Uticaj temperature i kvaliteta hrane na varijabilnost komponenti adaptivne vrednosti i fiziologiju varenja larvi gubara Lymantria dispar L.
Effect of temperature and food quality on variability of fitness components and physiology of digestion in the gypsy moth larvae Lymantria dispar L.
Doctoral thesis (Published version)
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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.
Keywords:Lymantria dispar L.; Temperature; Food quality; Life-history traits; Phenotipic plasticity; Digestive enzymes specific activities; Resistance
Source:University of Belgrade, Faculty of Biology, 2012, 1-231
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