Ana Ortega-Olivencia

Pollination mechanisms and pollen-ovule ratios in some Genisteae (Fabaceae) from Southwestern Europe

We studied the biology and floral rewards of 34 taxa ofGenisteae from the SW of Europe. Most of the floral attributes show a statistically significant direct relationship. Anther biomass of the lower whorl (lW) is significantly lower than that of the upper whorl (uW), and the ratio of the two (Rv) differs among the taxa. All taxa are polliniferous, andRetama sphaerocarpa also secretes nectar. They can be considered xenogamous or facultative xenogams on the basis of their high pollen/ovule (P/O) ratios. Three principal mechanisms of pollen releasing are identified in this tribe: valvular, pump and explosive; the latter comprises specialized and nonspecialized subtypes. Pollination is sternotribic except in the specialized explosive mechanism, in which it is noto-sternotribic. Thus some pollen serves as food (pollen from the uW, which adheres to the ventral surface of the insect) and part of the pollen fulfils a polliniferous function (pollen from the lW, which adheres to the dorsal surface). Species that use a pump mechanism have very low Rv values (Rv=0.08−0.26); species with valvular or nonspecialized explosive mechanisms have Rv values between 0.24 and 0.58; those with a specialized mechanism of pollen presentation have high Rv values (0.6−0.76). In contrast to expectations, the highest P/O ratios appear in the specialized explosive system, which allows a single visit from the insect.

Insects, birds and lizards as pollinators of the largest-flowered Scrophularia of Europe and Macaronesia.

BACKGROUND AND AIMS It has traditionally been considered that the flowers of Scrophularia are mainly pollinated by wasps. We studied the pollination system of four species which stand out for their large and showy flowers: S. sambucifolia and S. grandiflora (endemics of the western Mediterranean region), S. trifoliata (an endemic of the Tyrrhenian islands) and S. calliantha (an endemic of the Canary Islands). Our principal aim was to test whether these species were pollinated by birds or showed a mixed pollination system between insects and birds. METHODS Censuses and captures of insects and birds were performed to obtain pollen load transported and deposited on the stigmas. Also, a qualitative and quantitative analysis of the flowers and inflorescences was carried out. KEY RESULTS Flowers were visited by Hymenoptera and by passerine birds. The Canarian species was the most visited by birds, especially by Phylloscopus canariensis, and its flowers were also accessed by juveniles of the lizard Gallotia stehlini. The most important birds in the other three species were Sylvia melanocephala and S. atricapilla. The most important insect-functional groups in the mixed pollination system were: honey-bees and wasps in S. sambucifolia; bumble-bees and wasps in S. grandiflora; wasps in S. trifoliata; and a small bee in S. calliantha. CONCLUSIONS The species studied show a mixed pollination system between insects and passerine birds. In S. calliantha there is, in addition, a third agent (juveniles of Gallotia stehlini). The participation of birds in this mixed pollination system presents varying degrees of importance because, while in S. calliantha they are the main pollinators, in the other species they interact to complement the insects which are the main pollinators. A review of different florae showed that the large showy floral morphotypes of Scrophularia are concentrated in the western and central Mediterranean region, Macaronesia and USA (New Mexico).

The role of birds and insects in pollination shifts of Scrophularia (Scrophulariaceae).

The mixed vertebrate-insect pollination system is rare in Holarctic plants. Phylogenetic relationships of 116 Scrophularia taxa were investigated based on two plastid (ndhF and trnL-trnF) and one nuclear (ITS) DNA regions. A wider time-calibrated analysis of ndhF sequences of the Lamiales revealed that Scrophularia diverged as early as in the Miocene (<22 Ma). Results of maximum-likelihood optimizations supported wasp pollination as the ancestral pollination system from which other systems derived (hoverfly, mixed vertebrate-insect and bird systems). Four origins for a mixed vertebrate-insect (MVI) pollination system were inferred, in which two western Mediterranean species (S. sambucifolia and S. grandiflora) and two island species (the Tirrenian S. trifoliata and the Canarian S. calliantha) were involved. S. calliantha is the only species in which a more complex MVI system, including pollination by the lizard Gallotia stehlini, has evolved. In addition, bird (hummingbird) floral traits found in the New Mexican S. macrantha appear to have been independently acquired. In contrast, we failed to find evidence for an ancient role of hummingbirds in the evolution of European Scrophularia. Indeed, paleontological data revealed that extinction of European hummingbirds (30-32 Ma) occurred earlier than the divergence of European MVI lineages of Scrophularia. In conclusion, our results showed that a role of birds in pollination of Scrophularia may not have been effective in the Miocene-Pliocene, but bird pollination that shows its origin in the Pliocene-Pleistocene is still operating independently in different islands and continents.

