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.

Strange Bedfellows

Scott E. Baird, Marie E. Sutherlin, David H.A. Fitch, and Scott W. Emmons

Figure 1

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.

Figure 1