Document downloaded from: http://hdl.handle.net/10251/64812 This paper must be cited as: Català, S.; Campo, ED.; Barreno, E.; García-Breijo, F.; Reig Armiñana, J.; Casano, L. (2016). Coordinated ultrastructural and phylogenomic analyses shed light on the hidden phycobiont diversity of Trebouxia microalgae in Ramalina fraxinea. Molecular Phylogenetics and Evolution. 94:765-777. doi:10.1016/j.ympev.2015.10.021. The final publication is available at https://dx.doi.org/10.1016/j.ympev.2015.10.021 Copyright Elsevier Additional Information Coordinated ultrastructural and phylogenomic analyses shed light on the hidden phycobiont diversity of Trebouxia microalgae in Ramalina fraxinea q ⇑ Santiago Catalá a,d, Eva M. del Campo b, , Eva Barreno a, Francisco J. García-Breijo c, José Reig-Armiñana a, Leonardo M. Casano b a Dpto. Botánica, Jardí Botànic, ICBIBE, Fac. C. Biológicas, C/ Dr. Moliner 50, 46100 Burjassot, Valencia, Spain b Dpto. Ciencias de la Vida, Universidad de Alcalá, 28805 Alcalá de Henares, Madrid, Spain c Dpto. Ecosistemas Agroforestales, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain d Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain1 abstract The precise boundary delineations between taxa in symbiotic associations are very important for evolu- tionary and ecophysiological studies. Growing evidence indicates that in many cases, the use of either morphological characters or molecular markers results in diversity underestimation. In lichen symbioses, Trebouxia is the most common genus of lichen phycobionts, however, the diversity within this genus has been poorly studied and as such there is no clear species concept. This study constitutes a multifaceted approach incorporating aspects of ultrastructural characterization by TEM and phylogenomics to evalu- Keywords: ate the morphological and genetic diversity of phycobionts within the sexually reproducing lichen Coexistence Ramalina fraxinea in the context of Mediterranean and temperate populations. Results reveal an associa- Cryptic species Lichen tion with at least seven different Trebouxia lineages belonging to at least two species, T. decolorans and T. Ramalina jamesii, and diverse combinations of such lineages coexisting within the same thallus depending on the Symbiosis analyzed sample. Some of these lineages are shared by several other non-related lichen taxa. Our findings Trebouxia indicate the existence of a highly diverse assemblage of Trebouxia algae associating with R. fraxinea and suggest a possible incipient speciation within T. decolorans rendering a number of lineages or even actual species. This study stresses the importance of coordinated ultrastructural and molecular analyses to improve estimates of diversity and reveal the coexistence of more than one Trebouxia species within the same thallus. It is also necessary to have clearer species delimitation criteria within the genus Trebouxia and microalgae in general. Ó 1. Introduction (Chapman and Margulis, 1998). Such associations involve at least two very different organisms, a heterotrophic fungus (mycobiont) The term ‘‘symbiosis’’ was originally coined by de Bary in 1879 and a photobiont [cyanobacteria (cyanobiont) or unicellular green in his monograph ‘‘Die Erscheinung der Symbiose”, which described algae (phycobiont)]. The spatial genetic structure of lichen sym- close and long-term physical associations between different organ- bionts is influenced by both ecological and evolutionary factors. isms. Symbioses include different levels of mutualism encompass- These factors include the mode of photobiont transmission, ing interactions ranging from those in which both the host and geographical distance and adaptation to local environmental condi- the symbiont benefit from the interaction, to antagonistic interac- tions. Phycobionts can be transmitted either vertically (codepen- tions where the symbiont benefits, and the host suffers damage dency) or horizontally (independency). Vertical transmission (Wilkinson, 2001). Lichens are classic symbiotic associations result- involves phycobiont dispersal as part of the vegetative propagule ing in complex systems with a specific biological organization and is believed to be the predominant process in exclusively, or almost exclusively, asexual lichen species (Cassie and Piercey- Normore, 2008). Alternatively, horizontal transmission involves the incorporation of new phycobionts within a germinating spore E-mail address: [email protected] (E.M. del Campo). or vegetative structure (Werth and Sork, 2010). Concordant 1 Actual address. patterns in the genetic structure of symbionts are expected in 2 vertically transmitted symbioses. However, such patterns are rarely morphological and molecular analyses. TEM