Functional morphology of burrowing in the mayflies Hexagenia limbata and Pentagenia vittigera

A video system, consisting of a high-resolution, infrared-sensitive, surveillance television camera, time-date generator, video recorder and high-resolution monitor, was developed for naturalistic observation of the subaquatic activities of larval mayflies. Exemplars were isolated from light, sound and mechanical disturbance, and their burrowing behaviour was recorded for subsequent slow-motion analysis. Larvae of silt-inhabiting Hexagenia limbata were observed to be ploughers that displaced and compacted soft substrate in the excavation of an open tunnel. The head and prothoracic legs had the principal roles in substrate displacement, while the mesothoracic and metathoracic legs drove the body forward. Five stereotyped burrowing cycles were distinguished, although one, termed the Alternate Undercut because of the motions of the prothoracic legs, predominated. Larvae of clay-inhabiting Pentagenia vittigera were observed to chisel and gouge out compacted substrates, also creating an open burrow. Their mandibular tusks were used to dislodge substrate, while the prothoracic legs displaced loosened substrate and widened the opening. The body was driven forward either by strong abdominal flexions or by activity of the mesothoracic and metathoracic legs. Four burrowing cycles were distinguished, two of which, the Tusk Gouge and the Chisel and Sweep, predominated. Differences in proportion and armature of the head and appendages correlated with the different substrate types excavated.     

The sperm of Hexagenia (Pseudeatonica) albivitta Walker (Ephemeroptera: Fossoriae: Ephemeridae)

This study describes the sperm morphology of the mayfly Hexagenia (Pseudeatonica) albivitta (Ephemeroptera). Its spermatozoon measures approximately 30 μm of which 9 μm corresponds to the head. The head is composed of an approximately round acrosomal vesicle and a cylindrical nucleus. The nucleus has two concavities, one in the anterior tip, where the acrosomal vesicle is inserted and a deeper one at its base, where the flagellum components are inserted. The flagellum is composed of an axoneme, a mitochondrion and a dense rod adjacent to the mitochondrion. A centriolar adjunct is also observed surrounding the axoneme in the initial portion of the flagellum and extends along the flagellum for at least 2 μm, surrounding the axoneme in a half‐moon shape. The axoneme is the longest component of the flagellum, and it follows the 9+9+0 pattern, with no central pair of microtubules. At the posterior region of the flagellum, the mitochondrion has a dumb‐bell shape in cross sections that, together with the rectangular mitochondrial‐associated rod, is responsible for the flattened shape of the flagellum. An internal membrane is observed surrounding both mitochondrion and its associated structure.     

Life history of a lowland burrowing mayfly, Ephemera orientalis (Ephemeroptera: Ephemeridae), in a Korean stream

Life history aspects of Ephemera orientalis, a common lowland burrowing mayfly that resides in temperate East Asia, were studied in terms of voltinism, secondary production, and accumulated degree days for larval development. From March 1998 to June 1999, larvae were sampled monthly (weekly or biweekly during the emergence period) from a lower reach of the Gapyeong stream in Korea, a stream typical of temperate East Asia, using a Surber sampler (0.25 m², mesh 0.25 mm). As a result, the mean density of E. orientalis was 47.21 ± 13.58 indiv. m⁻² during the study period. Very small larvae less than 2 mm in body length were sampled on three separate occasions, and emergence was observed between late April and early October, except during late May. Based on the larval body length distribution and emergence time, two different developmental groups could be distinguished: the slow developmental group (S-group) and the fast developmental group (F-group). The F-group completed its life cycle within 4 months, whereas the S-group had a one-year life cycle. The S-group could be divided into two subgroups, dubbed the S1 and S2-groups, based on larval development. The developmental groups alternate their life cycles in the order: S1→F→S2→S1. Estimated annual production of the larvae was 68.81 mg DW m⁻² y⁻¹; mean biomass was 8.43 mg DW m⁻²; the annual production to mean biomass ratio was 8.16. The annual mean water temperature of the study year was 14.76 ± 6.63°C. The total accumulated degree days for larval development was 1396°C for the F-group, 2,055°C for the S1-group, and 1,975°C for the S2-group. Two different adult body size groups were distinguished (P < 0.001 by t-test): larger adults, which belonged to the S-group, were present throughout the emergence period, whereas smaller adults, which belonged to the F-group, were mainly present later in the emergence period (August–October). The difference in the accumulated degree days between the developmental groups may explain the size differences of adults.     

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.     

