The Feeding Strategies of the Leech Erpobdella octoculata (L.): A Laboratory Study

Abstract

The feeding behaviour of the freshwater leech Erpobdella octoculata was analysed by exposing potential invertebrate and vertebrate prey organisms (alive, wounded or dead) to leech attack in dishes, in the laboratory. The fact that E. octoculata is a macrophagous feeder that swallows living prey organisms whole (preferentially Chironomus larvae) is documented. However, it was repeatedly observed that adult leeches sucked the body fluids from wounded larvae. Likewise, cut pieces of earthworms, dead crustaceans and crushed water snails were attacked and the soft parts sucked in with the aid of the unarmed pharynx. Adult leeches sucked the body fluids from dead, decaying bodies of vertebrates (fish, newt larvae). Newly hatched young are blood suckers that rapidly attacked the wounded regions of Chironomus larvae and other invertebrates such as crushed water snails. It is concluded that the common leech E. octoculata is not only a predator, but also a fluid sucker and a scavenger. The ecological implications of this finding are discussed. IntroductionIn running waters throughout Europe, Erpobdella octoculata is one of the most common freshwater leeches (ELLIOTT and MANN, 1979;NEUBERT and NESEMANN, 1999). In streams that are polluted to some extent by organic substances, this species may occur in very high population densities (up to 900 individuals/m 2 ; SCHÖNBORN, 1985). This is largely due to the fact that the leeches feed extensively on oligochaetes such as Tubifex and on Chironomus larvae (ELLIOTT, 1973;TOMAN and DALL, 1997). In general, E. octoculata has been classified as a macrophagous, carnivorous predator that swallows its invertebrate prey organisms whole with the aid of an unarmed, musculous pharynx (HERTER, 1968;SAWYER, 1986; KUT-SCHERA and WIRTZ, 2001).Several quantitative analyses of the gut contents in natural E. octoculata-populations have been published (e.g., ELLIOTT, 1973; DALL, 1983;SCHÖNBORN, 1985;TOMAN and DALL, 1997). These studies led to the conclusion that, in its corresponding habitat, E. octoculata feeds predominantly on chironomid larvae (up to 80% of diet), followed by oligochaeta and other small invertebrates. Laboratory experiments on the food consumed by individual adult leeches that were kept in dishes corroborated and extended these results (YOUNG and IRON-MONGER, 1979;1980). However, corresponding studies with juvenile leeches (1-3 days after hatching) were not carried out. In spite of the importance of E. octoculata in aquatic ecosystems only one detailed study on the feeding behaviour of this species has been published (GREENE, 1974). This investigator used mature individuals of E. octoculata; he observed (and counted) the kinds and numbers of prey consumed, the influence of substrate on feeding efficiency and the effects of temperature on these processes. Only two kinds of prey

Sex-Gender-Conflicts in Aquatic Hermaphrodites: are Genes Immortal?

“…40 years of studies on populations of freshwater leeches ( Figures 1-3), it is illustrated here that the "Dawkinsian" interpretations [A] and [B] can be verified. This unequivocal conclusion rests on numerous observations and experiments [6,[11][12][13][14][15]. However, the idea [C], proposing selfish DNA-sequences, is more controversial.…”

“…Using its pharynx, the leech sucks off the proteinaceous fluid from the emerging cocoon of the reproducing conspecific, inclusive of the enclosed eggs. Hence, intra-specific destruction and feeding on the cocoons of competing individuals is a well-documented phenomenon [11][12][13][14][15]. individuals attach to each other and implant a canula-like male copulatory organ, the pseudospermatophore (Psp.)…”

“…and therefore are always in search of food (insect larvae, small annelids etc. are rapidly sucked off with the aid of the musculous pharynx) [13][14][15]. Hence, whenever they detect a fresh cocoon of a reproducing individual, they "interpret" this proteinaceous, soft material as prey, so that the term "intraspecific cocoon cannibalism" is appropriate [6].…”

“…This finding indicates that this drastic form of intraspecific competition has a genetic basis. It should be noted that in other populations of E. octoculata (and related species) the intensity of intraspecific cocoon cannibalism was not so severe as that described for the "Freiburg-leeches" [11][12][13][14][15].…”

The Golden Gate Leech Helobdella californica (Hirudinea: Glossiphoniidae): Occurrence and DNA‐Based Taxonomy of a Species Restricted to San Francisco

“…), Tubifex worms, or crustaceans (Gammarus sp.) as described by KUTSCHERA (2003). For microscopical examination and documentation, adult leeches were fixed in their original position in 70% ethanol.…”