Life Cycles of Allocapnia recta and Leuctra spp. (Plecoptera: Capniidae and Leuctridae) Across a Flow Gradient in a Central Kentucky Karst Headwater Stream
Scott A. Grubbs, Christopher M. Thomas, Benjamin T. Hutchins, and Jason M. Taylor
Southeastern Naturalist, Volume 5, Number 2 (2006): 321–332
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2006 SOUTHEASTERN NATURALIST 5(2):321–332
Life Cycles of Allocapnia recta and Leuctra spp.
(Plecoptera: Capniidae and Leuctridae) Across a Flow
Gradient in a Central Kentucky Karst Headwater Stream
Scott A. Grubbs1,*, Christopher M. Thomas1, Benjamin T. Hutchins1,
and Jason M. Taylor2
Abstract - Four species of stoneflies (Plecoptera) from an intermittent stream–
perennial spring continuum were the subject of comparative life-cycle analyses.
Allocapnia recta was common in each reach and exhibited univoltine-fast life cycles
and determinate voltinism. Leuctra alta from the intermittent reach and a L. alta–L.
sibleyi mix from the perennial reach each displayed an univoltine-fast cycle, implying
that L. alta demonstrated determinate voltinism. Leuctra cf. tenuis was absent
from the intermittent reach, and its growth followed a univoltine-slow cycle in the
Water flow is widely recognized as an important variable regulating
the distribution of aquatic biota in lotic systems (Power et al. 1988).
Several researchers have demonstrated that permanent streams support
different macroinvertebrate communities than those in intermittent
streams (Bottorff and Knight 1988, Delucchi and Peckarsky 1989,
Feminella 1996, Williams and Hynes 1976, Wright et al. 1984). While
macroinvertebrates of springs and perennial coldwater streams are dependant
on flow permanence and thermal stability (Erman and Erman 1995,
Smith and Wood 2002, Williams and Hogg 1988), intermittent streams, in
contrast, often support taxa with life-history characteristics for surviving
channel drying (Delucchi 1988, Williams 1996). In general,
macroinvertebrate assemblages along a flow gradient from permanent to
temporary respond to greater variability of physical conditions (e.g.,
temperature, dissolved oxygen), species-specific tolerance to drought adaptation
(e.g., diapausing eggs), and reduced predatory or competitive
abilities during stream drying.
There have been few studies comparing stonefly life cycles across environmental
gradients (e.g., Harper 1973). Life cycles and life histories have
been described for approximately 5% of the North American fauna (Stewart
and Stark 2002), but most of the research has been conducted in wadable
streams and rivers. Relatively little life-cycle work has focused on the fauna
of springs and intermittent streams (Dobrin and Giberson 2003, Snellen and
1Department of Biology and Center for Biodiversity Studies, Western Kentucky
University, Bowling Green, KY 42101. 2The Nature Conservancy, 6375 Riverside
Drive, Suite 50, Dublin, OH 43017. *Corresponding author - firstname.lastname@example.org.
322 Southeastern Naturalist Vol. 5, No. 2
Voltinism, or number of generations per unit time (e.g., per year), is
characterized either as determinate or indeterminate depending on whether
populations exhibit (a) the same pattern across habitats regardless of climatological
or hydrological conditions (determinate), or (b) a different pattern
due to environmental differences (indeterminate) (Stewart and Stark 2002).
For insect populations that have one generation per year (i.e., univoltine),
voltinism can also be described as fast or slow (Hynes 1961). Populations
that display univoltine-fast life cycles typically occur in an actively-growing
larval or nymphal stage for only a short time period. The egg or immature
stage remains for an extended period in some form of a delayed state (e.g.,
diapause). In contrast, univoltine-slow cycles have neither delayed egghatching
nor egg, larval, or nymphal diapause. Eggs usually hatch soon after
oviposition and larval or nymphal growth occurs for much of the year.
