Biology subjects

Graber, L. C.

Publications and source records attributed to Graber, L. C..

5 recordsLinked to original sources

bioRxiv2026

Evolution of neurometabolic frugality in harvester ants

Despite the importance of neurometabolic costs in brain size evolution, quantitative data on brain metabolic rates are lacking. We measured ex vivo brain metabolic rates among species of the ant genus Pogonomyrmex to differentiate the roles of sociality and body size in brain evolution in a phylogenetic context. Worker body size and colony size (a proxy for social complexity) vary significantly among Pogonomyrmex species and were positively correlated. However, sociality was not a determinant of brain energetics. Worker body size strongly affected brain metabolism: 38% of resting metabolic rate was attributable to brain metabolism in species with the smallest workers, compared to 6% in species with the largest workers. More derived species had strikingly lower mass-specific brain metabolic costs, suggesting that increases in worker body size have selected for neurometabolic frugality through reductions in brain mass-specific metabolic rate. Additionally, smaller worker body sizes may require higher brain mass-specific energetic costs to achieve comparable performance by absolutely smaller brains. Our study shows that the social brain hypothesis does not explain patterns of brain size in Pogonomyrmex, but body size and evolutionary history strongly influence brain evolution in regard to both size and metabolic cost.

zoology↗

bioRxiv2025

The power to resolve relationships: identifying incongruence and precision of reduced representation and genome-wide data in phylogenomics and population genomics

Target capture of ultraconserved elements (UCEs) and taxon-specific probes are widely used reduced-representation methods in phylogenomics and, increasingly, in population genomics for their ability to retrieve hundreds to thousands of homologous loci across divergent taxa. Meanwhile, declining costs and improved computational methods have made genome resequencing more accessible for non-model species, enabling the generation of datasets that can address evolutionary and ecological questions from micro- to macroevolutionary scales. Whether target capture approaches to likewise generate datasets that can address questions across broad hierarchical scales remains unclear. Here, we assess the efficacy of data collection (i.e., single nucleotide polymorphism (SNP) retention), predicted genetic variation across samples (i.e., heterozygosity), and phylogenetic congruence between data generated using reduced-representation methods and genome resequencing, leveraging publicly available datasets from plants and animals. We found that SNP retention varied by locus type, with genome-wide datasets retaining the highest proportion of SNPs and UCEs the lowest proportion. Heterozygosity also differed, with Benchmarking Universal Single-Copy Orthologs (BUSCOs) producing the lowest estimates, followed by UCEs; the inclusion of supercontig flanking regions raised heterozygosity values moderately. Across all phylogenetic trees, UCE datasets had the lowest bootstrap support, followed by BUSCOs and single copy orthologous genes. Population structure analyses frequently underestimated the number of ancestral populations in reduced-representation datasets, often identifying fewer populations than genome-wide datasets and assigning samples to different clusters. These discrepancies underscore the challenges of relying solely on reduced-representation methods for robust inferences of genetic diversity, phylogenetic relationships, and population structure.

evolutionary biology↗

bioRxiv2024

UCE phylogenomics inform the systematics and geographic range evolution of the harvester ant genus Pogonomyrmex

The harvester ant genus Pogonomyrmex is common in arid regions of North America, South America, and Hispaniola. Here, we use ultraconserved elements (UCEs) to infer the most comprehensive phylogeny of the genus to date. Our inferred topology largely supports previously hypothesized Pogonomyrmex evolutionary relationships and species groups. Our divergence dating analysis substantially pushes back the age of both Pogonomyrmex and the Pogonomyrmecini tribe, suggesting an early Eocene origin for Pogonomyrmex. We infer that Pogonomyrmex likely originated within the Pacific dominion ecoregion of Northern South America. Pogonomyrmex (excluding the Pogonomyrmex mayri clade) likely adapted to cooler and drier climates in the middle Eocene. The genus spread to North America in the late Eocene, likely aided by the ephemeral volcanic islands of the Panama Arc. A smaller group of Pogonomyrmex dispersed to Mesoamerica and North America in the Oligocene and to Hispaniola in the Miocene, most likely out of Mesoamerica. Our results suggest that adaptations to arid environments allowed Pogonomyrmex to spread and diversify in regions of the Americas that were actively becoming cooler and drier due to orogeny and other geologic processes.

