Size-related shifts in the physical habitat of two mayfly species (Ephemeroptera)

1. The spatial niche shifts of the nymphs of two mayfly species (Rhithrogena semicolorata and Ecdyonurus sp, gr. venosus) in relation to their growth were investigated in two lowland springs of northern Italy where they are dominant species. 2. Ordination of the different size classes of the two species revealed a canonical trend related to season and bottom roughness. 3. Larger nymphs of both species colonized rougher substrata. Differences between species in the roughness of areas colonized by small nymphs, which were very numerous, may have been due to competition for space.     

The role of parthenogenesis in the biology of two species of mayfly (Ephemeroptera)

1. From a single founder virgin female of each species, nine and seven successive parthenogenetic generations of Cloeon dipterum and Cloeon simile, respectively, were reared: all offspring were female. Eggs were removed from final instar nymphs, subimagos and virgin imagos of each generation and their development assessed. The life cycles of 487 individual C. dipterum and 315 C. simile were recorded, together with details of growth rate, egg production and adult size of these and other representatives of each generation. In order to distinguish between the effects of parthenogenesis and the effects of culture conditions, fertilized eggs of both species were reared under the same laboratory conditions. 2. Fewer unfertilized than fertilized eggs hatched. There was no consistent trend in the percentage hatch in successive parthenogenetic generations. In both species the time taken for parthenogenetic individuals to complete a generation varied considerably, and no relationship was found between generation length and the number of parthenogenetic generations that had passed, the developmental stage of the donor, or the time taken for the eggs to hatch. After 50 weeks there was, in both species, an overlap of up to six generations. The number of eggs produced by both species was significantly greater in the first parthenogenetic generation than in later generations but the numbers for later generations lie within the recorded range of egg number in imagos captured in the field. 3. To find if parthenogenetic individuals occur in the field, the sex ratios of last instar nymphs and subimagos of C. simile were measured in samples collected over 13 successive years from a set of small isolated pools. There was a female bias both in winter and at the start of the emergence season. It is possible that, when mature nymphs and emerging subimagos are damaged by predators, the eggs which are released from them survive and develop. 4. Mature, egg-containing nymphs of both species were present in the field throughout the year, although their numbers were small at the beginning of winter. 5. Oviposition by imagos captured from mating swarms and by virgin imagos, of both species, was recorded for the first time, showing that C. dipterum is not always ovoviviparous. It is suggested that early instar nymphs occurring in mid-winter come not only from unfertilized eggs released from injured nymphs and subimagos, but also from fertilized eggs laid in autumn.     

Mermithid nematode infections and drift in the mayfly Deleatidium spp. (Ephemeroptera).

Alterations in host phenotype induced by parasitic infection are often interpreted as either host or parasite adaptations, depending on which of the two appears to benefit. Mermithid nematodes typically castrate their insect hosts and, therefore, any change in host behavior has no further fitness consequences for the host; the adaptive value of the modified behavior must be assessed with respect to parasite fitness only. In a New Zealand stream, mermithid-infected nymphs of mayflies in the genus Deleatidium were disproportionately represented in drift samples compared with benthic samples, suggesting that infection by mermithids results in an increased tendency to drift. Drifting mayflies face a higher predation risk from trout, and the mermithid nematodes they harbor die if ingested by a fish. The change in mayfly behavior induced by mermithids thus appears to have negative fitness effects for the parasite, and one possible explanation for this phenomenon is that it is a nonadaptive, pathological side effect of infection.     

Discovery of an alien species of mayfly in South America (Ephemeroptera)

Despite its wide, almost worldwide distribution, the mayfly genus Cloeon Leach, 1815 (Ephemeroptera: Baetidae) is restricted in the Western hemisphere to North America, where a single species is reported. In the Neotropics, except for some species wrongly attributed to the genus in the past, there are no records of Cloeon. Recently, however, specimens of true Cloeon were collected along the coast of Espírito Santo, Southeastern Brazil. In order to verify the hypothesis that this species was recently introduced to Brazil, our aim was to identify the species based on morphological and molecular characters and to confirm the presence of true representatives of the genus in the Neotropics. Our results revealed that the specimens found in Brazil belong to the Afrotropical species C. smaeleni Lestage, 1924. The identity of the species, its distribution, along with its previous absence in regularly sampled sites, is a clear sign that the specimens of C. smaeleni found in Espírito Santo are introduced, well established, and that the colonization took place very recently.     

