Temperature increase altered Daphnia community structure in artificially heated lakes: a potential scenario for a warmer future

Under conditions of global warming, organisms are expected to track their thermal preferences, invading new habitats at higher latitudes and altitudes and altering the structure of local communities. To fend off potential invaders, indigenous communities/populations will have to rapidly adapt to the increase in temperature. In this study, we tested if decades of artificial water heating changed the structure of communities and populations of the Daphnia longispina species complex. We compared the species composition of contemporary Daphnia communities inhabiting five lakes heated by power plants and four non-heated control lakes. The heated lakes are ca. 3–4 °C warmer, as all lakes are expected to be by 2100 according to climate change forecasts. We also genotyped subfossil resting eggs to describe past shifts in Daphnia community structure that were induced by lake heating. Both approaches revealed a rapid replacement of indigenous D. longispina and D. cucullata by invader D. galeata immediately after the onset of heating, followed by a gradual recovery of the D. cucullata population. Our findings clearly indicate that, in response to global warming, community restructuring may occur faster than evolutionary adaptation. The eventual recolonisation by D. cucullata indicates that adaptation to novel conditions can be time-lagged, and suggests that the long-term consequences of ecosystem disturbance may differ from short-term observations

Cryoconite – from minerals and organic matter to bioengineeredsediments on glacier's surfaces

Cryoconite is a mixture of mineral and organic material covering glacial ice, playing important roles in biogeochemical cycles and lowering the albedo of a glacier surface. Understanding the differences in structure of cryoconite across the globe can be important in recognizing past and future changes in supraglacial environments and ice-organisms-minerals interactions. Despite the worldwide distribution and over a century of studies, the basic characteristics of cryoconite, including its forms and geochemistry, remain poorly studied. The major purpose of our study is the presentation and description of morphological diversity, chemical and photoautotrophs composition, and organic matter content of cryoconite sampled from 33 polar and mountain glaciers around the globe. Observations revealed that cryoconite is represented by various morphologies including loose and granular forms. Granular cryoconite includes smooth, rounded, or irregularly shaped forms; with some having their surfaces covered by cyanobacteria filaments. The occurrence of granules increased with the organic matter content in cryoconite.Moreover, amajor driver of cryoconite colouringwas the concentration of organicmatter and its interplay with minerals. The structure of cyanobacteria and algae communities in cryoconite differs between glaciers, but representatives of cyanobacteria families Pseudanabaenaceae and Phormidiaceae, and algae families Mesotaeniaceae and Ulotrichaceaewere themost common. Themost of detected cyanobacterial taxa are known to produce polymeric substances (EPS) that may cement granules. Organic matter content in cryoconite varied between glaciers, ranging from 1% to 38%. The geochemistry of all the investigated samples reflected local sediment sources, except of highly concentrated Pb andHg in cryoconite collected fromEuropean glaciers near industrialized regions, corroborating cryoconite as element-specific collector and potential environmental indicator of anthropogenic activity. Our work supports a notion that cryoconite may bemore than just simple sediment and instead exhibits complex structure with relevance for biodiversity and the functioning of glacial ecosystem

The significance of cyanobacterial filament morphology in a defence against grazing by Daphnia spp.

