BackgroundHybrid zones are regions where individuals of two species meet and produce hybrid progeny, and are often regarded as natural laboratories to understand the process of species formation. Two microevolutionary processes can take place in hybrid zones, with opposing effects on population differentiation. Hybridization tends to produce genetic homogenization, reducing species differences, whereas the presence of mechanisms of reproductive isolation result in barriers to gene flow, maintaining or increasing differences between taxa.ResultsHere we study a contact zone between two hybridizing toad species, Bufo bufo and B. spinosus, through a combination of molecular (12 polymorphic microsatellites, four nuclear and two mitochondrial SNP markers) and morphological data in a transect in the northwest of France. The results show largely concordant clines across markers, defining a narrow hybrid zone of ca. 30 km wide. Most hybrids in the centre of the contact zone are classified as F2 or backcrossed individuals, with no individuals assigned to the F1 hybrid class.ConclusionsWe discuss the implications of these results for our understanding of the evolutionary history of these species. We anticipate that the toad contact zone here described will become an important asset in the study of hybrid zone dynamics and evolutionary biology because of its easy access and the abundance of the species involved.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0184-7) contains supplementary material, which is available to authorized users.

BackgroundThousands of flowering plant species attract pollinators without offering rewards, but the evolution of this deceit is poorly understood. Rewardless flowers of the orchid Erycina pusilla have an enlarged median sepal and incised median petal (‘lip’) to attract oil-collecting bees. These bees also forage on similar looking but rewarding Malpighiaceae flowers that have five unequally sized petals and gland-carrying sepals. The lip of E. pusilla has a ‘callus’ that, together with winged ‘stelidia’, mimics these glands. Different hypotheses exist about the evolutionary origin of the median sepal, callus and stelidia of orchid flowers.ResultsThe evolutionary origin of these organs was investigated using a combination of morphological, molecular and phylogenetic techniques to a developmental series of floral buds of E. pusilla. The vascular bundle of the median sepal indicates it is a first whorl organ but its convex epidermal cells reflect convergence of petaloid features. Expression of AGL6 EpMADS4 and APETALA3 EpMADS14 is low in the median sepal, possibly correlating with its petaloid appearance. A vascular bundle indicating second whorl derivation leads to the lip. AGL6 EpMADS5 and APETALA3 EpMADS13 are most highly expressed in lip and callus, consistent with current models for lip identity. Six vascular bundles, indicating a stamen-derived origin, lead to the callus, stelidia and stamen. AGAMOUS is not expressed in the callus, consistent with its sterilization. Out of three copies of AGAMOUS and four copies of SEPALLATA, EpMADS22 and EpMADS6 are most highly expressed in the stamen. Another copy of AGAMOUS, EpMADS20, and the single copy of SEEDSTICK, EpMADS23, are most highly expressed in the stelidia, suggesting EpMADS22 may be required for fertile stamens.ConclusionsThe median sepal, callus and stelidia of E. pusilla appear to be derived from a sepal, a stamen that gained petal identity, and stamens, respectively. Duplications, diversifying selection and changes in spatial expression of different MADS-box genes shaped these organs, enabling the rewardless flowers of E. pusilla to mimic an unrelated rewarding flower for pollinator attraction. These genetic changes are not incorporated in current models and urge for a rethinking of the evolution of deceptive flowers.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0938-7) contains supplementary material, which is available to authorized users.

In a choice‐experiment, 42 chrysanthemum cultivars were screened for resistance to Frankliniella occidentalis (Pergande). Oviposition preference, two types of feeding damage and thrips numbers per flower were recorded as measures of resistance. A large genetic variation in thrips resistance was found among the cultivars screened. The amount of feeding damage was strongly determined by oviposition preference. Besides, a positive correlation was found between the oviposition preference in non‐flowering chrysanthemums (number of eggs) and flowering chrysanthemums (number of thrips per flower). Thrips feeding on young, developing tissues, causes growth damage because affected cells are unable to expand and leaves become distorted. Thrips feeding on older, expanded leaves causes cells to become filled with air, resulting in ‘silver’ damage. The amounts of growth‐ and ‘silver’ damage were negatively correlated suggesting that thrips chose either young or older leaves to feed on. The order of resistance among cultivars did not change during the experiment. In order to get more insight in resistance mechanisms the influence of some plant‐ and flower characters on resistance was examined. The plant characters height, number of leaves, flower production and flower weight were all negatively correlated with resistance. It is suggested that tall chrysanthemum cultivars with many and large flowers may invest less in defence than smaller cultivars, and therefore are more damaged by thrips.