Effects of temperature on gut-loading and gut-clearing times of the burrowing mayfly, Hexagenia limbata

SUMMARY. The effect of temperature on gut-loading times, gut-clearing times, and the calculated ingestion rates, egestion rates, and consumption indices of the deposit-feeding burrowing mayfly, Hexagenia limbata , were investigated in laboratory experiments. Rates of movement of two natural sediments of differing colour through the digestive tract were monitored to quantify feeding intensity when ambient water temperatures approached 5, 10, 15, 20, and 25°C.
At each temperature, gut-loading times (GLT) and gut-clearing times (GCT) increased as nymph length increased. Mean GLT and GCT values decreased as temperature increased from 5 to 20°C but were longer at 25°C than at 20°C. Relationships between GLT, GCT, and length of nymphs and temperature were best described by multiple regression equations. No diel variation in gutclearing times was observed. Low water temperatures resulted in lower ingestion and egestion rates and consumption indices. At most temperatures nymphs ingested over 100% of their dry body weights per day.     

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     

Recolonization and possible recovery of Burrowing Mayflies (Ephemeroptera: Ephemeridae: Hexagenia spp.) in Lake Erie of the Laurentian Great Lakes

Burrowing mayflies of the genus Hexagenia spp. were widely distributed (ca. 80% of sites) and abundant (ca. 160 nymphs/m²) in the western basin of Lake Erie of the Laurentian Great Lakes in 1929–1930, prior to a period of anoxia in the mid 1950s. Nymphs were absent or rare in the basin between 1961 and 1973–1975. In 1979–1991, nymphs were infrequently found (13–46% of sites) in low abundance (3–40 nymphs/m²) near shore (<7.5 km from shore), but were absent or rare offshore (0–7% of sites at 0–1 nymphs/m²). Increased abundance occurred offshore between 1991 (0% of sites) and 1993 (52% of sites at 7/m²). Annual sampling, beginning in 1995, indicates that nymphs increased in both nearshore and offshore waters. By 1997, nymphs were found throughout the lake (88% of sites) at a mean density 40-fold greater (392/m²) than that observed in 1993 (11/m²). In 1998, the distribution of nymphs remained the same as 1997 (88% of sites) but density declined 3-fold (392 to 134/m²). These data indicate that mayflies have recolonized sediments of western Lake Erie and that their abundance may be similar to levels observed before their disappearance in the mid 1950s. However, prior to the mid 1950s, densities were greater in offshore than nearshore waters, but between 1979 and 1998 greater densities occurred near shore than offshore. In addition, there were two areas in the 1990s where low densities consistently occurred. Therefore, recovery of nymphs in western Lake Erie may not have been complete in 1998. At present we do not know the cause for the sudden recolonization of nymphs in large portions of western Lake Erie. Undoubtedly, pollution-abatement programs contributed to improved conditions that would have ultimately led to mayfly recovery in the future. However, the explosive growth of the exotic zebra mussel, Dreissena polymorpha, undoubtedly diverted plankton foods to bottom substrates which could have increased the speed at which Hexagenia spp. nymphs recolonized sediments in western Lake Erie in the 1990s.     

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     

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.     

Swarm behaviour and mate competition in mayflies (Ephemeroptera)

Although mayfly swarms are frequently cited as an example of lekking by insects, little is known about the behaviour of individuals within a swarm, or how mate-selection takes place. A study of five species of mayfly over a period of 10 consecutive years has revealed species-specific differences in the flight pattern of swarming males and in the ability of males to recognize swarms of their own species. Males of four of the five species jostle other males in the swarm at all times except when mating: mating pairs are not jostled. The pattern of jostling varies with the species. Measurements of the sperm content of the vesicula seminalis and of the wing length of members of individual swarms show that larger wing size is positively correlated with the presence of less sperm. The vesicula seminalis is always filled with sperm at the beginning of the imaginal stage and the testes regress before the beginning of the imaginal stage. If the volume of sperm in the vesicula seminalis is a valid index of mating success then males with larger wings have the highest success. Large wings may bestow an advantage during jostling. The males of Ephemera danica , which do not jostle, glide with outspread wings; these outspread wings may attract females, the largest wings being the most attractive. Females of all five species enter the swarm a few at a time, although many females may be resting beneath the swarm. This phased entry may decrease the attraction of the swarm for predators. The number of females in a swarm is not correlated with swarm size, and the factors which enable females to regulate their entry into a swarm remain obscure.     

