Skip to main content
SpringerLink
Log in
Book cover

Chemical Signals in Vertebrates 14 pp 205–220Cite as

Chemistry Between Salamanders: Evolution of the SPF Courtship Pheromone System in Salamandridae

  • Conference paper
  • First Online:

Abstract

Chemical communication is an important aspect of courtship and reproduction in salamanders ( Urodela ), where males secrete several protein pheromones from various sexually dimorphic glands . The most widely used sex pheromone system consists of proteins of the Sodefrin Precursor-like Factor (SPF) family . This protein family already started diversifying through gene duplications in the Late Palaeozoic and continued to do so in various urodelan lineages. As a result, males of multiple extant salamander species secrete different sets or ratios of SPF protein pheromones which, as shown in behavioral tests, can evoke various female responses during the courtship process, such as following behavior , cloacal gaping , or an acceleration of courtship in general. Still, all observable effects essentially are a consequence of female receptivity enhancement, indicating a preserved role for SPF pheromones. Salamandridae is a large family with currently 119 described species that show a considerable variety in courtship behaviour . In this family , different lineages evolved various modes of pheromone transfer, ranging from direct application during amplexus on land, to an indirect transfer in which males abandoned physical contact and instead tail-fan pheromones underwater toward a nearby female. In one genus, an additional decapeptide pheromone, sodefrin , originated by cleavage from a precursor of the SPF family and was co-opted alongside uncleaved SPF protein pheromones. Here we discuss our current understanding and knowledge gaps on the use of the SPF pheromone system in salamandrids, and we define some testable hypotheses on its evolution in relation to changes in mating habitat and courtship modes.

This is a preview of subscription content, log in via an institution.

Chapter
USD   29.95
Price excludes VAT (USA)
  • Available as PDF
  • Read on any device
  • Instant download
  • Own it forever
eBook
USD   129.00
Price excludes VAT (USA)
  • Available as EPUB and PDF
  • Read on any device
  • Instant download
  • Own it forever
Softcover Book
USD   169.99
Price excludes VAT (USA)
  • Compact, lightweight edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info
Hardcover Book
USD   169.99
Price excludes VAT (USA)
  • Durable hardcover edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Learn about institutional subscriptions

References

  • Ahrenfeldt RH (1955) Mating behaviour of Euproctus asper in captivity. Br J Herpetol 2:194–197

    Google Scholar 

  • Amaya E, Ashurst JL, Bonfield JK, Croning MDR, Chen C-K, Davies RM, Francis MD, Garrett N, Gilchrist MJ, Grafham DV, McLaren SR, Papalopulu N, Rogers J, Smith JC, Taylor RG, Voigt J, Zorn AM (2006) Direct submission: nucleotide [Internet]. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information; [04 October 2006]—Accession No. CR761728.2, Xenopus tropicalis finished cDNA, clone TGas100l21 [cited 2018 January 14]. Available from: https://www.ncbi.nlm.nih.gov/nuccore/CR761728.2

  • Arnold SJ (1972) The evolution of courtship behaviour in salamanders (Doctoral dissertation). University of Michigan, Ann Arbor, Michigan, p 570

    Google Scholar 

  • Arnold SJ (1977) The evolution of courtship behavior in new world salamanders with some comments on old world salamandrids. In: Taylor DH, Guttman SI (eds) The reproductive biology of amphibians. Plenum Press, New York, USA, pp 141–183

    Chapter  Google Scholar 

  • Arntzen JW, Sparreboom M (1989) A phylogeny for the old world newts, genus Triturus: biochemical and behavioural data. J Zool 219:645–664

    Article  Google Scholar 

  • Baeckens S, Driessens T, Van Damme R (2016) Intersexual chemo-sensation in a “visually-oriented” lizard. Anolis sagrei. PeerJ 4:e1874

    Article  PubMed  Google Scholar 

  • Campbell LJ, Suárez-Castillo EC, Ortiz-Zuazaga H, Knapp D, Tanaka EM, Crews CM (2011) Gene expression profile of the regeneration epithelium during axolotl limb regeneration. Dev Dyn 240(7):1826–1840

