Worm Breeder's Gazette 11(4): 89
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
We have isolated a new species of Caenorhabditis, C. vulgariensis, that is an internal associate of the pill bug, Armadillidium vulgare. Four independent isolates were obtained from eight pill bugs from a Brooklyn compost heap (SWEs backyard). In addition, one isolate was obtained from an unidentified snail (1 of 2) from the same compost heap. No isolates were obtained from soil or from any other soil invertebrates. C. vulgariensis, which is amphimictic, is morphologically indistinguishable from C. remanei and C. elegans. Its designation as a separate species is based on its reproductive isolation from these species and from C. briggsae.In the course of this work, ethological isolation was not observed within Caenorhabditis as males of all four species mated to all congeneric females/hermaphrodites. However, ethological isolation was observed between Caenorhabditis males and extrageneric females (Rhabditis terricola and Cuticularia oxycerca). Extrageneric mating could not be induced by preincubation of plates with congeneric females or by their presence during mating assays. Therefore, matings within Caenorhabditis require congeneric recognition that is probably not pheremone mediated. Within Caenorhabditis, several different levels of post-mating isolation, including gametic isolation, hybrid inviability, and hybrid sterility, were observed (Table). Most congeneric matings did not result in fertilization. However, C. remanei females were promiscuous for fertilization. Some of the resulting embryos developed as far as gastrulation although none gastrulated successfully. C. briggsae males and C. vulgariensis females were also cross-fertile. Furthermore, briggsae/vulgariensis hybrid progeny frequently survived to larval stages and occasionally reached adulthood. All adults were female and invariably were self- and cross- sterile, generally having rudimentary and disorganized gonads. This distortion of the sex ratio is consistent with 'Haldane's rule' that states that in intergenic hybrids the heterogametic sex is generally less viable. [See Figure 1] Another remanei-like Caenorhabditis strain has been isolated by Bill Fixsen. This isolate is not cross-fertile with C. briggsae (J. Hodgkin, pers. comm.) as is C. vulgariensis. Therefore, although it has not yet been tested for cross-fertility with C. vulgariensis, this isolate may be another distinct species.