In a work published in the journal Frontiers in Physiology, researchers from Unesp (Universidade Estadual Paulista) showed that tadpoles of the species bokermannohyla ibitiguaraa tree frog endemic to Serra da Canastra, in Minas Gerais, have little ability to adapt to increases in temperature, which can compromise these amphibians in a scenario of climate change or deforestation.
In the laboratory, the group carried out tests in which the water temperature increased in relation to the average of the species’ habitat, which are streams surrounded by riparian forest. Then, physiological variables such as oxygen consumption and heart rate, among others, were measured in the tadpoles. In addition, the researchers verified whether the animals normally performed functions such as swimming, feeding and metamorphosis into adulthood.
“The species has limited plasticity. The average temperature in the stream where we collected the animals was 21.9ºC, reaching a maximum of 24.6ºC, even so in the hottest months of the year and at a very specific time. We estimate that an increase temperature of 3ºC above this temperature will profoundly impact the tadpoles, which are unable to modulate their physiological variables to adapt to this change”, explains Leonardo Longhini, first author of the study, carried out during his master’s degree at the Faculty of Agrarian and Veterinary Sciences (FCAV -Unesp), in Jaboticabal, with the support of a Fapesp grant.
In a recent study, researchers determined that the topography of Serra da Canastra itself may be a determining factor for the genetic diversity of the species, which is endemic to the cerrado, which is yet another warning for its conservation.
“The autonomic nervous system of these animals cannot compensate for changes caused by a higher temperature, for example in heart rate and metabolism. And this ends up impacting the life cycle of the species, since it cannot complete the metamorphosis”, says Luciane Gargaglioni , a professor at FCAV-Unesp supported by Fapesp, who coordinated the study with post-doctoral fellow Lucas Zena, from the Biosciences Institute of the University of São Paulo (IB-USP).
To arrive at the results, the researchers collected tadpoles in a rural area of ​​the municipality of Sacramento, in Minas Gerais. A temperature sensor was housed at the site for a little over a year to measure the temperature variation and obtain an average for carrying out the experiments. Non-invasive methods were developed by scientists to measure oxygen consumption and heart rate in tadpoles.
The animals were initially divided into two aquariums, one with a temperature of 8ºC, the lowest temperature found in the stream where they were collected, and another at 28ºC, three degrees higher than the maximum recorded in the habitat of the b. ibitiguara.
All tadpoles in this second group showed signs of poor food intake, their body mass was lower and they did not complete metamorphosis. This indicates limitations in the ability to absorb, process or assimilate sufficient nutrients to support high metabolic rates at elevated temperatures.
The researchers then collected more tadpoles, but this time acclimated them to 18ºC and 25ºC, a value close to the highest temperature recorded in the habitat. Subsequently, the animals were submitted to a heating ramp, in which the temperature progressively increases to 34ºC. In this case, an increase in lethality was observed.
“The maximum temperature they could withstand was not different between those acclimated to 18ºC and 25ºC, which shows that the animal does not adapt very well. If the stream is deforested and the temperature increases, it cannot increase the tolerance to withstand the warming “, says Longhini.
Heart rate was also not different between groups acclimated to different temperatures. This occurred even when metabolism, which is measured by oxygen consumption, increased at high temperatures, showing that the heart does not keep up with the new condition.
“The cerrado has a high susceptibility to warming resulting from human occupation, mainly by pastures and plantations. At the same time, it has a very high biodiversity and is even more threatened than the Amazon, with only 8% of its areas protected. endemic is a way of drawing attention to it”, concludes Gargaglioni.
