Pygmy Seahorses as Masters of Camouflage – Deep Look – PBS/KQED (2015)

Environmental cues can have profound effects on the developmental trajectory of juveniles. When predatory dragonfly nymphs are present, tadpoles develop bigger tails with fast twitch muscles. Similarly the crustacean water fleas (Daphnia) develop helmet structures preventing fish to swallow them easily. Epigenetics is a relatively new branch of genetics but we have learned quite a lot in a few decades. The molecular mechanism of what evolutionary biologists described as phenotypic plasticity – biological ability to generate multiple phenotypes from a single genome – is now largely explained by epigenetics.

Here seahorses display an amazing form of epigenetic transformation operating at later stages in development (similar to tadpoles and Daphnia examples) after the fish have hatched out of the brood pouch of their fathers. Juvenile fish undergo a radical re-programming that enables matching to the background coral habitat. The environmental cues guide the transformation through a molecular mechanism we do not yet know how. Species such as the seahorses with fascinating natural history provide rich source of information including male pregnancy.

Seahorse genome was sequenced in 2016.

One may assume that much of what we know about epigenetics comes from well-studied model organisms such as Humans. However long before genetic studies on animals, plants provided some of the best opportunities. Gregor Mendel’s landmark work on garden peas laid the foundations of genetics. Barbara McClintock’s seminal work on corn demonstrated a significant layer of epigenetics and lead to a Nobel Prize in Medicine in 1983. Plants continue to be fascinating systems for epigenetics

Now we know that genomes are not static but highly responsive to environmental influences. For instance the historical Dutch Famine experience have shown that pregnancies during that severe times lead to small babies. Babies of the famine generation also continued to be small. For a small fraction of genes in mammals it is extremely important that one copy of the gene inherited from parents is silenced. This is known as genomic imprinting and there are about 50 such genes in Humans. The maternal copy of the Growth Factor Receptor-bound Protein 10 (GRB10) is active in fetal and placental tissues while the paternal copy is found to be active in central nervous system and brain in Mice and Humans. GRB10 is a curious case study for testing various hypotheses on imprinting.

DEEP LOOK is an award-winning PBS program produced by KQED.