Biological and ecological constraints to the reintroduction of Eriocaulon heleocharioides (Eriocaulaceae): A species extinct in the wild

A reintroduction attempt of Eriocaulon heleocharioides Satake (Eriocaulaceae)—an annual amphibious herb species that is extinct in the wild—has been conducted in its last natural habitat from 2009. Unfortunately, this in-situ conservation measure has failed, probably due to environmental and genetic constraints related to long-term ex-situ cultivation. To evaluate the ex-situ conserved population and elucidate the factors impeding in-situ conservation, we investigated environmental and reproductive effects on life history traits to support appropriate conservation management strategies. First, we performed open outcross-pollination and self-pollination to verify the levels of reproductive success associated to the blooming sequence of the inflorescences (1 st to 6th inflorescences). Subsequently, growth experiments incorporating the maternal effect were conducted using inbred and outbred offspring under different environmental conditions (underwater and wet-soil). Based on hierarchical Bayesian models, we compared the effects of outcross-pollination and self-pollination on reproductive outputs and fitness traits. Analysis of the overall trend suggested that outcross-pollination significantly decreased the reproductive output, and negative effects were more pronounced in the first and in the last inflorescence. Regarding reproductive fitness, outcross-pollination was significantly correlated with greater seed mass. Post-germination, the growth of the outbred offspring was superior to that of the inbred offspring in approximately 30–40 % of the mother plants. Regarding the number of inflorescences and maximum leaf length, the overall negative effects of outcross-pollination increased with time. Outcross-pollination showed a significant positive effect on the survival rate in underwater conditions, whereas a negative effect was detected in wet-soil conditions. E. heleocharioides has a preference for self-pollination according to the pollen-ovule ratio. Increase of negative effects of outcross-pollination with time may suggest the genetic unhealthiness of E. heleocharioides. Inbreeding depression was lower under captivity, possibly reflecting adaptation to ex situ conditions (i.e., wet soil). This may have impeded a successful establishment of E. heleocharioides in the reintroduction site, because it was characterized by a higher water depth. In contrast, introducing underwater cultivation in the captive site could limit the spread of inbred individuals, by contributing to reduce the adaptation to ex situ conditions. To ensure the success of in-situ conservation, the use of appropriate environmental condition and lineages in which the mother plants exhibit low extent of inbreeding depression is required.