Tracing coco de mer's reproductive history: Pollen and nutrient limitations reduce fecundity

Abstract

Habitat degradation can reduce or even prevent the reproduction of previously abundant plant species. To develop appropriate management strategies, we need to understand the reasons for reduced recruitment in degraded ecosystems. The dioecious coco de mer palm (Lodoicea maldivica) produces by far the largest seeds of any plant. It is a keystone species in an ancient palm forest that occurs only on two small islands in the Seychelles, yet contemporary rates of seed production are low, especially in fragmented populations. We developed a method to infer the recent reproductive history of female trees from morphological evidence present on their inflorescences. We then applied this method to investigate the effects of habitat disturbance and soil nutrient conditions on flower and fruit production. The 57 female trees in our sample showed a 19.5‐fold variation in flower production among individuals over a seven‐year period. Only 77.2% of trees bore developing fruits (or had recently shed fruits), with the number per tree ranging from zero to 43. Flower production was positively correlated with concentrations of available soil nitrogen and potassium and did not differ significantly between closed and degraded habitat. Fruiting success was positively correlated with pollen availability, as measured by numbers and distance of neighboring male trees. Fruit set was lower in degraded habitat than in closed forest, while the proportion of abnormal fruits that failed to develop was higher in degraded habitat. Seed size recorded for a large sample of seeds collected by forest wardens varied widely, with fresh weights ranging from 1 to 18 kg. Synthesis: Shortages of both nutrients and pollen appear to limit seed production of Lodoicea in its natural habitat, with these factors affecting different stages of the reproductive process. Flower production varies widely amongst trees, while seed production is especially low in degraded habitat. The size of seeds is also very variable. We discuss the implications of these findings for managing this ecologically and economically important species.

Mate-choice for close kin is associated with improved offspring survival in Lodoicea maldivica, the largest-seeded plant in the world

“…Seed size is to a large extent determined by the amount of triploid endosperm produced, which depends upon the interplay between the two parental genomes 43 . In fact, Lodoicea is far more variable than most plants in the shape and size of its seeds, with fresh weights of individual seeds ranging from as little as 1.5 kg up to 18 kg 44 . It is also variable in the number of seeds produced per fruit, with most fruits containing one seed, but with some containing two and even three seeds.…”

Tree conservation can be constrained by agents from conservation permitting and funding agencies

“…In this case, the government conservation employees who were empowered to plan and implement the conservation agenda initiated the conservation efforts of the coco de mer palm (Lodoicea maldivica Gmelin) by including accomplished scientists as a beginning step, enabling the scientists to implement adaptive management research, allowing them to publish the results in the primary literature, then culminating the process by crafting conservation decisions based on the scientific publications [71]. The approach has resulted in the generation of informative multi-year data sets that have greatly improved conservation decisions [72,73].…”

Dispersal capacities of pollen, seeds and spores: insights from comparative analyses of spatial genetic structures in bryophytes and spermatophytes

“…In anemochorous species in particular, the range, at which seeds disperse, is correlated with their ornamentation patterns but also with their size, smaller particles dispersing further than larger ones due to their lower settling velocity, and thus, longer expected airborne time ( Bullock et al., 2006 ). Seed size ranges between 0.05 mm ( Arditti and Ghani, 2000 ) to tens of centimetres ( Morgan et al., 2017 ), largely exceeding the size of pollen grains, which range between 10 and about 100 µm in diameter ( Hao et al., 2020 ). Seeds and pollen grains have different potential for dispersal ( Santos et al., 2018 ), so that genetic variation in cpDNA is typically much more spatially structured than in nDNA ( Petit et al., 2005 ).…”