DIVE DRY WITH DR. BILL #791: SEX CHANGE... NO THANKS
No, I'm not announcing that I'm going to undergo one. I'm quite happy being a male and only wish there were more females who would be happy with me. Or even a mermaid that would succumb to my charms! However, there are some interesting sex changes occuring out there in Mother Ocean. I'm not talking about sequential hermaphrodites like the California sheephead that begin as girls but turn into men later in life.
A recent study of green sea turtles (Chelonia mydas) in Australia has produced some disturbing results. This research was conducted by a team of marine biologists from NOAA, the California State Universities and the Worldwide Fund for Nature Australia. They investigated two populations of the turtles on the Great Barrier Reef in Australia, one in the northern portion and one in the southern region of the GBR.
The gender of sea turtles is affected by the temperature at which the eggs are incubated in the sand nests. This is known as temperature-dependent sex determination (TSD). In this species, eggs incubated at temperatures below about 82° F become males and those developing in temperatures above about 88° F become females. The temperature difference between the northern (warmer) and southern (cooler) GBR regions is significant in determining the sex ratio in green turtle populations.
The researchers, led by Michael P. Jensen and Camryn D. Allen, found striking differences in the sex ratios of the two populations. In the cooler southern GBR, females made up a somewhat higher proportion (65-69%) of the population while in the warmer northern GBR females almost totally dominated at 99% in hatchlings. Even the adults showed an 87% dominance of females, indicating this has been going on for more than one generation. It only takes a difference of a few degrees in ambient temperature to cause such shifts.
A major concern of these researchers is the impact global warming may have in future generations. Yes, global warming is a FACT. And for those who don't believe that, may I emphasize that the Earth is NOT flat! Of course what it will cause is still open to speculation. We have models that predict Planet Ocean will be 2.6° C (about 4.7° F) warmer by 2100 AD. I emphasize that these are models and the predictions they forecast may not be 100% accurate. However, it is a well documented FACT that global temperatures are increasing over modern time and if that continues, it could bring about serious problems for species like the green sea turtle.
Increasing temperature affects turtle eggs in two important ways. I have already outlined the way increasing temperature can shift the sex ratio toward the female end of a population. Another serious impact is that higher temperatures also increase egg mortality. Thus, if the temperatures in this region continue to increase, fewer turtles will survive the egg stage and more of them will be female.
Now in my biology classes years ago, I often pointed out that it usually takes "two to tangle" and thereby procreate. In populations where individuals pair off and are essentially monogamous, a sex ratio of about 1:1 male-to-female is important unless you want to leave some behind. In sea turtles, males are often polygynous and mate with several different females so a lower number of males might not be as important a factor. However, when ladies comprise 99% of the population, the 1% of males would probably succumb to extreme exhaustion.
Males from a population tend to mate close to the beaches where they hatched. Therefore males from the southern population are unlikely to venture "way up north" to mate with the abundance of ladies there. In addition, due to this site fidelity to their original beaches, turtles are less likely to colonize new, cooler areas where their sex ratios may become more balanced.
Those who believe in evolution (yes, its a theory but with plenty of supporting evidence) might suggest that it will take care of this problem. However, the rate of global temperature change is fairly rapid compared to geologic time and turtle evolution is a slow process given that these turtles aren't sexually mature until about 25 years old. This makes it unlikely they will adapt evolutionarily given the rate of temperature change. This species is also threatened and this will most likely make their status even worse.
Back in 2001 I dove the GBR out of Cairns, Australia. I was able to hover in the waters of Norman Reef and watch from a "distance" of two feet as a green sea turtle chowed down on marine algae. That experience led to my getting my first underwater video rig when I returned to Catalina. It would be a real shame if future generations were not able to experience such events.
© 2018 Dr. Bill Bushing. For the entire archived set of nearly 800 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Green sea turtles.
No, I'm not announcing that I'm going to undergo one. I'm quite happy being a male and only wish there were more females who would be happy with me. Or even a mermaid that would succumb to my charms! However, there are some interesting sex changes occuring out there in Mother Ocean. I'm not talking about sequential hermaphrodites like the California sheephead that begin as girls but turn into men later in life.
A recent study of green sea turtles (Chelonia mydas) in Australia has produced some disturbing results. This research was conducted by a team of marine biologists from NOAA, the California State Universities and the Worldwide Fund for Nature Australia. They investigated two populations of the turtles on the Great Barrier Reef in Australia, one in the northern portion and one in the southern region of the GBR.
The gender of sea turtles is affected by the temperature at which the eggs are incubated in the sand nests. This is known as temperature-dependent sex determination (TSD). In this species, eggs incubated at temperatures below about 82° F become males and those developing in temperatures above about 88° F become females. The temperature difference between the northern (warmer) and southern (cooler) GBR regions is significant in determining the sex ratio in green turtle populations.
The researchers, led by Michael P. Jensen and Camryn D. Allen, found striking differences in the sex ratios of the two populations. In the cooler southern GBR, females made up a somewhat higher proportion (65-69%) of the population while in the warmer northern GBR females almost totally dominated at 99% in hatchlings. Even the adults showed an 87% dominance of females, indicating this has been going on for more than one generation. It only takes a difference of a few degrees in ambient temperature to cause such shifts.
A major concern of these researchers is the impact global warming may have in future generations. Yes, global warming is a FACT. And for those who don't believe that, may I emphasize that the Earth is NOT flat! Of course what it will cause is still open to speculation. We have models that predict Planet Ocean will be 2.6° C (about 4.7° F) warmer by 2100 AD. I emphasize that these are models and the predictions they forecast may not be 100% accurate. However, it is a well documented FACT that global temperatures are increasing over modern time and if that continues, it could bring about serious problems for species like the green sea turtle.
Increasing temperature affects turtle eggs in two important ways. I have already outlined the way increasing temperature can shift the sex ratio toward the female end of a population. Another serious impact is that higher temperatures also increase egg mortality. Thus, if the temperatures in this region continue to increase, fewer turtles will survive the egg stage and more of them will be female.
Now in my biology classes years ago, I often pointed out that it usually takes "two to tangle" and thereby procreate. In populations where individuals pair off and are essentially monogamous, a sex ratio of about 1:1 male-to-female is important unless you want to leave some behind. In sea turtles, males are often polygynous and mate with several different females so a lower number of males might not be as important a factor. However, when ladies comprise 99% of the population, the 1% of males would probably succumb to extreme exhaustion.
Males from a population tend to mate close to the beaches where they hatched. Therefore males from the southern population are unlikely to venture "way up north" to mate with the abundance of ladies there. In addition, due to this site fidelity to their original beaches, turtles are less likely to colonize new, cooler areas where their sex ratios may become more balanced.
Those who believe in evolution (yes, its a theory but with plenty of supporting evidence) might suggest that it will take care of this problem. However, the rate of global temperature change is fairly rapid compared to geologic time and turtle evolution is a slow process given that these turtles aren't sexually mature until about 25 years old. This makes it unlikely they will adapt evolutionarily given the rate of temperature change. This species is also threatened and this will most likely make their status even worse.
Back in 2001 I dove the GBR out of Cairns, Australia. I was able to hover in the waters of Norman Reef and watch from a "distance" of two feet as a green sea turtle chowed down on marine algae. That experience led to my getting my first underwater video rig when I returned to Catalina. It would be a real shame if future generations were not able to experience such events.
© 2018 Dr. Bill Bushing. For the entire archived set of nearly 800 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Green sea turtles.