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  • Clark K, Karsch-Mizrachi I, Lipman DJ, Ostell J, Sayers EW (2016) GenBank. Nucleic Acids Res 44(D1):D67–D72. https://doi.org/10.1093/nar/gkv1276

    Article  CAS  PubMed  Google Scholar 

  • Carranza S, Amat F (2005) Taxonomy, biogeography and evolution of Euproctus (Amphibia: Salamandridae), with the resurrection of the genus Calotriton and the description of a new endemic species from the Iberian peninsula. Zool J Linn Soc 145(4):555–582

    Article  Google Scholar 

  • Casey JR, Petranka JG, Kottra J, Fleenor DE, Rosse W (1994) The structure of the urokinase-type plasminogen activator receptor gene. Blood 84:1151–1156

    CAS  PubMed  Google Scholar 

  • Davis WC, Twitty VC (1964) Courtship behavior and reproductive isolation in the species of Taricha (Amphibia, Caudata). Copeia 1964:601–610

    Article  Google Scholar 

  • Dawley EM (1984) Recognition of individual, sex and species odours by salamanders of the Plethodon glutinosus-P. jordani complex. Anim Behav 32(2):353–361

    Article  Google Scholar 

  • Duellman WE, Trueb L (1994) Biology of amphibians. Johns Hopkins University Press, USA, p 670

    Google Scholar 

  • Dunn RD, Broady KW (2001) Snake inhibitors of phospholipase A2 enzymes. Biochim Biophy Acta (BBA)—Mol. Cell Biol. Lipids 1533(1):29–37

    Article  CAS  Google Scholar 

  • Fleming TJ, O’hUigin C, Malek TR (1993) Characterization of two novel Ly-6 genes. Protein sequence and potential structural similarity to alpha-bungarotoxin and other neurotoxins. J Immunol 150(12):5379–5390

    Google Scholar 

  • Fortes-Dias CL, Campos PC, Fernandes CAH, Fontes MRM (2017) Phospholipase A2 inhibitors from snake blood (sbPLIs). In: Gopalakrishnakone P, Inagaki H, Mukherjee A, Rahmy T, Vogel CW (eds) Snake venoms. Toxinology. Springer, Dordrecht, pp 105–122

    Chapter  Google Scholar 

  • Frost DR (2019) Amphibian species of the world, an online reference. Version 6.0. Accessed on 10 January 2019. Electronic database accessible at http://research.amnh.org/herpetology/amphibia/index.html. American Museum of Natural History, New York, USA

  • Gallien L (1952) Elevage et comportement du Pleurodèle au laboratoire. Bulletin de Société Zoologique de France 77:456–461

    Google Scholar 

  • Gong Y, Shu G, Huang F, He L, Li C, Xie F (2018) Courtship behaviour and male sexual competition of the Taliang crocodile newt, Liangshantriton taliangensis. Amphibia-Reptilia 39(3):275–288

    Article  Google Scholar 

  • Griffiths RA (1996) Newts and salamanders of Europe. Poyser Natural History, London, UK, p 188

    Google Scholar 

  • Guillaume O (1999) Does the Pyrenean salamander Euproctus asper use chemical cues for sex identification and mating behaviour? Behav Proc 46(1):57–62

    Article  CAS  Google Scholar 

  • Halliday TR (1974) Sexual behaviour of the smooth newt Triturus vulgaris (Urodela, Salamandridae). J Herpetol 8(4):277–292

    Article  Google Scholar 

  • Halliday TR (1977) The courtship of European newts: an evolutionary perspective. In: Taylor DH, Guttman SI (eds) The reproductive biology of amphibians. Plenum Press, New York, USA, pp 185–232

    Chapter  Google Scholar 

  • Halliday TR (1990) The evolution of courtship behavior in newts and salamanders. Adv Study Behav 19:137–169

    Article  Google Scholar 

  • Houck LD, Arnold SJ (2003) Courtship and mating behaviour. In: Sever DM (ed) Phylogeny and reproductive biology of Urodela (Amphibia). Science Publishers, Enfield, New Hampshire, USA, pp 383–424

