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Pheromone Gene Diversification and the Evolution of Courtship Glands in Plethodontid Salamanders

Abstract

Proteinaceous pheromones that diversify through gene duplication can result in shifts in courtship cocktails that may serve as a mechanism for reproductive isolation. The molecular evolution of pheromones has been extensively studied in salamanders, but how these genes and associated novel courtship glands have codiversified has not been evaluated. In this study we used transcriptional analyses to examine the relationship between pheromone diversification and gland type in three divergent lineages of plethodontid salamanders. Our results revealed that plethodontid salamanders express up to eight divergent Sodefrin Precursor-like Factor genes (spf, representing both alpha and beta subfamilies) along with Plethodontid Modulating Factor (pmf) and Plethodontid Receptivity Factor (prf). Expression of pheromone genes is tissue specific with pmf, prf, and some spf genes restricted to the mental gland. In contrast, the caudal gland shows strong expression of the other spf genes. We found evidence for punctuated changes in pheromone cocktail composition related to the loss of metamorphosis, and subsequent extreme reduction of the mental gland, in a paedomorphic lineage. Our study provides insight into how pheromone diversification can be partitioned into unique glands, which may lead to cocktail specificity in behavioral modules during courtship.

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Data Availability

Gene transcripts are available on GenBank. Histological slides, specimens, and tissue samples are available from RMB.

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Acknowledgements

We thank N. Ledbetter and B. Molone for assisting with field work and salamander collection. We would also like to thank A. Trujano, who helped with RNA extractions and cDNA synthesis and C. Burleson who annotated gene transcripts. Finally, we thank M. Howery of the Oklahoma Department of Wildlife Conservation and K. Irwin of the Arkansas Game and Fish Commission for permitting logistics.

Funding

This study was in part funded by the National Science Foundation (DEB1050322 and DEB1840987 to RMB; DEB1210859 to RMB and MAS) as well as by the University of Tulsa through the Student Research Grant program.

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MAH, MAS, and RMB designed the study and performed analyses. All authors participated in collecting data and preparing the manuscript.

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Correspondence to Madison A. Herrboldt.

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Specimens were handled in accordance with Institutional Animal Care and Use Committee (IACUC) protocols at the University of Tulsa (TU-0028 and TU-0029).

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Handling editor: Willie Swanson.

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Herrboldt, M.A., Steffen, M.A., McGouran, C.N. et al. Pheromone Gene Diversification and the Evolution of Courtship Glands in Plethodontid Salamanders. J Mol Evol 89, 576–587 (2021). https://doi.org/10.1007/s00239-021-10026-0

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Keywords

  • Caudal gland
  • Life cycle
  • Mental gland
  • Metamorphosis
  • Paedomorphosis
  • Subfunctionalization