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opencc-zeroDec 2018View details →

Data from: The evolution of eye size in response to increased fish predation in Daphnia

Variation in eye size is ubiquitous across taxa. Increased eye size is correlated with improved vision and increased fitness via shifts in behavior. Tests of the drivers of eye size evolution have focused on macroevolutionary studies evaluating the importance of light availability. Predator-induced mortality has recently been identified as a potential driver of eye size variation. Here we tested the influence of increased predation by the fish predator, the alewife (Alosa pseudoharengus) on eye size evolution in waterfleas (Daphnia ambigua) from lakes in Connecticut. We quantified the relative eye size of Daphnia from lakes with and without alewife using wild-caught and third generation laboratory reared specimens. This includes comparisons between lakes where alewife are present seasonally (anadromous) or permanently (landlocked). Wild-caught specimens did not differ in eye size across all lakes. However, third generation lab reared Daphnia from lakes with alewife, irrespective of the form of alewife predation, exhibited significantly larger eyes than Daphnia from lakes without alewife. This genetically based increase in eye size may enhance the ability of Daphnia to detect predators. Alternatively, such shifts in eye size may be an indirect response to Daphnia aggregating at the bottom of lakes. To test these mechanisms, we collected Daphnia as a function of depth and found that eye size differed in Daphnia found at the surface versus the bottom of the water column between anadromous alewife and no alewife lakes. However, we found no evidence of Daphnia aggregating at the bottom of lakes. Such results indicate that the evolution of a larger eye may be explained by a connection between eyes and enhanced survival. We discuss the cause of the lack of concordance in eye size variation between our phenotypic and genetic specimens and the ultimate drivers of eye size.

opencc-zeroOct 2020View details →

Data from: Resilience to changes in lake trophic state: nutrient allocation into Daphnia resting eggs

During past decades, many lakes underwent drastic human-caused changes in trophic state with strong implications for population dynamics and food web processes. We investigated the influence of trophic state on nutrient allocation into Daphnia resting eggs. The production of resting eggs is an important survival strategy, allowing Daphnia to cope with unfavorable environmental conditions. Allocation of essential nutrients into resting eggs may crucially influence embryonic development and offspring survival and thus is of great ecological and evolutionary interest. The capacity of Daphnia to adjust the allocation of nutrients into resting eggs may depend on the dietary nutrient supply, which may vary with trophic state-related changes in the phytoplankton community composition. Resting eggs were isolated from sediment cores taken from Lake Constance, a large pre-alpine lake with a distinct eutrophication and re-oligotrophication history, and analysed for elemental (carbon, nitrogen and phosphorus) and biochemical (sterols and fatty acids) nutrients. Carbon allocation into Daphnia resting eggs continuously decreased over time, irrespective of changes in trophic state. The allocation of nitrogen into Daphnia resting eggs followed the changes in trophic state, i.e. nitrogen concentrations in resting eggs increased with eutrophication and decreased again with re-oligotrophication. The allocation of phosphorus, sterols and long-chain polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA), into Daphnia resting eggs did not change significantly over time. Changes in trophic state strikingly influenced all trophic levels in Lake Constance. However, nutrient allocation into Daphnia resting eggs was mostly resilient to changes in lake trophic state.

opencc-zeroOct 2020View details →

Raw data used in: Variations in effects of ectosymbiotic microbes on the growth rates among different species and genotypes of Daphnia fed different algal diets

Several recent studies have shown that ectosymbiotic bacterial microbiota, including gut microbes, affect the growth and reproduction of Daphnia, a key organism in lake ecosystems. However, these studies examined specific species, such as the model organism, D. magna, and used green algae as food. It is unclear if symbiotic bacteria affect fitness in other Daphnia species common in lakes and ponds in Japan. In this study, we examined the growth rates of sterilized individuals of two D. pulex genotypes with D. magna using the green algae Scenedesmus and the diatom Cyclotella as algal diets. In addition, we examined the growth rate of the sterilized Daphnia pulex individuals infected by Limnohabitans spp., previously reported to promote the fitness of D. magna as ectosymbiotic bacteria. We found that the effects of ectosymbiotic bacteria on growth rate differed not only between different genotypes of D. pulex but also between individuals fed the different algal diets. The results suggest that the genotype- and diet-specific differences in fitness-dependency on the ectosymbiotic microbiota can be factors affecting the genetic structures of D. pulex populations.

opencc-zeroDec 2020View details →

Quantitative genetics of phosphorus content in the freshwater herbivore, Daphnia pulicaria

1. Phosphorus (P) is essential for growth of all organisms, and P content is correlated with growth in most taxa. Although P content was initially considered to be a trait fixed at the species level, there is growing evidence for considerable intraspecific variation. Selection on such variation can thus alter the rates at which P fluxes through food webs. 2. Nevertheless, prior work describing the sources and extent of intraspecific variation in P content were not genetically explicit, confounded by unknown genetic background and evolutionary history. We constructed an F2 recombinant population of the dominant freshwater grazer, Daphnia pulicaria to mitigate such issues. 3. F2 recombinants exhibited considerable variation in growth rate, P content (0.49% to 1.97%), P use efficiency (PUE; 51 to 208 mg biomass/mg P), and correlated traits such as hatching time of resting eggs, in common garden conditions. 4. These results clearly demonstrate the scope of genetic recombination in generating variation in ecologically-relevant traits. The absence of environmental selection is a likely component driving such variation not observed in natural settings. 5. Although phosphoglucose isomerase (PGI) genotype was significantly associated with variation in hatching time of resting eggs, contrary to prior work with less rigorous designs, allelic variation at the PGI locus did not explain variation in P content and PUE of Daphnia, indicating that such quantitative traits are under polygenic control. 6. Together, these results suggest that although there is considerable genetic scope for variation in key ecologically-relevant traits, such as P content and efficiency of P use, these traits are likely under strong stabilizing selection, most likely due to selection on growth rate and size. Importantly, our observations suggest that anthropogenic alterations to P supply due to eutrophication could alter selection on these traits, thereby rapidly altering the role Daphnia plays in the P cycle of lakes.

