Snails have a thing for sexy stems

by Angela Herring

In the marsh­lands of the south­east United States, the peri­winkle snail is among the most abun­dant grazing species. “You can look out at high tide and see them every­where, climbing up on the grasses,” said Ran­dall Hughes, assis­tant pro­fessor of marine and envi­ron­mental sci­ences at Northeastern’s Marine Sci­ence Center in Nahant, Mass.

According to Hughes, the peri­win­kles climb the marsh grasses for two rea­sons: food and safety. In terms of safety, the grasses’ height above the water gives the snails a place to escape their under­water preda­tors. For food, the snails nibble the grass itself as well as the fungi that grow in these grazing scars.

Peri­win­kles have been munching on marsh grasses for eons, Hughes explained, but recent droughts and high tem­per­a­tures, com­bined with lower num­bers of snail preda­tors, have increased the snails’ effect on the grasses’ sur­vival: “Occa­sion­ally,” she said, “you’ll see a whole area that’s com­pletely denuded.”

For this reason, researchers like Hughes have begun focusing on snails’ impact on marsh grasses. They’ve had a par­tic­ular interest in studying the veg­e­ta­tive form of the plants, which researchers have long believed to be more common than the sex­u­ally repro­duc­tive form. While the latter stems spread their genetic infor­ma­tion with flower seeds, veg­e­ta­tive stems do it by sending out under­ground rhi­zomes, or roots, which sprout new, genet­i­cally iden­tical ones.

In a paper recently pub­lished in the journal Marine Ecology Progress Series, Hughes and Robyn Zere­becki, a former grad­uate stu­dent in the Three Seas pro­gram, found an inter­esting pref­er­ence among the peri­win­kles: they seem to like hanging out on sex­u­ally repro­duc­tive grass stems more than veg­e­ta­tive stems.

Because it is gen­er­ally assumed that the dom­i­nant form of repro­duc­tion is veg­e­ta­tive, per­haps it doesn’t matter too much that the peri­win­kles prefer sex­u­ally repro­duc­tive stems.

But Hughes doesn’t agree with that assump­tion. “We’ve found there’s more genetic diver­sity in the marsh grasses than expected be if most repro­duc­tion is clonal,” Hughes explained. That means the sex­u­ally repro­ducing stems actu­ally play a rather impor­tant role in the community.

Hughes and Zere­becki decided to examine the snails’ impact on these stems. As it turns out, the answer is ‘min­imal.’ While pre­vious research has shown snails can destroy veg­e­ta­tive stems, the sex­u­ally repro­duc­tive ones seem to be tougher and less sus­cep­tible to the snails’ grazing.

Hughes noted that there’s vir­tu­ally no nutri­tional reason behind the snails’ pref­er­ence. So what is it about the flow­ering stems that makes them so desir­able? “They’ll climb the tallest, most rigid grasses avail­able,” she explained, adding that the veg­e­ta­tive stems tend to be shorter and more flex­ible than the flow­ering stems.

Regard­less of why they climb the repro­duc­tive grasses more, Hughes’ results point to a needed shift in the research com­mu­nity: “The atten­tion paid to the neg­a­tive effects of snails is all focused on one stage in the life­cycle,” she said. “But we can’t assume the same thing hap­pens across all stages.”

The results, in the midst of a growing wave of gloomy climate-​​related research, pro­vide a mod­icum of reas­sur­ance, said Hughes. “Even when we see obvious grazing on veg­e­ta­tive stems, this research sug­gests that sexual repro­duc­tion may pro­vide some resiliency for the marsh system to the neg­a­tive effects of snail grazing.”

Originally published in news@Northeastern on August 14, 2013

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Posted in Marine and Environmental Sciences

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