Molecular phylogeny and host‐plant use (Lamiaceae) of theThymogethespollen beetles (Coleoptera)

Abstract

The 24 members of the Euro‐Asiatic genus Thymogethes are highly specialized pollen beetles associated as larvae with flowers of Lamiaceae Nepetoideae. All members of the genus were analysed in within the framework of an integrative taxonomy approach, which was aimed to reconstruct the phylogenetic relationships, as well as the possible pattern of evolution of their larval‐host‐plant association. Evidence from multiple molecular markers [COI; 16S; H3], combined with an estimation of divergence times using an average rate of 0.0177 substitutions/site/My among branches, placed the origin of the genus at a minimum of 9–10 Mya. This date of origin approximates the known evolution of the host plants in Euro‐Mediterranean areas. Evidence from combined molecular and cladistic morphological analyses resulted in suitable agreement with the previously established morphology‐based systematics of the genus, although members of the exilis species‐group were split into three clades. The only disagreement between results of this new combined phylogeny and previous classification is in the exclusion of “Thymogethes” grenieri. This species is herein positioned outside the genus, based on molecular evidence. Our analysis depicts several Thymogethes species differentiating in the last few Mys, specifically those included in the T. lugubris species‐group. Combined evidence from DNA, morphology and ancestral state parsimony reconstruction of larval‐host‐plant associations suggests that subtribe Menthinae likely represents the ancestral host plants, with a series of independent host shifts during the radiation of the clade, in association first with Menthinae and subsequently with Lavandulinae and Nepetinae. Steno‐oligophagy is the most frequent (86%) condition, while strictly monophagous species are less numerous (14%).

Rosaceae, Brassicaceae and pollen beetles: exploring relationships and evolution in an anthophilous beetle lineage (Nitidulidae, Meligethes-complex of genera) using an integrative approach

“…Hence, given the lack of reliable fossil records or useful dated palaeogeographic events to calibrate our trees, we used an average value of the COI substitution rate in a range between 1.5 and 3.54%, which represent the most accurate estimated rate for mitochondrial DNA in coleopterans so far [ 68 – 70 ] and hence widely applied in molecular dating of beetle phylogeography and phylogeny (e.g. 6, 23, [ 71 – 75 ]). Therefore, for the molecular clock analysis we applied an average rate of 0.0126.…”

Rosaceae, Brassicaceae and Pollen Beetles: exploring relationships and evolution in an anthophilous beetle lineage (Nitidulidae, Meligethes-complex of genera) using an integrative approach

“…Hence, given the lack of reliable fossil records or useful dated palaeogeographic events to calibrate our trees, we used an average value of the COI substitution rate in a range between 1.5 and 3.54%, which represent the most accurate estimated rate for mitochondrial DNA in coleopterans so far [68][69][70] and hence widely applied in molecular dating of beetle phylogeography and phylogeny (e.g. 6, 23, [71][72][73][74][75]). Therefore, for the molecular clock analysis we applied an average rate of 0.0126.…”

Rosaceae, Brassicaceae and Pollen Beetles: exploring relationships and evolution in an anthophilous beetle lineage (Nitidulidae, Meligethes-complex of genera) using an integrative approach

“…To estimate the relative age of lineage divergences, an uncorrelated lognormal Bayesian molecular relaxed clock model and a Yule process prior were used on the mtDNA data set using the software BEAST v.1.8.2 [64]. Given the lack of fossil record or useful dated palaeogeographic records to calibrate trees we used, as a calibration point, an average value of the COI substitution rate in a range between 1.5% and 3.54%, which represent values estimated for mitochondrial DNA in insects [65][66][67][68], previously used for closely related groups [6,23,65]. Therefore, for the molecular clock analysis we applied an average rate of 0.0126.…”