Biological evolution occurs as alleles change in frequency over time. How allele frequencies change is affected by the mechanics of reproduction, including the number of copies of each chromosome an organism has (ploidy), whether the organism reproduces sexually or asexually, and how gametes are produced. Disentangling the rules of reproduction is therefore vital to understanding how evolution operates, and thorough study promises novel insights into fundamental cellular phenomena. In this thesis, I describe progress in understanding the reproductive biology of the clonal raider ant, Ooceraea biroi. This species has lost the queen caste, and all individuals are, morphologically, worker females that reproduce asexually. Males are produced occasionally, but are considered effectively vestigial because ant workers do not mate. Due to the ease of keeping these ants in the lab and setting up genetically identical age-matched cohorts, O. biroi is increasingly used for behavioral, molecular, and neurobiological studies of ant biology. However, fundamental questions remain about this species' reproductive biology. I first examine how O. biroi's genome avoids some of the deterioration associated with asexual reproduction. Because O. biroi reproduces via the \"fusion\" of two haploid pronuclei following a complete female meiosis, loss of heterozygosity is expected to occur regularly if crossover recombination occurs. Using a combination of whole genome sequencing, cytology, and binomial modeling, I show that crossovers occur regularly in O. biroi meiosis, but heterozygosity loss is avoided due to non-Mendelian inheritance of chromosomes that have recombined with each other. Most violations of Mendel's laws result from selfish genetic elements biasing their own transmission at the expense of the rest of the genome (i.e., meiotic drive), but this represents a rare example of \"unselfish\" meiotic drive, a phenomenon that can easily go undetected in traditional genetic studies, and which therefore might be more common than is currently appreciated throughout eukaryotes. Second, I describe my discovery of O. biroi's mode of sex determination. Like all ants, bees, and wasps, O. biroi is haplodiploid, meaning that males are haploid (have one copy of each chromosome) while females are diploid (have two copies of each chromosome). The sex determination mechanisms used by haplodiploids remain poorly understood. Sex chromosomes can not evolve in haplodiploid taxa, but one sex determination mechanism known from bees, ants, and some wasps is complementary sex determination, in which heterozygosity at a sex locus is required to trigger female development. Using whole genome sequencing, I mapped such a locus in O. biroi and determined that it is heterozygous in all females. Following theoretical predictions, many alleles at this locus are maintained at intermediate frequency. This locus is homologous to sex determination loci mapped in two other ant species, suggesting that this sex determination mechanism may have evolved over 100 million years ago. This putative sex determination locus lies in a non-coding genomic region, implying that heterozygosity in gene-regulatory elements may be required for female development in ants. Third, I explore the evolutionary history of asexual reproduction in the genus Ooceraea. Almost nothing is known of the reproductive biology of Ooceraea species other than O. biroi. I collected colonies and assembled the genome of a congeneric yet distant relative, Ooceraea australis. By comparing the whole genomes of multiple individuals from each colony, I found compelling evidence that, like O. biroi, O. australis reproduces asexually via a mechanism that usually (but not always) avoids loss of heterozygosity. This result hints at a rich evolutionary history of asexual reproduction within the genus Ooceraea. Fourth, I formally demonstrated that sexual reproduction occurs rarely in wild populations of O. biroi by characterizing the genome of an asexually reproducing colony that was produced via sexual reproduction between two other clonal lines of O. biroi. Rare sexual reproduction in O. biroi implies that this species' long-term persistence may be facilitated by enjoying the benefits of both sexual and asexual reproduction. Together, these results elucidate the reproductive biology of O. biroi and demonstrate the power of mechanistic studies of non-traditional model organisms to illuminate unappreciated biological processes.
