Biodiversity Journal , 2015, 6 (1): 123–138 MONOGRAPH Taxonomy faces speciation: the origin of species or the fading out of the species? Alessandro Minelli Department of Biology, University of Padova, Via Ugo Bassi 58 B, I 35131 Padova, Italy; email: [email protected] ABSTRACT Efficient field sampling and new investigation tools, including barcoding and other molecular techniques, are bringing to light an unexpected wealth of new species, including sets of morphologically quite uniform, but genetically distinct cryptic species. On the other hand, increasing appreciation of the dynamic nature of the species and a better knowledge of speciation processes and introgression phenomena challenges the taxonomists’ efforts to shoehorn all diversity of life into a formal classification of which the species would be the basic unit. Unfortunately, there is probably not a single best notion of species, either in theory or in practice. KEY WORDS barcoding; cryptic species; hybridization; speciation; species concepts. Received 25.01.2015; accepted 26.02.2015; printed 30.03.2015 Proceedings of the 2nd International Congress “Speciation and Taxonomy”, May 16th-18th 2014, Cefalù-Castelbuono (Italy) THE SPECIES - A SOLID PILLAR OF views, species have been created at the beginnings OUR REPRESENTATION OF LIVING of time and the naturalist’s job is to piously explore NATURE? Nature with the aim of completing their inventory. What does survive to our time, of this reassuring A substantial percentage of recent books and art- pre-Darwinian conception of biological diversity? icles in zoology, botany, palaeontology, biogeo- Little, if anything, in theory, but quite a lot in practice. graphy and ecology may suggest that the species has This is true both of the approach with which taxonom- damaged through the Darwinian revolu- passed un ists continue Linnaeus’ project for a global inventory tion. Although everybody, or so, in these disciplines of biodiversity and of the perspective from which is likely ready to accept that species are products of most of their colleagues in biology, ecology, biogeo- evolution, in practice a great many professionals graphy and stratigraphy look at the extant or extinct describe and analyze the living world of the past and forms of life that are the object of their studies. present time in terms not that different from those To be sure, there are also the ‘professionals of of Linnaeus and the other pre-Darwinian authors. the species problem,’ that is, biologists - but also In the title-page of his magnum opus, Linnaeus philosophers of biology - who take very seriously (1758) announced an arrangement of his Systema the Darwinian challenge and specifically focus on naturae per regna tria naturæ, secundum classes, all those contexts where the boundaries between ordines, genera, species. Firmly placed at the species are less precise or less complete, and often bottom of the hierarchy, the species category was largely arbitrary. thus proposed as the fundamental unit of classifica- The species problem has, in fact, two main tion. In the author’s creationist and largely fixist aspects. One is conceptual, the other is practical. The 124 ALESSANDRO MINELLI conceptual aspect of the species problem is how the species we know at present and, still worse, how species can, or should be defined, provided that this many species still await description. Estimates of question can be eventually answered to the general ‘valid’ described species range between 1.5 million satisfaction of biologists and philosophers alike. The and 2 millions; a document issued in 2011 by the practical aspect is, how species are recognized by International Institute for Species Exploration gave taxonomists working on the different groups of a figure of 1,922,710 species as described through- organisms and, most important, whether taxonom- out 2009. ists can all agree on a single species concept, to be Something, however, must be wrong with many adopted as the universal currency in describing the of these estimates. In the last few decades, the diversity of life. A comparison of taxonomic practice number of new species described each year has as performed by leading specialists in a diversity of been in the order of 17500 (International Institute taxa, from mammals to fungi, from bacteria to for Species Exploration, 2012). This means that flowering plants, has abundantly demonstrated that since 1985 about half a million new entries have the entities called species in a group have little in been added to the list of described species. The net common with the entities called species in another increase has been sensibly smaller, because of the group (Claridge et al., 1997). Unfortunately, this number of nominal species that in the same time heterogeneity is concealed under the (nearly) interval have been recognized to be just synonyms universal use of Linnaean binomens. It is thus all too of other species. However, the