Ecological significance of fruit displays in Myrtaceae: relationship between fruit colour, maturation stage, attractiveness and seed germination

Fruit colour has long fascinated scientists and is widely considered an
evolutionary adaptation to attract both avian and mammalian frugivores.
While fleshy fruits play a key role in plant–animal interactions by
promoting seed dispersal, the functional significance of colour variation,
particularly multicoloured displays during ripening, remains poorly
understood, largely because the selective and ecological drivers behind
these colour changes are still unclear. Here, we evaluate the relationship
between fruit colour, maturation stage, attractiveness and seed
germination in 12 Myrtaceae species, by testing three hypotheses: (1) the
visual delay hypothesis, which predicts that seeds reach physiological
maturity prior to the appearance of visual ripening signals in the fruit,
(2) the reward hypothesis, which predicts that mature fruits are more
consumed than fruits in intermediate ripening stages, and (3) the contrast
hypothesis, which suggests that multicoloured displays enhance
detectability and removal by frugivores. To test these hypotheses, we
quantified colour changes during fruit maturation, conducted germination
assays in the laboratory, and performed removal experiments with
artificial fruits in the field. Our results supported the visual delay
hypothesis, as all Myrtaceae species, regardless of display type,
exhibited high seed germinability even at early ripening stages. We also
corroborated the reward hypothesis, as fruits in the final ripening colour
were removed more often, independent of display type. Additionally,
multicoloured fruits were more frequently removed by frugivores,
supporting the contrast hypothesis and suggesting that multiple coloration
facilitates detection and extends the dispersal window. Our findings
contribute to a better understanding of the ecological role of fruit
colour in seed dispersal and highlight the importance of considering
species-specific traits in ecological studies, providing novel information
on germination speed index and germination percentages that can inform
restoration efforts, such as the selection and propagation of native
species.