Molecular Phylogeny of the Notomicrine Water Beetles (Coleoptera: Noteridae) Reveals Signatures of Gondwanan Vicariance and Ecological Plasticity

Abstract

Notomicrinae (Coleoptera: Noteridae) is a subfamily of minute and ecologically diverse aquatic beetles distributed across the Southeast Asia, Oceania, and the Americas. We investigate the evolution of Notomicrinae and construct the first species-level phylogeny within Noteridae using five nuclear and mitochondrial gene fragments. We focus on the genus Notomicrus Sharp (Coleoptera: Noteridae), sampling 13 of the 17 known Notomicrus species and an additional 11 putative undescribed species. We also include Phreatodytes haibaraensis Uéno (Coleoptera: Noteridae). Datasets are analyzed in Maximum Likelihood and Bayesian frameworks. With these, we 1) estimate divergence times among notomicrine taxa and reconstruct the biogeographical history of the group, particularly testing the hypothesis of Gondwanan vicariance between Old World and New World Notomicrus; 2) additionally, we assess ecological plasticity within Notomicrinae in the context of the phylogeny; and 3) finally, we test the monophyly of tentative species groups within Notomicrus and place putative new taxa. We recover a monophyletic Notomicrinae, with Phreatodytes sister to Notomicrus. We estimate the crown age of Notomicrinae to be ca. 110 Mya. The crown age of Notomicrus is recovered as ca. 75 Mya, there diverging into reciprocally monophyletic Old and New World clades, suggesting Gondwanan vicariance. Our phylogenetic estimate indicates a strong degree of ecological plasticity within Notomicrinae, with habitat switching occurring in recently diverging taxa. Finally, we recover five main species groups in Notomicrus, one Old World, Four New World, with tentative affirmation of the placement of undescribed species.

Figure 3 from: Baca SM, Short AEZ (2021) Review of the New World Notomicrus Sharp (Coleoptera, Noteridae) I: Circumscription of species groups and review of the josiahi group with description of a new species from Brazil. ZooKeys 1025: 177-201. https://doi.org/10.3897/zookeys.1025.60442

“…The monophyly of Notomicrus has been previously supported, with the Old and New World clades each also being found to represent reciprocally monophyletic lineages (Baca et al 2017;Baca and Short 2020). These studies have also revealed that, unsurprisingly, there remain many undescribed species in the genus, especially in South America.…”

Figure 1 from: Baca SM, Short AEZ (2021) Review of the New World Notomicrus Sharp (Coleoptera, Noteridae) I: Circumscription of species groups and review of the josiahi group with description of a new species from Brazil. ZooKeys 1025: 177-201. https://doi.org/10.3897/zookeys.1025.60442

“…8A), a character shared by the josiahi and tenellus species groups. With the Old World and New World taxa being reciprocally monophyletic (Baca and Short 2020) and the plesiomorphic appearance of these characters, we would speculate that this species is likely to be sister to one of the New World species groups.…”

“…Species of the traili group are difficult to discern and constitute a widespread species complex (see Baca and Short 2020). Personal observations coupled with the phylogenetic reconstructions of Baca and Short (2020) show that the diagnostic power of the dorsal punctation (see Young 1978) is unreliable, with multiple clades within the complex sharing similar patterns of punctation; for example, the pattern of punctation attributed to N. gracilipes by Young (1978) arises in multiple places within the complex. The group will require careful taxonomic investigation.…”

“…Both by presented character combination and even general gestalt, these are difficult to place with certainty. Molecular sequence data were unavailable for these species in the phylogenetic reconstruction of Baca and Short (2020). In particular, the species listed here both exhibit body shape, color, microsculpture and sparse punctation that would place them in the N. nanulus species group.…”

Figure 2 from: Baca SM, Short AEZ (2021) Review of the New World Notomicrus Sharp (Coleoptera, Noteridae) I: Circumscription of species groups and review of the josiahi group with description of a new species from Brazil. ZooKeys 1025: 177-201. https://doi.org/10.3897/zookeys.1025.60442

“…The species-level phylogenetic reconstruction of Baca and Short (2020) placed heavy emphasis on New World Notomicrus diversity. They recovered New World Notomicrus as diverging into four clades, the josiahi, nanulus, meizon and traili species groups, reciprocally supported by morphological characters.…”