Ohnesorge, Alica (2018) Respiration as a proxy for salinity stress in the invasive ctenophore Mnemiopsis leidyi: Do sub-populations display different adaptations to salinity stress?. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 72 pp.

Preview

Text AlicaOhnesorge_MSc_Thesis.pdf - Published Version Available under License Creative Commons: Attribution 4.0. Download (1MB) | Preview

Abstract

Translocation of species outside their natural dispersal ranges are of concern for biodiversity and food web functioning. Even though a large number of species are transported around the world on a daily basis, introduction events rarely lead to the permanent establishment of non-native species in their new habitat. Irrespectively, the few non-native species which achieve high population densities, and, hence become invasive, may have a large ecosystem impact and are suggested to lead to a homogenization of the earth’s biota. An example of a potent invasive species is the comb jelly Mnemiopsis leidyi. This comb jelly has been shown to successfully colonize a large variety of aquatic ecosystems with salinities ranging from 3 to 38. Regardless, the assemblages occupying various locations (=sub-populations) seem to differ in their salinity tolerance. For example, salinity has been shown to restrict the range expansion of some invasive sub-populations as shown for the northern invasive sub-populations in low saline areas of the Baltic Sea. In contrast, the southern invasive sub-population present in the Black Sea thrives at low salinities. This suggests that sub-populations do not tolerate the entire salinity window but are rather adapted to a narrower range. This leads to the question whether salinity tolerance is based on adaptations which are fixed to their respective habitat origins or if sub-populations from the northern invasive sub-population have the potential to acclimatize or adapt to the extreme low salinities of the Baltic Sea. We measured respiration rates and used it as a proxy for salinity stress investigating two different invasive sub-populations from high saline northern and low saline southern Eurasia. Animals were raised over two generations at their home salinity as well as at the contrasting salinity level of the respective other population. This led to two different selection salinities i.e. a high and a low salinity selection regime for both sub-populations. At the end of the second generation, respiration rates were measured at three different assay salinities with high, low and extremely low levels. We found lowest respiration rates in treatments where animals did not experience a salinity change. At the extremely low salinity (7.5) tested, respiration rates were significantly enhanced, especially the northern invasive sub-population where parents were selected and kept at the original high salinity level of 27. For this treatment, respiration rates were 2.5 times higher when exposed to the extremely low assay salinity, compared to unstressed conditions. In contrast, Black Sea sub-populations show similar intermediate values at all salinity stress treatments. In addition, respiration rates of sub-populations also depended on the salinity at which their parental lines were selected over two generations. Our results demonstrate that at a salinity of 7.5, individuals from the southern invasive sub-population have lower respiration rates than the northern invasive sub-populations. Thus, our results suggest southern invasive sub-populations are able to cope with low salinity stress much better compared to northern invasive sub-populations. This highlights the translocation of southern sub-populations to the low saline areas of northern Europe should be prevented by all means.

Actions (login required)

View Item