantly affected by interaction of food and temperature. Change of total protease activity with increasing temperature consisted in its increased activity on nutritionally poorest and reduced activity in the richest food, whereas the changes of α-amylase activity in response to increasing temperatures consisted in increased activities in low carbohydrates food conditions. Responses of lipase and acid phosphatase to low protein and high carbohydrate content in food, i.e. nutritionally poor food, were an increase in their activities, while alkaline phosphatase activity increased with increasing temperature on food that are low in both protein and carbohydrate content. In response to temperature, “reverse pattern" of activity was demonstrated between the endo and exopeptidase (elastase and leucine aminopeptidase), endo and exocarbohydrase (α-amylase and α-glucosidase) and among alkaline and acid phosphatases, as well as changes in phenotypic correlations between certain classes of digestive enzymes to adverse temperatures and suboptimal nutritional content of food. The effects of temperature and food quality were also noticeable at the level of expression of the genetic variability of developmental time, as well as by significant variability of phenotypic plasticity in response to temperature. At the optimal temperature there was an increase of heritability of larval weight on nutritionally poorest food, while rise in temperature decreased heritability of larval weight if the food was low in one or both nutrients. Within environments genetic correlations for developmental time and larval weight in adverse environmental conditions are negative, i.e. larvae, which were characterized by longer larval development had lower larval weight but, in optimal conditions did not reveal any significant correlation between these traits. Majority of the acrossenvironment genetic correlations both for developmental time and larval weight were positive, which was an expected result for generalist species. Acrossenvironments genetic correlations for developmental time were positive and not significantly different from “one”, which represented a constraint for the evolution of optimal phenotypic plasticity. Across-environments genetic correlations for larval weight were positive and significantly different from “1” and although, for larval weight was not found variability of phenotypic plasticity, evolution of plasticity was possible due to the significant difference in heritability between environments. The larvae of gypsy moth ”can benefit” from adverse conditions of nutritionally poor food, because the gypsy moth resistance to temperature stress, which was estimated based on survival time, showed the highest value particularly in such conditions. In contrast, the limiting factor for survival was the previous acclimation to (constant) elevated temperature during early larval stages and high content of protein and carbohydrates in food. Suboptimal temperature and food with the lowest ratio of proteins compared to carbohydrates, as well as an increase in temperature on nutrient-poorest food, significantly reduced the ability of gypsy moth larvae to molt in stressful temperatures.