Myofibril Changes in the Copepod Pseudodiaptomus marinus Exposed to Haline and Thermal Stresses

Abstract

Copepods are small crustaceans capable to survive in various aquatic environments. Their responses to changes in different external factors such as salinity and temperature can be observed at different integration levels from copepod genes to copepod communities. Until now, no thorough observation of the temperature or salinity effect stresses on copepods has been done by optical microscopy. In this study, we used autofluorescence to visualize these effects on the morphology of the calanoid copepod Pseudodiaptomus marinus maintained during several generations in the laboratory at favorable and stable conditions of salinity (30 psu) and temperature (18°C). Four different stress experiments were conducted: at a sharp decrease in temperature (18 to 4°C), a moderate decrease in salinity (from 30 to 15 psu), a major decrease in salinity (from 30 to 0 psu), and finally a combined stress with a decrease in both temperature and salinity (from 18°C and 30 psu to 4°C and 0 psu). After these stresses, images acquired by confocal laser scanning microscopy (CLSM) revealed changes in copepod cuticle and muscle structure. Low salinity and/or temperature stresses affected both the detection of fluorescence emitted by muscle sarcomeres and the distance between them. In the remaining paper we will use the term sarcomeres to describe the elements located within sarcomeres and emitted autofluorescence signals. Quantitative study showed an increase in the average distance between two consecutive sarcomeres from 2.06 +/- 0.11 μm to 2.44 +/- 0.42 μm and 2.88 +/- 0.45μm after the exposure to major haline stress (18°C, 0 psu) and the combined stress (4°C, 0 psu), respectively. These stresses also caused cuticle cracks which often occurred at the same location, suggesting the cuticle as a sensitive area for osmoregulation. Our results suggest the use of cuticular and muscle autofluorescence as new biomarkers of stress detectable in formalin-preserved P. marinus individuals. Our label-free method can be easily applied to a large number of other copepod species or invertebrates with striated musculature.

Response to salinity and temperature changes in the alien Asian copepod Pseudodiaptomus marinus introduced in the Black Sea

“…At the low temperature of 8.0°C P. marinus responded kinematically to the electrical stimuli by performing jumps through the sequential movement of the thoracic limbs (Gemmell & Buskey, ). The experiments by Ibrahim et al () evidenced thermal and haline shock in P. marinus , with most individuals becoming comatose in 75 min upon instantaneous reduction in T from 18.0°C to 4.0°C, and only in 1 min when also salinity was abruptly changed from 30.0 to 0.0 psu. These authors suggested that acute haline and thermal changes might induce myofibril stress in P. marinus , while the results presented in this study reveal a strong adaptability of this calanoid when temperature and saline variations occur over time spans of hours to days.…”

“…At the low temperature of 8.0°C P. marinus responded kinematically to the electrical stimuli by performing jumps through the sequential movement of the thoracic limbs (Gemmell & Buskey, 2018). The experiments by Ibrahim et al (2015Ibrahim et al ( , 2016…”

“…Therefore, it is not known how this species can survive and maintain metabolic activity within the range of the environmental parameters characterizing the newly introduced area. Ibrahim et al () and Ibrahim et al () investigated the effect of thermal and haline stress on the behavior, muscle fiber and cuticle structure of P. marinus . They reported that instantaneous drastic changes in temperature and salinity induced coma and myofibril stress (Ibrahim et al, ), with damages to muscular tissues (Ibrahim et al, ).…”

“…Ibrahim et al (2015) and Ibrahim et al (2016) investigated the effect of thermal and haline stress on the behavior, muscle fiber and cuticle structure of P. marinus. They reported that instantaneous drastic changes in temperature and salinity induced coma and myofibril stress (Ibrahim et al, 2015), with damages to muscular tissues (Ibrahim et al, 2016). Chen, Sheng, Lin, Gao, and Lv (2006) studied the survival of the congeneric Pseudodiaptomus annandalei after salinity change, highlighting an optimum at S = 15 psu.…”

WGEUROBUS – Working Group “Towards a EURopean OBservatory of the non-indigenous calanoid copepod Pseudodiaptomus marinUS”

“…Each of them, either alone or in combination, may provide an adaptive advantage by which adjusting to diversified environments and so facilitating the establishment in new areas. In addition, P. marinus has been indicated as suitable for mass rearing providing live feed for fish larvae (Mauchline 1998), and it has been proficiently used as target species for ecotoxicological (Arias et al 2016;Huang et al 2006;Tlili et al 2016Tlili et al , 2019 and myofibril structure (Ibrahim et al 2015(Ibrahim et al , 2016 studies.…”