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Baby alligators: Adorable, deadly, or endangered? You decide.

Yeah, I know, yet another post about baby alligators . . . can’t we find anything else to write about around here?

Lizzie points us to this tabloid news article which she files under the heading, “why we need priors in climate change biology”:

Why baby alligators in some spots could be 98% female by century’s end . . .

Rising global temperatures could shift the balance between males and females in crocodile and alligator populations, potentially leading to a sharp decline in the reptiles’ reproduction rates. . . .

Between 2010 and 2018, Samantha Bock at the University of Georgia in Athens and her colleagues measured the temperature of 86 nests made by American alligators (Alligator mississippiensis) in Florida and South Carolina. The researchers also collected data on daily air temperatures at these sites and found that average nest temperatures were higher during warmer years.

Using estimates of future climate change, the researchers predicted that, if global temperature continues to rise unabated, sex ratios at both sites will become highly male-skewed by the middle of this century. But, by 2100, higher nest temperatures could produce up to 98% females.

I asked Lizzie: Can the alligators adapt in some way or are they doomed?

She replied:

Doomed! According to folks in my field, who have no model they won’t extrapolate and are happy to ignore the climate variation alligators cope with today … and have over, say, their 37 million years or so on earth (including my favorite period, the Younger Dryas, potential source of Nordic myths).

The article on the Younger Dryas, by W. H. Berger, begins:

According to Nordic myth, the modem world begins when Odin slays Ymir, the Ice Giant. Ymir’s offspring drown in his blood, but two survive and start a new race of frost giants. Lodged in Utgard, they pose a constant threat. Only Odin’s son Thor, brandishing Mjollnir, the magic hammer, keeps them in check. The pronounced and abrupt changes in climate during the Glacial-Holocene transition suggest that the luck of battle switched sides frequently before Odin and Thor won over Ymir and his kin.

But enough about the Younger Dryas. Back to the alligators.

The research article in question, “Spatial and temporal variation in nest temperatures forecasts sex ratio skews in a crocodilian with environmental sex determination,” is here. If I read that paper right, they didn’t actually collect data on the sexes of their baby alligators.

I asked Lizzie, who replied:

I think you’re right. They just cite a 1994 paper to extrapolate sexes from next temperature, the paper has data on 20 nests and ends with “[t]herefore, we suggest that information on hatchling sex ratios be obtained by directly sexing hatchlings as opposed to relying solely on predictions based on nest temperatures. Monitoring of nest temperatures is useful for management and natural history reasons.”

I don’t think alligator biologists will much care about my opinion (I am not an expert at all) but it is an interesting example of jumping through so much uncertainty in estimates to end up at some extreme predictions. There are lots of bad consequences of climate change, and this could be one of them, I am just not convinced by this study.

When it comes to baby alligators, I’m still not sure whether to say Awwwww or Aaaaaa! The baby gators in this news report are pretty cute. It also says, “The American alligator teetered on the brink of extinction in the 1980s.” I had no idea.

32 Comments

  1. jim says:

    I bet the alligators would love those cats!

  2. John Williams says:

    I have just skimmed the alligator paper and won’t try to defend their statistical methods, but the underlying question whether alligators are particularly sensitive to climate change because of the effect of incubation temperature on their sex has been around for a long time, and not just among alligator biologists (I’m a geographer), so I don’t fault them for exploring it. Generally, the discussion section of the paper seems pretty reasonable, and there is more than the 1994 paper to go on (see e.g., their reference 18). Lizzie is of course correct that alligators have been around for a long time and have seen climate change before, but the rate of change matters.

    • Andrew says:

      John:

      Yes, it’s hard to know. I guess the next step is to do some experimentation and observation and see if the alligators can adapt their sex ratio to the changing conditions.

    • Joshua says:

      John –

      I had a similar reaction. I had written the following but didn’t post it out of concern for seeming like a gadfly:

      Andrew –

      To be clear, I’m not defending your critique of methodology, or diminishing the importance of examining the larger issues in play about how science is conducted. However:

      > I asked Lizzie: Can the alligators adapt in some way or are they doomed?

      Perusing the paper, they describe a huge range of potential impact on sex skew in association with temperature rise. They also talk, specifically, about mechanisms by which the alligators “can adapt” (a bit too teleological for my taste) their reproduction in response.