FIGURE 14 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 14. Morphometric comparison of Daphnia sakhaliensis sp.nov. (red quadrates) and Daphnia sinevi (blue triangles) males. A, x—rostrum length; y—rostrum length/head height ratio. B, x—rostrum length/head height ratio; y—1st postabdominal teeth/ 5th teeth length ratio.

FIGURE 13 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 13. Daphnia sakhaliensis sp.nov. (A–C, G–H) and Daphnia sinevi (D–F, I–J). A–F, head. G–J, seta 2 of exopod III. Scale bars denote 0.1 mm.

FIGURE 12 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 12. Daphnia sakhaliensis sp.nov. from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M0871. A–D, male postabdomen. E–G, postabdomenal claw. Scale bars denote 0.1 mm.

FIGURE 7 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 7. Daphnia sakhaliensis sp.nov. from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M-0871. A–F, armature of postero-ventral and posterior margin of valve. G, caudal spine. H, antenna I. I–J, antenna II and proximal portion of its basal segment. K–L, second segment of its exopod and its distal segment. M–O, apical setae of different individuals. Scale bars denote 0.1 mm.

FIGURE 2. Daphnia sinevi s.str., adult male from a in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 2. Daphnia sinevi s.str., adult male from a puddle near reservoir of Luchegorskaya power station, Primorski Territory, Russia, AAK M-651. A, adult male. B–D, its head, lateral view. E, anterior and ventral margin of valves. F, setae at ventral margin. G–I, armature of postero-ventral and posterior margin. J–K, caudal spine. L–M, postabdomen. N–P, armature of postabdominal claw. Scale bars denote 0.1 mm.

FIGURE 11 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 11. Daphnia sakhaliensis sp.nov., adult male from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M-0871. A–B, male antenna I. C, anterior and ventral margin of valves. D, setae at posterior portion of ventral margin. E–G, armature of postero-ventral and posterior margin of valve in male. H, caudal spine. I–J, limb I. K, copulatory hook of IDL. L–M, stiff setae of inner-distal portion of limb II. Scale bars 0.1 mm.

FIGURE 8 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 8. Daphnia sakhaliensis sp.nov. from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M-0871. A, limb I. B, ODL of limb I. C, limb II. D, limb III. E, seta 2 of exopod III. F, inner portion of limb III. G, limb IV. H–I, seta 1 of exopod IV. J, limb V. Scale bars denote 0.1 mm.

FIGURE 3. Daphnia sinevi s in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 3. Daphnia sinevi s.str., adult (A–G) and juvenile (H–K) male from a puddle near reservoir of Luchegorskaya power station, Primorski Territory, Russia, AAK M-651. A–B, adult male, antenna I. C, limb I of adult male and tip of its largest seta. D–E, outer distal lobe of limb I and armature of its distal portion. F–G, stiff setae of inner-distal portion of Limb II. H, juvenile male of second instar, general view. I, its head, lateral view. J, postabdomen. K, distal portion of limb I. Scale bars denote 0.1 mm.

FIGURE 1. Daphnia sinevi s in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 1. Daphnia sinevi s.str., parthenogenetic females from the type locality, a pond about 10 m in diameter in Avangard, AAK M-0061 (A), and a pool near road Avangard-Vostok (B–E), both localities are from Nakhodka Area, Primorski Territory. A–C, adult female. D–E, head. Scale bars denote 0.1 mm.

FIGURE 10 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 10. Daphnia sakhaliensis sp.nov. from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M0871. A, ephippial female, lateral view. B, reticulation on central portion of ephippium. C, dorsal portion of ephippium. D, adult male, lateral view. E–K, head, lateral view. Scale bars denote 0.1 mm.

FIGURE 9 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 9. Daphnia sakhaliensis sp.nov. from a puddle near River Tim', near Voskresenovka, Sakhalin Area, Russia, NMK 2432. A, limb I. B, ODL of limb I. C, seta of inner distal lobe = seta 1. D–E, setae 3 and 4. F–G, inner-distal portion of limb II. H, fragment of gnathobase II. I, seta 2 of exopod III. J, seta 1 of exopod IV. K, setae 1–2 of exopod V. Scale bars denote 0.1 mm.

FIGURE 6 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 6. Daphnia sakhaliensis sp.nov. from a puddle near River Tim', near Voskresenovka, Sakhalin Area, Russia, NMK 2432. A, adult parthenogenetic female. B–C, its head. D, postabdomen. E–I, postabdominal claw. J, armature of inner side of posterior margin. K, juvenile female, instar I. L, juvenile male, instar I, head. M, postabdominal claw of male I. Scale bars denote 1 mm for A, D, and 0.1 mm for B–C, E–O.

FIGURE 5 in A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East

FIGURE 5. Daphnia sakhaliensis sp.nov. from the Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M0871. A, adult parthenogenetic female. B–D, its head. E–F, postabdomen. G–J, postabdominal claw. Scale bars denote 1 mm for A, and 0.1 mm for B–J.