In the past few months, due to the ravages of the new crown virus, "social distancing" has become a hot word on the Internet, and not paying attention to maintaining social distancing is equivalent to adding fuel to the spread of the virus. In fact, in nature, shortening social distancing can sometimes have fatal consequences, and we will talk about one of the examples today.
Giant side-necked turtle
The giant side-necked turtle is the largest freshwater turtle in South America and one of the largest of several freshwater turtles in the world, with the largest individuals with a dorsal carapace length of 107 cm and a weight of up to 90 kg. This giant freshwater turtle has a unique collective nesting habit, with hundreds to thousands of adult females often using the same beach to lay their eggs at the same time.
During the breeding season, female giant side-necked turtles migrate long distances from the foraging area to the suitable nesting area, sometimes moving more than 700 kilometers. Once at the nesting site, the females leave the water and bask in the sun on the shore for a few days, raising their body temperature in preparation for the next nesting activities.
Giant side-necked turtles come ashore en masse to nest
<h1 class="pgc-h-decimal" data-index="01" > up to a dozen adult female giant lateral-necked turtles are buried alive during the breeding season</h1>
The Monte Cristo nesting area on the Taparos River in Brazil is one of the main nesting sites for giant side-necked turtles, an important breeding ground that has been under the monitoring and protection of the Brazilian Institute of Environment and Renewable Energy since 1978. Until 2013, the nesting site was only used by the Monte Cristo beach for giant side-necked turtles. In 2014, the institute also protected the andré river beach, the second nesting site in the area, and researchers remove weeds from the river beach every year, with the aim of creating better nesting conditions for female giant side-necked turtles.
Flocks of giant side-necked turtles
It is customary for researchers to review and count the reproduction of giant side-necked turtles along the riverbanks after the end of the nesting season each spring, but between 2013 and 2017, they found a strange, unprecedented phenomenon — more than a dozen female giant side-necked turtles were half-buried or completely buried in the sand, and most of them died.
In 2013, nine female turtles were found buried in the soil on Monte Cristo Beach, all of whom died. A similar example emerged the following year, when the buried female turtle had only one skeleton left, and inside the dorsal carapace a pile of eggs that could never hatch could be seen, apparently buried during the previous year's breeding season. In 2014, researchers also found a buried and dead female turtle on the Andrea River Beach, while no similar phenomenon occurred in the next two years.
By 2017, the nesting season of the year began on September 29 and lasted until November 21, and between October 22 and 29, researchers found female turtles buried in both nesting areas, and it is worth noting that a large number of female turtles have completed nesting activities during these days.
Female turtles were buried in 2017 for measurement
A total of 7 females were buried in the sand during spawning, one of them was completely buried in a vertical position and the rest of the 6 were buried in the soil on the back.
Five of the seven female turtles were found dead, the other two were rescued by the researchers, and after a period of rest and recovery, 2 were released back into the river, but unfortunately one of them died on the Andrea River beach 3 days later, probably because the turtle had been completely buried in the soil before, so it was ultimately unable to recover from the damage.
Female turtles nest
The buried female turtles have a straight line length of 50 cm to 71.5 cm and weigh 11.9 to 33.8 kg. The only surviving female turtle, whose nest was not found, may have been buried before laying eggs, and the female turtle that died 3 days later, a total of 41 turtle eggs were found in the fallopian tubes, combined with its buried posture, it should have been buried in the soil when digging a hole to build a nest. Eggs were also found in the bodies of three other females, suggesting that they died before they built their nests. As for the remaining 2 dead female turtles, the researchers were unable to find the location of their nests or examine their eggs.
At the same time, it should be noted that there are a large number of nests near the site where these female turtles are buried alive, and it is estimated that a large number of female giant side-necked turtles chose to nest in the area during those days.
Collectively go ashore to build a nest
<h1 class="pgc-h-decimal" data-index="02" > how did these female turtles die, and who buried them alive? </h1>
When it comes to natural mortality factors for female turtles during breeding, we usually think of predator predation first, but none of the giant side-necked turtles in these cases show signs of being attacked by predators, and as far as we know, this is the first time a similar death pattern has been recorded in the scope of scientific expeditions.
We know that breeding and nesting requires a lot of energy from adult females, and they tend to be tired after nesting, and the movement of returning to the water is more slow than usual. If the female giant side-necked turtle fails to return to the river in time after spawning, the excessive ambient temperature may cause heat stress to the female turtle, and once the turtle's body temperature soars above the lethal temperature, it may cause death, as has been seen in female green sea turtles.
