abstract: There is increasing evidence that ovarian status influcences behavioral phenotype in workers of the honey bee Apis mellifera. Honey bee workers demonstrate a complex division of labor. Young workers perform in-hive tasks (e.g. brood care), while older bees perform outside tasks (e.g. foraging for food). This age correlated division of labor is known as temporal polyethism. Foragers demonstrate further division of labor with some bees biasing collection towards protein (pollen) and others towards carbohydrates (nectar). The Reproductive Ground-plan Hypothesis proposes that the ovary plays a regulatory role in foraging division of labor. European honey bee workers that have been selectively bred to store larger amounts of pollen (High strain) also have a higher number of ovarioles per ovary than workers from strains bred to store less pollen (Low strain). High strain bees also initiate foraging earlier than Low strain bees. The relationship between ovariole number and foraging behavior is also observed in wild-type Apis mellifera and Apis cerana: pollen-biased foragers have more ovarioles than nectar-biased foragers. In my first study, I investigated the pre-foraging behavioral patterns of the High and Low strain bees. I found that High strain bees progress through the temporal polyethism at a faster rate than Low strain bees. To ensure that the observed relationship between the ovary and foraging bias is not due to associated separate genes for ovary size and foraging behavior, I investigated foraging behavior of African-European backcross bees. The backcross breeding program was designed to break potential gene associations. The results from this study demonstrated the relationship between the ovary and foraging behavior, supporting the proposed causal linkage between reproductive development and behavioral phenotype. The final study was designed to elucidate a regulatory mechanism that links ovariole number with sucrose sensitivity, and loading decisions. I measured ovariole number, sucrose sensitivity and sucrose solution load size using a rate-controlled sucrose delivery system. I found an interaction effect between ovariole number and sucrose sensitivity for sucrose solution load size. This suggests that the ovary impacts carbohydrate collection through modulation of sucrose sensitivity. Because nectar and pollen collection are not independent, this would also impact protein collection. / Dissertation/Thesis / Ph.D. Biology 2011

In dieser Arbeit wurden die Morpho-Physiologie und das Verhalten zweier Arten Afrikanischer schwach elektrischer Fische, Marcusenius victoriae und Petrocephalus degeni, im Labor und in einem ihrer natürlichen Habitate im Lwamunda Sumpf in Uganda untersucht. Die zwei Hauptziele dieser Arbeit waren (i) tageszeitabhängige Verhaltensrhythmen (Aktivität, Habitatnutzung) im Labor und im Freiland zu untersuchen und (ii) die Ausprägung und Plastizität der morpho-physiologischen Merkmale von P. degeni zu untersuchen, die ihnen erlauben bei natürlich vorkommender, geringer Sauerstoffverfügbarkeit (Hypoxie) zu überleben. Tageszeitabhängige Verhaltensrhythmen beider Arten wurden im Labor über 42 Stunden und im natürlichen Habitat dieser Fische für sechs Tage erfasst. In den Laborversuchen verbrachten beide Arten tagsüber annähernd 100% der Zeit in einem bereitgestellten Versteck und schwammen nachts heraus um aktiv ihre Umwelt zu erkunden. Im Habitat wurden die meisten Fische in strukturell komplexen Habitaten unter schwimmenden Pflanzen detektiert. Nachts schwammen die Fische aktiv in die offenen und ungeschützten Bereiche der Lagune, vermutlich um nach Futter zu suchen und zu interagieren. Die Begleitende in-situ Messung der Sauerstoffverfügbarkeit zeigte, dass beide Arten präsent und vermutlich sogar am aktivsten waren während Phasen extremer nächtlicher Hypoxie. Zur Untersuchung der respiratorischen Merkmale von P. degeni wurden Respirometrieversuche mit hypoxie-akklimatisierten Tieren durchgeführt, Hämoglobin- und Laktatkonzentration im Blut gemessen, und morphologische Parameter an den ersten beiden Kiemenbögen erfasst. Die Fische zeigten niedrige Sauerstoffverbrauchsraten, welche sie bis zu einem sehr niedrigem äußeren Sauerstoffpartialdruck aufrechterhielten. Zusätzlich zeigten sie hohe Hämoglobin- und Laktatkonzentrationen im Blut. Bis zu 75 Tage Normoxie-Akklimatisierung führte zu reduzierter Hämoglobinkonzentration und kürzeren Kiemenfilamenten. / In this thesis, I investigated the morpho-physiology and behavior of two species of African mormyrid weakly electric fish, Marcusenius victoriae and Petrocephalus degeni, in the laboratory and in one of their natural habitats, the Lwamunda Swamp in Uganda. The two main objectives of this work were to (i) observe behavioral rhythms and habitat use patterns of both species under natural and laboratory conditions, and (ii) assess expression and plasticity of morpho-physiological traits that might enable P. degeni to survive naturally occurring low oxygen conditions (hypoxia). Behavioral rhythms were recorded in the laboratory over 42 hours and in the habitat on six sampling days. In the laboratory, both species spent close to 100% of the time in their shelter during the day and actively explore their environment at night. In the swamp lagoon, fish were most often encountered in structurally complex habitats under floating vegetation and ventured into open and unsheltered areas of the lagoon at night, presumably to forage and interact. Concomitant in-situ oxygen measurements revealed that these fish were present, and presumably most active during periods of extreme nocturnal hypoxia in their swamp habitat. To investigate respiratory traits of swamp-dwelling P. degeni, I conducted respirometry experiments and measured blood lactate and hemoglobin and gill morphometrics on the first two gill arches. Fish showed low routine oxygen consumption rates, which they maintained until a very low ambient oxygen partial pressure was reached. Additionally, they had high concentrations of hemoglobin and lactate in their blood. Up to 75 days of normoxia exposure reduced blood hemoglobin and gill filament length.