","abstract_html":"<p>Biological evolution occurs as alleles change in frequency over time. How allele frequencies change is affected by the mechanics of reproduction, including the number of copies of each chromosome an organism has (ploidy), whether the organism reproduces sexually or asexually, and how gametes are produced. Disentangling the rules of reproduction is therefore vital to understanding how evolution operates, and thorough study promises novel insights into fundamental cellular phenomena. In this thesis, I describe progress in understanding the reproductive biology of the clonal raider ant, <em>Ooceraea biroi</em>. This species has lost the queen caste, and all individuals are, morphologically, worker females that reproduce asexually. Males are produced occasionally, but are considered effectively vestigial because ant workers do not mate. Due to the ease of keeping these ants in the lab and setting up genetically identical age-matched cohorts, <em>O. biroi</em> is increasingly used for behavioral, molecular, and neurobiological studies of ant biology. However, fundamental questions remain about this species' reproductive biology. I first examine how <em>O. biroi's</em> genome avoids some of the deterioration associated with asexual reproduction. Because <em>O. biroi</em> reproduces via the "fusion" of two haploid pronuclei following a complete female meiosis, loss of heterozygosity is expected to occur regularly if crossover recombination occurs. Using a combination of whole genome sequencing, cytology, and binomial modeling, I show that crossovers occur regularly in <em>O. biroi</em> meiosis, but heterozygosity loss is avoided due to non-Mendelian inheritance of chromosomes that have recombined with each other. Most violations of Mendel's laws result from selfish genetic elements biasing their own transmission at the expense of the rest of the genome (i.e., meiotic drive), but this represents a rare example of "unselfish" meiotic drive, a phenomenon that can easily go undetected in traditional genetic studies, and which therefore might be more common than is currently appreciated throughout eukaryotes. Second, I describe my discovery of <em>O. biroi</em>'s mode of sex determination. Like all ants, bees, and wasps, <em>O. biroi</em> is haplodiploid, meaning that males are haploid (have one copy of each chromosome) while females are diploid (have two copies of each chromosome). The sex determination mechanisms used by haplodiploids remain poorly understood. Sex chromosomes can not evolve in haplodiploid taxa, but one sex determination mechanism known from bees, ants, and some wasps is complementary sex determination, in which heterozygosity at a sex locus is required to trigger female development. Using whole genome sequencing, I mapped such a locus in <em>O. biroi </em>and determined that it is heterozygous in all females. Following theoretical predictions, many alleles at this locus are maintained at intermediate frequency. This locus is homologous to sex determination loci mapped in two other ant species, suggesting that this sex determination mechanism may have evolved over 100 million years ago. This putative sex determination locus lies in a non-coding genomic region, implying that heterozygosity in gene-regulatory elements may be required for female development in ants. Third, I explore the evolutionary history of asexual reproduction in the genus <em>Ooceraea</em>. Almost nothing is known of the reproductive biology of <em>Ooceraea </em>species other than <em>O. biroi</em>. I collected colonies and assembled the genome of a congeneric yet distant relative, <em>Ooceraea</em> australis. By comparing the whole genomes of multiple individuals from each colony, I found compelling evidence that, like <em>O. biroi</em>, <em>O. australis</em> reproduces asexually via a mechanism that usually (but not always) avoids loss of heterozygosity. This result hints at a rich evolutionary history of asexual reproduction within the genus <em>Ooceraea</em>. Fourth, I formally demonstrated that sexual reproduction occurs rarely in wild populations of <em>O. biroi</em> by characterizing the genome of an asexually reproducing colony that was produced via sexual reproduction between two other clonal lines of <em>O. biroi</em>. Rare sexual reproduction in <em>O. biroi</em> implies that this species' long-term persistence may be facilitated by enjoying the benefits of both sexual and asexual reproduction. Together, these results elucidate the reproductive biology of <em>O. biroi</em> and demonstrate the power of mechanistic studies of non-traditional model organisms to illuminate unappreciated biological processes.