      Yes, the authors should me more careful about how their work might be interpreted – particularly in the pop/sci media – but I do think that the paper should be viewed in full context and that people should be careful about something I’ll call “science quote mining.” For example, it seems that the authors kind of toggle between using “prediction” and “projection” and also use a fair amount of conditional language – and maybe the should be more careful to be more conditional more consistently…however, at the end of the abstract there is an important conditional “potential”:

      > By revealing the ecological drivers of nest temperature variation in the American alligator, this study provides important insights into the potential consequences of climate change for crocodilian species, many of which are already threatened by extinction.

    • Daniel Weissman says:

      Yes, as far as I can tell, Lizzie’s description of the underlying data is really unfair. Check out Figure 2a of reference 18 — looks like there have been many more than 20 *studies* that measured alligator hatchling sex at defined temperatures. I don’t see any major problem with the stats here, and as John says, they have a reasonable discussion of the prospects for adaptation.

    • confused says:

      Rate of change is important. One thing I’d like to see more discussion of is what was going on in terms of temperature change over “short” (a few centuries) time periods during previous interglacials. I’ve seen it claimed that the Eemian interglacial had a much less stable climate than the Holocene (before the last couple of centuries anyway), but not much real quantification of that.

      I would have to think crocodilians would be pretty low-risk for something like this, given that they are SO old that they have survived really dramatic crises before (there were alligators more or less like today’s, though not the exact species, around during the end-Cretaceous extinction – surely the century right after the impact had some pretty dramatic temperature swings) but that’s not necessarily particularly informative: frogs are a very old group too and they seem to be having major trouble.

  3. John Williams says:

    Andrew,
    The discussion section in the paper talks about this, as in the paragraph pasted in below. My point is that the paper isn’t as wacko as your post makes it out to be.

    “The observed lack of maternal compensation for changes in environmental conditions could result from other ecological constraints and conflicting selective pressures on nesting behaviour. Nest sites promoting embryonic viability, reducing predation pressure and residing in proximity to suitable juvenile habitat may take precedence over sites conferring favourable sex ratios [26,60,61]. In a study of maternal nesting behaviour across a latitudinal gradient in Chrysemys picta, variation in nest-site choice suggested that selection for embryonic survival outweighs sex ratio selection [59]. Similarly, Alligator mississippiensis embryos face multiple threats to survival including nest predators [62,63] and extreme environmental conditions (inundation and desiccation) [64]; and maternal nesting behaviours aimed at counteracting these threats are probably under strong positive selection. Further work to uncover the ecological drivers and constraints on alligator nesting behaviour would inform predictions regarding the compensatory capacity of this species to respond to a rapid environmental change.”

  4. confused says:

    This is one thing that I really wish was clearer in climate change popular news/public discussion (as opposed, I think, to actual scientific papers and professional reports like IPCC).

    The basic physics of more greenhouse gases = more infrared absorption = higher temperatures (planetary energy balance stuff) is really well established and hard to reasonably doubt.

    *Specific* predictions of how higher temperatures will affect any particular local ecosystem, species, or aspect of human life/civilization involve a lot more uncertainty. Some predictions can be made pretty confidently, but even there, there is an unfortunate disconnect between the science and the news (IE – as I understand it, it’s pretty clear that warmer oceans will mean more/worse hurricanes *overall*, averaged over many years, but I’ve seen far too much argument about whether one *particular* storm or bad season was “because of global warming”, or whether a mild season “disproves” it.)

    • Martha (Smith) says:

      Good points.

    • Anonymous says:

      “it’s pretty clear that warmer oceans will mean more/worse hurricanes”

      Is it? I’ve always wondered about this:

      I’m not a weather dude but the intensity of many processes in nature depends much less on the amount of energy available (i.e, absolute temp) than it does on the gradient that drives the process – for hurricanes correct me if I’m wrong but it would depend on the temp gradient between water and air, which determines how much the air warms and thus how fast it rises and thus the speed of the wind generated by the cyclone. If both air and ocean are warmer but the average gradient remains the same, it’s not clear to me how you get a more intense hurricane.

      Same with more intense rainfall. Yes, warmer air holds more water, but storm intensity is driven by the contrasting temps of air masses. So again if both air masses equally warmer, I’m not clear on how you get a more intense storm and increasing rainfall intensity.

      I’m pretty sure if you don’t sort this out for me someone else will…Phil?

