Meeting Abstract
The versatility of the articulated appendages of arthropods has contributed to their evolutionary success, granting them expansion of their ecological niche space. While the genetic mechanisms controlling the patterning of appendages are well understood for arthropod models like Drosophila melanogaster, the genetic basis for the patterning of appendages unique to arachnids (e.g., book lungs, chelicerae) remains a mystery. Within Arachnida, scorpions are among the oldest lineages and are distinguished from other arachnid groups by a unique pair of wing-like organs called pectines, whose relationship to the walking leg is unclear. We utilized a developmental transcriptome of Centruroides sculpturatus to identify homologs of appendage patterning genes common to arthropods, such as dachshund (dac), engrailed (en) and wingless (wg). To elucidate the nature of the scorpion pectine and build upon understanding of its positional and genetic homologies to other appendages, we surveyed the expression of these genes in developing scorpion embryos. Based upon these data, we homologize walking legs with the inner ramus of the pectine, whereas our data suggest that the blade of the pectine represents an exopod derivative. The lack of distal expression of Distal-less and aristal-less suggests that their patterning is fundamentally different from telopodal appendages (e.g., pedipalps or legs).
