Notomicrus

Baca, Stephen M. & Short, Andrew E. Z., 2020, Molecular Phylogeny of the Notomicrine Water Beetles (Coleoptera: Noteridae) Reveals Signatures of Gondwanan Vicariance and Ecological Plasticity, Insect Systematics and Diversity (AIFB) 4 (6), No. 4, pp. 1-11 : 8

Notomicrus

Our results are congruent with Baca et al (2017b), recovering reciprocally monophyletic New and Old World clades of Notomicrus . Within the Old World tenellus group, our recovered relationships support the status of N. punctulatus as a valid species (see Toledo 2010), sister to N. tenellus Sensu lato. It has been suspected that the broadly distributed N. tenellus , with several junior synonyms and records spanning from mainland Malaysia, south to Australia, and east to French Polynesia ( Toledo 2010, Nilsson 2011), likely encompasses multiple species ( Toledo 2010). Our results support this, and perhaps the disparity in New versus Old World Notomicrus diversity is not as great as current classification indicates. However, our study’s Old World sampling is too sparse to address the taxonomy of this group in the appropriate scope.

The New World Notomicrus relationships recovered in the full tree ( Fig. 1 ; Supp Figs. 1 and 2 [online only]) supports the validity of most described species and reveals the extent of undescribed diversity. With samples selected on merits of diverging morphology, our analyses also grant support to our tentative species hypotheses. This will find particular utility in revising New World members of Notomicrus (in prep). In that respect, the phylogeny also shows that certain morphological characters are indeed diagnostic and predictive of relationships, especially among major lineages. Male tarsal claws, genitalia, and microreticulation were especially indicative, with the ability to also diagnose most species, as shown previously ( Young 1978, Manuel 2015, Baca and Short 2018, Guimarães and Ferreira Jr 2019). That said, a comprehensive review of Notomicrus morphology is also beyond the scope of this paper and will be the subject of forthcoming revisions of the group.

The recovered trees of the ‘Full’ dataset support the status of most described species and several tentative new ones, but they depict a large complex within the traili group ( Fig. 1 ). The successive sisters to the traili complex (a species attributable to N. gracilipes and an undescribed species, N. sp.3) are much more clearly demarcated genetically. Within the complex we recover genetic structure, with generally well- to moderately supported larger clusters with short internodes. The morphological variation is subtle among members of the group, e.g., in the genitalia or pattern of punctation (see Young 1978, Manuel 2015, Baca and Short 2018), and identifying any outstanding morphological signal among the supported clusters will require close investigation. This difficulty is here exemplified in the scattered placement of specimens attributable to N. gracilipes following Young’s (1978) description and comparison to the holotype. In identification, particular note was paid to patterns of punctation, which here indicates that some diagnostic characters may be unreliable within the traili group. Recovered relationships indicate that the traili complex likely contains multiple species, with the complex experiencing repeated diversification and range expansion in the Neotropics. This is evidenced by the fact that individuals within the clusters range variably across South America, and in many cases, members of these clusters occur sympatrically, or at least in close enough proximity to assume contact, but maintain genetic and phylogenetic distinction. This complex will require further investigation before taxonomic action is taken. Given the issues of phylogenetic discordance at short internodes ( Degnan and Rosenberg 2006, Liu and Edwards 2009), a phylogenomic approach, e.g., with Ultraconserved elements, may be the most appropriate for parsing relationships within the traili complex.

Figures

Fig. 1. Phylogeny of Notomicrinae recovered by Maximum Likelihood analysis of ‘Full’ dataset in IQ-Tree2 with species groups indicated. Nodes with single black boxes indicate strong support in all analyses.Variable support across analyses is indicated by colored boxes as indicated by keys on left.Top key indicates respective analysis and dataset, Maximum Likelihood (ML) on left, Bayesian inference (BI) on right; ‘Full’ and ‘Trimmed’ indicate dataset; and lowest box indicates support recovered by divergence time estimate (DTE ‘Trimmed’) in BEAST2 with preferred prior models. Lower key indicates support by color for UltraFastBoot support (ML) and Posterior probability (PP) values. Inset depicts ‘traili’ branch expanded to show structure.

Fig. 2. Divergence time estimate and ancestral range reconstruction of Notomicrinae. Ancestral ranges recovered by DIVALIKE analysis in BioGeoBears with preferred divergence time estimate recovered by BEAST 2. Boxes on nodes indicate most probable ancestral area states with color correlating to left key; circles indicate differing result recovered from DEC analysis. Numbers on nodes correlate toTable 3. Maps indicate continental landmasses at respective ages, reproduced from Cao et al. (2017) with G-Plates (Müller et al. 2018).