Biology subjects

Theam, P.

Publications and source records attributed to Theam, P..

4 recordsLinked to original sources

bioRxiv2026

Evidence of a predator-prey co-evolutionary arms race within a nematode microhabitat

Predator-prey interactions are key drivers of behavioural and life-history evolution, yet their mechanisms remain difficult to study in natural contexts. The nematode Pristionchus pacificus is a model predator, but most studies exploring its behaviours use Caenorhabditis elegans as prey, a species that it likely only rarely encountered in nature. Here, we examine predation within nematode communities associated with beetle carcasses, the native necromenic habitat of P. pacificus. We identify Oscheius myriophilus as a cohabiting species, likely representing natural prey. Using predatory assays, automated tracking, and machine-learning-based behavioural analysis, we show that P. pacificus actively kills and consumes O. myriophilus. Strikingly, predation rates are lower than those observed for C. elegans, suggesting partial resistance or reciprocal adaptation in O. myriophilus. Consistent with this, O. myriophilus exhibits a mixed reproductive strategy, with early oviposition followed by ovoviviparity and matricide. As later developmental stages are more resistant to predation, internal hatching may protect offspring while providing maternal resources for development. These findings establish these nematodes as a tractable model for investigating predator-prey interactions and their evolutionary consequences, highlighting how behavioural strategies and life-history traits can co-evolve in natural communities.

evolutionary biology↗

bioRxiv2026

Plasticity in nonsense-mediated decay and translation initiation regulate polyphenism

Developmental plasticity is increasingly recognised as facilitator of evolutionary novelty. However, how plasticity itself evolves and how variation in plastic trait expression is structured in populations remain unknown1,2. The predatory nematode Pristionchus pacificus exhibits mouth-form plasticity with underlying molecular mechanisms being increasingly identified3. We investigate the temporal scale of natural variation of mouth-form plasticity. An 11-year survey characterised Adoretus beetle-derived isolates from Colorado, La Reunion Island and revealed a gradual shift in mouth-form preference. Quantitative trait locus mapping of mouth-form preferences identified a single peak harbouring the developmental switch gene eud-1. Through CRISPR-engineering and biochemical assays, we show that plasticity in nonsense-mediated decay coupled with alternative start codon selection resulting in different N-terminal proteoforms of EUD-1 are associated with natural variation of mouth-form preference. This work provides molecular explanations for variation in plastic trait expression and links nonsense variants in the major developmental switch locus to ecological and evolutionary processes.

evolutionary biology↗

bioRxiv2025

The dynamics of coexistence and succession in a decaying ecosystem

Elucidating the rules that govern community assembly and enable the coexistence of species is central to ecology. Much of the current understanding revolves around the composition of communities at equilibrium. In contrast, transient ecological dynamics, in particular the succession of species following an environmental disturbance, remain largely unexplored. We present Gymnogaster buphthalma beetle carcasses as a model to study species coexistence in disequilibrium. In this community, nematodes appear in succession - with multiple feeding and reproductive strategies, transience, and associated dispersal - creating a perfect model for metacommunity ecology. We computationally reconstructed decaying G. buphthalma beetles sampled from the wild using experimentally-derived life history data, i.e. emergence times, sex ratios, and fecundity measurements. Through agent-based modeling, we show that nematode coexistence is possible over a wide range of scenarios. This work provides a unique experimental and computational framework to synthesize various approaches to metacommunity and species succession theories.

ecology↗

bioRxiv2025

Biosynthesis of modular signaling molecules requires functional diversification of carboxylesterases in Pristionchus pacificus

The model nematode Pristionchus pacificus produces four types of complex ascaroside pheromones named UBAS, DASC, NPAR, and PASC. However, the exact biosynthetic pathways of these modular signaling molecules remain enigmatic. We have previously identified a carboxylesterase Ppa-UAR-1 for the biosynthesis of UBAS, enabling the attachment of ureidoisobutyric acid at the 4-position of simple ascarosides. Here, we report three new carboxylesterases Ppa-UAR-5, Ppa-UAR-6 and Ppa-UAR-12 from P. pacificus. Ppa-UAR-5 functions downstream of Ppa-UAR-1 to furnish the biosynthesis of ubas#1 and ubas#2, whereas Ppa-UAR-12 specifically links two ascr#1 at the 4-position to synthesize dasc#1. Finally, Ppa-UAR-6 is essential for the biosynthesis of npar#1-3 and part#9. The expression patterns of Ppa-uar-6 and Ppa-uar-12 in the intestinal and epidermal cells suggest pheromone biosynthesis to be restricted to specific tissues. These findings indicate that the expansion and functional diversification of carboxylesterases plays a crucial role in the evolution of complex pheromones in nematodes. SIGNIFICANCEOur study identified three new carboxylesterase genes (Ppa-uar-5, Ppa-uar-12 and Ppa-uar-6) from P. pacificus. The encoded enzymes separately regulated the biosynthesis of three types of modular pheromones (UBAS, DASC, and NPAR-types) in worms intestinal cells and exhibited extremely high substrate-specificity. For example, we verified that Ppa-UAR-12 specifically linked one ascr#1 to the 4-position of another ascr#1 to finally furnish the biosynthesis of ascaroside dimer dasc#1. These new discoveries largely clarify the delicate biosynthetic mechanisms of how diversification of carboxylesterases functions in P. pacificus to build up enormous complexity of modular signaling molecules. Such a biosynthetic mechanism of nematode pheromones might be widely conserved in the phylum Nematoda.

biochemistry↗