Abstract
A series of laboratory experiments tested the hypothesis that the Silver Carp (Hypophthalmichthys molitrix), an invasive river carp from China, employs a prostaglandin F2α-derived sex pheromone that is attractive and species-specific. Using electro-olfactogram recording (EOG), we found that the olfactory system of this species is acutely sensitive to three F-series prostaglandins (PGFs) at picomolar concentrations and that this sensitivity is enhanced when juveniles are masculinized using androgens, consistent with expectations of a sex pheromone. Individual PGFs had behavioral activity but it was low, suggesting a mixture might be important. To pursue this possibility, we implanted carps with osmotic pumps containing prostaglandin F2α (PGF2α), a treatment previously shown to elicit release of a PGF-based spawning pheromone in the Common Carp. We found that PGF2α-implanted Silver Carp released a species-specific odor that contained a blend of PGF2α and two of its metabolites, which masculinized individuals detected and were attracted to with high sensitivity. Finally, we found that a mixture of these PGFs was attractive to masculinized Silver Carp, while a different mixture released by Bighead Carp was not. We conclude that Silver Carp likely use a species-specific PGF2α-derived sex pheromone that is probably released at spawning and might be useful in its control. Confirmatory studies that explore pheromone function in naturally mature Silver Carp using natural odors in the field should now be conducted to further confirm our proof-of-concept study.
Highlights
Pheromones are chemical cues released by animals and many other organisms that drive behavioral and/or physiological changes in conspecifics in adaptive manners [1,2,3]
While there was no apparent difference between the olfactory sensitivities of untreated juvenile fish and ethanol-treated control fishes to PGFs, the olfactory sensitivity (EOG responses) of masculinized Silver Carp treated with methyltestosterone (MT) were greater than controls to 10−8 Molar (M) prostaglandin F2α (PGF2α) (p = 0.05; df = 2), 10−8 M 15K-PGF2α (p = 0.02; df = 2), and 10−8 M dh15K-PGF2α (p = 0.03, df = 2) (Figure 1)
electro-olfactogram recording (EOG) tests of whether binary mixtures of PGFs are detected by more than one type of olfactory receptor suggested that PGF2α is detected by its own independent olfactory receptor (the mean mixture discrimination index [MDI] for a mixture of PGF2α and 15K-PGF2α was 1.39 ± 0.7—different from 1.0 (p = 0.02, df = 2), the expected
Summary
Pheromones are chemical cues released by animals and many other organisms that drive behavioral and/or physiological changes in conspecifics in adaptive manners [1,2,3]. Sex pheromones are important in the regulation of reproduction and can serve both priming (physiological) and/or releasing (behavioral) roles [5,6]. With only one possible exception [7], all teleost sex pheromones described to date have been found to contain sex hormones and their derivatives [5,6]. Hormonal sex pheromones have been identified in about half a dozen model fish species including two Eurasian. Species-specific, and added to the water, sex pheromones are candidates for possible application as attractants for invasive fishes to facilitate their removal or quantification [9]
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