Abstract
Whole genome duplications (WGD) have occurred multiple times in the evolution of animals, including in the lineages leading to vertebrates, teleosts, horseshoe crabs and arachnopulmonates. These dramatic genomic events initially produce a wealth of new genetic material, which is generally followed by extensive gene loss. It appears that developmental genes such as homeobox genes, signalling pathway components and microRNAs, however, tend to be more frequently retained in duplicate following WGD (ohnologs). These not only provide the best evidence for the occurrence of WGD, but an opportunity to study its evolutionary implications. Although these genes are relatively well studied in the context of vertebrate WGD, genomic and transcriptomic data for independent comparison in other groups are scarce, with patchy sampling of only two of the five extant arachnopulmonate orders. To improve our knowledge of developmental gene repertoires, and their evolution since the arachnopulmonate WGD, we sequenced embryonic transcriptomes from two additional spider species and two whip spider species and surveyed them for three important gene families: Hox, Wnt and frizzled. We report extensive retention of ohnologs in all four species, further supporting the arachnopulmonate WGD hypothesis. Thanks to improved sampling we were able to identify patterns of likely ohnolog retention and loss within spiders, including apparent differences between major clades. The two amblypygid species have larger ohnolog repertoires of these genes than both spiders and scorpions; including the first reported duplicated Wnt1/wg, the first Wnt10 recovered in an arachnid, and broad retention of frizzled genes. These insights shed light on the evolution of the enigmatic whip spiders, highlight the importance of the comparative approach within lineages, and provide substantial new transcriptomic data for future study.
Competing Interest Statement
The authors have declared no competing interest.
