Effects of aggregative behaviour on the bioenergetics of the freshwater predatory leech Nephelopsis obscura (Erpobdellidae)

1. Supplied with ad libitum prey, the effects of different group sizes (one, five, ten, twenty-five, fifty or 100) on the acquisition and allocation of energy were examined over the entire life cycle of the freshwater predatory leech Nephelopsis obscura , to evaluate the bioenergetic costs and/or benefits of aggregation.
2. In terms of growth, asymptotic biomass and ingestion, group sizes larger than one and less than ten are optimal. As group size increases from ten to 100, N. obscura has slower growth and lower weekly food ingestion, suggesting interference competition. Single leeches had lower food consumption than group sizes of less than 100 animals. With a lower asymptotic biomass, single leeches have lower fecundity and presumed lower fitness. Lipid deposition was unaffected by group size.
3. Size- and time-specific respiration rates declined with increasing group size. For group sizes between five and fifty, the same relative proportion of ingested energy was allocated to respiration. Above this threshold group size, leeches allocated a higher proportion of ingested energy to growth, i.e. had higher growth efficiency, as did leeches cultured individually.
4. In the largest group size, total time spent in activity was highest (reflecting the high degree of interference between conspecifics), but as a result of the lower hourly costs of respiration they allocated a lower proportion of ingested energy to total respiration.
5. Optimum group size of N. obscura in the laboratory is within the typical range of group sizes found on stony shores in the field.     

Cosexuality in the Leech,Nephelopsis obscura (Erpobdellidae)

Summary

Hermaphroditism of the erpobdellid leach Nephelopsis obscura is described on the basis of macroscopic and histological studies of the gonads. Perivitellogenic cells (female primordial germ cells) proliferate from the septa of segments XII and XIII in individuals of 26–30 mg and spermatogenic cells from segments XII to XIII of 20–25 mg specimens. The majority of hatch- lings develop functional testisacs when they reach 170 mg and functional ovisacs when they reach 250 mg. Oocytes proliferate only after the formation of stage 5–6 spermatozoa. Thus, N. obscura is a sequential cosexual hermaphrodite with spermatogenesis and mature spermatozoa development commencing before oogenesis. During the second cycle of gametogenesis observed in larger animals, both mature spermatozoa and ova co-occur and N. obscura exhibits simultaneous hermaphroditism.     

Relative vulnerability of six freshwater gastropods to the leech Nephelopsis obscura (Verrill)

SUMMARY. 1. The vulnerability of six species of freshwater snails to the leech Nephelopsis obscura was determined in laboratory predation experiments.
2. Nephelopsis was unable to prey on prosobranch snails with an operculum, but did consume certain pulmonate species though predation rates were low, ranging from one to two snails per leech per night at 20°C. Apparently, Nephelopsis does not actively select prey, but merely consumes those species most easily handled.
3. Among pulmonates, leeches captured species in the following order: Physa gyrina (Say), Helisoma anceps (Menke). Lymnaea emarginata (Say) and Helisoma trivolvis (Say). Susceptibihty of size classes varied among snail species.
4. Neither environmental structure, such as cobble or macrophytes, nor gastropod escape behaviors, such as clamping to substrates or vertical migration away from bottom-feeding leeches, lowered capture rates by Nephelopsis.
5. In 2 years sampling, only one of seven lakes, however, had appreciable abundances of Nephelopsis. It is therefore suggested that the rarity, low feeding rates, and lack of strong gastropod preference limit the effect of Nephelopsis on field gastropod distributions.     

