Nematode biphasic ‘boom and bust’ dynamics are dependent on host bacterial load while linking dauer and mouth‐form polyphenisms

Abstract

Cross-kingdom interactions involve dynamic processes that shape terrestrial ecosystems and represent striking examples of co-evolution. The multifaceted relationships of entomopathogenic nematodes with their insect hosts and symbiotic bacteria are well-studied cases of co-evolution and pathogenicity. In contrast, microbial interactions in soil after the natural death of insects and other invertebrates are minimally understood. In particular, the turnover and succession of nematodes and bacteria during insect decay have not been well documentedalthough it represents a rich ecological niche with multiple species interactions. Here, we utilize developmentally plastic nematode Pristionchus pacificus and its associated scarab beetles as models. On La Réunion Island, we collected rhinoceros beetle Oryctes borbonicus, induced death, and placed carcasses in cages both on the island and in a mocknatural environment in the laboratory controlling for high spatial and temporal resolution. Investigating nematode population density and dispersal dynamics, we were able to connect two imperative plasticities, dauer and mouth form. We observed a biphasic 'boom and bust' dispersal dynamic of dauer larvae that corresponds to bacterial load on carcasses but not bacterial type. Strikingly, all post-dauer adults have the predatory mouth form, demonstrating novel intricate interactions on decaying insect hosts. Thus, ecologically relevant survival strategies incorporate critical plastic traits.

Sex or cannibalism: Polyphenism and kin recognition control social action strategies in nematodes

“…As St animals still feed on the carcasses of other nematodes under laboratory conditions ( 13 ), a scavenging strategy is one potential system, which we have not yet investigated in the wild and which may facilitate the adoption of the alternative morph. Furthermore, a recent analysis of the decaying beetle environment on which many of these nematodes are associated revealed intense competition for resources such as food availability that resulted in biphasic boom and bust nematode population dynamics ( 44 ). Therefore, Eu gonochoristic species may exploit a specific element of these ecological dynamics, despite the cost to mating chance.…”

Nematode Interactions on Beetle Hosts Indicate a Role of Mouth-Form Plasticity in Resource Competition

“…Competition among nematodes on insect cadavers is widespread and the conditions motley, depending on assorted factors including nematode species present, bacterial composition, and external environmental influences that may alter the already fluctuating settings (Dillman et al, 2012;Ali et al, 2013;Bertoloni Meli and Bashey, 2018;Blanco-Pérez et al, 2019;Renahan et al, 2021). The fight for food may be restricted to interspecies combat, but can also include conflict within species (Koppenhöfer et al, 1995;O'Callaghan et al, 2014).…”

Fisher vs. the Worms: Extraordinary Sex Ratios in Nematodes and the Mechanisms that Produce Them

“…The life histories of many free-living nematodes are marked by “boom-bust” cycles [ 74 , 100 ]; in which an individual arrives at a reproductive patch, often vectored by an Arthropod host with which it shares resources. From a few founders, the population rapidly expands until resources are exhausted.…”

“…For example, members of the Melodogyne and Heterodera genera produce female-biased sex ratios when nutrient availability is high and produce significantly more males under adverse environmental conditions [ 195 , 196 ]. Interestingly, while Pristionchus nematodes employ a conventional XX/XO GSD mechanism, the type of nutrients available within their local environment biases mouthpart polyphenisms that dictate whether they are carnivores, bacterivores, or fungivores [ 87 , 100 ].…”