SUBSCRIPTIONS In 2020 Phil. Trans. R. Soc. B (ISSN 0962-8436) will be published Continuing its long history of infl uential scientifi c publishing, Phil. Trans. R. Soc. B 26 times a year. For more details of publishes high quality theme issues on topics of current importance and general subscriptions and single issue sales interest within the life sciences, guest-edited by leading authorities and comprising please contact our fulfi lment agent: new research, reviews and opinions from prominent researchers. Each issue Turpin Distribution aims to create an original and authoritative synthesis, often bridging traditional The Royal Society Customer Services Pegasus Drive disciplines, which showcases current developments and provides a foundation for Stratton Business Park future research, applications and policy decisions. Biggleswade SG18 8TQ United Kingdom royalsocietypublishing.org/journal/rstb T +44 1767 604951 F +44 1767 601640 E [email protected] EDITOR Karen Lipkow Alternatively, please contact our customer John Pickett Karen Liu service team at: Satyajit Mayor E [email protected] SENIOR COMMISSIONING EDITOR Ewa Paluch Helen Eaton Ricard Solé PRICES FOR 2020 Roland Wedlich-Söldner PRODUCTION EDITOR Online Online Garrett Ziolek Neuroscience and cognition only and print Dora Biro EDITORIAL BOARD Anna Borghi £ UK/rest of World £2812 £3936 Organismal, environmental Nicole Creanza and evolutionary biology Patricia Pestana Garcez € Europe €3656 €5118 Julia Blanchard Anthony Isles $ US/Canada $5323 $7452 Patrick Butler Julie Morand-Ferron Roger Butlin Richard Morris Sebsebe Demissew Michael Petrides SUBMISSIONS Sonia Harmand Jenny Read For submission guidelines and access to Barbara Helm Anil Seth journal content visit: Nick Lane Joan Silk royalsocietypublishing.org/journal/rstb Cate Macinnis-Ng Mriganka Sur Nathalie Pettorelli Philosophical Transactions of the Royal Health and disease Naomi Pierce Society B: Biological Sciences Chetan Chitnis Zehao Shen ISSN: 0962-8436 Rodrigo Correa-Oliveira Stephen Simpson © The Royal Society, 2020 Michael Hochberg John Speakman Except as otherwise permitted under the Jonathan Hodgkin Xiangjiang Zhan Copyright, Designs and Patents Act, 1988, Peter Hudson this publication may only be reproduced, Cellular and developmental biology Gagandeep Kang stored or transmitted, in any form or by any Lionel Christiaen Joanne Lello other means, with the prior permission in Richard Dixon Katrina Lythgoe writing of the publisher, or in the case of Julian Dow C. Jessica Metcalf reprographic reproduction, in accordance Charlotte Förster Cliona O’Farrelly with the terms of a licence issued by the Andreas Hejnol Rebecca Sear Copyright Licensing Agency. In particular, Penny Jeggo Charles Wondji the Society permits the making of a single photocopy of an article from this issue (under Sections 29 and 38 of this Act) for an individual for the purposes of research or private study. Open access articles, which are published under a CC-BY licence, may be re-used without permission, but subject to acknowledgement.

Cover image The Hawaiian bobtail squid, Euprymna scolopes, deposits eggs on sand and coral rubble (shown) where embryos must successfully undergo development despite being surrounded by potential pathogenic and fouling microorganisms. Female bobtail squid incorporate bacteria directly into their eggs from a specialized organ, the accessory nidamental gland. These benefi cial bacteria produce antimicrobial compounds that are hypothesized to protect embryos in this example of a defensive symbiosis. Image credit: Mark Smith, Macroscopic Solutions.

Typeset by Nova Techset Private Limited, Bengaluru & Chennai, India. Printed in the UK by Henry Ling Limited. This paper meets the requirements of ISO 9706:1994(E) and ANSI/NISO Z39.48-1992 (Permanence of Paper) eff ective with volume 335, issue 1273, 1992. Phil. Trans. R. Soc. B (ISSN 0962-8436) is published 26 times a year for US$6461 per year by the Royal Society, and is distributed in the USA by Agent named Air Business, C/O Worldnet Shipping USA Inc., 149-35 177th Street, Jamaica, New York, NY11434, USA. US Postmaster: Send address changes to Phil. Trans. R. Soc. B, C/O Air Business Ltd, C/O Worldnet Shipping USA Inc, 149-35 177th Street Jamaica, New York, NY11414.

RRSTB_375_1808_Cover.inddSTB_375_1808_Cover.indd 55-7-7 331/07/201/07/20 111:551:55 AAMM ISSN 0962-8436 | Volume 375 | Issue 1808 | 28 September 2020 Phil. Trans. R. Soc. B |

The Royal Society is a self-governing Fellowship of many of the world’s most distinguished scientists

drawn from all areas of science, engineering, and Volume 375 medicine. The Society’s fundamental purpose, as it has been since its foundation in 1660, is to recognise, promote, and support excellence in science and to

encourage the development and use of science for |

the benefi t of humanity. Issue 1808 The role of the microbiome in host evolution The Society’s strategic priorities emphasise its commitment to the highest quality science, to Theme issue compiled and edited by Oren Kolodny, Benjamin J. Callahan and Angela E. Douglas

|

curiosity-driven research, and to the development 28 September 2020 and use of science for the benefi t of society. These priorities are: • Promoting science and its benefi ts • Recognising excellence in science • Supporting outstanding science • Providing scientifi c advice for policy • Fostering international and global cooperation The role of the microbiome in host evolution • Education and public engagement

For further information on the Royal Society The Royal Society 6 – 9 Carlton House Terrace London SW1Y 5AG T +44 20 7451 2500 W royalsociety.org

For further information on Philosophical Transactions of the Royal Society B T +44 20 7451 2602 E [email protected] W royalsocietypublishing.org/journal/rstb

0962-8436(20200928)375:1808

ISBN: 978-1-78252-476-2 ISSN 0962-8436 The Royal Society Registered Charity No 207043

RRSTB_375_1808_Cover.inddSTB_375_1808_Cover.indd 22-4-4 331/07/201/07/20 111:541:54 AAMM