Habitat characterization of the morphologically similar mayfly larvae,Caenis and Tricorythodes (Ephemeroptera)

The larvae of Caenis (Caenidae) and Tricorythodes (Tricorythidae), once considered to be confamilial, have notable morphological and behavioural similarities. Univariate and multivariate (discriminant analysis) techniques were used to determine which environmental variables best characterized the larval habitats of Caenis and Tricorythodes at 40 sample sites on 29 rivers within the Interior Plains of Alberta, Canada. River width, depth and substrate type distinguished riverine habitats of the two genera. Larvae of Tricorythodes occurred in wide rivers of varying depths that possessed coarse substrates. Although larvae of Caenis occurred in a variety of habitats, they were found more frequently on stable substrates in narrow, deep rivers.     

The relationship between sediment mobilisation and the entry of Baetis mayflies into the water column in a laboratory flume

Mass bedload movement is thought to play a key role in initiating stream invertebrate drift during extreme flood events. However, little is known of the importance of the shear of invertebrates from stone surfaces relative to their entrainment along with bed material at different discharges. In particular, it is unclear whether so-called catastrophic drift only occurs once mass bedload movement, and hence entrainment of invertebrates, occurs. We investigated the relationship between the mobilisation and transport of bed sediments and the entry of Baetis mayflies into the water column in a laboratory flume. Experiments quantified the percentage of Baetis drifting at a range of discharges that mobilised between 0 and 95% of the flume-bed sediments. Control experiments quantified drift losses from sediment fixed to the bed of the flume, such that sediments were immobile even at the highest discharges. Drift losses increased with increasing discharge and velocity in the flume. Sediment mobility contributed significantly to drift (ANCOVA, p < 0.001), with consistently greater drift losses in mobile sediment experiments than in those with fixed sediment. The discharge which resulted in a loss of 100% of Baetis from the mobile sediment bed (discharge 30 l s^–1) resulted in a loss of approximately 50% of individuals from the fixed bed. Results indicate that once bed sediments are mobilised, entry of Baetis into the drift is greater than expected from the shear of animals from stone surfaces alone. Thus, entrainment of animals along with sediment contributes significantly to drift at high flows. This implies that differences in bed stability between sites or streams, or temporal changes in sediment characteristics within a site, could influence patterns of drift.     

Croatian mayflies (Insecta,Ephemeroptera): species diversity and distribution patterns

Knowledge of the mayfly biodiversity in the Balkan Peninsula is still far from complete. Compared to the neighbouring countries, the mayfly fauna in Croatia is very poorly known. Situated at the crossroads of central and Mediterranean Europe and the Balkan Peninsula, Croatia is divided into two ecoregions: Dinaric western Balkan and Pannonian lowland. Mayflies were sampled between 2003 and 2013 at 171 sites, and a total of 66 species was recorded. Combined with the literature data, the Croatian mayfly fauna reached a total of 79 taxa. Of these, 29 species were recorded for the first time in Croatia while 15 species were not previously recorded in Dinaric western Balkan ecoregion. Based on the mayfly assemblage, sampling sites were first structured by ecoregion and then by habitat type. In comparison with the surrounding countries, the Croatian mayfly fauna is the most similar to the Hungarian and Bosnian fauna. Some morphologically interesting taxa such as Baetis cf. nubecularis Eaton, 1898 and Rhithrogena from the diaphana group were recorded. Ephemera cf. parnassiana Demoulin, 1958, the species previously recorded only from Greece, was also recorded.     

