Feeding plasticity in the nematode Pristionchus pacificus is influenced by sex and social context and is linked to developmental speed

Abstract

The increasing evidence for a role of developmental plasticity in evolution offers exciting prospects for testing interactions between ecological and developmental genetic processes. Recent advances with the model organism Pristionchus pacificus have provided inroads to a mechanistic understanding of a developmental plasticity. The developmental plasticity of P. pacificus comprises two discontinuous adult mouth-forms, a stenostomatous ("narrow mouthed") and a eurystomatous ("wide mouthed") form, the latter of which is structurally more complex and associated with predatory feeding. Both forms are consistently present in populations, but fundamental properties guiding fluctuations in their appearance have been poorly understood. Here, we provide a systematic characterization of the mouth plasticity in P. pacificus, quantifying a strong sexual dimorphism and revealing that, in an inbred genetic background, maternal phenotype is linked to that of male offspring. Furthermore, cues from conspecifics influenced the developmental decision in juvenile nematodes. Separating individuals from a population resulted in a lower eurystomatous frequency, which decreased incrementally with earlier isolation. Finally, the time to the reproductively mature stage was, in the presence of an abundant bacterial food supply, less for stenostomatous than for eurystomatous individuals, suggesting the potential for a fitness trade-off between developmental time and breadth of diet. This study provides a baseline understanding of the mouth dimorphism in P. pacificus as a necessary reference point for comparative analysis.

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

“…The conditional advantages of the Eu form, demonstrated here on a regimen of predatory feeding, complement the recent finding that the St form reaches the age of maturity faster on a bacterial diet [24]. Consistent with that finding, hermaphrodites that mature from the pre-adult stage on either a diet of prey or under starvation conditions, the St was reproductively active sooner than the Eu form.…”

“…However, differences were detected in the daily brood size in both test and control groups: the St form produced more offspring the first day after feeding (KW-H 3,145 ¼ 53.9, p , 0.0005), whereas the Eu form produced more on the second day (KW-H 3,145 ¼ 70.7, p , 0.0005) and on the third and fourth days (KW-H 3,145 ¼ 35.2, p , 0.0005). This result confirms the faster developmental time to maturity for the St form [24].…”

“…Third, we measured the fitness of forms when fed prey and then afterwards allowed to feed on bacteria, which we identified as a much more nutritional food source then prey. Finally, to complement an earlier study on developmental times on a bacterial diet [24], we tested for fitness advantages of the alternative forms in the presence of abundant bacteria.…”

“…This confirms that the Eu form is adaptive as a stress-resistant form in conditions of low bacteria but high prey availability. Second, the ability of the St form to produce as many offspring as the Eu form, when combined with a shorter generation time for the St form [24], could translate to higher fitness for that form in a bacteria-rich environment.…”

“…Starvation, specifically the deprivation of bacterial food, is one cue that triggers the formation of the Eu form [19]. The presence of conspecifics, which is sensed by small molecules, also induces development of the Eu form [24,25]. By responding to crowding, the dimorphism may result in a frequency-dependent switch to alternative food sources [6].…”