Canadian Journal of Arthropod Identification

The Taxonomy of the North American Species of Parameletus Bengtsson, 1908 (Ephemeroptera: Siphlonuridae), with Keys to Nymphs and Male Imagos

CJAI 33 -- November 1, 2017

Steven K. Burian

| Abstract | Introduction | Materials & Methods | Key to Parameletus species | Systematic Accounts | Acknowledgments | References | PDF | Cite | Appendix |



Among the mayflies of higher latitudes (i.e., 50°–70°N ) of the Northern Hemisphere, species of the genus Parameletus Bengtsson are conspicuous, widespread, and ecologically important (McDunnough 1923, 1930, 1938, Edmunds 1952, 1957, Harper and Harper 1981, Söderstrom 1988, Söderstrom and Nilsson 1986, 1987, Giberson et al. 2007, and Tiunova 2008). The genus Parameletus was described from Sweden by Bengtsson (1908) and since then it has been the subject of many studies (Bengtsson 1909, Esben-Petersen 1916, McDunnough 1923, 1930, 1938, Traver 1935, Speith 1938, Daggy 1941, Edmunds 1952, 1957, Brinck 1957, Edmunds et al. 1976, Hubbard 1977, Söderstrom and Nilsson 1986, 1987, Studemann and Tomka 1991, Tiunova 2008, and Webb et al. 2012). Historically, the complex nomenclatural history of Parameletus produced much confusion as to the validity of the genus and its type species. Hubbard (1977) reviewed and clarified the nomenclature of Parameletus and P. chelifer (its type species) and thereby produced the current level of taxonomic stability for Parameletus. All previous synonyms for Parameletus were listed by Hubbard (1977) and there have been no new additions to his list. Despite stability in the genus name there have been continuing problems concerning the taxonomy of its species.
In North America species of the Parameletus are known mostly from the male imago, but this life stage is rarely collected. Currently 4 species of Parameletus are known from North America, 3 restricted to the Nearctic (P. columbiae McDunnough, P. croesus (McDunnough), and P. midas (McDunnough)) and 1 that is Holarctic (P. chelifer Bengtsson). Although the imagos of all 4 species and the nymphs of all but 1 species of North American Parameletus have been variously described and partially figured (McDunnough, 1923, 1938, Traver 1935, Spieth 1938, Daggy 1941, Edmunds 1952, Jensen 1966, Söderstrom and Nilsson 1986, and Tiunova 2008) the taxonomic treatments are incomplete and not comparable. There are no comprehensive keys to imagos or nymphs. Consequently, because the appropriate taxonomic tools were lacking, we know little about the life history, ecology, or distribution of Parameletus species.
The earliest account of Parameletus in North America was given by McDunnough (1923) where he described both P. croesus and P. midas in a single paper. Even though McDunnough (1923) did include basic outline drawings of the male genitalia of these species, the lack of detail greatly limited their usefulness. The species accounts of P. croesus and P. midas focused mostly on details of color and color patterns of male imagos with female imagos receiving similar, but briefer treatment. McDunnough (1930) later provided additional details of the nymph of P. midas and indicated that the reader should compare his figures of the gill and mouthparts of P. midas to those of P. chelifer presented by Ebsen-Petersen (1916). Unfortunately, McDunnough’s figures (as well as those by Ebsen-Petersen) were too rudimentary to be used for any detailed comparison. Traver (1935) redescribed the male imago of P. midas and P. croesus (despite admitting that she was only able to study specimens of P. midas) and provided a key that relied on the use of pigmentation of the forewing membrane to separate these species. Traver (1935) did provide figures of the wings and male genitalia of P. midas. Although figures of the wings seem quite accurate, her figure of the male genitalia of P. midas has some problems. Principally Traver’s figure of the genitalia P. midas has 3 problems (1) the transparent inner edges of the lobes of the penes lobes were omitted, (2) the figure is presented from the dorsal perspective and shows paired blunt lobes crossing under the sharp inward curving paired spines; this is incorrect because the blunt lobes are actually ventral structures and should only be indicated as dotted lines dorsally, and (3) dorsally there appears to be 2 slender sharply pointed spines with diverging tips that arise near the base of the penes; these spines do not exist and what appears as spines are actually the thick edges of the large sharp inward curving spines of the dorsal surface of the penes.
Eight years after he described P. croesus and P. midas, McDunnough (1938) described P. columbiae based on imagos that were collected from a swarm above a glacial stream in British Columbia, Canada. In that same paper he also noted the first North American record of P. chelifer based on imagos collected from Churchill, Manitoba, Canada. In support of his earlier work McDunnough (1938) also provided much improved figures of the male genitalia of P. chelifer and P. midas. Although McDunnough’s new figures for these species were much needed so was information on P. croesus,  no new figures or details were presented. Until now this has been a problem concerning P. croesus, because except for the unpublished (and virtually unknown) figure of the male genitalia of P. croesus in Daggy’s (1941) Ph.D. thesis on Minnesota mayflies, there were no detailed illustrations of its genitalia available for study.
