Life Cycle, Feeding and Production of Isoptena Serricornis(Pictet, 1841

Internat. Rev. Hydrobiol. 89 2004 2 165–174

DOI: 10.1002/iroh.200310726

TOMÁSˇ DERKA1*, JOSÉ MANUEL TIERNO DE FIGUEROA2 and IL’JA KRNO1

1Department of Ecology, Faculty of Natural Sciences, Comenius University, Mlynská dolina B-2, SK-84215 Bratislava, Slovakia; e-mail: [email protected], [email protected] 2Departamento de Biología Animal y Ecología, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain; e-mail: [email protected]

Life Cycle, Feeding and Production of Isoptena serricornis (PICTET, 1841) (Plecoptera, Chloroperlidae)

key words: Plecoptera, feeding, life cycle, production, Slovakia

Abstract

Some aspects of the biology and ecology (life cycle, feeding and production) of a population of Isoptena serricornis in the Rudava River (Slovakia) are studied, reported and discussed. The life cycle is annual, with slow growth in autumn-winter and fast growth in late summer and spring. The growth decreased two weeks before the Fall Equinox and increased two weeks after the Spring Equinox. The flight period spans from the end of May to the beginning of July. The presence of large sand particles in the gut of all studied nymphs is of note, and indicates that I. serricornis acts as a deposit- collector species. Nymphal food is principally composed of detritus, unicellular organisms and, in nymphs of intermediate or large size, Chironomidae larvae. Adult food is composed fundamentally of different types of pollen grains. Males usually have lower food content than females. Annual production of this species (~694–750 mg · m–2) is very high in relation to other previously studied Chloro- perlidae. This is probably largely responsible for I. serricornis being one of the most abundant components of the macroinvertebrate community in its habitat in the Rudava River. A negative correlation between production and temperature was observed.

1. Introduction

Isoptena is a monospecific genus (one of the four Chloroperlidae genera present in Europe) with I. serricornis (PICTET, 1841) occurring in Northern, Central and Eastern Europe (ZWICK, 1973). ILLIES (1953) included this taxon among the species penetrating from the east to the west during the post-Pleistocene period. It is a rare and endangered species in Central Europe (KRNO, 1998b; SOLDÁN et al. 1998) and is affected by stream pollution (RAUSERˇ , 1971). The biology of I. serricornis is little known. According to WINKLER (1957), KITTEL (1976, 1980) and LILLEHAMMER (1988), nymphs inhabit rivers and slowly flowing lowland streams with sandy beds, and adults emerge in May-July. It is supposed to be a borrowing animal, probably with a one-year life cycle in Northern Europe (LILLEHAMMER, 1988). This species was reported to be one of the most abundant in the lowland Polish Pilica River, where it lives buried in the sandy bottom (KITTEL, 1976). A study in a Slovakian river (the Rudava River) showed that I. serricornis was strongly associated with the sandy substrate when, along with some members of the Chironomidae, it was the most important component of the macroinvertebrate community (DERKA et al., 2001). KAISER (1977) observed the presence of sand particles in the gut of this species. Recently, a study of I. serricornis eggs pointed out

