Rapid divergence in physiological and life-history traits between northern and southern populations of the British introduced neo-species, Senecio squalidus

Alien plants provide a unique opportunity to study evolution in novel environments, but relatively little is known about the extent to which they become locally adapted to different environments across their new range. Here, we compare northern and southern populations of the introduced species Senecio squalidus in Britain; S. squalidus has been in southern Britain for approximately 200 years and reached Scotland only about 50 years ago. We conducted common garden experiments at sites in the north and south of the species’ range in Britain. We also conducted glasshouse and growth chamber experiments to test the hypothesis that southern genotypes flower later, are more drought-tolerant, germinate and establish better at warmer temperatures, and are less sensitive to cold stress than their more northern counterparts. Results from the common garden experiments are largely consistent with the hypothesis of rapid adaptive divergence of populations of the species within the introduced range, with genotypes typically showing a home-site advantage. Results from the glasshouse and growth chamber experiments demonstrate adaptive divergence in ability to tolerate drought stress and high temperatures, as well as in phenology. In particular, southern genotypes were more tolerant of dry conditions and high temperatures and they flowered later than northern genotypes. Our results show that rapid local adaptation can occur in alien species, and they have implications for our understanding of the ecological genetics of range expansion of introduced weeds.

Chromosome fusions triggered by noncoding RNA

Chromosomal fusions are common in normal and cancer cells and can produce aberrant gene products that promote transformation. The mechanisms driving these fusions are poorly understood, but recurrent fusions are widespread. This suggests an underlying mechanism, and some authors have proposed a possible role for RNA in this process. The unicellular eukaryote Oxytricha trifallax displays an exorbitant capacity for natural genome editing, when it rewrites its germline genome to form a somatic epigenome. This developmental process provides a powerful model system to directly test the influence of small noncoding RNAs on chromosome fusion events during somatic differentiation. Here we show that small RNAs are capable of inducing chromosome fusions in four distinct cases (out of four tested), including one fusion of three chromosomes. We further show that these RNA-mediated chromosome fusions are heritable over multiple sexual generations and that transmission of the acquired fusion is associated with endogenous production of novel piRNA molecules that target the fused junction. We also demonstrate the capacity of a long noncoding RNA (lncRNA) to induce chromosome fusion of two distal germline loci. These results underscore the ability of short-lived, aberrant RNAs to act as drivers of chromosome fusion events that can be stably transmitted to future generations.