Floral trait variation in fourCyclamen (Primulaceae) species

The purpose of this study is to examine floral trait variation between fourCyclamen species that show variation in their ability to reproduce in the absence of pollinators and in levels of inbreeding. Pollen and ovule production, pollen/ovule ratio, pollen volume, petal length and width, diameter of the corolla mouth, pistil and stamen length, and stigma-anther separation varied significantly between the four study species. Flower, pollen and ovule production, pollen volume and corolla size were generally highest inC. hederifolium, the species with the lowest level of inbreeding (mean F_is = 0.329), intermediate in both species with relatively high levels of pollinator-mediated inbreeding,C. repandum (mean F_is = 0.658) andC. creticum (mean F_is = 0.748), and lowest in the highly inbredC. balearicum (mean F_is = 0.930). The two species with the most different inbreeding coefficients,C. hederifolium andC. balearicum, had lower pollen-ovule ratios and shorter longevities of stigma receptivity and pollen viability thanC. creticum andC. repandum. These patterns of variation in floral traits are discussed in relation to the relatedness, pollination ecology and levels of inbreeding of the four species.     

Biotic versus abiotic pollination in Oeceoclades maculata (Lindl.) Lindl. (Orchidaceae)

Geographical variation in the reproductive biology of widespread species often occurs at their distributional boundaries. We sought to determine whether such variation has occurred in an invasive orchid, Oeceoclades maculata, across its naturalized range. We compared its reproductive biology in a Brazilian population with that published for a population on the Caribbean island of Puerto Rico. In the state of São Paulo, O. maculata flowers between December and February, at the height of the rainy season. Similar fruit sets were observed in manual self (76%) and cross (70.4%) pollination treatments. The fruit set of plants protected from both pollinators and rainfall was 6.1%, whereas plants exposed only to rainfall had a fruit set of 41.4%, slightly less than the controls (48.3%). Like the Puerto Rico population, reproduction is primarily through rain‐assisted autogamy, but unlike observations made on the island, outcrossing can eventually occur. We observed two butterfly species (Heliconius ethilla narcaea and Heliconius erato phyllis) pollinating O. maculata. Secretory epidermal cells and trichomes of the spur lumen produced 0.7 µL of 25% (sucrose equivalents) nectar per flower each morning, which was stored in a dilated basal portion of the spur and reabsorbed by the afternoon. Thus, geographical variation in reproductive biology exists across the broad invasive range of O. maculata.     

Do inefficient selfing and inbreeding depression challenge the persistence of the rare Dianthus guliae Janka (Caryophyllaceae)? Influence of reproductive traits on a plant's proneness to extinction

The yellow carnation Dianthus guliae Janka is a rare endemic of the Italian peninsula. As numerous extinctions have occurred in the past, very few populations are still present. Two years of field surveys revealed high mortality and an absence of recruitment in the southernmost populations of this species. Work in a botanical garden, under semi-natural conditions, revealed the occurrence of proterandrous hermaphroditism and self-compatibility. The durable flower lifespan, the competitive effects among flowers and the different outcomes from spontaneous and hand-performed pollinations (with both self- and cross-pollen) suggested low pollination rates in the experimental stand. Pollinator exclusion experiments revealed a low frequency of delayed autonomous selfing, suggesting that self-fertilization in D. guliae relies mainly on facilitated selfing and geitonogamy. Studies of inbreeding depression during the early life-history stages revealed significant differences between selfed and crossed progenies in terms of seed mass, germination rates, developmental vigour and mortality rates. Therefore, when pollen delivery is scarce, the plant may fail reproductive assurance via autonomous selfing. The influence of inbreeding depression contributes to a further reduction in recruitment chances in very small D. guliae populations. Experimental reintroductions are urgent to avoid local extinction at the southern periphery of its range.     

