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Journal of Comparative Physiology A

, Volume 197, Issue 8, pp 799–817 | Cite as

Signal variation and its morphological correlates in Paramormyrops kingsleyae provide insight into the evolution of electrogenic signal diversity in mormyrid electric fish

  • Jason R. Gallant
  • Matthew E. Arnegard
  • John P. Sullivan
  • Bruce A. Carlson
  • Carl D. Hopkins
Original Paper

Abstract

We describe patterns of geographic variation in electric signal waveforms among populations of the mormyrid electric fish species Paramormyrops kingsleyae. This analysis includes study of electric organs and electric organ discharge (EOD) signals from 553 specimens collected from 12 localities in Gabon, West-Central Africa from 1998 to 2009. We measured time, slope, and voltage values from nine defined EOD “landmarks” and determined peak spectral frequencies from each waveform; these data were subjected to principal components analysis. The majority of variation in EODs is explained by two factors: the first related to EOD duration, the second related to the magnitude of the weak head-negative pre-potential, P0. Both factors varied clinally across Gabon. EODs are shorter in eastern Gabon and longer in western Gabon. Peak P0 is slightly larger in northern Gabon and smaller in southern Gabon. P0 in the EOD is due to the presence of penetrating-stalked (Pa) electrocytes in the electric organ while absence is due to the presence of non-penetrating stalked electrocytes (NPp). Across Gabon, the majority of P. kingsleyae populations surveyed have only individuals with P0-present EODs and Pa electrocytes. We discovered two geographically distinct populations, isolated from others by barriers to migration, where all individuals have P0-absent EODs with NPp electrocytes. At two sites along a boundary between P0-absent and P0-present populations, P0-absent and P0-present individuals were found in sympatry; specimens collected there had electric organs of intermediate morphology. This pattern of geographic variation in EODs is considered in the context of current phylogenetic work. Multiple independent paedomorphic losses of penetrating stalked electrocytes have occurred within five Paramormyrops species and seven genera of mormyrids. We suggest that this key anatomical feature in EOD signal evolution may be under a simple mechanism of genetic control, and may be easily influenced by selection or drift throughout the evolutionary history of mormyrids.

Keywords

Signal evolution Geographic variation Biogeography Electrocyte Electric organ 

Notes

Acknowledgments

Permits to collect fishes in Gabon and export them for this study were granted by l’Institut de Recherche en Ecologie Tropicale, l’Institut de Recherches Agronomiques et Forestières and the Centre National de la Recherche Scientifique et Technologique. We are grateful for the valuable assistance and logistical support we received from J. D. Mbega and students working in these institutions. All techniques used are in accordance with protocols approved by Cornell University’s Center for Research Animal Resources and Education (CARE). The authors thank G. Harned for assistance with histological processing, Charles Dardia at the Cornell Museum of Vertebrates for assistance in the preparation of Online Resource 2, Cornell Microscopy and Imaging Core Facility for use of their confocal microscopy equipment. Additionally, we thank A. McCune and K. Shaw, as well as two anonymous reviewers for comments on earlier versions of this manuscript. This work was supported by NIMH TG T32 MH015793 and NIH TG 2T32GM007469 to JRG, NIH RO1-DC6206 and NSF 0818305 to CDH, and NSF 0818390 to BAC.

Supplementary material

359_2011_643_MOESM1_ESM.pdf (145 kb)
Online Resource 1 For the convenience of the reader, the most recent diagnosis of Paramormyrops and P. kingsleyae is provided. Full text is available from: Hopkins CD, Lavoué S, Sullivan JP (2007) Mormyridae. In: Stiassny MLJ, Teugels GG, Hopkins CD (eds) Poissons D’eaux Douces Et Saumâtres De Basse Guinée: ouest de l’Afrique Central vol 1. Faune Et Flore Tropicales. IRD Éditions, Paris, pp 220–334. (PDF 145 kb)
359_2011_643_MOESM2_ESM.pdf (186 kb)
Online Resource 2 Tabulated list of all specimens included in this study. Their date of collection, collection coordinates, assigned locality, standard length (SL), sex, Cornell University Museum of Vertebrates accession numbers, and individual voucher numbers are included. (-) indicates no data available for sex and (ND) indicates no data available for standard length. (PDF 185 kb)
359_2011_643_MOESM3_ESM.pdf (1.3 mb)
Online Resource 3 Detailed discussion of temperature correction and its effects on EOD variation; variation due to temperature differences are compared to between and within population variation. (PDF 1364 kb)

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Jason R. Gallant
    • 1
  • Matthew E. Arnegard
    • 2
  • John P. Sullivan
    • 3
  • Bruce A. Carlson
    • 4
  • Carl D. Hopkins
    • 1
  1. 1.Department of Neurobiology and BehaviorCornell UniversityIthacaUSA
  2. 2.Department of ZoologyUniversity of British ColumbiaVancouverCanada
  3. 3.Museum of VertebratesCornell UniversityIthacaUSA
  4. 4.Department of BiologyWashington University in St. LouisSt. LouisUSA

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