Life history linked to immune investment in developing amphibians

Volume 4 • 2016 10.1093/conphys/cow025 Research article Life history linked to immune investment in developing amphibians Douglas C. Woodhams1,*, Sara C. Bell2, Laurent Bigler3, Richard M. Caprioli4, Pierre Chaurand5, Brianna A. Lam6, Laura K. Reinert7, Urs Stalder3, Victoria M. Vazquez8, Klaus Schliep1, Andreas Hertz1 and Louise A. Rollins-Smith7,9,10 1 *Corresponding author: Department of Biology, University of Massachusetts Boston, 100 Morrissey Blvd., Boston, MA 02125, USA. Tel: +1 617 287 6679. Email: .............................................................................................................................................................. The broad diversity of amphibian developmental strategies has been shaped, in part, by pathogen pressure, yet trade-offs between the rate of larval development and immune investment remain poorly understood. The expression of antimicrobial peptides (AMPs) in skin secretions is a crucial defense against emerging amphibian pathogens and can also indirectly affect host defense by influencing the composition of skin microbiota. We examined the constitutive or induced expression of AMPs in 17 species at multiple life-history stages. We found that AMP defenses in tadpoles of species with short larval periods (fast pace of life) were reduced in comparison with species that overwinter as tadpoles and grow to a large size. A complete set of defensive peptides emerged soon after metamorphosis. These findings support the hypothesis that species with a slow pace of life invest energy in AMP production to resist potential pathogens encountered during the long larval period, whereas species with a fast pace of life trade this investment in defense for more rapid growth and development. Key words: Antimicrobial peptides, disease ecology, innate immunity, life-history strategy, MALDI-TOF mass spectrometry, tadpoles Editor: Steven Cooke Received 18 December 2015; Revised 9 May 2016; accepted 14 May 2016 Cite as: Woodhams DC, Bell SC, Bigler L, Caprioli RM, Chaurand P, Lam BA, Reinert LK, Stalder U, Vazquez VM, Schliep K, Hertz A, Rollins-Smith LA (2016) Life history linked to immune investment in developing amphibians. Conserv Physiol 4(1): cow025; doi:10.1093/conphys/cow025. .............................................................................................................................................................. Introduction Recent ecological theory suggests that trade-offs exist between host defenses and pace of life (Martin et al., 2007; Previtali et al., 2012; Sandmeier and Tracy, 2014; Sears et al., 2015). In animals with complex life histories, such as amphibians, slow pace of life often refers to growth to a large size over a relatively long larval period, including overwintering as larvae in some species (Stoks et al., 2006; Johnson et al., 2012). Amphibians with a fast pace of life are more likely to use .............................................................................................................................................................. © The Author 2016. Published by Oxford University Press and the Society for Experimental Biology. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. 1 Department of Biology, University of Massachusetts Boston, 100 Morrissey Blvd., Boston, MA 02125, USA College of Marine and Environmental Sciences, James Cook University, Townsville, QLD 4811, Australia 3 Department of Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland 4 Mass Spectrometry Research Center and Department of Biochemistry, Vanderbilt University, Nashville, TN 37232-8575, USA 5 Department of Chemistry, Université de Montréal, Montreal, QC, Canada H3T 1J4 6 Department of Biology, James Madison University, MSC 7801, Harrisonburg, VA 22807, USA 7 Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232-2363, USA 8 Plant Biology Department, University of Georgia, Athens, GA 30602, USA 9 Department of Biological Science, Vanderbilt University, Nashville, TN 37235-1634, USA 10 Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, TN 37232-2363, USA 2 Research article Conservation Physiology • Volume 4 2016 .............................................................................................................................................................. behavioural defenses against parasitic trematodes than slow pace-of-life species, and they appear to invest less in costly immune defenses that would provide infection tolerance (Sears et al., 2015). Here, we examine an innate immune defense of amphibians, antimicrobial skin peptides, in relation to amphibian life history and pace of life. Little is known about the ontogeny of amphibian skin peptide defenses. By northern blot analysis and in situ hybridization, mRNA for the two most abundant antimicrobial peptides (magainin and PGLa) was first detected at the beginning of metamorphic climax in Xenopus laevis tadpoles. When whole animals were homogenized, mature peptides could be isolated (Reilly et al., 1994). In a similar study of Lithobates catesbeianus tadpoles, expression of mRNA for ranalexin was not detected by northern blot analysis in premetamorphic tadpoles (forelimbs had not emerged), but was detected in metamorphosing tadpoles and adults (Clark et al., 1994). In both studies, production of AMPs was localized to developing cutaneous granular glands (Clark et al., 1994; Reilly et al., 1994). Katzenback et al. (2014) found increasing mRNA expression of brevinin-1SY through tadpole development in Lithobates sylvaticus. A study of Rana ornataventris adds to the evidence that late stage (metamorphosing) tadpoles of some species, but not early stage tadpoles, produce AMPs that are also expressed by adults. Temporin-1O was produced at the end of pre-metamorphosis and increased in late stage tadpoles and adults of this species (Iwamuro et al., 2006). Wabnitz et al. (1998) observed small amounts of host defense peptides in protein extracts from larval Litoria splendida as early as 14 days after egg deposition, but the complete set of adult skin peptides was not detected until metamorphosis. An ultrastructural study of Phyllomedusa bicolor indicated that both mucous and granular glands were present in tadpoles, but the gland duct did not appear to develop until metamorphosis (Lacombe et al., 2000). Using mass spectrometry (MS), known antimicrobial peptides were not consistently expressed in Lithobates sphenocephalus until ~12 weeks after metamorphosis (Holden et al., 2015). Although all of these studies provide some information about when in ontogeny AMPs can be expressed, they do (...truncated)