Variation in self-fertility,inbreeding depression and levels of inbreeding in four Cyclamen species

The ability to self in the absence of pollinators, i.e. reproductive assurance, and the detrimental consequences of inbreeding, i.e. inbreeding depression, are central factors influencing plant mating system evolution. The purpose of this study was to quantify whether self-fertility and inbreeding depression are related to levels of inbreeding in four Cyclamen species, namely C. balearicum (mean F_is = 0.930), C. creticum (mean F_is = 0.748), C. repandum (mean F_is = 0.658) and C. hederifolium (mean F_is = 0.329). C. balearicum showed a markedly greater capacity to autonomously self-fertilize than the three other species, which may have favoured inbreeding in this species. Levels of inbreeding depression were highest in C. creticum and C. hederifolium at the fruit maturation (δ = 0.18 and 0.20, respectively) and seed number (δ = 0.32 and 0.30, respectively) stages, and for C. repandum at the seed weight stage (δ = 0.23). Although C. balearicum showed inbreeding depression on seed germination (δ = 0.45), this may be an artefact of the generally low levels of seed germination in the experiment. Overall, we observed only limited evidence for the predicted negative relation between inbreeding coefficients and levels of inbreeding since C. creticum had high levels of inbreeding and inbreeding depression. Other factors may thus influence the relationship between inbreeding and inbreeding depression in these species.     

Genetic structure of the widespread and common Mediterranean bryophyte Pleurochaete squarrosa (Brid.) Lindb. (Pottiaceae) - evidence from nuclear and plastidic DNA sequence variation and allozymes

The Mediterranean Basin as one the world's most biologically diverse regions provides an interesting area for the study of plant evolution and spatial structure in plant populations. The dioecious moss Pleurochaete squarrosa is a widespread and common bryophyte in the Mediterranean Basin. Thirty populations were sampled for a study on molecular diversity and genetic structure, covering most major islands and mainland populations from Europe and Africa. A significant decline in nuclear and chloroplast sequence and allozyme variation within populations from west to east was observed. While DNA sequence data showed patterns of isolation by distance, allozyme markers did not. Instead, their considerable interpopulation genetic differentiation appeared to be unrelated to geographic distance. Similar high values for coefficients of gene diversity (G(ST)) in all data sets provided evidence of geographic isolation and limited gene flow among populations (i) within islands, (ii) within mainland areas, and (iii) between islands and mainland. Notably, populations in continental Spain are strongly genetically isolated from all other investigated areas. Surprisingly, there was no difference in gene diversity and G(ST) between islands and mainland areas. Thus, we conclude that large Mediterranean islands may function as 'mainland' for bryophytes. This hypothesis and its implication for conservation biology of cryptogamic plants warrant further investigation. While sexually reproducing populations were found all over the Mediterranean Basin, high levels of multilocus linkage disequilibrium provide evidence of mainly vegetative propagation even in populations where sexual reproduction was observed.     

Genetic structure of continental and island populations of the Mediterranean endemic Cyclamen balearicum (Primulaceae)

Cyclamen balearicum is a self-compatible perennial herb endemic to the western Mediterranean Basin. This species occurs in five geographically isolated terrestrial islands in southern France and on four Balearic islands. In this study, we compare genetic variability and differentiation within and among 11 terrestrial island populations and 17 true island populations. Of nine readable enzyme loci, five were polymorphic in both terrestrial and true islands. F statistics showed a significant heterozygote deficiency in all populations, probably due to high levels of autonomous selfing, restricted gene flow, and subsequent genetic drift. Genetic diversity was higher in terrestrial islands than on the Balearic islands, suggesting that the Balearic islands were colonized when they were in contact with the continent. Population differentiation was greater among terrestrial islands (Fst = 0.417 and Gst = 0.344) than among true islands (Fst = 0.112 and Gst = 0.093). Furthermore, differentiation among populations on the Basses Cévennes terrestrial island was greater (Fst = 0.254) than among populations on the true island of Mallorca (Fst = 0.163). The greater genetic differentiation among terrestrial islands could have been caused by genetic bottlenecks associated with changes in climate and human land use that may have reduced population sizes more severely in terrestrial islands in southern France than on the Balearic islands.     