Fever in the leech,Nephelopsis obscura (Annelida)

Summary Leeches were placed in a 0.8 m linear temperature gradient from 0°C to 40°C. The temperature selected by the leeches was recorded over 30 min intervals; series of animals then received an injection of either pure sterile water,Escherichia coli endotoxin (LPS) at doses of 0.05, 0.25 and 10 g·g^–1, alcohol, or prostaglandin E₁ (PGE₁) at doses of 2 and 4 g·g^–1. After a latency of about 90 min, the leeches developed a dose-dependent fever in response to LPS. Maximal preferred temperature was near 29.6±1.4 whereas the control was 20.5±0.6°C. PGE₁ also evoked dose-dependent fevers of the same magnitude as LPS (30.0±1.0°C), but without latency. Another series of leeches received an injection of LPS of 10 g·g^–1 while in water containing 1.6 mg acetaminophen per 20 l water. Acetaminophen prevented the development of LPS fever. It is concluded that annelids respond to infection with a behavioral fever analogous to that of vertebrates.     

Chemosensory detection of prey by Nephelopsis obscura (Hirudinoidea: Erpobdellidae)

The chemosensory detection of prey by the freshwater leech Nephelopsis obscura (Erpobdellidae) was investigated in the laboratory. Without direct tactile contact N. obscura of all three size classes tested were unable to detect and react to any of the prey types (Gammarus lacustris, Chironomus sp., Tubifex sp) or prey conditions (live, asphyxiated, homogenate) tested. The length of the starvation period (0–56 days) did not affect these results, nor did it increase activity. N. obscura thus appears to be an opportunistic wanderer rather than a stalker-hunter.     

Effects of anoxia, hyperoxia, and salinity on neurons in the leech Nephelopsis obscura (Erpobdellidae): RNA redistribution by fluorescence histochemistry

The histochemical distribution of cytoplasmic RNA in ganglion cells of the freshwater leech Nephelopsis obscura has been studied using the fluorochrome acridine orange as a marker of nucleic acids. Two series of experiments, employing 50 adult animals, involved changes in oxygen tension in the water and changes in salinity. Normal leech neurons exhibit finely granular orange fluorescence uniformly distributed throughout the cytoplasm, with a perinuclear ring of especially strong fluorescence. After exposure to anoxic (0% O2), hypoxic (20% O2), or hyperoxic (200% O2) conditions at 20 degrees C for 1-15 days, the orange cytoplasmic fluorescence is no longer uniformly distributed; the redistribution is generally toward the periphery, leaving the perinuclear zone without RNA fluorescence, but irregular zones of cytoplasm devoid of RNA also occur not as a gradient. Leeches exposed to salinity of, or greater than, 2.5 ppt for 15 days exhibit similar changes. These alterations are confirmed by electron microscopy. Seasonal fluctuations in oxygen tension and salinity of lake water affect the distribution and abundance of organisms. The acridine orange method provides one measure of stress to the nervous system in freshwater invertebrates that might be applicable to ecological studies as well as to metabolic studies of individual animals.     

Inter-population genetic variation in the freshwater leech Nephelopsis obscura in relation to environmental heterogeneity

The temporal distribution of populations of aquatic macroinvertebrates have been extensively investigated in temperate arctic regions, but little information is available for alpine regions in North America. This paper describes phenology patterns of the aquatic macroinvertebrates of a high elevation wetland (3593 m) in the Green Lakes Valley, Colorado Front Range.Abundant taxa were Chironomidae (primarily Orthocladius and the limnephilid trichopteran Asynarchus curtus (Banks). Temperature patterns were related to the seasonal timing of life stages of most species. Phenology of most alpine aquatic macroinvertebrates appears to be controlled by seasonal climatic patterns, particularly temperature patterns. All chironomid species and Asynarchus curtus (Banks) had univoltine life cycles. Multi-year life cycles were not observed at this alpine site, although they have been observed at some arctic sites with colder temperature regimes than observed in this study.     

The effects of water temperature, ionic content and total dissolved solids on Nephelopsis obscura and Erpobdella punctata (Hirudinoidea, Erpobdellidae)

Using a three-way factorial experimental design the effects of water temperature, ionic content (water type) and total dissolved solids on the mortality rates of Nephelopsis obscura and Erpobdella punctata were examined. A strong interaction between temperature and water type and temperature and total dissolved solids was observed on the mortality of E. punctata . Other than differences in mortality due to reproductive condition, N. obscura showed uniformly low mortality not significantly affected by temperature, water type or total dissolved solids. Thus the numerical dominance shown by N. obscura in Alberta and Western Canada could be explained by the differentially higher mortality of E. punctata with respect to the three tested independent variables.     