    Google Scholar 

  • Houck LD, Bell AM, Reagan-Wallin NL, Feldhoff RC (1998) Effects of experimental delivery of male courtship pheromones on the timing of courtship in a terrestrial salamander, Plethodon jordani (Caudata: Plethodontidae). Copeia 1998:214–219

    Article  Google Scholar 

  • Houck LD, Palmer CA, Watts RA, Arnold SJ, Feldhoff PW, Feldhoff RC (2007) A new vertebrate courtship pheromone, PMF, affects female receptivity in a terrestrial salamander. Anim Behav 73(2):315–320

    Article  Google Scholar 

  • Houck LD, Watts RA, Mead LM, Palmer CA, Arnold SJ, Feldhoff PW, Feldhoff RC (2008) A candidate vertebrate pheromone, SPF, increases female receptivity in a salamander. In: Hurst JL, Beynon RJ, Roberts SC, Wyatt TD (eds) Chemical signals in vertebrates 11. Springer-Verlag Inc., New York, USA, pp 213–221

    Chapter  Google Scholar 

  • Iwata T, Conlon JM, Nakada T, Toyoda F, Yamamoto K, Kikuyama S (2004) Processing of multiple forms of preprosodefrin in the abdominal gland of the red-bellied newt Cynops pyrrhogaster: regional and individual differences in preprosodefrin gene expression. Peptides 25(9):1537–1543

    Article  CAS  PubMed  Google Scholar 

  • Iwata T, Ishizuka Y, Nakada T, Toyoda F, Yamamoto K, Conlon JM, Kikuyama S (2005) Regionally specific occurrence of an active sodefrin variant in the red-bellied newt. Ann NY Acad Sci 1040(1):351–353

    Article  CAS  PubMed  Google Scholar 

  • Janssenswillen S, Bossuyt F (2016) Male courtship pheromones induce cloacal gaping in female newts (Salamandridae). PLoS ONE 11(1):e0144985

    Article  PubMed  PubMed Central  Google Scholar 

  • Janssenswillen S, Vandebergh W, Treer D, Willaert B, Maex M, Van Bocxlaer I, Bossuyt F (2014) Origin and diversification of a salamander sex pheromone system. Mol Biol Evol 32(2):472–480

    Article  PubMed  Google Scholar 

  • Janssenswillen S, Willaert B, Treer D, Vandebergh W, Bossuyt F, Van Bocxlaer I (2015) High pheromone diversity in the male cheek gland of the red-spotted newt Notophthalmus viridescens (Salamandridae). BMC Evol Biol 15:54

    Article  PubMed  PubMed Central  Google Scholar 

  • Kawamura T, Sawada S (1959) On the sexual isolation among different species and local races of Japanese newts. J Sci Hiroshima Univ Ser B 18:17–31

    Google Scholar 

  • Kieffer B, Driscoll PC, Campbell ID, Willis AC, van der Merwe PA, Davis SJ (1994) Three-dimensional solution structure of the extracellular region of the complement regulatory protein CD59, a new cell-surface protein domain related to snake venom neurotoxins. Biochemistry 33(15):4471–4482

    Article  CAS  PubMed  Google Scholar 

  • Kieren S, Sparreboom M, Hochkirch A, Veith M (2018) A biogeographic and ecological perspective to the evolution of reproductive behaviour in the family Salamandridae. Mol Phylogenet Evol 121:98–109

    Article  PubMed  Google Scholar 

  • Kikuyama S, Toyoda F, Ohmiya Y, Matsuda K, Tanaka S, Hayashi H (1995) Sodefrin: a female-attracting peptide pheromone in newt cloacal glands. Science 267:1643–1645

    Article  CAS  PubMed  Google Scholar 

  • Kikuyama S, Toyoda F (1999) Sodefrin: a novel sex pheromone in a newt. Rev Reprod 4(1):1–4

    Article  CAS  PubMed  Google Scholar 

  • Kini RM, Doley R (2010) Structure, function and evolution of three-finger toxins: mini proteins with multiple targets. Toxicon 56(6):855–867

