Great Basin Naturalist

Volume 35 | Number 1 Article 4

3-31-1975 Life history and ecology of Megarcys signata (: ), Mill Creek, Wasatch Mountains, Utah Mary R. Cather University of Utah

Arden R. Gaufin University of Utah

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Recommended Citation Cather, Mary R. and Gaufin, Arden R. (1975) "Life history and ecology of Megarcys signata (Plecoptera: Perlodidae), Mill Creek, Wasatch Mountains, Utah," Great Basin Naturalist: Vol. 35 : No. 1 , Article 4. Available at: https://scholarsarchive.byu.edu/gbn/vol35/iss1/4

This Article 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 Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. LIFE HISTORY AND ECOLOGY OF MEGARCYS SIGNATA (PLECOPTERA: PERLODIDAE), MILL CREEK, WASATCH MOUNTAINS, UlAH^

Mary R. Gather- and Arden R. Gaufin-

Abstract.— During an investigation of some of the stoneflies (Plecoptera) of Mill Creek, Wasatch Mountains, Utah, Megarcys signata, a large omnivorous stonefly, was found to have a univoltine life history and a slow seasonal life cycle. Temperature appears to affect the growth rate of Megarcys signata. Warmer stream temperatures accompany the acceleration of the growth rate, whereas cooler stream temperatures apparently retard the growth rate. Periods of maximum absolute growth rate con-espond with maximum carnivorous feeding from August to September and March to April. Ghironomidae, Ephemeroptera, and Plecoptera, in that order, were the most abundant prey in the foreguts. Young n^-mphs ingested considerable amounts of diatoms, filamentous algae, and detritus but not as much matter as did older nymphs. Megarcys signata was unifonnly distributed throughout Mill Creek, except at the lowest station, where few nymphs were found. Emergence occurred in May and June, the peak occurring in June. The mean size of females and males decreased as emergence progressed.

This report is part of an eighteen-month calcium bicarbonate 109-189 mg/1, calci- study of some of the stoneflies of Mill vmi carbonate 0-2.4 mg/1, pH 7.5-8.3, Creek, Wasatch Mountains, Utah. Be- total hardness 100-340 mg/1, and conduc- cause a detailed description of the study tivity 312-859 mhos/cm. area and the methods and materials is given in another paper (Cather and Gau- Methods and Materials fin 1975, only a summary is included here. Nymphs of Megarcy signata were col- Mill Creek Canyon is located 11 km lected at least monthly from June 1971 to southeast of Salt Lake City, Utah, in the December 1972 at each of six stations. Wasatch Mountains of the Middle Rocky Additional nymphs were collected in Mountain Province. Six stations were se- spring 1973 for food habit studies. Hand- lected along a 12 km length of the stream screens of mesh sizes 7 and 9 sq/cm were in the Wasatch National Forest with ele- used, the smaller handscreen being used vations ranging from 1,605 to 2,280 m. during the majority of the study in an The sampling stations were nimibered attempt to collect the smaller instars. An consecutively. Station I denoting the high- area of about 80 cm- of the stream bottom est elevation. The three lower stations was disturbed in an attempt to collect at (1,605-1,785 m) are easily accessible all least 100 nymphs monthly. All nymphs year, but the three upper stations (1,995- were preserved in 80 percent ethanol. 2,280 m) are accessible only in the simi- Adults were collected weekly through- mer and fall. Average minimum and out the emergence period and biweekly maximum daily flows were 0.3 m^/sec during peak emergence using a sweep net and 1.2 mVsec, respectively, during the and handpicking from vegetation, rocks, study period. Depth averaged 11-45 cm, and bridges. All adults were preserved in and current averaged 0.2-0.7 m/sec during 80 percent ethanol. the fall when measurements were taken. The interocular distance of all nymphs The substrate of the sampling area at all and adults was measured to the nearest stations ranged from coarse sand to small 0.1 mm using an ocular micrometer in a cobbles. Minimum water and air tempera- dissecting microscope for determining tures recorded during adult emergence growth rates and to see if the mean size of were 3 C and 9 C, respectively. Maximum the adults decreased as emergence pro- water and air temperatures during this gressed. The nymphs were identified as period were 13 C and 26 C, respectively. males and females when possible. Water chemistry was similar at all sta- Foregut analyses were conducted on 200 tions. Dissolved oxygen ranged from 6.0 nymphs collected from the field. Nymphs to 8.5 mg/1 (70-120 percent saturation). were selected from an upper (I) and a

^Study supported by Environmental Protection Agency Traineesliip Grant No. 5T2-WP-542-03. ^Department of Biology, University of Utah, Salt Lake City.

