Feminization of Male Brown Treesnake Methyl Ketone Expression via Steroid Hormone Manipulation

Authors

M. Rockwell Parker, James Madison UniversityFollow
Saumya M. Patel, Washington and Lee University
Jennifer E. Zachry, Washington and Lee University
Bruce A. Kimball, USDA National Wildlife Research CenterFollow

Document Type

Article

Date of this Version

2018

Citation

Journal of Chemical Ecology (2018) 44:189–197

Comments

Copyright Springer Science+Business Media

This document is a U.S. government work and is not subject to copyright in the United States.

https://doi.org/10.1007/s10886-018-0935-3

Abstract

Pheromones are useful tools for the management of invasive invertebrates, but have proven less successful in field applications for invasive vertebrates. The brown treesnake, Boiga irregularis, is an invasive predator that has fundamentally altered the ecology of Guam. The development of control tools to manage Boiga remains ongoing. Skin-based, lipophilic pheromone components facilitate mating in brown treesnakes, with females producing the same long-chain, saturated and monounsaturated (ketomonoene) methyl ketones known to function as pheromones in garter snakes, Thamnophis sirtalis. Boiga also express novel, diunsaturated methyl ketones (ketodienes) with a purported function as a sex pheromone. In our study, we implanted 17 β- estradiol in adult male brown treesnakes in order to manipulate methyl ketone expression as sex attractants, an effect that would mirror findings with garter snakes. Specifically, estrogen promoted production of two ketomonoenes, pentatriaconten-2-one and hexatriaconten-2-one, and suppressed production of one ketodiene, heptatriacontadien-2-one. In bioassays, estrogen-implanted males elicited tongue-flicking and chin rubbing behavior from unmanipulated males, though the responses were weaker than those elicited by females. On Guam, wild males exhibited greatest responses to whole female skin lipid extracts and only weak responses to the methyl ketone fractions from females and implanted males. Our results suggest that sex identity in brown treesnakes may be conferred by the ratio of ketomonoenes (female) to ketodienes (male) from skin lipids and may be augmented by a sex-specific endocrine signal (estradiol). However, a blend of long-chain methyl ketones alone is not sufficient to elicit maximal reproductive behaviors in male Boiga.