Journal of Hymenoptera Research Into Two Lateral Arms, Termed the Sternal Apophy- MATERIA! S and METHODS Ses (Snodgrass 1927, Chapman 1992, Lawrence Et Al
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J. HYM. RES. Vol. 3, 1994, pp. 241-277 Phylogenetic Implications of the Mesofurca and Mesopostnotum in Hymenoptera John M. Heraty, James B. Woolley and D. Christopher Darling (JMH) Biological Resources division, CLBRR, Agriculture Canada, C.E.F., Ottawa, Ontario, Canada Kl A 0C6 (present address: Department of Entomology, University of California, Riverside, California, USA 92521); (JBW) Department of Entomology, Texas A&M University, College Station, Texas, USA 77843; (DCD) Department of Entomology, Royal Ontario Museum, Toronto, Ontario, Canada M5S 2C6 — Abstract. The skeleto-musculature of the mesofurca and the mesopostnotum is examined in Hymenoptera. Character systems based on internal structure of the mesothorax support recent hypotheses that suggest sawflies are paraphyletic with respect to Apocrita. Unique character states for Hymenoptera include the presence of two mesofurcal-laterophragmal muscles, a mesofurcal-third basalare muscle, and a scutellar-metanotal muscle. Other possible apomorphies include the medial emargination of the mesopostnotum and the formation of anterior furcal arms. The arrangement of mesofurcal muscles that attach to the and the profurca laterophragma are described and interpreted in light of recent phylogenetic hypotheses. in attachment Changes sites, fusion or loss of the anterior arms of the mesofurca and features of the laterophragma provide characters that are consistent with + the monophyly of Tenthredinoidea (Cephoidea + (Siricoidea (including Anaxyelidae) + + (Xiphydriidae Orussoidea + Apocrita))). Groundplan states for the Apocrita are proposed that include retention of a mesofurcal bridge, retention of an anterior process on the bridge that supports the interfurcal muscles, reduction of the mesofurcal-laterophragmal muscles from two to one, retention of the mesotergal-laterophragmal muscle, loss of the mesofurcal-third basalare muscle, and loss of the metafurcal-spina muscle. Within Apocrita the distribution of character state is less informative than in changes Symphyta, but provide evidence for relationships of some taxa. The mesofurcal bridge is lost convergently in Ceraphronoidea, Pelecinidae, Platygastroidea, Mymarommatoidea, Mymandae and some Chalcidoidea. The tergal-laterophragmal muscle and associated posterior lobe of the laterophragma are postulated to have been lost in nine of independently lineages Apocrita. The development of the laterophragma into an axillary lever is a synapomorphy for Vespoidea and Apoidea, and in Apiformes the lever is an independent sclerite. The distribution of states for 12 characters is discussed for 62 families of Hymenoptera. Parsimony analysis of these data result in trees that generally agree with the current hypotheses for Symphyta but not for Apocrita. INTRODUCTION 1969, 1980,Matsuda 1970,Shcherbakov 1980, 1981, Gibson 1985, Johnson 1988, Whitfield et al. 1989). "Students of these [hymenopteran] parasites discover that The determination of homologous structures and the thorax valuable characters for the determination presents polarity of characters in Hymenoptera are crucial and classification of but are r > species, they handicapped by the _• ,, .• i .• i for a lack of reliable studies on the structure of the thorax" understanding phylogenetic relationships, to lc recentl addressed various authors Snodgrass 1910 p 37 P y by (Rasnitsyn 1969, 1980, 1988, Brothers 1975, Konigsmann 1977, 1978a 1978b, 1986, Since Snodgrass (1910) first attempted to ex- Carpenter Brothers ^d Carpenter 1993). pand our knowledge of the structure of the hy- The mesofurca is an of the ster- menopteran thorax, additional studies have de- invagination scribed num mto the thorax that forms a central oint of the skeleto-musculature of single species P attachment f°r the ventral muscles, or single families (Weber 1925, 1927, Tulloch 1935, longitudinal the muscles, the coxal and trochant- Maki 1938, Duncan 1939, Michener 1944, Bucher sterno-pleural eral muscles ' and the muscles 1948, Alam 1951, Saini et al. 1982, Daly 1964, mesopostnotal ( Kelse 1957 < Matsuda The mesofurca is Gibson 1986, 1993). Fewer studies have compared Y 1970). com nsed of a basal thoracic structures among families of Hy- P plate (discrimenal lamella) that rises vertically f™ the discrimen, slopes menoptera (Snodgrass 1942, Daly 1963, Rasnitsyn posteriorly to the furcal base, and divides dorsally 242 Journal of Hymenoptera Research into two lateral arms, termed the sternal apophy- MATERIA! S AND METHODS ses (Snodgrass 1927, Chapman 1992, Lawrence et al. 1992). The mesopostnotum is one of the pri- Terms for structures and muscles generally mary dorsal sclerites involved in flight