Pigment composition and photoacclimation as keys to the ecological success of Gonyostomum semen (Raphidophyceae, Stramenopiles)

Abstract

Aquatic habitats are usually structured by light attenuation with depth resulting in different microalgal communities, each one adapted to a certain light regime by their specific pigment composition. Several taxa contain pigments restricted to one phylogenetic group, making them useful as marker pigments in phytoplankton community studies. The nuisance and invasive freshwater microalga Gonyostomum semen (Raphidophyceae) is mainly found in brown water lakes with sharp vertical gradients in light intensity and color. However, its pigment composition and potential photoadaptations have not been comprehensively studied. We analyzed the photopigment composition of 12 genetically different strains of G. semen by high performance liquid chromatography after acclimation to different light conditions. We confirmed the pigments chl a, chl c1c2, diadinoxanthin, trans-neoxanthin, cisneoxanthin, a and b carotene, which have already been reported for G. semen. In addition, we identified, for the first time, the pigments violaxanthin, zeaxanthin, and alloxanthin in this species. Alloxanthin has never been observed in raphidophytes before, suggesting differences in evolutionary plastid acquisition between freshwater lineages and the well-described marine species. The amount of total chl a per cell generally decreased with increasing light intensity. In contrast, the increasing ratios of the prominent pigments diadinoxanthin and alloxanthin per chl a with light intensity suggest photoprotective functions. In addition, we found significant variation in cellspecific pigment concentration among strains, grouped by lake of origin, which might correspond to genetic differences between strains and populations.

Asynchronous changes in abundance over large scales are explained by demographic variation rather than environmental stochasticity in an invasive flagellate

“…However, these variables had no effect on lakes of the Fennoscandian region where temperature is the limiting factor. These results corroborate previous findings showing that G. semen is very plastic and their populations are diverse, not locally adapted, and can grow at a variety of pH, DOC, and light intensities (Sassenhagen et al 2014(Sassenhagen et al , 2015b.…”

“…), or the presence of grazers (Hansson ) may affect internal dynamics through altering cyst production, recruitment and cell survival, genetic recombination, which occurs during sexual cyst production, together with G. semen 's high phenotypic plasticity may favour survival and adaptation of the species in changing environments (Figueroa & Rengefors ; Lebret, Kritzberg & Rengefors ; Sassenhagen et al . , ,b). Hence, in high density populations where more cysts will typically be produced, internal demographic processes related to cyst recruitment and survival may overlie establishment limitations and modulate the effects of environmental variation on G. semen density changes.…”

“…These results corroborate previous findings showing that G. semen is very plastic and their populations are diverse, not locally adapted, and can grow at a variety of pH, DOC, and light intensities (Sassenhagen et al . , ).…”

“…Resting cysts common to many bloom forming harmful species, are sexually produced (Figueroa & Rengefors 2006) and can act as a seed population inoculating the water with cells in the next season (Anderson & Wall 1978;Mcgillicuddy et al 2003;Garc es et al 2004;Stock et al 2005). Although environmental factors, such as light and temperature (Genovesi et al 2009), or the presence of grazers (Hansson 2000) may affect internal dynamics through altering cyst production, recruitment and cell survival, genetic recombination, which occurs during sexual cyst production, together with G. semen's high phenotypic plasticity may favour survival and adaptation of the species in changing environments (Figueroa & Rengefors 2006;Lebret, Kritzberg & Rengefors 2013;Sassenhagen et al 2014Sassenhagen et al , 2015a. Hence, in high density populations where more cysts will typically be produced, internal demographic processes related to cyst recruitment and survival may overlie establishment limitations and modulate the effects of environmental variation on G. semen density changes.…”

Growth responses of the nuisance algae Gonyostomum semen (Raphidophyceae) to DOC and associated alterations of light quality and quantity

“…Alternately, the success might be caused by competitive advantages in humic conditions. For instance, G. semen is suspected to possess the ability to utilize humic substances directly as a carbon source; also, based on the recent findings of photosynthetic pigments and carotenoids in G. semen cells, we would expect that this alga is able to utilize both green and red light in addition to blue light (Kirk 1983, Rengefors et al 2008, Sassenhagen et al 2014. The altered light conditions caused by DOC that will have negative effects on phytoplankton in general might give certain algal groups a competitive advantage if they are able to benefit from these conditions (Kirk 1977, Thrane et al 2014.…”