Comparative ecology of Gammarus pulex (L.) and Asellus aquaticus (L.) I: population dynamics and microdistribution

Gammarus pulex and Asellus aquaticus generally occupy different zones in rivers; the former occurs in upper reaches but is replaced by the latter in lower reaches. Microdistribution and life-history patterns of G. pulex and A. aquaticus in sympatry and allopatry, were analyzed. Both species exhibited similar patterns of microhabitat selection, with larger individuals associated predominantly with large-sized substratum particles, and juveniles with weed. Coexisting populations of G. pulex and A. aquaticus had similar densities and population dynamics. Within each species, differences in population dynamics of allopatric and sympatric populations were observed. Although variation in population dynamics of G. pulex may be explained in terms of competition between the two species, the evidence is weak and equivocal. Differences in the dynamics of the two A. aquaticus populations were possibly a consequence of coal-mine and organic pollution, reducing the survival of offspring in the allopatric population.     

The biology of Brachycentrus subnubilus Curtis (Trichoptera) in the River Frome,Dorset

Aspects of life-history, oviposition and microdistribution within beds of Ranunculus penicillatus var. calcareus (R. W. Butcher) C.D.K. Cook are considered. Brachycentrus subnubilus Curtis has one generation each year, with five larval instars. Larvae favour sites beneath the weedbeds for most of the year, migrating to more exposed areas in the spring to pupate. Pupation, emergence, oviposition and eclosion are completed in just over two months. Eggs are usually laid on submerged marginal vegetation but any semi-submerged object may be utilized. Larvae appear to disperse mainly as first instars; in this they are likely to be seriously affected by weedcutting activities. Initial development is rapid to fourth instar. Larvae overwinter as fifth instars. Sex ratios show a predominance of males.     

Global diversity of mayflies (Ephemeroptera, Insecta) in freshwater

The extant global Ephemeroptera fauna is represented by over 3,000 described species in 42 families and more than 400 genera. The highest generic diversity occurs in the Neotropics, with a correspondingly high species diversity, while the Palaearctic has the lowest generic diversity, but a high species diversity. Such distribution patterns may relate to how long evolutionary processes have been carrying on in isolation in a bioregion. Over an extended period, there may be extinction of species, but evolution of more genera. Dramatic extinction events such as the K-T mass extinction have affected current mayfly diversity and distribution. Climatic history plays an important role in the rate of speciation in an area, with regions which have been climatically stable over long periods having fewer species per genus, when compared to regions subjected to climatic stresses, such as glaciation. A total of 13 families are endemic to specific bioregions, with eight among them being monospecific. Most of these have restricted distributions which may be the result of them being the relict of a previously more diverse, but presently almost completely extinct family, or may be the consequence of vicariance events, resulting from evolution due to long-term isolation. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Hydraulic microdistribution patterns of larval fire salamanders (Salamandra salamandra salamandra) in the Weidlingbach near Vienna, Austria

1. This study examined the longitudinal distribution of larval fire salamanders ( Salamandra salamandra salamandra L.) in the Weidlingbach system, a first- to fourth-order tributary of the Danube near Vienna, Austria. On the microhabitat scale, actual current velocities, Reynolds numbers and Froude numbers at larval locations were measured and larval positions mapped.
2. Larval densities were highest in shallow first- and second-order tributaries where mean current speeds were less than 20 cm s⁻¹, mean Reynolds numbers were less than 12 000 and mean Froude numbers were less than 0.30. Young larvae appeared on 26 April, fully grown larvae were observed from 11 May and larvae started metamorphosis from 27 June. Young adults left the brook between 26 August and 8 September. A severe flood on 25 May significantly reduced larval density, especially at sites near the source.
3. At a given sampling station young larvae favoured microhabitats exposed to only minor hydraulic stress. As larvae grew, they also colonized microhabitats with moderate current velocity (4–15 cm s⁻¹). At sites with generally low discharge, larvae were distributed over a wider range of current velocities than at sites with higher discharge; at the latter, larvae were constricted to sheltered microhabitats.     