Morfologia nitek jest jednym z kluczowych czynników kształtujących odporność sinic na presję filtratorów planktonowych tj. Daphnia. Nitki sinic mogą zapychać aparat filtracyjny Daphnia i upośledzać jego funkcjonowanie. Ponadto krótkie nitki sinic są efektywniej wyjadane przez filtratory niż dłuższe. Celem pracy było wyjaśnienie znaczenia szerokości nitek sinic dla ich odporności na wyjadanie. Wykazano, że szersze nitki sinic są bardziej odporne na presję filtratora w porównaniu z cieńszymi nitkami. Istotne znaczenie ma również stan fizjologiczny nitek oraz grubość ściany komórkowej, czynniki, które w dużej mierze determinują sztywność nitek. W eksperymentach historii życia wykazano, że gatunki sinic o szerszych nitkach ograniczają w większym stopniu wzrost somatyczny oraz reprodukcję filtratorów niż sinice o cieńszych nitkach. Analiza morfologiczna aparatu filtracyjnego Daphnia ujawniła, że szczeciny filtracyjne w obecności sinic nitkowatych ulegają zgrubieniu, co pozwala filtratorom minimalizować negatywny wpływ nitek sinic. Nie stwierdzono przy tym jednak, aby sinice o szerszych nitkach wywoływały silniejszą reakcję morfologiczną filtratora. W pracy zawarto także wyniki opisujące reakcje morfologiczne samych sinic nitkowatych na fizyczną jak i wyłącznie chemiczną obecność filtratorów. Wykazano, że wydzieliny filtratorów jak i siarczan oktylu sodu (komercyjnie dostępny kairomon Daphnia), stymulują różne gatunki sinic do tworzenia szerszych nitek, co może być mechanizmem obronnym przed wyjadaniem.Filament morphology is one of the key factors determining the resistance of cyanobacteria to grazing by planktonic filter-feeders, Daphnia. Cyanobacterial filaments clog filtering apparatus in daphnids and impair its functioning. Moreover, shorter filaments are grazed more efficiently by daphnids than longer ones. The aim of this study was to explain the significance of cyanobacterial filament thickness in a resistance or defence against grazing. This study revealed that thicker filaments have a greater resistance to grazing than thinner ones. The physiological state of filaments and their cell wall thicknesses, factors determining the stiffness of filaments, are also important in thickness-related resistance of cyanobacterial filaments to grazing . Life history experiments revealed that cyanobacteria with thicker filaments suppress more somatic growth and reproduction of daphnids than cyanobacteria having thinner filaments. Analysis of Daphnia’s filtering apparatus morphology showed that filtering setae increase in thickness in the presence of filamentous cyanobacteria, what enable animals to minimize the negative influence of cyanobacterial filaments. However, this response of daphnids was not strengthened in the presence of cyanobacteria with thicker filaments. Doctoral dissertation contains also results describing morphological reactions of filamentous cyanobacteria to physical presence of Daphnia as well as their infochemicals alone. It was reported that Daphnia cues stimulate various species of cyanobacteria to increase in thickness, what might be a defence mechanism against grazing.Wydział Biologi

The significance of cyanobacterial filament morphology in a defence against grazing by Daphnia spp.

Morfologia nitek jest jednym z kluczowych czynników kształtujących odporność sinic na presję filtratorów planktonowych tj. Daphnia. Nitki sinic mogą zapychać aparat filtracyjny Daphnia i upośledzać jego funkcjonowanie. Ponadto krótkie nitki sinic są efektywniej wyjadane przez filtratory niż dłuższe. Celem pracy było wyjaśnienie znaczenia szerokości nitek sinic dla ich odporności na wyjadanie. Wykazano, że szersze nitki sinic są bardziej odporne na presję filtratora w porównaniu z cieńszymi nitkami. Istotne znaczenie ma również stan fizjologiczny nitek oraz grubość ściany komórkowej, czynniki, które w dużej mierze determinują sztywność nitek. W eksperymentach historii życia wykazano, że gatunki sinic o szerszych nitkach ograniczają w większym stopniu wzrost somatyczny oraz reprodukcję filtratorów niż sinice o cieńszych nitkach. Analiza morfologiczna aparatu filtracyjnego Daphnia ujawniła, że szczeciny filtracyjne w obecności sinic nitkowatych ulegają zgrubieniu, co pozwala filtratorom minimalizować negatywny wpływ nitek sinic. Nie stwierdzono przy tym jednak, aby sinice o szerszych nitkach wywoływały silniejszą reakcję morfologiczną filtratora. W pracy zawarto także wyniki opisujące reakcje morfologiczne samych sinic nitkowatych na fizyczną jak i wyłącznie chemiczną obecność filtratorów. Wykazano, że wydzieliny filtratorów jak i siarczan oktylu sodu (komercyjnie dostępny kairomon Daphnia), stymulują różne gatunki sinic do tworzenia szerszych nitek, co może być mechanizmem obronnym przed wyjadaniem.Filament morphology is one of the key factors determining the resistance of cyanobacteria to grazing by planktonic filter-feeders, Daphnia. Cyanobacterial filaments clog filtering apparatus in daphnids and impair its functioning. Moreover, shorter filaments are grazed more efficiently by daphnids than longer ones. The aim of this study was to explain the significance of cyanobacterial filament thickness in a resistance or defence against grazing. This study revealed that thicker filaments have a greater resistance to grazing than thinner ones. The physiological state of filaments and their cell wall thicknesses, factors determining the stiffness of filaments, are also important in thickness-related resistance of cyanobacterial filaments to grazing . Life history experiments revealed that cyanobacteria with thicker filaments suppress more somatic growth and reproduction of daphnids than cyanobacteria having thinner filaments. Analysis of Daphnia’s filtering apparatus morphology showed that filtering setae increase in thickness in the presence of filamentous cyanobacteria, what enable animals to minimize the negative influence of cyanobacterial filaments. However, this response of daphnids was not strengthened in the presence of cyanobacteria with thicker filaments. Doctoral dissertation contains also results describing morphological reactions of filamentous cyanobacteria to physical presence of Daphnia as well as their infochemicals alone. It was reported that Daphnia cues stimulate various species of cyanobacteria to increase in thickness, what might be a defence mechanism against grazing.Wydział Biologi