* Corresponding author

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1434-2944/04/205-0165 166 T. DERKA et al. that the maximum quantity of eggs found per dissected female is less than 50, which shows low fecundity for this species (TIERNO DE FIGUEROA and DERKA, 2003). Studies on the life cycles of some Plecoptera species have been carried out at different latitudes by several authors. Thus, considerable variation in life cycle characteristics has been described. This variation reflects the species studied (SÁNCHEZ-ORTEGA and ALBA-TER- CEDOR, 1991), and also the ecological conditions (particularly the climatic ones). Given this, it is generally accepted that Chloroperlidae have a one-year life cycle pattern (univoltine cycle) or two-year cycle pattern (semivoltine cycle) (HYNES, 1976), but periods of fast and slow growth and egg development are different among the studied species (HYNES, 1976; STEWART and STARK, 1988). In Central Europe, and particularly in Slovakia, life cycles of some Plecoptera species, including some Chloroperlidae species, have been studied in detail (KRNO, 1982, 1984, 1996, 1998a); but previous to now there had not been an annual study on the life cycle of the genus Isoptena. Feeding in adult stoneflies is a poorly known aspect of their biology (TIERNO DE FIGUEROA and FOCHETTI, 2001). Although traditionally it was thought that adult Perloidea species (at least the European ones) did not ingest food, subsequent work demonstrated that some Chloroperlidae [Siphonoperla torrentium (PICTET, 1841)] can metabolize food ingested in the adult stage (RUPPRECHT, 1990) and gain weight through imaginal feeding (ZWICK, 1990). ZWICK (1973) and SURDICK (1985) indicated that some adult Chloroperlidae feed on the pollen of coniferous plants. TIERNO DE FIGUEROA and SÁNCHEZ-ORTEGA (1999) and TIERNO DE FIGUEROA et al. (1998) showed that adults of one species of the family Chloroperlidae (Chloroperla nevada ZWICK, 1967), and three species of the family Perlodidae changed the proportions of dietary components over the flight period. This change reflected the availability of various components. In contrast, it was found that adult feeding was unim- portant in Perlidae and large-sized Perlodidae (TIERNO DE FIGUEROA and SÁNCHEZ-ORTEGA, 1999; TIERNO DE FIGUEROA and FOCHETTI, 2001). In Plecoptera, as in other orders of amphibious insects, nymphal feeding has been studied more extensively than adult feeding (STEWART, 1994). Studies have concentrated on the ecological role nymphs play in structuring aquatic communities, e.g., in the processing and cycling of nutrients (MERRIT et al., 1984), as primary consumers (LAMBERTI and MOORE, 1984) or as secondary consumers (PECKARSKY, 1984). According to MERRIT et al. (1984), nymphs of Chloroperlidae can be classified as engulfers according to their feeding mechanism. However, STEWART and STARK (1988) pointed out that the food habits of an unstudied species can not be inferred or deduced from the placement of a genus or a higher taxon in a generalized grouping based on studies of congeners. Moreover, the nymphal diet of a particular species can change with individual size during the developmental cycle (BERTHÉLEMY and LAHOUD, 1981; LILLEHAMMER, 1988). The feeding of European Chloroperlidae species in particular is almost unknown. Knowledge of the secondary production of aquatic insects is of considerable ecological importance (applied as well as theoretical) from population and community perspectives. In terms of population dynamics, it combines two parameters that are considered to be of major ecological significance (individual growth and population survivorship) in a single measurement (BENKE, 1984). Nevertheless, study of the contribution of Plecoptera assemblages to overall benthic community production in various biotopes is in its infancy (STEWART and STARK, 1988). In contrast to this general affirmation, studies on stonefly production in Central Europe have increased in the last twenty years (KRNO, 1982, 1996, 1997, 1998a, 2000). More research is needed, however, to complete this knowledge, especially in lowland rivers which have not yet been studied. Although there have been studies on the production of some European and North American Chloroperlidae species (see BENKE, 1984; STEWART and STARK, 1988), there is no such information published for the genus Isoptena despite its importance in the macroinvertebrate community of its habitat (KRNO et al., 1994; DERKA et al., 2001).

The aim of this study is to increase the overall knowledge of Isoptena serricornis biology through discussion of its life cycle, production, and nymphal and adult feeding. In addition to expanding the available information about a particular stonefly species, in this case a monospecific genus whose biology is almost unknown, it is hoped that this study will make an important contribution to the general knowledge of stonefly biology.

2. Study Area

The study was carried out in the Rudava River, a tributary of the Morava River in south- western Slovakia. The sampling site (GPS coordinates 48° 30′ 41.1′′ N; 17° 07′ 26.8′′) is situated at 180 meters above sea level, close to Studienka Village. The river catchment area is 280.32 km2, and the average discharge is 0,73 m3 ·s–1. The discharge fluctuated from 0,35 to 2.61 m3 ·s–1. The river width is approximately 7 m, mean depth is 34 cm and maximum depth is 75 cm. The bottom consists of sand (55%), detritus (25.5%), woody debris (14.5%), submersed root mats of riparian tress (3.9%), and hard mud (2.1%). The riparian vegetation consists mainly of the alder Alnus glutinosa (L.) (DERKA et al., 2001). I. serricornis inhabits the study site along with the other stonefly species such as Perlodes dispar (RAMBUR, 1842), Isoperla tripartita ILLIES, 1954, Taeniopteryx nebulosa (LINNAEUS, 1758), Nemoura flexuosa AUBERT, 1949, and Leuctra hippopus KEMPNY, 1899 (KRNO et al., 1994; DERKA et al., 2001). The studied river is not affected by pollution or human activities and is included among the areas protected by the Ramsar Convention.

