Candidate: Julie Kozaczka Stahlhut

Degree of: Doctor of Philosophy

Department: Biological Sciences

Title: Inbreeding, Male Diploidy, and Complementary Sex Determination in the Solitary Wasp
Euodynerus Foraminatus

Committee:
Dr. David P. Cowan, Chair
Dr. Karim Essani
Dr. D. DeWayne Shoemaker
Dr. Elwood B. Ehrle
Dr. Michael R. Stoline

Date: Friday, October 25, 2002 3 :30 p.m. - 5:30 p.m.
1718 Wood Hall

Abstract:
In the insect order Hymenoptera, which includes wasps, bees, and ants, females normally develop from fertilized eggs and are diploid, while males develop from unfertilized eggs and are haploid. Underlying mechanisms of sex determination are more complex and vary among different hymenopteran taxa. One such method is single-locus complementary sex determination, or sl-CSD, in which sex is determined by a single gene locus with many alleles. In species with sl-CSD, diploid individuals that are heterozygous at the sex locus develop as normal females and hemizygous (haploid) individuals as normal males, but diploids homozygous at the sex locus will also develop as males. In many hymenopteran species, such diploid males are inviable or sterile, imparting a high cost to the parents that produce them.

In the solitary vespid wasp Euodynerus foraminatus , brothers and sisters frequently mate at the entrance of their natal nest.However, sl-CSD is present in species closely related to E.foraminatus. Single-locus CSD and inbreeding are considered incompatible, because inbreeding increases the chances of homozygosity at all loci, including the sex locus, and therefore increases the production of abnormal diploid males.

This study had four parts. First, microsatellite DNA markers were developed for genetic studies of E. foraminatus . Second, a controlled breeding experiment was carried out and followed by microsatellite genotyping to confirm the presence of sl-CSD in thisspecies. Third, individuals sampled from a natural population of E.foraminatus from southwest Michigan were genotyped to determine the actual incidence of inbreeding in nature by comparison with Hardy-Weinberg expectations. Fourth and finally, a multi-generation controlled breeding experiment was carried out to determine whether diploid E. foraminatus males had normal fertility, as assessed by their ability to father viable, fertile daughters.

E. foraminatus was found to have sl-CSD, and the southwestern Michigan population was found to have inbreeding levels consistent with more than 60% of all matings occurring between siblings. This paradox may be partially resolved by the additional finding that diploid E. foraminatus males have normal viability and near-normal fertility, and are capable of fathering viable and fertile diploid daughters.

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