Production by Hexagenia limbata in a warm-water reservoir and its association with chlorophyll content of the water column

We investigated the productivity of nymphs of the mayfly Hexagenia limbata in Lake Waco, a central Texas reservoir, and assessed its association with chlorophyll content of the water. We hypothesized that food availability measured as chlorophyll content of the water may directly associate with growth of Hexagenia and predict population productivity. To test this, we compared production by mayfly populations at two stations in the same reservoir; a northern station receiving water input with high chlorophyll content, and a southern station receiving water with low chlorophyll content. Both stations had similar substrate type and abundant mayflies. Benthic samples were collected from October 1984 through September 1985, and dissolved oxygen and temperature of the water were monitored.Annual production (size-frequency method) was 1270 mg m^–2 (P/B = 7.5) at the northern station and 1990 mg m^–2 (P/B = 6.1) at the southern station. The mean standing crop was 323 mg m ^{– 2} at the southern station and 169mg m^–2 at the southern station. Densities of mayflies at the two stations were not significantly different.Mean chlorophyll concentration (total mg pigment) during the sampling period was 23.5 mg m^–3 at the northern station and 16.7 mg m ^{– 3} at the southern station. Therefore, the station with lower mean chlorophyll content had higher secondary productivity by Hexagenia. Conversely, the station with higher mean chlorophyll content had lower mayfly productivity. The productivity of the mayfly populations did not positively associate with the chlorophyll content of the water, and chlorophyll content did not predict the success of the population of Hexagenia. Variation in mayfly growth success was associated with differences in temperature and dissolved oxygen. The northern station with higher chlorophyll content and lower productivity had low dissolved oxygen and temperatures higher than optimum for growth.     

Early embryonic development of the mayfly Ephemera japonica McLachlan (Insecta: Ephemeroptera,Ephemeridae)

In the newly laid egg of the mayfly Ephemera japonica, an egg nucleus (oocyte nucleus) at metaphase of the first maturation division is in the polar plasm at the mid-ventral side of the egg, and a male pronucleus lies in the periplasm beneath a micropyle situated just opposite the polar plasm or at the mid-dorsal side of egg. The maturation divisions are typical. An extensive and circuitous migration of the male pronucleus is involved in the fertilization process: it first moves anteriad in the periplasm from beneath the micropyle to the anterior pole of the egg and then turns posteriad in the yolk along the egg's long axis to the site of syngamy, near the center of the egg. Cleavage is superficial. The successive eight cleavages, of which the first five are synchronized, result in the formation of the blastoderm, and about ten primary yolk cells remain behind in the yolk. Even in the newly formed blastoderm, the thick embryonic posterior half and the thin extraembryonic anterior half areas are distinguished: the former cells are concentrated at the posterior pole of the egg to form the germ disc, and the latter cells become more flattened, forming serosa. Time-lapse VTR observations reveal a yolk stream that is in accord with the migration of the male pronucleus in time and direction. The yolk stream is also generated in activated unfertilized eggs, and it is probable that the migration of the male pronucleus in association with the fertilization may be directed by the yolk stream. J. Morphol. 238:327–335, 1998. © 1998 Wiley-Liss, Inc.     

Swarming and mating behavior in Ephemera orientalis Mclachlan, 1875 (Ephemeroptera: Ephemeridae) with morphological analyses

Swarming and mating behaviors of a mayfly species, Ephemera orientalis Mclachlan, 1875 were observed in 2015, 2016, and 2018 at a river bank of the Asahi River, Japan. Males started to make swarms between late April and middle May in 2016 and 2018. The numbers of mated pairs in a swarm correlated with the numbers of flying males in a swarm in 2016 and 2018. Swarms were formed during a limited period at dusk most probably because that interval is free from natural enemies. Males competed with each other to copulate with females in swarms. We clarified the function of the forelegs of males, which are significantly longer than those of females. Males used their forelegs to hold up a female from below. Besides forelegs, males have longer tails than females. We will discuss why sexual differences are found in these traits. Our results represent the first observation of swarm mating behavior in E. orientalis.     

Trans-oceanic and endemic origins of the small minnow mayflies (Ephemeroptera, Baetidae) of Madagascar

We investigated the relative importance of dispersal and vicariance in forming the Madagascar insect fauna, sequencing approximately 2300bp from three rRNA gene regions to investigate the phylogeny of Afrotropical small minnow mayflies (Ephemeroptera: Baetidae). Six lineages contained trans-oceanic sister taxa, and variation in genetic divergence between sister taxa revealed relationships that range from very recent dispersal to ancient vicariance. Dispersal was most recent and frequent in species that spend the larval stage in standing water, adding to evidence that these evolutionarily unstable habitats may select for ecological traits that increase dispersal in insects. Ancestral state likelihood analysis suggested at least one Afrotropical lineage had its origin in Madagascar, demonstrating that unidirectional dispersal from a continental source may be too simplistic. We conclude that the Malagasy mayfly fauna should be considered in a biogeographical context that extends beyond Madagascar itself, encompassing trans-oceanic dispersal within multiple lineages.     