马先蒿属植物花冠分化与繁殖适应的研究进展

结合已有的研究报道和作者近年来的工作,对马先蒿属（Pedicularis）植物的花冠多样化成因与繁殖适应特性进行了总结和探讨。通过对该属4种进化花冠型的花器官发生和分化的研究发现,花部各器官在发生和发育初期基本一致,后期上唇形态的分化是导致成熟花形态结构产生较大差异的重要阶段。孢粉学研究认为,花冠类型与花粉萌发孔类型之间具有显著相关性;萌发沟的演化可能与繁殖适应有一定的关系。分子系统学研究表明,多样化的花冠类型在不同的谱系内经过若干次的独立进化而表现出了高度的平行演化（parallelism）。传粉生物学研究证实,该属植物花冠多样化与其主要传粉者熊蜂属（Bombus）昆虫的传粉行为存在较为密切的关系。具有相同（似）花冠类型的马先蒿可能被同种或不同种的熊蜂以相同的方式访问,但在花粉落置位置上存在显著差异,这可能有助于同域分布重叠的物种间在生殖上的机械隔离,而花冠的分化在一定程度上促进了新的物种形成。     

Pollen limitation and inbreeding depression in an 'old rare' bumblebee-pollinated grassland herb

Habitat fragmentation and reduction of population size have been found to negatively affect plant reproduction in 'new rare' species that were formerly common. This has been attributed primarily to effects of increased inbreeding but also to pollen limitation. In contrast, little is known about the reproduction of 'old rare' species that are naturally restricted to small and isolated habitats and thus may have developed strategies to cope with long-term isolation and small population size. Here we study the effects of pollen source and quantity on reproduction of the 'old rare' bumblebee-pollinated herb, Astragalus exscapus. In two populations of this species, we tested for pollen autodeposition, inbreeding depression and outbreeding depression. Caged plants were left unpollinated or were pollinated with pollen from the same plant, from the same population or from a distant population (50 km). Additionally, we tested for pollen limitation by pollen supplementation in four populations of different size and density. In the absence of pollinators, plants did not produce seed whereas self-pollinated plants did. This indicates a self-compatible breeding system dependent on insect pollination. Both self-pollination and, in one of the two populations, cross-pollination with pollen from plants from the distant population resulted in a lower number of seeds per flower than cross-pollination with pollen from plants from the resident population, indicating inbreeding and outbreeding depression. Pollen addition enhanced fruit set and number of seeds per flower in three of the four populations, indicating pollen limitation. The degree of pollen limitation was lowest in the smallest but densest population. Our results suggest that, similar to 'new rare' plant species, also 'old rare' species may be at risk of inbreeding depression and pollen limitation.     

Single large or several small? Population fragmentation in the captive management of endangered species

Captive populations of endangered species are typically maintained effectively as single random-mating populations by translocating individuals between institutions. Genetic, disease, and cost considerations, however, suggest that this may not be the optimal management strategy. Genetic theory predicts that a pooled population derived from several small isolated populations will have greater genetic diversity, less inbreeding, and less genetic adaptation to captivity than a single large population of equivalent total size, provided there are no population extinctions. These predictions were tested using populations of Drosophila with effective size comparisons of 50 vs. 2 × 25; 100 vs. 2 × 50 vs. 4 × 25, and 500 vs. 2 × 250 vs. 4 × 100 + 2 × 50 vs. 8 × 25 + 6 × 50. Populations were maintained at the indicated sizes as separate pedigreed populations for 50 generations. The several small treatments were subsequently pooled and maintained for eight to 10 generations prior to determination of fitness and evolutionary potential. Several small populations (pooled), when compared to single large populations of equivalent total size, were found to have lower average inbreeding coefficients, significantly higher reproductive fitness under competitive conditions, similar fitness under benign captive conditions, higher genetic diversity, and equivalent evolutionary potential. Trends favored the several small (pooled) populations in all comparisons at population sizes of 50 and 100. We recommend that endangered species in captivity be maintained as several small populations, with occasional exchange of genetic material. This has genetic benefits over current management both in captivity and especially for reintroductions, as well as reducing translocation costs and risks of disease transfer. Zoo Biol 17:467–480, 1998. © 1998 Wiley-Liss, Inc.