The sperm pumps of Strepsiptera and Antliophora (Hexapoda)

Abstract

Male genital structures of representatives of Strepsiptera, Siphonaptera and Diptera are described in detail, with special emphasis on sperm pumps. The parts involved in the apparatus are evaluated with respect to their homology. Functional interpretations are presented based on the morphological observations. The phylogenetic significance of characters related to the male genital apparatus is discussed. The sperm pumps differ strongly in Strepsiptera and Antliophora (s.s.) and are not homologous. The strepsipteran type, which lacks any sclerotized parts, has evolved independently. Autapomophies of the male genital apparatus are the compact testes, the large balloon-shaped vesicula seminalis, the strongly developed musculature of the proximal ductus ejaculatorius, the strongly simplified copulatory organ, the unusual muscles of segments VIII and IX, and the complete absence of accessory glands. The median fusion and almost globular shape of the vesicula are potential autapomorphies of Corioxenidae. The absence of the furrow separating the testes from the vesicula seminalis is a derived condition found in Xenos and Myrmecolax. A sperm pump is absent in Boreus (Mecoptera) and Culicomorpha and the functionally relevant parts and their arrangement differ strongly in Siphonaptera, Pistillifera and Diptera (excl. Culicomorpha). The presence of a functional and homologous pumping apparatus does not belong to the groundplan of Antliophora, which implies that this alleged autapomorphy of the clade is invalid. A sperm pump belongs to the groundplan of Diptera and was secondarily reduced in Culicomorpha, many representatives of Bibionomorpha, and in Diopsidae. It was very likely primarily absent in Mecoptera. However, the precise reconstruction of the groundplan depends on the position of Nannochoristidae within Mecoptera and on the possible affinities of Siphonaptera and Boreidae. Sperm pumps should be considered as a functional term and not be used as a character for phylogenetic reconstruction, unless specific similarities are included in the character definition.

Ribosomal protein genes of holometabolan insects reject the Halteria, instead revealing a close affinity of Strepsiptera with Coleoptera

“…Another potential synapomorphy of Halteria (or Strepsiptera + Antliophora) is the sperm pump (Wheeler et al, 2001;Whiting, 1998;Whiting et al, 1997). Yet here, revisions suggest that insect sperm pumps have multiple independent origins and are unreliable phylogenetic estimators, again weakened by homoplasy (Hünefeld and Beutel, 2005;Sinclair et al, 2007). Consequently, most morphological evidence originally proposed to support the inclusion of Strepsiptera in Antliophora (Whiting et al, 1997;Whiting and Karthirithamby, 1995) has since been critically reinterpreted.…”

“…Despite this, morphological evidence for the Antliophora (without Strepsiptera), comes from recent re-analyses of the male reproductive tract between Diptera, Mecoptera and Siphonaptera, which suggests these three 'mecopteroid' orders share a unique configuration of a U-shaped vas deferens that is continuous to the accessory gland, with derived modifications in some Diptera. In contrast, Strepsiptera lack the accessory gland, the vas deferens is weakly distinguished from the testes, and seminal vesicles may actually be modified vasa deferentia (Hünefeld and Beutel, 2005;Sinclair et al, 2007). Most other putative synapomorphies of Antliophora have now been reinterpreted as reductions or losses that are plesiomorphic for a broader suite of orders (Beutel and Pohl, 2006;Sinclair et al, 2007).…”

“…metathoracic hindwings), arising from reversed segment identity via a radical homeotic transformation (Whiting and Karthirithamby, 1995;Whiting and Wheeler, 1994). However, such interpretation allows the topological position of a homologous structure to be mutable (Beutel and Pohl, 2006;Hünefeld and Beutel, 2005). In earlier interpretations, strepsipteran forewing modifications were simply deemed convergent with hindwing dipteran halteres, through modifications on different thoracic segments (Nalbach, 1993;Pix et al, 1993).…”

“…Other characters proposed to support the close affinities of these two orders (e.g. Wheeler et al, 2001;Whiting et al, 1997) have since been critically reinterpreted (Beutel and Pohl, 2006;Hünefeld and Beutel, 2005;Krenn, 2007;Kristensen, 1999;Sinclair et al, 2007). Studies using 28S rRNA data conflicted with results from 18S rRNA alone, as they did not recover the Halteria, and even placed Strepsiptera outside Holometabola altogether (Huelsenbeck, 2001;Hwang et al, 1998).…”

The adult head structures of Tipulomorpha (Diptera, Insecta) and their phylogenetic implications

“…Despite the rejection of the spermpump as autapomorphy of Antliophora (Hünefeld and Beutel 2005;Mickoleit 2008), the monophyly of the group is well established Wiegmann et al 2009;Friedrich and Beutel 2010). The distinct reduction of the dorsal tentorial arm Hepburn 1969;Owen 1985;) is one potential synapomorphy of the three traditional orders as pointed out by .…”