In May 2002, we initiated a comparative life-cycle study on Leuctra
sibleyi Claassen from a headwater intermittent-stream–karst (perennial)-
spring continuum. During the first year, Allocapnia recta (Claassen) and L.
alta James were collected from both reaches and added to the study. In
addition, L. cf. tenuis (Pictet) was later collected as adults only along the
perennial spring and was also added to the study.
The contrasting hydrology of the study stream, the first reach distinctly
intermittent and the second perennial, provided an opportunity to compare
life cycles. The purpose of this study was to examine life-history attributes
of A. recta, L. alta, L. sibleyi, and L. cf. tenuis in the intermittent vs. the
perennial reaches to assess whether voltinism patterns were determinate or
indeterminate across the two habitats.
Site Description and Methods
The study stream was located in Hart County, KY (elevation: 255 m a.s.l.),
and within the Crawford-Mammoth Cave Upland Level IV Ecoregion (Interior
Plateau Level III Ecoregion; Woods et al. 2002). This region is characterized by
sandstone cliffs and limestone valleys. Subterranean streams, springs, and
karst windows associated with the latter feature are common.
The headwater study stream originates on a small sandstone ridge and
flows 35 m as an intermittent reach before dropping 16 m over a hollowed
cliff. The stream continues intermittently before two springlets contribute
perennial surface flow for 18 m. Flow ceases downstream of the perennial
reach flow and the channel becomes ephemeral.
Both pH (6.73 vs. 5.68) and conductivity (90 vs. 40 μmhos) were slightly
higher in the perennial reach. Mean width (0.7 m) and depth (4.9 cm) in the
intermittent reach were similar to the perennial reach (1.1 m, 3.1 cm.). Depth
was monitored at a single point for each reach (Fig. 1) during each site visit
(n = 47). Water temperature was measured initially in each reach independently
at 1-hr. intervals with a Ryan RL100 temperature recorder (Fig. 1),
but only from the perennial reach after July 2003 due to non-significant
differences (t = 1.32, p = 0.19, n = 116).
2006 S.A. Grubbs, C.M. Thomas, B.T. Hutchins, and J.M. Taylor 323
Each reach was partitioned longitudinally into transects 0.5 m apart.
Monthly sampling for nymphal stoneflies took place between May 2002 and
April 2004. Three transects were randomly selected per reach and sampling
occurred at the midpoint of each channel. Sampling methods for the two
reaches differed. The intermittent reach was sampled with a petite ponar
dredge (0.023-m2 sampling area) from May–June 2002 and January–May
Figure 1. Temperature (A) and stage data (B) for the period May 2002 through
April 2004. The temperature graph is based on mean daily temperature recorded
from perennial reach.
324 Southeastern Naturalist Vol. 5, No. 2
2003 and with an Ekman dredge (0.023-m2 sampling area) from December
2003–April 2004. No samples were taken from the intermittent reach from
July–December 2002 and June–November 2003 because this channel was
dry. Sampling in the perennial reach from May 2002–December 2003
was based on brushing cobble substrates into a bucket and scooping finer
substrates with a 250-μm sieve. The Ekman dredge was used from January–
April 2004. The three replicate samples per reach were composited in the
field, rinsed through a 250-μm sieve, and preserved with 95% ethanol.
Each composite sample was rinsed through a 250-μm sieve in the laboratory
and sorted under a dissecting microscope. To compare nymphal growth
between the intermittent and perennial reaches, head-capsule widths were
measured for all individuals and used to construct size-frequency histograms.
Nymphs of Leuctra are difficult to distinguish to species (Stewart
and Stark 2002). Hence, all three species were represented on a single graph.
Adults of all species were collected weekly during each species’ emergence
period. Allocapnia recta adults were obtained from tree trunks and by
beating tree branches into a beating sheet. Leuctra spp. adults were collected
with the beating sheet and searching under streamside rocks. Adult flight
records were superimposed onto each nymphal histogram.
Small diapausing nymphs of Allocapnia recta were first encountered in
both reaches in May 2002 (Fig. 2). Nymphs were obtained again in the
perennial reach in July 2002, yet not prior to emergence in winter 2002–
2003. In contrast, mature nymphs were collected from the intermittent reach
in January and February 2003 coincidental with emergence.
