Island formation drove penguin evolution

Most penguin species orginated within the last 2 million years.

Penguins did not just waddle into existence. This iconic group of birds has a fossil record that extends back to as far as 60 million years, suggesting a rich evolutionary history. But when did the majority of living pengiun species – the so-called crown group – originate? A study from 2006 suggested that global cooling drove penguins out of Antarctica during the Eocene (56 to 34 million years ago). As Antarctica became covered with ice, the penguins expanded outwards and colonized several oceanic islands. A recent study in the journal Molecular Biology and Evolution questions this timeframe, living penguin species might be considerably younger.

 

Mitogenomes

Theresa Cole and her colleagues sequenced the entire mitochondrial genome of all extant penguin species and several recently extinct groups. Molecular clock analyses revealed that the penguin crown group originated during the Miocene (23 to 5 million years ago), which is earlier than previous estimated. Moreover, most penguin species arose during the past 2 million years.

Penguin phylogeny

The evolutionary history of penguins. The crown group originated during the Miocene while most extant species came to the scene within the last 2 million years. From: Cole et al. (2019) Molecular Biology and Evolution

 

Rockhoppers

An interesting observation is that penguin species on islands are consistently younger than the islands they inhabit. This led the researchers to propose that penguin speciation is tightly linked with island formation. For example, the divergence between Moseley’s Rockhopper Penguin (Eudyptes moseleyi) and two other Rockhopper species – E. chrysocome and E. filholi – dates back to between 2.7 and 1.2 million years ago. The island on which this species lives, Gough Island, emerged around 2.5 million years ago.

This scenario of island colonization is in line with the 2006 study in which the authors stated that “as Antarctica became ice-encrusted, modern penguins expanded via the circumpolar current to oceanic islands within the Antarctic Convergence, and later to the southern continents.” The timeframe, however, is a bit different.

Northern_Rockhopper_Penguin_on_Inaccessible_Island_(portrait)

Northern Rockhopper Penguin on Inaccessible Island © Brian Gratwicke | Flickr

References

Baker, A.J., Pereira, S.L., Haddrath, O.P., & Edge, K.A. (2005). Multiple gene evidence for expansion of extant penguins out of Antarctica due to global cooling. Proceedings of the Royal Society B: Biological Sciences, 273(1582):11-17.

Cole, T.L., Ksepka, D.T., Mitchell, K.J., Tennyson, A.J.D., Thomas, D.B., Pan, H., Zhang, G., Rawlence, N.J., Wood, J.R., Bover, P., Bouzat, J.L., Cooper, A., Fiddaman, S.R., Hart, T., Miller, G., Ryan, P.G., Shepherd, L.D., Wilmshurst, J.M. & Waters, J.M. (2019) Mitogenomes uncover extinct penguin taxa and reveal island formation as a key driver of speciation. Molecular Biology and Evolution, 36(4):784–797.

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