Ocellar fine structure inCaenis robusta (Ephemeroptera), Trichostegia minor,Agrypnia varia,andLimnephilus flavicornis (Trichoptera)

Summary Three dorsal ocelli are present inCaenis robusta (Ephemeroptera), Trichostegia minor, Agrypnia varia, andLimnephilus flavicornis (Trichoptera). The dioptric apparatus of the ocelli differs between the four species. InTrichostegia andAgrypnia a biconvex corneal lens is present, inLimnephilus the corneal lens is convexo-concave complemented by an underlying haemocoelic space, whereas a cellular vitreous body is found between the cuticle and the retinal layer in the ephemerid. In the three trichopteroid species the ocelli are surrounded by an array of longitudinally arranged tracheoles; inCaenis a layer of screening pigments is found in this position. In this species the rhabdoms formed by microvilli of neighbouring retinula cells have a randomly arranged meshwork pattern; in the three trichopteroid species the rhabdoms are isolated, built up of four retinula cells. Cells with basally situated nuclei and lamellar extensions between the retinular cells are found in the ocelli ofTrichostegia, Agrypnia, andLimnephilus.     

Dominance,age, and reproductive success in free-ranging female hanuman langurs (Presbytis entellus)

Correlations among female age, dominance, and reproduction were investigated for a 12-year period in free-ranging, provisioned Hanuman langurs (Presbytis entellus), living in one-male groups near Jodhpur in Rajasthan, India. Of 2940 displacement episodes, 27% occurred over natural food, 26% over provisioned food, 8% over grooming, 23% over position and shade, and 16% for other reasons. It was possible to reconstruct a displacement hierarchy that was linear and stable over short periods but fluctuated according to the age composition of the troop, resulting in an age inversed dominance structure. Females occupied top ranks as soon as they experienced menarche (around 2.4 years of age) and gradually declined thereafter, with postmenopausal females (≥30 years) being the lowest ranking individuals. Old females tended to be peripheral, while young females were highly social and active. Fertility peaked at about 7 years and gradually decreased thereafter, but infant mortality was much higher in young females than in old ones. During years when females gave birth, their ranks, especially those of old females, were higher than the average expectation for their age class, which suggests that females compete more vigorously if they have an infant. Reproductive success (i.e., infant survival to ≥2 years) declined significantly from high-over middle-to low-ranking females but did not differ for the three age classes investigated, because the higher fecundity of young females was balanced by better rearing success of older females. These results are discussed in light of the controversy over whether the langur social system is strongly influenced by kin selection (Hrdy and Hrdy, 1976; Dolhinow et al., 1979).     

Integrative taxonomic revision of Campylocia (mayflies: Ephemeroptera,Euthyplociidae)

A morphological comparison of type and non-type material of species of Campylocia, including their junior synonyms, was conducted, in addition to neighbour joining based on K2P distances and Bayesian inference analyses of 376?bp of the mitochondrial gene cytochrome oxidase I (COI) of recently collected specimens. Results revealed the lack of distinguishing characters between C. bocainensis and C. dochmia supported by the molecular analysis, where the overlap of intra- and interspecific genetic divergences suggested genetic flow among individuals. Campylocia burmeisteri is revalidated as a senior synonym of Brazilian south-eastern species C. bocainensis and C. dochmia and of E. guntheri, formerly a synonym of C. anceps. Campylocia burmeisteri is redescribed based on material from its type-locality, Nova Friburgo, Rio de Janeiro State. Two new species, C. demoulini sp. nov. and C. araca sp. nov., are described from the Amazon rain forest and a third species, C. orosi sp. nov., is described from Costa Rica. Possible cryptic species and the utility of egg morphology in the taxonomy of Campylocia are discussed for the first time for the genus. A key to the identification of adult stages of Campylocia is provided based on male genitalia and egg morphologyhttp://zoobank.org/urn:lsid:zoobank.org:pub:6779DC2C-DB98-41DF-8C52-FF97366AAF7A     

Emergence patterns of three species of Caenis Stephens (Ephemeroptera: Caenidae)

Distribution of the watermould Achlya americana in Jabalpur, India, was investigated. The influence of temperature, pH, BOD, CO₂ and pollution is discussed.     

