The roles of age, parentage and environment on bacterial and algal endosymbiont communities in Acropora corals

Abstract

The bacterial and microalgal endosymbiont (Symbiodiniaceae spp.) communities associated with corals have important roles in their health and resilience, yet little is known about the factors driving their succession during early coral life stages. Using 16S rRNA gene and ITS2 metabarcoding, we compared these communities in four Acropora coral species and their hybrids obtained from two laboratory crosses (Acropora tenuis × Acropora loripes and Acropora sarmentosa × Acropora florida) across the parental, recruit (7 months old) and juvenile (2 years old) life stages. We tested whether microbiomes differed between (a) life stages, (b) hybrids and purebreds, and (c) treatment conditions (ambient/elevated temperature and pCO2). Microbial communities of early life stage corals were highly diverse, lacked host specificity and were primarily determined by treatment conditions. Over time, a winnowing process occurred, and distinct microbial communities developed between the two species pair crosses by 2 years of age, irrespective of hybrid or purebred status. These findings suggest that the microbial communities of corals have a period of flexibility prior to adulthood, which can be valuable to future research aimed at the manipulation of coral microbial communities.

Maternal effects in gene expression of interspecific coral hybrids

“…The bacterial and microalgal endosymbiont (Symbiodiniaceae spp.) communities associated with these corals did not differ between the reciprocal hybrids and their maternal and paternal purebreds (Chan et al, 2019). Since these microorganisms carry vital functions to the coral hosts and can contribute to holobiont fitness differences (Blackall et al, 2015;Rosenberg et al, 2007), this finding suggests that the microbial communities were unlikely responsible for the observed holobiont fitness differences, and that these are probably underpinned by coral host genetic and/or nongenetic transgenerational factors.…”

“…Chan et al 2018Size (7 months) Offspring groups were not different in size under both ambient and elevated conditions Elevated temperature and pCO 2 conditions resulted in smaller size of all purebred and hybrid offspring groups Chan et al (2018) Size (1 year) Hybrid LT and its maternal purebred LL grew bigger (290-366 mm 2 ) than hybrid TL (47 mm 2 ). Purebred TT had no survivors Chan et al (2018) Bacterial community (7 months) Offspring groups were not associated with different bacterial communities as determined with 16S rRNA gene metabarcoding Chan et al (2019) Microalgal symbiont community (7 months) Offspring groups were not associated with different microalgal symbiont communities as determined with ITS2 metabarcoding Chan et al (2019) Interestingly, maternal effects were weaker in the hybrid cross of the other direction, with 334 and 661 DEGs observed when compared to its maternal and paternal population respectively (Videvall et al, 2016). Only one previous study has examined maternal effects in coral hybrid gene expression and only coral larvae were studied.…”

Maternal effects in gene expression of interspecific coral hybrids

“…In addition to the coral host, the host-associated microbiome can also have an impact on host gene expression (Barfield et al, 2018;Helmkampf et al, 2019). In our study, however, the bacterial and microalgal endosymbiont communities of the corals were similar at the time of sampling (Chan et al, 2019). The consistency between host gene expression and phenotypic results thus suggests that maternal host-related factors were likely the drivers behind the observed fitness differences.…”

“…The bacterial and microalgal endosymbiont (Symbiodiniaceae spp.) communities associated with these corals did not differ between the reciprocal hybrids and their maternal and paternal purebreds (Chan et al, 2019). Since these microorganisms carry vital functions to the coral hosts and can contribute to holobiont fitness differences (Blackall et al, 2015;Rosenberg et al, 2007), this finding suggests that the microbial communities were unlikely responsible for the observed holobiont fitness differences, and that these are likely underpinned by coral host genetic and/or non-genetic transgenerational factors .…”

“…However, exposure to elevated temperature and p CO 2 conditions did not result in differential coral gene expression. Although the composition of bacterial and microalgal endosymbiont communities of these corals was similar under ambient and elevated conditions and between hybrids and purebreds (Chan et al, 2019), these microbes may have expressed different genes and contributed to holobiont phenotypic differences. Other less studied members of the coral holobiont, such as viruses and fungi (that were not examined), may also have contributed to coral survival and size differences.…”