Guest essay by Eric Worrall
According to Australian scientists, even mild global warming could push important tropical species beyond their limits of survival. What they inadvertently showed, however, is the improbability of those limits to be exceeded.
MALE FERTILITY “CLOSE BEFORE” IN ORDER TO CHANGE LIMITS FOR AIR CONDITIONING
Loss of fertility in men as a result of climate change, especially in the tropics, may be a better indicator of vulnerability to extinction
From Dr. Belinda van Heerwaarden, University of Melbourne
As temperatures rise around the world, species will increasingly be exposed to environmental conditions that exceed their tolerance limits and pose a major risk to biodiversity, food production and health.
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In our study recently published in Nature Communications, we exposed different species of Drosophila flies in the laboratory to environmental conditions that mimicked climate change.
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By tracking population growth and extinction We found that tropical species actually became extinct at temperatures below that of the widely distributed species. Although these species lived in the warm tropics, they were no more heat-resistant than species with distributions much further from the equator.
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However, male fertility loss, which occurs at temperatures well below lethal temperatures, was a better predictor of individual vulnerability to climate change.
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How much closer are species to their male fertility limits than to their critical thermal limits?
Some of the rainforest species we have examined currently have maximum habitat temperatures around 7 ° C below their critical thermal limit, i.e. their warming tolerance is around 7 ° C.
In contrast, Some species already have average temperatures within 1 ° C of their male fertility limit during the summer months.
Instead of a 7 ° C buffer zone, they may only be able to handle 1 ° C of warming before populations plummet.
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Given that many species – especially tropical species – may be much closer to their thermal limits, the The current projected 1.5 to 4 ° C warming can result in much greater biodiversity loss than most of us are likely to believe.
Read more: https://pursuit.unimelb.edu.au/articles/male-fertility-precariously-close-to-climate-change-extinction-limits
The summary of your studies;
The thermal limits of male fertility predict vulnerability to global warming
Belinda van Heerwaarden and Carla M. Sgrò
Nature communication Volume 12, Article number: 2214 (2021) Quote this article
abstract
Predicting which species / ecosystems are most vulnerable to global warming is important in guiding conservation strategies to minimize extinction. Tropical / mid-latitude species are predicted to be most at risk as they live close to their Upper Critical Thermal Limits (CTLs). However, these assessments assume that CTL upper estimates like CTmax are accurate predictors of vulnerability and ignore the potential of evolution to improve temperature increases. Here we use experimental evolution to assess extinction risk and adaptation in tropical and widespread Drosophila species. We find that tropical species are threatened with extinction from widespread species. The thermal limits for male fertility, which are much lower than CTmax, are better predictors of current distribution and species extinction in the laboratory. We find little evidence of adaptive warming responses in any species. These results suggest that species live closer to their upper thermal limits than currently believed and that evolution / plasticity is unlikely to save populations from extinction.
Read more: https://www.nature.com/articles/s41467-021-22546-w
Why are tropical species less resistant to warmer temperatures? The answer is obvious – tropical species have never had to develop sustained genetic resistance to higher temperatures.
Ignoring the possibility of experimental error, either the genetic plasticity or genetic variation of the entire population is greater than what scientists deduce from cooking a few laboratory samples, or the tropics are so resistant to climatic temperature fluctuations that species are within 1 ° C their survival can comfortably survive limit.
The earliest winged insects appeared 480 million years ago. They have changed a lot since then; I suspect that short-lived species like Drosophila, which reproduce rapidly, are split into a new species every time someone looks closely at them.
The point is, the ancestors of the current Drosophila flies have likely been exposed to pretty much every level of CO2 and global temperature the earth could throw at them, likely including levels of CO2 many times higher than what they are today geologically low level of ~ 417 ppm CO2.
h / t Tom Nelson, Bill Illis
The study’s obvious conclusion that fruit flies cannot exist in the tropics during warm periods with high CO2 emissions is absurd. Even if some tropical insect species had been temporarily eradicated by past climatic excursions, their range would have been quickly repopulated by tropical and subtropical species that survived the excursion. Nature abhors an unused source of food.
The main study included a few weasel words: “… It is also possible that extreme temperature events could more effectively control evolutionary responses to these traits, especially for CTmax. However, other studies that opted directly for CTmax or acute heat reduction also showed no sustained response… ”.
My suggestion; Given the Earth’s geological history, the hypothesis that an entire species is likely to have more adaptability than a tank full of laboratory samples should be the standard assumption, not a grudging admission. Fruit flies are a tough agricultural pest that has repeatedly demonstrated the ability to evolve quickly to overcome threats to their species such as: B. the development of resistance to new pesticides. I suspect if you’ve filled lab tanks of fruit flies with a new pesticide, you can also conclude that they have very little adaptability. But of the myriad trillions of fruit flies in the wild, some always manage to survive attempts to exterminate them.
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