MorphologyBlackwell Science, Ltd and evolution of the tarsal plantulae in Hymenoptera (Insecta), focussing on the basal lineages SUSANNE SCHULMEISTER* Accepted: 5 June 2002 Schulmeister, S. (2003). Morphology and evolution of the tarsal plantulae in Hymenoptera (Insecta), focussing on the basal lineages. — Zoologica Scripta, 32, 153–172. The morphology of the plantulae (= tarsal pulvilli = plantar lobes), structures attached to the underside of the tarsus in Hymenoptera, was examined in 55 genera from all 14 families of the basal lineages of Hymenoptera (‘Symphyta’) and a few species of Apocrita, using scanning electron microscopy. Two distinct types of plantula were found: (1) integrated, an unsclerotized patch positioned ventro-distally on each tarsomere, and (2) distal, a membranous vesicle attached to the apical end of each tarsomere. The evolution of these two types is discussed in the light of current phylogenetic hypotheses. The plantulae exhibit an astonishing variety of form and structural details; their potential phylogenetic and taxonomic value is discussed. Susanne Schulmeister, Institute of Zoology and Anthropology and Zoological Museum, Berliner Str. 28, 37073 Göttingen, Germany. E-mail: [email protected]. Introduction the plantulae to characterize some of his taxonomic groups, A multitude of different structures attached to the tarsi and but did not discuss their evolution. Due to the lack of a com- pretarsi of insects has evolved. A comparative study on the parative study, there has been no attempt to use the plantulae ordinal level was recently undertaken within a cladistic as a character in phylogenetic analysis. Königsmann (1977) context by Beutel & Gorb (2001), in which they concluded mentions their presence or absence in certain groups and that that the plantulae found in the Hymenoptera are unique to they probably belong to the groundplan of Hymenoptera, this insect group. The plantulae (plantar lobes, tarsal pulvilli) but did not use them in his phylogeny of lower Hymenoptera. are membranous structures on the underside of the tarsus, Vilhelmsen (1997) mentions the plantulae (‘plantar lobes’) integrated in or attached to the ventro-distal part of each as potentially informative characters, but did not use them tarsomere. because they were insufficiently surveyed; in more recent It has been known for a long time that two distinct types phylogenetic treatments (Ronquist et al. 1999; Vilhelmsen 2001), of tarsal plantulae, integrated and distal, are found in the the plantulae are not mentioned at all. Hymenoptera (Börner 1919; Benson 1945a, 1954). In spite of The present study has been written with the aim of bring- this, they have not been the subject of a comparative study. ing these structures to the attention of both morphologists Due to the broad scope of their investigation, Beutel & Gorb and systematists. (2001) examined only two species of Hymenoptera with plantulae, both of which have the distal type. It seems that Materials and methods the existence of these structures has been overlooked by Classification (following Vilhelmsen 2001) and names of the morphologists. species included in the present study, as well as the methods The presence of two types of plantulae raises a number of of preservation and examination of the specimens study, are questions about their evolution. Whether they are homologous, given in Table 1. and if so, which type is plesiomorphic and which apomorphic. Most specimens were fixed in Bouin’s fluid following How they might have originated and their potential value as collection and subsequently stored in 70% ethanol. They a source of phylogenetic information. These problems have were examined with a stereomicroscope (Zeiss Stemi SV 11, also escaped the attention of systematists. Börner (1919) used maximum magnification 66×). One hind tarsus of each specimen chosen for scanning electron microscopy was cut off and cleaned twice using ultrasound. Alcohol concentration *Present address: Division of Invertebrate Zoology, American Museum of Natural History, Central Park West at 79th St., New York, NY 10024, USA. was slowly raised to 100% in 5% steps over the course of E-mail: [email protected] several days in order to avoid collapsing of the plantulae. The © The Norwegian Academy of Science and Letters • Zoologica Scripta, 32, 2, March 2003, pp153–172 153 Tarsal plantulae in Hymenoptera • S. Schulmeister Table 1 Taxa examined in the present study. The column ‘Pres.’ specifies the preservation method: p.a. = pure alcohol; Bouin = kept in 70% alcohol after Bouin fixation; pinned = pinned and dried museum specimen. SEM = scanning electron microscopy and stereo light microscopy, SLM = stereo light microscopy only. Species Sex Pres. M. 1 2 3 4 5 6 7 MECOPTERA Panorpa communis f Bouin SEM 0 — 0 2 — — — HYMENOPTERA XYELOIDEA Xyelidae Macroxyela ferruginea (Say, 1824) m Bouin SEM 1 — 1 0 1 0 0 Xyelecia nearctica Ross, 1932 f pinned SEM 3 0 1 0 0 0 0 Xyela sp. f + m Bouin SEM 1 — 1 2 ? 