Two methods were used to measure the resistance of 5 chrysanthemum cultivars to thrips Frankliniella occidentalis Pergande (Thysanoptera, Thripidae). As a measure of resistance of a cultivar, growth and survival of the insect population were taken. First, leaf cages were used to look at the survival of thrips larvae on a single leaf. The survival of thrips larvae differed significantly between cultivars. After 3 weeks only 14 % of the thrips survived on the most susceptible cultivar and over the entire period only 16 % became adult. On the most resistant cultivar all larvae died before becoming adult. Second, thrips population growth was studied on whole plants with and without flowers in cages. After 4 weeks the cultivars differed significantly in thrips numbers in both experiments. Twenty to sixty times as many thrips were found on plants with flowers as on the plants without flowers. For the plants with flowers the number of flowers explained 44.6 % of the variance in thrips numbers, whereas cultivar explained 10.5%. When corrected for the number of flowers, these results bore a striking resemblance to the differences in susceptibility found in the experiment with plants without flowers. Similar rank orders were found for the 5 cultivars with respect to resistance with the leaf cage experiment, the whole‐plant cage experiment without flowers and the whole‐plant cage experiment with flowers, after correction for the number of flowers. Both methods are useful in the evaluation of thrips resistance. Zusammenfassung Populationswachstum und Überlebensdauer von Frankliniella occidentalis Pergande (Thysanoptera, Thripidae) an verschiedenen Chrysanthemum‐Sorten. Zwei Methoden zur Bestimmung des Resistenzgrades Zwei Methoden zur Bestimmung der Resistenz von 5 Chrysanthemum‐Sorten gegenüber dem Thrips Frankliniella occidentalis wurden miteinander verglichen. Bei der 1. Methode wurde das Überleben der Thripslarven am einzelnen Blatt durch Kontrolle von Blattkäfigen ermittelt. Hierbei differierte die Überlebensdauer der Larven zwischen den Sorten signifikant. Nach 3 Wochen waren an der empfindlichsten Sorte noch 14 % der Larven am Leben. An der resistentesten Sorte starben alle Larven vor Erreichen des Adultenstadiums ab. Die 2. Methode beruhte auf der Beobachtung von Käfigen mit einer Thripspopulation an der ganzen Pflanze mit oder ohne Blüten. Nach 4 Wochen differierte in beiden Experimentreihen die Resistenz der Chrysanthemum‐Sorten erheblich. Es wurden 20‐ bis 60 mal mehr Thripse an den Pflanzen mit Blüten als an jenen ohne Blüten gefunden. Pflanzen ohne Blüten erwiesen sich als allgemein resistenter als Pflanzen mit Blüten. Es wurden gleiche Rangordnungen der Resistenz für die 5 Sorten bei den Experimenten mit Blattkäfigen, mit Gesamtpflanzen ohne Blüten sowie mit Gesamtpflanzen mit Blüten (nach Zugrundelegung der gleichen Blütenzahl) gefunden. Daher sind beide Methoden zur Ermittlung der Resistenz bei Chrysanthemum‐Sorten geeignet.

Efficient seed dispersal in flowering plants is enabled by the development of fruits, which can be either dehiscent or indehiscent. Dehiscent fruits open at maturity to shatter the seeds, while indehiscent fruits do not open and the seeds are dispersed in various ways. The diversity in fruit morphology and seed shattering mechanisms is enormous within the flowering plants. How these different fruit types develop and which molecular networks are driving fruit diversification is still largely unknown, despite progress in eudicot model species. The orchid family, known for its astonishing floral diversity, displays a huge variation in fruit dehiscence types, which have been poorly investigated. We undertook a combined approach to understand fruit morphology and dehiscence in different orchid species to get more insight into the molecular network that underlies orchid fruit development. We describe fruit development in detail for the epiphytic orchid species Erycina pusilla and compare it to two terrestrial orchid species: Cynorkis fastigiata and Epipactis helleborine . Our anatomical analysis provides further evidence for the split carpel model, which explains the presence of three fertile and three sterile valves in most orchid species. Interesting differences were observed in the lignification patterns of the dehiscence zones. While C. fastigiata and E. helleborine develop a lignified layer at the valve boundaries, E. pusilla fruits did not lignify at these boundaries, but formed a cuticle-like layer instead. We characterized orthologs of fruit-associated MADS-domain transcription factors and of the Arabidopsis dehiscence-related genes INDEHISCENT (IND)/HECATE 3 (HEC3), REPLUMLESS (RPL) and SPATULA (SPT)/ALCATRAZ (ALC) in E. pusilla , and found that the key players of the eudicot fruit regulatory network appear well-conserved in monocots. Protein-protein interaction studies revealed that MADS-domain complexes comprised of FRUITFULL (FUL), SEPALLATA (SEP) and AGAMOUS (AG) /SHATTERPROOF (SHP) orthologs can also be formed in E. pusilla , and that the expression of HEC3, RPL , and SPT can be associated with dehiscence zone development similar to Arabidopsis. Our expression analysis also indicates differences, however, which may underlie fruit divergence.