39 40 GREAT BASIN NATURALIST Vol. 35, No. 1 lower (IV) station during each season lowed Gaufin et al. (1966), and nomen- (Station V had to be substituted for Sta- clature followed lilies (1966) and Zwick tion I during winter and spring). The (1973). method used followed Swapp (1972). All prey were enumerated and identi- Results and Discussion fied to order except where family or generic determination was possible. Three The only systellognathan stonefly pres- types of the family Chironomidae were ent in Mill Creek in numbers large enough recognized and designated as species a, b, for analysis is Megarcys signata. This and c (based on morphology of head species exhibits a slow seasonal type of capsule). These are discussed under re- life cycle. Emergence and oviposition oc- sults and discussion but are not separated cur in May and June with hatching soon in Table 1. All algae were determined to after. Small nymphs (0.5 mm interocular genus where possible. Percentage compo- distance) appear in July at the lower sta- sitions of algae and detritus were esti- tions. Nymphs of comparable size gen- mated when present, and dominant items erally appear for the first time in August, were recorded. A volume analysis was September, and October at the upstream not conducted. stations. Rapid growth occurs from Aug- Identification of nymphs and adults fol- ust to emergence (Figs, la, b, c). The size

lOOn

75

50-

25

2.5-

-. 2.0- E

o

].o^

0.5

Month

Fig. 1. Growth of Megarcys signata. Arrows indicate emergence. I. O. indicates interocular dis- tance: (a) Monthly mean size as a percentage of total mean size at Station IV; (b) Monthly mean cumulative growth at Station IV; (c) Monthly mean absolute growth rate (data pooled from all sta- tions). A indicates change in I. O. distance. March 1975 GATHER, GAUFIN: UTAH PLECOPTERA 41

frequencies of nymphs and the mean (September-January). Growth apparently cumulative growth at each station are slows, but does not stop, during the winter shown in Figs. 2 and 3, respectively. (January-March), increases from March A comparison of the cumulative growth to April, and then decreases from April to at all stations reveals that the most rapid May, prior to emergence. Sheldon (1972) growth occurs at the lowest (warmest) reported similar results in his study on the stations (Fig. 4). Thus, there seems to be Arcynopteryx species complex he studied a direct correlation between growth and in California. However, Schwarz (1970) temperature. Baumann (1967) found no reported no growth at times during the direct correlation in this species in Mill winter in other Systellognatha. The corre- Creek. Seasonally the most rapid growth lation between growth and food habits will occurs during the fall and early winter be discussed later.

2.0' 34 103 2 A 27 101

II J 4 3 O 1,0

2.0- •l 'h 33

1.0- 50

F J J "n ^ J A 30 ND J MAM ASO

Month

AC 15 9 1 ^^ 38 33 <^h°^n r Sfa 2.0-| b 10 5 'l'^ IV

1.0-1

ly ,3 1/

1 2.0-

O 1.0- 9 6

? cf: 2 3

10' ' I

50

J A S 5 S 5 ] F M A ?ir 5 6 N F

Month

Fig. 2. [Frequency distribution of nymphal size classes of M. signata. Number of individuals shown above each polygon; males and females as indicated: (a) Stations I, II, and III; (b) Stations IV, V, and VI. r

42 GREAT BASIN NATURALIST Vol. 35, No. 1

Megarcys signata seems to show no The emergence of M. signata began in preference for either the upstream or early May at the lower stations and lasted downstream stations. This species is even- until late June at the higher stations (Fig. ly distributed throughout the stream ex- 5). Peak emergence was in June. Bau- cept at Station VI. Here the substrate is mann (1967) found this species emerg- almost entirely cemented. Where the ing from late April to mid-July in Mill water is deep enough for this large , Creek. Emergence is progressively later the current is too slow; where the current as the elevation increases. Baumann is fast enough, the water is too shallow (1967), Hynes (1970), and Nebeker and the substrate too homogeneous. More (1971) reported similar results. They individuals were collected at Station IV were first collected at Stations III and V than at any other station. in early May, when the water tempera-

Sta

2.0- --HH

O ).0-

2.0-

J ASONDJ FMAMJ JASOND Month

Sta

2.0-

1.0-

o - la

T~y ~r~T T—

Fig. 3. Mean cumulative growth of nymphs of M. signata. Vertical line represents size range of nymphs; shaded area represents standard deviation; unshaded area represents standard eiTor of the mean; solid line connects means; rectangle represents emergence period: (a) Stations I, II, and III; (b) Stations IV, V, and VI. March 1975 GATHER, GAUFIN: UTAH PLECOPTERA 43