Life histories, production dynamics and resource utilisation of mayflies (Ephemeroptera) in two tropical Asian forest streams

SUMMARY 1. A 2‐year study of the life histories, production dynamics and resource utilisation of five mayfly species was undertaken in two forest streams in Hong Kong [Tai Po Kau Forest Stream (TPKFS) and Shing Mun River (SMR)]. Afronurus sp. and Cinygmina sp. (Heptageniidae), Procloeon sp. and Baetiella pseudofrequenta (Baetidae), and Choroterpes sp. (Leptophlebiidae) were abundant in both streams and contributed more than 50% of the total mayfly populations. 2. All species had asynchronous larval development with recruitment occurring throughout the year. Mean annual production (all mayflies combined) was 3.1 and 2.0 g dry weight m^?2 year^?1 in SMR and TPKFS, respectively – the higher value at SMR reflecting greater mayfly densities – with more than 70% of production occurring during the wet season. Mayfly production varied between years, decreasing by 5% in TPKFS and 43% in SMR during 1996–97, reflecting lower densities of heptageniids relative to 1995–96. Annual biomass turnover rates (P/B) were high in both sites ranging from 27.2 to 94.6 in TPKFS (Cinygmina sp. and Procloeon sp.) and from 31.8 to 109.8 in SMR (Cinygmina sp. and B. pseudofrequenta). 3. Patterns of daily production in both streams showed that Afronurus sp., Cinygmina sp. and Choroterpes sp. were most productive during the wet season, while Procloeon sp. maintained high production levels throughout the year. The highest daily production of B. pseudofrequenta occurred during the wet season in TPKFS, but in the dry season at SMR. Temporal overlap in production and hence resource utilisation in both streams, calculated using the proportional similarity index (PS), ranged from 0.39 to 0.81. It was highest (0.63–0.81) between pairs of species of Heptageniidae and Baetidae, and lowest between Choroterpes sp. and other mayflies (0.39–0.61). No clear temporal segregation was observed among any species. However, when using the fraction of production attributable to each food, lower PS values were obtained for all species in both sites. In SMR, trophic segregation may have occurred between the two species pairs Procloeon sp.–Cinygmina sp. and Procloeon sp.–Choroterpes sp. (PS=0.17 and 0.03, respectively). 4. A combination of production data and information on the stable isotope signature of mayflies revealed that, during both the wet and dry seasons, more than 50% of total mayfly production in TPKFS was derived from autochthonous foods. In SMR, 68% of production was supported by allochthonous foods during the wet season, and 72% by autochthonous sources in the dry season. Considering that more than 70% of the total production occurred in the wet season, the trophic basis of mayfly production in SMR is mostly allochthonous (58%) while in TPKFS it is mainly of autochthonous origin (66%). The year‐round importance of autochthonous foods in shaded streams such as TPKFS is surprising, but the wet season contribution of allochthonous foods (especially in SMR) may have resulted from depletion of algal biomass during spates.     

Structure and spatial variability of mayfly (Ephemeroptera) communities in the upper Hron River basin

Mayflies were sampled from eleven sites in six tributaries of the upper Hron River. Mayfly communities were ordinated and related to environmental factors using multiple regression and principal component analysis. Communities of headwater sites were dominated by Rhithrogena iridina which was gradually replaced by Baetis alpinus, at the lower reaches. Total mayfly species richness was inversely related to stream slope and overall abundance was inversely related to altitude. The prominent factor influencing mayfly communities was a complex longitudinal gradient as proposed by the river continuum concept. There were no significant differences in community composition and structure between the left-and right-hand tributaries of the Hron River.     

Patterns in the distribution of heptageniid (Ephemeroptera) species in Saskatchewan, Canada

SUMMARY. 1, The distribution patterns of twenty-one species of heptageniid mayflies were examined in Saskatchewan and west-central Manitoba, Canada. Presence/absence data from 174 stream sites were analysed using two complementary multivariate techniques, classification (Ward's method with Euclidean distance) and ordination (detrended correspondence analysis).
2. Multivariate analyses revealed two large, distinct groups of sites within the study area. The first included sites characterized by the presence of Heptagenia elegantula (Eaton) and Stenonema terminatum (Walsh). The second included sites characterized by the presence of Stenonema vicarium (Walker), Leucrocuta hebe (McDunnough) and/or Nixe species. The two groups contained, respectively, three and four subgroups.
3. Groups and subgroups defined by multivariate analyses were compared using large-scale environmental features obtained from topographic and other maps. Differences in environmental features between the two groups were mainly in stream order, terrestrial vegetation and annual number of degree-days (calculated from air temperature). The first group could be characterized as warm, large river habitat in grassland and parkland vegetation regions. The second included cooler, small to midsized streams and rivers in boreal forest. Most differences among subgroups were also in stream order, terrestrial vegetation and degree-days, although some subgroups in the second group differed also in stream gradient.
4. The observed groups and subgroups were not associated with drainage basins.     

Microsatellite loci for the mayfly Baetis rhodani (Baetidae,Ephemeroptera)

The first microsatellite primers are described for the mayfly family Baetidae (order Ephemeroptera). Seven polymorphic loci were isolated and characterized for the species Baetis rhodani from two enriched genomic libraries. A total of 183 individuals were genotyped using these loci. Allelic diversity was high for all loci, and observed heterozygosities ranged between 0.382 and 0.772. A heterozygote deficiency was detected in some loci, suggesting the presence of ‘null’ alleles.     

