Reduction of predation risk under the cover of darkness: Avoidance responses of mayfly larvae to a benthic fish

Summary Mayfly larvae of Paraleptophlebia heteronea (McDunnough) had two antipredator responses to a nocturnal fish predator (Rhinichthys cataractae (Valenciennes)): flight into the drift and retreat into interstitial crevices. Drift rates of Paraleptophlebia abruptly increased by 30 fold when fish were actively foraging in the laboratory streams but, even before fish were removed, drift began returning to control levels because larvae settled to the substrate and moved to areas of low risk beneath stones. This drifting response was used as an immediate escape behavior which likely decreases risk of capture from predators which forage actively at night. Surprisingly, drift most often occurred before contact between predator and prey, and we suggest that in darkness this mayfly may use hydrodynamic pressure waves for predator detection, rather than chemical cues, since fish forage in an upstream direction. Although drifting may represent a cost to mayfly larvae in terms of relocation to a new foraging area with unknown food resources, the immediate mortality risk probably out-weighs the importance of staying within a profitable food patch because larvae can survive starvation for at least 2 d. In addition to drifting, mayflies retreated from upper, exposed substrate surfaces to concealed interstitial crevices immediately after a predator encounter, or subsequent to resettlement on the substrate after predator-induced drift. A latency period was associated with this response and mayflies remained in these concealed locations for at least 3 h after dace foraging ceased. Because this mayfly feeds at night and food levels are significantly lower in field refugia under stones, relative to exposed stone surfaces, predator avoidance activity may limit foraging time and, ultimately, reduce the food intake of this stream mayfly.     

A new record of monogeneric family Vietnamellidae (Insecta: Ephemeroptera) from India

A new record of monogeneric family Vietnamellidae (Insecta: Ephemeroptera) is established for India with Vietnamella sp. A described based on the larvae from Arunachal Pradesh, India. This species can be distinguished from other known species of this genus in the larval stage by the following combination of characters: (i) outer pair of projections in head large and stout, triangular, cone-shaped with serrated spines; (ii) posterolateral angles of abdominal terga 2–9 extended into sharp projections; (iii) caudal filaments pale yellowish brown with dense lateral setae on inner and outer margins of middle part; (iv) femora of mid- and hind-legs broader; and (v) second segment of the maxillary palpi shorter than first segment.     

Reproductive mode of the geographic parthenogenetic mayfly Ephoron shigae, with findings from some new localities (Insecta: Ephemeroptera, Polymitarcyidae)

The burrowing polymitarcyid mayfly Ephoron shigae is distributed widely in Japan. Some populations are bisexual, others are unisexual, and the distributions of the two types overlap broadly. Experimental evidence of parthenogenetic reproduction, long suspected in unisexual populations, is presented here, based on a comparative analysis of the developmental rate of fertilized and unfertilized eggs. The developmental rate of fertilized eggs from 20 mated females in a bisexual population was 98.4% ± 0.73% (mean ± SD), and no unfertilized eggs from 20 virgin females in that population developed. The developmental rates of unfertilized eggs in two unisexual populations were 89.0% ± 4.59% and 84.2% ± 1.96%, respectively. This article presents experimental evidence of geographic parthenogenesis in E. shigae and provides support for the previous interpretation. In addition, we discuss the relationship between the sex ratio of each population and the developmental rate of fertilized versus unfertilized eggs from the females in those populations.     

蜉蝣稚虫形态多样性及其适应性变化

根据蜉蝣稚虫的生活环境,可简单地将其分为静水区种类和流水区种类。静水区种类可生活于水体中、底质表面和底质中三种不同的小栖境,流水区种类可生活于水体中、底质表面和底质缝隙间三类小栖境。形态各异的不同种类蜉蝣稚虫生活在不同的小环境,表明种类演化和形态变化与环境有密切关系。     

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.     