Aphanizomenon gracile increases in width in the presence of Daphnia. A defence mechanism against grazing?

<p><em>Filamentous cyanobacteria are frequently consumed by grazers like </em>Daphnia<em>, which can break filaments and make them more readily available to filter-feeders. However, various defence mechanisms against grazing have also been observed in cyanobacteria. Data concerning changes in the morphology of filamentous algae, especially their width in the presence of a grazer, are scarce. Field studies of filament morphology of cyanobacteria relate their changes to nutrient availability and temperature. Moreover, filament morphology displays significant differences in filament length and width among seasons. We hypothesised that the morphological changes in filament observed in the field – especially their width – could be a defence mechanism that is induced by the presence of a grazer, such as </em>Daphnia<em>. Thus, two experiments were conducted in order to test the influence of </em>Daphnia <em>(direct grazing and infochemicals together in the first experiment) and the chemicals it released (grazing excluded, only chemicals present in the second experiment) on </em>Aphanizomenon gracile<em>’s morphology, in controlled laboratory conditions. </em>Aphanizomenon <em>filaments became significantly shorter and thicker in both experiments. However, </em>Daphnia<em>’s grazing combined with excreted chemicals had stronger effect than chemicals alone. To our knowledge, this is the first report describing the shortening and thickening of filaments in the presence of </em>Daphnia <em>infochemicals. It seems that the </em>Aphanizomenon <em>filaments in the presence of </em>Daphnia <em>switch their growing mode and invest more heavily in width than length. Our results support the hypothesis that </em>Daphnia <em>is at least partly responsible for the changes in filament width observed in the field. This could be a strategy that helps </em>Aphanizomenon <em>to withstand grazer’s pressure during early stages of a bloom.</em></p

Countergradient variation concealed adaptive responses to temperature increase in Daphnia from heated lakes

To test the general assumption that global warming will induce body size reduction in aquatic organisms, we used a system of lakes continually heated for six decades by warm water discharge from power plants. Their temperature elevation of 3–4°C corresponds with climate change forecasts for the end of the 21st century. We compared body size and reproduction of Daphnia longispina complex communities inhabiting heated and non‐heated (control) lakes nearby. No difference in body size was found, but Daphnia communities from heated lakes had a wider thermal breadth for reproduction. The two lake groups varied in the taxonomic composition of Daphnia communities. Thus, to disentangle inter‐ and intraspecific sources of variation, and to examine evolution vs. phenotypic plasticity of investigated traits, we performed two life history experiments: (1) a between‐species experiment compared D. galeata inhabiting heated lakes with D. longispina typical of nearby control lakes, under three temperature regimes; (2) a within‐species experiment compared D. galeata from heated lakes with conspecifics from high latitude (cold control) and low latitude (warm control) lakes, under two temperature regimes. The experiments revealed countergradient variation: environmental constraints on body size in situ concealed evolution of larger potential body size in Daphnia from heated lakes. In turn, evolution of increased body size plasticity resulted in an efficient resource allocation trade‐off: more effective reproduction at high temperature, at the cost of size reduction. We suggest that large size is adaptive during active overwintering, while plastic size reduction is a coping strategy for high temperatures.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655Ministerstwo Nauki i Szkolnictwa Wyższego http://dx.doi.org/10.13039/501100004569Narodowe Centrum Nauki http://dx.doi.org/10.13039/50110000428