Kimberly A. Matthews and Donald C. Tarter.
Ecological life history, including laboratory investigation, of the mayfly, Ameletus tarteri (Ephemeroptera: Siphloneuridae).
Psyche 96:21-38, 1989.

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ECOLOGICAL LIFE HISTORY, INCLUDING
LABORATORY RESPIRATORY INVESTIGATION,
OF THE MAYFLY, AMELETUS TARTER1
(EPHEMEROPTERA: SIPHLONEURIDAE)*
BY KIMBERLY A. MATTHEWS AND DONALD C. TARTER Department of Biological Sciences,
Marshall University, Huntington, WV 25701 Mayflies, such as Ameletus, are considered by many to be largely influenced by their environment. This study not only provides information concerning the basic life history of the species in ques- tion, but also elucidates the role that environment can play in this life history.
The objectives of this study were: (1) to describe the life history of Ameletus tarteri, a newly described species, (2) to investigate the role environment plays in this life history, and (3) to add to the general knowledge concerning mayflies.
TAXONOMY AND DISTRIBUTION
The genus Ameletus was first described by Eaton in 1885. The type species was Ameletus subnotatus; the type locality was Colo- rado (Edmunds et al., 1976). There are currently thirty-three nomi- nal species of Ameletus from North America. Members of the genus Ameletus are found throughout the Holarctic region. According to Edmunds et al. (1976), in the Nearactic region they are most abun- dant "in the north, extending along the mountains south to Califor- nia, New Mexico, Illinois, and Georgia." Ameletus tarteri Burrows was first described in 1987. The holo- type was found in Greenbrier County, West Virginia, at Hamrick Run near its confluence with the North Fork of Cherry River. Ameletus tarteri was collected by Burrows in Greenbrier County of West Virginia. This species was also identified from Chemung County, New York, and Giles County, Virginia (Burrows, 1987). *Manuscript received by the editor February 14, 1989. Psit-fn. %:21-17 (1989). hup //psyche cnlclub org/WÌö-021.htin



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Psyche
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This study was conducted at Carpenter Run, a tributary of the North Fork of Cherry River, Greenbrier County, West Virginia. Carpenter Run originates at an elevation of 3750 feet (1 125 m) and flows generally to the southwest to join the North Fork of Cherry River at an elevation of 3200 feet (960 m) for a total fall of 550 feet (165 m). The stream transverses 1.18 miles (1.89 km) and has a drainage area of 0.93 square miles (2.46 m2) (Price and Heck, 1939). Geologically, the underlying rock of Carpenter Run is of the New River Group, Pottsville series. These Pennsylvanian rocks are com- posed mainly of sandstones, shales, and coals. Structurally, the Webster springs anticline surfaces along the North Fork of Cherry River. The axis of the Kovan syncline crosses the North Fork of Cherry River between Coats Run and Little Lick Run with out- croppings along the valleys of both the North Fork and the South Fork of Cherry River (Price and Heck, 1939). MATERIALS AND METHODS
Ameletus tarteri nymphs were collected monthly from November 1986 to November 1987 from Carpenter Run. The nymphs were collected using a small aquarium net, which was gently scraped across the rocks and boulders in the stream. In addition to this, the aquarium net was placed below smaller rocks, which were lifted to dislodge any nymphs. The amount of time spent collecting was recorded. Any nymphs captured were immediately transferred using forceps to a vial containing 70 percent ethanol. Relative abundance of nymphs was determined by dividing the number of nymphs col- lected by the time spent collecting.
The stream bank was examined weekly from May to July and again in September, dates when pre-emergent nymphs were col- lected, for the presence of nymphal exuviae. Exuviae were collected, preserved in 70 percent ethanol, and returned to the lab. They were then counted and examined using a Bausch and Lomb dissecting microscope to determine sex.
Attempts were made to trap adults using Ward's insect trap with an ultraviolet light source. Each attempt lasted one hour and was begun at darkness. Seventy percent ethanol was used as a preserva- tive for any insects captured. All captured insects were returned to the laboratory, and any mayflies were removed from the collection.



