Mother Nature is Weird… Kalutas

Male Kalutas, a small mammal, dies shortly after mating. Article might be behind a paywall.

One to two months before the onset of the mating season, male kalutas stop producing sperm and start producing large amounts of testosterone and corticosteroids. Although this influx of hormones drives them to mate, it also suppresses their immune system and puts immense stress on their internal organs.
“The precise cause of death is usually ulceration of the gut track,” Dr. Dickman said. “They’ll be leaking blood into their body and begin to suffer organ collapse.”

New York Times, These Marsupials Go Out With a Bang, Annie Roth, Aug 28, 2019

Kalutas, which reach sexual maturity at just 10 months, have only one two-week window in early September during which resources in their environment are abundant enough to support reproduction. During these brief, frenzied breeding seasons, male kalutas mate with several females — for up to 14 hours at a time — until they succumb to exhaustion and die.

New York Times, These Marsupials Go Out With a Bang, Annie Roth, Aug 28, 2019