The effect of a predatory leech,Nephelopsis obscura,on mortality,growth, and production of chironomid larvae in a small pond

Summary The effect of a predatory leech, Nephelopsis obscura, on survivorship, growth, and production of chronomid larvae was studied by enclosure experiments carried out in a small pond. The prey population was composed almost entirely of the tubiculous, microphagous chironomid larvae, Chironomus riparius and Glyptotendipes paripes. Nephelopsis significantly reduced chironomid survivorship within the enclosures, and accounted for most of the measured mortality of fourth instar larvae. The cropping by Nephelopsis was not significantly biased toward either prey species. In long-term experiments (66 d) chironomid biomass in enclosures without leeches reached much higher levels than in enclosures containing Nephelopsis. This increase in biomass was due to growth of surviving larvae, rather than recruitment, since emergence and oviposition were not going on during the course of the experiments. The enhanced survivorship of larvae within leech-free enclosures was eventually accompanied by reduced growth and specific production (daily production/biomass) for C. riparius, which made up about 90% of the larval population. Growth and specific production of G. paripes (10% of larval population) was not affected. Short-term experiments (25 d) involving manipulation of densities and species ratio (9:1 CR:GP and 1:9 CR:GP) of larvae revealed that growth of the majority species was strongly influenced by larval density, whereas growth of the minority species was not. The same pattern was observed both in the presence and in the absence of Nephelopsis and was a result of differences in resource utilization between the two species. In the shortterm experiments, growth rates estimated for larvae exposed to leeches were significantly less than those for larvae in leech-free enclosures. This could be due either to size-biased consumption of larvae by Nephelopsis, or possibly a disturbance factor leading to reduced larval food intake and/or increased metabolic costs.     

The effects of different oxygen regimes on the feeding and vertical distribution of Nephelopsis obscura (Hirudinoidea)

The feeding rates and vertical distribution of the freshwater leech Nephelopsis obscura, fed on different densities of third instar Chironomus riparius, were determined in the laboratory at three different constant dissolved oxygen regimes (10%, 100%, 300% saturation) at 15 °C. The rate of feeding increased linearly with prey density up to maximal field prey densities, with no satiation response. Analysis of covariance showed that the rate (slope) at which prey were consumed was not significantly different among oxygen regimes but the amount eaten at any given prey density was higher in higher dissolved oxygen saturations. Analysis of the vertical distribution of N. obscura at different oxygen saturations and prey densities showed a higher proportion of N. obscura on or in the mud substrate compared to the water column at 100% and 300%. No correlation was found between prey density and the vertical distribution of N. obscura, but the numbers of prey eaten were correlated with the proportion of N. obscura on the mud substrate. These results indicate that higher percentage dissolved oxygen regimes increase the feeding of N. obscura and are of potential importance in explaining the seasonal depth distribution and microdistribution patterns recorded for N. obscura.     

A cave leech (Hirudinea, Erpobdellidae) from Croatia with unique morphological features

Croatobranchus mestrovi is a troglobitic leech from deep shaft-like caves in the Velebit Mountain, Dinaric karst, Croatia, living in cold (4–6 °C) water. Its oral sucker extends to form four pairs of triangular tentacles, each with about five finger-like papillae, but widening into a marginally crenulated disc when attached to a substrate. Pairs of stiff, finger-like lateral projections, probably gills, occur along the body behind the clitellum. Somites are simple five-annulate. Despite the unique head morphology and the presence of lateral outgrowths, the anatomy and 18S rRNA gene sequence of this species indicate that it is a member of the Erpobdellidae, closely related to Dina .     