net increase has been easy to take taxonomic species as a set of broadly probably in the order of 350 000-400 000, whereas comparable units, of which we can make statistics the most recent estimates of the number of de- scribed species are not correspondingly larger than for the most different purposes, e.g. biodiversity the estimates produced 30 years ago. assessments and comparisons of extant or extinct In the last two decades of the XX century a faunas and floras. This practice should be best number of papers offered estimates of the number avoided (Minelli, 2000) but we do not have a real of living species that still await description, one of substitute for it; the global biodiversity estimates the first and most often cited being May (1988). offered below are not exempt from this ‘original sin.’ Some estimates were based on the percentage of In this article I will focus on this practical aspect undescribed species in small but dense samplings to the species problem, mostly taking examples from in areas and habitats with high diversity, e.g. papers published in 2014: with this temporal restric - Hodgkinson & Casson (1991) for tropical insects tion I only wish to stress the lively interest surround- and Grassle & Maciolek (1992) for deep-sea ing these questions. The relevant literature is animals. Other estimates included ecological enormous, and rapidly increasing with the increas- considerations, such as the degree of hostplant spe - ing availability of morphological and especially cialization of phytophagous insects, as in Erwin’s molecular methods, and their massive application to (1982) pioneering paper or Stork’s (1988) revisita - the most diverse kinds of organisms. Enormous is tion of the same. One of the most recent papers on also the literature about the conceptual aspects of the the subject adjusts the estimates to ∼8.7 million (±1.3 species problem, but I will only mention here two million SE) eukaryotic species globally, of which articles (Bernardi & Minelli, 2011; Mallett, 2013) to ∼2.2 million (±0.18 million SE) are marine (Mora et which I refer the interested reader and summarize in al., 2011); anothe r, more sensible one (Scheffers et Table 1 the most important among the more than 20 al., 2012) acknowledges the plurality of unknown or different species concepts proposed to date. poorly known factors, as a consequence of which uncertainty remains bet ween a global total as low as 2 million species, microbes excluded, and estimates HOW MANY SPECIES? as high as 50 millions and over. Even if we temporarily ignore the problems caused by the lack of a satisfactory species concept PROLIFERATION OF NEW SPECIES applicable to every kind of living things and thus simply frame the question in terms of taxonomic Strong catalysts favouring the description of (named) species, it is difficult to say how many new species are the new megajournals specifically Taxonomy faces speciation: the origin of species or the fading out of the species? 125 devoted to taxonomy. In zoology, the leading role described by Riedel et al. (2013). Another 98 new of Zootaxa and ZooKeys is by now unrivalled and species of Trigonopterus have been described in a undisputed. According to the journal’s editor- paper (Riedel et al., 2014) devoted to materials in-chief, in 2010 Zootaxa contributed about 20% of recently collected in Indonesia (Sumatra, Java, all animal taxa described that year as new, that is, a Bali, Palawan, Lombok, Sumbawa, Flores), a large number in the order of 4000 (Zhang, 2011). area from where only one species of Trigonopterus Launched a few years after their zoological was previously known. equivalents, Phytotaxa and PhytoKeys have been Perhaps less expected, there are also large num - also rapidly growing and by now outcompete the bers of undescribed species in the Lepidoptera, biggest journals long established in the field. especially among the so-called micros. A recent According to Zhang et al. (2014), the total number study of the gelechioid genus Ethmia in Costa Rica of new plant taxa described in 2011 was 6024 (of revealed the presence of 22 undescribed species which 575 in Taxon, 473 in Phytotaxa, 183 in in addition to 23 described in the past (Phillips- Novon, 169 in the Botanical Journal of the Linnean Rodríguez et al., 2014). Society); in 2012, the total was 6647 (of which 632 Virtually unfathomed is, in some specialists’ in Phytotaxa, 465 in Systematic Botany, 340 in view, the world of Fungi, of which the number of Phytoneuron, 301 in the Kew Bulletin, 267 in existing species is estimated between 1.5 and 5 Taxon); in 2013 the number decreased to 5116 (of million, i.e. 15 to 50 times the number of currently which 501 in Phytotaxa, 248 in PhytoKeys, 199 in described species. The wealth of undescribed fungal Biodiversity Research and Conservation, 196 in the diversity is not limited to the microscopic forms: a Botanical Journal of the Linnean Society).