Adaptive radiation in a heterogeneous environment

Abstract

Successive adaptive radiations have played a pivotal role in the evolution of biological diversity. The effects of adaptive radiation are often seen, but the underlying causes are difficult to disentangle and remain unclear. Here we examine directly the role of ecological opportunity and competition in driving genetic diversification. We use the common aerobic bacterium Pseudomonas fluorescens, which evolves rapidly under novel environmental conditions to generate a large repertoire of mutants. When provided with ecological opportunity (afforded by spatial structure), identical populations diversify morphologically, but when ecological opportunity is restricted there is no such divergence. In spatially structured environments, the evolution of variant morphs follows a predictable sequence and we show that competition among the newly evolved niche-specialists maintains this variation. These results demonstrate that the elementary processes of mutation and selection alone are sufficient to promote rapid proliferation of new designs and support the theory that trade-offs in competitive ability drive adaptive radiation.

A family of variably expressed outer-membrane proteins (Vomp) mediates adhesion and autoaggregation in Bartonella quintana

“…YadA confers the ability to bind epithelial cells (23), ECM constituents of the host, including collagen (27), and other Y. enterocolitica bacilli (autoaggregation; (26)). Autoaggregation, which facilitates intraspecies communication and biofilm formation, is involved in pathogenesis pathways of Gram-negative bacteria (33,34). We observed autoaggregation of JK-31, but not of BQ2-D70.…”

Antibiotics as intermicrobial signaling agents instead of weapons

“…Again, this finding indicates that subinhibitory antibiotic concentrations do not necessarily produce a burden on bacterial physiology but in some occasions may enhance some potentially adaptive characteristics useful for colonization of specific environments. Indeed, in agreement with the idea that antibiotics might trigger some phenotypes that can be advantageous for the ecological behavior of bacterial populations, it has been described that subinhibitory antibiotic concentrations might increase mutation frequency in P. aeruginosa (12), favoring adaptive radiation (13) and allowing more efficient colonization of heterogeneous environments by this opportunistic pathogen.…”

The evolution of a pleiotropic fitness tradeoff in Pseudomonas fluorescens

“…To test the hypothesis that the differences between WS genotypes and the ancestral SM clone in Biolog substrate utilization are a pleiotropic effect of the same mutation that causes the WS phenotype, we reinoculated six WS genotypes that express varying degrees of catabolic impairment (mean catabolic defects ϭ 16, SD ϭ 7.9, range ϭ 6-25) into undisturbed microcosms. Derived SM genotypes directly descended from WS evolved in every reverse-selection line, presumably because of the fitness benefits associated with colonizing the uninhabited broth phase of a WS-dominated microcosm (23,26). Four derived SM genotypes completely recover the full spectrum of ancestral catabolic function.…”

“…One of the most ecologically successful derived types is the ''wrinkly spreader'' (WS), which colonizes the air-liquid interface of the microcosm and forms colonies on agar plates that can be easily distinguished from the broth-colonizing ancestral genotype ''smooth'' (SM). Both the frequency and density of WS morphs rapidly increases, such that both SM and WS morphs are present at a density of Ϸ10 9 cells per ml Ϫ1 after 7 days of incubation (15,23). In undisturbed microcosms, SM and WS morphs can stably coexist at similar frequencies for hundreds of generations, because the fitness of each morph is negative frequencydependent.…”