Daily (circadian) rhythms exist at molecular, physiological, and behavioral levels and
coordinate many life functions. This coordination is believed to contribute to an
organism's fitness, however, such contributions have not been convincingly demonstrated
in any animal. The most significant measure of fitness is the reproductive output of the
individual and species. In this thesis I examine the consequences of loss of clock function
on reproductive fitness in Drosophila melanogaster. I demonstrated that single mating
among couples with mutated period (per���), timeless (tim���), cycle (cyc���), and Clock
(Clk[superscript Jrk]) genes resulted in approximately 40% fewer progeny compared to wild-type flies.
Male and female contribution to this phenotype was demonstrated by a decrease in
reproductive capacity among per��� and tim��� flies mated with wild-type flies of the
opposite sex. The important role of clock genes for reproductive fitness was confirmed
by reversal of the low fertility phenotype in flies with rescued per or tim function. These
results prompted an investigation to determine the relative contribution of each sex to the
fertility phenotype. Males lacking a functional clock showed a significant decline in the
quantity of sperm released from the testes to seminal vesicles (SV), suggesting that this
peripheral oscillator is involved in sperm maturation. We found that clock genes are
rhythmically expressed in these tissues and the cycling of per and tim expression
continued in vitro, hence the testes and SV complex contained an autonomous circadian
clock. In contrast to males, PER and TIM were constantly present in the cytoplasm of
follicular cells in fly ovaries. Ovarian expression of per and tim is not disrupted by
constant light and females lacking per and tim produced nearly 50% fewer mature
oocytes then wild-type flies. These results suggest that per and tim are acting in a non-circadian
pathway in the ovaries. Taken together, this data demonstrates that circadian
clock genes significantly contribute to the fitness of Drosophila melanogaster by
affecting the fecundity of both sexes. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32044 |
| Date | 10 December 2002 |
| Creators | Beaver, Laura M. |
| Contributors | Giebultowicz, Jadwiga M. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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