Physiological evaluation of the behavior and epidermis of freshwater planarians (Girardia tigrina and Girardia sp.) exposed to stressors

Abstract

Planarians are metazoan freshwater flatworms which are free-living organisms. Their body has pluripotent stem cell promoters of tissue regeneration capacity. The water temperature and the potential of hydrogen (pH) of lentic ecosystems are important factors involved in the distribution and abundance of these animals. Although the pH factor is directly related to the physiology and behavior of planarians, their adaptive and regenerating capacities still remain unknown. The Critical Thermal Maximum (CTM) is a very widespread method used in the evaluation of thermal tolerance. In this study, Girardia tigrina (Girard, 1850) and Girardia sp., a species found in Brazil, which is under study as a new species, had their epidermis assessed by scanning electron microscopy (SEM) to analyze their physiological structures before and after exposure to different stressors. SEM was used as a method to evaluate the planarians' epidermis as a result of the increasing temperature (CTM) and pH alterations, the latter with the use of a new methodology defined as Critical Hydrogen ion concentration Maximum (CHM). In increasing temperatures from 20°C to 37°C, both Girardia tigrina and Girardia sp. proved to be adaptable to thermal stress. Girardia sp. was shown to be more resistant to higher temperatures. However, Girardia tigrina was more resistant to extreme pH conditions (4.0 to 10.0). SEM analysis showed morphological differences among planarian species, such as the arrangement of the structures and cell types of the dorsal epidermis. Moreover, planarians demonstrated the ability to change the surrounding pH of their external environment in order to maintain the function of their physiological mechanisms, suggesting that these animals have a complex survival system, possibly related to protonephridia, flame cells and excretory pores..

Estimation of the DNA damage in Girardia tigrina (Girard, 1850) after exposure to radiation under extreme conditions / Estimativa dos danos do DNA em Girardia tigrina (Girard, 1850) após exposição à radiação em condições extremas

“…In ectothermic organisms other than planarians, species the fish Bathygobius soporator and Parablennius marmoreus, shrimps Palaemon northropi and Hippolyte obliquimanus, and crabs Eurypanopeus abbreviatus and Menippe nodifrons [9], all show similar findings with symptoms such as loss of balance and spasms. Corroborating the actions described by Díaz and Bückle [10], for the fish Ictalurus punctatus, and by Oliveira et al [11] for freshwater planarians Girardia tigrina and Girardia sp., the animals showed spasms and loss of balance in response to extreme thermal conditions. Girardia sp.…”

“…Girardia sp. is unable to survive in waters below pH 3.0 [11], a fact also recorded made for Girardia dorotocephala, Cura foremanii, Dendrocelopsis vaginatus and asexual specimens of G. tigrina planaria by Rivera and Perich [12].…”

“…Before death, limnic planarians exposed to extreme temperature conditions show contortions, slowness, peeling of the epidermis and loss of the ability to move properly [5,11,12,13].…”

“…Animals such as freshwater planarians are able to withstand wide pH variations by homeostatic regulation of their internal metabolism. However, limit points exist, perhaps determined by alterations to physiology and behavior [12,11].…”

Extreme Environmental Stress-Induced Biological Responses in the Planarian

“…The structure of epidermis has been damaged when the temperature increased over 33°C for Girardia tigrina and 37°C for Girardia sp. There were fewer rhabdites and fewer and disorganized secretory droplets [63], which form the mucus to help planarians to respond and escape stress [64,65].…”