Geographical variation in the forewing shape of the red dwarf honeybees revealed by landmark-based geometric morphometrics

Accurate intraspecific variation assessment is the prerequisite for determining subspecies, evolutionarily significant units, or management units across a species range. However, intraspecific variation assessment is often hindered by inaccurate morphological results from traditional methods or high-cost genetic analyses. Geometric morphometrics is a promising technique for quantifying and visualizing intraspecific diversity. We used landmark-based geometric morphometrics to investigate forewing shape variation and microtaxonomy of populations of Apis florea Fabricius 1787 (Apidae: Apini), which originated from some parts of Asia and Africa based on the 19 landmarks plotted at the venation intersections of forewings. We collected samples of 162 colonies from 36 different localities. On average, 13 workers per colony were analyzed (1,851 bees in total). Distinct spatial structures and significant differences in wing shape between the studied populations were revealed using canonical variate analysis, and no considerable overlap was detected between the colonies belonging to the western and eastern populations. The populations at higher latitudes showed significantly larger centroid sizes than those at lower latitudes, and a clinal variation in forewing size was confirmed. Significant distance-decay relationships between the studied populations were observed so that the populations located at the maximum geographical distance (∼ 7,000 km) showed the most significant distance from each other and vice versa. Wing geometric morphometrics was an accurate tool for the reliable estimation of the population structure of the red dwarf honeybees. It is essential to increase the reliability of these variations by combining the results with further molecular data.