Mounting of erratic histoincompatible responses in hermatypic corals: a multi-year interval comparison

Abstract

SUMMARYStudies on allorecognition in the phylum Cnidaria have disclosed complex arrays of effector mechanisms, specificity and competency to distinguish precisely between self and non-self attributes, and have revealed the existence of allogeneic maturity. Here we studied allo-responses between young Stylophora pistillata colonies by following 517 allogeneic interactions between naturally settled kin aggregates and by establishing 417 forced allogeneic and autogeneic assays made of solitarily settled spat that were cut into two similar size subclones, of which one had been challenged allogeneically. Fused assays were exposed to a second allorecognition challenge, made of three allogeneic types. Whereas about half of the kin allogeneic interactions led to tissue fusions and chimera formations, none of the 83 non-sibling pair combinations were histocompatible. In contrast to previous results we recorded rejections between siblings at the age of less than two months. More challenging, we documented cases of fusions between interacting siblings at ages older than one-year-old partners, all differing from a previous study made on the same coral population more than a decade ago. Similar erratic histoincompatible responses were recorded in other pocilloporid species. We suggest that these results reflect reduced genetic heterogeneity caused by chronic anthropogenic impacts on shallow water coral populations where planulae originating from the same mother colony or from different mother colonies that are genetically related share increasing parts of their genomes. Offspring born to related parents may also reveal an increase in genomic homozygosity, and altogether impose erratic alloimmunity.

Maternal-larval population genetic traits in Stylophora pistillata, a hermaphroditic brooding coral species

“…In Eilat, Red Sea, planula larvae of S. pistillata are a product of sexual reproduction with possibile partial inbreeding, which may indicate family relatedness between colonies populating the reef brought about by aggregated and rapid settlement of larvae (Amar et al 2008a;Amar and Rinkevich 2010;Atoda 1947;Nishikawa et al 2003;Linden and Rinkevich 2011) near maternal colonies. Reduced genetic heterogeneity in S. pistillata populations at Eilat, an alarming omen in the long-term, has also been documented in allogeneic response portraits characteristic to this species (Amar and Rinkevich 2010). Following this trend, planulae originating from the same maternal colony or from different mothers genetically related would share increasing parts of their genomes.…”

“…Larvae of S. pistillata display rapid settlement and a relatively short competency period (Atoda 1947;Nishikawa et al 2003;Linden and Rinkevich, 2011). They also exhibit dispersal polymorphism in early versus late released larvae during the reproductive season ) and chimera formation following an aggregated mode of settlement (Frank et al 1997;Amar et al 2008a;Amar and Rinkevich 2010). Low levels of gene flow between adjacent S. pistillata populations were further documented in two reef locations (Ayre and Hughes 2000;Nishikawa et al 2003; the GBR, Australia and Okinawa Island, Japan, respectively), indicating relatively weak connectivity between neighboring reefs and local recruitment of corals.…”

Self-recognition in corals facilitates deep-sea habitat engineering

“…In cases where fusion has been identified, it has been assumed that both colonies were closely related, and were displaying characteristics which have also been noted in tropical corals345.…”

“…True skeletal fusion in tropical corals occurs in conjunction with allogeneic tissue fusion, which is controlled by allorecognition, a major characteristic in invertebrate immunity4 that depends upon the ability to recognise self and non-self46. In tropical corals, the ability to allorecognise depends largely on the maturity of the individuals with allogeneic fusion only reported in juvenile corals.…”

“…In tropical corals it is thought that the lack of an active historecognition system during the early stages of ontogeny (4–8 months) allows juveniles of the same species to occasionally allogeneically fuse678. However, allorecognition in corals is a complex synergy of effector mechanisms, specificity and competency469, which may have evolved as far back as 400 million years ago10. Allogeneic interactions between juvenile tropical corals fall into three groups: (A) true fusion (resulting in a chimaera), (B) incompatible fusion, or (C) non-fusion6.…”