Differentiation in stingless bee honey composition
The pairwise comparison of SBH between each pair of tropical regions
using PERMANOVA showed significant differences (p=0.003) in the
composition of honeys across regions. However, the proportion of the
variation explained by the geographic group was low (<20%, R²
ranging from 0.05 to 0.183) , with the lowest value recorded being
between the Neotropics and the Afrotropics (5%).
Random forests models and hierarchical clustering (Table 1 &
Supplementary Fig. 3) illustrated that the distinction between groups of
honey samples was ambiguous, particularly among samples from the
Neotropics and the Afrotropics. None of the clusters included samples
from a single tropical region; instead they were composed of a mix of
samples from widely different geographical origins. Amino acids,
fermentation makers and sugars were significantly varying among each
tropical regions (Fig. 3), especially those involved in lactic acid
fermentation (sugars including fructose glucose, raffinose and maltose,
pyruvic acid and lactic acid) which were the most important compounds in
the random forest classification. Indicator compound analysis showed
that honeys from the Afrotropics were associated to kynurenic acid (stat
= 0.424, p-value = 0.005) and acetoin (stat = 0.511, p-value = 0.01) and
honeys from the Neotropics to methylglyoxal (stat = 0.532, p-value =
0.005) while we found no significant association between a specific
compound and honeys from the Indo-Malayan region.
Table 1 : Prediction results of the conditional random forest
models to predict the geographical origin of SBH samples.