Classical wing angles, geometric wing analysis, and full body character suites

A main difficulty associated with this recent diversification of wing character suites is lack of downward compatibility. The morphometric definition of the currently recognized Apis mellifera subspecies has been based on traditional classical morphometry; consequently, studies based on a geometric character set cannot utilize reference data generated with traditional wing angle measurements accumulated in previous work by various authors, including the reference subspecies descriptions as given in Ruttner’s (1988) monograph.

Fortunately, however, there is a high degree of consensus concerning the marking points between the different kinds of wing shape analysis. Fig. 2 shows the 20 landmarks predominantly used in geometric morphometry. Tofilski (2004, 2008) omitted landmark 15, while Kandemir et al. (2011), following Zelditch et al. (2004), moved point 15 from the apex of the radial cell to the junction of Rs5 and the costa, and located one additional point at the end of the vannal fold. Classical morphometry and the DAWINO method use the same landmarks, omitting point 15. However, the methods disagree in the sequence of numbering these points, which is of no major concern.

To overcome the present sets of incompatible data and to avoid further parallel development of incompatible data sets in honey bee morphometry, our suggestion for a standardization of wing measurements is to store all future data as point coordinates (instead of the format of derived characters such as angles) to facilitate data exchange between different studies and research teams. We suggest using the point format exemplified in the description of Apiclass (http://apiclass.mnhn.fr), shown in Fig. 2. From these coordinates, used in a majority of geometric studies, all 30 DAWINO characters can be calculated, which include the Ruttner (1988) wing angles as a subset. Storing the point coordinates instead of calculated characters will also keep all options open for any future progress in analysis techniques. Unfortunately, however, the coordinates cannot be recreated from classical wing angles, but first attempts have been made to re-measure reference samples with the geometric method (Kandemir et al., 2011) to link geometric morphometry to subspecies characterizations obtained by the classical method.

As a further issue the question arises whether geometric morphometry should replace "classical" morphometry for good, meaning that the accurate, powerful and labour-effective shape analysis based on wing geometry alone should replace the full set of classical characters, including all traditional body characters. Phylogenetically, the wing venation is more informative compared to the more environment–sensitive character categories of size, colour or pilosity (Diniz Filho et al., 2000), and thus represents a character set somewhat comparable to molecular characters. A high degree of consistency between wing morphometry and molecular information has been demonstrated by Miguel et al. (2010). Therefore, wing geometry is particularly suitable to track phylogenetic relationships between subspecies, where the full "classical" character set can be misleading. However, aiming at an inventory of honey bee variation as a numerical account of ecotype morphology, it appears indispensable to maintain classical morphology with a broad character set to represent the actual features of subspecies or ecotypes, apart from and in addition to the question of their phylogeny. However, geometric wing venation morphometry might replace the classical wing angles even within the classical morphometry set, but no attempt has been made so far to combine these methods.

Fig. 2. Location of the nineteen landmarks on the fore-wing of honeybee workers considered in the geometric morphometric analysis (CC = cubital cell) http://apiclass.mnhn.fr; Miguel et al., 2010).

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