Welcome! I'm an evolutionary biologist at the University of Oulu in Finland. My research is focused on testing predictions from inclusive fitness theory about the evolution of cooperation. My model systems are cooperatively breeding birds and ants, which I study using phylogenetic comparative methods, meta-analysis, and experiments. Scroll down to find out more.
GitHub: https://github.com/pipdowning
GitHub: https://github.com/pipdowning
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Ecology and Life History Predict Avian Nest Success in the Global Tropics
Zachariah F Smart, Philip A. Downing, Suzanne H Austin, Harold F Greeney, Gustavo A. Londoño , Mominul I. Nahid, Douglas W Robinson, and Christina Riehl When birds nest, a lot can go wrong. The whole brood might be eaten, and / or one or both parents. Things are thought to be especially bad in fragmented forests, where high nest predation plays a major role in the disappearance of some bird populations. But is this globally true? The available data is strongly biased towards the temperate world. To find out, we assembled 50 years of data from the global tropics. Surprisingly, neither forest fragmentation nor disturbance reduced nest survival. Our results suggest that nest predation alone cannot explain declines in avian biodiversity in tropical forest fragments, raising questions about the drivers of extinction in the tropics. [Top image: some fictitious tropical birds. Bottom image: Fig 4a from the paper]. Read the paper and get the data and code here: www.pnas.org/doi/abs/10.1073/pnas.2402652121https://www.pnas.org/doi/abs/10.1073/pnas.2402652121 |
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Altruism and Natural Selection in a Variable Environment
Miguel dos Santos, Philip A. Downing, Ashleigh S. Griffin, Charlie K. Cornwallis and Stuart A. West (2024) Evolutionary theory predicts that natural selection usually favours strategies that lower the variance in reproductive success in unpredictable environments. As environmental variability is often linked to sociality, recent theory suggested that selection can favour helping behaviours that lower the reproductive variance of relatives. We show that decreasing the reproductive variance of relatives can either favour or disfavour helping and examine reproductive success in 15 species of cooperatively breeding birds. [Top image: inequality 1 from the paper. Bottom image: Figure 3a]. Read the paper here: www.pnas.org/doi/abs/10.1073/pnas.2402974121 Data / R code here: osf.io/8mc3n/ Steven Frank commentary here: www.pnas.org/doi/abs/10.1073/pnas.2417410121 |
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Michener's Group-size Paradox in Cooperatively Breeding Birds
Philip A. Downing (2024) About 250 of the 10000 bird species on our planet raise their young in cooperative groups. These groups typically consist of a breeding pair and their mature offspring who stay at home and help raise their younger siblings. Although groups in these species can be large, up to 15 individuals, the most common group size in nature is just three. And herein lies a mystery. Surely, bigger is better when it comes to group size, because there are more individuals to take care of the young. So why are most groups tiny? Well, according to evolutionary theory, groups should be small. This is due to the law of diminishing returns: as groups get larger, the benefit of each extra group member becomes smaller. This makes it better to go at it alone than to stay in a big group where your help won't count for much. I investigated if this was the case using published data on the number of offspring produced by different sized groups across 26 cooperative birds. [Top image: the paper's graphical abstract Bottom image: Figure 2]. Read the paper here: academic.oup.com/jeb/article/37/3/353/7575391?login=false Data / R code here: via the link above |
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Genetic Sex Determination, Sex Chromosome Size and Sex-specific Lifespans Across Tetrapods
Zahida Sultanova, Philip A. Downing and Pau Carazo (2023) The Y chromosome is the laughing stock of the human genome. Compared with other chromosomes it’s tiny, and contains just a handful of genes. But is being small really so bad? Our research suggests not. Making use of the fact that different mammal species have different sized Y chromosomes, we found that males from species with relatively big Y chromosomes have shorter lifespans than females. In contrast, mammal species with small Y chromosomes have less extreme sex differences in lifespan. This suggests that there is something about big Y chromosomes that is particularly toxic for males. Figuring out exactly what is causing these toxic Y effects will take more work, but one thing is clear: less is more when it comes to Y chromosomes. [Top image: a toxic Y chromosome. Bottom image: Figure 2a]. Read the paper here: academic.oup.com/jeb/article/36/2/480/7326098 Data / R code here: doi.org/10.5061/dryad.hhmgqnkm3 |
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Hard-working Helpers Contribute to Long Breeder Lifespans in Cooperative Birds
Philip A. Downing, Ashleigh S. Griffin and Charlie K. Cornwallis (2021) Mother nature is a fierce guardian when it comes to the secrets of long life. The only general rule we know of is that having lots of offspring appears to limit lifespan. An exception to this rule are species that raise young in groups where a breeding pair are aided by non-breeding helpers. In these species, breeders live for decades and produce lots of young. How do they do this? While breeders produce the young in group-living species, they often don't take care of them. Parental care is largely provided by the non-reproductive group members. This means that breeders can avoid the energetic costs of reproduction, potentially allowing them to live longer. We compared the survival and workloads of breeders with and without helpers across 23 cooperatively breeding bird species to test this idea. [Top image: four of the species included in the study (Figure 1 from the paper). Bottom image: Figure 3a from the paper]. Read the paper here: royalsocietypublishing.org/doi/10.1098/rstb.2019.0742 Data / R code here: rs.figshare.com/collections/Supplementary_material_from_Hard-working_helpers_contribute_to_long_breeder_lifespans_in_cooperative_birds_/5300835 |
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The Benefits of Help in Cooperative Birds: Nonexistent or Difficult to Detect?