zoology↗

bioRxiv2023

Comparative phylogenomic analyses of SNP versus full locus datasets: insights and recommendations for researchers

PremiseIn phylogenomic analyses, no consensus exists on whether using single nucleotide polymorphisms (SNPs) or including flanking regions (full locus) is best, nor how strictly missing data should be filtered. Moreover, empirical evidence on whether SNP-only trees are suitable for downstream phylogenetic comparative methods such as divergence time estimation and ancestral state reconstructions is lacking. MethodsUsing GBS data from 22 taxa of Glycine, we addressed the effects of SNP vs. locus usage and filtering stringency on phylogenomic inference and phylogenetic comparative methods. We compared branch length, node support, and divergence time estimation across eight datasets with varying amounts of missing data and total size. ResultsOur results reveal five aspects of phylogenomic data usage: 1. tree topology is largely congruent regardless of data type or filtering parameters; 2. filtering missing data too strictly reduces the confidence in some relationships; 3. absolute branch lengths vary by two orders of magnitude between datasets; 4. data type and branch length variation have little effect on divergence time estimation; 5. phylograms significantly alter the estimation of ancestral states. DiscussionWhen conducting phylogenomic analyses we recommend not to filter datasets too strictly to minimize the risk of misleading topologies, low support, and inaccurate divergence times.

evolutionary biology↗

bioRxiv2021

Evaluating the contribution of aestivation to the persistence of malaria mosquitoes through the Sahelian dry season using stable isotopes

Data suggests the malaria vector Anopheles coluzzii persists in the Sahel by dry-season aestivation though evidence is scant. We have marked Anopheles mosquitoes using deuterium (2H) to assess the contribution of aestivation to persistence of mosquitoes through the seven-month dry season. If local aestivation is the only way A. coluzzii persists, the frequency of marked mosquitoes should remain stable throughout, whereas finding no marked mosquitoes would be evidence against aestivation. Larval sites were spiked with 2H at the end of the 2017 wet season in two Sahelian villages in Mali. We monitored 2H-enriched populations until the onset of rains. By the end of the enrichment period, 33% of A. coluzzii mosquitoes were clearly marked. Expectedly, 2H levels in marked mosquitoes degraded over time, resulting in a partial overlap of the marked and non-marked 2H distributions. We utilized three methods to estimate the fraction of marked mosquitoes in the population. Seven months after enrichment, 7% of the population had 2H values above the highest pre-enrichment value. An excess of 21% exceeded the 3rd quartile of the pre-enrichment population. A finite mixed population model showed 2.5% represented a subpopulation of marked mosquitoes with elevated 2H, compatible with our predictions. We provide evidence that aestivation is a major persistence mechanism of A. coluzzii in the Sahel, contributing at least 20% of the adults at the onset of rains, suggesting A. coluzzii utilizes multiple persistence strategies enabling its populations rapid buildup, facilitating subsequent malaria resurgence. These may complicate vector control and malaria elimination campaigns. Significance statementHere we estimated the contribution of aestivation to the persistence of mosquitoes through the seven-month long dry season, by marking a known fraction of the adult population through larval site 2H-spiking by the end of the wet season and assessing the change in this fraction through the dry season, until after the onset of the first rain of the subsequent wet season. In a mark-release-recapture study using stable isotopes, we provide compelling evidence that the primary Sahelian malaria vector Anopheles coluzzii aestivates on a population-scale, contributing at least 20% of the adults which reestablish the population of the subsequent wet season. The capacity to use multiple strategies of persistence in time and space might complicate vector control and elimination campaigns.

ecology↗