Developmental changes in the intensity and distribution pattern of green fluorescence in coral larvae and juveniles

Abstract

Coral larvae and juveniles often exhibit green fluorescence due to green fluorescence proteins (GFP). Ontogenetic changes in the distribution pattern of green fluorescence in coral are not fully understood. We investigated changes in the intensity and distribution pattern of green fluorescence of the corals Acropora tenuis, Pocillopora damicornis, and Isopora palifera during early developmental stages. Green fluorescence distribution in larvae differed among the three species studied and changed after the larvae metamorphosed into primary polyps. Green fluorescence distributed mainly in the epidermis of P. damicornis and I. palifera larvae but in the gastrodermis in A. tenuis larvae. In P. damicornis and A. tenuis primary polyps, green fluorescence was present around the oral opening and in a ring structure below the tentacular ring. Green fluorescence was also present on the tips of the tentacles of P. damicornis and I. palifera primary polyps. Furthermore, green fluorescence intensity in A. tenuis primary polyps increased significantly after inoculation of symbionts, irrespective of the success of symbiont acquisition. In I. palifera, the fluorescence in tensity decreased and, in some cases, disappeared after the acquisition of symbionts. Moreover, bleaching stress increased green fluorescence in P. damicornis juveniles. The present observations suggest that green fluorescence intensity in juvenile corals is influenced by the presence or acquisition of symbiont cells as well as by stressful conditions. This study also suggests that GFP might have different functions among coral species and at different developmental stages of the corals.

Rapid counting and spectral sorting of live coral larvae using large-particle flow cytometry

“…Fluorescent proteins in corals have many hypothesized physiological and ecological roles, including protecting symbionts under high-light conditions and enhancing light availability under low-light conditions 22,25,28 , protecting the host from oxidative stress 29 , reducing herbivory 30 , and attracting photosymbionts to the larvae 31,32 . The concentration of GFP varies naturally among species and individuals, and throughout embryogenesis and larval development 23,27 . Here we rapidly quantified the patterns of GFP among (Fig.…”

“…Understanding the role of intrinsic fluorescence of coral gametes and larvae in coral biology and physiology is an active area of research 23 , 25 – 27 , and flow cytometry is well-placed to exploit this fluorescence and other spectral properties for rapid sorting and analysis of fluorescent properties. Fluorescent proteins in corals have many hypothesized physiological and ecological roles, including protecting symbionts under high-light conditions and enhancing light availability under low-light conditions 22 , 25 , 28 , protecting the host from oxidative stress 29 , reducing herbivory 30 , and attracting photosymbionts to the larvae 31 , 32 .…”

“…The optics assembly unit was tested with two excitation solid state lasers (488 and 561 nm), a photodiode detector for measuring extinction and time of flight (to estimate particle size), and photomultiplier tubes for fluorescence emission detection in the green (bandpass 525/50), yellow (bandpass 543/22), red (bandpass 586/20) and far red (bandpass 680/42) regions of the visible light spectrum. A 488 nm excitation laser with a power of 100 mW was chosen to excite the corals' cyan-green fluorescent proteins (GFP), which emit fluorescence in the green (~ 500 nm, green detector; see Spectral Sorting below; 25,27,50 . The 561 nm excitation laser with a power of 50 mW was selected to measure the endosymbiotic Symbiodiniaceae (sensu 51 ), which fluoresce in the red (see Spectral Sorting below) 50 .…”

“…are vertical transmitters 43 ; therefore, their eggs, embryos and larvae contain photosynthetic Symbiodiniaceae cells, which, when excited by green wavelengths ~ 560 nm, emit fluorescence in the far red spectrum (~ 685 nm)]. Adult and larval Montipora capitata also contain pigments that are (at least partially) homologous to cyan-green fluorescent proteins (GFP), common in anthozoans 22,25,27 .…”

Application of RNA Interference Technology to Acroporid Juvenile Corals

“…GFP is a fluorescent protein naturally present in coral, and thus its expression in planula larvae and juvenile polyps is easily monitored using fluorescence stereomicroscopy (Strader et al, 2015;Yuyama et al, 2018). GFP is expressed throughout tissues in the planula, and is especially abundant in the endoderm (Haryanti and Hidaka, 2019). The GFP intensity of juvenile polyps was reportedly changed due to the algal symbiosis and stress exposure (Yuyama et al, 2012a).…”