Who’s your daddy? Male seahorses transport nutrients to embryos

Researchers have discovered male seahorses transport nutrients to their developing embryos in their brood pouch. The next step is to find out how they do this and if they have a placenta.

Seahorse mating “dance”

Male pot-bellied seahorses have bulging white pouches, which they pump full of seawater during courtship “dances”.

Pregnancy discovery

New research by Dr Camilla Whittington and her team at the University of Sydney has found male seahorses transport nutrients to their developing babies during pregnancy. This discovery provides an opportunity for further comparative evolutionary research.

Seahorses and their relatives are the only vertebrates that have male pregnancy. The expectant fathers incubate developing babies inside a pocket called a “brood pouch”. We know a male seahorse can have more than a thousand embryos in the pouch at once but until now, researchers had limited understanding of how the babies are fed.

“This work adds to the growing evidence that male pregnancy in seahorses could be as complex as female pregnancy in other animals, including ourselves,” said Dr Whittington, from the School of Life and Environmental Sciences. “We now know that seahorse dads can transport nutrients to the babies during pregnancy, and we think they do this via a placenta. It’s not exactly like a human placenta though – they don’t have an umbilical cord, for example. We need to do further histological work to confirm this.”

Photo of juvenile pot-bellied seahorses in the lab

Juvenile pot-bellied seahorses being reared in the lab. Photo: Camilla Whittington

Seahorses are emerging as important model species for understanding the evolution of live-bearing reproduction, said Dr Whittington.

“We can draw some parallels between seahorse pregnancy and human pregnancy,” she said. “Seahorse dads seem to do some of the same things that human mums do, including transporting nutrients and oxygen to developing embryos, and immune modulation to protect the babies from infection.”

photo of Dr Camilla Whittington and honours student Zoe Skalkos who led the research

Dr Camilla Whittington and honours student Zoe Skalkos who led the research.

The research published in Journal of Comparative Physiology B was led by University of Sydney Honours student Zoe Skalkos in collaboration with Dr James Van Dyke at La Trobe University.

The study builds on previous genetic evidence suggesting that male seahorses might transport nutrients to developing embryos. This new study confirms, in the first experimental evidence of ‘patrotrophy’ (nutrient transport from dad to babies). It also identified one of the classes of nutrients being transported: energy-rich fats.

“My team is using a range of techniques to investigate the biology of seahorse pregnancy,” Dr Whittington said. “We want to understand more about the seahorse pouch and the ways it protects and supports the baby seahorses.”

Honours student Zoe Skalkos, who led the research, said: “It’s really exciting because it’s a big step in understanding the relationship between dad and baby in male pregnancy.”

photo of male seahorses with big white bellies

Male pot-bellied seahorse with females. Male seahorses have a large brood pouch used to incubate developing embryos. During courtship rituals, they pump water into the brood pouch until it reaches enormous dimensions, before the female transfers eggs into the pouch. Photo: Jacquie Herbert

Key Points:

  • Seahorses and their relatives are the only vertebrates that have male pregnancy. Dads incubate developing babies inside a pocket called a “brood pouch”.
  • Male seahorses transport nutrients, including fats, to developing babies during pregnancy. The babies use these energy-rich fats for growth and development.
  • The new results raise the question of whether seahorse embryos can influence how much nutrition they can get from dad while they are in the brood pouch.

Declaration: This research was supported by the Australian Research Council and a University of Sydney SOAR Fellowship.

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