Albert C. Hendricks

Gene flow, dispersal, and nested clade analysis among populations of the stonefly Peltoperla tarteri in the southern Appalachians.

We examined the genetic structure and phylogeography of populations of the stonefly Peltoperla tarteri in the Southern Appalachians to determine the extent and likely mechanism for dispersal of this stream insect. A 454‐base‐pair (bp) portion of the mitochondrial control region was sequenced from a minimum of 20 individuals from eight populations. Pairwise FST and exact tests showed high levels of differentiation among almost all populations except those on the same stream. amova analysis detected significant genetic differentiation between streams within drainages (φSD = 0.14, P < 0.001), and there was a slight positive correlation between aquatic distance and genetic distance (r = 0.295, P = 0.03). According to nested clade analysis, the present day pattern of genetic variation in P. tarteri is the result of a historical range expansion coupled with restricted gene flow with isolation by distance. Together, these analyses suggest that adult dispersal is limited and that movement by larvae is the primary dispersal mechanism for P. tarteri.

Structural and functional responses of stream insects to copper pollution

Benthic invertebrate assemblages and leaf decomposition rates were usedto assess the effects of copper on community structure and function in EastProng Creek, VA. Copper concentrations ranged from 12–32 µgl−1 at three downstream disturbed sites and 0.1–2.0µg l−1 at an upstream reference site. Benthic samplingshowed reduced taxonomic richness and numbers of individuals at thedisturbed sites and leaf decomposition rates at the disturbed sites were1.4–2.7 times slower than at the upstream reference site. Partialrecovery of community structure occurred after a passive treatment systemreduced copper to levels below chronic effect concentrations. Post-treatmentbenthic sampling indicated a recovery in taxonomic richness in the threedisturbed sites. During the 6-week period of treatment, themacroinvertebrate community in the disturbed sites recovered to a similarcomposition to that found in the reference site. However, no significantdifference in leaf decomposition rate was observed, suggesting a residualeffect of copper on our measure of functional response. Our results indicatethat copper pollution significantly interrupts the action of shreddersprocessing leaf material in polluted streams.

Life history, growth, survivorship, and production of Hydropsyche slossonae in Mill Creek, Virginia

We describe life history and production of Hydropsyche slossonae Banks in Mill Creek, Virginia, a first-order stream in the Central Appalachian Ridges and Valleys ecoregion. Each adult female laid approximately 230 eggs which hatched in 13 d. Five larval instars were recorded with most individuals overwintering in instars III and IV. Pupation and emergence occurred primarily over a 6-wk period in May and June. No mortality in the egg stage was detected, while high mortality in instar I (92.9%) was due partly to sibling cannibalism. Instars II-V showed constant low mortality, with high mortality again in the pupal stage; 0.5% of the original eggs survived to adulthood. Growth analysis revealed two distinct growth phases: one from hatching through instar IV (0.007 mg/d) and a much faster growth rate for instar V in May (0.148 mg/d). Production estimates for the entire generation ranged from approximately 3 to 5 g/m2 and were highly variable. On a per-day basis, production occurred at specific times of the year. Yield per day peaked slightly later than peaks in production. High daily production occurred immediately after hatching as a result of growth of many small individuals. At the end of the generation, there was another period of high daily production due to fast growth by fewer larger individuals. Most production occurred from March through June. At other times, daily production was relatively low. It may be more accurate to estimate production by predicting biomass from survivorship and growth functions than directly from sample data.

Acute toxicity of zinc and copper singly and in combination to the bluegill (Lepomis macrochirus)

Zinc and copper are common components of aquatic effluents from various industrial and mining sources. The acute toxicity of various compounds of Cu and Zn has been determined for many species of fish using continuous flow as well as static toxicity tests under different chemical, temperature, and temporal regimes. Similarly, the toxicity of mixtures of these two, as well as of more complex mixtures of heavy metals, has been studied by many researchers. While many of these studies report the toxicity of Cu and/or Zn to the bluegill (Lepomis macrochirus), to our knowledge the literature does not mention the acute toxicity of mixtures of these two metals to this species. The present study was undertaken to investigate the acute toxicity of divalent Zn-Cu mixtures to the bluegill.

