University of Montana ScholarWorks at University of Montana Biological Sciences Faculty Publications Biological Sciences 1981 Larval Specialization and Phenotypic Variation in Arctopsyche- Grandis (Trichoptera, Hydropsychidae) F. Richard Hauer University of Montana - Missoula, [email protected] Jack Arthur Stanford The University of Montana, [email protected] Follow this and additional works at: https://scholarworks.umt.edu/biosci_pubs Part of the Biology Commons Let us know how access to this document benefits ou.y Recommended Citation Hauer, F. Richard and Stanford, Jack Arthur, "Larval Specialization and Phenotypic Variation in Arctopsyche-Grandis (Trichoptera, Hydropsychidae)" (1981). Biological Sciences Faculty Publications. 314. https://scholarworks.umt.edu/biosci_pubs/314 This Article is brought to you for free and open access by the Biological Sciences at ScholarWorks at University of Montana. It has been accepted for inclusion in Biological Sciences Faculty Publications by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. Ecology, 62(3), 1981, pp. 645-653 ) 1981 by the Ecological Society of America LARVAL SPECIALIZATION AND PHENOTYPIC VARIATION IN ARCTOPSYCHE GRANDIS (TRICHOPTERA: HYDROPSYCHIDAE)1 F. RICHARD HAUER AND JACK A. STANFORD University of Montana Biological Station,2 Bigfork, Montana 59911 USA and Department of Biological Sciences, North Texas State University, Denton, Texas 76203 USA Abstract. Life history, trophic dynamics, abundance, and microdistribution of Arctopsyche grandis (Banks) were investigated in the Flathead River Basin, Montana. Two morphologically and ecologically distinct larvae (Type I, with a head stripe; and Type II, without a head stripe) were found throughout the drainage except in lower order streams. Type II larvae grew more rapidly and attained a larger size in final instar than Type I larvae. In areas where A. grandis biomass was greatest, Type I larvae were > 10 times as abundant as Type II larvae. Type II larvae selected microhabitats char- acterized by larger interstitial spaces; Type I larvae were more common in tightly compacted sub- strata. Food items consumed by both larval phenotypes varied between sites, indicating a natural variability in the environment. Significant differences in foods ingested were also observed between larval types within particular riverine locations, suggesting phenotypic differentiation in food habits. Larvae of both phenotypes were reared in laboratory streams. Type I were both male and female, but all Type II were female. We concluded that the presence of Type II larvae increased resource utilization and species fitness. Key words: Arctopsyche; caddisflies; Flathead River; habitat selection; life histories; Montana; phenotypic variation; species fitness; trophic dynamics. INTRODUCTION slightly different microhabitats (i.e., built retreats in differentially (e.g., fre- Net-spinning larvae often contribute significantly to different areas) and responded resource zoobenthic biomass and energy processing in running quency ratios, abundance) along specific gra- water ecosystems (Cummins 1974, Wallace et al. 1977, dients within the river system. Although A. grandis in western North America and has been Ward and Short 1978). Although stream size prefer- is widespread ence (Gordon and Wallace 1975, Wiggins and Mackay the subject of numerous taxonomic (Smith 1968, Giv- Alstad 1978) and the importance of various environmental ens 1976) and ecological (Furnish 1979, 1980, differentia- factors such as current velocity (Wallace 1975, Had- Cuffney 1980) studies, such morphological dock 1977) have been documented for certain species tion has not been investigated. To delineate fully the means of apparent morphological heterogeneity within of hydropsychid larvae, the biology of caddisflies is emergence, hab- not well known, especially in western Montana. the species, we examined growth and As part of an ongoing study of the limnology of the itat selection, and possible sexual differences between Flathead River-Lake Ecosystem, we investigated eco- the two larval phenotypes. logical relationships of Arctopsyche grandis (Banks). STUDY AREA We found this large hydropsychid widely distributed is located along the west throughout the Flathead Basin in third- and fourth-or- The Flathead River Basin areas of the Continental Di- der high mountain streams, as well as in the riffles of slope in heavily glaciated the southeastern the mainstream rivers above Flathead Lake. A. gran- vide in northwestern Montana and There are three major trib- dis larvae were very abundant (maximum 600 larvae/ corner of British Columbia. utaries of the Flathead River: the North Fork, with a mi2) in fifth- and sixth-order segments