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19891 Matthews & Tarter - Ameletus 23
Water chemistry was tested monthly (excluding January due to adverse weather conditions) using a Hach Ecology Testing Kit- Model AL-360T. The parameters analyzed included dissolved oxy- gen, alkalinity, acidity, total hardness, carbon dioxide, and pH (November 1986 through May 1987). All of the above parameters listed were measured in mg/L except pH. From June 1987 to November 1987, pH was measured with a Chemtrix Oyster pH meter. Temperature was measured monthly using a Celcius ther- mometer.
In the laboratory, all Ameletus tarteri nymphs were measured with an ocular micrometer in a Bausch and Lomb compound micro- scope. The increments of the grid were calibrated using an American Optical stage micrometer. This calibration was done at magnifica- tions of lox, 15X, and 25X so that measurements made at any of these three magnifications could be converted to the nearest 0.01 mm. The body length of each nymph was determined from the anterior tip of the head to the base of the caudal filaments (10X). Head width was measured at the widest part of the head (15X). A length frequency histogram was completed using increments of one millimeter for body length. A size frequency distribution was also constructed in increments of 0.1 mm for head width. Monthly growth rates were determined by calculating the percent increase in growth from one month to the next. Head width varia- tion was shown using population range diagrams which included mean head width, range, and two standard errors of the mean for each month. Significant differences between means were determined by comparing the overlap of the two standard errors of the mean (0.05 confidence level). The number of instars in the life cycle was determined using the Janetscheck method (Janetscheck, 1967). The sex of each nymph was determined using two characters. The eyes of the male nymphs were larger and closer together. The male genitalia could be seen developing in the nymphs. Sex was deter- mined for nymphs which had developed to a point at which these two characteristics were clear. All other nymphs were termed "im- mature." A chi-square analysis was performed to determine if the sex ratio was significantly different from 1: 1 at the 0.05 confidence level.
Foregut analysis was performed on five relatively larger nymphs per month using an ocular micrometer (as for the length frequency



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24 Psyche [vo~. 96
distribution). Microdissecting scissors were used to remove the head as well as to make a ventral midthoracic cut. The integument was placed to the side, and the foregut was removed using a stainless steel probe. All five foreguts were placed in 3 ml of water to which 5 drops of iodine solution were added. For August the three foreguts were placed in 1.5 ml of water and 3 drops of iodine were added. After the five foreguts were thoroughly agitated, 1 ml of the mixture was removed using a pipet and placed in a Sedgwick-Rafter cell. This cell was examined under an Olympus compound microscope containing a Whipple grid (200X). Ten grids were randomly selected to be examined. This milliliter of fluid was then replaced with a second milliliter of foregut contents from the same month. Ten more grids were then randomly selected for examination. The rela- tive abundance of four food categories was determined by calculat- ing percentages of small grid squares within each field that contained each of the different food items: (1) plant detritus, (2) mineral detritus, (3) filamentous algae, and (4) diatoms. A Gilson differential respirometer was used to measure the oxy- gen consumption of the nymphs at three temperatures (7, 11, 14O C) and two pH's (5.0, 7.2). For this test, nymphs were collected from Hamrick Run, a nearby tributary of the North Fork of Cherry River. This stream shares many characteristics of Carpenter Run, includ- ing a low pH, and is only 750 m downstream from Carpenter Run. Nymphs were collected in April and May of 1987 and were allowed to acclimate in the lab for no longer than two days before the study was begun. For the pH = 5.0 test, nymphs and stream water were placed in the reaction flask. Nymphs and stream water from Twelve- pole Creek in Wayne County, West Virginia, were placed in the reaction vial for the pH = 7.2 test. For each pH test, the water bath was maintained for three hours at each of the following tempera- tures: 7, 11, and 14' C. At the end of each hour, a reading was taken from the micrometer. For each temperature, these three readings were averaged. Nymphs were sacrificed and heated at 40å¡ for 24 hours. They were weighed using a Bosch S2000 analytical scale. An average oxygen consumption rate in microliters per milligram dry weight per hour was then calculated. Analysis of variance was used to determine if temperature or pH had a significant influence on oxygen consumption. Data were plotted to determine the influence of body weight on oxygen consumption for both pH's. Slopes of the



