Investigation of two hypotheses on the maintenance mechanism of fruit color dimorphism of Viscum coloratum in northeastern China

Abstract Viscum coloratum, a semi-parasitic evergreen shrub exhibiting fruit color dimorphism, was investigated in this study to test the two hypotheses of forager preference and habitat heterogeneity selection. A study in northeastern China examined frugivorous bird preferences for color morphs and seed germination performance across three populations. Observations were conducted from November 2018 to March 2019, focusing on fruit removal rates and seed collection. Fruit counts and seed germination experiments were conducted to assess color morph preferences and germination rates at different observation stages and under various temperature conditions. Results indicated no preference for frugivorous birds between color morphs, contrary to the forager preference hypothesis. However, in the northern population (FY), the germination speed of red morph seeds was slightly faster under low-temperature conditions (15°C). In contrast, in the southern population (FC), seeds of the yellow morph germinated slightly faster under higher temperatures (20°C). These differences in germination speed were attributed to fitness differences among populations, supporting the habitat heterogeneity selection hypothesis. Frugivorous birds didn’t favor specific color morphs, but seed germination rates vary subtly with local conditions, indicating adaptation to habitat differences. This underscores how habitat variation influences V. coloratum’s ecological dynamics.