Reproductive biology of the indian freshwater leech,Poecilobdella viridis (Blanchard)

Annual reproductive cycle of the protandrous hermaphroditic freshwater leech, Poecilobdella viridis has been traced from August 1974 to July 1975. Spermatogenesis initiated a little earlier than oogenesis. The reproductive programme is as follows; commencement of spermatogenesis in February followed by oogenesis in March. Breeding begins in late March extending upto late May and early June while breeding terminated towards late June. From August to January reproductive quiescence was observed. Among the environmental factors temperature, possibly coupled with photoperiod, plays a key role in synchronising the reproductive cycle.     

Underwater predatory behaviour of the American mink (Mustela vison)

Fishing behaviour of the American mink ( Mustela vison Schreber) was investigated in the laboratory. Data were recorded using ciné film and tape recorded commentaries. Three species of prey were presented to mink, namely, carp ( Cyprinus curpio ), goldfish ( Carassius auratus ) and minnows ( Phoxinus phoxinus ).
It was found to be necessary to train ranch-bred mink to enter water and catch fish; young mink appeared to be easier to train than adults. Mink spent 5–20 sec under water when fishing; prey had usually previously been located from an aerial vantage point. Predatory behaviour was highly organized sequentially whereas fish were more prone to indulge in unpredictable stratagems; the behaviour of mink and fish were highly correlated.
The mink's efficiency in catching fish was related to prey size (smaller individuals being more vulnerable to capture) and shoaling. Minnows, which form highly organized shoals, were less easily caught when present in large numbers; this was not true of a loosely shoaling species, the carp.
Of the three species of prey presented, vulnerability to capture took the form goldfish> carp> minnow; these differences, however, may have been influenced by the fish's previous experience of underwater predators.     

Egg-feeding in the freshwater piscicolid leech Cystobranchus virginicus (Annelida, Hirudinea)

Abstract. Leeches are common terrestrial and aquatic annelids, parasitizing or feeding on a wide range of host taxa. Here we report evidence for an unusual feeding behavior of egg‐feeding in the piscicolid leech Cystobranchus virginicus. We identified distended specimens of C. virginicus in the nests of at least 4 different fish species: Campostoma anomalum, Moxostoma carinatum, Moxostoma sp. (either M. anisurum and/or M. breviceps), and Nocomis leptocephalus. We collected a total of 41 leeches from the nests of these host species and documented at least 1 leech in 19 of 55 nests (35%), with many sites containing multiple leeches. Individuals of C. virginicus were not identified feeding on any of the 41 adult specimens of Moxostoma spp. or the 635 adult specimens of Nocomis leptocephalus examined, and were never found in the absence of active host spawning (26 sites). These results are consistent with individuals of C. virginicus being an opportunistic or possibly even an obligate egg‐feeder, potentially timing their own reproductive activities with the spawning of their fish hosts. The current distribution of C. virginicus has been expanded to include North Carolina, South Carolina, and Tennessee. The potential for leech species to induce mortality in developing fish eggs could be a concern for fish conservation and merits further investigation.     

Effects of strobe lights on the behaviour of freshwater fishes

When dealing with invasive fishes, permanent barriers may be best in preventing spread; however, they may not be feasible due to various costs and/or logistical constraints. Alternatively, various non-permanent barriers using electricity, light, sound, pressure, bubbles, and CO₂ are being developed and deployed in efforts to limit the spread of aquatic invasive species or to achieve fish guidance and conservation. However, the effectiveness of these barriers is quite variable, and testing is often lacking for both target and non-target species. We conducted a series of laboratory trials to examine the effects of strobe light on behaviour of Common Carp, Brown Bullhead, and Largemouth Bass. In response to strobe lights, Common Carp and Brown Bullhead stayed significantly farther away compared to the control period and resumed their normal activity once the strobe light was turned off. This suggests that strobe lights may prove to be a useful fish deterrent in the field. Our results also highlight the importance of examining the response of both target and non-target species when evaluating fish deterrent technologies.     