Impact of flooding on the densities of selected aquatic insects

Data from a four-year study of five aquatic insect species,Hydropsyche betteni, H. morosa, H. bronta, Isonychia bicolor, andEphoron leucon, were utilized to evaluate the impact of a 60-year flood and a few lesser floods. The survey began in August, 1984 and was terminated in October, 1987 with the 60-year flood occurring in November, 1985. Four sampling sites were established on the South River and six quantitative samples were taken each month from each site. Gauging stations on the South River provided accurate discharge data for the sampling sites and useful historical data. Densities for the five species were utilized in the evaluation of the floods. The importance of timing is pointed out, that is, floods that occur very close together or near the end of the life cycle of an insect make it difficult to evaluate floods as disturbances. The importance of life history traits, such as behavior and egg diapause, are discussed in respect to floods. Densities were reduced to less than 50% of their average values immediately after the 60-year flood for the threeHydropsyche spp. and at three sites forI. bicolor. Ephoron leucon showed no response to the 60-year flood. Densities of the four impacted species returned to previous levels in the following generation. The 60-year flood was considered a disturbance in the near term but not for more than one generation.

Life history and secondary production of Cheumatopsyche spp. in a small Appalachian stream with two different land uses on its watershed

We studied life history and secondary production of Cheumatopsyche spp. (Trichoptera: Hydropsychidae) in StroublesCreek, a 3rd order stream near Blacksburg, Virginia to compare lifehistories and production dynamics in two reaches with differentland-uses. The upstream reach was influenced by agriculturalactivities and more annual degree-days accumulated in this sectionof the stream. The downstream reach was surrounded by forest,received less thermal input than the upstream reach, and showedlittle evidence of human disturbance. Differences between the twosites included a shift in dominant taxa and changes in voltinismand production of hydropsychids. Cheumatopsyche pettiti(Banks) was dominant at the upstream site, while C. pettitiand Cheumatopsyche oxa Ross were both abundant downstream.Cheumatopsyche larvae and other aquatic insects had higherdensities at the forested downstream site. C. pettiti wasbivoltine at the upstream site, but C. pettiti and C. oxa were partially bivoltine downstream, with a small summergeneration overlapping with continuous emergence of overwinteringlarvae. Cheumatopsyche production at the two sites inStroubles Creek was higher than in forested, low-order streams ofNorth America, but similar to some values obtained at streams inagricultural areas and large rivers. Production was higher at thedownstream site, but the superior bivoltinism at the upstream sitecounterbalanced, to some extent, the increase in larval densitythat caused higher production downstream. The adjustment in lifehistory and production dynamics, in the two reaches, showed theecological plasticity of Cheumatopsyche and the importance ofhydropsychids in the energy flow of moderately disturbedstreams.

Zinc resistance in Chironomus riparius: evidence for physiological and genetic components

Heavy metal resistance has been well documented in many aquatic invertebrate species, but its nature has been clearly demonstrated on only a few occasions. We investigated 2 mechanisms, acclimation and adaptation, that are commonly thought to be responsible for this resistance. Data were obtained from growth and respiration experiments using instar III and IV Chironomus riparius under the influence of 0.0, 62.5, 125, 250, and 500 μg/L Zn. Comparisons were made between larvae that were cultured in clean water conditions and larvae from cultures that had been exposed to 10 μg/L for >18 mo. Instar III larvae from clean water cultures showed significant reductions in growth and respiration rates when exposed to zinc concentrations ≥62.5 μg/L; in instar IV larvae, growth and respiration rates were significantly reduced at 250 and 62.5 μg/L, respectively. Instar IV larvae from zinc cultures had increased tolerance to the metal whereas instar III larvae displayed no additional tolerance. To determine if the resistance was due to acclimation or population adaptation, additional growth and respiration experiments were conducted with F2 progeny of zinc-cultured adults that had been reared in clean water. Growth rates of F2 progeny larvae were affected by the same concentration that affected untreated larvae, suggesting that acclimation-based resistance to zinc can be induced in C. riparius. Because respiration rates of F2 generation instar IV larvae were affected only by high zinc concentrations (500 μg/L), the results suggest that larvae evolved resistance to Zn during the course of this study.

