Partitioning of Respiration in an Animal-Algal Symbiosis: Implications for Different Aerobic Capacity between Symbiodinium spp.
Date
2016-04-18
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Frontiers Media S.A.
Abstract
Cnidarian-dinoflagellate symbioses are ecologically important and the subject of much
investigation. However, our understanding of critical aspects of symbiosis physiology,
such as the partitioning of total respiration between the host and symbiont, remains
incomplete. Specifically, we know little about how the relationship between host and
symbiont respiration varies between different holobionts (host-symbiont combinations).
We applied molecular and biochemical techniques to investigate aerobic respiratory
capacity in naturally symbiotic Exaiptasia pallida sea anemones, alongside animals
infected with either homologous ITS2-type A4 Symbiodinium or a heterologous isolate of
Symbiodinium minutum (ITS2-type B1). In naturally symbiotic anemones, host, symbiont,
and total holobiont mitochondrial citrate synthase (CS) enzyme activity, but not host
mitochondrial copy number, were reliable predictors of holobiont respiration. There
was a positive association between symbiont density and host CS specific activity
(mg protein−1), and a negative correlation between host- and symbiont CS specific
activities. Notably, partitioning of total CS activity between host and symbiont in this
natural E. pallida population was significantly different to the host/symbiont biomass
ratio. In re-infected anemones, we found significant between-holobiont differences in
the CS specific activity of the algal symbionts. Furthermore, the relationship between the
partitioning of total CS activity and the host/symbiont biomass ratio differed between
holobionts. These data have broad implications for our understanding of cnidarian-algal
symbiosis. Specifically, the long-held assumption of equivalency between symbiont/host
biomass and respiration ratios can result in significant overestimation of symbiont
respiration and potentially erroneous conclusions regarding the percentage of carbon
translocated to the host. The interspecific variability in symbiont aerobic capacity provides
further evidence for distinct physiological differences that should be accounted for when
studying diverse host-symbiont combinations.
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Hawkins TD, Hagemeyer JCG, Hoadley KD, Marsh AG and Warner ME (2016) Partitioning of Respiration in an Animal-Algal Symbiosis: Implications for Different Aerobic Capacity between Symbiodinium spp. Front. Physiol. 7:128. doi: 10.3389/fphys.2016.00128