Gene expression was unaffected by long-term exposure to
elevated temperature and pCO2 conditions
Elevated temperature and p CO2 conditions had a
negative impact on survival and size of the corals used in this study
(Table 1), yet gene expression within an offspring group did not differ
between ambient and elevated conditions (Figure 1). Nevertheless, gene
expression changes under short-term acute stress are commonly
found in coral. This often
involves the regulation of genes encoding heat shock proteins, ion
transport, apoptosis, immune responses and/or oxidative stress (Barshis
et al., 2013; Desalvo et al., 2008; Meyer et al., 2011; Ruiz-Jones &
Palumbi, 2017). The absence of DEGs in corals under ambient versus
elevated conditions was unexpected and may be due to the relatively mild
and long-term nature of the treatments. The elevated conditions of this
study (ambient +1 °C, 685 ppm p CO2) were
relatively mild compared to many other longer-term studies (e.g.,
ambient +7 and + 12 ºC, Maor-Landaw et al., 2017; 856-3880 ppmp CO2, Vidal-Dupiol et al., 2013). In addition,
gene expression responses of corals under long-term stress have been
shown to differ from those under short-term stress. Despite significant
differences in CO2 concentration under control and
natural CO2 seep sites (i.e., ~355
versus 998 ppm), only 61 DEGs were found in A. millepora from the
two sites (Kenkel et al., 2017).
Similarly, the expression of calcification-related genes changed
significantly in A. millepora subjected to short-term (i.e., 3
days) high p CO2 exposure (Moya et al., 2012,
2015), but far fewer DEGs were found as exposure time increased (Moya et
al., 2015; Rocker et al., 2015). Since cellular stress gene expression
responses can be transient (Kültz, 2003), certain expression changes may
only be detectable during the initial exposure and therefore fewer
differentially expressed genes are generally found in long-term studies.