4.1. Multi-generational influences of DEHTP on fitness
The fitness evaluation was performed in reproduction, lifespan and
behavior. In the aspect of reproduction, the oscillation between
stimulation and inhibition over generations was also reported in the
multi-generational effects of ionic liquids and antibiotics
(Zhang and Feng, 2022; Zheng et
al., 2022). On one hand, the alteration from inhibition in earlier
generation (e.g., in F2) to stimulation in later one (F3) showed
generation-dependent hormesis, which was also observed in the
reproductive effects of antibiotics (Zheng et al., 2022), ionic liquids
(Shi et al., 2021; Zhang and Feng, 2022) on C. elegans and those
of graphene oxide on Acheta domesticus (Dziewięcka et al., 2020).
Hormesis over generations (also referred as trans-hormesis) were found
in various organisms (Agathokleous et al., 2022; Costantini, 2022). On
the other hand, the alteration in effects across generations indicated
that the organisms actively adjusted fetal response to the maternal
challenges, which is essential to ensure the fitness or adaption to
sustain the population survival (Yue et al., 2021). Notably, the
responses in the offspring did not always match the stresses that the
offspring actually experience. From an ecological perspective,
pre-conditioning hormesis can improve resilience to subsequent exposure
(Costantini et al., 2010; Costantini et al., 2014). From a health
perspective, it may even strengthen therapeutic benefit (Dhawan et al.,
2020). However, pre-conditioning hormesis is costly under the mismatch
between the actual environment in offspring and the predicted
environment by parents. Therefore, the long-term effects of DEHTP
deserve ecological concerns.
The trade-off effects between lifespan and reproduction by DEHTP were
also observed in the toxicities of other pollutants, e.g., ionic liquids
(Shi et al., 2021; Zhang and Feng, 2022) and antibiotics (Yu et al.,
2017). The trade-off relationship showed a common strategy to balance
energy investment in adapting environments for better fitness. On one
hand, more reproduction at the expense of lifespan is essential to the
population’s survival and continuation (Yu et al., 2017). On the other
hand, lower reproduction with an extended lifespan aids individual
organisms to escape from environmental stress. Both aspects were
observed in the effects of DEHTP but in different generations. Again,
the trade-off effects over generations also supported the active
adjustment of organisms to environmental stresses. The results
collectively indicated that phthalate might potentially disturb
adaptation and evolutionary changes.
In the aspect of behavior, the results demonstrated that DEHTP caused
avoidant behavior in nematodes, which allows the individuals to escape
from environmental stresses. Notably, the influences of DEHTP on
reproduction, lifespan, growth and behavior were all observable at 0.8
mg/L and even lower concentrations that are environmental realistic
(e.g., 0.07-6.1 mg/kg as the arithmetic mean values in dust) (Nagorka et
al., 2011). The results also brought up an assumption that DEHTP
resulted in caloric restriction by less foraging behavior and less
efficient food uptake. The caloric restriction decreased the overall
available energy, which subsequently resulted in energy allocation among
life traits according to the energy budget theory (Matyja et al., 2020;
Yu et al., 2018). The energy allocation also influenced the trade-off
relationships over generations (Wang et al., 2022a). Moreover, the
caloric restriction is important in the evolutionary responses with more
resilient to other stressors, and therefore partially explained the
pre-conditioning hormesis (Speakman, 2020). Therefore, further studies
on the caloric restriction would explain the aforementioned trade-off
relationships between reproduction and lifespan, and also the
generational effects.