Summary � Hybridization is an important evolutionary force in plants, but the mechanisms underlying it have not been well studied for many groups. In particular, the drivers of non-random patterns of interspecific gene flow (asymmetrical hybridization) remain poorly understood, especially in the seed-free vascular plants. Here, we examine patterns of asymmetrical hybridization in two widespread fern hybrids from eastern North America and study the role of gametophyte ecology in the determination of hybridization bias. � We characterized the maternal parentage of > 140 hybrid sporophytes by sequencing a c. 350-bp region of chloroplast DNA (cpDNA). To identify factors contributing to patterns of asymmetrical hybridization, we cultured gametophytes of the parental species and evaluated critical aspects of their reproductive biology. � We found that asymmetrical hybridization was prevalent across the populations of both hybrids. Reproductive traits varied across species and suggest that selfing potential, antheridiogen responsiveness, sperm dispersal capacity and gamete size all contribute to the mediation of the direction of hybridization in this group. � Our findings suggest that asymmetrical hybridization in ferns is driven by an array of reproductive traits. This study helps to sharpen and define a mechanistic understanding of patterns of hybridization in this group and demonstrates the importance of considering gametophyte biology when studying evolutionary processes in ferns.

/pdf/dynamics-of-asymmetrical-hybridization-in-north-american-4jjoodnyc1.pdf

Dynamics of asymmetrical hybridization in North American wood ferns: reconciling patterns of inheritance with gametophyte reproductive biology

Autecology of pteridophytes may be refined by defining the plant community and habitat, and phytogeographic occurrence, of the species studied. Work with Blechnum spicant in the Pacific Northwest, and with Lorinserea areolata in the Southeastern U.S.A. has uncovered autecological differences for these species across habitats differing in overstory and hydrology. Natural history observations are necessary to suggest the most appropriate hypotheses to investigate objectively. A modification of Daubenmire's Canopy-Coverage method provides a grid across which many factors may be recorded or tested in repeatable objective manner. Such an analysis was used to test the association between L. areolata life-history classes and hummocks in hardwood swamps. Contingency tables were used to disprove the null hypothesis that L. areolata was distributed randomly with regard to hummocks. Hummocks were thus ‘safe sites’ for the completion of the life-cycle of L. areolata , and additional considerations of safe sites for Lygodium japonicum and Dryopteris ludoviciana are introduced. Analysis of biomass and coverage of Onoclea sensibilis where it is very abundant suggests that it is highly susceptible to competition where it shares plots with L. areolata. The concept of the optimum habitat with regard to abundance of the taxon, frequency of the habitat-type, successful reproduction, and susceptibility to competition between similar life forms is discussed.

Life-history studies of ferns: a consideration of perspective

Summary


1. This account presents information on all aspects of the biology of Dryopteris carthusiana (Vill.) H. P. Fuchs, D. dilatata (Hoffm.) A. Gray, and D. expansa (C. Presl) Fraser-Jenk. & Jermy that are relevant to an understanding of their ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, reproductive characteristics, herbivores, history, and conservation.



2. All three species are native deciduous ferns that are morphologically similar and genetically interrelated. Dryopteris dilatata, one of the commonest ferns in the British Isles, is found in many different habitats, but is above all a woodland species. Dryopteris carthusiana is less widely distributed, being mostly a species of wetlands and wet woodlands. Dryopteris expansa is the least common, mostly found in mountains, but also in wet woodlands at lower altitudes.



3. Dryopteris dilatata is mainly a species of semi-shade, and in the British Isles is considered to be the most shade-tolerant of the three. Dryopteris carthusiana occurs in a wide range of habitats, from exposed, well-illuminated to moderately shaded ones. Dryopteris expansa mainly grows in better illuminated habitats, often in the shade of sparse canopies or rocks. D. expansa is thus the most light-demanding species of the three.



4. The response to competition from neighbouring herbs has been shown to differ among the three species; D. expansa is clearly more vulnerable to competition than D. carthusiana and D. dilatata.



5. Dryopteris dilatata and D. carthusiana are both tetraploid, whereas D. expansa is diploid. Natural hybrids among all three species in the British Isles, as well as hybrids of D. carthusiana with D. filix-mas and D. cristata. The hybrid D. carthusiana × D. dilatata = D. × deweveri is the most common. The hybrids D. carthusiana × D. expansa = D. × sarvelae and D. cristata ×D. carthusiana = D. × uliginosa are extremely rare and at high risk of extinction.



