Reproductive patterns, genetic diversity and inbreeding depression in two closely related Jumellea species with contrasting patterns of commonness and distribution

Abstract

Backgrounds and aims: Theory predicts that the long-term persistence of plant populations exposed to size reduction can be threatened by a loss of genetic diversity and increased inbreeding. However, several life-history and ecological traits can influence the response to population size reduction. The reproductive patterns, levels of genetic diversity and magnitude of inbreeding depression of the rare and fragmented Jumellea fragrans and of its widespread congener J. rossii were studied. The aim was to evaluate the effects of over-collection and fragmentation on J. fragrans and to enhance our knowledge of the biology and ecology of the two species, used for their aromatic and medicinal properties on Réunion.

Methods: Hand pollination experiments were conducted to determine the breeding system and to evaluate the potential for inbreeding depression in both species. Nuclear microsatellite markers were used to investigate selfing rates and levels of genetic diversity.

Key results: Jumellea rossii revealed a mixed-mating system, and inbreeding depression at the germination stage (δ = 0·66). Levels of genetic diversity were relatively high [allelic richness (AR) = 8·575 and expected heterozygosity (He) = 0·673]. In J. fragrans, selfing rates suggest a mainly outcrossing mating system. Genetic diversity was lower than in J. rossii, but not yet critically low (AR = 4·983 and He = 0·492), probably because of the mainly outcrossing mating system and the relatively high density of individuals in the studied population. Jumellea fragrans did not show inbreeding depression, and it is hypothesized that the population had progressively purged its genetic load during successive fragmentation events.

Conclusions: Even if the persistence of the J. fragrans population is not threatened in the short term, its genetic diversity has probably been reduced by fragmentation and over-collection. In situ conservation actions for J. fragrans and ex situ cultivation of both species are recommended in order to meet the demand of local people.

Keywords: Jumellea fragrans; Jumellea rossii; fragmentation; genetic diversity; inbreeding depression; mating system; over-collection.

Fig. 1.

Floral morphology of Jumellea fragrans. ds, dorsal sepal; pt, petal; ls, lateral sepal; lb, labellum; ov, ovary; pl, pollinarium; rs, rostellum; sc, stigmatic cavity; sp, spur. Scale bar = 1 cm.

Fig. 2.

Inbreeding depression (δ) magnitude for each stage recorded in J. fragrans and J. rossii. The bars give the value of δ, with above the significance found from associated crossed and selfed comparison (Mann–Whitney tests; *P < 0·05, **P < 0·01, ***P < 0·001). At each stage, the significance for species comparison is indicated across the top of the graph (Mann–Whitney tests; n.s., not significant, P-values as for individual bars). Stages are indicated as follows: fset, fruit set; wght, fruit weight; lgth, fruit length; wdth, fruit width; viab; seed viability; germ, seed germination.

Fig. 3.

Mean ± s.e. pollen removal (male reproductive success) and pollen deposition (female reproductive success) in J. fragrans (A) and J. rossii (B) for the 3 years studied. For each year, the numbers of flowers and individuals studied are given in parentheses, and the significance for removal vs. deposition comparisons is indicated accross the top of the graph (Mann–Whitney tests; n.s., not significant, *P < 0·05, **P < 0·01, ***P < 0·001).