The duplication of genes can occur through various mechanisms and is thought to make a major contribution to the evolutionary diversification of organisms. There is increasing evidence for a large-scale duplication of genes in some chelicerate lineages including two rounds of whole genome duplication (WGD) in horseshoe crabs. To investigate this further, we sequenced and analyzed the genome of the common house spider Parasteatoda tepidariorum. We found pervasive duplication of both coding and non-coding genes in this spider, including two clusters of Hox genes. Analysis of synteny conservation across the P. tepidariorum genome suggests that there has been an ancient WGD in spiders. Comparison with the genomes of other chelicerates, including that of the newly sequenced bark scorpion Centruroides sculpturatus, suggests that this event occurred in the common ancestor of spiders and scorpions, and is probably independent of the WGDs in horseshoe crabs. Furthermore, characterization of the sequence and expression of the Hox paralogs in P. tepidariorum suggests that many have been subject to neo-functionalization and/or sub-functionalization since their duplication. Our results reveal that spiders and scorpions are likely the descendants of a polyploid ancestor that lived more than 450 MYA. Given the extensive morphological diversity and ecological adaptations found among these animals, rivaling those of vertebrates, our study of the ancient WGD event in Arachnopulmonata provides a new comparative platform to explore common and divergent evolutionary outcomes of polyploidization events across eukaryotes.

The discovery of multi-species synchronous spawning of scleractinian corals on the Great Barrier Reef in the 1980s stimulated an extraordinary effort to document spawning times in other parts of the globe. Unfortunately, most of these data remain unpublished which limits our understanding of regional and global reproductive patterns. The Coral Spawning Database (CSD) collates much of these disparate data into a single place. The CSD includes 6178 observations (3085 of which were unpublished) of the time or day of spawning for over 300 scleractinian species in 61 genera from 101 sites in the Indo-Pacific. The goal of the CSD is to provide open access to coral spawning data to accelerate our understanding of coral reproductive biology and to provide a baseline against which to evaluate any future changes in reproductive phenology.

Haplotype webs (haplowebs) and conspecificity matrices have recently been proposed as graphical methods for species delimitation. However, performing such analyses by hand can be error‐prone and time‐consuming, and no program is currently available to generate these graphs automatically. Here we present two online tools called HaplowebMaker and CoMa (short for ‘Conspecificity Matrices') that fill this gap. Starting from one or several FASTA sequence alignments, HaplowebMaker generates median‐joining (or minimum spanning) networks, then adds connections between sequences found co‐occurring in heterozygous individuals, thereby turning each network into a haploweb. HaplowebMaker also returns a partition matrix summarizing the partitions inferred from each marker using the criterion of mutual allelic exclusivity. CoMa then turns the partition matrix into a conspecificity matrix and orders it, producing a figure in which each species is revealed as a square along the diagonal. HaplowebMaker and CoMa are open source and written in Haxe; webserver implementations are available at https://eeg‐ebe.github.io/HaplowebMaker and https://eeg‐ebe.github.io/CoMa/.

High-quality genome assembly of ancient asexual rotifer reveals homologous chromosomes that frequently recombine.