Nectar Production in Anagyris foetida (Fabaceae): Two Types of Concentration in Flowers with Hanging Droplet

In Anagyris foetida, a shrubby legume with autumn–winter flowering, the flowers produce great amounts of very dilute nectar during the first half of their life, consonant with their pollination by passeriforms. With advancing age, the volume of nectar diminishes and the concentration increases to values characteristic of bee‐pollinated flowers. The daily nectar secretion is greatest in volume early in the morning, damping during the day, whereas the concentration usually undergoes a gradual rise from morning to evening. The flowers visited for the first time in any day in the first half of anthesis have greater accumulated final nectar volumes than those first visited in the second half of anthesis. The accumulated nectar per flower is less in flowers that receive one visit per day than in those that receive three visits per day and is less in shrubby plants than in arboreal plants. In unvisited flowers, the rate of production of nectar depends on the environmental conditions, and at the end of their life there is a major loss of volume due to evaporation and of solutes possibly due to reabsorption. These flowers usually present a large hanging droplet of nectar that has a greater concentration and sugar content than does the nectar inside the calyx. The sugar, hexose dominant, is homogeneous in both locations.

Self-sterility in two Cytisus species (Leguminosae, Papilionoideae) due to early-acting inbreeding depression

In most angiosperms, the endosperm develops before the embryo, but with harmony between the two structures until final seed formation. In an embryological study, we show that inbreeding depression causes disharmony in development of the two structures in two Leguminosae shrubs, Cytisus multiflorus and C. striatus. Our main objective was to test the causes of self-sterility in the two species by comparing the embryological development of the self seeds with that of cross seeds. In developing selfed seeds of C. multiflorus, the embryo reaches at most the globular stage and never forms mature seeds, while in C. striatus a few mature selfed seeds are formed. In both species, the main cause of abortion of developing selfed seeds is diminished endosperm development (low values of the ratio of endosperm to embryo), which triggers collapse of the endosperm and embryo. The results indicate that self-sterility in C. striatus is postzygotic because of strong, early inbreeding depression, while in C. multiflorus there exists a mixed pre- and postzygotic mechanism; the prezygotic mechanism causes rejection of some self-pollen tubes in the style/ovary, and the early inbreeding depression triggers abortion of fertilized ovules that escaped that action.

Pollinator shifts drive petal epidermal evolution on the Macaronesian Islands bird-flowered species.

Pollinator shifts are considered to drive floral trait evolution, yet little is still known about the modifications of petal epidermal surface at a biogeographic region scale. Here we investigated how independent shifts from insects to passerine birds in the Macaronesian Islands consistently modified this floral trait (i.e. absence of papillate cells). Using current phylogenies and extensive evidence from field observations, we selected a total of 81 plant species and subspecies for petal microscopy and comparative analysis, including 19 of the 23 insular species pollinated by opportunistic passerine birds (Macaronesian bird-flowered element). Species relying on passerine birds as the most effective pollinators (bird-pollinated) independently evolved at least five times and in all instances associated with a loss of papillate cells, whereas species with a mixed pollination system (birds plus insects and/or other vertebrates) evolved at least five times in Macaronesia and papillate cells were lost in only 25% of these transitions. Our findings suggest that petal micromorphology is a labile trait during pollinator shifts and that papillate cells tend to be absent on those species where pollinators have limited mechanical interaction with flowers, including opportunistic passerine birds that forage by hovering or from the ground.

