Interplay of Multilayered Transcriptomic Plasticity in Response to Temperature Fluctuations During Biological Invasions: A Case Study in Invasive <scp><i>Styela plicata</i></scp>

Phenotypic plasticity is a crucial responsive strategy for invasive species to colonise new habitats. Rapid plastic responses enable invaders to instantly survive environmental fluctuations during invasion processes; however, the interplay and relative contributions of different plastic mechanisms remain largely unexplored. Here, we exposed the invasive ascidian Styela plicata from the Mediterranean Sea to a time series of high- and low-temperature stress to investigate the multilayered transcriptomic plasticity mechanisms, including gene expression, alternative splicing (AS) and alternative polyadenylation (APA). We observed rapid, pervasive and diverse responsive changes, with more genes exhibiting expression changes than those showing APA and AS changes. Approximately 50% differentially alternatively spliced genes and differentially expressed APA genes also exhibited differential expression under heat stress; however, this proportion declined to 34% under cold stress, suggesting stronger interactions among plastic mechanisms in response to heat stress and greater independence under cold stress. Although a considerable proportion of responsive genes were commonly triggered by both heat and cold stress, we found more pronounced gene expression plasticity and greater flexibility under heat stress, which may help explain S. plicata's preference for tropical and subtropical habitats. Whereas cold stress induced a greater number of AS events and distinct AS profiles, with a consistent trend of exon skipping across all stress durations. Altogether, our findings reveal environment-dependent interactions among distinct plastic response mechanisms and highlight the importance of post-transcriptional regulatory strategies. Our insights into the complex interplay of multilayered transcriptomic plasticity contribute to a deeper understanding of their roles in adaptive evolution.