</p>","abstract_has_math":false,"creators":["Lacy, Kip D"],"institution":null,"degree_name":"Doctor of Philosophy (PhD)","degree_level":"Thesis","degree_discipline":null,"degree_department":null,"school":null,"contributors":["Daniel Kronauer"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-01-01T08:00:00Z","date_published":"2025-01-01T08:00:00Z","updated_at":"2026-07-24T04:11:05Z","subjects":["Ooceraea biroi","asexual reproduction","meiosis","heterozygosity","sex determination","haplodiploidy","Life Sciences"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/810","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Daniel Kronauer"]},{"key":"dc:creator","label":"Author","values":["Lacy, Kip D"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2027-05-13T07:00:00Z"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Thesis"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Ooceraea biroi","asexual reproduction","meiosis","heterozygosity","sex determination","haplodiploidy","Life Sciences"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/810"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Biological evolution occurs as alleles change in frequency over time. How allele frequencies change is affected by the mechanics of reproduction, including the number of copies of each chromosome an organism has (ploidy), whether the organism reproduces sexually or asexually, and how gametes are produced. Disentangling the rules of reproduction is therefore vital to understanding how evolution operates, and thorough study promises novel insights into fundamental cellular phenomena. In this thesis, I describe progress in understanding the reproductive biology of the clonal raider ant, Ooceraea biroi. This species has lost the queen caste, and all individuals are, morphologically, worker females that reproduce asexually. Males are produced occasionally, but are considered effectively vestigial because ant workers do not mate. Due to the ease of keeping these ants in the lab and setting up genetically identical age-matched cohorts, O. biroi is increasingly used for behavioral, molecular, and neurobiological studies of ant biology. However, fundamental questions remain about this species' reproductive biology. I first examine how O. biroi's genome avoids some of the deterioration associated with asexual reproduction. Because O. biroi reproduces via the \"fusion\" of two haploid pronuclei following a complete female meiosis, loss of heterozygosity is expected to occur regularly if crossover recombination occurs. Using a combination of whole genome sequencing, cytology, and binomial modeling, I show that crossovers occur regularly in O. biroi meiosis, but heterozygosity loss is avoided due to non-Mendelian inheritance of chromosomes that have recombined with each other. Most violations of Mendel's laws result from selfish genetic elements biasing their own transmission at the expense of the rest of the genome (i.e., meiotic drive), but this represents a rare example of \"unselfish\" meiotic drive, a phenomenon that can easily go undetected in traditional genetic studies, and which therefore might be more common than is currently appreciated throughout eukaryotes. Second, I describe my discovery of O. biroi's mode of sex determination. Like all ants, bees, and wasps, O. biroi is haplodiploid, meaning that males are haploid (have one copy of each chromosome) while females are diploid (have two copies of each chromosome). The sex determination mechanisms used by haplodiploids remain poorly understood. Sex chromosomes can not evolve in haplodiploid taxa, but one sex determination mechanism known from bees, ants, and some wasps is complementary sex determination, in which heterozygosity at a sex locus is required to trigger female development. Using whole genome sequencing, I mapped such a locus in O. biroi and determined that it is heterozygous in all females. Following theoretical predictions, many alleles at this locus are maintained at intermediate frequency. This locus is homologous to sex determination loci mapped in two other ant species, suggesting that this sex determination mechanism may have evolved over 100 million years ago. This putative sex determination locus lies in a non-coding genomic region, implying that heterozygosity in gene-regulatory elements may be required for female development in ants. Third, I explore the evolutionary history of asexual reproduction in the genus Ooceraea. Almost nothing is known of the reproductive biology of Ooceraea species other than O. biroi. I collected colonies and assembled the genome of a congeneric yet distant relative, Ooceraea australis. By comparing the whole genomes of multiple individuals from each colony, I found compelling evidence that, like O. biroi, O. australis reproduces asexually via a mechanism that usually (but not always) avoids loss of heterozygosity. This result hints at a rich evolutionary history of asexual reproduction within the genus Ooceraea. Fourth, I formally demonstrated that sexual reproduction occurs rarely in wild populations of O. biroi by characterizing the genome of an asexually reproducing colony that was produced via sexual reproduction between two other clonal lines of O. biroi. Rare sexual reproduction in O. biroi implies that this species' long-term persistence may be facilitated by enjoying the benefits of both sexual and asexual reproduction. Together, these results elucidate the reproductive biology of O. biroi and demonstrate the power of mechanistic studies of non-traditional model organisms to illuminate unappreciated biological processes.