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19891 Matthews & Tarter - Ameletus 25
two regression lines were compared with a z-distribution to deter- mine if they were significantly different. Laboratory-reared female subimagoes were dissected for egg counts. A midsaggital longitudinal cut was made on the ventral surface to open the body cavity. All eggs were carefully removed and direct egg count made under a Bausch and Lomb dissecting microscope. A regression of fecundity and body length was calcu- lated, and a correlation coefficient was determined for the relation- ship. Ten percent of the eggs obtained from each female subimago were measured using an ocular micrometer in a Bausch and Lomb dissecting microscope at 25X magnification. Water chemistry.
Dissolved oxygen ranged from 3.7 mg/L
(July) to 1 1.8 mg/ L (February) with a mean of 8.7 mg/ L. Dissolved carbon dioxide ranged from 2.5 mg/ L (November 1987) to 10 mg/ L (June) with a mean of 4.4 mg/L. Alkalinity had a mean value of 5 mg/ L CaCO3 with a minimum value of 1 mg/ L CaC03 in April, May, and September and a maximum value of 15 mg/ L in October. Acidity ranged from 8 mg/L (November 1987) to 28 mg/1 (July) with a mean equal to 15 mg/ L. Total hardness was less variable with a minimum value in March of 3 mg/ L CaC03 and maximum values of 8 mg/ L CaCOs in April and November 1987; the mean value was 6 mg/ L CaCO3. The mean hydrogen ion concentration (pH) was 4.5 with a range from 4.2 (November 1987) to 5.0 (November 1986 through February 1987). Detailed water chemistry can be found in Matthews (1988).
Monthly water temperature values varied from -1 .Oå¡ in January to 18.gå¡ in July. The mean annual water temperature was 8Så¡C Habitat observations. The habitat preference of A. tarteri is ver- tical rock surfaces perhaps even slanted beyond the perpendicular for the mature nymphs, while flat rock surfaces in shallow eddies were preferred by the younger nymphs. The larger, more mature nymphs were more often found on the vertical sides of the larger boulders in the stream while the younger nymphs were easily obtained from large horizontal rock surfaces. Ameletus tarteri nymphs have been found to have a preference for high elevation streams. Burrows (pers. comm.) found these mayflies at an elevation of 3000 ft. (900 m), North Fork of Cherry River, but not at 2000 ft



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I I
1
I
,
May 22 May 24 May 30 Jun 6
MONTH
Figure 1. Nymphal exuviae collected, shown with bar graph, from May 22 through July 31, 1987, indicating the pattern of n
emergence for Ameletus tarteri in Carpenter Run, Greenbrier County, West Virginia. The water temperature (C) during the 2.
study period is indicated by the line graph. <o a\




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Matthews & Tarter - Ameletus
0-
35:
Nov
Body length (mm)
Figure 2.
Length frequency distribution showing monthly body length of nymph- al Ameletus tarteri from Carpenter Run, Greenbrier County, West Virginia. The number of individuals collected per month is at the right.



