Hidden biodiversity in gentoo penguins

Blog written by Josh Tyler. Read the full paper here. Featured photo by Gemma Clucas.

How many species of bird are there? Depending on who you ask, that number can range from 9,000 to 20,000, which is usually down to which definition of species you use. Often when a new species of bird is discovered, it represents an organism that has not been found before, be it from the depths of forests, the peaks of mountains or the coast of a remote island. These animals will look, sound and potentially behave differently from other species and be geographically separate, making the designation of a new species very straightforward. Sometimes however, a species could be hiding in plain view, in museum drawers or out in the field. We call these cryptic species, which refer to taxa that cannot be readily identified or differentiated using physical characters but can be discerned using genetic and/or ecological evidence. Finding these new species requires looking back at existing species and investigating whether they are harbouring hidden biodiversity.

Given their large geographic range and already noted genetic and morphological differences, gentoo penguins were strong candidates for harbouring hidden species-level biodiversity. The gentoo penguin (Pygoscelis papua) is the largest of the three Pygoscelis species (the others being the chinstrap and Adélie) and identifiable by its charismatic, red-toned bill, black head, and two contrasting white patches on the face. With a circumpolar range covering the Antarctic Peninsula to the Sub-Antarctic Islands (e.g. Crozet, South Georgia, Falklands etc), gentoo penguins live in a diverse set of environmental conditions. Populations across this range are experiencing the varied effects of changing climatic conditions. Uncovering hidden species is particularly important for organisms like this that may be at risk now or in future, because only recognised species (not populations) are typically considered in conservation assessments and have measures brought in to protect them. Whilst many populations of gentoos are increasing in size, this is not a universal trend and if there is hidden biodiversity within the species then these unique populations will not be protected under the current measures.

Although studies in the past have looked at the genetic variation in gentoo penguins, none have used an integrative taxonomic framework combining contemporary multivariate morphological analyses with genomic data. We therefore aimed to test whether the four genetic lineages of gentoo penguins described in Clucas et al. 2018 (Kerguelen, Falklands, South Georgia, South Shetlands/Western Antarctic Peninsula, see map) are also morphologically distinct, and therefore warrant recognition as distinct species.

We applied a range of analytical techniques to genetic samples taken from the field and morphological data collected from museum specimens in London and New York to tease apart any variation that might exist between the different gentoo populations. The genetic results seen in the phylogeny below highlight how members of each population are more closely related to each other than they are to any member of a different population.

We measured the skulls, bills, flippers, and legs of museum specimens and compared these among populations to see if there are physical differences. We found that there is a significant size difference between members of each population with those living on the Antarctic Peninsula being smallest and those on the Falkland Islands being the largest. Interestingly, and in keeping with the ideas of cryptic species, there are no plumage differences between the different lineages, all keeping the monochrome feathers and bright red bill.

All this evidence combined with habitat and diet data points to clear species-level variation within gentoo penguins and we therefore recommend the recognition of four different species: P. papua for the Falklands lineage, P.ellsworthi for the gentoos on the South Shetlands and Western Antarctic Peninsula, P. taeniata for the Kerguelen gentoos and finally P. poncetii, named after Sally Poncet, whose body of work has significantly influenced the field of polar biology, particularly in relation to South Georgia where this new species can be found.

The most fascinating aspect of this result is that the gentoo penguin was originally described in 1781 by J.R. Forster and nearly 240 years later, using tools from across ecology and evolution, we have found that the gentoo is in fact four species. Given that there are currently 18 recognised species of penguin, these new gentoos represent a 15% increase in species number for the penguin family.

Ultimately, this discovery of new species is bittersweet. Whilst the overall population of gentoos is increasing, that population is now split between 4 species, meaning that some or all may require increased conservation efforts. The species are now far more geographically isolated than previously considered and experiencing different levels of success due to warming and decreasing ice. A reassessment by the IUCN Red List of all four species in the coming years will help ensure all four species are protected.

The discovery of new species is one of the most exciting parts of biology. This study shows that through the application of genetic, morphological, and ecological data, we can find new diversity in the most surprising of places, including in very well-known fauna like penguins.

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