Transgeneralional MHW effect was independent of fish predator cues
There is mixed evidence of transgenerational effects of multiple
stressors on the vulnerability of aquatic species. On the one hand,
there is evidence that corals (Torda et al., 2017) coral fishes
(Donelson et al., 2012) show rapid transgenerational acclimation to
warming, and that can be linked to a complete compensation in aerobic
scope (Donelson et al., 2012), the epigenetic changes (Ryu et al., 2018)
or the associated microbes (Torda et al., 2017). On the other hand,
there is evidence that transgenerational exposure to extreme warming,
metal and fish predator cues (Pham, Dinh, Nguyen, & Quoc, 2020),
pesticides (Tran, Janssens, Dinh, & Stoks, 2018) may reduce the
offspring performance in same stressors as the cumulative impacts of
stressors across generations. This study found the different levels of
transgenerational acclimation of P. incisus to MHW in shaping the
F2 performance. Indeed, P. incisus showed a rapid
transgenerational acclimation to the lethal MHW effect as indicated by
increased survival in F1-MHW × F2-MHW exposed males and females to the
control temperature. As MHW induced mortality in F1 which may result in
some genetic selection for higher thermal tolerance. Interestingly, FPC
played a minor role in MHW transgenerational acclimation as indicated by
no or minor variation in the effect size of the transgenerational
acclimation to MHW in the presence or absence of FPC, suggesting the
dominant effect of MHW.
At the sublethal effect, the magnitude of transgenerational MHW
acclimation was much smaller than survival. Indeed, we found consistent
and clear evidence that transgenerational effects of MHWs (F1-MHW ×
F2-MHW) resulted in 5-10% better performance of F2 P. incicusthan the direct MHW effect (F2-MHW alone); all were substantially lower
than the performance of P. incisus in the control temperature.
The transgenerational MHW effects caused ~50%
reductions in cumulative nauplii and faecals; both parameters were
significantly and positively correlated, suggesting that the lowered
energy intake constrained the reproduction. Furthermore, the lower
number of nauplii hatched per F1-MHW × F2-MHW exposed females further
contributed to the lowered cumulative nauplii and suggested the lethal
transgenerational MHW effect on embryonic development (see also
Grønning, Doan, Dinh, Dinh, & Nielsen, 2019 for Pseudodiaptomus
annandalei ). Similar lower cumulative nauplii and faecals have been
previously observed in P. incisus that was exposed to MHW for two
generations (Dinh et al., 2021). The reduced F2 P. incisusperformance was likely a direct cost of maintaining a high survival and
the selection for tolerant genotypes from the F1 generation.
Similar to the survival, the presence of FPC in F1 (F1-FPC) or F2
(F2-FPC) generally only played a minor role in shaping the parental
effect of MHW (F1-MHW) or direct effect of MHW (F2-MHW) on the F2
generation as indicated by the change in the effect size of parental and
transgenerational MHW effects was typically smaller 5% of the total
effects of both MHW and FPC. The dominant effect of MHW is likely
widespread for most marine invertebrates, as indicated by massive
ecological consequences during MHWs (Hughes et al., 2019; Smale et al.,
2019), even mass mortality of various groups of coastal aquatic taxa
(Garrabou et al., 2009; 2019).