Abstract
BackgroundHarpalinae is a species rich clade of carabid beetles with many unusual morphological forms and ecological interactions. How this diversity evolved has been difficult to reconstruct, perhaps because harpalines underwent a rapid burst of diversification early in their evolutionary history. Here we investigate the tempo of evolution in harpalines using molecular divergence dating techniques and explore the rates of lineage accumulation in harpalines and their sister group.ResultsAccording to molecular divergence date estimates, harpalines originated in the mid Cretaceous but did not diversify extensively until the late Cretaceous or early Paleogene about 32 million years after their origin. In a relatively small window of time, harpalines underwent rapid speciation. Harpalines have a relative high net diversification rate and increased cladogenesis in some regions of the clade. We did not see a significant decrease in diversification rate through time in the MCCR test, but a model of diversification with two shift points to lower diversification rates fit the harpaline lineage accumulation through time the best.ConclusionsOur results indicate harpalines are significantly more diverse and have higher diversification than their sistergroup. Instead of an immediate burst of explosive diversification, harpalines may have had a long "fuse" before major lineages diversified during the early Paleogene when other taxa such as mammals, birds, and some flowering plants were also rapidly diversifying.
Highlights
Harpalinae is a species rich clade of carabid beetles with many unusual morphological forms and ecological interactions
We evaluate the fit of six models of diversification [63,64] in LASER using Akaike Information Criteria (AIC) and/or hierarchical likelihood ratio tests for the full all-data-combined BEAST chronogram, the harpaline clade and the brachinine clade
Results of the constant rate (CR) and Monte Carlo constant rate (MCCR) tests showed the observed value of g in the Harpalinae clade was negative (g = -10.606), which rejects the hypothesis that rates of lineage accumulation remained constant over time, when compared to the distribution of g statistics of the simulations, the harpaline g statistic was not statistically significant (MCCR test: p = 0.98)
Summary
Harpalinae is a species rich clade of carabid beetles with many unusual morphological forms and ecological interactions. The signature can be described as close temporal spacing of a number cladogenetic or lineage-splitting events in a phylogeny, such that the internal branches (internodes) that link taxa together are very short. Such a phylogenetic pattern is to be expected from an ancient rapid radiation, the pattern can be observed in the case of other factors involved in phylogenetic reconstruction such as inadequate data, conflict within or among data sets, loss of phylogenetic signal over time, or data with inappropriate evolutionary rates [10]. The difficulty in confidently resolving basal splits in these phylogenies may be a result of insufficient time during cladogenesis to accumulate strong phylogenetic signal in the data because of rapid lineage splitting
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