23 December 2009

Papa pipefish - not so motherly after all

Like seahorses, in pipefishes it is the papa that looks after the eggs. The typical papa pipefish holds his eggs in a kind of pouch on his belly, where blood vessels nourish the eggs until they hatch into miniature pipefishies. Alligator pipefish (Syngnathoides biaculeatus)The Alligator pipefish (Syngnathoides biaculeatus) is sometimes seen among our seagrasses. Here is a papa pipefish with eggs on his belly.

But a study of the broad-nosed pipefish (Syngnathus typhle) observed that some or all embryos tend to completely disappear while in Dad's care. The researchers expected some of the nutrients to end up in other embryos. Instead, the vanishing embryos' nutrients turned up inside the father!

"Pregnant" Fish Fathers Suck the Life From Their Young
Matt Kaplan, National Geographic News 21 Dec 09;
With the fathers taking on the responsibility of "gestating" their young, the story of pipefish reproduction is among the more heartwarming in biology.

Well, it was.

A new study shows that "pregnant" pipefish fathers actually suck the life out of some of their own offspring.

Pipefish are long, slender, upright-swimming seahorse cousins that tend to live in warm seas among sea grasses.

After conception, the female pipefish passes the hundred or so fertilized eggs to the male. Dad carries and—via specialized blood vessels—nourishes them in a small pouch until they emerge as fully functional baby pipefish.

So far, so good. But researchers studying broad-nosed pipefish recently noticed that some or all embryos tend to completely disappear while in Dad's care.

Study co-author Gry Sagebakken and colleagues thought the developing embryos were probably taking nutrients from one another somehow.

On the other hand, "we suspected paternal nutrient uptake was an option, but it was not our first guess," Sagebakken, a doctoral student in animal ecology at Sweden's University of Gothenburg, told National Geographic News.

To solve the mystery, the team placed radioactive markers on nutrients in the eggs before they were transferred to the father.

The researchers expected some of the nutrients to end up in other embryos. Instead, the vanishing embryos' nutrients turned up inside the father.

The father, it seems, uses his pouches' blood vessels not only to supply nutrients but also to siphon them away—and not to redistribute them to the neediest embryos either, because none of the traveling nutrients ended up in a sibling.

Sagebakken suspects that when fathers themselves aren't getting enough food to nourish all their young, the fathers sacrifice a few embryos so that the rest might live.

She's planning a follow-up study to see whether malnourished pipefish fathers drain more nutrients from their offspring. The answer should determine whether the fathers are just breaking a few eggs to make omelettes—or whether they're the ocean's answer to vampires.

Findings published on November 25 in the journal Proceedings of the Royal Society B.

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