Regeneration of Tarsomeres in the Fused Tarsi Trait of the German Cockroach

Wild-type tarsi of cockroach legs have five tarsomeres, but this number is usually reduced to four in regenerated tarsi. There were two possible explanations for the tetramerous condition. One was that the 3rd tarsomere of normal 5-segmented tarsi has disappeared. The other was that the 2nd and 3rd tarsomeres have fused to reduce the number of tarsomeres. For further information on this issue, we carried out regeneration experiments using the fused tarsi trait (ftt). Legs of ftt nymphs were amputated at 10 different tarsal levels. The number of tarsomeres, pads, and distolateral spines were counted in regenerated tarsi and unoperated controls. Regardless of the level of amputation, the number of tarsomeres and pads never changed in regeneration. However, double pairs of distolateral spines on the 2nd-3rd fused tarsomere were usually replaced by a single pair of spines on the regenerated corresponding tarsomere. These observations suggest that one of the latent tarsomeres that composed part of the fused tarsomere disappeared in the regenerated tarsi. This finding in ftt agrees with an hypothesis that the 3rd tarsomere of wild-type tarsi has disappeared in tetramerous regenerates. We discuss relationships of phylogeny, ontogeny, and regeneration, suggesting that regeneration is an abbreviated process of normal development.