Life history evolution in Lodoicea maldivica (Arecaceae)

Abstract

Lodoicea maldivica, a palm endemic to two small islands in the Seychelles group, has the largest seed in the plant kingdom. We present here an interpretation of the ecological and evolutionary significance of this seed in terms of the island environment where the species grows. We begin by reviewing the available information about the biology and ecology of Lodoicea and present some original data on the growth and development of Lodoicea in its native habitat. A remarkable feature of young plants is the enormous size of their leaves and the great length of their petioles, these being especially elongated when growing beneath the canopy. As a result, juvenile plants can reach a height of 15 m and hold their foliage in the forest canopy. This capacity to produce such an enormous juvenile plant is related in part to the large food reserves in the seed. We suggest that Lodoicea evolved from a more typical borassoid palm (perhaps a plant like Borassus aethiopum which is widespread in the savannas of Africa) and propose two hypotheses to explain why this occurred. According to the ‘shade hypothesis’, increasingly humid conditions on the Seychelles led to strong selection for plants with the tallest seedlings, since these would be the most likely to establish successfully under the low light conditions prevailing on the forest floor of closed forest. The ‘sibling competition hypothesis’ postulates that the island populations of the ancestral palm lost any means for seed dispersal, and their seeds simply fell to the foot of the parent tree. This resulted in a strong selection pressure for reduced fecundity. The two hypotheses are not mutually exclusive, and together they may help us to understand many of the unusual features of this remarkable species.