      • confused says:

        >>Is it?

        Well, maybe I am just accepting what I’ve read without checking it sufficiently :)

        I think the increase in rainfall makes sense, though, since the warmer ocean surface will mean more evaporation, thus more water vapor in the atmosphere. And the things I was primarily thinking about were referring more to rainfall intensity of the hurricanes — these were studies that have come out in the last few years after the mega-flooding of Texas by Hurricane Harvey: that was a category 4 hurricane, but the damage was overwhelmingly done by flooding rather than winds, and largely rainfall-induced flooding rather than storm surge, which is traditionally the worst part of a hurricane, at least along the very flat Texas coast.

        There may also be a difference between what happens in the next few centuries, while things are changing, vs. what happens after the world settles into a new, stable warmer state.*

        *If that actually ever happens. I think it’s more likely that during the 2nd half of this century, maybe even sooner, humanity will do geoengineering measures to remove CO2 from the atmosphere.

        • Anonymous says:

          “maybe I am just accepting what I’ve read without checking it sufficiently :)”

          I don’t know about that but this is something I’ve always been curious about.

          “the warmer ocean surface will mean more evaporation”

          but if air is warmer and thus already holding more water – it’s going to equilibrate as the atmosphere warms, right? – why would there be more evaporation?

          Your note about a period of change followed by stability is interesting. I’ve thought about that too. I guess more rapid warming would create more disruption during warming…

          • confused says:

            >>but if air is warmer and thus already holding more water – it’s going to equilibrate as the atmosphere warms, right? – why would there be more evaporation?

            Well, warm air isn’t necessarily already holding more water. You can have warm air at 0% humidity.

            Beyond that, I’m just not informed enough to say.

            >>Your note about a period of change followed by stability is interesting. I’ve thought about that too. I guess more rapid warming would create more disruption during warming…

            Right. In my opinion, it’s the rate of change that makes this a problem.

            We know the Earth’s ecosystem can be stable and biologically rich at very warm temperatures, since it was for much of the Mesozoic and for the first half of the Cenozoic.

            I doubt we will continue using fossil fuels on a large scale long enough to reach, say, 1000 ppm CO2; and I believe it was higher than that during the Cretaceous.

            I doubt a Cretaceous climate, in and of itself, would present much of a problem for our civilization (some tropical areas might be uninhabitably hot, and many coastal areas would be flooded; but many cold areas that are now practically uninhabited would become quite livable).

            The problem is the speed of transition. If the climate zones move too fast, plant communities can’t keep up, and animal communities dependent on them would die off. Billions of people live at low elevations; moving them all to higher ground, even over a century or so, would be very hard.

            Even a slow transition would lead to some extinctions (mountaintop endemics, ice-dependent Arctic species, etc.), but if it happened over geological time, new species would evolve as well, so biodiversity overall might not be harmed.

  5. confused says:

    >>“The American alligator teetered on the brink of extinction in the 1980s.” I had no idea.

    Yeah, they were badly overhunted at one point.

    However, that statement is probably not exactly accurate. The point when they were really at risk was somewhat earlier, more like the 50s and 60s; they were *removed* from the endangered species list in 1987, so they were recovering during the 80s – and given ‘lag time’ for official decisions like de-listing a species, they may have been in pretty good shape for the 80s overall.

    A lot of species that are pretty common now were badly overhunted at one time – white-tailed deer and egrets at the beginning of the 20th century; wild turkeys in the mid-20th century.

  6. RoyT says:

    If there is one animal species that isn’t concerned about climate changes, it’s the alligator. Haven’t they been around in some form for over 200 million years?? Loss of habitat would be the chief worry for them. Climate change? Way down the list.

  7. Lizzie says:

    Those are some cute cats!

    I am perhaps more of a stickler for what I think is science that’s useful enough to be worth doing. I agree this is a fascinating question (and I could totally be wrong on how old alligator species are — I didn’t check the phylogenies, my point was old enough to have experienced a lot of climate variation), but the work required skipping over a lot of uncertainty to get the estimates — to a point where I am not sure those estimates are useful.

    It’s easy today to find a way to come up with a really bad and shocking potential consequence of climate change by combining climate projections with some other ecological data (and to be clear: I am really worried about the bad consequences underway given habitat loss and fragmentation, plus hunting, plus climate change), even if the answers have hidden massive uncertainty and don’t seem that believable. These studies get published and Nature picks them up, but I don’t think they’re very useful (I am not even sure they’re useful for getting the public to care about alligators or climate change at this point, because we publish so many of them and they’re so weak). It’s much harder to me to do the work to come up with useful estimates.

