快猫短视频

Male elephant seals with the largest harems end up dying younger than those with fewer females.

Elephant seal harems consist of anywhere from five to 50 females associated with one dominant male. Subordinate males sometimes creep along the edges of the beach attempting to mate with some of the females.

Dominant males have to defend the females and their pups, as well as the beach they live on, from rivals, which can wear them down. They can also incur serious injuries during fights with other males. And because they stay on land throughout the breeding season, the 5-tonne marine mammals don鈥檛 eat for three months while expending significant energy patrolling their beaches and mating with all the females in their group.

As such, male elephant seals reproduce using an 鈥渋nvest now, pay later鈥� strategy, says at the University of Pretoria in South Africa.

鈥淭hese breeding seasons are quite chaotic,鈥� he says. 鈥淭here鈥檚 lots happening; the beaches are so busy, and the males are working hard. There鈥檚 a big cost to breeding, and males with larger harems have lower subsequent survival.鈥�

Lloyd was helping to tag and count southern elephant seals (Mirounga leonina) at Marion Island in the sub-Antarctic Indian Ocean as part of the university鈥檚 marine mammal conservation programme when he realised that some of the males 鈥� especially those with the most females 鈥� were clearly losing weight and body condition over the breeding season.

Curious whether the challenges of defending large numbers of females might be affecting the males鈥� health, Lloyd and his colleagues decided to investigate. They examined 34 years鈥� worth of records about the Marion Island elephant seal population, based on annual tagging and counting campaigns, including the life histories of 324 breeding males.

They found that dominant males usually survive to an age of 8 to 10 years, and that they died younger when their harems were bigger, Lloyd says. That was particularly true for males that had their first harem at a younger age 鈥� starting at about 5 years old. By contrast, females generally live at least 20 years.

If the males continued to have large harems year after year, they might father up to 200 pups, but their chance of survival was lower and lower each year. 鈥淭hat cost just got worse and worse,鈥� says Lloyd. But in evolutionary terms, that cost is worth paying, because these males have already passed on their genetic material, he says.

Subordinate males without a harem had even lower survival rates than dominant males 鈥� probably because they have lower quality genes to start with, says Lloyd.