Genetic races associated with the genera and sections of host species in the holoparasitic plant Cytinus (Cytinaceae) in the Western Mediterranean basin

* Speciation via race formation is an important evolutionary process in parasites, producing changes that favour their development on particular host species. Here, the holoparasitic plant Cytinus, which has diverse host species in the family Cistaceae, has been used to study the occurrence of such races. * Amplified fragment length polymorphism (AFLP) analyses were performed on 174 individuals of 22 populations parasitizing 10 Cistaceae species in the Western Mediterranean basin. * Neighbour-joining, multivariate ordination analyses, and individual-based Bayesian analyses, clustered Cytinus populations into five well-characterized genetic races that, overall, agreed with the taxonomic sections of their hosts. In the AMOVA, among-races differences accounted for almost 50% of the genetic variation. The isolation-by-distance model was not supported by a Mantel test among Cytinus populations (r = 0.012; P = 0.456). All races showed low within-population genetic diversity, probably as a result of restricted pollen flow aggravated by flowering asynchrony, restricted seed dispersion, or stochastic processes. * The genetic differentiation among the five races of Cytinus is congruent with the view that these races are well-characterized lineages that have evolved independently as a result of selective pressures imposed by their hosts. This pattern, with genetically distinctive groups associated with the infrageneric sections of the host species, has not been reported previously for parasitic angiosperms.     

The endophytic system of mediterranean Cytinus (cytinaceae) developing on five host Cistaceae species

BACKGROUND AND AIMS: One of the most extreme manifestations of parasitism is found in the genus Cytinus, a holoparasite whose vegetative body is reduced to an endophytic system living within its host root. There are two species of Cytinus in the Mediterranean, C. hypocistis and C. ruber, which parasitize various genera of Cistaceae, one of the most characteristic families of the Mediterranean scrublands. The aim of this work is to describe the endophytic systems of C. hypocistis and C. ruber, and their tissue relationships with their host. METHODS: Roots from five different hosts infected with C. hypocistis and C. ruber were harvested, and examined by anatomical techniques under light microscopy to elucidate the characteristics of the endophytic system of Cytinus, and to determine if differences in endophytic systems occur between the two species and in response to different hosts. KEY RESULTS: The endophyte structure is similar in both Cytinus species irrespective of the host species. In the initial stages of the endophyte, rows of parenchymal cells spread through the host pericyclic derivatives and phloem, and begin to generate small nodules in the outermost region of the host xylem. Later the nodules anastomose, and bands of parasitic tissue are formed. The host cambium continues to develop xylem tissue, and consequently the endophyte becomes enclosed within the xylem. The bands of parasitic tissue fuse to form a continuous sheath. This mature endophyte has well-developed vascular system with xylem and phloem, and forms sinkers with transfer cells that grow through the host xylem. CONCLUSIONS: The endophytic system of Cytinus develops in all host root tissues and reaches its most mature stages in the host xylem. It is more complex than previously reported, showing parenchyma, xylem and phloem tissues. This is the first report of well-developed phloem in a holoparasitic endophytic species.     

Ultrastructural study of change from free-nuclear to cellular endosperm in Ipomoea purpurea Roth and Cytinus hypocistis L.

Abstract

The process of cellularization of the endosperm was studied in Ipomoea purpurea Roth and Cytinus hypocistis L. In both the examined species normal cytochinesis, involving the formation of the phragmoplast, characterizes the change from the nuclear to cellular condition. Nevertheless, some ultrastructural aspects of the cell wall initiation seem to indicate that the modality of freely-growing walls cannot be excluded. The hypothesis of a unique method of wall initiation for the endosperm of the nuclear type, formulated by some Authors, is discussed.     

Endozoochory by beetles: a novel seed dispersal mechanism

Background and Aims

Due in part to biophysical sized-related constraints, insects unlike vertebrates are seldom expected to act as primary seed dispersers via ingestion of fruits and seeds (endozoochory). The Mediterranean parasitic plant Cytinus hypocistis, however, possesses some characteristics that may facilitate endozoochory by beetles. By combining a long-term field study with experimental manipulation, we tested whether C. hypocistis seeds are endozoochorously dispersed by beetles.

Methods

Field studies were carried out over 4 years on six populations in southern Spain. We recorded the rate of natural fruit consumption by beetles, the extent of beetle movement, beetle behaviour and the relative importance of C. hypocistis fruits in beetle diet.

Key Results

The tenebrionid beetle Pimelia costata was an important disperser of C. hypocistis seeds, consuming up to 17·5 % of fruits per population. Forty-six per cent of beetles captured in the field consumed C. hypocistis fruits, with up to 31 seeds found in individual beetle frass. An assessment of seeds following passage through the gut of beetles indicated that seeds remained intact and viable and that the proportion of viable seeds from beetle frass was not significantly different from that of seeds collected directly from fruits.

Conclusions

A novel plant–animal interaction is revealed; endozoochory by beetles may facilitate the dispersal of viable seeds after passage through the gut away from the parent plant to potentially favourable underground sites offering a high probability of germination and establishment success. Such an ecological role has until now been attributed only to vertebrates. Future studies should consider more widely the putative role of fruit and seed ingestion by invertebrates as a dispersal mechanism, particularly for those plant species that possess small seeds.     

Diademed sifakas (Propithecus diadema) use olfaction to forage for the inflorescences of subterranean parasitic plants (Balanophoraceae: Langsdorffia sp., and Cytinaceae: Cytinus sp.)

Primates usually locate food resources using visual cues and memory, yet the potential for olfactory-guided (or olfactory-assisted) food location remains relatively unexplored. Here we report observations of wild Propithecus diadema that strongly suggest that olfaction is used to locate the inflorescences of two subterranean parasitic plant species (Langsdorffia sp. and Cytinus sp.). These valued but seasonal food resources are found obscured in leaf litter, and sifakas spend considerable time on the ground engaged in what appears to be olfactory exploration before they locate the inflorescences. Because they are visually obscured and occur within a substrate that is rarely used by sifakas, accidental discovery of these resources seems unlikely. Individuals may learn to exploit them by watching conspecifics.     

Mammal pollinators lured by the scent of a parasitic plant

To communicate with animals, plants use signals that are distinct from their surroundings. Animals generally learn to use these signals through associative conditioning; however, signals are most effective when they elicit innate behavioural responses. Many plant species have flowers specialized for pollination by ground-dwelling mammals, but the signals used to attract these pollinators have not been elucidated. Here, we demonstrate the chemical basis for attraction of mammal pollinators to flowers of the dioecious parasitic plant Cytinus visseri (Cytinaceae). Two aliphatic ketones dominate the scent of this species; 3-hexanone, which elicits strong innate attraction in rodents, and 1-hexen-3-one, which repels them in isolation, but not in combination with 3-hexanone. The aliphatic ketone-dominated scent of C. visseri contrasts with those of insect-pollinated plants, which are typically dominated by terpenoids, aromatic or non-ketone aliphatic compounds. 3-hexanone is also known from some bat-pollinated species, suggesting independent evolution of plant signals in derived, highly specialized mammal-pollination systems.