Abstract
BackgroundRepeated colonisation of novel host-plants is believed to be an essential component of the evolutionary success of phytophagous insects. The relative timing between the origin of an insect lineage and the plant clade they eat or reproduce on is important for understanding how host-range expansion can lead to resource specialisation and speciation. Path and stepping-stone sampling are used in a Bayesian approach to test divergence timing between the origin of Acacia and colonisation by thrips. The evolution of host-plant conservatism and ecological specialisation is discussed.ResultsResults indicated very strong support for a model describing the origin of the common ancestor of Acacia thrips subsequent to that of Acacia. A current estimate puts the origin of Acacia at approximately 6 million years before the common ancestor of Acacia thrips, and 15 million years before the origin of a gall-inducing clade. The evolution of host conservatism and resource specialisation resulted in a phylogenetically under-dispersed pattern of host-use by several thrips lineages.ConclusionsThrips colonised a diversity of Acacia species over a protracted period as Australia experienced aridification. Host conservatism evolved on phenotypically and environmentally suitable host lineages. Ecological specialisation resulted from habitat selection and selection on thrips behavior that promoted primary and secondary host associations. These findings suggest that delayed and repeated colonisation is characterised by cycles of oligo- or poly-phagy. This results in a cumulation of lineages that each evolve host conservatism on different and potentially transient host-related traits, and facilitates both ecological and resource specialisation.
Highlights
Repeated colonisation of novel host-plants is believed to be an essential component of the evolutionary success of phytophagous insects
A considerably younger Acacia thrips common ancestor compared to that of Acacia is consistent with colonisation of a lineage that has not been used as a host in its recent evolutionary past
We propose that colonisation of Acacia was initially characterised by either oligophagy or polyphagy and subsequent recolonisations by a number of ancestral lineages
Summary
Repeated colonisation of novel host-plants is believed to be an essential component of the evolutionary success of phytophagous insects. Alternative explanations argue host-plant conservatism can be driven by predictability [14], climate [15], lifehistory characteristics [16], geographical contexts [17], plasticity [18], genetic predispositions or ecological compatibilities suited to the use of a resource [19], and hostrange ecology [20] or genetics [21]. To distinguish among these causal mechanisms it is necessary to study evolutionary periods that are meaningful to the association of interest. Determining the period that separates the origin of the insect group and the hostplants they feed on is essential to unraveling hypotheses explaining the origin or loss of narrow host ranges
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