The turtle prepares to return to the water
If heat stress and exhaustion do cause the death of giant side-necked turtles during the nesting season, then it stands to reason that we will observe female turtles dying on their way back to the river or in their nests at nesting sites in the Amazon, but this phenomenon has never been recorded, so heat stress or fatigue alone may be difficult to explain these deaths in this article.
So what exactly is the cause of death of these turtles? Scholars started with the respiratory physiology of turtles, combined with their posture when they were found, and analyzed that they were likely to die of suffocation. Turtles, because of their hard carapace, have a limited thoracic capacity that cannot be enlarged or shrunk, so they breathe differently than most amniotic animals.
Huge giant side-necked turtle
First of all, turtles change the volume in the mouth with the help of the up and down movement of the tongue, the air can be absorbed, and then through the expansion and contraction of the head and neck and limbs to affect the expansion and contraction of the lungs, so as to complete the lung breathing. In addition, in order to adapt to aquatic life, aquatic turtles also have parabladders on both sides of the pharyngeal wall and cloaca as auxiliary respiratory organs, even in water can also exchange gases.
Because the hind limbs of these giant side-necked turtles were buried in the soil and could not move, scholars believe that this will cause them to have difficulty breathing and eventually die. The researchers noticed that when the 2 live females were dug up and placed in a horizontal position, they began to breathe heavily, which may be a symptom of lack of oxygen.
Dig holes to build nests
Some people may say that some small domestic turtles are buried deep in the soil during hibernation and do not produce hypoxia and suffocation. Hibernation is a kind of adaptation mechanism of turtles to the external low temperature environment, hibernating turtles will minimize metabolism as much as possible, so only very low oxygen and energy are needed to maintain survival, and the giant side-necked turtles in the breeding period themselves consume a lot of energy because of long-distance migration and nesting activities, because they are located in the tropics, the temperature of the environment is quite high, which is very different from the situation of some turtles when hibernating, and the oxygen required will naturally be much more.
Of course, it cannot be ruled out that the giant side-necked turtles have experienced both hypoxia and heat stress after being buried, and past studies have pointed out that some box turtles eventually die due to overheating after falling into ditches or trapped in railway sleepers, and these side-necked turtles trapped in the soil are exposed to high temperature for a long time, and their body temperature may reach a lethal temperature.
Two female turtles are digging holes
The last question is who buried these female turtles alive, and human activities can certainly be ruled out, after all, these two nesting areas are under the supervision of the institute, and even if they are committed by humans, it is impossible not to leave a trace. Other animals are also impossible, leaving no evidence of footprints, and there is no motivation to do so.
As has been emphasized many times earlier, from October 22 to 29, 2017, researchers monitored a large number of female side-necked turtles nesting in the burial area, which means that the female turtles are likely to be next to each other when digging holes in the planing soil. Most likely, some of the female turtles may have just finished the long journey and were tired, so they were buried alive by the sand dug up by their nearby counterparts.
So, were these female turtles who buried their companions alive careless, or were they deliberate? Although from the result, this is beneficial to the murderer's own turtle eggs, which is equivalent to eliminating competitors for future generations, but it should not be deliberate. The female turtle has traveled a long way here to build a nest and lay eggs, and she is exhausted, and her body is in danger, so as not to waste her energy to create such deliberate murder.
Female turtles nest next to each other, and it is easy to accidentally bury each other alive
<h1 class="pgc-h-decimal" data-index="03" > the live burial event is a manifestation of density-constrained mortality</h1>
This kind of live burial event caused by intensive nesting activities is ecologically a manifestation of density-constrained mortality, that is, high-density, high-concentration nesting behavior increases the mortality rate of female turtles. Previous studies have shown that density-constrained mortality is not uncommon in some turtles with collective nesting habits, mainly reflected in the fact that females during the breeding period sometimes destroy the nests left by the previous group of female turtles, thus reducing the hatching rate of turtle eggs, which is present in green sea turtles, lily turtles, leatherback turtles and giant side-necked turtles in this article.
Juvenile giant side-necked turtle
However, density-constrained mortality may be the first time that the mortality rate is directly reflected in adult turtles, and the role of female adult turtles in the population is crucial, if a total of about 10,000 female turtles nested in the nesting area of Monte Cristo in 2015, then 0.06% of female turtles died in 2017 due to live burial. The reason for this phenomenon is that a large number of female turtles nest intensively in a certain area in a short period of time, and the essence of the problem is that the nesting space is limited. Therefore, in order to prevent the recurrence of such situations, while searching for and rescuing buried females in time during the breeding period, it is also a top priority to create a larger nesting suitable area for giant side-necked turtles.