Phylogeny

Evolution of Musth and Chemical Signals

Elephants have their origin in Africa, with the earliest ancestral skeletons dating back 7 million years (Rasmussen, L. E. L. 1999). By the early Pliocene era, the ancestors of elephants had differentiated into the gereras Mammuthus, Elephas, and Loxodonta (the generas containing mammoths, Asian elephants, and African elephants, respectively). Elephas and Mammuthus slowly migrated out of Africa and into Europe and Asia.

Mating cycles for ancient elephants were likely more synchronized, with females coordinating their oestrus cycles with peak male reproductive activity (Rasmussen, L. E. L. 1999). The males likely underwent rut, which differs from musth in that it’s synchronized between males, and represents the only breeding period for males of a species (Wingate).

It has been suggested that male and female ungulates sharing the same range may benefit from sexual segregation, which produces different feeding patterns, and thus reduces food competition (Haynes 76). Low species density, and clumped distribution in response to limited resources may have favored the development of ‘sire’ bulls who seek out mates more actively than other males.

 As group organization gradually shifted away from large herds to small, female-dominated family units, mechanisms had to evolve to allow communication between females and solitary males (Rasmussen, L. E. L 1999). Female-to-male signaling was initially likely of the highest priority, allowing solitary males to know when a particular female was receptive. Female-to-female signaling within family groups was also likely important.

Climate change forced Elephas maximas, the Asian elephant, into Southeast Asia, subjecting them to different environmental factors (Rasmussen, L. E. L. 1999). In addition to new chemical processes brought on by their changing diets, the more tropical climes today’s elephants inhabit resulted in larger ears, thicker skin, and the loss of fur.

With the loss of their fur came the loss of the ability to use the sebaceous glands to pass on chemical signals (Rasmussen, L. E. L 1999). Paleolithic engravings suggest that mammoths had much larger temporal glands than modern elephants. The temporal gland was likely used for signaling for males and females, as it is in African elephants. The reduced temporal gland in elephants resulted in a shift to urine as a primary medium for chemical communication, initially by females, then by males in musth.

As E.maximas moved into warmer, shadier climates, new chemical signals were created (Rasmussen, L. E. L 1999). They no longer required durable molecules like proteins and lipids to act as signals. In such warm, humid climates more volatile compounds could act as signals, with proteins and lipids acting as carriers.

As the reproductive systems of females fell out of sync, males did not all have to compete at once (Rasmussen, L. E. L, 1999). As a result, asynchronous musth periods could develop. Now, though competition for mating was less fierce, males had to develop methods of communicating their musth stage to other males, in order to assess a challenger’s willingness to fight. Temporal gland secretions became an important messenger, in addition to urine. Female selectivity for dominant males may have created pressure for younger males to go into rut out of synch with older males (Schulte 2001).