Many marine organisms release their gametes into the water and let the currents bring them together. Although this seems like a wasteful practice, it obviously offers advantages over presumably more costly mechanisms, especially in sessile organisms, that would be necessary to bring the males and females together. Likewise, many terrestrial plants rely on winds or insects for the transport of their pollen from the male to the female parts.
A recent report in Science1 presents evidence indicating that mosses may also have evolved at least a partial dependency on microarthropods, including springtails and mites, for the transport of sperm from the male to the female structures when there is no connecting water film in which the sperm would otherwise swim.
Cronberg et al. showed that in the laboratory female mosses separated from male mosses by 2 cm and 4 cm would be fertilized only when there were springtails and mites present.
Sporophyte production in female moss patches in presence versus absence of springtails or mites. Figure from Cronberg et al.1
Now it is necessary to demonstrate that this phenomenon also takes place in the wild.
Is there a case in which the reproduction of one animal species depends on the transport of its gametes by another animal species?
1. Nils Cronberg, Rayna Natcheva, and Katarina Hedlund. Microarthropods Mediate Sperm Transfer in Mosses. Science 313:1255 (2006). Abstract