Allogeneic recognition and sex differentiation in chimeras of the freshwater sponge Ephydatia muelleri

Abstract

AbstractAllogeneic recognition and sex differentiation in Ephydatia muelleri were studied with two types of chimeric sponges, mixed and unmixed. Using gemmules of nine original sponges (stocks) collected in a pond, chimeras were prepared in the laboratory. Subsequently, the chimeric sponges were transferred to and cultured in the pond of their origin. They were observed macroscopically and histologically. The unmixed chimeras consisted of halves of different stocks. All unmixed chimeras grew as a continuous sheet for more than 10 days. Then, some of them showed a demarcation line at the boundary of the paired partners. Histologically, the demarcation line of a grown chimera was detected as a gap, on either side of which a narrow zone of tissue was more or less disorganized, containing no sexual elements. The combinations of stocks showing a demarcation line in unmixed chimeras are called incompatible, and those with no demarcation line compatible. Five histocompatibility strains were distinguished among the nine stocks used. Some interstrain combinations were compatible. In the chimeric individuals, the putative male region contained spermatic cysts, and the putative female region contained oocytes and embryos. In compatible heterosexual chimeras, male and female sexual elements were sometimes more or less separated but often were intermingled in the boundary zone. Gender seems to be genetically determined. The mixed chimeras were produced from randomly mixed gemmules of different stocks. Mixed chimeras of heterosexual combinations gave the following results. Many chimeras of the incompatible combinations showed a few to several irregular demarcation lines and contained both male and female sexual elements. Some incompatible mixed chimeras, however, did not show a demarcation line and contained only male sexual elements. Some compatible mixed chimeras contained both male and female sexual elements, but the male area was usually larger than the female area. Moreover, some compatible mixed chimeras contained only male sexual elements. Thus, a dominance of the male over the female was revealed in the mixed chimeras. A replacement of female tissues by male tissues during a short period following gemmule hatching is assumed. This may be considered an example of somatic cell parasitism. © 1992 Wiley‐Liss, Inc.