Philip A. Downing, Ashleigh S. Griffin and Charlie K. Cornwallis (2020) Live long and reproduce a lot. This is a good way of passing on genes to future generations. But in a variety of species, from hairy-faced hover wasps to grey-crowned babblers, some individuals give up their opportunity to reproduce and help raise the offspring of others. Why do this? Evolutionary theory has the answer: help when you can pass on more genes this way than by reproducing yourself. For this to work, your help must boost the reproductive success of individuals with whom you share genes. Only part of this solution has empirical support. Helpers are typically related to those they help, but they don’t always boost their reproductive success. We used phylogenetic meta-analysis across 19 cooperative bird species to make sense of the inconsistent evidence. [Top image: presenting at ESEB in Turku. Bottom image: Figure 1 from the paper]. Read the paper here: www.journals.uchicago.edu/doi/pdfplus/10.1086/708515 Data / R code here: datadryad.org/stash/dataset/doi:10.5061/dryad.gmsbcc2j3 |
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Group Formation and the Evolutionary Pathway to Complex Sociality in Birds
Philip A. Downing, Ashleigh S. Griffin and Charlie K. Cornwallis (2020) Lots of animal species raise young in cooperative groups. Familiar examples include things like ants and meerkats but weirder things like snapping shrimp and social spiders do it too. These species are remarkably diverse in terms of group complexity: some groups are small, others huge, some groups have just one pair of breeders, in others everyone reproduces and in some groups, individuals specialize in performing specific tasks. In this study, we used cooperatively breeding birds as a model system to test a key prediction from evolutionary theory about why some groups have evolved to be complex and others not. [Top image: the Alexander Library of Ornithology in Oxford, where I did the research for the paper. Bottom image: Figure 2 from the paper]. Read the paper here: www.nature.com/articles/s41559-020-1113-x Data / R code here: datadryad.org/stash/dataset/doi:10.5061/dryad.sn02v6x11 Blog post here: natureecoevocommunity.nature.com/users/358908-philip-downing/posts/60831-what-cooperative-birds-tell-us-about-the-evolution-of-complex-groups-starting-conditions-matter |
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Sex Differences in Helping Effort Reveal the Effect of Future Reproduction on Cooperative Behaviour in Birds
Philip A. Downing, Ashleigh S. Griffin and Charlie K. Cornwallis (2018) From honey bees to naked mole-rats, family living has a cost: most group members don’t reproduce. Part of this cost is offset by helping to raise siblings. This allows individuals to make an indirect genetic contribution to the future. This can't be the whole story though - female and male helpers often differ in how hard they work, despite being equally related to the young they are raising. One possibility is that individuals that stand to inherit the group (a fitness jackpot), help more. We tested this in cooperatively breeding birds by correlating how much each sex helps with their chance of inheriting the group. [Top image (@vicaloart): a group of grey-crowned babblers, one of the species included in our analysis. Bottom image: Figure 2 from the paper]. Read the paper here: royalsocietypublishing.org/doi/full/10.1098/rspb.2018.1164 Data / R code here: datadryad.org/stash/dataset/doi:10.5061/dryad.gp14p82 |
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How to Make a Sterile Helper
Philip A. Downing, Charlie K. Cornwallis and Ashleigh S. Griffin (2017) Animals that raise young in cooperative groups have some of the most wonderfully bizarre lifespans around. Queens of the slave-making ant can live for > 10 years while their worker daughters live for just three. Similarly, naked mole-rat breeders can live for > 17 years in the wild while helpers live for just four. Even more bizarre are the proximate mechanisms thought to underlie differences in lifespan between group members. Sexual activity seems to enhance the lifespans of breeders in both Ansell’s mole rat and Cardiocondyla obscurior ants. This paper provides an overview of what's known about lifespan evolution in group-living species, from ants and bees to cooperative birds and mammals. We suggest that differences in lifespan between breeders and workers, resulting in completely overlapping generations, is crucial for the evolution of sterile worker castes. If breeders live longer than workers, then workers have a life-long supply of full siblings they can raise. What causes lifespan differences between breeders and helpers? Reproductive division of labour seems vital here because it gives the unusual condition that members of the same group experience vastly different rates of extrinsic mortality. [Top image: Figure 3 from the paper, showing the difference in lifespan between breeders (hatched bars) and helpers (dotted bars) across 11 species. Bottom image: the paper's graphical abstract - we suggest that completely overlapping generations are required for the evolution of sterile helpers]. Read the paper here: onlinelibrary.wiley.com/doi/full/10.1002/bies.201600136 |
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Sex, Long Life and the Evolutionary Transition to Cooperative Breeding in Birds
Philip A. Downing, Charlie K. Cornwallis and Ashleigh S. Griffin (2015) Birds that raise their young in cooperative family groups appear to be super-long-lived. There are a couple of explanations for this association, which both fit with existing theory. Either long-life is a consequence of breeding in groups, which lowers mortality, or long-life drives the evolution of cooperative breeding by ensuring a long breeding tenure once a group is inherited. We reconstructed the origins of cooperative breeding and survival in birds to test between these. [Top image: our dream time machine. Bottom image: our actual time machine]. Read the paper here: royalsocietypublishing.org/doi/full/10.1098/rspb.2015.1663?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed Data / R code here: royalsocietypublishing.org/doi/suppl/10.1098/rspb.2015.1663 |