3. Material and Methods

Quantitative and qualitative samples of I. serricornis nymphs were taken at approximately three-week intervals from July 2001 to June 2002. Three to five quantitative samples were collected using Kubícˇek’s benthic sampler (area 0.1 m2, mesh size 0.5 mm). Qualitative samples were taken using a kick net (mesh size 0.5 mm). Adults were collected during their flying period by sweeping the riparian vegetation (May to June, 2002). Specimens were preserved in 70% alcohol in plastic dram bottles and, in the laboratory, were labelled and preserved in glass vials. Water temperature data were obtained from the Slovak Hydrometeorological Institute. To study the production and life cycle, all collected nymphs were measured (total length) with an ocular micrometer of a binocular microscope. Nymphal length was measured with 0.5 mm accuracy. Annual production of I. serricornis was evaluated using various techniques: the size-frequency, instantaneous growth, increment summation methods (BENKE, 1984), Morin and Dumont’s method (MORIN and DUMONT, 1994), and Zelinka’s method (ZELINKA and MARVAN, 1976). The seasonal daily production of I. serricornis was evaluated using a method developed by MORIN and DUMONT (1994). Estimation of nymph biomass was made according to BENKE et al. (1999) using the equation:

M (mass) = a L (length)b where (for Chloroperlidae): a = 0.0062 b = 2.724.

The transparency method employed to study the digestive contents was the one proposed by Dr. BELLO (personal communication) and used in other Plecoptera feeding studies by TIERNO DE FIGUEROA et al. (1998), TIERNO DE FIGUEROA and SÁNCHEZ-ORTEGA (1999, 2000) and TIERNO DE FIGUEROA and FOCHETTI (2001). Individuals (20 adults and 22 nymphs) were placed in vials with Hertwig’s liquid (a variation of Hoyer’s liquid) and kept at 65 °C in an oven for 20 hours. They were then mounted on

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 168 T. DERKA et al. slides directly with Hoyer’s liquid and oven-dried. A microscope (40, 100 and 200× magnification) was used to observe and identify the gut contents. For quantitative analysis of gut contents, the percentage of different types of food (measured as % occupied area) was estimated using an ocular micrometer. Four size classes of nymphs were recognized to evaluate diet variation with growth. The limits of these intervals of size classes were obtained by dividing the range of total length of the species into approximately regular intervals.

4. Results

4.1. Life Cycle

A total of 963 nymphs were collected and measured for the study of I. serricornis life cycle. Nymphs of different sizes were found burrowed in the sandy substrate. From our data (Fig. 1) we can infer a one-year life cycle. Normally, first instars were found from the end of July to the beginning of October; they hatched from eggs deposited principally in May– June. Small individuals were also found throughout the winter (typical asynchronic growth). Intermediate instars were found throughout the autumn and winter, while large nymphs were found at the end of spring. Emergence occurred principally in May and June and the flight period spanned from the end of May to the beginning of July. The species seems to undergo maximum growth from July to September (two weeks before Fall Equinox) and from early spring (two weeks after Spring Equinox) to early summer, coinciding with an increase in temperature (Figs. 1 and 2).

4.2. Feeding

The composition of nymph and adult guts is shown in Tables 1 and 2. Although the number of studied specimens is relatively low, the obtained data are indicative of the composition of the diet of the species.

12 emergence 10 8 6 4

Body length (mm) 2 hatching 0

1 2 V C 2 B R 1 2 1 2 UG P1 P2 N1 N E R R N1 N2 JUL A E E CT CT NO A A F MA P P S S O O DE J J A A MAY MAY JU JU

Figure 1. Life cycle of I. serricornis. Horizontal axis: sampling date (numbers after months indicate more than one sampling in the same month). Vertical axis: total length (mm). Vertical lines: body length range of nymphs; vertical boxes: confidence interval (95%) for body length of nymphs.

Table 1. Nymphal gut contents: * Included bacteria, algae, and fungal spores. D = more than 20% of the gut content (dominant); S = 5 – 20% of the gut content (subdominant); – = absent. For Chironomidae, the number of individuals is reported.

Contents/size <3 mm (n = 5) 3–5.5 mm (n = 6) 5.5–8 mm (n = 6) >8 mm (n = 5)

Sand D D D D D D D D D D D D D D D D D D D D D D Detritus (FPOM) – S – S S – – – – – – S – – – – – D – – S – Leaves (CPOM) – – – – – – D – – – – – – – – – – – – – – – Unicellular – – S S S S S D S S S S – – – – S D S – S S organisms * Chironomidae – – – – – – 1 – – – 2 1 – – – – – 1 1 – 4 –

Table 2. Adult gut contents: D = more than 20% of the gut content (dominant); S = 5 – 20% of the gut content (subdominant); – = absent.

