KempsRidleySeaTurtle_ClimateChange_Owens_David_CharlestonSC_12April2021_Reel4051.mp3

David Owens [00:00:00] We realized that sea turtles have this really strange reproductive system where temperature of the incubation nest determines which sex it's going to be. Now a lot of other turtles do. All crocodiles do this kind of thing too.

David Owens [00:00:14] But this was a stunner because we were, as biologists, we were so used to the whole X/Y chromosome thing, like, like people and animals have, that we never guessed there could be any other system. And so I was actually the first one to write this down in a paper and got a lot of attention from various people who thought I was crazy. But lo and behold, other people did some really good research and proved that it's true.

David Owens [00:00:37] And so here's the issue, bringing it up to modern time: the beaches are actually getting warmer. All the beaches around the world, for the most part, are getting warmer.

David Owens [00:00:49] And so, for example, right now in Florida and even in Rancho Nuevo, we know this is true in Rancho Nuevo. In Florida, 90 to 95 percent of the baby turtles coming off Florida beaches are female. That's now. OK?

David Owens [00:01:05] We think that as global climate change happens, that is warming, becomes more and more common over the years, that beach temperature will continue to rise, and continue to produce more and more females.

David Owens [00:01:20] Initially, you'd say, "Oh, my God, more females. That's good." We want more eggs, more females.

David Owens [00:01:24] But the bad news is these guys are sexually reproducing animals and so they need males to provide the sperm to produce fertilization.

David Owens [00:01:34] And not only that, but there's a, there's an evolutionary argument that's pretty powerful that I'm not very good at making. But if you have, if you want an animal to change and adapt to climate change over time, you want that animal to have a lot of variability. Variability is the secret for lots of long-term evolutionary development of animals.

David Owens [00:01:54] And so if you don't have males providing any variation - one male mates with 20 females, that's good. They all may be successful, but that means that a number of new genes come into that gene pool is much reduced, over what it could have been, or should have been, historically. But anyway, those kinds of arguments are being used today for the issue of climate change and what's going on with sea turtle reproduction and so on.

David Owens [00:02:24] And there's one other. I may as well throw this in. One other thing we've done some research on ourselves, is, OK, we, we did studies where we looked at what the sex ratios of juveniles were in the ocean. You go out in the ocean with a trawler, and you capture a 100-pound loggerhead. A 100-pound loggerhead, it's a teenager. It's a long way from being sexually mature. And you can't tell much about what sex it is. But if you look inside of it with laparascopy or measure hormone levels, you can tell which sex it is.

David Owens [00:02:51] And we were finding about 60 percent female, maybe 70 percent female, which this shocked everbody. And so it turns out you've got a beach producing 95 percent female, and yet the juveniles are only 60 percent female.

David Owens [00:03:07] The question is, what happened to the other 20 or 30 percent of the girls that were produced? It turns out that when the temperature is really warm in the nest, the development is screwed up. They do not develop. They use their yolk sac more rapidly. They have more abnormalities. They are very weak.

David Owens [00:03:28] We did an experiment where we, we put the turtles - if you turn a turtle on its back, it flips over. Almost all turtles have this. It's called the righting response (R-I-G-H-T), righting response. And if you do this experiment with turtles that have been incubated, say, let's say, for example, 31 degrees compared to turtles incubated at 29 degrees. The 29-degree turtles are much faster at flipping over. Sometimes, the 31-degree centigrade turtles can't even flip over, they're so weak and so lethargic.

David Owens [00:04:01] And so you can imagine all these girl turtles in, off the coast of, of Florida, trudging down the beach much slower than the males produced at cooler temperatures. And yet there's just so many of them, they're still overwhelming the population, but they're very weak.

David Owens [00:04:18] So they're, I call them, I call them, "natural turtle fish lures", because along the coast of Florida, man, the dolphin fish, mahi mahi, they cruise and they eat them by the hundreds and I think a little female turtle is going to be much less successful.

David Owens [00:04:38] So here's another reason why temperature may be a long-term problem for the success of sea turtles. Even though the numbers are coming back, they may not be very successful in repopulating the population.