Germination and seed bank biology in some Iberian populations of Anagyris foetida L. (Leguminosae)

In Anagyris foetida, the fruits are disseminated by fall under gravity. No dispersing agent is as yet known, so that the fruits are located near the mother plant. The species presents an important seed bank that differs between the two populations studied, probably due to their different production of seeds/individual and to the livestock pressure. The germination of control seeds was found to be null or very low, with no improvement following exposure to high temperatures, but reaching high values following scarification in all the populations studied. This indicates that the failure in germination must be attributed to the hardness of the testa, with the seeds presenting physical dormancy. Also, the browsing of sheep on ripe fruit increases germination to 48% due to mechanical scarification, with this being the only positive effect those animals have on these plants. There were differences in germination after scarification between populations and years which could have been due to intrinsic characteristics.

Scrophularia arguta, a widespread annual plant in the Canary Islands: a single recent colonization event or a more complex phylogeographic pattern?

Abstract Many studies have addressed evolution and phylogeography of plant taxa in oceanic islands, but have primarily focused on endemics because of the assumption that in widespread taxa the absence of morphological differentiation between island and mainland populations is due to recent colonization. In this paper, we studied the phylogeography of Scrophularia arguta, a widespread annual species, in an attempt to determine the number and spatiotemporal origins of dispersal events to Canary Islands. Four different regions, ITS and ETS from nDNA and psbA‐trnH and psbJ‐petA from cpDNA, were used to date divergence events within S. arguta lineages and determine the phylogenetic relationships among populations. A haplotype network was obtained to elucidate the phylogenetic relationships among haplotypes. Our results support an ancient origin of S. arguta (Miocene) with expansion and genetic differentiation in the Pliocene coinciding with the aridification of northern Africa and the formation of the Mediterranean climate. Indeed, results indicate for Canary Islands three different events of colonization, including two ancient events that probably happened in the Pliocene and have originated the genetically most divergent populations into this species and, interestingly, a recent third event of colonization of Gran Canaria from mainland instead from the closest islands (Tenerife or Fuerteventura). In spite of the great genetic divergence among populations, it has not implied any morphological variation. Our work highlights the importance of nonendemic species to the genetic richness and conservation of island flora and the significance of the island populations of widespread taxa in the global biodiversity.

Causes of Low Fruit and Seed Set in Bird-Pollinated Anagyris foetida (Leguminosae): Pollen Limitation and Other Extrinsic Factors

We studied the extrinsic factors behind the low number of offspring in two populations of Anagyris foetida, a bird-pollinated leguminous shrub of the Mediterranean region. Fruit initiation was pollen limited, but fruit maturation was not. This limiting effect varied between flowering seasons and between populations, and also within a given phenological stage. In the first season, the early flowers had the lowest fruit set, while in the second season fruit set was highest in these early flowers. This was possibly related to the pollination environment. Seed initiation (fertilized ovules) increased following pollen supplementation, but this was not translated into a significant increase in either the number of seeds per fruit, or seed mass. This indicates that seed initiation is pollen limited but that other factors (e.g., resource availability) are involved in seed maturation. Abiotic factors such as excess humidity during flowering were responsible for the loss of inflorescences, especially in one of the two populations. In this population, the prevailing wind in autumn-winter was less effective in drying the flowers when there was excess humidity. Also, significantly fewer inflorescences were lost from solitary plants than from clustered plants, probably reflecting the beneficial action of the wind and the greater light levels during flowering. Of the biotic factors analyzed, sheep predation was the most important, being worse in drought years. This predation, by affecting population density, could modify the plant-pollinator interaction and severely reduce the plant’s breeding success because of its pollen limitation.

Regulation of fruit and seed set in Anagyris foetida L. (Fabaceae): The role of intrinsic factors

Abstract We investigated the role of resource limitation, ovary reserve, and selective abortion in controlling flower and fruit set in the Mediterranean leguminous shrub Anagyris foetida. The removal of bracts, but not that of leaves, reduced the initiation of fruit with respect to controls. The removal of a large proportion (2/3 of the total) of preanthesic inflorescences increased the reproductive capacity of individuals via two different strategies: (1) maintaining the number of fruit-bearing inflorescences, but increasing the number of fruits per inflorescence and seeds per fruit; and (2) increasing the number of fruit-bearing inflorescences, while maintaining fruits/inflorescence and seeds/fruit ratios unchanged. At the level of the inflorescence, most of the ripe fruits were located on the basalmost whorls of the raceme. Within the legume, fertilization was independent of the position of ovules, although the more basal presented lower rates of fertilization than the more central-stylar. The same was observed for the probability of a fertilized ovule to develop into a mature seed.