A reference quality genome assembly for the Jewel scarab Chrysina gloriosa

The jewel scarab Chrysina gloriosa is one of the most charismatic beetles in the United States and is found from the mountains of West Texas to the Southeastern Arizona sky islands. This species is highly sought by professional and amateur collectors worldwide due to its gleaming metallic coloration. However, the impact of the large-scale collection of this beetle on its populations is unknown, and there is a limited amount of genetic information available to make informed decisions about its conservation. As a first step, we present the genome of C. gloriosa, which we reconstructed using a single female specimen sampled from our ongoing effort to document population connectivity and the demographic history of this beetle. Using a combination of long-read sequencing and Omni-C data, we reconstructed the C. gloriosa genome at a near-chromosome level. Our genome assembly consisted of 454 scaffolds spanning 642 MB, with the ten largest scaffolds capturing 98% of the genome. The scaffold N50 was 72 MB, and the BUSCO score was 95.5%. This genome assembly will be an essential tool to accelerate understanding C. gloriosa biology and help make informed decisions for the conservation of Chrysina and other species with similar distributions in this region. This genome assembly will further serve as a community resource for comparative genomic analysis.

Drift drives the evolution of chromosome number I: The impact of trait transitions on genome evolution in Coleoptera

Chromosomal mutations such as fusions and fissions are often thought to be deleterious, especially in heterozygotes (underdominant), and consequently are unlikely to become fixed. Yet, many models of chromosomal speciation ascribe an important role to chromosomal mutations. When the effective population size (Ne) is small, the efficacy of selection is weakened, and the likelihood of fixing underdominant mutations by genetic drift is greater. Thus, it is possible that ecological and phenotypic transitions that modulate Ne facilitate the fixation of chromosome changes, increasing the rate of karyotype evolution. We synthesize all available chromosome number data in Coleoptera and estimate the impact of traits expected to change Ne on the rate of karyotype evolution in the family Carabidae and 12 disparate clades from across Coleoptera. Our analysis indicates that in Carabidae, wingless clades have faster rates of chromosome number increase. Additionally, our analysis indicates clades exhibiting multiple traits expected to reduce Ne, including strict inbreeding, oligophagy, winglessness, and island endemism, have high rates of karyotype evolution. Our results suggest that chromosome number changes are likely fixed by genetic drift despite an initial fitness cost and that chromosomal speciation models may be important to consider in clades with very small Ne.

Domestication is associated with increased interspecific hybrid compatibility in landfowl (order: Galliformes)

Some species are able to hybridize despite being exceptionally diverged. The causes of this variation in accumulation of reproductive isolation remain poorly understood, and domestication as an impetus or hindrance to reproductive isolation remains to be characterized. In this study, we investigated the role of divergence time, domestication, and mismatches in morphology, habitat, and clutch size among hybridizing species on reproductive isolation in the bird order Galliformes. We compiled and analyzed hybridization occurrences from literature and recorded measures of postzygotic reproductive isolation. We used a text-mining approach leveraging a historical aviculture magazine to quantify the degree of domestication across species. We obtained divergence time, morphology, habitat, and clutch size data from open sources. We found 123 species pairs (involving 77 species) with known offspring fertility (sterile, only males fertile, or both sexes fertile). We found that divergence time and clutch size were significant predictors of reproductive isolation (McFadden's Pseudo-R2 = 0.59), but not habitat or morphological mismatch. Perhaps most interesting, we found a significant relationship between domestication and reproductive compatibility after correcting for phylogeny, removing extreme values, and addressing potential biases (F1,74 = 5.43, R2 = 0.06, P-value = 0.02). We speculate that the genetic architecture and disruption in selective reproductive regimes associated with domestication may impact reproductive isolation, causing domesticated species to be more reproductively labile.

Tempo and Mode of Genome Structure Evolution in Insects

The division of the genome into discrete chromosomes is a fundamental characteristic of eukaryotic life. Insect taxonomists' early adoption of cytogenetics has led to an incredible amount of data describing genome structure across insects. In this article, we synthesize data from thousands of species and use biologically realistic models to infer the tempo and mode of chromosome evolution among insect orders. Our results show that orders vary dramatically in the overall rate of chromosome number evolution (a proxy of genome structural stability) and the pattern of evolution (e.g., the balance between fusions and fissions). These findings have important implications for our understanding of likely modes of speciation and offer insight into the most informative clades for future genome sequencing.

Genomic investigation refutes record of most diverged avian hybrid

The most diverged avian hybrid that has been documented (Numida meleagris × Penelope superciliaris) was reported in 1957. This identification has yet to be confirmed, and like most contemporary studies of hybridization, the identification was based on phenotype, which can be misleading. In this study, we sequenced the specimen in question and performed analyses to validate the specimen's parentage. We extracted DNA from the specimen in a dedicated ancient DNA facility and performed whole-genome short-read sequencing. We used BLAST to find Galliformes sequences similar to the hybrid specimen reads. We found that the proportion of BLAST hits mapped overwhelmingly to two species, N. meleagris and Gallus gallus. Additionally, we constructed phylogenies using avian orthologs and parsed the species placed as sister to the hybrid. Again, the hybrid specimen was placed as a sister to N. meleagris and G. gallus. Despite not being a hybrid between N. meleagris and P. superciliaris, the hybrid still represents the most diverged avian hybrid confirmed with genetic data. In addition to correcting the "record" of the most diverged avian hybrid, these findings support recent assertions that morphological and behavioral-based identifications of avian hybrids can be error-prone. Consequently, this study serves as a cautionary tale to researchers of hybridization.