Temperature elevation reduces the sensitivity of invasive cladoceran Daphnia lumholtzi to filamentous cyanobacterium Raphidiopsis raciborskii

Abstract

Exotic cladoceran Daphnia lumholtzi is a highly invasive species in the north and south American continents and can potentially also invade European freshwaters and outcompete native Daphnia populations. However, European waterbodies are frequently dominated by less edible filamentous cyanobacteria including also invaders such as Raphidiopsis raciborskii, which might affect the fitness of D. lumholtzi. Furthermore, temperature may influence the sensitivity of D. lumholtzi to R. raciborskii filaments. In this study, we determined whether the presence of R. raciborskii could obstruct the invasion of Europe by D. lumholtzi, through reducing its fitness, and whether this depends on temperature. We compared the population growth rate (r) and the somatic growth rate of D. lumholtzi maintained at two temperatures (20 or 26°C) and fed with two diets: green microalgae alone or green microalgae mixed with filaments of R. raciborskii. Three clones of D. lumholtzi were used to evaluate potential variation in response to the treatments among different clones. At 20°C, the population growth rate of D. lumholtzi fed with cyanobacterial filaments declined sharply. This reduction was caused by increased egg abortion, egg degeneration, and mortality of newborn daphnids. At 26°C, R. raciborskii lost its harmful effect on the population growth of D. lumholtzi. The presence of cyanobacteria did reduce the somatic growth rate of D. lumholtzi at both temperatures and in all three clones except for one that had a similar somatic growth rate on both diets at 26°C. The presence of filamentous cyanobacteria does affect growth in D. lumholtzi and may thereby substantially reduce its invasive potential, but only at lower temperatures. Therefore, the presence of filamentous cyanobacteria may not present an obstacle to the invasion of Europe by D. lumholtzi in a warmer future climate.

Food quantity and quality shapes reproductive strategies of Daphnia

“…Future studies should therefore consider both the number and the size of eggs produced, as well as the offspring fitness. Additionally, it was shown that the presence of cyanobacteria in the environment may increase embryo mortality or even cause egg abortion (Bednarska & Slusarczyk, 2013 , Wejnerowski et al, 2020 ); thus, to correctly assess the cyanobacteria‐driven fitness costs, besides the number/size of eggs, the number and size of vital neonates should be taken into consideration as well.…”

“…The influence of cyanobacteria depends greatly on both the species/clone of Daphnia (e.g., Bednarska et al, 2014 ; Jiang et al, 2013 ) and the species/strain of cyanobacteria (Hochmuth & De Schamphelaere, 2014 ; Wejnerowski et al, 2015 ), or the combination of these two variables (Lemaire et al, 2012 ). The vulnerability of Daphnia to the presence of cyanobacteria may depend also on other environmental factors, such as temperature (Bednarska et al, 2011 ; Wejnerowski et al, 2020 ). Thus, although the detrimental effect of cyanobacteria on Daphnia fitness should always be expected, the degree to which they are impacted is highly context‐dependent.…”

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

“…This in turn underscores the importance of the 'change of space' mechanism rapidly following climate change 14,19,21 . The spread of species and genotypes from a warmer climate seems to be facilitated not only by the increased temperature of local habitats, but also by the poor biotic resistance of local communities, which is limited by disturbances in community structure (e.g., 35 ) and by the poorer performance of indigenous populations compared to that of invaders (e.g., 23,25,26 ).…”

“…In temperate freshwater communities, climate warming increases the risk of invasion that can ultimately lead to community restructuring [23][24][25][26] . There is abundant evidence that the community structure of the model organism for temperate lakes-the planktonic crustacean Daphnia-is shaped by variations among taxa in sensitivity to environmental constraints.…”