J a 100-

1 5"

^^

Fig. 4. Comparison of mean cumulative growth of nymphs of (D) M. signata at Stations I-V. Station I represented by (o); Station II by (•); Station III by (); Station IV by (A); Station V by (A); and Station VI by (D): (a) July, 1971 through June, 1972; (b) July, 1972 through December, 1972.

tures were 3 C and 5 C, respectively. Emergence ended in late May (water tem- perature 9 C) at Station V, but lasted until mid-June (12 C) at Station IV and late June (5.5-7 C) at the three upper stations. Megarcys signata is a secretive insect that hides in cracks under bridges or among vegetation to escape warm summer tem- peratures. Clusters of these stoneflies usually containing one female and several males were often collected in these hiding places. Brinck (1949) reported the same phenomenon in related species. The col- lection data probably reflect this secretive habit in that M. signata should have been collected earlier at Station IV. Females and males generally emerged together in a 1:1 ratio. Harper and Pilon (1970) reported similar findings. Only 55 44 GREAT BASIN NATURALIST Vol. 35, No. 1

(1972) reported a similar phenomenon. nymphs were selected from upper and The mean size of females decreased from lower stations and from each season of the 2.4 mm to 2.3 nun, while that of males year. Table 1 gives the results of this decreased from 1.9 mm to 1.8 mm (Fig. analysis. Of those foreguts examined, 39 7). The data were rather inconclusive were empty (some of these stoneflies were because only small numbers of adults were beginning to molt; others had just collected in May. More intensive collect- molted). Chironomids seemed to be the ing may reveal this trend more strongly. preferred food item. Three types of chi- Sheldon (1972) reported similar results in ronomids based on differences in the head the Arcynopteryx species complex he capsules were recognized. Of these three studied and suggested that the decrease in types, one was much more frequently mean size also influenced fecundity; that found in the foreguts. A total of 442 were is, the smaller females carried fewer eggs. found in 39 percent of the ex- Warmer stream temperatures and in- amined. The other two types were found creasing photoperiod may act as emer- only occasionally. Mayflies were the sec- gence cues before growth and egg develop- ond most abundant food item ingested (37 ment are completed (Khoo 1968, Hynes percent of all individuals). Baetis spp. 1970). were most frequently recognized. Stone- A total of 200 nymphs of M. signata flies, notably chloroperlids, comprised a were dissected and the foreguts examined considerable portion of the gut contents, for a preliminary food-habit analysis. The also (27 percent of the individuals). Rich-

T.\BLE 1. Percentage of dissected nymphs of Megarcys signata containing specific food items.