The next major contribution to the study of North American Parameletus was made by Edmunds (1952, 1957) who reported on a population of P. columbiae that he discovered at altitude (~2100–2500 m ASL) in the Rocky Mountains of Utah. In his Ph.D. thesis, Edmunds (1952) redescribed the male and female imago and provided the first account of the nymph of P. columbiae, but none of these taxonomic accounts were ever published. Edmunds did however publish his observations of the life history of P. columbiae noting its remarkably short development time, 16–21 days at the Brighton, UT site (Edmunds 1957, Edmunds et al.1976). Despite not publishing some of his earlier taxonomic work, Edmunds’ studies facilitated the survey of Idaho mayflies by Jensen (1966), wherein he reported additional new records of P. columbiae. Subsequently P. columbiae became the best studied of any species of Parameletus in North America, but because of the lack of knowledge of the other Nearctic species of Parameletus this contributed to a rather narrow view of the life history and habitat of the genus at that time. Details of the of life history and habitat of P. columbiae were presented by Edmunds et al.(1976) in a way that has frequently led to a misunderstanding of the entire genus in North America. Studies on the biology of the Holarctic species P. chelifer (Söderstrom and Nilsson 1987, Söderstrom and Johansson 1988, and Söderstrom 1988) clearly indicate a wider range of environmental tolerances and a more variable developmental period than what is known for P. columbiae. New data on the habitat of nymphs and estimates of development times are presented here for P. midas, P. croesus, and P. chelifer.
Jacobus and McCafferty (2002) briefly commented on the status of P. croesus based on their study of the types. They noted that even though P. croesus had not been collected for 75 years, it was premature to declare it extinct. This was a prudent decision, especially since Daggy (1941) collected a swarm of P. croesus in 1939, only 63 years earlier. Wing characters discussed by Jacobus and McCafferty (2002) for separating P. croesus from P. midas are now determined to be unreliable based on the study of additional specimens of these species. Webb et al. (2012) presented some data on Parameletus species as part of a larger project to quantify a portion of the regional species pool of the Canadian lower Arctic using DNA barcodes. The use of molecular marker sequences to assist in determining species has been a positive step toward addressing the problems of identifying species from life stages and material for which there are no useful traditional taxonomic keys. Webb et al. (2012) used the COI marker sequence to confirm the co-occurrence of P. midas and P. chelifer in samples from Churchill, Manitoba. Their consensus analysis of sequence divergence values also showed a strong association of samples of P. midas from Manitoba and New Brunswick with clear separation from samples of P. chelifer. The previous record of P. midas at the Churchill site (Harper and Harper 1981) had been somewhat suspect because it was far removed from what had been believed to the major part of the range of P. midas in eastern Canada, because there were no other sites known for the species between those two areas, and because the original adult material upon which the record was based could not be located for study. Kjærstad et al. (2012) briefly commented on the high degree of similarity in molecular marker sequences obtained for specimens of P. chelifer from Finmark region of Scandinavia and from Churchill, Manitoba, Canada. Their findings strongly support the true Holarctic status of P. chelifer and recognize the important genetic connection between Nearctic and Palearctic populations. The most recent treatment of Nearctic Parameletus was by Klubertanz (2016) who summarized the known distribution of the genus in Wisconsin, but did not include any new records for that region. Finally there are other publications that include either brief taxonomic overviews of the genus (e.g., Burks 1953) or enigmatic distribution records without specifics (e.g., Edmunds et al. 1976); in most instances these treatments simply summarized what was already known about the genus and do not contribute any new information.
Despite all of the work done on North American Parameletus during the past 89 years, nymphs (the most frequently collected life stage) cannot be reliably identified to species. Moreover, the use of incomplete keys to nymphs has led to widespread misidentifications adversely affecting estimates of regional species diversity and inhibited new studies on the biology and ecology of the Nearctic species of Parameletus. To a lesser extent, incomplete and poorly illustrated keys for male imagos have also contributed to this problem. The focus of this study was to update and complete the taxonomy of the species of Parameletus in North America and produce new keys for nymphs and imagos. The distributions of all species are plotted and discussed. New information on the aquatic habitats, emergence times, and conditions are also presented.