    Article  CAS  PubMed  Google Scholar 

  • Kozak KH (2003) Sexual isolation and courtship behavior in salamanders of the Eurycea bislineata species complex, with comments on the evolution of the mental gland and pheromone delivery behavior in the Plethodontidae. Southeast Nat 2(2):281–293

    Article  Google Scholar 

  • Loughner CL, Bruford EA, McAndrews MS, Delp EE, Swamynathan S, Swamynathan SK (2016) Organization, evolution and functions of the human and mouse Ly6/uPAR family genes. Hum Genomics 10(1):10

    Article  PubMed  PubMed Central  Google Scholar 

  • Maex M, Van Bocxlaer I, Mortier A, Proost P, Bossuyt F (2016) Courtship pheromone use in a model urodele, the Mexican axolotl (Ambystoma mexicanum). Sci Rep 6:20184

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  • Maex M, Treer D, De Greve H, Proost P, Van Bocxlaer I, Bossuyt F (2018) Exaptation as a mechanism for functional reinforcement of an animal pheromone system. Curr Biol 28(18):2955–2960.e5

    Article  CAS  PubMed  Google Scholar 

  • Maki N, Martinson J, Nishimura O, Tarui H, Meller J, Tsonis PA, Agata K (2010) Expression profiles during dedifferentiation in newt lens regeneration revealed by expressed sequence tags. Mol Vision 16:72–78

    CAS  Google Scholar 

  • Malacarne G, Vellano C (1987) Behavioral evidence of a courtship pheromone in the crested newt, Triturus cristatus carnifex Laurenti. Copeia 1987(1):245–247

    Article  Google Scholar 

  • Mitchell J, Gibbons W (2010) Salamanders of the Southeast. University of Georgia Press, Georgia, USA, p 324

    Google Scholar 

  • Nakada T, Toyoda F, Iwata T, Yamamoto K, Conlon JM, Kato T, Kikuyama S (2007) Isolation, characterization and bioactivity of a region-specific pheromone, [Val8] sodefrin from the newt Cynops pyrrhogaster. Peptides 28(4):774–780

    Article  CAS  PubMed  Google Scholar 

  • Nakada T, Toyoda F, Matsuda K, Nakakura T, Hasunuma I, Yamamoto K, Onoue S, Yokosuka M, Kikuyama S (2017) Imorin: a sexual attractiveness pheromone in female red-bellied newts (Cynops pyrrhogaster). Sci Rep 7:41334

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  • Nelson J (1960) Courtship display in the Italian crested newt (Triturus cristatus carnifex). Biol J 1:6–9

    Google Scholar 

  • Okomura K, Masui K, Inoue S, Ikeda K, Hayashi K (1999) Purification, characterization and cDNA cloning of a phospholipase A2 inhibitor from the serum of the non-venomous snake Elaphe quadrivirgata. Biochem J 341(1):165–171

    Article  Google Scholar 

  • Osikowski A, Cierniak-Zuzia K (2013) Cloacal anatomy of the male Carpathian newt, Lissotriton montandoni (Amphibia, Salamandridae), in the breeding season. Zool Sci 30(9):748–753

    Article  PubMed  Google Scholar 

  • Palmer CA, Watts RA, Houck LD, Picard AL, Arnold SJ (2007) Evolutionary replacement of components in a salamander pheromone signaling complex: more evidence for phenotypic-molecular decoupling. Evolution 61(1):202–215

    Article  CAS  PubMed  Google Scholar 

  • Petranka J (2010) Salamanders od the United States and Canada. Smithsonian books, Washington, USA, p 592

    Google Scholar 

  • Pool TB, Dent JN (1977) The ultrastructure and the hormonal control of product synthesis in the hedonic glands of the red-spotted newt Notopthalmus viridescens. J Exp Zool 201(2):177–201

    Article  CAS  Google Scholar 

  • Poschadel JR, Rudolph A, Plath M (2007) Nonvisual mate choice in the Pyrenean mountain newt (Euproctus asper): females prefer small males. Acta Ethologica 10(1):35–40

    Article  Google Scholar 

  • Protein [Internet]. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information; 2004—[cited 2018 January 21]. Available from: https://www.ncbi.nlm.nih.gov/protein/