Newly-hatched A. recta nymphs were present in both reaches in March
2003, suggesting a direct hatch of eggs, and were likewise present in the
perennial reach through July 2003. Similar to 2002, diapausing nymphs were
not collected during late summer and autumn from the perennial reach.
Nymphs in both reaches grew rapidly during November and December 2003
prior to emergence in January and February 2004. Newly-hatched nymphs
were collected from February–April 2004.
Leuctra cf. tenuis was collected as adults only along the perennial reach
in September (2002 and 2003) and October (2003) (Fig. 3). In contrast, L.
alta and L. sibleyi were obtained as adults along both reaches in May–June
2002, April–May 2003, and April 2004 at ratios of L. alta:L. sibleyi of
44:21 (perennial reach) and 144:1 (intermittent reach). Because of the
rarity of L. sibleyi and lack of L. cf. tenuis from the intermittent reach,
subsequent life-cycle descriptions for the intermittent reach refer only to L.
alta. Life cycles for the perennial reach referred individually both to L. cf.
tenuis and a L. alta–L. sibleyi mix. Nymphs of L. alta and L. sibleyi could
not be distinguished.
Presumably, the only nymphs collected from the perennial reach from
May–July and September 2002 were of L. cf. tenuis. Mature nymphs with
2006 S.A. Grubbs, C.M. Thomas, B.T. Hutchins, and J.M. Taylor 325
Figure 2. Size-frequency histograms of head-capsule width for Allocapnia recta from the intermittent and perennial reaches. Reaches are
separated as intermittent (left side of kite diagram, solid boxes) and perennial (right side of kite diagram, striped boxes). n = 169 nymphs
(intermittent reach) and 129 nymphs (perennial reach). Arrows refer to adult flight periods.
326 Southeastern Naturalist Vol. 5, No. 2
Figure 3. Size-frequency histograms of head-capsule width for Leuctra spp. from the intermittent and perennial reaches. Reaches are separated
as intermittent (left side of kite diagram, solid boxes) and perennial (right side of kite diagram, striped boxes). n = 690 nymphs (intermittent
reach) and 835 nymphs (perennial reach). The longer dashed lines separate nymphs of L. cf. tenuis. Arrows refer to adult flight periods of each
species: solid arrow = L. alta and L. sibleyi, dashed arrow = L. cf. tenuis.
2006 S.A. Grubbs, C.M. Thomas, B.T. Hutchins, and J.M. Taylor 327
developed wingpads were absent during this period, strongly suggesting the
emergence period for L. alta and L. sibleyi had ended. Tracking the timing of
egg hatching of L. cf. tenuis, however, was problematic. The early-instar
Leuctra nymphs collected in December 2002 in the intermittent reach were
L. alta, but those in the perennial reach likely were a mix of all three species
(Fig. 3). Early-instar nymphs of L. cf. tenuis were apparent by January 2003,
and growth was steady through spring and summer 2003 prior to emergence
in September and October. Early-instar nymphs L. cf. tenuis also likely
appeared by February 2004. During both 2002 and 2003, early-instar
nymphs of L. cf. tenuis were not collected in November, implying that a
slight delay of egg hatch was evident.
There were two distinct size classes of Leuctra nymphs in the perennial
channel from January–March 2003, indicating that the smallest nymphs
were of L. cf. tenuis and the larger nymphs were the L. alta–L. sibleyi mix.
The L. alta–L. sibleyi nymphs from the perennial channel grew steadily from
January through March 2003 prior to emergence in April and May. A similar
pattern of two distinctive size classes in the perennial channel was seen in
January–February 2004. In contrast, there was only a single size class
present in the intermittent reach from January–March 2003 and 2004 that
was L. alta. Early-instar L. alta–L. sibleyi (perennial reach) and L. alta
(intermittent reach) nymphs did not reappear in both reaches until January
2004, suggesting an extended delay in egg hatching.