Season March 1975 gather, gaufin: 46 GREAT BASIN NATURALIST Vol. 35, No. 1

spp. were found in all stoneflies ex- amined). Filamentous algae and detritus were also present in many guts. Entero- morpha spp., a filamentous green algae, was the dominant plant material in 14 per- cent of the guts, while detritus was the dominant item in 77 percent of the guts. This herbivorous material may have come from the stomachs of the chironomid prey (mayflies present in only 5 percent of the stoneflies) since Oliver (1971) states that some chironomids feed on algae and detritus. However, many guts contained detritus as the dominant material without chironomids being present. It is conceiv- able that during the summer the newly hatched nymphs of M. signata could feed at least partially on diatoms, filamentous algae, and detritus. At this stage they are probably not as effective a predator as at later life stages. Coffman, Cimmiins, and Wuycheck (1971) found a similar pattern in other groups of insects, in that young individuals consumed primarily detritus but shifted to algal or animal ingestion as Month they matured. The lowest absolute growth Fig. 7. Size range of adults of M. signata. rate occurs in the summer from July to August despite increased carnivorous feed- diatom frustules, leaf fragments, and other ing. Growth increases sharply from Au- plant remains were found in 30 percent of gust to September, however. the insects examined. Other diatoms en- In the fall (mid-October) at the two countered were Gomphonema spp., Cym- stations analyzed, Ephemeroptera were bella spp., and Nitzschia spp. These are found in 19 percent of the guts at Station common stream dwellers of Mill Creek, IV and in none of the guts at Station I. occurring on the rocks in shallow water. This can probably be explained on the There are some significant seasonal dif- basis of emergence of many of the mayfly ferences in the food items found in the species. One mayfly adult was found in- guts. In the summer (July-early Septem- gested, however. Plecoptera were also ber) significantly more M. signata (58 relatively rare in the fall, many having percent) ingested mayflies than in the fall emerged already. Many summer and fall at Station IV, but at Station I the num- emergers may still be in the egg stage or bers feeding on Ephemeroptera were low too small to be prey. Chironomidae were (5 percent). Stoneflies were found in only least numerous at this time of year also 9 percent of the guts examined at Stations (present in only 17 percent of the insects I and IV. Chironomids, on the other hand, examined). Diatoms and detritus were the were present in 32 and 45 percent of the most numerous items found in the guts guts at Stations I and IV, respectively. during the fall. Since M. signata emerges The number of chironomid head capsules mostly in the summer, the fall specimens found was also greater than in the fall. represent some of the smaller sizes. They At Station IV diatoms were notably lack- would not require as much food and thus ing in the gut contents, although mayflies are adapted to the relative paucity of and chironomids were present. This could prey species. At Station IV even diatoms be because the swift current dislodges the except Navicula spp. were not numerous algae from the substrate and because the in those stonefhes examined. The swift deeper water and suspended solids from current could be a factor in removing spring runoff shut out sufficient light. many from the substrate. At this station However, at Station I, where the water more individuals had fed- on mayflies and was shallower, diatoms were found in the stoneflies than at Station I. Another dif- majority of the guts examined {Navicula ference was that more empty foreguts March 1975 GATHER, GAUFIN: UTAH PLEGOPTERA 47 were found in those stoneflies dissected was present in 43 percent of the guts and from Station IV (maximum number comprised the dominant item in 29 per- of reached) than at Station I (9 vs. 2). The cent of those examined. The mmiber lack of sufficient prey could be a limiting empty foreguts increased to a maximum factor. However, the period October- again during this time. November represents one of the highest The early spring (March) was also a absolute growth rates during the year. time of increased carnivorous feeding. The growth rate data were obtained by This also coincides with a significant in- rate. this pooling all samples from all stations, how- crease in the absolute growth At mayflies are ap- ever. time many stoneflies and their maximum size prior to During the winter (January-February) proaching emergence. The quiescent stage just be- mayflies, stoneflies, caddisflies, and chi- emergence may also make them easi- ronomids in the guts increased signifi- fore prey. The percentage of mayflies and cantly. Sheldon (1972) reported similar er stoneflies in the guts increased at Station results in some of the Arcynopteryx spe- but decreased at Station IV. One ex- cies complex he studied. In the winter at V planation for this may be that during Station IV, there were prey species present spring runoff, the water level is deeper in more of the guts than at any other time IV than at Station V. However, during the year. This represents an in- at Station occurrence of chironomids decreased crease in the absolute growth rate but a the significantly at Station V but remained decrease from the previous month. The Station IV. The reason for this calculated absolute growth rates from No- high at was not determined. Some emergence vember to December and from December could have occurred at Station V, but be- to January are questionable, since only 3 stations are in close proximity M. signata nymphs were collected in De- cause the not seem to be the answer. cember. This increase in growth rate is this would stated that mature probably correlated with the availabilit}^ Sheldon (1972) nymphs of the Arcynopteryx species com- of food, because only the family Capniidae plex he studied decrease their consumption are emerging. Chironomids were the most in the spring (April). At numerous, being present in 88 percent of of animal food this time M. signata in Mill Creek under- the guts examined. These slower-moving goes a noticeable decrease in absolute insects would be easier prey than the fast- growth rate prior to emergence. Diatoms er mayflies and stoneflies. Stoneflies also other algae were still relatively rare increased dramatical!}^ in the guts despite and in the guts examined. Presumably spring the fact that the numbers available de- runoff created spates which might have creased due to winter emergence. By win- removed these forms from the substrate. ter, however, the summer and fall emerg- Detritus was found in 85 percent of the ers, such as the family Chloroperlidae, V. Increased runoff due to may have attained a sufficient size to be guts at Station melt contributed large amounts of suitable prey. Surprisingly, the increase in snow allochthonous detritus to the stream. The numbers of prey found in the guts also depth of water at Station IV may coincides with one of the periods of the greater have prevented the concentration of detri- least amount of growth. The low winter- removed it. On the stream temperature could stress the tus and effectively at Station V the channel is nymphs enough that some growth may be other hand, enough that shallow areas are avail- sacrificed even though an adequate food wide to collect. supply may be available. The number of able for detritus In discussing food habits it is important fliatoms and other algae decreased signifi- that the partitioning of re- (antly, probably due to the decreased to remember accomplished by the w^ide distri- water temperature and lack of sufficient sources is in size range, which decreases in- solar radiation. Nevertheless, Nayicula bution traspecific competition (TTartland-Rowe, spp. and Gomphoncma spp. were still nu- Radford and Hartland-Rowe, 1971). merous. Enteromorpha spp. were domi- 1964; samples a difference in inter- nant in 21 percent of the guts examined In most measurement of M. signata aver- (luring this period. The stoneflies dissect- ocular aged 0.6-1.0 from the smallest to (h1 from Station V were collected in Feb- mm This was a significant- ruary, however, when stream tempera- largest individuals. than in the euholog- tures were beginning to warm slightly and ly larger size range solar radiation was increasing. Detritus nathan species studied. 48 GREAT BASIN NATURALIST Vol. 35, No. 1

