Comparison of spermatheca morphology between reproductive and non-reproductive females in social wasps Ayako Gotoh a , Johan Billen b , Rosli Hashim c , Fuminori Ito d, * a The United Graduate School of Agricultural Sciences, Ehime University, Tarumi, Matsuyama 790-8566, Japan b Zoological Institute, K.U. Leuven, Naamsestraat 59, B-3000 Leuven, Belgium c Institute of Biological Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia d Faculty of Agriculture, Kagawa University, Ikenobe, Miki 761-0795, Japan Received 25 May 2007; received in revised form 9 November 2007; accepted 9 November 2007 Abstract Social wasps show an obvious evolution of the differentiation in behavior and external size between reproductive and non-reproductive fe- males, with no clear differences in the Stenogastrinae, via overlap in the Polistinae, to clear differences in the Vespinae. In this study, we ex- amined the morphological appearance of the spermatheca in representative species of these three subfamilies. The general anatomical organization of the spermatheca comprises a reservoir, a duct and two spermathecal glands, and is in line with its common structure in other social Hymenoptera. All examined wasp species have a spermathecal reservoir with uniform wall thickness, which is similar to the situation in the bees, but differentiates them from the ants. Within the wasps, the shape of the reservoir, the shape of the spermathecal glands and their attachment site to the spermatheca differs among the Stenogastrinae, Polistinae and Vespinae. The reservoir wall is thick in the Polistinae and Vespinae, while in the Stenogastrinae, it varies from thin in Parischnogaster to thick in Eustenogaster, with an intermediate situation in Liostenogaster. In all examined species, we found no differences in the spermathecal development between reproductive and non-reproductive wasps. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Spermatheca; Caste difference; Hymenoptera; Vespidae; Social wasps 1. Introduction In insects, females after mating store sperm in the sperma- theca, which is located at the dorsal side of the common ovi- duct and which is known to contribute to the maintenance of sperm until it is released at the time of egg fertilization (Dallai et al., 1993; Palit and Pal, 1999; Costa-Leonardo and Patricio, 2005). The structure of the spermatheca has been investigated in several hymenopteran species including Colletidae, Andre- nidae, Halictidae, Apidae, Vespidae and Formicidae (Poole, 1970; Dallai, 1975; Wheeler and Krutzsch, 1994; Pabalan et al., 1996; Martins and Serr~ ao, 2002; Martins et al., 2005; Gobin et al., 2006). The spermatheca consists of a sperm re- servoir, a pair of spermathecal glands and a sperm duct which connects the reservoir to the common oviduct. The associated spermathecal glands are supposed to provide energy to the sperm when it is released from the reservoir (Wheeler and Krutzsch, 1994), while a muscular sperm pump located at the distal portion of the spermathecal duct may regulate the number of sperm released. The reservoir wall consists of a sin- gle cuticle-lined layer of epithelial cells. In social Hymenoptera, the specialization of the spermatheca becomes an especially important feature of their reproductive biology, because they only mate once at the beginning of their adult life and then have to keep sperm viable for the rest of their often long lifetime. In bees, the reservoir size is correlated with colony size, and the thickness of the cell layer of the reservoir as well as gland shape is correlated with social structure (Pabalan et al., 1996; Martins and Serr ~ ao, 2002). Furthermore, spermathecal * Corresponding author. Present address: Faculty of Agriculture, Kagawa University, Ikenobe 2393, Miki-cho 761-0795, Japan. Tel.: þ81 87 891 3146. E-mail address: ito@ago.kagawa-u.ac.jp (F. Ito). 1467-8039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.asd.2007.11.001 Arthropod Structure & Development 37 (2008) 199e209 www.elsevier.com/locate/asd