The life cycles of four species of stoneflies (Allocapnia recta, Leuctra
alta, L. sibleyi, L. cf. tenuis) are described, with each Leuctra species for the
first time. In addition, this is the first attempt to describe the life cycles of
multiple species of Leuctra from the same stream. The inability to discriminate
among nymphs of multiple species has hampered previous efforts
(Grubbs and Cummins 1996, Huryn and Wallace 1987).
Both A. recta and L. alta were sufficiently abundant to allow for between-
reach comparisons of voltinism. The dissimilar hydrologic regimes
did not result in life-cycle flexibility for either species. Adults were free to
disperse between reaches, implying that the stream as a whole supported
genetically contiguous populations. Allocapnia recta and L. alta exhibited
univoltine-fast cycles and determinate voltinism, yet their life-history strategies
were distinctly different. Eggs of A. recta hatched soon after oviposition
and early-instar nymphs entered into a diapause stage that lasted through
most of autumn. Diapause was broken by late autumn and nymphal growth
occurred rapidly prior to emergence in December through February. In
contrast, the L. alta eggs remained in a delayed stage through summer and
autumn. Early-instar nymphs were evident by early winter and growth proceeded
rapidly prior to emergence in April and May.
Only one L. sibleyi adult was obtained from the intermittent reach, and L.
cf. tenuis was restricted to the perennial reach. That L. cf. tenuis was absent
328 Southeastern Naturalist Vol. 5, No. 2
from the intermittent reach was expected, because the emergence period for
this species was during September and October when that channel had been
dry since early summer. Nymphal growth in the perennial reach of L. cf.
tenuis was steady during the summer months prior to emergence. The lack of
summer and autumn flow clearly prevented establishment of this species in
the intermittent channel. The life cycle displayed by L. cf. tenuis in the
perennial reach closely resembled the univoltine-slow cycles displayed by L.
tenuis (Pictet) in permanent streams in Ontario (Harper 1973) and Oklahoma
(Ernst and Stewart 1985). This species is undescribed and closely allied to L.
While the Leuctra nymphs from the intermittent reach were of L. alta,
the inability to distinguish between L. alta and L. sibleyi hampered a
clearer life-cycle comparison of (a) these two species in the perennial
reach, and (b) the former species between reaches. However, the two
distinct size classes in the perennial reach from January–March (Fig. 3)
indicated that both L. sibleyi (larger) and L. alta (smaller) were present.
The adults of L. alta and L. sibleyi are morphologically similar (Grubbs
2005) but readily separated by size.
The life cycle demonstrated by L. alta (intermittent reach) and the L.
alta–L. sibleyi mix (perennial reach) mirrored the univoltine-fast cycles
exhibited by L. duplicata Claassen from an intermittent stream in Quebec
(Harper 1990) and L. iliberis Sanchez-Ortega and Alba-Tercador in Spain
(Sanchez-Ortega and Alba-Tercador 1988). The lack of early-instar Leuctra
nymphs in either reach by the time the intermittent channel had dried
implied that eggs had not hatched and were developing very slowly. Harper
(1973, 1990) discussed that both L. ferruginea and L. duplicata lacked
diapausing eggs, even in intermittent habitats, but rather possessed eggs that
developed directly albeit slowly. Egg hatching of L. alta in both reaches
occurred after approximately the same embryonic development period and
was likely induced by a common environmental signal. Hence, the rewetting
of the intermittent stream channel in late autumn was not the hatching
stimulus for L. alta in light of the perennially flowing condition in the
perennial channel. Egg hatching of both L. alta and L. sibleyi was likely
triggered by other environmental cues (e.g., decreasing temperature or day
length). The L. alta eggs also possessed the mechanism to survive channel
desiccation in the intermittent channel.