0 0 Pleroneura bruneicornis Rohwer, 1910 f + m pinned SEM 0 — 1 0 — — — TENTHREDINOIDEA Blasticotomidae Runaria reducta Malaise m p.a. SEM 3 0 0–1 0 1 0 0 Tenthredinidae Monophadnoides sp. m Bouin SEM 3 ? 1 0 0 1 0 Strongylogaster xanthocera (Stephens, 1835) f Bouin SEM 3 1 1 0 0 1 0 Selandria serva (Fabricius, 1793) m Bouin SEM 3 1 1 0 0 2 0 Taxonus agrorum (Fallén, 1808) m Bouin SEM 3 0 1 0 0 4 0 Allantus didymus (Klug, 1818) m Bouin SEM 3 ? 1 0 0 4 0 Dolerus pratensis (Linnaeus, 1758) m Bouin SEM 3 1 1 0 0 1 0 Dolerus sp. m Bouin SEM 3 1 1 0 0 5 0 Dolerus gonager (Fabricius, 1771) m Bouin SEM 3 1 1 0 0 0 0 Tenthredo campestris Linnaeus, 1758 m Bouin SEM 3 1 1 0 0 2 0 Tenthredo mesomela Linnaeus, 1758 m Bouin SEM 3 1 1 0 0 1 0 Aglaostigma lichtwardti (Konow, 1892) m Bouin SEM 3 ? 1 0 0 1/4 0 Tenthredopsis stigma (Fabricius, 1798) m Bouin SEM 3 1 1 0 0 1 0 Tenthredopsis tarsata (Fabricius, 1804) m Bouin SEM 3 1 1 0 0 1 0 Siobla sturmii (Klug, 1817) m Bouin SEM 3 1 1 0 0 5 0 Athalia rosae (Linnaeus, 1758) m Bouin SEM 3 1 1 0 0 0 0 Athalia sp. m Bouin SEM 3 ? 1 0 0 0 0 Nematus sp. f Bouin SEM 3 1–2 1 0 0 1 0 Hoplocampa fulvicornis (Panzer, 1801) m Bouin SEM 3 ? 1 0 0 1 0 Cladius pectinicornis (Geoffroy, 1785) m Bouin SEM 3 ? 1 0 0 1/4 0 Diprionidae Monoctenus juniperi (Linnaeus, 1758) f Bouin SEM 3 2 1 0 3 3 0 Gilpinia sp. f Bouin SEM 3 2 1 0 1 3 0 Diprion sp. (pini or similis) f + m Bouin SEM 3 2 1 0 3 3 0 Macrodiprion nemoralis (Enslin, 1917) f Bouin SEM 3 2 1 0 3 3 0 Cimbicidae Corynis crassicornis (Rossi, 1790) m Bouin SEM 3 0 1 0 1 5 0 Cimbex connatus (Schrank, 1776) f pinned SEM 3 1 1 ? 5 3 0 Zaraea sp. f p.a. SEM 3 1 1 2 5 3 0 Abia fasciata (Linnaeus, 1758) f p.a. SEM 3 1 1 0 5 3 0 Abia nitens (Linnaeus, 1758) m pinned SEM 3 ? ? ? 5 6 0 Argidae Arge ochropus (Gmelin, 1790) m Bouin SEM 3 1 1 0 0 0 0 Arge cyanocrocea (Forster, 1771) m Bouin SEM 3 ? 1 0 0 0 0 Arge gracilicornis (Klug, 1814) m Bouin SEM 3 ? 1 0 0 0 0 Sterictiphora furcata (Villers, 1789) m Bouin SEM 3 1 1 0 0 0 0 Pergidae Perga sp. m pinned SLM 3 1 1 ? 1 0 0 Lophyrotoma analis (Costa) m Bouin SEM 3 1 1 0 1 0 0 Neoeurys sp. m Bouin SEM 3 ? 1 0 2 0 0 Decameria sp. m Bouin SEM 3 3 0 ? 2 0 0 Phylacteophaga froggatti Riek f p.a. SEM 3 ? 0 0 0 0 0 PAMPHILIOIDEA Pamphiliidae 154 Zoologica Scripta, 32, 2, March 2003, pp153–172 • © The Norwegian Academy of Science and Letters S. Schulmeister • Tarsal plantulae in Hymenoptera Table 1 Continued. Species Sex Pres. M. 1 2 3 4 5 6 7 Neurotoma fasciata (Norton, 1862) m pinned SLM 2 — ? ? ? ? ? Pamphilius hortorum (Klug, 1808) f p.a. SEM 2 — 1 0 1 0 0 Onycholyda amplecta (Fabricius, 1804) f + m Bouin SEM 2 — 1 0 1–2 0 0 Cephalcia sp. m Bouin SEM 2 — 1 0 2 0 0 Acantholyda sp. m Bouin SEM 2 — 1 0 2 0 0 Megalodontesidae Megalodontes cephalotes (Fabricius, 1781) f + m Bouin SEM 2 — 1 0 0 0 0 Megalodontes panzeri (Leach, 1817) m Alkohol SEM 2 — 1 0 0 0 0 CEPHOIDEA Cephidae Cephus pygmeus (Linnaeus, 1767) m Bouin SEM 3 0 0 1 0 4 0 Calameuta filiformis (Eversmann, 1847) f + m Bouin SEM 3 0 1 0 0 0/4* 0 Hartigia trimaculata (Say, 1824) f + m Bouin SEM 3 0 1 0 0 0 0 Janus integer (Norton, 1861) m Bouin SEM 3 0 0 0 + 1 0 4 0 Caenocephus sp. m Pinned SLM 3 0 0? ? ? ? ? Pachycephus sp. m Pinned SLM 3 0 1? ? ? ? ? ANAXYELOIDEA Anaxyelidae Syntexis libocedrii (Rohwer, 1915) f Bouin SLM 0 — 0 ? — — — SIRICOIDEA Siricidae Urocerus gigas (Linnaeus, 1758) f + m Bouin SEM 1 — 1 2 0 0 1 Xeris spectrum (Linnaeus, 1758) m Bouin SEM 0 — 1 2 — — — Sirex noctilio Fabricius, 1793 ? p.a. SEM 1 — (1) 2 0 0 1** Tremex columba (Linnaeus, 1763) f p.a. SEM 1 — 1 2 4 0 1 XIPHYDRIOIDEA Xiphydriidae Xiphydria camelus (Linnaeus, 1758) m Bouin SEM 4 1 1 0 0 0 0 Xiphydria prolongata (Geoffroy, 1785) f Bouin SLM 4 1 1 ? ? ? ? Derecyrta lugubris Westwood f pinned SEM 0 — 0 ? — — — Steirocephala sp.