Species Concepts as Applied to the Whitefly Bemisia tabaci Systematics:How Many Species Are There?

The worldwide distribution and extensive genetic diversity of the whitefly,Bemisia tabaci,has long been recognized.However,the levels of separation within B.tabaci and the nomenclature of the various genetic groups have been a subject of debate.Recent phylogenetic analyses indicate that B.tabaci is a complex composed of 28 morphologically indistinguishable species.In this article,we first review the debate and difficulties associated with B.tabaci＇s taxonomy and systematics,and argue for the need to apply the biological species concept in order to elucidate B.tabaci＇s systematics.We summarize the accumulated genetic and behavioural data on reproductive incompatibilities evident amongst phylogenetic mtCOI groups of B.tabaci.Crossing studies have been conducted with 14 of the 28 putative species covering 54 reciprocal inter-species pairs,and observations on mating behaviour have been conducted for seven species pairs.Data from both crossing trials and behavioural observations indicate a consistent pattern of reproductive isolation among the putative species.We then discuss the technical and conceptual complexities associated with crossing experiments and behavioural observations designed to reveal reproductive incompatibility.Finally,we elaborate on a strategy for further clarifying the pattern of reproductive isolation between B.tabaci groups and propose future research directions on the systematics of this complex.

Fusulinid species determination based on population variation:An example from Eopolydiexodina

To make fusulinid morphospecies more accordant with biological species, it is necessary and reasonable to constrain the conventional determination of fusulinid species with population-level morphological variation. As an example, morphospecies identification on population level was conducted on Eopolydiexodina specimens from a single bed of the Middle Permian Shazipo Formation of Xiaoxinzhai Section in western Yunnan, China. These specimens were identified with the consideration of fossil population by morphometric analysis of their characteristic morphological variates (diameter of proloculus, size and ratio of inner and outer volutions). The results reveal that the studied variates have wide but overall continuous variation and generally follow the normal distribution. The studied individuals, therefore, have consistent morphological variation with a single population and should belong to one fusulinid morphospecies. This study supports the assumption that fusulinid individuals of one genus from the same bed in one locality should constitute a single fossil population.

Species in lichen-forming fungi:balancing between conceptual and practical considerations,and between phenotype and phylogenomics

Lichens are symbiotic associations resulting from interactions among fungi(primary and secondary mycobionts),algae and/or cyanobacteria(primary and secondary photobionts),and specific elements of the bacterial microbiome associated with the lichen thallus.The question of what is a species,both concerning the lichen as a whole and its main fungal component,the primary mycobiont,has faced many challenges throughout history and has reached new dimensions with the advent of molecular phylogenetics and phylogenomics.In this paper,we briefly revise the definition of lichens and the scientific and vernacular naming conventions,concluding that the scientific,Latinized name usually associated with lichens invariably refers to the primary mycobiont,whereas the vernacular name encompasses the entire lichen.Although the same lichen mycobiont may produce different phenotypes when associating with different photobionts or growing in axenic culture,this discrete variation does not warrant the application of different scientific names,but must follow the principle"one fungus=one name".Instead,broadly agreed informal designations should be used for such discrete morphologies,such as chloromorph and cyanomorph for lichens formed by the same mycobiont but with either green algae or cyanobacteria.The taxonomic recognition of species in lichen-forming fungi is not different from other fungi and conceptual and nomenclatural approaches follow the same principles.We identify a number of current challenges and provide recommendations to address these.Species delimitation in lichen-forming fungi should not be tailored to particular species concepts but instead be derived from empirical evidence,applying one or several of the following principles in what we call the LPR approach:lineage(L)coherence vs.divergence(phylogenetic component),phenotype(P)coherence vs.divergence(morphological component),and/or reproductive(R)compatibility vs.isolation(biological component).Species hypotheses can be established based on either L or P,then using either P or L(plus R)to corroborate them.The reliability of species hypotheses depends not only on the nature and number of characters but also on the context:the closer the relationship and/or similarity between species,the higher the number of characters and/or specimens that should be analyzed to provide reliable delimitations.Alpha taxonomy should follow scientific evidence and an evolutionary framework but should also offer alternative practical solutions,as long as these are scientifically defendable.Taxa that are delimited phylogenetically but not readily identifiable in the field,or are genuinely cryptic,should not be rejected due to the inaccessibility of proper tools.Instead,they can be provisionally treated as undifferentiated complexes for purposes that do not require precise determinations.The application of infraspecific(gamma)taxonomy should be restricted to cases where there is a biological rationale,i.e.,lineages of a species complex that show limited phylogenetic divergence but no evidence of reproductive isolation.Gamma taxonomy should not be used to denote discrete phenotypical variation or ecotypes not warranting the distinction at species level.We revise the species pair concept in lichen-forming fungi,which recognizes sexually and asexually reproducing morphs with the same underlying phenotype as different species.We conclude that in most cases this concept does not hold,but the actual situation is complex and not necessarily correlated with reproductive strategy.In cases where no molecular data are available or where single or multi-marker approaches do not provide resolution,we recommend maintaining species pairs until molecular or phylogenomic data are available.This recommendation is based on the example of the species pair Usnea aurantiacoatra vs.U.antarctica,which can only be resolved with phylogenomic approaches,such as microsatellites or RADseq.Overall,we consider that species delimitation in lichen-forming fungi has advanced dramatically over the past three decades,resulting in a solid framework,but that empirical evidence is still missing for many taxa.Therefore,while phylogenomic approaches focusing on particular examples will be increasingly employed to resolve difficult species complexes,broad screening using single barcoding markers will aid in placing as many taxa as possible into a molecular matrix.We provide a practical pro-tocol how to assess and formally treat taxonomic novelties.While this paper focuses on lichen fungi,many of the aspects discussed herein apply generally to fungal taxonomy.The new combination Arthonia minor(Lücking)Lücking comb.et stat.nov.(Bas.:Arthonia cyanea f.minor Lücking)is proposed.

Delimiting species in Basidiomycota:a review

Species delimitation is one of the most fundamental processes in biology.Biodiversity undertakings,for instance,require explicit species concepts and criteria for species delimitation in order to be relevant and translatable.However,a perfect species concept does not exist for Fungi.Here,we review the species concepts commonly used in Basidiomycota,the second largest phylum of Fungi that contains some of the best known species of mushrooms,rusts,smuts,and jelly fungi.In general,best practice is to delimitate species,publish new taxa,and conduct taxonomic revisions based on as many independent lines of evidence as possible,that is,by applying a so-called unifying(or integrative)conceptual framework.However,the types of data used vary considerably from group to group.For this reason we discuss the different classes of Basidiomycota,and for each provide:(i)a general introduction with difficulties faced in species recognition,(ii)species concepts and methods for species delimitation,and(iii)community recommendations and conclusions.