6. Although not currently threatened, the distribution of all three species may be susceptible to continued habitat loss arising from changes in land use, management for control of Bracken and predicted climate change.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2745.2012.01985.x

Biological Flora of the British Isles: Dryopteris carthusiana, D. dilatata and D. expansa

Reproductive and Competitive Interactions Among Gametophytes of the Allotetraploid Fern Dryopteris corleyi and its Two Diploid Parents

Se describe y se compara la morfogenesis de la fase sexual de seis especies mexicanas de Dryopteris . Las esporas de todas las especies estudiadas son monoletes y elipsoidales, la perina es plegada, de color pardo claro a pardo obscuro, su superficie es rugosa y de contornos tuberculados. El patron de germinacion es tipo Vittaria y el desarrollo protalico es tipo Aspidium. Los gametangios son del tipo caracteristicos de los helechos leptosporangiados. Se desarrollaron esporofitos en cinco de las seis especies y solamente en D. pseudo-filix- mas es de origen apogamico (80 dias). Se hace un analisis comparativo de las caracteristicas gametofiticas presentes en las 12 especies mexicanas del genero y se concluye que el tipo de germinacion Vittaria y el patron de desarrollo protalico tipo Aspidium y gametofitos con tricomas unicelulares, capitados marginales y superficiales, de aspecto irregular, son caracteristicas que le dan unidad y caracterizan a los generos que conforman la familia Dryopteridaceae (Moran, 1995) a excepcion del genero Didymochlaena .

https://revista-ciencia-tecnologia.ucr.ac.cr/index.php/rbt/article/download/16927/16384

Morfogénesis de la fase sexual de seis especies mexicanas del género Dryopteris (Dryopteridaceae), Parte II

The study of sexuality in fern gametophytes has stimulated research in the genetic consequences of gametophyte sex expression (Klekowski, 1971) and in the physiology of sex determination in ferns (Dopp, 1950; Voeller, 1971). A class of antheridia-inducing hormones, antheridogens, has been discovered in several genera of ferns including Dryopteris (Dopp, 1950; Voeller, 1964). Homosporous ferns differ fundamentally from heterosporous plants in their potential for intragametophytic selfing, which eliminates heterozygosity by the union of genetically identical egg and sperm derived mitotically from a single gametophyte (Klekowski & Lloyd, 1968). Homeologous pairing in polyploids is a possible mechanism for expression of heterozygosity following intragametophytic selfing (Klekowski & Hickok, 1974). Intragametophytic selfing and intergametophytic crossing are genetically equivalent to self pollination and cross pollination in heterosporous plants. The occurence of bisexual, male, and female gametophytes in multispore cultures of Dryopteris ludoviciana suggested that gametophytes of this genus are not regularly bisexual (Cousens & Horner, 1970). This paper extends the observation of gametophyte sex expression to seven additional species of Dryopteris. Various patterns of sex expression may be adaptive in allowing different balances of intraand intergametophytic mating in different environments (Klekowski, 1972). Dryopteris is a large genus of ferns notable for frequent hybridization between species (Wagner, 1970). Three tetraploid species studied, D. campyloptera, D. spinulosa, and D. celsa, probably arose by chromosome doubling of sterile hybrids; their ancestral taxa are either known or hypothesized (Wagner, 1970; Walker, 1961, 1962). Dryopteris clintoniana is a hexaploid hybrid of D. goldiana and D. cristata (Wagner, 1970). Dryopteris intermedia, D. goldiana, D. marginalis, and D. ludoviciana are all sexual diploids. Cultures of Dryopteris gametophytes were initiated by inserting a sterile wooden applicator into 25 ml spore vials and transferring 400-600 adherent spores to a 5 ml beaker which was then filled with sterilized water to which a trace of detergent had been added. Each species studied was represented by spore samples from two or more sporophytes. After the spores were dispersed in the liquid, the suspension was divided among three sterile 60 mm petri dishes filled with sterile clay-loam soil. Only cultures which resulted in a gametophyte population density of 1-3 gametophytes per cm2 were used because previous work has shown that culture density modifies sex expression (Cousens & Horner, 1970; Rashid,

Gametophyte Sex Expression in Some Species of Dryopteris

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Gametophyte Sex Expression in Some Species of Dryopteris