Date of Award

Spring 2006

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

Michelle Scott

Abstract

Burying beetles, Nicrophorus orbicollis, have extended biparental care. They bury and prepare small vertebrate carcasses as food for their young. While females provide the most care, single males show a remarkable behavioral compensation after a mate loss. Here, I integrate behavioral and physiological analyses of parental behavior in burying beetles by exploring how hormonal and social factors may interact to mediate brood care.

In Chapter I, I establish Juvenile Hormone (JH) profiles during a breeding bout and show that after larvae hatch, JH titers of single males and paired females are similar. JH titers of single males also respond to brood size and are positively correlated with measures of parental effort such as increased brood mass. Chapter II explores interindividual variation in JH titers and shows that there is little inter-annual variation at the onset of a breeding season and no dramatic diurnal changes. In Chapter III, I explore how paternal responsiveness to larvae is related to hormone changes by manipulating various cues from young. Between rejecting (48 h or 24 h prehatch) and accepting larvae (when broods hatch), JH titers of single males increase. In addition, providing protracted care for successive broods of newly hatched larvae maintains elevated JH. In contrast, single males that commit infanticide when their broods hatch have significantly depressed JH. However, treating single males with a JH antagonist does not interfere with care. These results combined suggest that while high JH titers are correlated with the onset and intensity of care, expression of parental behavior may occur despite low hormone levels.

Chapter IV shows that JH alone is not sufficient to upregulate Vitellogenin (Vg) gene expression in females. Neither increasing or lowering JH significantly affects Vg mRNA levels, suggesting that JH may not be the sole gonadotropin. Chapter V explores the role of octopamine, dopamine and serotonin during brood care by combining direct treatments and individual measurements of amine brain levels. Preliminary findings suggest that studies of neuromodulation by biogenic amines could be an important tool to further decipher the complexity of biparental care in burying beetles.

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