Physiological consequences of long duration flight in the migratory grasshopper, Melanoplus sanguinipes fabricius
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This study sought to examine the physiological correlates of migratory flight performance the North American migratory grasshopper Melanoplus sanguinipes Fabricius (Orthoptera: Acrididae) with a focus on mechanisms of resource allocation, the dynamics of hemolymph proteins, their interface with immune function, and the mechanism of flight-enhanced oogenesis. The performance of long duration flights has been shown previously to be of reproductive benefit to females who make them. Examination of possible mechanisms of resource compensation for the costs of flight showed no significant increase in either feeding, mating or digestion in females who performed long duration flight. A comparison of two populations of M. sanguinipes from Arizona and Colorado showed significant variation in body size, diapause regulation as well as internal and external morphology. The two populations did not differ in taxonomic characters or in short sequences of genomic and mitochondrial DNA. The follicle cell epithelium of ovaries from M. sanguinipes was examined for its relationship to juvenile hormone III (JH III). JH III induces patency in vitro in intercellular spaces of M. sanguinipes follicular epithelium as well as the characteristic apical endocytosis at the follicle cell oocyte interface. Exogenous JH III treatment of females on day 7 in lieu of flight reduced the threshold for induction of patency to 10-7 M JH III from 10-5 M JH III. These results indicate that JH III can act as a prime to the pump of oogenesis. An HPLC/LC-MS peptidomic survey of the hemolymph of M. sanguinipes following flight performance showed the presence of and changes in serine protease inhibitors. These peptides regulate numerous protease cascades involved in reproduction and immunity which suggested that flight might have a more broad impact than previously thought. Males who performed these flights showed a higher probability of surviving a bacterial challenge. The duration of flight performance was positively correlated in males with increases in titers of the hemolymph lipoproteins apolipophorin I and hexemerin. The exchangeable apolipophorin III showed no variation in correlation with flight. Females were not affected by flight performance in terms of hemolymph protein titers or the probability of surviving a bacterial challenge. These results suggest that the lipid transport system plays an important role in the immune response of this insect.