Adaptive value of a predatory mouth-form in a dimorphic nematode

Abstract

Polyphenisms can be adaptations to environments that are heterogeneous in space and time, but to persist they require conditional-specific advantages. The nematode Pristionchus pacificus is a facultative predator that displays an evolutionarily conserved polyphenism of its mouthparts. During development, P. pacificus irreversibly executes either a eurystomatous (Eu) or stenostomatous (St) mouth-form, which differ in the shape and number of movable teeth. The Eu form, which has an additional tooth, is more complex than the St form and is thus more highly derived relative to species lacking teeth. Here, we investigate a putative fitness trade-off for the alternative feeding-structures of P. pacificus. We show that the complex Eu form confers a greater ability to kill prey. When adults were provided with a prey diet, Eu nematodes exhibited greater fitness than St nematodes by several measures, including longevity, offspring survival and fecundity when followed by bacterial feeding. However, the two mouthforms had similar fecundity when fed ad libitum on bacteria, a condition that would confer benefit on the more rapidly developing St form. Thus, the two forms show conditional fitness advantages in different environments. This study provides, to our knowledge, the first functional context for dimorphism in a model for the genetics of plasticity.

Predatory feeding behaviour in Pristionchus nematodes is dependent on a phenotypic plasticity and induced by serotonin

“…Omnivorous nematodes including Pristionchus are capable of both microbial feeding and predatory feeding on other nematodes, and also have teeth for lacerating open the cuticle of their prey. Interestingly, this mouth specialisation is often dimorphic with one morph, the stenostomatous (St) form thought to be optimised for bacterial food sources and a second morph, the eurystomatous (Eu) form optimised for predation (Serobyan et al, 2013(Serobyan et al, , 2014. Pristionchus therefore offers an ideal opportunity to study behaviour under both morphological and behavioural contexts.…”

Adult influence on juvenile phenotypes by stage-specific pheromone production

“…However, dimorphic species like P. pacificus have 229 evolved an alternative strategy that senses population densities of adults. When nematode prey 230 is the only available food source, the Eu morph provides longer life spans leading to more 231 progeny 29 , and presumably increased fitness. Going forward, the challenge will be to test these 232 relationships and predictions in more natural simulated environments with increasing complexity 233 of variables.…”

“…If this holds true on the decaying beetle it may 65 provide a fitness benefit when microbes are abundant. However, it is predicted that bacterial 66 food will eventually become limiting in this isolated environment 27 , and the Eu mouth form will be 67 advantageous to exploit additional food sources and remove competitors 29 . Presumably, second 68 or third generation juveniles can predict depleting resources by specifically sensing large 69 numbers of adults, triggering development of the Eu mouth form.…”

Assaying Predatory Feeding Behaviors in <em>Pristionchus</em> and Other Nematodes

“…However, numerous nematode species including P. pacificus display behaviors, which are absent or vary in complexities from the model organism C. elegans and therefore raise fascinating questions regarding the evolution and regulation of these behaviors. One such additional behavior found in many other nematode species including P. pacificus is the capacity to supplement their bacterial diet by engaging in predatory feeding 1,20 . We have therefore developed and described a detailed protocol for easy and rapid characterization of these previously unanalyzed predatory behaviors in nematodes.…”