observations and observed in lichen symbioses [e.g. Lobaria pulmonaria (Werth and molecular tools were used to investigate nine populations obtained Scheidegger, 2012)]. Conversely, markedly different genetic from different locations within the Iberian Peninsula, characterized structures of photobionts and mycobionts are more often observed, by diverse environmental conditions within the context of even in vertically transmitted lichen species (Leavitt et al., 2015; Mediterranean and temperate climates. These studies provided Otálora et al., 2010; Piercey-Normore, 2006; Werth and Sork, evidence that there are at least seven different lineages of the 2010; Wornik and Grube, 2010; Yahr et al., 2006). Changes in a genus Trebouxia in the analyzed populations. Six of them are sim- symbiotic organism’s reproductive mode may be governed by ilar to T. decolorans s.a., while the other one seems to be T. jamesii. trade-offs in the fitness of the symbiosis, as proposed by These lineages differ in their morphologies and genotypes and Buschbom and Mueller (2006). In lichen species with both asexual coexisted in different number and combinations within the studied and sexual modes of propagation, the asexual propagation system thalli. Five of the seven Trebouxia lineages identified in Ramalina preponderates when the relationships between symbionts is opti- fraxinea were previously detected in other non related lichens, mal in a given environment [e.g. Lobaria pulmonaria (Dal Grande while two lineages seem to symbiotize only with Ramalina et al., 2012)]. Conversely, when the established symbiosis becomes fraxinea. suboptimal, decreasing global fitness due to changes in the environ- ment, sexual reproduction may be preferred, providing access to 2. Materials and methods new partners. Under the assumption of high flexibility in the speci- ficity and ecological selection of the phycobionts, the ability to 2.1. Taxon sampling establish new fungus-phycobiont associations has enabled lichens to colonize varied and wide-ranging habitats (Doering and For this study, all the analyzed Ramalina fraxinea thalli were col- Piercey-Normore, 2009). Several studies have demonstrated that lected from nine populations within the Iberian Peninsula (Table 1) lichen mycobionts associate with different phycobionts under dif- in four geographic areas (A–C in Figs. 3 and 5). The areas are char- ferent environmental conditions, or in different geographical acterized by different ecological conditions and thalli were col- regions (Blaha et al., 2006; Casano et al., 2011; Cordeiro et al., lected on different phorophytes (Table 1). Sampling areas were 2005; del Campo et al., 2013; Muggia et al., 2008, 2010; Peksa located in natural habitats, or abandoned farmlands, at different and Škaloud, 2011; Schmull et al., 2011; Fedrowitz et al., 2012; altitudes. All of the studied materials were deposited in the Lichen Rikkinen, 2013). Symbiogenesis Laboratory of the Department of Botany, Universi- In lichens, most interactions between the photobionts and the tat de València (Valencia, Spain), and stored at a temperature of outside world are mediated by the mycobiont mitigating many À20 °C. adverse environmental conditions. As environmental changes rarely affect all lichens within a local community in the same way and with the same intensity, a wide range of compatible 2.2. Morphological analysis of ‘in thallus’ lichen phycobionts mycobionts can increase photobiont resistance against many detri- mental factors (Rikkinen, 2003). Reciprocally, a wide spectrum of Phycobionts inside thallus were examined in pieces of rehy- compatible photobionts can increase mycobiont stress tolerance. drated R. fraxinea thalli from different areas (Table 1) by light In some cases the coexistence of phycobionts with complementary physiological performances within the same thallus can increase Table 1 resistance against adverse environmental conditions (Casano Areas in which samples of Ramalina fraxinea were collected. et al., 2011). Additionally, lichen behavior seems to be modulated Site Area/geographic coordinates/ Phorophyte Specimens by the predominant phycobiont (Álvarez et al., 2015). Since the altitude/collection data success of the lichen seems to depend to some extent on photo- A Tarna (Caso, Asturias)/43°06051.8900N Quercus AA1-6 bionts, knowledge about the photobiont composition of lichens 0 00 5°13 19.14 W/1219 m/(leg. S. Català, A. faginea will enhance our understanding of how some lichens can evolve Avellanosa, R. Barbero and H. de Dios, 22- tolerance to certain environmental stresses. In addition, observa- 05-2010) tions in Ramalina farinacea support a model where ecological A Saliencia (Somiedo, Asturias)/ Quercus AB1-6 ° 0 00 °