Spatial and Temporal Variation in the Growth and Production of Ephoron leukon (Ephemeroptera:Polymitarcyidae)

Variation in growth rates, maximum nymphal sizes, densities, and production estimates of Ephoron leukon (Ephemeroptera:Polymitarcyidae) were investigated at two sites over a 3-yr period on the South River, Virginia. Ephoron leukon is univoltine with development confined to a short (3-4 mo) period during the summer followed by a long (8-9 mo) egg diapause. The short growing season combined with a high degree of developmental syncrony makes this species ideal for comparative field studies. Relative growth rates ranged from 0.014 to 0.028 mg/mg/day and significant differences were observed between sites and years. Spatial differences in growth rates were explained by between-site differences in thermal regime but between-year differences were not. Differences in average densities between years may have been important in explaining annual differences in growth rates. Maximum nymphal weights averaged between 3.22 and 4.78 mg (AFDM) and were significantly higher at the downstream site for all three years. Differences were attributed to faster growth rates combined with relatively small differences in cohort production intervals. Average densities ranged from 117 to 602 individuals/m2, and significant differences were observed between sites and years, with annual differences being most pronounced. Average densities were related more to initial densities than to mortality rates and thus factors governing number of eggs laid and hatching success were responsible for annual differences in densities. The data suggest that hatching success may have been influenced by the thermal regime of the previous winter. Annual production ranged from 398 to 2857 mg/m2/yr and differences were significant between sites and years. Much of the between-site variation in production estimates was explained by differences in maximum nymphal weight, while differences in mean densities explained much of the annual variation in production.

Effect of seasonally changing feeding habits on whole-animal mercury concentrations in Hydropsyche morosa (Trichoptera: Hydropsychidae)

Food habits, net-spinning activity, and whole-animal mercury concentrations in Hydropsyche morosa Hagan were examined monthly over a one year period on the South River, Virginia. Gut content analysis revealed seasonal patterns in the consumption of food that was correlated with net-spinning activity. Between April and October, when feeding nets were widespread, detritus represented between 72 and 94% of the total volume of food material found in the guts, while algae represented less than 18%. However, between November and March, when feeding nets were rare or absent, the relative contribution of each of the three food types (i.e., detritus, algae, and animal) changed significantly. Detritus declined to between 51 and 60%, and algae increased to between 39 and 47% of the total food volume. Whole-animal mercury concentrations ranged from 0.14 to 1.20 µg g−1 and were significantly higher in the summer. Seasonal differences were not related to environmental mercury levels and only weakly related to body size. In contrast, whole-animal mercury levels were strongly related to seasonal changes in diet. In summer, when H. morosa larvae were filtering highly contaminated seston, whole-animal mercury levels were high. Conversely, in winter, when larvae were grazing less contaminated algae, whole-animal mercury levels were significantly lower. The primary component of seston was detritus (>81%) throughout the year. Therefore, the high mercury concentration in seston was probably associated with detritus. As a result, a significant relationship was observed between whole-animal mercury concentration and the relative amount of detritus consumed. These patterns indicate that in streams with highly productive hydropsychid populations, the rate of processing of mercury and other heavy metals may be related to seasonal changes in feeding behavior.

Proficiencies of two artificial substrates in collecting stream macroinvertebrates

Proficiencies in collecting stream macroinvertebrates by two types of artificial substrates, #200 3M conservation webbing and cone-shaped concrete blocks, were compared with bottom net collections. Conservation webbing collected more individuals than cone substrates, but fewer taxa than either cone substrates or bottom nets. Diversity indices calculated for collections made with the three techniques were lowest for webbing collections, highest for net collections and intermediate for cone collections. It was concluded that collections made with webbing substrates gave an extremely distorted view of macroinvertebrate community balance due to a preponderance of net spinning and case building forms, and that cone substrates were better suited for use in the particular situation studied.