Results
Of the 29,464 available COI barcode sequences, geographical coordinates were available for 29,349 individuals (Figure 1). Excluding identical syntopic haplotypes and individuals with incomplete geographical coordinates, we retained for the analysis 16283 individuals of 3967 species from 124 Coleoptera families. From these, we retained only those species for which comprehensive ecological information was available, such as feeding style, habitat and biotope preference, and body size resulting in 12207 specimens available for final meta-analysis representing 1785 species and 95 families of Coleoptera from Germany.
The majority of the species (above 400) was distributed in the distance class “300”, the fewest species were in the class “>300” (Figure S1). The number of species decreased exponentially with the rising of the number of localities, with one exception where only 190 species recorded 3 sampling localities (Figure S1). Most species were zoophagous (n= 674) or phytophagous (n= 585), while the preferred habitat was vegetation, which made up more than 600 species (n= 632) while dead wood and soil habitats accounted for 398 and 400 species, respectively (Figure S2). Across the preferred biotopes, 691 species preferred forest, many others either open-land (n= 420) or wetland (n=369), and 305 had not specific preferences (Figure S2). The most represented size-classes were, as expected, very small (n= 594) and small (n= 626) species. The medium size class accounted for 386 species, while the large and largest beetles counted 157 and 22 species, respectively (Figure S2).
Infraspecific genetic distances resulted to be inversely proportional to the number of sampled individuals and number of sampling localities (Figure 3A-C), while intraspecific geographic distances were not affected by sampling issues. Despite numerous cases with elevated infraspecific divergence, distance plots across the four major eco-classes of central European beetles (habitat, feeding preferences, biotope, size class) revealed generally low intraspecific distances (<3 % sequence divergence). Nevertheless, at first glance, patterns of geographical and genetic differentiation differ clearly among ecological and eco-morphological traits. Indeed, the plots (all data) of geographical distance matrices versus genetic matrices showed different shapes across different ecological guilds (Figure 3B-H, Figure S3), particularly for habitat and feeding style. However, for the biotope types no principal differences were visually evident (Figure 3G), although in biotopes, wetland and open land included more long-distance samples than did forest and eurytopic biotopes. Body size showed a clear trend that with the increase of body size (from extra-small to extra-large) followed a mostly gradual decrease of the infraspecific genetic distances (Figure 3F, Figure S3C). Larger geographical distances occurred in saprophagous and phytophagous taxa or species preferring wetland and vegetation, for which specimens had been sequenced from outside of Germany (Figure S3). In saprophagous taxa, a large amount of pairwise distances of specimens followed a nearly proportional increase in both genetic and geographic distances. The same was found for the xylophagous and zoophagous species. A different pattern was evident in mycetophagous species where the genetic distances were already much higher even with short geographic distances, while in necrophagous, polyphagous and coprophagous species we observed the opposite (with some minor exceptions), i.e., a clearly limited amount of genetic variation even with increased geographic distance (Figure 3D). In regard of habitat preferences, vegetation, rotten matters, and dead woods had similar trends as taxa with phyto-, sapro-, and xylophagous feeding style, obviously due to the connection between these eco-classes. Species with habitats such as soil and nests had also a higher genetic variation at same geographical scale, while others such as the ”mushrooms/ fungi” inhabitants had comparatively lower genetic structure despite a vast geographical sampling (Figure 3E).
All the three methods of correlation analysis between genetic and geographical differentiation detected cases in which the expected relationship between geographical and genetic distances were confirmed, i.e., where all correlation approaches were positive (Figures S4, S5). The Mantel test identified 250 species having a significant relationship between the two distances (14% of the total number of examined species), NMDS 160 species (9% of the total number of examined species) and PCA 123 (6.8% of the total number of examined species). Overlap of significant species between NMDS and Mantels test was 9.2%, while species overlap of PCA with Mantel test was 9.6 % of and 32.5 % with NMDS. This apparent discordance in identifying the significant species with correlated patterns was evident from pairwise plots of significance and statistic values of each species from the three methods (Figure S6): while the PCA and NMDS methods agreed in both significance and statistic values in most of the cases, both methods highly diverged with the mantel resulting scores. Furthermore, maximum and minimal values of significant species differed between the three methods (Tab. 1).
Significance for the ecological traits and their sub-guilds was rather rare in all three approaches of correlation analysis (Figure S5). Significance levels were too low to further use the outcome for further trait investigation: these were in mean for all ecological guilds 7.5, 9.4, or 15.6 % for PCNM+PCA, NMDS+PCA, and Mantel test, respectively, or at best 28% for a single guilt (Tab. 2). Some beetle families entirely did not show significance (Figure S7). All three correlation tests found coprophagous species to have the significantly more species with significant correlation between genetic and geographic distances (Tabs 1, 2). While the mantel test identified nest dwellers with the lowest percentage the opposite was the case for NMDS and PCNM where the nest dweller guild was the most dominant in significance. PCA and NMDS recorded high percentages in significant species in nest habitat and body size (i.e., extra-large), while small species were those dominant for the Mantel test.