Biology and genome of a newly discovered sibling species of Caenorhabditis elegans

A ‘ sibling’ speciesof the model organism Caenorhabditis eleganshas long been sought for use in comparative analyses that would enable deep evolutionary interpretations of biological phenomena. Here, we describe the first sibling speciesof C. elegans, C. inopinata n. sp., isolated from fig syconia in Okinawa, Japan. We investigate the morphology, developmental processes and behaviour of C. inopinata, which differ significantly from those of C. elegans. The 123-Mb C. inopinata genome was sequenced and assembled into six nuclear chromosomes, allowing delineation of Caenorhabditis genome evolutionand revealing unique characteristics, such as highly expanded transposable elementsthat might have contributed to the genome evolutionof C. inopinata. In addition, C. inopinata exhibits massive gene losses in chemoreceptorgene families, which could be correlated with its limited habitat area. We have developed genetic and molecular techniques for C. inopinata; thus C. inopinata provides an exciting new platform for comparative evolutionary studies.