Elephants insect pheromones

Abstract A relatively small number of mammalian pheromones has been identified, in contrast to a plethora of known insect pheromones, but two remarkable Asian elephant/insect pheromonal linkages have been elucidated, namely, (Z)-7-dodecen-1-yl acetate and frontalin. In addition, behavioral bioassays have demonstrated the presence of a chemical signal in the urine of female African elephants around the time of ovulation. Our search for possible ovulatory pheromones in the headspace over female African elephant urine has revealed for the first time the presence of a number of known insect pheromones. This search has been facilitated by the use of a powerful new analytical technique, automated solid phase dynamic extraction (SPDE)/GC-MS, as well as by novel macros for enhanced and rapid comparison of multiple mass spectral data files from Agilent ChemStation . This chapter will focus on our methodologies and results, as well as on a comparison of SPDE and the more established techniques of solid phase microextraction (SPME) and stir bar sorptive extraction (SBSE). 

Our recent NSF-funded collaboration with Bets has yielded, for example, the first statistically significant evidence that male African elephants can distinguish conspecific female urine collected at the time of ovulation from urine obtained at the mid-luteal time of the estrous cycle (Bagley, Goodwin, Rasmussen and Schulte 2006). Additionally, we have published the first report of insect pheromones in the urine of female African elephants (Goodwin, Eggert, House, Weddell, Schulte and Rasmussen 2006). These findings bode well for the eventual discovery of the first African elephant pheromones. 

Fig. 2.1 Compounds identified in female African elephant urine headspace that are known insect pheromones...

Use of automated headspace SPDE/GC-MS not only enabled the identification in female African elephant urine of a number of known insect pheromones (compounds 2-6, Fig. 2.1), but also revealed the presence of the beetle biochemical precursors to frontalin (2), exo-brevicomin (3) and ent/o-brevicomin (4), thus suggesting a common biosynthetic pathway (Goodwin et al. 2006). Extensive behavioral bioassays must be performed to determine whether any of these compounds is functioning as a pheromone among African elephants. 

The structural similarities between the putative mammalian chemosignals and the pheromones identified previously in the insect world are quite striking. The farnesenes [257, 258] (entries 66, 67) and 2-heptanone [259] (entry 68) have been implicated previously as insect pheromones. There is only one double bond distinguishing the male mouse pheromone 3,4-dehydro-exo-brevicomin (entry 65) from a bark beetle pheromone [260], brevicomin. In addition, the elephant pheromone (Z)-7-dodecen-l-yl acetate (entry 69) is also known to be an insect pheromone [259]. While the potency may not compare to the insect system, investigators are beginning to find evidence that many mammals ranging from pigs to elephants can have a pheromone-type response to a sniff of secretions even humans appear to respond [261],... 

Rasmussen LEL, Lee TD, Roelofs WL, Zhang AJ, Daves GD (1996) Insect pheromone in elephants. Nature 379 684... 

Not only is the structure of the sex pheromone identical in both moths and Asian elephants and its function similar, but the study of protein carriers promises to be equally fascinating. The delineation of postulated protein carriers for this acetate has the potential to provide similar evolutionary information about lipocalin-like urinary proteins and pheromone binding proteins. Insect pheromone binding proteins that bind Z7—12 Ac have a different amino acid composition and two-dimensional structure than vertebrate odorant binding proteins so far described, including major urinary proteins (Robertson, Cox, Gaskell, Evershed Beynon, 1996 Steinbrecht, 1996 Pelosi, 1994). 

In addition to their prevalence in plants, esters play biological roles in the animal kingdom. Section 12-17 included several examples of esters that function as insect pheromones. Perhaps the most bizarre of these esters is ( -7-dodecenyl acetate, a component of the pheromone mixture in several species of moths. This same compound was recently found to also be the mating pheromone of the elephant (who said nature has no sense of humor ). Section 20-5 will describe a number of more conventional biological functions of esters. 

In rabbits, the as yet unidentified maternal signal during lactation has analogous properties in guiding the reliable orientation of suckling, mainly via MOS input (Hudson and Distel, 1986 Schaal et al., unpubl.). Minor fractions may still function as flag contributors, exemplified by the attractiveness of proestrous elephant urine. Male responses show that intact urine is conspicuously more attractive in comparison with the pure insect mammal pheromone (9.) presented in water (Rasmussen et al., 1996). 

Compared to the large number of chemical signals identified in insects, only a small number of proven mammalian pheromones are known, two of which have been identified in elephants (Albone 1984 Brown and Macdonald 1985 Wyatt 2003 Burger 2005). Female Asian elephants (Elephas maximus) release a... 

Pheromones are also important in mammals, although many fewer have been identified. As one example, (Z)-7-dodecen-l-yl acetate has recently been identified in the urine of female elephants when they are in heat. This ester elicits a specific sexual response in male elephants. Interestingly, this same ester is part of the pheromone mixture that many insects, especially moths, use as a sexual attractant. 

First identified in Asian elephants during a headspace analysis of volatiles collected from secretions of the musth temporal gland of adult males,156 frontalin (52) is a bicyclic ketal, which is structurally reminiscent of the male mouse priming pheromone component 3,4-dehydro-ara-brevicomin (37). Frontalin (52), Z-7-dodecen-l-yl acetate (51), was already known because of its chemosensory role in the insect world it is an aggregation pheromone in bark beetles.157 Interestingly, the ratio of the two enantiomers of frontalin (52) changes with age and stage of musth and elicits different behavioral responses.158... 

Elephant pheromone. Female elephants, e.g., the Asian elephant (Elephas maximus), use (Z)-7-dodece-nyl acetate (C,4H2602, Mr 226.36, oil) as a pheromone to indicate their readiness for mating. The same compound is also used by more than 126 species of insects, especially by lepidoptera (butterflies), in their pheromone mixtures for attracting males. ... 

Here is an example. The pheromone frontalin is a remarkable compound used by both insects and by elephants to attract a mate. Its structure and H NMR spectrum are shown below. 

The majority of insect and mammalian pheromones are small and relatively simple molecules with low polarity. Nonpolar polysiloxane phases such as 100% polysiloxane or 5% polyphenylmethyl siloxane are the preferred column for pheromone research due to a broad range, thermal stability, and long lifetime. Five per cent (phenyl)methylpolysiloxane columns were used in the identification of dodecenyl acetate and dodecenol, the sex pheromones of the citrus fruit borer, and anisole, the sex pheromone of the scarab beetle. A 100% polysiloxane column was used in the analysis of dodecenyl acetate, the female sex pheromone of the Asian elephant. 

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