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Gene “archaeology” sheds light on male pregnancy

Dec. 4, 2006
Courtesy Michigan State University 
and World Science staff

A bit of “ge­netic ar­chae­o­lo­gy” may be il­lu­mi­nat­ing one of the fish world’s great mys­ter­ies, re­search­ers say: how did a fam­i­ly of fish come to em­brace male preg­nan­cy?

The sea­horse Hip­po­cam­pus erec­tus (cour­te­sy NOAA)

Research in the gulf pipe­fish hints that a gene orig­i­nal­ly busy with kid­ney and liv­er func­tions may have learn­ed new ones in the male womb, said April Har­lin-Cog­nato, a zo­ol­o­gist at Mich­i­gan State Uni­ver­si­ty in East Lan­s­ing, Mich.

“We’re in­ter­est­ed in the ev­o­lu­tion of nov­el­ty,” Har­lin-Cog­nato said. “We’re won­der­ing if it’s a mat­ter of old genes gain­ing new tricks.” 

Gulf pipe­fish are a mem­ber of the same fam­i­ly as sea­horses, which they in fact re­sem­ble, ex­cept for the curved tails. 

As with sea­horses, the male fish ac­cepts eggs from fema­les, fer­til­izes them and car­ries them in a pouch, a com­plex or­gan that nur­tures and pro­tects the eggs. One of its func­tions is to reg­u­late sa­line con­tent in the womb, ac­cord­ing to Har­lin-Cog­nato.

She and col­leagues found a new gene that makes a type of pro­tein mol­e­cule called an astac­in—one a fam­i­ly of pro­teins found in bony fish. 

The gene, which the re­search­ers dubbed pa­tristacin, ap­pears to sup­port the pouch, but this was­n’t its orig­i­nal job, she ar­gues. Mem­bers of her team sus­pect that pa­tristacin, pos­si­bly thou­sands of years ago, was in­volved in kid­ney and liv­er func­tion, and was lat­er drafted in­to a “moon­light­ing” gig sup­porting the then-newfangled male brood pouch. Pa­tristacin is found in the brood pouch of pipe­fish and sea­horses and in the kid­ney and liv­er of bony fish.

“We know the gene codes for a pro­tein in the brood pouch dur­ing male preg­nan­cy, but we don’t know yet what it is do­ing in the brood pouch. It’s a whole new ball of wax to un­der­stand how this gene func­tions in its new job,” Harlin-Cog­nato said.

The team’s study ap­pears in the Nov. 4 edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tion­al Acad­e­my of Sci­ences.

“The genes show you an­ces­try,” she said. “They show you the over­all fam­i­ly tree and can tell you when things took place dur­ing the ev­o­lu­tion of a new struc­ture. From this fam­i­ly tree we can make ed­u­cat­ed guesses about the struc­ture and func­tion of these pro­teins.”

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A bit of “genetic archaeology” may be illuminating one of the greatest gender bending mysteries in the fish world: How did a family of fish come to embrace male pregnancy? A new gene discovered in the gulf pipefish hints that an gene originally busy with kidney and liver function may have learned new tricks in the male womb, said April Harlin-Cognato, a zoologist at Michigan State University. “We’re interested in the evolution of novelty,” Harlin-Cognato said. Why is this the only group of fish that exhibits male pregnancy is one of the trickier questions of evolution ary biology, she added. “We’re wondering if it’s a matter of old genes gaining new tricks.” Gulf pipefish are a member of the same family as seahorses, which they in fact resemble, except for the curved tails. As with seahorses, the male fish accepts eggs from females, fertilizes them and carries them in a pouch, a complex organ that nurtures and protects the eggs. One of its functions is to regulate the saline content in the womb of these saltwater fish, according to Harlin-Cognato. She and colleagues found a new type of gene that makes a protein molecule called an astacin—one a family of proteins found in bony fish. The gene, which the researchers dubbed patristacin, appears to support the pouch, but this wasn’t its original job, she argues. Members of her team suspect that patristacin, possibly thousands of years ago, was involved in kidney and liver function, and was later drafted into a “moonlighting” gig supporting the then-newfangled male brood pouch. Patristacin is found in the brood pouch of pipefish and seahorses and in the kidney and liver of bony fish. “We think it was a new job for an old gene,” Cognato said. “We know the gene codes for a protein in the brood pouch during male pregnancy, but we don’t know yet what it is doing in the brood pouch. It’s a whole new ball of wax to understand how this gene functions in its new job,” Harlin-Cognato said. The team’s study appears in Monday’s edition of the research journal Proceedings of the National Academy of Sciences. “The genes show you ancestry,” she said. “They show you the overall family tree and can tell you when things took place during the evolution of a new structure. From this family tree we can make educated guesses about the structure and function of these proteins… It’s like doing genetic archaeo logy.”