The Progress of Research on Phylogeny and Higher Classification of Ephemeroptera (Insecta)
Abstract
The major opinions on phylogeny and classification systems of Ephemeroptera are introduced and compared. The history of study on this theme is reviewed. The problems of the higher classification of Ephemeroptera are revised and uncovered.
The mayflies (Ephemeroptera) are relics of ancient insects and the living fossils, which are very useful in the study on origin and evolution of Pterygota. Thus, from the Linnaeus' time to recent years, entomologists paid great attention to them and a large number of papers about mayflies were published. Because of diversity and the lack of important extant intergroups and fossils evidence, the phylogeny and higher classification of this order are not clear up to now, although almost every worker on mayflies may have suggested a system or believe in one.
Linnaeus (1758, cited by Eaton 1883-1888) placed six mayflies in the genus Ephemera. They were divided into two groups: the species with two long cerci were put together into one group, the species with three caudal filaments were put into the other one.
In his monograph, Eaton (1883-1888) described 300 mayflies of the world (in 55 genera). Among them, 270 species were divided into 3 groups, 9 series and 14 sections. With the development of study, more and more species were reported, several new family-level groups were established. So Needham et al. (1935) modified Eaton's system to a new one. In their classification, the Ephemeroptera is divided into 3 families and 17 subfamilies. The families were named Ephemeridae, Heptageniidae and Baetidae respectively.
| System suggested by Needhem et al. (1935) | |
| ORDER EPHEMEROPTERA | |
| I. Family Ephemeridae | |
| 1. Palingeniinae | |
| 2. Ephoroninae | |
| 3. Ephemerinae | |
| 4. Potamanthinae | |
| 5. Campsurinae | |
| 6. Neoephemerinae | |
| II. Family Heptageniidae | |
| 7. Heptageniinae | |
| III. Family Baetidae | |
| 8. Oligoneurinae | |
| 9. Ametropinae | |
| 10.Metretopinae | |
| 11.Siphlonurinae | |
| 12.Baetiscinae | |
| 13.Ephemerellinae | |
| 14.Leptophlebiinae | |
| 15.Caeninae | |
| 16.Baetinae | |
| 17.Prosopistomatinae | |
Edmunds et Traver (1954) suggested a new system of the classification and phylogeny, which was modified by Edmunds (1962, 1972) and Edmunds et al. (1976). During this period, Demoulin (1958, cited by Hennig 1981 and some others), Tshernova (1970), Riek (1973, cited by several workers), Landa (1969, 1973) also proposed or reviewed the higher classification of Ephemeroptera. These systems (expect Demoulin's) are similar to each other on the whole.
The precise criteria for the formulation of higher classification in Ephemeroptera have been suggested by Edmunds (1962) and McCafferty et Edmunds (1976). They said the phyletic relationship was an important consideration among these criteria. Edmunds (1972) discussed the relationships between classification, evolution and biogeography, and hypothesized the pattern of plate tectonics history of Gondwanaland based on the mayfly distribution.
The breakthrough of the higher classification of Ephemeroptera was made by McCafferty et Edmunds (1979). They divided the Order Ephemeroptera into two Suborders: Pannota (larval wingpads fused with the mesonotum, and a general enlargement of the mesonotum) and Schistonota (retained the ancestral condition of larval thorax, and mature larvae usually have forewing pads free from notal fusion for one half or more of the length). The system is shown in the table of next page, left column.
But McCafferty (1991) asserted that the rationales of the system mentioned above are the adoption of "evolutionary taxonomy" principles in establishing higher classification of Ephemeroptera. Its essence is that in addition to phylogenetic relationships, the existence of major character gaps (often indicative of major adaptive shifts or its absence) is a function of the classification. Instead, using the cladistic principle and method, he divided the Ephemeroptera into three Suborders named Rectracheata, Setisura and Pisciforma respectively. This system is very much alike with that suggested by Needham et al. (1935)! In 1997, he modified his system (please see the table in next pages, right column). The Heptagenioidea (the Suborder Setisura sensu McCafferty 1991) was placed together with Siphlonuroidea comprising the Suborder Pisciforma. A new Suborder Carapacea including Baetiscidae (and Prosopistomatidae ?) was established.
Also in 1991, using same method, Tomka et Elpers proposed another system. This system differs greatly from all systems of McCafferty's though Tomka et Elpers did not give the hierarchical names of higher ranks (Suborder, Superfamily). There are three main branches in this system. Like the system of McCafferty in 1997, Heptageniidae-like families (the Suborder Setisura sensu McCafferty 1991) are put together with the Baetidae and Siphlonuridae (the families from the Suborder Pisciforma sensu McCafferty 1991). The Suborder Rectracheata sensu McCafferty 1991 was divided into two branches, Ephemeridae-like families comprised one branch, the other represents the Ephemerelliidae-like and Caenidae-like group, Baetiscidae and Prosopistomatidae.
When we compare these systems carefully, we can find that the positions of the Heptagenioidea, Prosopistomatidae, Baetiscidae and Neoephemeridae are not stable. The origin of Heptagenioidea is unknown, the species in Baetiscidae and Prosopistomatidae are very specialized, the adults of Neoephemeridae are very closely alike with the adults of Ephemeroidea, but the nymphs of it are very similar to that of Caenoidea.