Acknowledgments Hynes, H. B. N. 1941. The and ecology of the nymphs of British Plecoptera This study is part of a Ph.D. research with notes on the adults and eggs. Proc. Roy. project by the senior author. The authors Entomol. Soc. London 91:459-557. . 1970. The ecology of stream insects. wdsh to thank Bill P. Stark for his helpful Ann. Rev. Entomol. 15:25-42. suggestions. Illies, J. 1966. 'Katalog der rezenten Plecoptera. Das Tierreich, 82. Walter de Gruyter and Co., Berlin. 632 pp. Literature Cited Khoo, S. G. 1968. E.xperimental studies on dia- pause in stoneflies. L Nymphs of Capnia bi- Baumann, R. W. 1967. A study of the stone- frons (Newman). Proc. Roy. Entomol. Soc. flies (Plecoptera) of the Wasatch Front, Utah. London 43:40-48. Unpublished M.S. thesis, Univ. Utah, Salt Nebeker, A. V. 1971. Effect of temperature at Lake City. 114 pp. different altitudes on the emergence of Brinck, p. 1949. Studies on Swedish stoneflies. aquatic insects fi-om a single stream. J. Kans. Opusc. Entomol. 11:1-250. Entomol. Soc. 44:26-35. C.\THER, M. R.. AND A. R. G.\UFiN. 1975. Com- Oliver, D. R. 1971. Life history of the Chiro- parative ecologv of three Zapada species of nomidae. Ann. Rev. Entomol. 16:211-230. Mill Creek. Wasatch Mountains, Utah (Ple- Radford, D. S.. and R. Hartland-Rowe. 1971. coptera: Nemouridae). Submitted to Amer. The life cycles of some stream insects (Eph- Midi. Nat. emeroptera, Plecoptera) in Alberta. Can. En CoFFMAN, W. P., K. W. Cummins, and J. C. tomol. 103:609-617. WuYCHECK. 1971. Energy flow in a wood- Richardson, J. W., and A. R. Gaufin. 1971. land stream ecosystem. I. Tissue support Food habits of some western stonefly nymphs. trophic structure of the autumnal communitv. Trans. Amer. Entomol. Soc. 97:91-121. Arch. Hydrobiol. 68:232-276. ScHW.'^RZ, p. 1970. Autoekologische Untersuch- ungen zum Legenszyklus von Setipalpia-Ar- Fenneman, N. M. 1931. Physiography of west- ten (Plecoptera). Arch. Hydrobiol. 67:103-140. ern United States. McGraw-Hill Book Co., Sheldon, A. L. 1972. Comparative ecology of New York. 534 pp. Arcynopteryx and Diura (Plecoptera) in a Gaufin. a. R., a. V. Nebeker, and J. Sessions. California stream. Arch. Hydrobiol. 69:521- 1966. The stoneflies of Utah. Univ. Utah 546. Biol. Ser. 14:1-93. Swapp, T. E. 1972. Food habits and life history Harper, P. P., and J. G. Pilon. 1970. Annual of stoneflies of the Cle Elum River, Washing- patterns of emergence of some Quebec stone- ton. Unpublished M.S. thesis. East. Washing- flies. Can. J. Zool. 48:681-694. ton State Coll.. Bellingham. 58 pp. Hartland-Rowe, R. 1964. Factors influencing ZwicK, P. 1973. Insecta: Plecoptera. Phylo- the life histories of some stream insects in genetisches system und katalog. Das Tier- Alberta. Verb. Internat. Verein. Limnol. 15: reich, 94. Walter de Gioiyter and Co., Berlin. 917-925. 465 pp.