Western North American Naturalist Volume 69 Number 4 Article 15 12-17-2009 Note on the occurrence of Siphlonurus autumnalis (Ephemeroptera: Siphlonuridae) in a Montana spring brook Robert L. Newell University of Montana, Polson, [email protected] Michelle L. Anderson University of Montana Western, Dillon Follow this and additional works at: https://scholarsarchive.byu.edu/wnan Recommended Citation Newell, Robert L. and Anderson, Michelle L. (2009) "Note on the occurrence of Siphlonurus autumnalis (Ephemeroptera: Siphlonuridae) in a Montana spring brook," Western North American Naturalist: Vol. 69 : No. 4 , Article 15. Available at: https://scholarsarchive.byu.edu/wnan/vol69/iss4/15 This Note is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 69(4), © 2009, pp. 551–555 NOTE ON THE OCCURRENCE OF SIPHLONURUS AUTUMNALIS (EPHEMEROPTERA: SIPHLONURIDAE) IN A MONTANA SPRING BROOK Robert L. Newell1 and Michelle L. Anderson2 ABSTRACT.—The little-known mayfly Siphlonurus autumnalis McDunnough (Ephemeroptera: Siphlonuridae) was col- lected from several locations in its floodplain habitats along the Middle Fork of the Flathead River in western Montana. To confirm identification, nymphs were reared along with an associated species, S. occidentalis Eaton (Ephemeroptera: Siphlonuridae). Adults emerged from 6 September until 16 October. Habitats are described and the first photos of the 2 sexes are provided. Key words: mayfly, Siphlonurus autumnalis, emergence, habitats, Montana, spring brook. The biology of the mayfly Siphlonurus This spring brook arises from groundwater autumnalis McDunnough is so poorly known seeps at about 1009 m elevation and flows that the nymphs were only recently described westward, eventually into a side channel of (Jacobus and McCafferty 2002). Siphlonurus the Middle Fork of the Flathead River. During autumnalis has been recorded in Montana the annual peak in the river hydrograph (Newell 1970, Randolph 2002, McCafferty and (June–July), the spring channel contains a por- Newell 2007), Washington (Jensen 1966, tion of the Flathead River discharge. This flow Jacobus and McCafferty 2002, Randolph 2002), of surface water from the main channel into and the Canadian provinces of Alberta and the spring brook is cut off when the river dis- British Columbia (McDunnough 1931, Ran- charge declines by late July. The sampling dolph 2002). Jacobus and McCafferty (2002) location was approximately 100 m from the suggested that this species is seldom collected spring source in an area 4 m wide and a maxi- because of the difficulty in accessing larvae mum of 30 cm deep with a substrate of cobble, habitat, which includes the rocky edgewaters gravel, sand, and silt. Flow was barely percep- of large rivers (Edmunds et al. 1976). We sug- tible at <1 cms. gest there may be other reasons why S. autum- Anderson (2008) and Chilcote (2004) col- nalis is rarely collected: notably, the immature lected at this location on numerous occasions nymphs are nearly impossible to identify, the during 2002–2005. Their summer sampling species is often associated with other species revealed mature nymphs of S. occidentalis and of Siphlonurus, and the published habitat is a smaller unidentifiable Siphlonurus. Late sum- incomplete. mer collections (12 September 2003) revealed Opportunities to collect large numbers of subimagoes of S. autumnalis. It was concluded Siphlonurus from a variety of habitats was the small previously collected nymphs were afforded through a long-term ecological study probably S. autumnalis. The presence of these of aquatic habitats associated with the Nyack 2 Siphlonurus species in this small spring Floodplain of the Middle Fork of the Flathead brook provided an opportunity to learn more River in western Montana. The study area was about the biology of these species through fur- located in Flathead County, Montana, approxi- ther sampling. Our goals were to determine mately 16 km northeast of West Glacier along population composition of the 2 species, deter- the southern boundary of Glacier National mine emergence timing, and provide photos Park. Siphlonurus occidentalis and S. autum- of the 2 sexes of S. autumnalis. nalis were particularly abundant in a small Crazy Beaver Spring Brook was visited on spring brook, locally called Crazy Beaver 31 August 2007, 15 September 2007, and 5 Spring Brook (48°28፱16.77፳N, 113°49፱21.11፳W). October 2007 for the purpose of obtaining 1Flathead Lake Biological Station of The University of Montana, 32125 Bio Station Lane, Polson, MT 59860-6815. E-mail: [email protected] 2Biology Department, University of Montana Western, 710 S. Atlantic, Dillon, MT 59725. 