Fine sediment effects on feeding and growth in the invertebrate grazers Potamopyrgus antipodarum (Gastropoda,Hydrobiidae) and Deleatidium sp. (Ephemeroptera,Leptophlebiidae)

The influence of fine sediment (<63 m diameter) upon the assimilation rates of the snail Potamopyrgus antipodarum, and the mayfly Deleatidium sp. were determined by allowing individuals to feed upon ¹⁴C radiolabelled periphyton which had been contaminated with varying quantities of sediment (sediment:food ratios of: 0:1, 1:1, 5:1, 10:1, 50:1, 100:1 [dry weight]). For both grazers, the assimilation rate falls in direct proportion to the sediment fraction in the (sediment+food) matrix. In a second experiment the growth of P. antipodarum was monitored over 3 months when fed organic matter that had been contaminated with fine sediment at ratios of 0:1, 1:1, 5:1, 10:1, 50:1, 100:1, 500:1. In contrast to the monotonic relation between sediment and short-term assimilation, growth rates (mm shell height d^–1) were highest at intermediate levels of sediment contamination (5:1 and 10:1 by dry weight) and lowest in the treatment with no sediment added. Growth rates were significantly lower, and mortality high, at sediment:food contamination ratios above 50:1. The reasons for the contrast between the results from the short-term and the long-term experiments are unknown at present, but the fact that snail growth was greatest at intermediate levels of sediment contamination might indicate that they derive trace nutrients from ingested sediment.     

Ecology of Potamanthus myops (Walsh) (Ephemeroptera: Potamanthidae) in a Michigan stream (USA)

The ecology of Potamanthus myops (Potamanthidae) was examined for a one year period in a central Michigan fourth order stream. Lowest nymphal densities (4.7 m^-2) occurred in mid-summer after adult emergence, while highest densities were found during late summer and fall (68.0 m^-2 and 66.2 m^-2) after the new cohort had hatched. Biomass was the inverse of density with highest values, 67.7 mg m^-2, just prior to peak adult emergence in June and lowest in late summer (16 mg m^-2). Nymphs maintained a contagious spatial distribution with k values ranging between 0.19 and 1.40. P. myops nymphs fed mostly on detritus (96.8%), placing them in the collector-gatherer functional group. Nymphs were always found in erosional zones associated with rock substrate. Nymphs used their mandibular tusks for positioning themselves beneath rocks, while also appearing to use them for defensive purposes.     

The influence of diet on the growth of Stenonema vicarium (Walker) (Ephemeroptera: Heptageniidae)

Laboratory studies compared the growth rate of Stenonema vicarium (Walker) nymphs on diets of detritus and natural stream periphyton. In three consecutive runs of the experiment, growth rates were consistently higher on periphyton (mean growth rate = 2.1% wet wt. d⁻¹) than detritus (mean = 1.8% wet wt. d⁻¹). The starting date of each run also significantly influenced growth rates. In each treatment growth rates generally decreased over the course of the 3 runs, and ca. one-half of the nymphs in the last run did not molt or grow. It appeared that growth of S. vicarium may be partially controlled by seasonal factors.     

Observations on the biology of nymphs of Povilla Adusta Navas (Ephemeroptera: Polymitarchidae) in Lake Kainji,Nigeria

Observations onPovilla adusta Navas nymphs in Lake Kainji revealed that seasonal fluctuations in abundance were due to a shortage of food during the period of rising lake level rather than a depletion of oxygen in the water column; this shortage was caused by the increased turbidity of the flood waters restricting the growth of both planktonic and periphytic algae. Planktonic algae apparently formed the diet of nymphs <4–6 mm and also of larger nymphs if their preferred diet of periphytic algae was in short supply. Both depth distribution and individual size of the nymphs were closely related to the distribution of periphytic algae. Depth distribution patterns of the nymphs revealed a peak between 2–4 m below the surface.The dimensions of the nymphs and the duration of the aquatic stages (3–4 months) in Lake Kainji correspond closely with results obtained elsewhere as does the mean percentage of males in the population (28%±10%). Seasonal fluctuations in the sex ratio were apparently caused by variations in the intensity of predation.Department of Zoology, University of Reading     

