The Sister Group of Aculeata (Hymenoptera) – Evidence from Internal Head Anatomy, with Emphasis on the Tentorium
Total Page：16
File Type：pdf, Size：1020Kb
74 (2): 195 – 218 10.10.2016 © Senckenberg Gesellschaft für Naturforschung, 2016. The sister group of Aculeata (Hymenoptera) – evidence from internal head anatomy, with emphasis on the tentorium Dominique Zimmermann *, 1 & Lars Vilhelmsen 2 1 Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria; Dominique Zimmermann [[email protected]] — 2 Natural History Museum of Denmark, SCIENCE, University of Copenhagen; Zoological Museum, Universitetsparken 15, DK-2100, Copen- hagen, Denmark; Lars Vilhelmsen [[email protected]] — * Corresponding author Accepted 23.viii.2016. Published online at www.senckenberg.de/arthropod-systematics on 21.ix.2016. Editor in charge: Benjamin Wipfler Abstract The Aculeata comprises some of the best known Hymenoptera. Traditionally, their sister group has been considered to be the Ichneumo- noidea; however, recent phylogenetic analyses contradict this hypothesis. We evaluate three potential candidates for the sister group of aculeate wasps: Ichneumonoidea, Evanioidea and Trigonaloidea. This is addressed by investigating the internal head anatomy of repre- sentatives of the relevant taxa, specifically the tentorium, musculature and glands. One species each of the families Braconidae, Evaniidae, Gasteruptiidae, Aulacidae and Trigonalidae, as well as Sphecidae and Sapygidae as representatives of Aculeata, and Ibaliidae as outgroup is examined. 33 head anatomical characters are mapped on the three competing hypotheses. Aculeata + Evanioidea are corroborated by the presence of a secondary bridge, the presence of a subforaminal cup and the presence of one medial sulcus on the ventral head sclerotisation instead of two sublateral ones. Trigonaloidea + (Aculeata + Evanioidea) is corroborated by the presence of a bent cibarium. The presence of a hypopharyngeal gland, the backwards shift of the origin of the antennal muscles, the loss of the connection of the dorsal tentorial arms with the head capsule and the loss of ventral salivarial dilators are retrieved as synapomorphies of Aculeata. Two hitherto unknown glands, a hypopharyngeal salivary gland in Sphecidae and Sapygidae and a hypopharyngeal-maxillary gland in Evaniidae, are described. Key words Evanioidea, Trigonaloidea, phylogeny, head musculature, glands, microCT. 1. Introduction Aculeata or stinging wasps include some of the insect identifying Aculeata’s closest relatives has not been an- taxa with the highest ecological and economic impact swered satisfactorily. such as ants and bees, in addition to other charismatic Three hypotheses have emerged repeatedly in recent groups, e.g., gold wasps, velvet ants and spider wasps. analyses of hymenopteran phylogeny: They fill vital ecological roles as predators and pollina- 1. Aculeata + Ichneumonoidea. Traditionally, Acu- tors, often to the benefit of humankind, although their leata have been regarded as the sister group of the Ich- medical impact is usually detrimental. Furthermore, the neumonoidea, one of the most diverse superfamilies of occurrence of eusociality among Hymenoptera is re- parasitoid wasps. Two morphological characters, the stricted to Aculeata, having evolved multiple times with- presence of ovipositor valvilli and distinct propodeal ar- in the group (e.g. DANFORTH 2002). Though a lot is known ticulating processes, were suggested by RASNITSYN (1988) about this fascinating group, the fundamental question of as synapomorphies in his analysis which, though intui- ISSN 1863-7221 (print) | eISSN 1864-8312 (online) 195 Zimmermann & Vilhelmsen: The sister group of Aculeata tive, can be regarded as a milestone in the reconstruc- ed by MIKO et al. (2007) and POPOVICI et al. (2014), the tion of hymenopteran phylogeny. However, VILHELMSEN latter being limited to the labiomaxillary complex but ex- et al. (2010) found the presence of propodeal articulating amined with confocal laser scanning microscopy which processes to be widespread among the Apocrita, not re- excellently illustrates the internal anatomy in great detail. stricted to just Aculeata and Ichneumonoidea. RONQUIST Finally RONQUIST & NORDLANDER (1989) provided an ex- et al. (1999) performed a formal cladistic reanalysis of tensive description of the skeletal morphology of the ba- Rasnitsyns dataset and found moderate support for the sal cynipoid Ibalia rufipes Cresson, 1879, which serves ichneumonoid-aculeate relationship, as it was retrieved as an outgroup taxon for our analyses. under implied weighting, but not among the equally The best-examined aculeate taxon is, unsurprisingly, weighted most parsimonious trees. Additional moder- the honeybee (Apis mellifera Linné, 1758). SNODGRASS’ ate support was provided by an early molecular