Equal relevance of omega‐3 and omega‐6 polyunsaturated fatty acids for the fitness of Daphnia spp.

Abstract

Essential polyunsaturated fatty acids (PUFAs) have been recognized as a crucial factor that determines the trophic transfer efficiency in plankton communities. As many animals cannot synthesize the classes of ω3‐ and ω6‐PUFAs, the dietary availability of these PUFAs can constrain the fitness of freshwater zooplankton such as Daphnia spp. In particular, eicosapentaenoic acid (EPA, 20:5ω3) is considered to be a crucial determinant of the transfer of biomass at the freshwater plant‐herbivore interface. In contrast to ω3‐PUFAs, the group of ω6‐PUFAs has previously been considered to be of less ecological relevance, although the potential role of the ω6‐PUFA arachidonic acid (ARA, 20:4ω6) remains controversial. To investigate its potential role, we conducted dose‐response growth experiments with two Daphnia species, D. pulex and D. magna, supplemented with EPA or ARA, which allowed us to calculate EPA and ARA saturation thresholds for growth and reproduction of both Daphnia species. Our results provide evidence that not only the availability of ω3‐PUFAs, but also the availability of a ω6‐PUFA, namely ARA, can limit both the growth and reproduction of Daphnia spp. to an equal extent. The saturation thresholds for growth and reproduction were consistently, but not significantly, higher for EPA than for ARA in both Daphnia species. As shifts in phytoplankton community composition might result in environmental fluctuations in the dietary availability of ω3‐ and ω6‐PUFAs, our findings present a significant step in understanding the consequences of the ongoing global biodiversity loss for trophic transfer efficiency at the phytoplankton‐zooplankton interface.

Intrapopulation variability in a functional trait: Susceptibility ofDaphniato limitation by dietary fatty acids

“…Although the availability of EPA was strongly emphasised in previous studies as the PUFA that limits the fitness of Daphnia (von Elert, 2002; Martin‐Creuzburg et al., 2010; Sperfeld & Wacker, 2011), in our study, the reduced fitness of Daphnia genotypes was even more pronounced when the ω6‐PUFA ARA was absent. This corroborates our related findings that ARA is limiting the fitness of two Daphnia species to a similar extent as the ω3‐PUFA EPA (Ilić et al., 2019). The even stronger effect of the absence of ARA on the fitness of D. longispina in the present study might be due to local adaptation by the D. longispina population in Lake Klostersee to the availability of ω3‐ and ω6‐PUFAs.…”

“…Although the availability of EPA was strongly emphasised in previous studies as the PUFA that limits the fitness of Daphnia (von Elert, 2002;Martin-Creuzburg et al, 2010;Sperfeld & Wacker, 2011), in our study, the reduced fitness of Daphnia genotypes was even more pronounced when the ω6-PUFA ARA was absent. This corroborates our related findings that ARA is limiting the fitness of two Daphnia species to a similar extent as the ω3-PUFA EPA (Ilić et al, 2019).…”

“…Besides these ω3-PUFAs, the supplementation of the ω6-PUFA arachidonic acid (ARA, 20:4ω6) to a C 20 -PUFA-free diet was shown to increase the somatic growth (Ilić et al, 2019) Similar to other arthropod animals, Daphnia are incapable of synthesising ω3-and ω6-PUFAs de novo (Harrison, 1990;Leonard et al, 2004;Stanley-Samuelson et al, 1987). However, previous studies suggest that at least some Daphnia species are able to convert ω3-and ω6-PUFAs within the respective PUFA family (Weers et al, 1997;Eric von Elert, 2002;Schlechtriem et al, 2006), albeit at conversion rates insufficient to cover their PUFA demands (Taipale et al, 2011).…”

“…Daphnia galeata , Daphnia magna , Daphnia pulex ) fed with algal food supplemented with single ω3‐PUFAs such as ALA, EPA, and docosahexaenoic acid (22:6ω3) (von Elert, 2002; Martin‐Creuzburg et al., 2010; Ravet et al., 2003). Besides these ω3‐PUFAs, the supplementation of the ω6‐PUFA arachidonic acid (ARA, 20:4ω6) to a C 20 ‐PUFA‐free diet was shown to increase the somatic growth (Ilić et al., 2019) and reproduction (Martin‐Creuzburg et al., 2010) of Daphnia sp. Furthermore, Schlotz et al.…”

Food Quantity and Quality Interactions at Phytoplankton–Zooplankton Interface: Chemical and Reproductive Responses in a Calanoid Copepod

“…Essential FAs (EFAs) cannot be synthesized by consumers, or the synthesis rate is not sufficient to meet the basic biochemical needs of consumers (Arts et al, 2001;Kainz et al, 2004), and thus must be acquired through diet. ω3and ω6-polyunsaturated FAs (PUFAs) such as eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA) are essential for animals and have received intense attention (Müller-Navarra, 2008;Parrish, 2009;Taipale et al, 2011;Ilić et al, 2019). There is evidence for the significance of phytoplankton elemental stoichiometry or EFAs in regulating marine zooplankton growth (Malzahn and Boersma, 2012;Diez et al, 2013), egg production (Augustin and Boersma, 2006;Jónasdóttir et al, 2009;Franco-Santos et al, 2018), development rate (Marja et al, 1998;Malzahn et al, 2010;Mathews et al, 2018), feeding behavior (Meunier et al, 2016), and movement patterns (Herstoff et al, 2019).…”