Discovered: Crustaceans help to fertilize seaweeds

A small marine isopod plays a role in fertilizing red seaweed, according to a new report that presents evidence of animal-mediated “pollination” in the marine environment – a fertilization strategy that was until recently considered to be exclusive to terrestrial plants. The findings in this seaweed – a type of algae, and thus only very distantly related to what are considered true plants – extend the scope of species that use animals as pollinators. According to Emma Lavaut and colleagues, they also suggest that animal-mediated fertilization strategies may have evolved many millions of years earlier than thought  – perhaps even earlier than terrestrial plants themselves – or, that animal-mediated fertilization strategies evolved independently and repeatedly in terrestrial and marine environments. “The study by Lavaut et al. has broadened both the variety and the history of animal-mediated male gamete transfer, taking the concept of pollination from plants to algae and potentially pushing it back to the earliest evolution of marine invertebrates,” write Jeff Ollerton and Zong-Xin Ren in a related Perspective. Insect pollination is the most common form of fertilization in terrestrial flowering plants. However, recent evidence has demonstrated that foraging marine invertebrates can carry and disperse grains of pollen from male to female seagrass plants, overturning a long-held belief that animal-mediated pollination was absent in marine environments. These findings have sparked a search for other examples of undersea pollination, particularly in red algae species where male gametes lack the ability to reach remote female reproductive organs themselves. Because of this, these plants have been thought to reproduce passively via water flows. Through a series of experiments, Lavaut et al. discovered that the isopod Idotea balhica, a creature commonly found living on and amongst the red algae Gracilaria gracilis, dramatically increases the plant’s fertilization success. The authors found that as the isopods forage along the strands of male G. gracilis, they pick up and carry the seaweed’s spermatia on their bodies and deliver them to female plants. What’s more, the authors provide evidence that suggests that the relationship between G. gracilis and I. balhica could be mutualistic. For the isopods, the seaweed provides shelter and food in the form of diatoms that attach to the surface of the plants, and in return, the plants gain increased growth rates and improved reproductive success.