Dr Phil Cox and red squirrel anatomy news goes nuts in the media

Researchers from the UCL Centre of Integrative Anatomy, led by Dr Phil Cox, report that changes in skull & jaw shapes in beleaguered UK red squirrels (after the invasion of grey squirrels) were impacted by being fed peanuts - which has implications for future conservation efforts

The lab of UCL Centre for Integrative Anatomy's Dr Phil Cox has just had a paper published by The Royal Society about skull & lower jaw shape in UK red squirrels. It investigates differences in shape (morphology) between different UK red squirrel populations following the invasion of grey squirrels. Kim Chandler of Hull York Medical School & the University of York is lead author and one of Phil's PhD students orioginating from his time at York before moving to UCL.  The topic seems to have caught the public's imagination, with articles appearing in national newspapers, the scientific press generally, and via podcasts and radio station interviews, as well as the usual social media.  It's all gone - and is about - nuts!

The mechanical properties of dietary items are known to influence skull morphology, either through evolution or by phenotypic plasticity. Phil's research team investigated the impact of supplementary feeding of peanuts on the morphology of red squirrels (Sciurus vulgaris) from five populations in Britain (North Scotland, the (Scottish/English) Borders and Jersey (off the south coast), and two temporally distinct populations from Formby on Merseyside, England.

Stable isotope analysis confirmed dietary ecology in 58 squirrel specimens. Geometric morphometrics were used to analyse three-dimensional and two-dimensional shape variation across 113 crania (skulls) and 388 mandibles (jaws), respectively. Results obtained suggest a diet with an increased proportion of peanuts in the 1990s and 2010s Formby squirrels but the opposite in other populations.

The above figure shows mandibular shape variation along principal components (PC) by using colour maps representing areas of relative expansion and contraction.  Warped crania in (a–c) dorsoventral, (d–f) left lateral and (g–i) ventrolateral view showing areas of relative expansion (warm colours) and contraction (cool colours) when moving from the minimum to maximum values along (a,d) PC1, (b,e) PC2, and (c,f) PC3.

Significant differences in cranio-mandibular shape were found between all populations, with 1990s Formby red squirrels exhibiting a shape associated with reduced masticatory efficiency. This effect was partially reversed following a reduction in supplementary feeding of peanuts.

The researchers, who also include Eloy Gálvez-López from this Centre, and Stuart Black, Andrew C. Kitchener, Kat Hamill, Bethan Roberts and Sean Doherty from around the UK, propose that these morphological changes are related to the reduced mechanical effort needed to process peanuts, relative to naturally-occurring food items. This could be an example of diet-induced plastic changes to the skeleton in non-muroid wild mammals, ie rodents other than mice, rats, voles, hamsters, lemmings, gerbils, etc. However, further research is needed to check whether or not other driving factors, such as genetics, are at work here.

 

Incidentally, Phil and his co-researchers are not, as some media reports imply, suggesting that squirrels should not be fed peanuts, but rather that care should be taken when providing food for wild and captive animals, since the results from this work and the conclusions drawn from it have implications for conservation.  In other words, it would be wise to match any supplementary food to what the animals are most likely to find in the wild, in order to give them the best chance of survival.

More information: 

Kim E. Chandler et al, Morphological change in an isolated population of red squirrels (Sciurus vulgaris) in Britain, Royal Society Open Science (2025). DOI: 10.1098/rsos.240555

Dr Phil Cox's article Red squirrels fed on peanuts have weaker jaws – here’s why that matters for conservation, The Conversation, 15 January 2025

 

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