analysis (1910) pioneering comprehensive study of honeybee based on 16S rRNA (DOWTON & AUSTIN 1994). Further- anatomy is a good starting point. For head anatomy, more, VILHELMSEN et al. (2010) retrieved Aculeata + Ich- YOUSSEF (1971) provided a detailed topography of the neumonoidea in their analyses based on morphological cephalic musculature and nervous system and also a first data, but again solely under implied weighting. Under attempt to homologize hitherto described head anatomi- equal weighting and with higher K values (K=25) the cal structures in Hymenoptera. A detailed investigation Aculeata were placed as sister group to the remaining of the honeybee tentorium has been performed by ERICK- Apocrita except Stephanoidea. SON & SHENG (1984), and it is also covered in BERRY & 2. Aculeata + Evanioidea. The Evanioidea comprise IBBOTSON (2010) and PORTO et al. (2016). Besides bees, three families united by having the metasoma inserted there are a couple of classical detailed anatomical studies high on the mesosoma, but which are otherwise highly of other aculeates, JANET (1900, 1905) on ants (Myrmi divergent morphologically and biologically: the Aulaci- ca rubra [Linné, 1758]) and DUNCAN (1939) on vespids dae are parasitoids of wood-dwelling insects, the Gaster- (Vespula pensylvanica [de Saussure, 1857]) which are uptiidae nest parasites of solitary bees and the Evanii- still unsurpassed in their level of detail. dae cockroach egg capsule predators. The Evanioidea Head anatomical data for the three evanioid families emerged as the sister group of Aculeata in the most com- and for Trigonaloidea are provided in the present study prehensive analysis of hymenopteran relationships to for the first time. date (SHARKEY et al. 2012). This analysis was performed by the Tree of Life project: morphological characters and molecular data were compiled from all sources available at the time, and analyzed using a combined approach. 2. Material and methods However, only the molecular data supported Aculeata + Evaniodea in SHARKEY et al. (2012). Additional mo- lecular support was found in a subsequent analysis of 2.1. Specimens examined 120.000 sequences from 80.000 sites that were extracted from GenBank (PETERS et al. 2011). To evaluate the putative sister groups of the Aculeata, 3. Aculeata + Trigonaloidea. The Trigonaloidea are we examined one ichneumonoid, one trigonaloid, and another small superfamily containing only the Trigonali- one representative of each of the three evanioid families, dae with less than 100 species worldwide (CARMEAN & in addition to two aculeates and an ibaliid as outgroup. KIMSEY 1998). Most of them are highly specialized hy- A detailed list of the material is given in Table 1. The perparasitoids of other parasitoid Hymenoptera (WEIN- specimens were chosen based on the taxon sample of STEIN & AUSTIN 1991). In molecular analyses by HERATY the Hymenopteran Tree of Life Project (SHARKEY et al. et al. (2011) and KLOPFSTEIN et al. (2013) the Trigona- 2012). For each species one microCT scan, one sagittal loidea were retrieved as the sister group of the aculeates. and one cross section were acquired except for Doryctes Again, morphological support is missing. erythromelas, where no microCT scan was obtained. For In the present study we use characters from the inter- morphological investigations the specimens were killed nal head anatomy to test these hypotheses. Head charac- in 90% alcohol, and then fixed in alcoholic Bouin’s fluid ters have proven to be informative on higher phyloge- for 3 hours. The voucher specimens are deposited in the netic levels in previous studies in other holometabolan Hymenoptera Collection of the Natural History Museum orders (e.g. BEUTEL et al. 2009; DRESSLER & BEUTEL 2010; Vienna. RANDOLF et al. 2014), while in apocritan Hymenoptera this is a hitherto underexplored character complex. A few head anatomical studies have been done for basal Hyme- 2.2. Histological sections noptera, either on the complete head anatomy of selected species (MATSUDA 1957; BEUTEL & VILHELMSEN 2007) or In order to better allow the resin to infiltrate the speci- with focus on specific regions of the head (VILHELMSEN men, the head was carefully cut open with a scalpel on 1996, 1999, 2011). Thorough studies of the head also both sides at the eye region so that none of the structures exist for Braconidae: ALAM (1951) and, more recently, studied were damaged. Subsequently the heads were em- KARLSSON & RONQUIST (2012). Platygastridae were treat- bedded in Araldite. Semithin histological sections (2 µm) 196 ARTHROPOD SYSTEMATICS & PHYLOGENY — 74 (2) 2016 Table 1. List of studied material. Family Species Sex MicroCT Saggital his- Cross histol. Label data tol. sections sections Aulacidae Pristaulacus strangaliae f Morphosource file × × USA, West Virginia, Hardy Co. [unty],