  • Rafinski J, Pecio A (1992) The courtship behaviour of the Bosca’s newt, Triturus boscai (Amphibia: Salamandridae). Folia Biol 40:155–165

    Google Scholar 

  • Rollins RE, Staub NL (2017) The Presence of caudal courtship-like glands in male and female ouachita dusky salamanders (Desmognathus brimleyorum). Herpetologica 73(4):277–282

    Article  Google Scholar 

  • Rollmann SM, Houck LD, Feldhoff RC (1999) Proteinaceous pheromone affecting female receptivity in a terrestrial salamander. Science 285(5435):1907–1909

    Article  CAS  PubMed  Google Scholar 

  • Rollmann SM, Houck LD, Feldhoff RC (2003) Conspecific and heterospecific pheromone effects on female receptivity. Anim Behav 66:857–861

    Article  Google Scholar 

  • Rusconi M (1821) Amours des salamandres aquatiques et developpement du tetard de ces salamandres depuis l’oeuf jusqu’a l’animal parfait. Paolo Emilio Giusti, Milano, Italy, p 91

    Google Scholar 

  • Sacerdote M (1956) Per una migliore conoscenza della topografia delle ghiandole annesse alla cloaca nel tritone crestato. Bolletino di zoologia 23(1):33–50

    Article  Google Scholar 

  • Salthe SN (1967) Courtship patterns and the phylogeny of the urodeles. Copeia 1967:100–117

    Article  Google Scholar 

  • Secondi J, Haerty W, Lodé T (2005) Female attraction to conspecific chemical cues in the palmate newt Triturus helveticus. Ethology 111(8):726–735

    Article  Google Scholar 

  • Sever DM, Verrell PA, Halliday TR, Griffiths M, Waights V (1990) The cloaca and cloacal glands of the male smooth newt, Triturus vulgaris vulgaris (Linnaeus), with especial emphasis on the dorsal gland. Herpetologica 46(2):160–168

    Google Scholar 

  • Sever DM (1991) Comparative anatomy and phylogeny of the cloacae of salamanders (Amphibia: Caudata). I. Evolution at the family level. Herpetologica 47(2):165–193

    Google Scholar 

  • Sever DM (1992) Comparative anatomy and phylogeny of the cloacae of salamanders (Amphibia: Caudata) IV. Salamandridae. Anat Rec 233(2):229–244

    Article  CAS  PubMed  Google Scholar 

  • Sever DM (1994) Comparative anatomy and phylogeny of the cloacae of salamanders (Amphibia: Caudata). VII. Plethodontidae. Herpetol Monogr 8:276–337

    Article  Google Scholar 

  • Sever DM (2003) Courtship and mating glands. In: Sever DM (ed) Phylogeny and reproductive biology of Urodela (Amphibia). Science Publishers, Enfield, New Hampshire, USA, pp 323–381

    Google Scholar 

  • Spallanzani L (1780) Dissertazioni di fisica animale e vegetabile. Presso La Societa Tipografica, Modena, Italy, p 361

    Google Scholar 

  • Sparreboom M (2014) Salamanders of the old world. KNNV Publishing, Zeist, The Netherlands, p 431

    Book  Google Scholar 

  • Tinbergen N, Ter Pelkwijk JJ (1938) De kleine watersalamander. De Levende Natuur 43(8):232–237

    Google Scholar 

  • Toyoda F, Tanaka S, Matsuda K, Kikuyama S (1994) Hormonal control of response to and secretion of sex attractants in Japanese newts. Physiol Behav 55(3):569–576

    Article  CAS  PubMed  Google Scholar 

  • Treer D, Maex M, Van Bocxlaer I, Proost P, Bossuyt F (2017) Divergence of species-specific protein sex pheromone blends in two related, nonhybridizing newts (Salamandridae). Mol Ecol 27(2):508–519

    Article  PubMed  Google Scholar 

  • Treer D, Van Bocxlaer I, Matthijs S, Du Four D, Janssenswillen S, Willaert B, Bossuyt F (2013) Love is blind: indiscriminate female mating responses to male courtship pheromones in newts (Salamandridae). PLoS ONE 8(2):e56538