Defining patch contribution in source-sink metapopulations: the importance of including dispersal and its relevance to marine systems

In metapopulations, individual patch contribution (source or sink) is typically calculated as a patch growth rate (the intrinsic lambda, _I) dependent only upon local demographics. We demonstrate that when dispersal is explicitly included in the model, the growth rates for all patches calculated in an analogous manner (the observed lambda, _O) equilibrate to the overall metapopulation growth rate and thus no longer serve as a useful reflection of the demographic and dispersive characteristics of a given patch. In these situations we suggest an alternative method of estimating patch contribution (the contribution lambda, _C) in which a patch is decremented for losses that occur within it and credited for gains that occur anywhere in the metapopulation because of it. We compare values of _I, _O, and _C for individual patches in discrete-time density-independent metapopulation models of two organisms with very different life histories, mayflies with adult dispersal, and reef fish with larval dispersal. Results confirm that when dispersal is included only _C clearly indicates the contribution of a particular patch. _I–_C comparisons indicate that inclusion of dispersal in the mayfly model was only important if connectivity patterns were random or directional. In the reef fish model, however, results were very different when dispersal was included and there were many cases of patches being misidentified (e.g., as a source when it was really a sink) depending upon the metric used (_I or _C). Our results demonstrate the importance of including dispersal in metapopulation models when considering the contribution of individual patches.     

Assessing the impact of gold mining in headwater streams of Eastern Amazonia using Ephemeroptera assemblages and biological traits

Whilst the biological traits composition of invertebrate assemblages has been successfully used to monitor temperate rivers, it has been seldom tested in tropical areas. We compared the trait composition of Ephemeroptera assemblages (five traits, 21 modalities) in three categories of headwater streams of FG: reference (undisturbed) sites, sites formerly impacted by gold-mining, and sites currently impacted by gold-mining. Differences in macroinvertebrate assemblage according to environmental characteristics and disturbance were evaluated using correspondence analysis and MANOVA. Among the considered traits, food acquisition, respiration and locomotion detected both past and current disturbance associated with gold-mining in headwaters. A fuzzy correspondence analysis showed a significant segregation of currently gold-mined, formerly gold-mined, and reference sites according to species traits. Shifts in trait composition were mostly related to changes in assemblage composition. Interestingly, no significant decline in diversity indices was observed in formerly gold-mined sites compared to the reference sites, 2 years after abandonment, while the taxonomic and trait composition of communities changed at these sites. These results support the case for further fundamental quantification of species traits, and for the inclusion of sensitive, trait-related metrics in upcoming multimetric indices for the assessment of river health.     

Biology of the mayfly <Emphasis Type="Italic">Bleptus fasciatus</Emphasis> Eaton (Insecta: Ephemeroptera,Heptageniidae), with special reference to the distribution,habitat environment,life cycle,and nuptial behavior

As the habitats of the mayfly Bleptus fasciatus (Ephemeroptera, Heptageniidae) are unique and specialized, information on the distribution and biology of the mayfly is very poor. In this article, the biology of the mayfly is described, with special reference to the distribution and life cycle: the voltinism, emergence and reproductive season, nuptial behavior (i.e., swarming), egg period, and the early stage of postembryogenesis. The life cycle of the mayfly was judged as semivoltine, in contrast to the previous interpretation. Also, the unique nuptial behavior or the swarming of the mayfly is revealed.     

Do nymphs of Parameletus chelifer and P. minor (Ephemeroptera) reduce mortality from predation by occupying temporary habitats?

Summary The possible effect of predation on the habitat selection of nymphs of the two mayfly species Parameletus chelifer Bengtsson and P. minor (Bengtsson) was investigated for different habitats of a North Swedish boreal river. In spring, these two species migrate to river margins and subsequently, in different proportions, to adjacent seasonal ponds. Feeding rates on mayfly nymphs and mosquito larvae by some dytiscid beetles and larvae, a corixid waterbug and a caddisfly larva were studied in the laboratory. In the seasonal pond, the consumption rate of invertebrate predators on Parameletus nymphs was below that expected from their relative abundance, and mosquito larvae were preferred. At the river margin, where mosquito larvae were absent, Parameletus nymphs were consumed in agreement with their relative abundance. The absolute abundance of macroinvertebrate predators was similar at the river margin and in the pond. Fish predators visited the seasonal pond only during a short time of flood, while at the river margin their presence was continuous. In the seasonal pond, minnow and roach consumed nymphs of both P. chelifer and P. minor in a lower proportion than expected. At the river margin, nymphs of P. chelifer were consumed by minnow and ten-spined stickleback in a higher proportion than expected. Nymphs of P. minor were consumed according to expectance. Imagines of P. minor emerged early, and nymphs were equally abundant in the river and in the seasonal pond. In contrast, almost all nymphs of P. chelifer migrated to the seasonal pond. The later emergence of P. chelifer would probably result in a very high mortality from predation if it remained at the river margin.