551 552 WESTERN NORTH AMERICAN NATURALIST [Volume 69 Fig. 1. Emergence sequence of laboratory-reared Siphlonurus occidentalis. Fig. 2. Emergence sequence of laboratory-reared Siphlonurus autumnalis. specimens of Siphlonurus for identification and Digital photos were taken of nymphs, subima- rearing. Nymphs were collected using a kicknet goes, and imagoes. Nymphs of some associated (125-micron mesh). Part of the sample was pre- mayfly species were also retained, allowed to served in 80% ethyl alcohol and returned to the emerge, and identified to species. laboratory where nymphs were identified and On 31 August 2007, we collected 35 S. occi- counted. The remainder of the sample was dentalis nymphs, most of which had black wing placed into aerated chambers with spring water, pads. We also collected 20 Siphlonurus nymphs refrigerated, and transported to the University that were unidentifiable to species but were of Montana’s Flathead Lake Biological Station presumably S. autumnalis. Water temperature (FLBS). In the laboratory, the live nymphs were in the spring brook was 10 °C. On 15 Septem- placed into flow-through, aerated emergence ber 2007 we collected 7 S. occidentalis nymphs chambers at a temper ature of 11°C. Screening with black pads, 20 S. autumnalis nymphs with was placed over the emergence chambers to black pads, and 10 Siphlonurus nymphs without retain adults. The light cycle was 12 hours of black pads that were unidentifiable to species. light and 12 hours of dark. The chambers were Water temperature in the spring brook was checked daily for adults. Adults and nymphal again 10 °C. On 5 October 2007, no Siphlonurus skins were collected, identified, and preserved. nymphs were present and water temperature 2009] NOTES 553 Fig. 3. Ventral abdomen of Siphlonurus occidentalis subimago. in the spring brook was 8 °C. Additional mayfly (McDunnough 1931); Utah—May–October taxa present during the collection dates were (Edmunds 1952); Washington—July and August Timpanoga hecuba (Eaton) (Ephemeroptera: (Meyer and McCafferty 2007b); and Montana— Ephemerellidae), Paraleptophlebia bicornuta July–September (Newell unpublished data). We (McDunnough) (Ephemeroptera: Leptophlebi- also found evidence to support the observation idae), Ameletus validus McDunnough (Ephem - that S. autumnalis is a fall emerger (McDun- er optera: Amel etidae), Ameletus similior Mc - nough 1931, Jacobus and McCafferty 2002). Dunnough (Eph em eroptera: Ameletidae), and Siphlonurus occidentalis and S. autumnalis Centroptilum conturbatum McDunnough (Eph - clearly coexist in Crazy Beaver spring brook. em eroptera: Baetidae). Both species were nearly equal in abundance A total of 37 S. occidentalis and 34 S. autum- in our fall 2007 samples (Figs. 1, 2). Subima- nalis adults emerged from the emergence goes were collected in the field on 12 Septem- chambers. The rearing chamber results may ber 2007, but it is questionable if emergence not reflect the true emergence patterns of these to maturity occurred in the field during late species, but coupled with the results of previous September and early October in the study field collections (Chilcote 2004, Anderson 2008), area. Freezing air temperatures are common the results do offer an index of relative after mid-September, and ice formed in shal- abundance and a possible range of dates for low reaches of the spring in early October, emergence (Figs. 1, 2). Our results support although the spring typically retains some ice- the pre viously reported emergence timing free reaches throughout the winter. for S. occidentalis as summer–fall: Oregon— In the process of identifying Siphlonurus March–August (Meyer and McCafferty 2007a); specimens to species, we found that mature Alaska—July (Harper and Harper 1981); nymphs and subimagoes of S. occidentalis were Idaho—July, September (Jensen 1966); Ari- easily identified by the U-shaped pattern on zona—June (Allen and Chao 1981); Alberta each sternite (Fig. 3). This pattern appears some and British Columbia—August, September time before the nymphs mature, just prior to 554 WESTERN NORTH AMERICAN NATURALIST [Volume 69 Fig. 4. Ventral surface of male (left) and female (right) Siphlonurus autumnalis nymphs. development of black wing pads, thus increas- actually the color of the subimago adult show- ing the chance of identifying nymphs to species ing through the nymphal skin, similar to S. using abdominal coloration. Male S. autum- occidentalis (Edmunds 1952). The late sum- nalis nymphs can be identified by the dorsal mer emergence of S. autumnalis and the lack touching of the eyes, a