The ciliate epibiont Epistylis pygmaeum: selection for zooplankton hosts, reproduction and effect on two rotifers

Abstract

SUMMARY 1. A clonal culture of the peritrich Epistylis pygmaeum was used for all observations and experiments. Motile cells preferentially attached to the eggs of three species of Brachionus but also attached to the body of adult B. angularis. Zooids on the transitory egg substratum developed only short stalks, while those on the body often developed long stalks and branched colonies. Selection for the eggs positions the ciliate near the cloaca, and thus high concentrations of fine particulate material excreted by the host. Settlement on eggs occurred equally well in the light and dark, and on moving and stationary eggs. 2. Motile Epistylis cells attached to a wide variety of rotifer and crustacean zooplankton, but exhibited some pronounced selectivity. They readily settled on the eggs of other rotifers (Epiphanes, Polyarthra), on the carapace of several cladocerans (Ceriodaphnia, Daphnia, Diaphanosoma), and on the egg sacs of a copepod (Tropocyclops). They settled less readily on the bodies of the rotifers Asplanchna and Synchaeta, and rarely or never settled on the rotifer Keratella, the cladocerans Bosmina and Scapholeberis, and the body of the copepod. 3. Epistylis populations initiated with a single zooid on Brachionus increased exponentially and often contained several hundred attached zooids and motile cells after 3 days at 20 °C. Observations of a culture initiated from a single telotroch provided new information about peritrich life cycles: (1) motile cells reproduced themselves at a rapid rate (λ = 4.26 day−1); (2) telotrochs produced or transformed into swimming zooids and vice versa. Functions of the two types of motile cells remain to be clarified. Telotrochs likely are specialised for finding and attaching to hosts. Swimming zooids can feed and reproduce, producing both their own cell type and telotrochs. Together, they should enhance dispersal and population growth, especially when hosts are rare. 4. Life‐table experiments with two species of Brachionus showed that colonisation by Epistylis had no effect on adult survival but significantly decreased fecundity, by 29% in both cases. Zooids attached to eggs could be a weight burden, increase drag, and possibly inhibit egg development. Those on the body of B. angularis also could interfere with coronal cilia, inhibiting feeding and further slowing locomotion. The ability of E. pygmaeum to select and then interfere with its hosts indicates that this epibiont has the potential to influence the species structure of zooplankton communities.

Cryptic speciation in the cosmopolitan Epiphanes senta complex (Monogononta, Rotifera) with the description of new species

“…This species was referred to as E. senta in previous publications (Schröder, 2001(Schröder, , 2003Gilbert & Schröder, 2003;Schröder & Gilbert, 2004;Schröder, 2005). …”

Attachment of the peritrich epibiont Zoothamnium intermedium Precht, 1935 (Ciliophora, Peritrichia) to artificial substrates in a natural environment

“…Studies emphasizing epibiont host specificity have pointed out that some peritrichs are able to attach to only one or two host species, failing to colonize non-living substrates (Clamp, 1973;Henebry and Ridgeway, 1979;Gilbert and Schröder, 2003). By contrast, some authors demonstrated that other epibionts are opportunistic, being able to attach to living or non-living substrates (Mayén-Estrada and Aladro-Lubel, 2000).…”

Growth of the peritrich epibiont Zoothamnium intermedium Precht, 1935 (Ciliophora, Peritrichia) estimated from laboratory experiments

“…The only other record of growth rates estimated in the laboratory for a peritrich epibiont is that of Gilbert and Schröder (2003), who observed colony development of Epistylis pygmaeum attached to Brachionus angularis. They reported an exponential increase in zooids and the colonies originated from a single attached zooid, but the actual growth rates were not calculated for the trophont stage.…”

“…They sampled colonies of Carchesium polypinum Linnaeus, 1758 and individuals of Vorticella microstoma Ehrenberg, 1830 attached to transparent plastic films and found growth rates of 1.37 and 1.01 per day for the two peritrichs respectively. Considering peritrichs as epibionts, only one study so far, performed by Gilbert and Schröder (2003) has dealt with growth rates of peritrichs attached to living substrates in the laboratory. The authors observed an exponential growth of colonies of Epistylis pygmaeum Ehrenberg, 1838, from a single zooid, attached to the rotifer Brachionus angularis (Gosse, 1851), but no actual growth or colonization rates were calculated for the trophont stage of this species.…”