Dietary Essential Amino Acids Affect the Reproduction of the Keystone Herbivore Daphnia pulex

Recent studies have indicated that nitrogen availability can be an important determinant of primary production in freshwater lakes and that herbivore growth can be limited by low dietary nitrogen availability. Furthermore, a lack of specific essential nitrogenous biochemicals (such as essential amino acids) might be another important constraint on the fitness of consumers. This might be of particular importance for cladoceran zooplankton, which can switch between two alternative reproductive strategies – the production of subitaneously developing and resting eggs. Here, we hypothesize that both the somatic growth and the type of reproduction of the aquatic keystone herbivore Daphnia is limited by the availability of specific essential amino acids in the diet. In laboratory experiments, we investigated this hypothesis by feeding a high quality phytoplankton organism (Cryptomonas) and a green alga of moderate nutritional quality (Chlamydomonas) to a clone of Daphnia pulex with and without the addition of essential amino acids. The somatic growth of D. pulex differed between the algae of different nutritional quality, but not dependent on the addition of dissolved amino acids. However, in reproduction experiments, where moderate crowding conditions at saturating food quantities were applied, addition of the essential amino acids arginine and histidine (but not lysine and threonine) increased the total number and the developmental stage of subitaneous eggs. While D. pulex did not produce resting eggs on Cryptomonas, relatively high numbers of resting eggs were released on Chlamydomonas. When arginine and histidine were added to the green algal diet, the production of resting eggs was effectively suppressed. This demonstrates the high, but previously overlooked importance of single essential amino acids for the reproductive strategy of the aquatic keystone herbivore Daphnia

Life-history characteristics and fitness in descendents of parthenogenetic and ex-ephippio females of Daphnia magna

Daphnids of ex-ephippial and parthenogenetic origin differ substantially in life-history. Possible maternally transmitted ex-diapause effects of differing female origin on the fitness of their offspring were studied across multiple clones in Daphnia magna. Ex-ephippial daphnids responded in egg size to different constant food concentrations with the same pattern as parthenogenetic females. Significant differences in egg characteristics between females of different origin were only found for the first clutch produced under high food. The smaller size of eggs in ex-ephippial females, however, did not translate into size differences of first-clutch neonates. A trend for lower mass density per body volume was detected in offspring from ex-ephippial females in comparison with parthenogenetic daphnids. Hence, an ex-diapause effect transmitted by ex-ephippial mothers to their parthenogenetic offspring is likely. However, there was no difference in life-histories and fitness between offspring produced by females of ex-ephippial and parthenogenetic origin at both, high and low food concentrations across multiple clones. Thus, a significant ex-diapause effect on fitness in successive parthenogenetic generations may not be expected in D. magna at the population leve

Seasonal adaptation of ex-ephippio and parthenogenetic offspring of Daphnia magna: differences in life history and physiology

1. Physiology and life history of ex-ephippial and parthenogenetic offspring of Daphnia magna Straus were compared to test the hypothesis that females hatching from resting eggs are well adapted to the predictable high-food conditions of the spring algal bloom. 2. Although ex-ephippial neonates were smaller than parthenogenetic neonates, they showed higher juvenile growth rates that compensated for the size difference by the time of maturation. 3. At high food concentration, ex-ephippial females were even larger at maturation than parthenogenetic females, produced more eggs, and reached a higher rate of population increase. 4. The high activity of the ex-ephippial females was accompanied by higher metabolic rates, which in combination with the low initial mass resulted in reduced survival times under starvation. 5. Thus, the two phenotypic types of offspring produced by Daphnia are adapted to differing conditions. Ex-ephippial females are superior to parthenogenetic offspring under high food conditions, but inferior when food is limiting. 6. This pattern selects for synchronous hatching of resting eggs in spring when the spring algal bloom is to be expected

Initial and long-term consequences of attempts to improve fish-food resources in Lithuanian waters by introducing alien peracaridan species: a retrospective overview

In this overview, we consider the rationale and practice of invertebrate introductions into Lithuanian waters, the current distribution of introduced species, test the theoretical expectations of introduction of peracaridan species into lakes, and summarize the large-scale consequences of these translocations. After some early attempts to transfer locally available species within the country, peracaridan species from the Ponto-Caspian region were introduced into Lithuanian waters during the 1960s (Pontogammarus robustoides, Obesogammarus crassus, Chaetogammarus warpachowskyi, Paramysis lacustris, Limnomysis benedeni and Hemimysis anomala). After their establishment at the site of first introduction in a newly constructed water reservoir on the Nemunas River, further deliberate introductions into Lithuanian lakes and water reservoirs, as well as into more distant areas, were undertaken. These introduced species soon contributed to fish diet and a subsequent increase in the production of commercially important fish was envisaged. However, our collation of available data does not support the enhancement of fish production in Lithuanian lakes. Although perch (selected as a model fish species) assimilated the introduced species into diet and sometimes in large quantities, there was no subsequent influence on somatic growth rates when compared with perch from lakes devoid of alien peracaridans. Comparisons of littoral fish communities of different lakes, and commercial catches in the lake with the most numerous populations of introduced species also indicate no significant effect on fish production. Negative consequences of introduction are more than obvious in contrast. To date, most of the introduced Ponto-Caspian amphipod and mysid species occur in different sites of the Baltic Sea basin outside Lithuania, and their further dispersal may be expected. These species, especially amphipods, have proved to be highly ecologically aggressive, inducing change in resident macroinvertebrate communities and causing increase of biological contamination (i.e. detract from naturalness). Thus, the introduction of alien fodder species was ill advised from an economic, and even adverse from an environmental perspective

The killer shrimp Dikerogammarus villosus (Crustacea, Amphipoda) invades Lithuanian waters, South-Eastern Baltic Sea

The killer shrimp Dikerogammarus villosus was recorded for the first time in Lithuanian waters in 2015. The species was detected in three sites in the Curonian Lagoon (on two buoys in the lagoon strait and the harbour, and one littoral sampling site) and in the mouth of the Šventoji River. The species presence in the buoy fouling suggests the involvement of shipping in species introduction. Most likely D. villosus has arrived to the Curonian Lagoon with commercial ships, while the invasion into the mouth of the Šventoji River may be associated with leisure shipping as the port situated therein is not currently functioning. Further northward expansion of the killer shrimp in the Baltic Sea basin seems very probable. As the species is highly aggressive, alterations of local macroinvertebrate assemblages can also be predicted

Report on national ICP IM activities in Lithuania

Vytauto Didžiojo universitetasŽemės ūkio akademij

Report on national ICP IM activities in Lithuania

Vytauto Didžiojo universitetasŽemės ūkio akademij