Molecular re-assessment of some phylogenetic,taxonomic and biogeographic relationships between the leech genera Dina and Trocheta (Hirudinea: Erpobdellidae)

The three most abundant and species-rich genera of erpobdellid leeches – Erpobdella, Dina and Trocheta – have traditionally been distinguished by their annulation pattern. Erpobdella has five unsubdivided annuli per somite, in Dina the last annulus is widened and subdivided once, and in Trocheta, the last and often also the first annulus is further subdivided. The last two genera are often referred to as the subfamily Trochetinae. The presented molecular phylogenetic analysis, based on mitochondrial 12S rDNA sequences and nuclear ITS2 sequences, has revealed a sister relationship between Trocheta and Erpobdella rather than between Trocheta and Dina. Furthermore, the annulation pattern has proved to be inappropriate for the diagnosis of Dina and Trocheta. The taxon Trocheta bykowskii krasensehas been classified on the basis of its Trocheta-like annulation; however, according to the molecular phylogeny, it belongs to the Dina clade. A pair of diagnostic PCR primers were developed to identify unambiguously individuals with intermediate annulation. In summary, (1) the traditional genus diagnosis of Dina and Trocheta is no longer tenable, and the genera are not always morphologically distinguishable by traditional characters; (2) T. b. krasense Sket, 1968, should be re-classified as Dina krasensis; (3) the subfamily Trochetinae should be annulled because it does not represent a monophyletic assemblage.     

Effects of some extrinsic factors on the respiratory metabolism of the freshwater leech,poecilobdella viridis (blanchard): desiccation and temperature

The influence of desiccation and temperature on the respiratory metabolism of P. viridis have been investigated. There was a significant (p < 0.05) downfall in the respiratory rates as the period of desiccation increased, but for after 18 hours where it was enhanced significantly. The respiration augmented significantly (p < 0.03) when the temperature of the medium increased. Q₁₀ was significantly high at 32–28°C and was low between 35 and 32°C and 20–10°C Functional significance of these changes to the leeches in combating environmental hazards is briefly discussed.     

Effect of thermal acclimation on gametogenesis of the indian freshwater leech,Poecilobdella Viridis (Blanchard)

The effect of thermal acclimation for 15 days on the gametogenesis of Poecilobdella viridis was studied. Leeches conditioned at laboratory temperature (25.5°–27.5°C), when warm acclimated (32.0° ± 0.5° C), displayed a significant (p < 0.05) increase in the percentage of oocytes having a diameter of 12.5 µ and 15.0 µ and in the percentage of fully mature sperm clusters over the controls, whereas cold acclimation (10.0° ± 0.5°C) did not induce significant (p > 0.05) changes in the oocytes and sperm clusters. Thus it is concluded that in P. viridis temperature is of paramount importance in initiating gametogenesis.     

Some aspects of osmotic biology of the freshwater leech,Poecilobdella viridis (Blanchard)

Ability of the freshwater leech, Poecilobdella viridis to withstand osmotic changes was investigated by following the fluctuations of the body weight in tap-water and in different salt concentrations. The salinity tolerance limit (lethal salt concentration) of this leech was found to be 1.54% NaCl which equilibrates approximately 51.359% sea-water. There was a significant weight loss in P. viridis when kept in both, hypo- and hypertonic media. It is concluded that volume regulation (through weight changes) was slight in hypotonic media whereas in hypertonic media there was an incessant decline in body weight. Adaptive significance of these findings is discussed.     

A redescription of Nosema herpobdellae (Microspora: Nosematidae), a parasite of the leech Erpobdella octoculata (Hirudinea: Erpobdellidae)

Nosema herpobdellae was recorded in populations of the leech Erpobdella octoculata from lakes in northwest England and North Wales and is redescribed using light and transmission electron microscopy. It differes from N. glossiphoniae in the nature of the infection and tissues parasitized and from N. tractabile in its larger spore size, longer polar filament, in the angle of the anterior coils of the polar filament to the spore long axis, and apparently in its developmental cycle. The infection was found in a massive xenoma, in the connective tissue surrounding the gut, which was presumed to be formed from a single hypertrophied cell. Its developmental cycle included merogony and sporogony.