There are only a few things in this life animals really have to do. They have to eat, they have to crap, and they have to bang. So when conservation biologists transplant a bunch of wild animals in order to save them, but half of them stop getting laid as a result, it's cause for concern.
A desert tortoise. Image: Andrew Walde
That's the issue scientists are now grappling with in the Mojave Desert. In 2008, 570 threatened desert tortoises were translocated -- moved from their homes at the Fort Irwin Army National Training Center to a different tortoise-filled neighbourhood a few kilometres south, to make way for expansion of the base's desert warfare practice areas.
Years later, a genetic analysis has revealed something alarming: The translocated male tortoises aren't banging. Or at least, they aren't having babies. The implications go beyond tortoise-kind, raising concerns about the hidden risks of translocation, a popular conservation strategy.
Well, OK, maybe these tortoises are banging. Image: Andrew Walde.
"A big take home is that mitigation isn't always what it seems to be," Robert Fleischer, head of the Center for Conservation Genomics at the Smithsonian Conservation Biology Institute, told Gizmodo. "In the case of the female [tortoises], it's a success, but the males aren't reproducing, at least after four years. It looks like they're duds."
The researchers reached that conclusion through a massive genotyping analysis, examining the DNA of hundreds of translocated tortoises, plus hundreds more tortoises living in the area the newcomers were moved to. During an egg laying season four years later, biologists returned to collect blood samples from hatchlings for maternity and paternity testing. Of 92 baby tortoises genotyped, not a single one appeared to be sired by a translocated male. Translocated females, meanwhile, were popping out babies at roughly the same rate as the local ladies.
"Every single offspring we were able to identify was ID'd to a resident male," Fleischer said. "We can't say [the translocated males] didn't father any, but it's very likely" they did not.
Translocation is an increasingly popular conservation strategy, used to move vulnerable populations out of harm's way, or to boost a species' genetic vigour by mixing genes between isolated groups. But it's also known to carry risks, including increased stress and mortality, increased conflict with humans or livestock, impacts on resident wild animals, or the unintentional spread of disease, according to a 2008 review paper. A study published in 2015 indicated that translocation can be particularly stressful for animals with an established social hierarchy, according to a Nature blog post.
To the authors' knowledge, their results published in Biological Conservation are the first time genetic paternity testing has revealed a fertility problem with males following translocation. The study points to yet another potential factor conservation biologists need to consider before moving populations of vulnerable animals around.
Two male desert tortoises fighting near the United States Army's Fort Irwin Army National Training Center. Image: Joel Strong
In the case of the desert tortoises, it's anybody's guess why the males have lost their spark. "We're guessing either the trauma of being moved affects males more than females, or the males in the new territory are subordinate to the males already there," Fleischer said. "We don't really know."
Brian Horne, Tortoise and Freshwater Turtle Coordinator at the Wildlife Conservation Society, called the study "incredibly important", saying that it "opens up a large amount of area for new study".
"I think it has very broad implications," Horne told Gizmodo. "I think it's surprising that so many previous conservation programs based on the assumption that there was equal probability of mating between males and females never really tested [that] assumption."
It's important to note that this single study only tells us about desert tortoise translocations, and right now, there are more questions than answers. Fleischer would like to return to the field and see whether any of the translocated males have, over time, managed to turn their rotten reproductive luck around. A follow-up study would require additional funding, and if you're wondering what US government agency has made understanding the sex lives of desert tortoises a priority, you may be surprised to learn it's the Department of Defence.
Now, I don't think any of us would mind if a bit of that $US54 billion ($72.5 billion) US defence spending boost went toward making sure the tortoises are still banging.