Contents/sexes males (n = 12) females (n = 8) Gymnosperm pollen – D D S S S D D – D – D D D D D D D – S Angiosperm pollen – D S D D D D D – – D D D D D – S – S S Fungal hyphae and spores – S S S S S S – – – S – S – – S S – – D Cyanobacteria – S – – – – – – – – – – – – – – – – – – Detritus (FPOM) – – – – – – – – – – S – – – S – – – – – Sand – – – – – – – – – – – – – – – – – D D –

An interesting observation was the presence of sand particles of relatively large size (0.1 to 0.4 mm) in the gut of all studied nymphs (as previously observed by KAISER, 1977). These large sand particles were always a dominant element, constituting more than 20% of the gut content. Animal remains (particularly Chironomidae), detritus, unicellular organisms (including bacteria, algae, and fungal spores), and CPOM constitute the remaining gut content. The gut content of six nymphs (27%) contained only sand. In adults of both sexes, the principal ingested components were angiosperm and gymnosperm pollen. Other components, such as fungal hyphae and spores, Cyanobacteria, and detritus, were usually consumed less frequently and perhaps only coincidentally. Only two males (17%) and no females had empty guts. However the contents were sometimes abundant and constituted food packs. Males usually had lower food content than females. Few eggs were found in some females, supporting the observation by TIERNO DE FIGUEROA and DERKA (2003) that the species has low fecundity. The presence of sand particles in two female guts is notable.

4.3. Production

The annual production rate (Table 3) of I. serricornis fluctuated from 292 to 1303 mg · m–2 (dry matter), annual P/B ratio from 1.7 to 7.6, and cohort P/B ratio from 1.6 to 7.2 according to applied method. Cohort production interval (CPI) was 335 days. Mean mass of individuals was 0.95 mg, maximal mass of an individual was 3.93 mg and mean population biomass was 170.1 mg · m–2. The annual course of daily production (Fig. 2) shows the greatest values in October (after a notable increase in mid-September). After that, there is a gradual decrease followed by a prominent final decrease (from May to July).

Table 3. Annual production (July 2001 – June 2002) of Isoptena serricornis, in mg dry matter: SF – size-frequency method (BENKE, 1984), MD – MORIN and DUMONT (1994) method, IG – instantaneous growth method (BENKE, 1984), IS – increment-summation method (BENKE, 1984), Z – Zelinka method (ZELINKA and MARVAN, 1976).

Method SF MD IG IS Z annual production 693.9 749.6 416.2 292.2 1303.4 annual P/B ratio 4.1 4.5 2.4 1.7 7.6 cohort P/B ratio 3.9 4.2 2.3 1.6 7.2

18 18

16 16

14 PRODUCTION 14 TEMPERATURE 12 12

10 10

8 8

6 6 Temperature (ºC) 4 4

2 2 Daily production (in dry mass mg. m-2) 0 0 3-Apr-02 7-Jun-02 8-Jan-02 2-Oct-01 24-Jul-01 7-May-02 24-Apr-02 25-Jun-02 29-Jan-02 30-Oct-01 21-Nov-01 18-Feb-02 14-Mar-02 11-Dec-01 23-Aug-01 10-Sep-01 20-Sep-01 24-May-02 Sampling date (July 2001 to June 2002)

Figure 2. Annual course of daily temperature and production of I. serricornis.

In general, the annual course of daily production of I. serricornis was negatively correlat- ed with temperature. A resulting equation shows that production = 3.4694 – 0.1224 * temperature, r = –0.34, p < 0.05.

5. Discussion

5.1. Life Cycle

Our results confirm that I. serricornis has a univoltine life cycle (LILLEHAMMER, 1988) with rapid spring growth and slow growth in autumn and winter. The presence of small individuals, as well as intermediate ones, throughout all of autumn and winter could indicate (in addition to slow autumn-winter growth) a long hatching period contrasting with the relatively short emergence period that was observed. This has

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Life Cycle, Feeding and Production of Plecoptera 171 been reported for other stonefly species (HYNES, 1976), including Chloroperlidae species (CUSHMAN et al., 1977). Our data (Figs. 1 and 2) indicate two different periods relating growth to temperature. In the first period, from the end of summer to October rapid growth (Fig. 1, body length) was observed. From October to March, there was little change in growth. In the third period, starting in March, a continual increase in temperature corresponds with a period of rapid growth. It is possible that the temperature increase stimulated a physiological response for more rapid growth. Growth and other events in the developmental cycle of stoneflies have been shown in other studies to be related to changes in temperature (CORBET, 1964; HYNES, 1976; SWEENEY, 1984). A similar life cycle pattern has been reported for Chloroperla tripunctata (SCOPOLI, 1763) from central Slovakia (KRNO, 1996). The presence of active nymphs throughout the year suggests that the species does not undergo diapause. This absence of diapause has been reported for other stonefly species with similar life cycle patterns (HYNES, 1976).

