Fruit heteromorphism and germination success in the perennial shrub tithonia diversifolia (Asteraceae)

Abstract

Studies of fruit or seed heteromorphism (the presence of two or more fruit or seed morphs within an individual) provide valuable information about the influence of environmental variation on the evolution of reproductive strategies. Such heteromorphisms are more likely to be favoured by selection in annual species, because short-lived plants are in a disadvantaged position to gather information about environmental conditions their offspring are likely to face when they germinate, compared with perennial counterparts. Here, we describe fruit heteromorphism of Tithonia diversifolia, a perennial shrub found in habitats with contrasting environmental conditions. We tested whether fruit morphs differ in weight and germination success, and whether populations differed in fruit morph ratio. To do this, we first determined fruit morph ratio of three populations from contrasting ecosystems (evergreen high forest, evergreen medium forest and oak-pine forest), and compared germination success in a common-garden setting. In all populations, two fruit morphs were consistently distinguishable within the same capitulum. Although fruit morph ratios differed significantly across populations. Furthermore, fruit morphs differed in weight and germination success, but the direction of the difference was dependent on the population. These results suggest that fruit heteromorphism in the perennial T. diversifolia might represent distinct reproductive strategies allowing it to adapt to uncertain environmental conditions.