Developmental gene expression as a phylogenetic data class: support for the monophyly of Arachnopulmonata

Genomic resources and toolkits for developmental study of whip spiders (Amblypygi) provide insights into arachnid genome evolution and antenniform leg patterning

“…In accordance with this hypothesis, we discovered that the whip spider P. marginemaculatus presents homologs of all ten Hox genes, and all excepting proboscipedia appear to be duplicated, as supported by our alignment and phylogenetic analysis. Our survey in the two and a second copy with a divergent expression, with these two sets of expression patterns shared by a spider and a scorpion [75]. For instance, dac1 of surveyed arachnopulmonates retains the plesiomorphic expression pattern of a broad median band in the appendages, the condition observed in the single-copy dac of all non-arachnopulmonate arachnids surveyed to date [20,28], whereas dac2 is expressed as a proximal and a medial domain at the patellatibia boundary [38,67,69,75].…”

“…Moreover, Pmar-dac and Pmar-hth have paralog-specific expression patterns shared with spiders and a scorpion: In arachnids with three segmented chelicerae, such as the daddy-long-legs Phalangium opilio, dac is expressed in the proximal segment of the appendage [28]. The same is true for the three-segmented chelicera of scorpions, in which both dac1 and dac2 are expressed in the proximal segment [75]. In the two-segmented chelicera of spiders, dac1 is not expressed in the chelicera save for a non-ectodermal faint staining in late embryonic stages [38,[67][68][69]84].…”

“…Our survey in the two and a second copy with a divergent expression, with these two sets of expression patterns shared by a spider and a scorpion [75]. For instance, dac1 of surveyed arachnopulmonates retains the plesiomorphic expression pattern of a broad median band in the appendages, the condition observed in the single-copy dac of all non-arachnopulmonate arachnids surveyed to date [20,28], whereas dac2 is expressed as a proximal and a medial domain at the patellatibia boundary [38,67,69,75]. Similarly, hth1 retains a plesiomorphic expression pattern on the proximal-median appendage excluding the tarsus, whereas hth2 presents a strong short proximal domain and stripes of expression at podomere boundaries [39,67,69,75].…”

“…The expression pattern dachshund in P. marginemaculatus early embryos reveals a further interesting aspect of this allometry. The expression of dac (including duplicates) in the legs of arachnids surveyed to date occurs on podomeres proximal to the tibia, so that the tibia-metatarsus-tarsus territory may be identified as the a dac-free domain [20,27,38,67,69,75,84]. The distal boundary of Pmar-dac1 and Pmar-dac2 in stages long before podomere formation reveals that the distal domain (Pmar-dac1-free cells) of L1 is already longer with respect to the proximal leg and the other legs (compare Fig.…”

“…We collected embryos of different embryonic stages as described above, and conducted total Table S1). For the analysis of Distal-less, dachshund, and homothorax we selected terminals used in Nolan et al [75] and included the peptide sequence for P. marginemaculatus candidates (Additional file 5, Table S1). Peptides were predicted with ORF Finder (NCBI), TransDecoder v. 5.5.0 [92], or obtained as CDS when possible from publicly available NCBI database.…”