Temperature-dependent benefits of bacterial exposure in embryonic development of Daphnia magna resting eggs

Abstract

The environments in which animals develop and evolve are profoundly shaped by bacteria, which affect animals both indirectly through their role in biogeochemical processes and directly through antagonistic or beneficial interactions. The outcomes of these activities can differ according to environmental context. In a series of laboratory experiments with diapausing eggs of the water flea Daphnia magna, we manipulated two environmental parameters, temperature and presence of bacteria, and examined their effect on development. At elevated temperatures (≥26°C), resting eggs developing without live bacteria had reduced hatching success and correspondingly higher rates of severe morphological abnormalities compared with eggs with bacteria in their environment. The beneficial effect of bacteria was strongly reduced at 20°C. Neither temperature nor the presence of bacteria affected directly developing parthenogenetic eggs. The mechanistic basis of this effect of bacteria on development is unclear, but these results highlight the complex interplay of biotic and abiotic factors influencing animal development after diapause.

The microbiota of diapause: How host–microbe associations are formed after dormancy in an aquatic crustacean

“…If the necessary beneficial microbiota are transmitted by the parent into the resting stage, then the micro‐organisms can be considered a form of parental effect or a source of heritable nongenetic variation in their host (Badyaev & Uller, ; Zilber‐Rosenberg & Rosenberg, ). The occurrence of microbial transmission through resting stages would also support the often untested assumption that the microbial symbionts are deriving a benefit from the association (Mushegian & Ebert, ), since host and symbiont reproduction would be linked across host generations. Where the host is dependent on acquiring beneficial microbes from the environment after dormancy, we would expect low taxon‐specificity in the host–microbe association, because selection would disfavour reliance on specific microbes whose presence is not guaranteed in the environment where hatching occurs.…”

Host-Associated Bacterial Communities Vary Between Daphnia galeata Genotypes but Not by Host Genetic Distance

“…Studies in Daphnia magna indicate that host-associated bacterial communities are generally required for survival, reproduction, and nutrition [ 16 ]. Daphnia- associated bacteria also influence ecologically relevant traits such as tolerance to cyanobacteria [ 17 , 18 ], host embryonic development [ 19 ], and overall ecological success [ 20 ]. The community composition of gut bacteria in D. magna is influenced by both the host genotype and by a variation in environmental bacteria [ 21 , 22 ].…”

“…Paleo-genetic reconstruction studies suggest that the genetic architecture of Daphnia populations varies by sediment depth and reflects responses to environmental stressors over time [ 27 ]. The bacterial communities associated with Daphnia -resting eggs deposited in the sediment have a beneficial effect on the survival of Daphnia hatched from those eggs, and may be required for the establishment of clonal lines [ 19 ]. However, no studies so far have utilized naturally occurring genetic variation among Daphnia across sediment depth to address host genotypic variation as a determinant of composition of bacterial communities in Daphnia .…”

The Mercury-Tolerant Microbiota of the Zooplankton Daphnia Aids in Host Survival and Maintains Fecundity under Mercury Stress

“…A similar report also showed that a Pseudomonas strain isolated from a D. magna host is beneficial to the development of D. magna resting eggs at warm conditions. 84 Under mercury stress, lower survival rates were observed for the three mercury-treated groups when compared to their counterparts at the end of the assay (day 18): Bac-Suppl + Hg (43%, n = 13/30), Pse-Inf + Hg (70%, n = 21/30), and Bac- Free + Hg (60%, n = 18/30). Daphnids from the Bac-Suppl + Hg were most severely affected under mercury stress (χ 2 = 17.22, p < 0.0001) while the survival rates of Pse-Inf + Hg daphnids were statistically similar to those of Pse-Inf daphnids (χ 2 = 2.18, p = 0.14).…”