Brain development and behavior are sensitive to environmental stimuli. To gain an understanding of how and to what extent environmental variations, particularly with regard to thermal stress and sensory input, affect brain development, function, and genomic activity, in this dissertation, three interrelated studies were conducted in Drosophila melanogaster.
The first study examined the effects of ecologically-relevant hyperthermia stress on development of the Drosophila mushroom body (MB), a conserved sensory integration and associative center in the insect brain. A daily hyperthermic episode throughout larval and pupal development was shown to severely disrupt MB anatomy by reducing intrinsic Kenyon cell neuron numbers, but had little effect on other brain structures or general anatomy. This heat stress also greatly impaired associative odor learning in adults, despite having little effect on memory or sensory acuity.
In the second study, individual and combined effects of sub-adulthood hyperthermia stress, larval density, and early-adulthood living space enrichment on brain anatomy and olfactory learning in adult flies were investigated. Both larval crowding and early-adulthood space enrichment did not significantly increase brain structure volumes or improved odor learning capacities, and did not mitigate heat stress induced MB or learning reductions.
In the third study, a mild thermal pretreatment was applied to Drosophila before the acute thermal stress treatment. The heat pretreatment moderately mitigated the hyperthermia-induced MB volume reduction and fluctuating asymmetry increment, but did not protect flies from odor learning defects or male specific early-stage sterility. Moreover, genome-wide transcript analyses revealed that the variation of gene expression pattern in flies exposed to both heat pretreatment and heat stress was much smaller than that in flies exposed to only heat stress. A set of heat stress long-term down regulated genes were tested through mutant analysis and CG32444 was found to significantly affect MB anatomy.
By establishing empirical linkages between environmental factors, brain structures, and behavior, this research demonstrates that brain’s plasticity is reflected not only by its ability to change, but also its adaptability to retain developing and functioning authenticity in response to environmental variations.