of the Flathead flow of 85 m3/s; the Middle Fork, with a River and were frequently one of the numerically dom- mean annual South inant caddisfly species in riffle areas. mean annual flow of 84 m3/s; and the Fork, by Hungry Horse Dam, with a mean Soon after the initiation of our research, it became which is regulated annual flow of 101 m3/s (Fig. 1). These fifth-order apparent that two morphologically distinct larvae of by cobble and small-boulder A. grandis were commonly found in close association. rivers are characterized are extensive in the flood- The two morphs had different color patterns and after substrata. Gravel deposits of habitat (Stan- close examination, we observed that they selected plains, creating large areas hyporheic ford and Gaufin 1974). Most physicochemical parameters, such as temper- I Manuscriptreceived 11February 1980; revised 20 August 1980;accepted 29 September 1980;final version received 3 ature, alkalinity, pH, and flow are similar in the North October 1980. and Middle Forks. The North Fork valley is open, 2 Mailingaddress. broad, and rounded, but the Middle Fork courses This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 18:44:27 PM All use subject to JSTOR Terms and Conditions 646 F. RICHARD HAUER AND JACK A. STANFORD Ecology, Vol. 62, No. 3 A ' ' ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..... ' '..- ..... _ _ _ _ l.~~~~CONINNALTO A~~~~~~~~~~~~~~~~A " ON T;^AO~~~~~~~~~~~~~~A < SH~AIER 10 0 1.Okm g-9 HLINGRY X FLATHEADAT A FIG. 2. Two morphologicalvariations of Arctopsyche grandis larvae from the Flathead Rivers Montana Pheno MAINSTREAtr typeI1(A) has a distinctstripe on headand thorax, Phenotype ORK 11 does not. UPPER- d (B) loat ons. ols h A tD L~, 20-30Cin comparisonto the North and Middle Forks; winter waters are warmed 10-20Cby hypolimniondis- BASIN X charges from HungryHorse Reservoir. This river sec- tion differs significantlyfrom the unregulatedtributar- ies in that algae are sloughed by the sluicing effect of FIG. 1. Map of FlatheadRiver Basin indicatingsampling the filaments were fre- locations. regulated discharges. Algal quentlyobserved heavily packed into and trailingfrom A. grandis filter nets. Green and diatomaceous algae throughnarrow canyon sections. Althoughboth rivers contributedsignificantly to the trophicdynamics of A. erode extensive deposits of glacial clays, the Middle grandis in this river segment. Fork carries a largersediment load duringspring run- METHODS off (R. Hauer and J. Stanford,personal observation). It does not clear as rapidly as the North Fork after Three stations were established for collection of runoff and becomes turbidfollowing occasional sum- quantitative,time-series data (Fig. 1): Station A was mer rainstormsin the drainagebasin. Fine particulate located on the North Fork -20 km above confluence organic matter(FPOM), composed of both allochtho- with the Middle Fork, Station B on the Middle Fork nous and autochthonousmaterials, is closely associ- -15 km above confluence with the North Fork; and ated with the clay sedimentsin a colloidal matrix.The Station C on the MainstreamRiver -15 km down- organically rich sediments are transported down- stream from the South Fork confluence. In addition, stream and are deposited on and within the substrata qualitative samples were obtained in a variety of of both rivers. Because the Middle Fork carries a smaller tributary streams throughout the drainage, higher sediment load than the North Fork, more in- particularlythe North Fork tributary streams, Trail terstitial space in the rubble has been partiallyfilled Creek and Kintla Creek. with fine sediments, coarse sands, and gravel. Immatureand adult stages of A. grandis were col- The South Fork below HungryHorse Reservoirhas lected in 1977-1979using both quantitativeand qual- been significantly altered due to hypolimnial dis- itative techniques to establish microdistributionalre- charges; flow may fluctuatebetween 7.5 and 300 m3/s lationships, levels of abundance, and to provide diurnally. A. grandis no longer occurs in this river sufficientnumbers of individualsto document life his- segment, apparentlydue to frequent alterationof dis- tory events. Larvae were collected with a 225-gm charge, thermal regime, and trophic dynamics (see mesh, 1.2 mnx 1 mn,modified kick net. Quantitative Stanfordand Ward 1979). larval collections were made monthly from August The MainstreamRiver below the confluence of the throughApril. Seasonal abundancedata sets were es- regulatedSouth Fork is also characterizedby a rubble tablished as fall, August through 15 November; win- substrateand abundantriffles. However, this reach of ter, 16 November through 15 February;and spring, 16 the river is influencedin late