Kluge (1998) proposed a new classification system of Ephemeroptera, which is totally different from those before. His viewpoint and terms used differ dramatically from other systems. He put the Baetiscidae and Prosopistomatidae together into the Posteritorna (tornus, the hind angle of the fore wing is situated distinctly behind CuP, usually behind A1; CuA and CuP run nearly parallel to each other, without branches or intercalaries between them) (this is alike with that of McCaffety's in 1997, He put them in a Suborder Carapcea). The other families were put into the Anteritorna (tornus is situated between CuA and CuP, these veins are strongly divergent, with branches of CuA or intercalaries between them). In contrast of establishing a suborder Setisura for Heptageniidae-like group as McCafferty (1991) or put them into Suborder Pisciforma (McCafferty 1997), Kluge (1998) established a Branchiterglinae for them. The Branchiterglinae and Furcaterglinae (somewhat like the Suborder Rectracheata sensu McCafferty 1991) originated from a common ancestor.
From above, we can see that the higher classification and hierarchic level of Ephemeroptera is unstable. Why?
On one hand, large morphological gaps in at least one life stage are common and often profound in recent Ephemeroptera, perhaps due in part to the antiquity and presumed large degree of extinction or decimation in the order (McCafferty et Edmunds 1979). On the other hand, the convergence and parallel are common in Ephemeroptera too.
China has a vast territory, all kinds of eco-environments and high level of biodiversity, but the reported Chinese mayflies are only 227 species (599 in USA, less than 110 species in Japan, 76 in Korea, 84 in Australia) and the nymphs are poorly known. The knowledge of Chinese Ephemeroptera, if improved greatly, would contribute much more to the higher classification, geodistribution, phylogeny, origin and evolution of the order as a whole.
References
Demouli G. 1958. Nouve aus chema de classification des Archodonates et des Ephemeropteres. Bull. Inst. Roy.Sci. Nt.Belg. 34(27):1-19
Edmunds G F Jr. 1962. The principles applied in determining the hierarchic level of the higher categories of Ephemeroptera. Syst. Zool., 11(1):22-31
Edmunds G F Jr. 1972. Biogrography and evolution of Ephemeroptera. Annu. Rev. Entomol., 17:21-42
Edmunds G F Jr, J R Traver. 1954. An outline of a reclassification of the Ephemeroptera. Proc. entomol. Soc.Wash.,56:236-240
Edmunds G F Jr, S L Jensen,L Berner. 1976. The mayflies of North and Central America. University of Minnesota Press, Minniapolis, 330pp
Eaton A E. 1883-1888. A revisional monograph of recent Ephemeridae or mayflies. Trans. Linn. Soc. Lond., (2)3:352p., 65 pl
Hennig W. 1981. Insect Phylogeny. Translated and edited by A.C.Pont. John Wiley & Sons Press
Kluge N J. 1998. Phylogeny and Higher classification of Ephemeroptera. Zoosystematica Rassica, 7(2):255-269
Koss R W, G F Edmunds Jr. 1974. Ephemeroptera eggs and their contribution to phylogenetic studies of the order. Zool.J.Linn.Soc., 55:267-344
Landa V. 1969. Comparative anatomy of mayfly larvae (Ephemeroptera). Acta entomol. Bohemslav., 66:289-316
Landa V. 1973. A contribution to the evolution of the order Ephemeroptera based on comparative anatomy, pp.155-159. In W. L.Peters & J.G.Peters (eds.): Proceedings of the first international conference on Ephemeroptera. Brill, Leide
McCafferty W P. 1991. Toward a phylogenetic classification of the Ephemeroptera (insecta): a commentary on systemactics. Ann. Ento. Soc. Amc., 84(4):343-360
McCafferty W P. 1997. Ephemeroptera. Pages 89-117. In: R.W.Poole and P. Gentili (eds.). Nomina Insecta Nearctica, a checklist of the insects of North Ameriva. Volume 4: Non-holometabolous orders. Entomological Information Services, Rockville, Maryland
McCaffety W P, Edmunds G F Jr. 1976. Redefinition of the family Palingeniidae and its implications for the higher classification of Ephemeroptera. Ann. Entomol. Soc. Am., 69:486-490
McCaffety W P, Edmunds G F Jr. 1979. The higher classification of the Ephemeroptera and its evolutionary basis. Ann.Entomol.Soc.Am., 72:5-12
Needham J G, J R Traver, Y C Hsu. 1935. The biology of mayflies. Ithaca:Comstock
Riek E F. 1973. Classification of the Ephemeroptera. In W. L.Peters & J.G.Peters (eds.): Proceedings of the first international conference on Ephemeroptera. Brill, Leide
Tomka I, C Elpers. 1991. Problems in the phylogeny of the Ephemeroptera. In Alba-tercdor & Sanchezortega: Overview and strategies of Ephemeroptera and Plecoptera. The Sandhill crane Press. Gainesvill, Florida, USA
Tshernova O A. 1970. On the classification of the fossil and recent Ephemeroptera.(in Russian). Entomol. Obozr., 49:124-145