Giant mitochondria-driven sperm elongation: A potential promoter of reproductive isolation in divers insect species

Insect group are consist of millions of species. This intense diversity must be supported by accelerated mechanism to produce new species when there is a new niche to occupy. The idea of the frequent speciation needs intraspecific reproductive isolation suggesting a trade-off of reduced fertility among the specie. However, to date, detailed mechanism of reproductive isolation at very early stage of speciation is still unclear. Drosophila group provides unique but valuable opportunity to tackle these questions. Sperm tail of Drosophilidae elongate up to 6 cm as a result of evolutionary selection for reproductive fitness among competing sperms. Cell biological study of elongating spermatids of D. melanogaster demonstrated that sperm elongation is driven by extension of giant mitochondria. The giant mitochondria in large sized sperm with significant morphological variation are shared features seen in wide variety of arthropods. This rapidly changing reproductive organ can cause incompatibility between male and female, and become a promoter for mild reproductive isolation which would have a crutial effect on the early stage of speciation.