The effects of extended photoperiods on the drift of the mayfly ephemerella subvaria McDunnough (Ephemeroptera : Ephemerellidae)

Field drift studies indicated that the nocturnal drift density of E. subvaria nymphs was greater in early May than in early November.Laboratory studies showed that the number of individuals appearing in the drift was a linear function of the duration of the preceding photoperiod. Nymphs had a greater propensity to drift when they were not in a state of active growth than when they were growing. The tendency of individuals in a single laboratory population to drift was observed to change under conditions of constant temperature and randomized photoperiod. This suggests that the shift was due to some internal physiological change rather than to an external cue.It is suggested that drift in E. subvaria functions as a method relocation from fast-water areas to slow-water pools and stream margins. Redistribution to these areas may reduce mortality incurred during spring run-off and during emergence.     

The daily activity patterns of mayfly nymphs (Ephemeroptera)

Nymphs of Baëtis rhodani (Pictet), Ephemerella ignita (Poda), Ecdyonurus venosus (Fabricius), Rhithrogena semicolorata (Curtis), and Heptagenia lateralis (Curtis) showed a similar endogenous rhythm of activity under conditions of natural illumination, continuous light and continuous darkness; and were most active at night when they moved from the lower to the upper surface of the stone. The nymphs were positively thigmotactic and negatively phototactic in flowing water, but these taxes and the endogenous activity rhythm of all species except Heptagenia lateralis changed markedly when the flow of water ceased.     

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.     

Life cycle and secondary production of two species of Campsurus (Ephemeroptera,Polymitarcyidae) in reservoirs of southeastern Brazil

The aim of this paper was to study the life cycle, the annual secondary production, and the spatial and temporal variation of the species Campsurus truncatus and C. violaceus in two reservoirs in Minas Gerais, Brazil. Campsurus truncatus was recorded in 11 months and had a multivoltine lifecycle with a secondary production of 4.61 g.m^?2.year^?1. Campsurus violaceus was collected in eight months and had a bivoltine lifecycle with a secondary productivity of 1.96 g.m^?2.year^?1.     

Comparison of mayfly (Ephemeroptera) taxocenes of permanent and intermittent Central European small streams via species traits

The recurrent drying out of small streams in past decades has shown an urgent need to pay attention to the impact of global climate change. The objectives of this study were to describe the effect of drying out on the composition of the mayfly taxocene and evaluate the relevance of individual species traits for survival of mayflies to drying out. The mayfly taxocenes of two model localities, one at an intermittent and one at a permanent brook, were investigated in 2002, 2003 and 2005. Compared with the permanent stream, the taxocene of the intermittent stream was short of nine species, foremost rheobionts and high oxygen demand species. To explain further differences between both stream types in survival and recolonisation ability, 15 species traits were evaluated. These included so-called “ecological traits” (e.g., habitat and substrate range, density, distribution, current velocity adaptation) and “biological traits” connected with life cycle and larval/adult adaptations. Species showing the highest number of advantageous traits (with only exception of Electrogena sp. cf. ujhelyii — species of taxonomically unclear status) were able to successfully survive under the unfavourable conditions of the intermittent brook. Biological traits considered more important in many respects seem to be good predictors for assessing sensitivity to extreme temperature changes, hydrological regime fluctuations and the survival/recolonisation ability of species in exposed habitats.     

New mayfly nymphs (Insecta: Ephemeroptera) from Yixian Formation,China

Three new species of mayfly nymphs, Clavineta excavata sp. nov., Clavineta brevinodia sp. nov., and Siberiogenites branchicillus sp. nov., from the Yixian Formation (Late Jurassic-Early Cretaceous) in western Liaoning Province, China, are described. These mature nymphs are small-sized, with the body less than 16.0 mm long. The systematic position of the genera Clavineta and Siberiogenites, which are recorded for the first time in the Yixian Formation, is briefly discussed.     

Biometric studies of some stoneflies and a mayfly (Plecoptera and Ephemeroptera)

Aspects of the nymphal/adult developmental change were investigated in biometric studies of several species of Plecoptera: Nemouridae near Schlitz, Hesse, Germany. Preliminary information on the mayfly, Baetis vernus Curtis, is also provided. Nemourid nymphs pass through 3 wing bearing stages before reaching adulthood. Instars can be identified by their characteristic shapes, as expressed by the wing length/head width (WL/HW) ratio. Size does not allow instar discrimination, mainly due to sexual size differences. HW is ca 10% larger in last instar female than in male nemourid nymphs; exuviae shed at the moult to adult represent about 14% of nymphal ash free dry weight (AFDW). Biomass lost with exuviae during the many larval moults should be accounted for in estimates of production. Freshly emerged nemourid females are about 6% larger and 30% heavier than males. The HW/AFDW relationship is the same in both sexes. Through terrestrial feeding during adult life, males double their weight on average. Mature females are up to three times heavier than freshly emerged ones. They invest about 30% of their final AFDW in reproduction.Shape of last instar nymphal Baetis was expressed as the ratio wing length/mesonotum length. It is size-dependent, a characteristic, instar-specific shape may not occur in this mayfly. Nymphal and subimaginal exuviae together represent about 14% of last instar nymphal dry weight. Females of Baetis are about 55% heavier than males. Unlike in Plecoptera, the size/weight (ML/AFDW) relationship differs between sexes.