Influence of adult experience on host microhabitat location by the generalist parasitoid,Campoletis sonorensis (Hymenoptera: Ichneumonidae)

The effect of adult experience on microhabitat location behavior of the generalist parasitoid Campoletis sonorensis (Cameron)was examined in a wind tunnel bioassay. Responses were tested to the odors of two host plants (cotton and sesame) of Heliothis virescens (F.) or a nonhost plant (potato), either damaged and infested with host larvae and host products (host/plant complex) or intact, clean and uninfested. Parasitoid females remained naive or were allowed one oviposition experience on either of the plants, 1 min, 2 h, or 24 h prior their introduction into the wind tunnel. In a no-choice test, parasitoids experienced 1 min prior to bioassay completed significantly more flights to sesame and potato host/plant complexes than did naive parasitoids. However, 24 h after experience, only females experienced on potato completed more flights to the host/ plant complex than did naive females. Parasitoids experienced 1 min prior to flight to undamaged plants showed a slight increase in flight response (significant only for potato) but, after 24 h, completed only as many flights as naive parasitoids. In a dual-choice situation, parasitoids did not show a preference for either of the two host plants but did prefer a host to a nonhost plant. This innate plant preference was not changed by a single oviposition experience. The potential significance of these results to the microhabitat location behavior of C. sonorensisin the field is discussed.     

Effect of Aeolosoma sp. (Aphanoneura: Aeolosomatidae) on the Population Dynamics of Selected Cladoceran Species

Although oligochaete worms naturally coexist with cladocerans in many shallow freshwater ponds and lakes, their influence on the latter is not well established. In this work we studied the effect of Aeolosoma sp. on the population growth of Alona rectangula, Ceriodaphnia dubia, Daphnia pulex, Macrothrix triserialis and Moina macrocopa. Population growth studies were conducted at one algal food density (1 × 10⁶cells ml^–1 of Chlorella vulgaris). The experimental design was similar for all five cladoceran species, where we used 100 ml capacity transparent jars containing 50 ml of EPA medium with the desired algal density and three replicates for each treatment. The test medium was changed daily and fresh algal food was added. The initial density of each of the cladoceran species in the population growth studies was 0.4 ind ml^–1 while that of the worms 1.0 ind ml^–1. Following inoculation, we estimated daily the number of cladocerans and the worms for duration of 21 days. Regardless of the presence of worms, Moina macrocopa and Macrothrix triserialis showed rapid population growth while A. rectangula took more than 2 weeks to reach peak abundances. With the exception of M. triserialis, all the other our cladoceran species declined in the presence of Aeolosoma sp. The lowest peak population density (about 1 ind ml^–1) was observed for M. triserialisin controls. The remaining species had peak densities of about 3–5 ind ml^–1. The rates of population increase per day varied from 0.03 to 0.19 depending on the cladoceran taxa and the treatment. In general we found that pelagic taxa were more adversely affected by the presence of the worms than were the littoral cladocerans.     

Life history and production of Caenis luctuosa (Burmeister) (Ephemeroptera, Caenidae) in two nearby reaches along a small stream

Population dynamics and production of C. luctuosa were compared in two reaches of the Agüera stream (northern Spain). This species showed univoltine winter life history in both sites. However, the start of the recruitment period, and the cohort production interval differed in 1 month between reaches. Secondary production of C. luctuosa ranged from 76 mg m^–2 year^–1 (upper site) to 93 mg m^–2 year^–1 (lower site). Although annual production seemed to be mainly influenced by the biomass found at each site, changes in life history may have also been important. The need to have accurate information about life history of the analysed species at the study sites when assessing secondary production is highlighted.