Data from: Comparing ant morphology measurements from microscope and online AntWeb.org 2D z-stacked images

Unprecedented technological advances in digitization and the steadily
expanding open-access digital repositories are yielding new opportunities
to quickly and efficiently measure morphological traits without
transportation and advanced/expensive microscope machinery. A prime
example is the AntWeb.org database, which allows researchers from all over
the world to study taxonomic, ecological, or evolutionary questions on the
same ant specimens with ease. However, the reproducibility and reliability
of morphometric data deduced from AntWeb compared to traditional
microscope measurements has not yet been tested. Here, we compared 12
morphological traits of 46 Temnothorax ant specimens
measured either directly by stereomicroscope on physical specimens or via
the widely used open access software tpsDig utilizing AntWeb digital
images. We employed a complex statistical framework to test several
aspects of reproducibility and reliability between the methods. We
estimated (i) the agreement between the measurement methods and (ii) the
trait value dependence of the agreement, then (iii) compared the
coefficients of variation produced by the different methods, and finally,
(iv) tested for systematic bias between the methods in a mixed
modelling-based statistical framework. The stereomicroscope measurements
were extremely precise. Our comparisons showed that agreement between the
two methods was exceptionally high, without trait value dependence.
Further, the coefficients of variation did not differ between the methods.
However, we found systematic bias in eight traits: apart from one trait
where software measurements overestimated the microscopic measurements,
the former underestimated the latter. Our results shed light on the fact
that relying solely on the level of agreement between methods can be
highly misleading. In our case, even though the software measurements
predicted microscope measurements very well, replacing traditional
microscope measurements with software measurements, and especially mixing
data collected by the different methods, might result in erroneous
conclusions. We provide guidance on the best way to utilize virtual
specimens (2D z-stacked images) as a source of morphometric data,
emphasizing the method’s limitations in certain fields and applications.