Lifetime reproductive output in a hermaphrodite cestode when reproducing alone or in pairs: a time cost of pairing

Abstract

Abstract. The cestode Schistocephalus solidus is a facultatively self-fertilising simultaneous hermaphrodite. Here we test for di erences in the starting point, the rate, and the magnitude of egg production between individuals allowed to reproduce alone (only self-fertilisation possible) or in pairs (both self-and cross-fertilisation possible). Speci®cally, we want to distinguish between alternative processes responsible for the lower egg production in paired individuals observed in an earlier study (Wedekind et al., 1998). We designed an improved in vitro system, replacing the bird ®nal host that allows us to measure, with high temporal resolution, the timing and magnitude of lifetime egg production of worms in these two social situations. We found that the experimental groups did not di er signi®cantly in the starting point of egg production. However, the temporal pattern in egg production di ered between them, in that paired individuals had a lower rate of egg production. This, however, did not lead to a signi®cant reduction in lifetime egg production, as pairs compensated for the lower rate by producing eggs longer than single individuals. We argue that the lower rate of egg production may nevertheless lead to a time cost of pairing in the study species, and that this cost is likely to represent a cost of outcrossing due to sexual selection.

Outcrossing Increases Infection Success and Competitive Ability: Experimental Evidence From a Hermaphrodite Parasite

“…However, we found no difference in egg size, in contrast to Wedekind et al (1998) and Schärer and Wedekind (1999) who found that worm pairs produced larger eggs than singles. We calculated the standardized effect size from the data given in Schärer and Wedekind (1999) and used this to estimate that we had a power of 79% to detect such an effect (Cohen 1988). Again, the discrepancy between our and the previous results might be a consequence of differences between the study populations (see above).…”

“…Such a difference in hatching rate is in accordance with results of earlier studies on Schistocephalus solidus Schärer and Wedekind 1999), which, in contrast to our results, could be due to a smaller size of selfed eggs (see below). The outcrossing advantage was even stronger in our study and overall hatching rate was more than twice as high.…”

“…Parasites were removed from the fish's body cavity aseptically (Smyth 1946) and allowed to reproduce in an in vitro system replacing the final host's gut ). They were transferred to one of 20 culture bottles either singly (n ϭ 10) or in pairs (n ϭ 10) and were allowed to reproduce for eight days, a period which comprises the entire reproductive output (Schärer and Wedekind 1999;S. Schjørring unpubl.…”

The role of prezygotic isolation mechanisms in the divergence of two parasite species

“…Both species use piscivorous birds as definitive hosts, where the adult worms reproduce sexually. These parasites are simultaneous hermaphrodites, mature rapidly and usually complete the reproduction within one week in the definitive host [38, 39]. The eggs are then released with the bird’s feces into the water, where they hatch into free-swimming larvae.…”

“…For this purpose, worms are placed into sealed net bags and incubated in a 40 °C warm culture medium (for details see [41]) in the dark for a time period of up to 8 days, where most of the egg production is accomplished [38, 39]. The eggs are then washed and stored in tap water at 4 °C before development is induced.…”