Morphogen-Based Chemical Flypaper for Agaricia humilis Coral Larvae

Abstract

Larvae of the scleractinian coral Agaricia humilis settle and metamorphose in response to chemosensory recognition of a morphogen on the surfaces of Hydrolithon boergesenii and certain other crustose coralline red algae. The requirement of the larva for this inducer apparently helps to determine the spatial pattern of recruitment in the natural environment. Previous research showed that the inducer is associated with the insoluble cell wall fraction of the recruiting algae or their microbial epibionts, and that a soluble but unstable fragment of the inducing molecule can be liberated by limited hydrolysis, either with alkali or with enzymes specific for cell wall polysaccharides. We now show that the parent morphogen can be solubilized by gentle decalcification of the algal cell walls with the chelators EGTA or EDTA, suggesting that the morphogen may be a component of the calcified recruiting alga itself, rather than a product of any noncalcified microbial epibionts. The solubilized inducer is subsequently purified by hydrophobic-interaction and DEAE chromatography. The purified, amphipathic morphogen retains activity when tightly bound to beads of a hydrophobic-interaction chromatography resin, and this activity (tested with laboratory-reared larvae) is identical in the ocean and the laboratory. We have attached the purified, resin-bound inducer to surfaces coated with a silicone adhesive and thus produced a potent artificial recruiting substratum--i.e., a morphogen-based chemical "flypaper" for A. humilis larvae. This material should prove useful in resolving the role of chemosensory recognition of morphogens in the control of substratum-specific settlement, metamorphosis, and recruitment and in the maintenance of species isolation mechanisms in the natural environment.

Elevated seawater temperature causes a microbial shift on crustose coralline algae with implications for the recruitment of coral larvae

“…Coral larvae actively select their site of permanent attachment using chemical cues to induce metamorphosis (Morse et al, 1988(Morse et al, , 1994(Morse et al, , 1996Heyward and Negri, 1999). The primary source of these chemical morphogens is various species of non-geniculate calcareous coralline algae (CCA).…”

Pre-planular external development in the brooding coral Agaricia humilis

“…Our observations further show that coralline algae on the tiles were not ultimately necessary for settlement (some coralline algae are known to induce settlement in A. humilis: Morse et al 1994, Raimondi & Morse 2000. The catholic settlement of the small planulae may indicate choice of a less optimal substrate by individuals with a low survival chance.…”

Proceedings of the Smithsonian Marine Science Symposium

“…Coral larvae possess a wide array of behaviors that allow them to enhance the likelihood of successful settlement, including, but not limited to, sensitivity to light (Lewis, 1974;Mundy and Babcock, 1998), depth (Carlon, 2001Baird et al, 2003;Suzuki et al, 2008), and chemical cues (Morse et al, 1994). One fi eld study showed that multiple behavioral choices determined the larval settlement site of the Caribbean brooder Agaricia humilis (Raimondi and Morse, 2000).…”

“…Chemical cues are implicated for both settlement and metamorphosis of corals and may be released by conspecifi cs and other organisms that indicate appropriate habitat for survival and growth. Research in the Caribbean showed that a membrane-bound carbohydrate complex from the coralline red alga Hydrolithon boergesenii induced settlement and metamorphosis in the brooded larvae of Agaricia humilis (Morse and Morse, 1991;Morse et al, 1994). It was suggested that many corals require an algal cue for the induction of settlement, indicating a common chemosensory mechanism for settlement and metamorphosis among coral larvae (Morse et al, 1996).…”