Biology subjects

Baldwin-Brown, J. G.

Publications and source records attributed to Baldwin-Brown, J. G..

2 recordsLinked to original sources

bioRxiv2017

A new standard for crustacean genomes: the highly contiguous, annotated genome assembly of the clam shrimp Eulimnadia texana reveals HOX gene order and identifies the sex chromosome

Vernal pool clam shrimp (Eulimnadia texana) are a promising model system due to their ease of lab culture, short generation time, modest sized genome, a somewhat rare stable androdioecious sex determination system, and a requirement to reproduce via desiccated diapaused eggs. We generated a highly contiguous genome assembly using 46X of PacBio long read data and 216X of Illumina short reads, and annotated using Illumina RNAseq obtained from adult males or hermaphrodites. 85% of the 120Mb genome is contained in the largest 8 contigs, the smallest of which is 4.6Mb. The assembly contains 98% of transcripts predicted via RNAseq. This assembly is qualitatively different from scaffolded Illumina assemblies: it is produced from long reads that contain sequence data along their entire length, and is thus gap free. The contiguity of the assembly allows us to order the HOX genes within the genome, identifying two loci that contain HOX gene orthologs, and which approximately maintain the order observed in other arthropods. We identified a partial duplication of the Antennapedia gene adjacent to the few genes homologous to the Bithorax locus. Because the sex chromosome of an androdioecious species is of special interest, we used existing allozyme and microsatellite markers to identify the E. texana sex chromosome, and find that it comprises nearly half of the genome of this species. Linkage patterns indicate that recombination is extremely rare and perhaps absent in hermaphrodites, and as a result the location of the sex determining locus will be difficult to refine using recombination mapping.

genomics↗

bioRxiv2017

Pooled population resequencing of clam shrimp (Eulimnadia texana) from different vernal pools reveals signatures of local adaptation

Vernal pool clam shrimp (Eulimnadia texana) are a promising model due to ease of culturing, short generation time, modest genome size, and obligate desiccated diapaused eggs. We collected Illumina data (Poolseq) from eleven pooled wild vernal pool clam shrimp populations. We hypothesized that restricted gene flow between vernal pools, separated by distances of 0.36 to 253 km, in concert with Poolseq data from each population, could be used to identify genes important in local adaptation. We adapted Bayenv2 to genome-wide Poolseq data and detected thirteen genomic regions showing a strong excess of population subdivision relative to a genome-wide background. We identified a set of regions that appear to be significantly diverged in allele frequency, above what is expected based on the relationships amongst the populations. Regions identified as significant were on average 9.5 kb in size and harbored 3.8 genes. We attempted to identify correlations between allele frequencies at each genomic region and environmental variables that may influence local adaptation in the sequences populations, but found that there were too many confounding environmental variables to draw strong conclusions. One such genomic region harbored an ortholog of Drosophila melanogaster CG10413, a gene predicted to have sodium/potassium/chloride activity. Finally, we demonstrate that the identified regions could not have been found with less powerful statistics, i.e. FST, or with a less contiguous genome assembly.

evolutionary biology↗