Leuctridae exhibit broad life-cycle patterns in eastern North America,
including semivoltine populations of Leuctra ferruginea (Walker) in
warm-water Ontario streams (Harper 1973) and complex cycles of
Zealeuctra claasseni (Frison) and Z. hitei Ricker and Ross in Texas
(Snellen and Stewart 1979). Harper (1973) further revealed a univoltine
population of L. ferruginea in the coldest stream he studied, demonstrating
indeterminate voltinism due to a temperature gradient that influenced the
number of generations per year. A similar pattern of indeterminate
voltinism has been demonstrated in the European species L. nigra (Olivier)
2006 S.A. Grubbs, C.M. Thomas, B.T. Hutchins, and J.M. Taylor 329
(e.g., Hildrew et al. 1980, Iversen 1978). Zealeuctra claasseni and Z. hitei
also exhibited indeterminate voltinism, yet this variation was within a
single stream and induced by channel drying (Snellen and Stewart 1979).
Egg hatching of univoltine populations was direct during wetter years, but
delayed during drier years.
Most studies examining stonefly life cycles have implied voltinism
mainly on the presence of one (univoltine), two (semivoltine), or several
(merovoltine) nymphal cohorts present per year. Several mechanisms that
result in more complex life cycles, namely cohort splitting (Moriera and
Peckarsky 1994), seed banking of eggs (Snellen and Stewart 1979, Zwick
1996), and cryptic semivoltinism (Taylor et al. 1999), have been demonstrated
among stonefly taxa. There have been few investigations of the
effect of stream drying on egg viability or time needed to induce hatching
(e.g., Snellen and Stewart 1979) or of quantifying the length of the egg
development period. Taylor et al. (1999) revealed that the perlodine
stonefly Megarcys signata (Hagen) displayed a semivoltine life cycle because
the eggs diapaused for up to 10 months. Prior research on M. signata
examined only nymphal growth and adult emergence and assumed a
univoltine cycle (Cather and Gaufin 1975). Perhaps L. alta eggs develop at
different rates depending on dry versus wet channel conditions similar to Z.
claasseni and Z. hitei.
Many studies on Allocapnia have shown that eggs hatched soon after
emergence, nymphs diapaused through summer and autumn, and life cycles
were univoltine-fast (e.g., Harper and Hynes 1972, Harper et al. 1991). The
A. recta adults in this study were collected mainly during January and
February. Only the smallest size class nymphs were collected from spring
through autumn (Fig. 2), indicating that A. recta eggs hatched soon after
oviposition, and nymphs from the perennial reach were in the typical curled
diapaused shape. Despite the dry intermittent reach during summer and
autumn, late-instar post-diapause nymphs were present in January–February
2003 and again in December 2003–January 2004 immediately prior to and
during the emergence period. Allocapnia recta nymphs must have survived
in a hyporheic environment beneath the intermittent channel prior to
rewetting in late autumn.
Research that has compared macroinvertebrate communities across flow
gradients have generally found distinct assemblages in perennial versus
intermittent channels (e.g., Bottorff and Knight 1988, Feminella 1996,
Wright et al. 1984). Similarly, aside from the species germane to this study,
there were several taxa found exclusively in either the intermittent or perennial
reach. Taxa found solely in the intermittent channel included
Rhyacophila glaberrima Ulmer (Trichoptera), Ameletus sp.,
(Ephemeroptera) and Sphaerium sp. (Pelecypoda). In contrast, taxa restricted
to the perennial spring included Diploperla robusta Stark and
Gaufin (Plecoptera), Paraleptophlebia debilis Walker (Ephemeroptera),
Pseudostenophylax sp. (Trichoptera), and Dixa sp. (Diptera). Clearly the
330 Southeastern Naturalist Vol. 5, No. 2
environmental extreme associated with channel drying has imposed similar
selective pressures on life-cycle evolution across taxonomic groups.
Mr. Dan Givens kindly allowed access to his property during the entire study
period. Assistance in the field and laboratory was provided by Charles Boswell,
Jason Butler, Jon Cambron, Joseph Ferguson, Michael Romans, and Jered Studinski.
Wayne Clark, Auburn University, kindly arranged for the loan of Leuctra alta
paratypes. Alexander Huryn and two anonymous referees provided critical reviews
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