through follow Snodgrass (1910, 1942), Daly (1963), Gibson the posterior inflection of the antecosta (second (1985, 1986, 1993) and Ronquist and Nordlander phragma) which forms the posterior attachment (1989). Muscles were identified using the systems of the longitudinal flight muscles. Recent studies proposed by Kelsey (1957) and Daly (1963) (Table involving skeleto-musculature of the hy- 1). Figures 1 and 2 are used to place the skeleto- menopteran thorax have focused on the pleural musculature within the context of the mesosoma. attachments (Shcherbakov 1980, 1981, Gibson 1985, Muscles and stuctures are extensively labeled in 1993), the extrinsic musculature of the mesocoxa Figs. 3 and 4. The Kelsey system uses a fixed set of (Johnson 1988), and the development of the numbers and is useful for comparisons across the metapostnotum (Whitfield et al. 1992). Rasnitsyn Endopterygota. Daly's system is preferred for clar- (1969, figs. 187-194) was the first person to com- ity because the insertion-origin of attachment sites pare the different skeletal structures for the are readily identified and new muscles can be mesofurca of 8 families of Symphyta. His illustra- added to the system; for example, the new muscle tions show the transformation series for was the abbreviation fbl for the Symphyta fu,-ba 3 given that are discussed in this paper. Rasnitsyn (1988) Kelsey system as it could not be assigned a nu- refers to the furca for features supporting meric value that would signify its relative position Tenthredinoidea and for Cephoidea + Siricoidea + to other muscles in the mesothorax. Terms pro- Apocrita. Similarly, Snodgrass (1942) presented a posed by Matsuda (1970) are comprehensive and pictorial evolutionary history for development of may be referenced across orders of insects; how- the axillary lever of Apoidea. This work expands ever his abbreviated system is difficult to use and upon these initial studies and extends the com- is not followed here. parative aspects of these works to include most Several new classifications of families within families of Apocrita. Hymenoptera have been proposed recently that This study of the mesofurca and differ largely in placement of certain families as mesopostnotum began as an attempt to under- separate superfamilies, families, or subfamilies. stand the polarity and homology of mesofurcal We follow the classification of Huber and Goulet structures and muscles of Aphelinidae (1993), as it represents the most current synthesis (Chalcidoidea) and the phylogenetic implications of information across the order. of these attributes within the Chalcidoidea. Even- Dissections were based on specimens pre- the entire to tually Hymenoptera needed be sur- served in 70%ethanol or initially fixed in Dietrich's veyed to resolve what we initially thought were or Kahle's solution and then transferred to etha- In relatively simple questions. this study, all nol. All specimens were critical point-dried prior muscles attaching to the mesofurca and to dissection. The mesosoma of Monomachns mesopostnotum are identified and compared to (Monomachidae) was rehydrated using Barber's homologous muscle groups in Neuropterida and solution, transferred through increasing concen- Mecopterida (sensu Kristensen 1992), as they are trations of ethanol to 98% and then critical point- considered to be phylogenetically close to Hy- dried. For each dissection, the mesosoma was menoptera (Kristensen 1992), and have a mesotho- anchored onto a standard SEM stub using chloro- rax is which structured similar to the Symphyta. form-based silver paint. Dissections were made Within Hymenoptera, we have concentrated our using hooked minuten pins or fragments of razor analysis on the skeletal structure of the mesofurca blades. Dried haemolymph and extraneous tis- and mesopostnotum, and on the muscles attach- sues were removed from dissections using small ing between the thoracic furcae and the amounts of glue obtained by dragging a hooked of the laterophragma mesopostnotum. The evi- minuten pin across clear sticky tape (Gibson 1985). dence the provided by mesofurca and Exemplar taxa were chosen to represent the mesopostnotum for relationships within the maximum variation within taxa. In some groups Chalcidoidea will be discussed in a subsequent (e.g. Apoidea), there was virtually no variation; within paper. whereas some taxa (e.g. Diapriidae) both Volume 3. 1994 243 structure and presence of muscles varied and more + remaining Hymenoptera), the anterior furcal genera were dissected to characterize this varia- arms are either absent, short, or elongate and well tion. Our primary concern was for establishing separated along their entire length. The anterior groundplan states for higher taxa, although arms, or the equivalent region on the lateral arms autapomorphies are discussed. The taxa exam- of the mesofurca, form the posterior