Smart males ration sperm to maximise offspring

London, July 10 (Inditop.com) Attractive males release fewer sperm per mating to maximise their chances of producing offspring across a range of females, according to a new study.

The findings by researchers at UCL (University College London) and the University of Oxford suggest that, paradoxically, mating with attractive males may be less fertile than those with unattractive ones.

The team mathematically modelled a range of male ejaculation strategies to look for the optimum “sperm load” per mating, and how this might vary depending on mating patterns.

Previous studies have shown that domestic fowl, and fish such as the Arctic charr, males with privileged access to females produce ejaculates of lower fertilising quality than subordinate males.

Sam Tazzyman, UCL CoMPLEX (Centre for Mathematics and Physics in the Life Sciences and Experimental Biology), said: “In some species, females mate with many different males.”

“Each male’s sperm competes with that of other males in a process known as ’sperm competition.’ Since males have finite resources to allocate to breeding, they allocate them carefully to each mating to maximize their number of offspring,” Tazzyzman added.

“If a male puts a lot of resources into each mating he will get more offspring per mating, but at the expense of fewer matings. If, on the other hand, a male puts few resources into each mating he will secure less paternity per mating, but will be able to carry out more matings overall. Thus, there is a trade-off between number of matings and success per mating.”

“A possible case can be seen in chickens, which in the wild live in groups of varying numbers of males and females. Females mate with many males, so males are subject to sperm competition,” Tazzyman said.

However, the attractiveness of a male is determined in large part by his social standing. Males higher up the pecking order find it easier to secure matings with the females, but they transfer fewer sperm to females.

The study is slated for publication in the American Naturalist.