Dr Stefan Lpold, from Syracuse University in New York, said: "It is quite costly to invest in everything. You don't get something for nothing in evolution, so we wanted to see which species invested in weapons over testes.
"Some of these species invest in both, and that is a bit of a mystery. We will now look at whether maximising investment in sexual traits means you pay the price in some other aspect of life."
Pheasants, minnows, and bush crickets invested in both weapons and testes, while pinnipeds, such as elephant seals where males are almost five times the size of females, and acanthocephalan (a type of worms) invested more in weaponry but not testes.
Other examples of males investing in weaponry are antlers in red deer, horns in dung beetles, spurs in pheasants and canine teeth in primates.
Dr Lpold added: "Understanding the ways animals reproduce is important as it helps us understand how species evolve and can prove important for conservation."
|Contact: Alison Barbuti|
University of Manchester