An increase in transmission‐related traits and in phenotypic plasticity is documented during a fungal invasion

Abstract

The adaptive rapid evolution of phenotypic traits is potentially a key contributor to invasiveness, but has been relatively little studied for the fungi, even though these organisms are responsible for devastating losses in agriculture and natural resources. In this study, we compare biologically relevant phenotypic characters of spore‐generated individuals from two native and two invasive populations of the fungal pathogen Seiridium cardinale to infer which traits may be adaptive and rapidly evolving during an ongoing biological invasion. Results show that: (1) lower growth rate and smaller spore size are selected for in invasive populations, independent of the stage of invasion; (2) there is no selection evident towards increased rapid sporulation, but overall reproductive potential increases in later stages of the invasions; and (3) demographic plasticity of most traits increases during the initial stages of invasion, but decreases in a later phase. Comparisons against levels of neutral genetic variation (Qst‐Fst comparisons) showed that the decrease in spore size is strongly adaptive, despite the trade‐off of reduced viability. Lesion size of isolates inoculated on the naïve Italian cypress host was not correlated with their growth rate, and was significantly lower in invasive than in native populations. This last result indicates that rate of host colonization is a complex trait affected both by host and pathogen, which may not be necessarily adaptive and/or which may not easily evolve. In summary, the success of S. cardinale as an invasive in the Mediterranean basin is associated with reduced spore size and increased plasticity of almost all traits in initial phases, followed by further decreased spore size, increased overall sporulation, and decreased plasticity in a second phase of the invasion. Interestingly, growth rate by population results show that invasive populations are well adapted only to moderate temperatures, while native populations fare well also when exposed to relative extremes in temperature. This different adaptation suggests a “master‐of‐some” specialization scenario for the invasion by S. cardinale in the Mediterranean.

Pattern of local adaptation to quantitative host resistance in a major pathogen of a perennial crop

“…The share of local adaptation due to the habitat effect is investigated by measuring ΔHA, while the share of local adaptation due to the pathogen is investigated with ΔLF. When population genetics data are available, another method for separating the effect of diversifying selection from neutral genetic drift between populations can be used, by comparing phenotypic differentiation (measured with the Q ST parameter from quantitative traits) with genetic differentiation (measured with the F ST parameter from molecular neutral markers; Garbelotto, Rocca, Osmundson, di Lonardo, & Danti, ; Herrmann et al, ; Leinonen, McCairns, O'Hara, & Merilä, ). When Q ST falls outside the distribution of F ST , this can be used as an evidence of divergent ( Q ST > F ST ) or uniform ( Q ST < F ST ) selection among populations.…”

Epidemiological History of Cypress Canker Disease in Source and Invasion Sites

“…Variation of phenotypic traits of the introduced Mediterranean population of S. cardinale derived from the movement and settlement of the fungus from the California source population was studied to evaluate the adaptive evolution of the pathogen during the invasive process [35]. Variability (phenotypic plasticity) of a set of characteristics considered important for establishment, infection, and spread of the pathogenic fungus were studied to determine which characteristics may favor the invasion and which are in rapid evolution.…”

“…Isolates from California have also demonstrated a higher virulence, an increased growth rate, a greater adaptability to a wider range of temperatures, and greater reproductive capacity (sporulation and germination) compared to the Mediterranean isolates [35]. So, new introductions from California to the Mediterranean could have serious consequences for the local common cypress populations that survived the previous epidemics, causing a higher mortality rate and eventually new disease outbreaks.…”

“…After this first outbreak, cypresses have not been used for extensive plantings in California, but they were still planted for hedges or as shade trees or, in some cases, for protective purposes, e.g., C. macrocarpa along the coastal area. Today, both S. cardinale and S. unicorne are known to be present in California [33][34][35][36][37][38][39], threatening ornamental plantations of Cupressus sp.-mainly C. sempervirens, C. macrocarpa, ×Cup. leylandii, and Juniperus spp.…”

“…A total of 2385 trees of C. sempervirens (790), C. macrocarpa (611) (Figure 2), and ×Cup. leylandii (984) were Today, both S. cardinale and S. unicorne are known to be present in California [33][34][35][36][37][38][39], threatening ornamental plantations of Cupressus sp.-mainly C. sempervirens, C. macrocarpa, ×Cup. leylandii, and Juniperus spp.…”