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28 Psyche [vo~. 96
(600 m) in Cherry River. This preference for high elevation is seen at Carpenter Run; the elevation of this stream is 3200 ft (960 m) (Price and Heck, 1939).
Emergence period. Nymphal exuviae were recovered from ver- tical rocks along the stream from May 30 to July 3, 1987 (Fig. 1). Exuviae were searched for but not recovered on May 22, May 24, and June 2. A large storm occurred on June 1 which could account for the absence of exuviae on this date. The largest number of exuviae were recovered on June 6. No exuviae were found on July 1 1, 1987 or July 3 1, 1987. Because of this, weekly examination for exuviae ceased. A nymph with dark wing pads was found on Sep- tember 26; examination for exuviae was undertaken, but none were found. Data from this study (nymphs with dark wing pads and cast exuviae) suggest that emergence of A. tarteri occurs from late May to early July and again in late September, constituting a bimodal emergence pattern.
Collection of adults.
Eleven attempts to collect adults of A.
tarteri using an ultraviolet light source beginning May 9 and ending July 31 were unsuccessful. According to Edmunds et al. (1976), the adults and subimagoes of some species are attracted to lights only at certain times of the night; perhaps A. tarteri is one of these species. Length frequency distribution.
A length frequency histogram of
body length in 1 mm increments was constructed for the nymphs (Fig. 2). The smallest nymph, measuring 1.1 mm, was found in October. The largest nymph, measuring 11.9 mm, was collected in April. A size frequency distribution of head width in 0.1 mm incre- ments is found in Figure 3. The smallest head width was 0.2 mm and was found in October while the largest measured 1.9 mm and was collected in May.
Data summarized in Figures 2 and 3 indicate a univoltine life cycle. This is also true for Ameletus inopinatus Eaton as described by Gledhill (1959). Ameletus inopinatus emerged from late May until August with two periods of egg hatching; one in autumn and another in spring. This results in overlapping cohorts and an extended emergence period.
In A. tarteri, there appears to be no egg diapause. Nymphs with dark wing pads were found in May, June, and September suggesting emergence occurred at these times (Fig. 3). Eggs are laid in late May as "physiologically ready individuals" emerge, and immediately



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' 1 Il-
l -1 r 1
11 II
Matthews & Tarter - Ameletus
['I I I
I, I
A M J J I
Number of Individuals
Figure 3. Size frequency distribution for head width of nymphal Ameletus tarteri from Carpenter Run, Greenbrier County, West Virginia, from November 1986 to November 1987. Sex is indicated for nymphs with a head width greater than 1.1 mm. Closed circles represent black wing pads. hatch, accounting for the increased relative abundance at this time. Emergence and hatching continue through June. At this time, the water temperature averaged l2.7O C. During middle July through August the temperature rose to 18.9OC, and the stream flow decreased as the water level dropped; no subimagoes emerged. As the temperature dropped to 1 1.7' C in September, emergence began again (Fig. 3). At this time the remaining individuals of the genera- tion emerged. A large number of eggs hatched and the relative abundance increased. Because there were two emergence periods in this bimodal cycle, a variety of size classes were found throughout the year. This type of emergence pattern is adaptive in periods of



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30 Psyche [vo~. 96
environmental stress such as high temperatures or dryness. Both of these conditions were present at Carpenter Run in the summer of 1987.
Growth.
Population range diagrams demonstrate the monthly progression of head width sizes during the study period. This is seen in conjunction with a temperature curve (Fig. 4). The largest amount of growth occurred between October and November 1987 (31.4%) and December 1986 to January (29.3%). The largest decrease in size occurred between June and July (-34.9) and Sep- tember to October (-37.9). This corresponds with the months fol- lowing a period of emergence and further supports the bimodal theory of emergence.
Significant amounts of growth, based on amount of overlap between two standard errors of the mean in the population range diagrams, occurred between March and April (prior to emergence) and between October and November 1987. A significant decrease in size occurred between April and May, June and July, and Sep- tember and October (Fig. 4).
MONTH
Figure 4. Population range diagram showing head width variations of nymphal Ameletus tarteri from Carpenter Run, Greenbrier County, West Virginia from November 1986 to November 1987. Open circles are the means, vertical lines are the two standard errors of the means, and solid line is temperature (C).



