Biology subjects

Lacy, K. D.

Publications and source records attributed to Lacy, K. D..

4 recordsLinked to original sources

bioRxiv2026

Rare sex punctuates strict asexual reproduction in the clonal raider ant, Ooceraea biroi

While asexual species can often outcompete their sexual counterparts over ecological timescales, their long-term evolutionary success is hindered by a diminished ability to purge deleterious mutations and to adapt to changing environments. However, some asexual species persist for millions of years, and a major question in evolutionary biology is how they do so. One solution is to occasionally reproduce sexually, as has been shown in a handful of primarily asexual species. Here, we investigate the possibility of rare sex in the clonal raider ant, Ooceraea biroi. We report the whole-genome sequence of a previously uncharacterized clonal line and, using population genetic and phylogenetic analyses, show that it originated through sexual reproduction between two extensively studied clonal lines. The mitochondrial genome of this clonal line differs from that of the maternal clonal line at only a single nucleotide, suggesting that the sexual reproduction event occurred within the past few hundred years. These results demonstrate that sex occurs sporadically in the clonal raider ant, allowing it to generate new genetic combinations and potentially to overcome some of the costs of asexuality.

evolutionary biology↗

bioRxiv2025

Heterozygosity at a conserved candidate sex determination locus is associated with female development in the clonal raider ant

Sex determination is a developmental switch that triggers sex-specific developmental programs. This switch is "flipped" by the expression of genes that promote male- or female-specific development. Many lineages have evolved sex chromosomes that act as primary signals for sex determination. However, haplodiploidy (males are haploid and females are diploid), which occurs in ca. 12% of animal species, is incompatible with sex chromosomes. Haplodiploid taxa must, therefore, rely on other strategies for sex determination. One mechanism, "complementary sex determination" (CSD), uses heterozygosity as a proxy for diploidy. In CSD, heterozygosity at a sex determination locus triggers female development, while hemizygosity or homozygosity permits male development. CSD loci have been mapped in honeybees and two ant species, but we know little about their evolutionary history. Here, we investigate sex determination in the clonal raider ant, Ooceraea biroi. We identified a 46kb candidate CSD locus at which all females are heterozygous, but most diploid males are homozygous for either allele. As expected for CSD loci, the candidate locus has more alleles than most other loci, resulting in a peak of nucleotide diversity. This peak negligibly affects the amino acid sequences of protein-coding genes, suggesting that heterozygosity of a non-coding genomic sequence triggers female development. This locus is distinct from the CSD locus in honeybees but homologous to a CSD locus mapped in two distantly related ant species, implying that this molecular mechanism has been conserved since a common ancestor that lived approximately 112 million years ago.

evolutionary biology↗

bioRxiv2024

Unselfish meiotic drive maintains heterozygosity in a parthenogenetic ant

According to Mendels second law, chromosomes segregate randomly in meiosis. Non-random segregation is primarily known for cases of selfish meiotic drive in females, in which particular alleles bias their own transmission into the oocyte1,2. Here, we report a rare example of unselfish meiotic drive for crossover inheritance in the clonal raider ant, Ooceraea biroi. This species produces diploid offspring parthenogenetically via fusion of two haploid nuclei from the same meiosis3. This process should cause rapid genotypic degeneration due to loss of heterozygosity, which results if crossover recombination is followed by random (Mendelian) segregation of chromosomes4,5. However, by comparing whole genomes of mothers and daughters, we show that loss of heterozygosity is exceedingly rare, raising the possibility that crossovers are infrequent or absent in O. biroi meiosis. Using a combination of cytology and whole genome sequencing, we show that crossover recombination is, in fact, common, but that loss of heterozygosity is avoided because crossover products are faithfully co-inherited. This results from a programmed violation of Mendels law of segregation, such that crossover products segregate together rather than randomly. This discovery highlights an extreme example of cellular "memory" of crossovers, which could be a common yet cryptic feature of chromosomal segregation.

evolutionary biology↗

bioRxiv2022

Sparse and stereotyped encoding implicates a core glomerulus for ant alarm behavior

Ants communicate via large arrays of pheromones and possess expanded, highly complex olfactory systems, with antennal lobes in the brain comprising ~500 glomeruli. This expansion implies that odors could activate hundreds of glomeruli, which would pose challenges for higher order processing. To study this problem, we generated the first transgenic ants, expressing the genetically encoded calcium indicator GCaMP6s in olfactory sensory neurons. Using two-photon imaging, we mapped complete glomerular responses to four ant alarm pheromones. Alarm pheromones robustly activated [≤]6 glomeruli, and activity maps for the three pheromones inducing panic-alarm in our study species converged on a single glomerulus. These results demonstrate that, rather than using broadly tuned combinatorial encoding, ants employ precise, narrowly tuned, and stereotyped representation of alarm pheromone cues. The identification of a central sensory hub glomerulus for alarm behavior suggests that a simple neural architecture is sufficient to translate pheromone perception into behavioral outputs.

neuroscience↗