O. Strauch et al., CULTURE CONDITIONS DEFINE AUTOMICTIC OR AMPHIMICTIC REPRODUCTION IN ENTOMOPATHOGENIC RHABDITID NEMATODES OF THE GENUS HETERORHABDITIS, Fundamental and applied nematology, 17(6), 1994, pp. 575-582
Heterorhabditis spp. were cultured monoexenically in shaken liquid med
ia inoculated with dauer juveniles (DJ). In all cultures some female p
henotype adults produced offspring while others had only unfertilized
eggs in their uteri. When Heterorhabditis spp. are grown on agar media
they exhibited a ''y'' or ''lambda'' type copulation behaviour. In co
ntrast to Steinernema spp., heterorhabditid males were unable to attac
h to the vaginal region in liquid culture. Consequently, under liquid
culture conditions only self-fertilizing hermaphrodites reproduce and
the amphimictic part of the F1 generation can be identified by the pre
sence of unfertilized eggs without shell in their uteri. During daily
observations of the nematode development in liquid cultures containing
approximately 20 F1 generation eggs, 30 % developed to amphimictic fe
males, 38 % to males and 32 % to hermaphrodites. Single F1 generation
first stage juveniles (J1) were either directly inoculated into Photor
habdus luminescens cultures or starved for 24 h in Ringer's solution b
efore inoculation. Starvation significantly increased the automictic p
art in the F1 generation (53.3 % DJ, 40 % hermaphrodites and 6.6 % amp
himictic adults). The ratio amphimictic: automictic adults was 1.84 wh
en J1 were directly transferred to culture medium and 0.07 when they w
ere starved prior to transfer. In all experiments males developed a da
y earlier than amphimictic females and females 2-3 days earlier than h
ermaphrodites. Obligatory for automictic reproduction is a yet undescr
ibed second juvenile pre-dauer stage (J2d) distinguishable from amphim
ictic J2 by its corn-cob like structure of the cuticle in the head reg
ion. A preceding development from a J2d to a DJ is not obligatory for
automictic reproduction. The F1 sex ratio males: amphimictic females w
as between 0.84 and 1.3. The observations have a significant impact on
liquid culture population dynamics of Heterorhabditis species.