ORIGINAL PAPER The intermediate sperm type and genitalia of Zorotypus shannoni Gurney: evidence supporting infraordinal lineages in Zoraptera (Insecta) Romano Dallai • Marco Gottardo • David Mercati • Jose ´ Albertino Rafael • Ryuichiro Machida • Yuta Mashimo • Yoko Matsumura • Rolf Georg Beutel Received: 16 May 2014 / Revised: 4 September 2014 / Accepted: 8 September 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract The sperm ultrastructure and the male and female genital apparatus of Zorotypus shannoni were examined and documented in detail, mainly using trans- mission electron microscopy micrographs. The findings suggest an evolutionary trend shared with Z. hubbardi and Z. impolitus. The three species are characterized by enlarged mitochondrial derivatives and related modifica- tions. Giant sperm are probably a synapomorphy of Z. hubbardi and Z. impolitus, whereas an intermediate con- dition of this feature is found in Z. shannoni. The mono- phyletic origin of Z. caudelli, Z. magnicaudelli, Z. huxleyi and Z. weidneri is suggested by characteristically modified axonemes. The presence of extra-acrosomal material is also an unusual feature for Zoraptera, but this condition also occurs in the majority of polyneopteran groups. The long and convoluted female spermathecal duct with secretory and duct-forming cells is a constant feature in Zoraptera. The enlarged seminal receptacle suggests an evolutionary link between the male genital structures and the sperm size on one hand, and the size of the female spermatheca on the other. The small and otherwise uniform group Zoraptera exhibits a remarkable variation of sperm types and genital structures, suggesting the impact of different types of selection. It is likely that cryptic female choice plays a major role in shaping the genital apparatus. Keywords Polyneoptera Á Spermatozoa Á Ultrastructure Á Transmission electron microscopy (TEM) Á Phylogeny Introduction Zoraptera (ground lice) are a small group of insects with a tropical and subtropical distribution. Discovered almost a Communicated by Andreas Schmidt-Rhaesa. R. Dallai (&) Á M. Gottardo Á D. Mercati Department of Life Sciences, University of Siena, Via A. Moro 2, 53100 Siena, Italy e-mail: romano.dallai@unisi.it M. Gottardo e-mail: gottardo@unisi.it D. Mercati e-mail: david.mercati@unisi.it J. A. Rafael Instituto Nacional de Pesquisas da Amazonia, Caixa Postal 2223, 69067-375 Manaus, AM, Brazil e-mail: jarafael@inpa.gov.br R. Machida Á Y. Mashimo Sugadaira Montane Research Center, University of Tsukuba, Nagano 386-2204, Japan e-mail: machida@sugadaira.tsukuba.ac.jp Y. Mashimo e-mail: mashimo@sugadaira.tsukuba.ac.jp Y. Matsumura Á R. G. Beutel Entomology Group, Institut fu ¨r Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich- Schiller-Universita ¨t Jena, Erbertstr. 1, 07743 Jena, Germany e-mail: yoko.matumura.hamupeni@gmail.com R. G. Beutel e-mail: rolf.beutel@uni-jena.de 123 Zoomorphology DOI 10.1007/s00435-014-0244-5