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  1. Abstract

    Loss and reduction in paired appendages are common in vertebrate evolution. How often does such convergent evolution depend on similar developmental and genetic pathways? For example, many populations of the threespine stickleback and ninespine stickleback (Gasterosteidae) have independently evolved pelvic reduction, usually based on independent mutations that caused reducedPitx1expression. ReducedPitx1expression has also been implicated in pelvic reduction in manatees. Thus, hindlimb reduction stemming from reducedPitx1expression has arisen independently in groups that diverged tens to hundreds of millions of years ago, suggesting a potential for repeated use ofPitx1across vertebrates. Notably, hindlimb reduction based on the reduction inPitx1expression produces left‐larger directional asymmetry in the vestiges. We used this phenotypic signature as a genetic proxy, testing for hindlimb directional asymmetry in six genera of squamate reptiles that independently evolved hindlimb reduction and for which genetic and developmental tools are not yet developed:Agamodon anguliceps,Bachia intermedia,Chalcides sepsoides,Indotyphlops braminus,Ophisaurus attenuatuas and O. ventralis, andTeius teyou. Significant asymmetry occurred in one taxon,Chalcides sepsoides, whose left‐side pelvis and femur vestiges were 18% and 64% larger than right‐side vestiges, respectively, suggesting modification inPitx1expression in that species.However, there was either right‐larger asymmetry or no directional asymmetry in the other five taxa, suggesting multiple developmental genetic pathways to hindlimb reduction in squamates and the vertebrates more generally.

     
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