Ageing Sperm

[1] Male Houbara Bustard extends his neck feathers
as part of his display
Image credit: Yves Hingrat

For up to 18 hours a day, 6 months of the year, the male Houbara Bustard can be seen performing his impressive dance in the hopes of attracting a female. But new research shows that some males may be reaching their sexual peak too soon, thanks to their high investment in sexual displays. 

The paper published in Ecology Letters has revealed that males with highly energetic displays are experiencing premature ageing of sperm at a much faster rate than their less 'showy' rivals. With the numbers of good quality (motile) sperm produced when mating used as a marker for sexual investment. 

[2] Whilst energetic display levels are maintained 
throughout life (top graph), sperm quality takes a 
serious hit at around 4 years of age in the most
 energetic males (bottom graph).
Image credit: Preston et al. 2011

Analysis of male ejaculations over several years showed that those who invested the most in their displays in early life, had the lowest sperm quality in later years. 

Past the age of 6 sperm numbers dropped dramatically, with high levels of dead or abnormal sperm being produced. But despite this, 'showy' males continued to perform high energy displays year after year, regardless of their decrease in biological fitness. 

Although male reproductive success is only limited by the number of mating's he achieves. Some of the most energetic males, reach their sexual peak at around 4 years of age. Which seems crazy when you consider they can live up to 20 years old! 

However, males who invested most in their sexual displays also produced the highest quality sperm before they 'peaked' at around 4 years of age. Perhaps this would be an advantage if the species was heavily predated. 

Find Out More:

Sexually extravagant male birds age more rapidly, but try to hide it - Science Daily summary
Male Bustard Mating Display - Video quality is not great, but still a fascinating dance display

Sources:

• PRESTON, B. T., SAINT JALME, M., HINGRAT, Y., LACROIX, F. & SORCI, G. 2011. Sexually extravagant males age more rapidly. Ecology Letters, 14, 1017-1024.