5.2. Feeding

The presence of sand particles in the guts of all studied nymphs clearly indicates a deposit-collecting feeding mechanism (LAMBERTI and MOORE, 1984), a feeding mechanism rare for a Chloroperlidae stonefly. This feeding mechanism has been recorded throughout the nymphal development of some Taenyopterygidae, Leuctridae and Peltoperlidae. However Chloroperlidae (as well as Perlidae and Perlodidae) are typically engulfers (carnivores) that also utilize detritus during early instars (STEWART and STARK, 1988). The remains of Chironomidae larvae in the gut contents indicate that I. serricornis nymphs greater than 3 mm are also predaceous or, as suggested by KAISER (1977), necrophagous. This has been noted for some other insects that apparently switch between deposit-collecting and another feeding mechanism, as in the case of some Chironomidae (LAMBERTI and MOORE, 1984). Our results show that the feeding mechanism of I. serricornis nymphs is more similar to that of some Tanypodinae larvae, which are considered predaceous but are also known to consume detritus through deposit-collecting (e.g. OLIVER, 1971; BAKER and MCLACHLAN, 1979), than to other stonefly species. The presence of Chironomidae as the only animal content in the gut of I. serricornis nymphs could suggest a consistent pattern of selection for this type of prey. However, the fact that Chironomidae are the most abundant macroinvertebrates (other than I. serricornis) in the Rudava River (DERKA et al., 2001) indicates that feeding is probably indiscriminate, as STEWART and STARK (1988) pointed out for Plecoptera nymphs in general. Moreover, the high proportion of its biomass in the macroinvertebrate community indicates that I. serricornis is not an obligatory predator. The adult diet, consisting principally of pollen for both sexes, is similar to that observed in other Chloroperlidae (ZWICK, 1973; TIERNO DE FIGUEROA and SÁNCHEZ-ORTEGA, 1999). The similar (gut content) percentages of specimens of both sexes indicate that feeding is not more important for one sex more than the other. The higher food quantity found in females is probably due to their greater reproductive effort. This fact has been pointed out previously for other Chloroperlidae (TIERNO DE FIGUEROA and SÁNCHEZ-ORTEGA, 1999). Moreover, our data support the hypothesis that small-sized stonefly species feed during the adult stage. This feeding is probably as a consequence of their high metabolic rate and reduced accumulation of reserves during the nymphal stage (TIERNO DE FIGUEROA and FOCHETTI, 2001). Finally, the presence of sand particles inside some adult female guts, probably left over from nymphal feeding, is notable. This is noteworthy because it contrasts with the generally accepted idea that nymphs usually stop feeding and eliminate all gut contents before moult- ing (ZWICK, 1980). This elimination process may not always be completed.

5.3. Production

Because of the outstanding asynchronic growth pattern, particularly in autumn and winter, production values are strongly underestimated when instantaneous growth and increment summation methods are used (BENKE, 1984, see also Table 3). In contrast, Zelinka’s method (ZELINKA and MARVAN, 1976) leads to overestimated production values. Thus, only two methods seem to provide reliable production estimates, i.e., the size-frequency method (BENKE, 1984) and Morin and Dumont’s method (MORIN and DUMONT, 1994), in which the annual P/B ratio is close to 4, the value typical for univoltine species (WATERS, 1977). The annual production value of I. serricornis in the study area (694 to 750 mg · m–2) is much higher than those reported for other previously studied Chloroperlidae species such as Siphonoperla torrentium (PICTET, 1841) (13 mg · m–2) and Chloroperla tripunctata (12 mg · m–2) from Slovakia (KRNO, 1997), or Sweltsa mediana (BANKS, 1911) (98.7 mg · m–2) in North America (CUSHMAN et al., 1977). This is probably related to the fact that I. serricornis is one of the most abundant components of the macroinvertebrate community in its habitat in the Rudava River (DERKA et al. 2001). The highest values of daily production in October (Fig. 2) are probably related to a hatching of new individuals. The strong continual final decrease (from May to July) is related to adult emergence.

6. Acknowledgements

This work and the stay of JMTF at Comenius University (Slovakia) were supported by the Slovak Grant Agency for Science VEGA, project No 1/1292/04 and the project No EVK-CT-2001–00089 STAR. The stay of TD at Granada University (Spain) was supported by a mobility grant from Comenius University, Bratislava (Slovakia). The authors want to thank to ANNE L. DOVCIAK, MSc. for English language correction.

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Manuscript received June 20th, 2003; revised December 5th, 2003; accepted December 29th, 2003