Performance of pairwise shape dissimilarity morphometrics on nonmammalian taxa (Insecta: Neuroptera: Mantispidae)

Abstract

Morphometric dissimilarity metrics aim to quantify the variation between compared specimens such that inferences about their relatedness and alpha taxonomy can be made. Recently, the technique has developed metrics that purport to quantify shape dissimilarity between specimens-employing the use of least squares regression analysis. These metrics have been well applied by studies in the hominin fossil record with an arguably unsubstantiated backing for the technique. Originally postulated was the log10 sem metric which subsequently led to the standard error test of the null hypothesis metric. Following this, the standard deviation of logged ratios (SLR ) metric arose as a pairwise dissimilarity metric that constrains the regression to a zero-intercept, that is, a significant development in the robustness of the technique. This metric was tested on extant primates in order to evaluate its effectiveness alongside the two other metrics. It was shown to be the most reliable for comparisons between specimens of primates, but was unable to discriminate between heterospecific and conspecific comparisons. Arguably, an alternative model organism with which to compare the technique is lacking. This study considers shape dissimilarity metrics with respect to a group of nonmammalian organisms (mantidflies) and tests the metrics against three lines of evidence (morphology, CO1-DNA, and geographic distribution) that can delimit the species-level taxonomy for the group. It is shown that the metrics are unable to discriminate between pairwise comparisons of closely related species, resulting in biologically erroneous groupings, and contradicting the groupings derived from morphological, CO1-DNA, and distributional comparisons. It is thus asserted that the technique is unsuitable for use in alpha taxonomy as an additional line of evidence in mantidflies. It is further supposed that morphometrics in general should be employed with caution in studies of evolutionary history as phylogeny is not the only information contained within morphometric data.

Extreme natural size variation in both sexes of a sexually cannibalistic mantidfly

“…More work is clearly needed to better understand how and why body size varies with geography, if indeed these patterns hold up with more data. In another mantidfly species from Africa, extreme body size variation was reported that appeared to be independent of geography, but this study was limited to a relatively small sample size of only male specimens [ 24 ].…”

“…Adult mantidflies (Neuroptera: Mantispidae) are highly visual and voracious predators with elaborate courtship displays and both sexes can be aggressive or cannibalistic during courtship [ 21 – 23 ]. Regardless of sex, adult mantidflies can vary considerably in size ( figure 1 ) and are therefore an ideal system to use in studying the role of variable SSD on courtship and sexual cannibalism [ 22 , 24 , 25 ]. The intriguing natural history of this system may play a key role in the size variation we observe in adults.…”

“…Previous studies that have directly measured body size in large samples of mantidflies are limited, and only include individuals from a relatively small geographical range in the midwestern United States ([ 25 ]; but see data included in Bakkes et al . [ 24 ] for a small sample of males of two African species). Little is known about how body size varies across wide geographical ranges and among geographically distinct populations.…”

“…One of these fascinating and overlooked groups is the mantidflies (Neuroptera: Mantispidae). Adult mantidflies (Neuroptera: Mantispidae) are highly visual and voracious predators with elaborate courtship displays and both sexes can be aggressive or cannibalistic during courtship [21][22][23]. Regardless of sex, adult mantidflies can vary considerably in size (figure 1) and are therefore an ideal system to use in studying the role of variable SSD on courtship and sexual cannibalism [22,24,25].…”