    Side note:
    – I didn’t check reference 18 but my sense is we have lots of lab studies on temperature and far fewer on sex ratios nest temperature in the wild.
    – The rate of change is important, that is partly why I mentioned the Younger Dryas (I am sad there wasn’t more interest in how that might relate to Norse myths).

    • confused says:

      The Younger Dryas/Norse myth connection is definitely interesting.

      If there’s a connection, though, I always thought it was perhaps to the melting of glaciers at the end of the last glacial period – Ymir, the ice-giant, is killed, there is a great flood, and his blood ultimately becomes the oceans.

      The world being made of the body of a primeval monster/deity is a widespread trope – in Aztec mythology the world is made from the monster/deity Cipactli or Tlaltecuhtli, in Mesopotamian mythology from Tiamat the primeval sea-deity and mother of monsters, etc.

      And the great deluge myth is practically universal, and a “war in heaven” is also pretty widespread. I think the Younger Dryas cooling wasn’t worldwide, but the rise of sea levels would have affected all continents.

      Anything like this is probably unprovable, though…

  8. zbicyclist says:

    “If I read that paper right, they didn’t actually collect data on the sexes of their baby alligators.”

    What? No first year grad students around to learn alligator sexing?

    So how is this done, anyway? Curious, I found the answer at https://animals.mom.me/how-to-tell-the-sex-of-an-alligator-12548249.html

    Easiest when they are young:

    “Flip the baby alligator upside down and examine the “vent,” which is located between the lower legs. Lightly press down on either side of the vent to expose the reproductive organs of the baby alligator. If the alligator is a male, a penis will emerge. If the alligator is female, there will be no penis but a small dot that is the clitoris.

    Warnings
    When holding baby alligators, hold the head away from your fingers to prevent any accidents.”

    A bit harder when they are older:

    “Roll an adult alligator on its back and have two or three people hold it down, depending on how large the alligator is. Place a few drops of oil on the “vent” area between the lower legs and spread the vent using your forceps. If a penis emerges from the vent, the alligator is male. If a clitoris pops out of the vent, the alligator is a female.”

  9. John Williams says:

    As far as I can tell, the new information in the paper has to do with temperatures in alligator nests and their relationship to weather station temperatures; the part about the effects of global warming on alligator sex ratios explains why this is of any interest, but is also hype of the sort that is now rewarded, as shown by the commentary. The relationship between nest temperature and weather station temperature is not obvious, so there is some substance to the paper, which makes it better than some applied ecology papers that have gotten prominent attention recently.

    On the extinction question, there is a scale issue. Obviously, some crocodillians survived the Cretaceous extinction, but we don’t know how many species or genera didn’t. We know that some dinosaurs survived (birds), but the ones little kids know the names of didn’t. Getting more personal about it, most of my work over the last 30 years has dealt with Pacific salmon. Climate change is shrinking the range and abundance of Pacific salmon more or less drastically, depending on the species. Probably the various species will survive, but the river not far from my house is on the verge of losing a species, coho, and probably won’t get it back until the next ice age. I think this matters.

  10. steven t johnson says:

    I’m so far behind I haven’t figured out how more female alligators leads to a population decline, instead of a population boom.

    • jim says:

      Excellent point / question.

      “Crocodilians are generally polygynous, and individual males try to mate with as many females as they can.[93] Monogamous pairings have been recorded in American alligators.[94]” wikipedia

      One “study shows that at least 70 percent of female alligators chose to mate with the same alligator time and time again, over a period of many years. However, there are still many male alligators out there that will mate several females at once.” (random nature blog)

      So it appears that male gators are two-, three- and possibly even four-timing womanizers, cavorting around the swamp in a wild reproducing frenzie while the poor ladies are stuck being housewives and mothers. Shameful.

    • Carlos Ungil says:

      > sex ratios at both sites will become highly male-skewed by the middle of this century. But, by 2100, higher nest temperatures could produce up to 98% females.

      We just need to accelerate global warming, so the period of decline due to female scarcity and frustrated males doesn’t last long and we quickly proceed to the next phase of female abundance and happy males.

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