"]},{"key":"dc:title","label":"Title","values":["How Clonal Ants Clone: The Reproductive Biology of the Clonal Raider Ant, Ooceraca Biroi"]}]}],"canonical_facts":{"dc:contributor":["Daniel Kronauer"],"dc:creator":["Lacy, Kip D"],"dc:date.available":["2027-05-13T07:00:00Z"],"dc:description.abstract":["Biological evolution occurs as alleles change in frequency over time. How allele frequencies change is affected by the mechanics of reproduction, including the number of copies of each chromosome an organism has (ploidy), whether the organism reproduces sexually or asexually, and how gametes are produced. Disentangling the rules of reproduction is therefore vital to understanding how evolution operates, and thorough study promises novel insights into fundamental cellular phenomena. In this thesis, I describe progress in understanding the reproductive biology of the clonal raider ant, Ooceraea biroi. This species has lost the queen caste, and all individuals are, morphologically, worker females that reproduce asexually. Males are produced occasionally, but are considered effectively vestigial because ant workers do not mate. Due to the ease of keeping these ants in the lab and setting up genetically identical age-matched cohorts, O. biroi is increasingly used for behavioral, molecular, and neurobiological studies of ant biology. However, fundamental questions remain about this species' reproductive biology. I first examine how O. biroi's genome avoids some of the deterioration associated with asexual reproduction. Because O. biroi reproduces via the \"fusion\" of two haploid pronuclei following a complete female meiosis, loss of heterozygosity is expected to occur regularly if crossover recombination occurs. Using a combination of whole genome sequencing, cytology, and binomial modeling, I show that crossovers occur regularly in O. biroi meiosis, but heterozygosity loss is avoided due to non-Mendelian inheritance of chromosomes that have recombined with each other. Most violations of Mendel's laws result from selfish genetic elements biasing their own transmission at the expense of the rest of the genome (i.e., meiotic drive), but this represents a rare example of \"unselfish\" meiotic drive, a phenomenon that can easily go undetected in traditional genetic studies, and which therefore might be more common than is currently appreciated throughout eukaryotes. Second, I describe my discovery of O. biroi's mode of sex determination. Like all ants, bees, and wasps, O. biroi is haplodiploid, meaning that males are haploid (have one copy of each chromosome) while females are diploid (have two copies of each chromosome). The sex determination mechanisms used by haplodiploids remain poorly understood. Sex chromosomes can not evolve in haplodiploid taxa, but one sex determination mechanism known from bees, ants, and some wasps is complementary sex determination, in which heterozygosity at a sex locus is required to trigger female development. Using whole genome sequencing, I mapped such a locus in O. biroi and determined that it is heterozygous in all females. Following theoretical predictions, many alleles at this locus are maintained at intermediate frequency. This locus is homologous to sex determination loci mapped in two other ant species, suggesting that this sex determination mechanism may have evolved over 100 million years ago. This putative sex determination locus lies in a non-coding genomic region, implying that heterozygosity in gene-regulatory elements may be required for female development in ants. Third, I explore the evolutionary history of asexual reproduction in the genus Ooceraea. Almost nothing is known of the reproductive biology of Ooceraea species other than O. biroi. I collected colonies and assembled the genome of a congeneric yet distant relative, Ooceraea australis. By comparing the whole genomes of multiple individuals from each colony, I found compelling evidence that, like O. biroi, O. australis reproduces asexually via a mechanism that usually (but not always) avoids loss of heterozygosity. This result hints at a rich evolutionary history of asexual reproduction within the genus Ooceraea. Fourth, I formally demonstrated that sexual reproduction occurs rarely in wild populations of O. biroi by characterizing the genome of an asexually reproducing colony that was produced via sexual reproduction between two other clonal lines of O. biroi. Rare sexual reproduction in O. biroi implies that this species' long-term persistence may be facilitated by enjoying the benefits of both sexual and asexual reproduction. Together, these results elucidate the reproductive biology of O. biroi and demonstrate the power of mechanistic studies of non-traditional model organisms to illuminate unappreciated biological processes.
"],"dc:identifier":["https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/810"],"dc:subject":["Ooceraea biroi","asexual reproduction","meiosis","heterozygosity","sex determination","haplodiploidy","Life Sciences"],"dc:title":["How Clonal Ants Clone: The Reproductive Biology of the Clonal Raider Ant, Ooceraca Biroi"],"thesis:degree_level":["Thesis"],"thesis:degree_name":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T04:11:05Z"}