Transgenerational plasticity in the eye size of Daphnia

Transgenerational epigenetic inheritance increases trait variation but is not adaptive

Understanding processes that can produce adaptive phenotypic shifts in response to rapid environmental change is critical to reducing biodiversity loss. The ubiquity of environmentally induced epigenetic marks has led to speculation that epigenetic inheritance could potentially enhance population persistence in response to environmental change. Yet, the magnitude and fitness consequences of epigenetic marks carried beyond maternal inheritance are largely unknown. Here, we tested how transgenerational epigenetic inheritance (TEI) shapes the phenotypic response of Daphnia clones to the environmental stressor Microcystis. We split individuals from each of eight genotypes into exposure and control treatments (F0 generation) and tracked the fitness of their descendants to the F3 generation. We found transgenerational epigenetic exposure to Microcystis led to reduced rates of survival and individual growth and no consistent effect on offspring production. Increase in trait variance in the F3 relative to F0 generations suggests potential for heritable bet hedging driven by TEI, which could impact population dynamics. Our findings are counter to the working hypothesis that TEI is a generally adaptive mechanism likely to prevent extinction for populations inhabiting rapidly changing environments.

Developmental defects in cognition, metabolic and cardiac function following maternal exposures to low environmental levels of selective serotonin re-uptake inhibitors and tributyltin in Daphnia magna

Aquatic organisms are exposed to low concentrations of neuro-active chemicals, many of them acting also as neuroendocrine disruptors that can be hazardous during earlier embryonic stages. The present study aims to assess how exposure early in live to environmental low concentrations of two selective serotonin reuptake inhibitors (SSRIs), fluoxetine and sertraline, and tributyltin (TBT) affected cognitive, metabolic and cardiac responses in the model aquatic crustacean Daphnia magna. To that end, newly brooded females were exposed for an entire reproductive cycle (3-4 days) and the response of collected juveniles in the first, second and third consecutive broods, which were exposed, respectively, as embryos, provisioned and un-provisioned egg stages, was monitored. Pre-exposure to the selected SSRIs during embryonic and egg developmental stages altered the swimming behaviour of D. magna juveniles to light in a similar way reported elsewhere by serotonergic compounds while TBT altered cognition disrupting multiple neurological signalling routes. The studied compounds also altered body size, the amount of storage lipids in lipid droplets, heart rate, oxygen consumption rates and the transcription of related serotonergic, dopaminergic and lipid metabolic genes in new-born individuals, mostly pre-exposed during their embryonic and provisioning egg stages. The obtained cognitive, cardiac and metabolic defects in juveniles developed from exposed sensitive pre-natal stages align with the "Developmental Origins of Health and Disease (DoHAD)" paradigm.

Environmental Stress and the Morphology of Daphnia pulex

AbstractMorphological variation is sometimes used as an indicator of environmental stress in animals. Here, we assessed how multiple morphological traits covaried in Daphnia pulex exposed to five common forms of environmental stress (high temperature, presence of predator cues, high salinity, low food abundance, and low Ca). We measured animal body length, body width, head width, eyespot diameter, and tail spine length along with mass in animals of five different ages (3, 6, 9, 12, and 15 d). There were strong allometric relationships among all morphological traits in reference animals and strong univariate effects of environmental stress on body mass and body length. We found that environmental stressors altered bivariate relationships between select pairwise combinations of morphological traits, with effects being dependent on animal age. Multivariate analyses further revealed high connectivity among body size-related traits but that eyespot diameter and tail spine length were less tightly associated with body size. Animals exposed to natural lake water with and without supplemental food also varied in morphology, with body size differences being suggestive of starvation and other unknown nutritional deficiencies. Yet our results demonstrate that the scaling of body morphological traits of Daphnia pulex is largely invariant with possible context-dependent plasticity in eye size and tail spine lengths. The strong coordination of traits indicates tight molecular coordination of body size during development despite strong and varied environmental stress.