Life histories, microdistribution and drift of two mayfly (Ephemeroptera) species in the Pembina River, Alberta, Canada

Ephemerella inermis Eaton is a univoltine species that emerges in July. Eggs hatch in August and larvae grow rapidly in autumn and spring, but not during winter. Baetis tricaudatus Dodds produces three cohorts per year. Emergence periods occur in early June, July and early September. Only one cohort overwinters as larvae.
Microdistribution of both species is controlled largely by the discharge pattern of the river. During 1978, a year of frequent floods, animals were equally distributed among slow and fast water portions of the river. Nocturnal drift densities of both species were much greater in slow than in fast water areas. During 1979, a year of relatively stable flow, benthic larval densities were significantly greater in fast water than in slow water.
Early instar E. inermis larvae are most abundant in nearshore areas, but move to deeper water in late autumn. Baetis tricaudatus larvae are seldom numerous in near-shore areas.
Densities of both species were positively associated with concentrations of detritus and of other invertebrates, but only when relationships were considered in areas of similar current velocity independently of season.     

The microdistribution of mayflies (Ephemeroptera) in myriophyllum beds in Pennington Creek,Johnston County,Oklahoma

I studied the population densities and the microdistributions of the four most abundant mayfly (Ephemeroptera) nymphs in Myriophyllum heterophyllum beds in Pennington Creek, Johnston County, Oklahoma, from May to December, 1977. The section of the stream studied has relatively constant flow rates and temperatures throughout the year due to continuous inflow from groundwater. This uniform physical environment allows the plant beds to grow throughout the year and provide a permanent habitat. The four mayflies are Tricorythodes fictus (Tricorythidae), Caenis delicata (Caenidae), Baetis favistriga and B. quilleri (Baetidae). All four species are of similar size and feed by scraping periphyton from the surface of the Myriophyllum. T. fictus and the two species of Baetis have overlapping microdistributions in the leafy, upper one-half of the plant bed. T. fictus and C. delicata have overlapping microdistributions in the lower portion of the plant bed and roots. Each species has similar population densities where their distributions overlap. There is no significant selection for position with respect to current flow in the Myriophyllum for any of the species. Food and space are always abundant, especially in the top one-half of the Myriophyllum. There are no major changes in these trends over the year.     

Phylogenetic analyses of the isonychiid mayflies (Ephemeroptera: Isonychiidae) in the northeast palearctic region

We investigated the molecular phylogeny of isonychiid mayflies inhabiting the East Palearctic region, Isonychia (Isonychia) japonica, Isonychia (Isonychia) ignota, Isonychia (Isonychia) ussurica and Isonychia (Prinoides) shima. We discuss their genetic structures, phylogeny and phylogeography. We collected a total of 100 specimens of isonychiid mayfly species from 47 localities of the Northeast Palearctic region (the Japanese archipelago, the Korean peninsula, the Russian Far East and Mongolia). We analyzed the DNA sequences at the mtDNA COI and 16S rRNA regions, and the nuDNA Histone H3 region. As a result of our genetic analyses of the four Northeast Palearctic isonychiid mayflies, their monophyly at the species level was supported by both the mtDNA (COI and 16S rRNA regions) and the nuDNA (Histone H3 region). In addition, it also became clear that significantly large genetic differentiation exists at the inter‐species level; thus, the relationship of “shima + (japonica + (ignota + ussurica))” is supported. Among the four isonychiid mayflies of the Northeast Palearctic area, I. (P.) shima was shown to be a basal‐most linage within the included species     

Life history and production of the burrowing mayfly Ephoron virgo (Olivier, 1791) (Ephemeroptera: Polymitarcyidae) in the lower Ebro river: a comparison after 18 years

The life history of the burrowing mayfly Ephoron virgo (Olivier, 1791) (Ephemeroptera: Polymitarcyidae) was studied during spring and summer 2005 in the lower Ebro river (Catalonia) and compared to a previous study performed in 1987 (Ibáñez, Escosa, Muñoz and Prat 1991). The results showed an advancement of Ephoron virgo life cycle and an increase of production estimates. In 2005 larval development reached the maximum size one month earlier than in 1987, and adult emergence peak began three weeks earlier. Comparing adult sex ratios (F:M), there was a major presence of females in 2005 (1:4), while the opposite was observed in 1987 (2:1). Secondary production was higher in 2005 than in 1987, obtaining 950 mg dry weight/m²/year with the increment summation method and 1080 mg dry weight/m²/year using the removal summation method. Higher water temperatures were measured for the entire 2005 larval growth period, which were related to higher air temperatures. Therefore, that temperature increment was likely the main cause of changes observed in the Ephoron virgo life cycle.