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19891 Matthews & Tarter - Arneletus 31
The number of instars for nymphal A. tarteri was estimated using Janetscheck method (Janetscheck, 1968) (Fig. 5). When body length in increments of 0.099 mm was used for nymphal A. tarteri, 21 instars could be discerned (Fig. 5c).
Sex ratio. A 1:l sex ratio was not observed for A. tarteri nymphs. A chi square test was applied to 71 females and 49 males. The difference was significant at the 0.05 level. The difference could be influenced by sexual dimorphism. The males may be slightly smaller than the females and could have been classified as imma- ture. If the sex of the exuviae recovered from the creek and the sex of the subimagoes that emerged in the laboratory are added to the TOTAL LENGTH FREQUENCY (rnm)
Figure 5.
Instar determination for Ameletus tarteri from Carpenter Run using the Janetscheck method. a. frequency histogram of total length of nymphs b. trendlines of the population, calculated by the method of gliding means over five successive size-class frequencies at a time c. periodicity of maximum frequency of size




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32 Psyche [vo~. 96
chi-square calculation, then the chi square comparison would be between 99 females and 75 males. When this is done, there is not a significant difference at the 0.05 level, supporting a 1: 1 sex ratio. Foregut analysis. Nymphal A. tarteri can be classified as a detritivore; the major factor of its diet is plant detritus (77.3%) (Table 1). Mineral detritus composed 19.0 percent of the diet. Dia- toms, composing 2.8 percent of the diet, were seen consistently. Diatoms may not be an essential component of the diet. Diatoms identified include Eunotia sp., Tabellaria sp., Frustulia sp. and Suri- rella sp. Eunotia and Tabellaria were the most commonly found diatoms, present in virtually every month. Frustulia was present only in January and August while Surirella was found only in Janu- ary, March and June. The filamentous algae Microspora sp. was found in the foreguts only during March, April and May. This may coincide with an algae bloom in the stream. It is perhaps more likely that A. tarteri reverted to this algae as food when the leaves were washed from the stream in the spring. Merritt and Cummins (1978) classified Ameletus as collector-gatherers of fine organic particulate matter.
PLANT DETRITUS
MINERAL DETRITUS
FIL. ALGAE
DIATOMS
90
80
70
60
50
40
30
2 0
10
WINTER SPRING SUMMER FALL
Figure 6. Seasonal foregut content of nymphal Ameletus tarteri from Carpenter Run, December 1986 to November 1987.




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19891 Matthews & Tarter - Arneletus 33
Table 1.
Relative foregut contents of nymphal Ameletus tarteri at Carpenter Run, November 1986-November 1987.
Month Plant Mineral Algae Diatoms
Nov 71.12
21.71 0.00 7.17
Dec 75.87
21.16 0.00 2.97
Jan 66.58
26.55 0.00 6.87
Feb 77.24 21.57
0.00 1.19
Mar 74.53
15.88 1.42 8.17
AP~ 66.87
21.33 9.1 1 2.69
May 65.76
33.40 0.63 0.21
Jun 74.35
24.22 0.00 1.43
Jul 77.93
20.88 0.00 1.19
Aug 86.43
10.71 0.00 2.86
S~P 86.23
11.37 0.00 2.40
Oct 83.98 14.06
0.00 1.99
Nov 92.25 6.42
0.00 1.34
MEAN 77.34 18.96 0.93 2.78
If the foregut data are examined with regard to season (Fig. 6), it can be seen that the spring diet and the fall diet are considerably different. In spring there was an increase in algae consumption and a decrease in plant detritus consumption. In fall, the consumption of plant detritus increases correspondingly with an increase in the leaf litter in the stream. There is a decrease in the consumption of min- eral detritus and diatoms. Algae is absent from the fall diet. Respiratory studies. Analysis of variance was used to evaluate the effects of temperature and pH on oxygen consumption. Temperature and pH each exerted a significant influence on oxygen consumption. There was no significant interaction between the two parameters. Using Ameletus spp. and Eccopteura xanthenes (New- man), Doherty and Hummon (1980) found that the low pH of acid mine drainage did not consistently alter the oxygen consumption rate. Mayflies in general are considered to be the most sensitive order of aquatic insects to low pH. Ameletus tarteri seems to have developed adaptations to low pH. At a lower pH, oxygen consump- tion is decreased at a time when oxygen demand is higher (Havas, 1980).
Figure 7 shows the relationship between dry weight and oxygen consumption. At pH 5.0, there exist very small nymphs (less than 1



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