Selection for Increased Starvation Resistance Using Drosophila melanogaster: Investigating Physiological and Life History Trait Responses to Starvation and Dietary Supplementation in the Context of an Obese Phenotype

Artificial selection for starvation resistance provided insight into the relationships between evolved physiological and life history trait responses following exposure to biologically induced stress. Investigations of alterations to body composition, metabolic rate, movement, and life history traits including development time, female egg production, and longevity in response to brief periods of starvation were conducted on genetically based starvation-resistant and control lines of Drosophila melanogaster. Analysis of the starvation-resistant lines indicated increased energy storage with increased triglyceride deposition and conversion of carbohydrates to lipid, as identified by respiratory quotient values. Correlations between reductions in metabolic rates and movement in the starvation-resistant lines, suggested the presence of an evolved physiological response resulting in energy conservation. Investigations of life history traits in the starvation-resistant lines indicated no significant differences in development time or reproduction between the selected and control lines. Measurements of longevity, however, indicated a significant reduction in starvation-resistant D. melanogaster lifespan. These results suggested that elevated lipid concentrations, similar to that observed with obesity, were correlated with premature mortality. Exposure of the starvation-resistant and control lines to diets supplemented with glucose, palmitic acid, and a 2:1 mixture of casein to albumin were used to investigate alterations in body composition, movement, and life history traits. Results obtained from this study indicated that increased sugar in the diet led to increased carbohydrate, glycogen, total sugar, trehalose, and triglyceride concentrations, while increased fat and protein in the diet resulted in increased soluble protein, carbohydrate, glycogen, total sugar, and trehalose concentrations. Examination of life history trait responses indicated reduced fecundity in females exposed to increased glucose concentrations. Increased supplementations of palmitic acid was consistently correlated with an overall reduction in lifespan in both the starvation-resistant and control Drosophila lines, while measurements of movement indicated increased female activity levels in flies exposed to diets supplemented with fat and protein. Analyses of the physiological and life history trait responses to starvation and dietary supplementation on Drosophila melanogaster used in the present study has implications for investigating the mechanisms underlying the development and persistence of human obesity and associated metabolic disorders.

HAWAIIAN SUGAR CANE RAT CONTROL METHODS AND PROBLEMS

The problem of rats in our Hawaiian sugar cane fields has been with us for a long time. Early records tell of heavy damage at various times on all the islands where sugar cane is grown. Many methods were tried to control these rats. Trapping was once used as a control measure, a bounty was used for a time, gangs of dogs were trained to catch the rats as the cane was harvested. Many kinds of baits and poisons were used. All of these methods were of some value as long as labor was cheap. Our present day problem started when the labor costs started up and the sugar industry shifted to long cropping. Until World War II cane was an annual crop. After the war it was shifted to a two year crop, three years in some places. Depending on variety, location, and soil we raise 90 to 130 tons of sugar cane per acre, which produces 7 to 15 tons of sugar per acre for a two year crop. This sugar brings about $135 dollars per ton. This tonnage of cane is a thick tangle of vegetation. The cane grows erect for almost a year, as it continues to grow it bends over at the base. This allows the stalk to rest on the ground or on other stalks of cane as it continues to grow. These stalks form a tangled mat of stalks and dead leaves that may be two feet thick at the time of harvest. At the same time the leafy growing portion of the stalk will be sticking up out of the mat of cane ten feet in the air. Some of these individual stalks may be 30 feet long and still growing at the time of harvest. All this makes it very hard to get through a cane field as it is one long, prolonged stumble over and through the cane. It is in this mat of cane that our three species of rats live. Two species are familiar to most people in the pest control field. Rattus norvegicus and Rattus rattus. In the latter species we include both the black rat and the alexandrine rats, their habits seem to be the same in Hawaii. Our third rat is the Polynesian rat, Rattus exlans, locally called the Hawaiian rat. This is a small rat, the average length head to tip of tail is nine inches and the average body weight is 65 grams. It has dark brownish fur like the alexandrine rats, and a grey belly. It is found in Indonesia, on most of the islands of Oceania and in New Zealand. All three rats live in our cane fields and the brushy and forested portions of our islands. The norway and alexandrine rats are found in and around the villages and farms, the Polynesian rat is only found in the fields and waste areas. The actual amount of damage done by rats is small, but destruction they cause is large. The rats gnaw through the rind of the cane stalk and eat the soft juicy and sweet tissues inside. They will hollow out one to several nodes per stalk attacked. The effect to the cane stalk is like ringing a tree. After this attack the stalk above the chewed portion usually dies, and sometimes the lower portion too. If the rat does not eat through the stalk the cane stalk could go on living and producing sugar at a reduced rate. Generally an injured stalk does not last long. Disease and souring organisms get in the injury and kill the stalk. And if this isn't enough, some insects are attracted to the injured stalk and will sometimes bore in and kill it. An injured stalk of cane doesn't have much of a chance. A rat may only gnaw out six inches of a 30 foot stalk and the whole stalk will die. If the rat only destroyed what he ate we could ignore them but they cause the death of too much cane. This dead, dying, and souring cane cause several direct and indirect tosses. First we lose the sugar that the cane would have produced. We harvest all of our cane mechanically so we haul the dead and souring cane to the mill where we have to grind it with our good cane and the bad cane reduces the purity of the sugar juices we squeeze from the cane. Rats reduce our income and run up our overhead.