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Conservation of Developmental Diapause in Heterorhabditis Bacteriophora, Ancylostoma Caninum, and Caenorhabditis Elegans Open Access

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Developmental arrest is an important and common feature of nematode development. Many parasitic and non-parasitic nematodes have arrested third stage larvae (L3), or dauers, that may be either obligate or facultative stages in the life cycle. In addition, the non-parasitic nematode Caenorhabditis elegans facultatively undergo a dormant first larval (L1) stage in response to starvation. Similarly, the free-living stages of the hookworm life cycle occur in the environment, and could conceivably be subject to adverse conditions such as starvation. In contrast, entomopathogenic nematodes [EPN], except for the non-feeding dauer juvenile dispersal stage, complete their entire life cycle in a food-rich environment within the host. Given the abundant availability of nutrients, an L1 arrest stage may no longer be necessary in this nematode. To determine if L1 arrest is conserved in the EPN Heterorhabditis bacteriophora and the hookworm Ancylostoma caninum, we plated eggs in the presence or absence of a bacterial food source. Worms were measured every 6 hours over a period of 5 days. In both nematode species, starved worms failed to develop past the L1 stage, whereas fed worms grew in length and molted. Furthermore, the starved L1 of both species that were later fed resumed development and molted. To investigate why L1 diapause is conserved in H. bacteriophora, we examined the effects of diapause on reproduction by recording the developmental stage and number of offspring produced by 48-hour starved and re-fed hermaphrodites. H. bacteriophora which entered L1 diapause laid fewer eggs than continuously fed worms. However, the eggs laid by starved worms had a higher hatch rate than the eggs of fed worms. Additionally, starved worms were more likely to undergo endotakia matricida, a process in which larval worms hatch inside the mother and consume her internal tissues. These results indicate that despite significant differences in life history and environmental conditions, both A. caninum and H. bacteriophora undergo starvation-induced developmental arrest at the L1 stage, suggesting conservation of this characteristic in nematodes. Additionally, L1 arrest may provide a reproductive advantage in the form of more viable offspring production during stress periods.

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