Trhypochthonius species

Weigmann, Gerd & Raspotnig, Günther, 2009, Comparative morphological and biometrical studies on Trhypochthonius species of the tectorum species group (Acari: Oribatida: Trhypochthoniidae), Zootaxa 2269 (1), pp. 1-31 : 20-22

Comparison of Trhypochthonius species

Within this section, Trhypochthonius tectorum is represented by two slightly differing local populations from the six studied in detail (see last section). Population (3) from Austria was analysed also with respect to opisthonotal gland secretion profiles ( Raspotnig et al. 2004) and molecular genetics (M. H.) and therefore is most important for the joint research-project; population (6) from northern Italy is nearest to the type locality of Berlese’s T. tectorum and therefore is most representative for the species. Significant differences of the biometrical data sets—notogastral setae lengths (as % of individual notogaster lengths) and notogaster lengths (in µm)—are documented in table 4.

The number of genital setae pairs ( Fig. 12b ) varies within the populations and differs among the species. Therefore it is one of the specific characters: there is the same median value (7 pairs) and the same range in T. americanus and the non-related T. silvestris europaeus n. subsp.; in T. tectorum the median is 10 pairs, in T. silvestris from North America 10.5 pairs, in T. japonicus from Japan 8 pairs, but in the European T. japonicus forma occidentalis the median is 13 pairs.

Regarding the notogaster length (as representative value of body size) we observe three size groups of species ( Fig. 12a ): Trhypochthonius silvestris and T. silvestris europaeus n. subsp. with mean notogaster lengths between 400 and 420 µm; T. tectorum and T. americanus with mean notogaster lengths between 450 and 470 µm; T. japonicus with largest bodies—the population from Japan with a mean about 475 µm and forma occidentalis from Europe with a mean about 505 µm.

The relative lengths of notogastral setae (%) mostly vary in a small range within the populations, but between the species the data sets of each notogastral seta are very often significantly different (see table 4). In figures 13–15 characteristic patterns of six notogastral setae are presented for the populations (left side); on the right side corresponding scatter plots combine individual notogaster length with setal length values (%) of all studied specimens, causing clusters of plot-groups marked by specific symbols and subjectively drawn ovals. In several cases the two-dimensional scaling is sufficient to discriminate species or species-pairs from each other.

Figures 13a and b present the analysis on c 1 -setae across the taxa. There are two highly separated groups of c 1 - setae lengths (13a), with tectorum and americanus versus the other four taxa, but nevertheless within the two groups are still some significant differences (see table 4). Figure 13b contains three separate larger clusters: one cluster with silvestris and s. europaeus indicates close relation of the two taxa, which still are significantly separated by the c 1 -setae lengths. The second cluster with japonicus and japonicus forma occidentalis is separated from the first cluster by the notogaster length values, it includes also two separated subclusters with the both taxa each, characterized by significant length differences of c 1 -setae. The third cluster with the two tectorum populations and americanus is separated from the other two clusters mainly by the distinctly major c 1 -setae values, but there is no species-related internal grouping.

The results for seta c 2 (figures 13c and d) are similar to those for seta c 1, but the values of japonicus and japonicus forma occidentalis are not significantly different. Regarding setae d 1 and e 1 ( Figs 14a,b and 14 c,d ) we observed similar three plot-clusters: the japonicus -cluster indicates greater setae length than the silvestris - cluster and again significantly less length than the tectorum-americanus -cluster. For both setae d 1 and e 1, the plot-group of silvestris is neighboured to that of s. europaeus but is significantly separated. The plots of japonicus for setae d 1 are separated from those of japonicus forma occidentalis, but not for setae e 1. Generally, the cluster patterns for the two parameters (setae values plotted against notogaster lengths) of the mediodorsal setae e 1, d 1 and h 1 (not figured, see significant differences in tab. 4) are similar to those presented in Figs 13b,d and 14b,d .

Regarding seta h 1 length ( Figs 15a,b ), the tectorum populations do not differ from the japonicus populations, but the values for americanus are greater; both clusters with the named species overlap but are distinctly separated from the silvestris -cluster in which neither taxon is separated. The results for seta p 2 are quite different ( Figs 15c,d ); the values for silvestris are extraordinarily high and in Fig. 15d form a fairly separated cluster from that of s. europaeus. Similarly, the plots of tectorum form their own cluster separated from that of americanus . The significance data regarding the further notogastral setae can be found in table 4. Especially the sets for setae h 3 and p 3 have more similarities than significant differences between the taxa and therefore are not suitable for discriminating the taxa.

Figures

FIGURE 12. Biometrical data of Trhypochthonius species. a—notogaster length data; b—numbers of genital setae pairs.—Abbreviations of species: te3—tectorum population (3); te6—tectorum population (6); am—americanus; si— silvestris; eu—silvestris europaeus; jaB—japonicus forma occidentalis; ja—japonicus.

FIGURE 13. Ranges of length-values of notogaster setae (a, c) and individual length-values plotted against notogaster lengths (b, d) of Trhypochthonius species. a, b—c1 setae; c, d—c2 setae. Abbreviations of species at plots: see fig. 12.

FIGURE 14. Ranges of length-values of notogaster setae (a, c) and individual length-values plotted against notogaster lengths (b, d) of Trhypochthonius species. a, b—d1 setae; c, d—e1 setae. Abbreviations of species at plots: see fig. 12.

FIGURE 15. Ranges of length-values of notogaster setae (a, c) and individual length-values plotted against notogaster lengths (b, d) of Trhypochthonius species. a, b—h1 setae; c, d—p2 setae. Abbreviations of species at plots: see fig. 12.