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  • Treer D, Bossuyt F (2010) Chemical ‘versus’ visual cues in newts (Salamandridae): experiments in total darkness and in a Y-maze. In: 17th Benelux Congress of Zoology, Ghent, Belgium. Conference abstract, p 87

    Google Scholar 

  • Tsetlin V (1999) Snake venom α-neurotoxins and other ‘three-finger’proteins. Eur J Biochem 264(2):281–286

    Article  CAS  PubMed  Google Scholar 

  • Van Bocxlaer I, Maex M, Treer D, Janssenswillen S, Janssens R, Vandebergh W, Proost P, Bossuyt F (2016) Beyond sodefrin: evidence for a multi-component pheromone system in the model newt Cynops pyrrhogaster (Salamandridae). Sci Rep 6:21880

    Article  PubMed  PubMed Central  Google Scholar 

  • Van Bocxlaer I, Treer D, Maex M, Vandebergh W, Janssenswillen S, Stegen G, Kok P, Willaert B, Matthijs S, Martens E, Mortier A, de Greve H, Proost P, Bossuyt F (2015) Side-by-side secretion of late palaeozoic diverged courtship pheromones in an aquatic salamander. Proc R Soc Lond B Biol Sci 282:20142960

    Article  Google Scholar 

  • Verrell P (1982) The sexual behaviour of the red-spotted newt, Notophthalmus viridescens (Amphibia: Urodela: Salamandridae). Anim Behav 30(4):1224–1236

    Article  Google Scholar 

  • Wells KD (2007) The ecology and behavior of amphibians. The University of Chicago Press, Chicago, USA, p 1148

    Book  Google Scholar 

  • Yamamoto K, Kawai Y, Hayashi T, Ohe Y, Hayashi H, Toyoda F, Kawahara G, Iwata T, Kikuyama S (2000) Silefrin, a sodefrin-like pheromone in the abdominal gland of the sword-tailed newt, Cynops ensicauda. FEBS Lett 472:267–270

    Article  CAS  PubMed  Google Scholar 

  • Zhang P, Papenfuss TJ, Wake MH, Qu L, Wake DB (2008) Phylogeny and biogeography of the family Salamandridae (Amphibia: Caudata) inferred from complete mitochondrial genomes. Mol Phylogenet Evol 49(2):586–597

    Article  CAS  PubMed  Google Scholar 

Download references

Acknowledgements

This work was supported by the European Research Council (ERC 204509 StG grant to FB), Fonds voor Wetenschappelijk Onderzoek-Vlaanderen (FWO research project G026715 N), and the Strategic Research Program of the Vrije Universiteit Brussel (SRP30). We are very grateful to Kim Roelants for providing drawings.

Author information

Authors and Affiliations

  1. Amphibian Evolution Lab, Biology Department, Vrije Universiteit Brussel, Pleinlaan 2, B-1050, Brussels, Belgium

    Franky Bossuyt, Margo Maex, Dag Treer, Lisa M. Schulte, Ines Van Bocxlaer & Sunita Janssenswillen

Authors
  1. Franky Bossuyt
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Margo Maex
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Dag Treer
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Lisa M. Schulte
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Ines Van Bocxlaer
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Sunita Janssenswillen
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Franky Bossuyt .

Editor information

Editors and Affiliations

  1. Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, Abingdon, Oxfordshire, UK

    Christina D. Buesching

Rights and permissions

Reprints and permissions

Copyright information

© 2019 Springer Nature Switzerland AG

About this paper

Check for updates. Verify currency and authenticity via CrossMark

Cite this paper

Bossuyt, F., Maex, M., Treer, D., Schulte, L.M., Van Bocxlaer, I., Janssenswillen, S. (2019). Chemistry Between Salamanders: Evolution of the SPF Courtship Pheromone System in Salamandridae. In: Buesching, C. (eds) Chemical Signals in Vertebrates 14. Springer, Cham. https://doi.org/10.1007/978-3-030-17616-7_15

Download citation

Publish with us

Policies and ethics

Search

Navigation