Molecular markers and the species concept: New techniques to resolve old disputes?

Abstract

Key words: fish, molecular marker, speciation, species conceptIntroductionAlthough all biologists recognize the value of parti-tioning biodiversity into recognizable units organizedintodifferenthierarchicallevels, therehasbeena long-standing, and at times unhelpful, controversy on thenature and significance of the species as the basic unitof biodiversity. Despite the exhaustive considerationof various species concepts over many decades, thereappears to be no abatement to the outpouringof strongsentiments, as evidenced by the articles herein. Suchforceful and dedicated considerations are perhaps notsurprising in light of the fundamental role that speciesplay in the biological world, though have they reallyhelped our understandingof biodiversity? Here, in thisbrief personalized viewpoint, we do not present yetmore critiques of species concepts or their variants,but rather make some comments on the underlyingforcesgeneratingsuch focus, and considerwhethertheapplication of molecular genetic markers is an aid or ahindrance.Species as biological entitiesThe extensive (and often repetitive) literature onthe species concept reveals several features of thecontinuing dispute on the species concept: (1) mostauthors believe that the species is the only biologi-cally meaningful taxonomic unit, and that it is adefinable entity; (2) most authors vigorously defendtheir favourite (or their own) definition of that unit,and discard others as completely wrong; and (3)almost 250 years of Linnaeus’ binomial classificationof species were apparently insufficient to define thespecies to a level acceptable to most scientists. Theseobservations may give rise to the suspicion that thecourse of the species concept dispute is a result of‘typological’ thinking, as expressed in the typolog-ical species concept, and itself a result of Platonicphilosophy stating that there is an ideal ‘universal’with material manifestations(see Turner,this volume).While the typological species concept is now gener-ally disregarded, the search for an definable, ideal‘universal’ of a species, despite ubiquitous imperfectmanifestations of that ideal in the natural world, maybe a legacy of typological thinking in biology. This isnot to say that we do not need the species as a taxo-nomic unit, but rather that the biological reality of aspecies may not always be amenable to rigid defini-tion. It may be more helpful for the understanding ofbiodiversity and our research efforts to recognize theimperfections of each species concept and to acceptexceptions as a fact of life rather than a conceptualnuisance.Clearly, the species is crucial to the classifica-tion of biodiversity, and abandoning it would meanto throw our current description of biodiversity intodisarray. Nevertheless, the belief that the unit ofbiodiversity as defined by taxonomists is in all casesa real biological entity may be questionable, and thusthe search for a universal definition of that entity maybe futile. Indeed, an uncritical adherence to a givenspecies conceptmay be counter-productiveby fuellingadditional confusion and unnecessary dispute, and byaffecting the way many empirical studies are carriedout. For example, typological conceptions seem toinfluence many phylogenetic publications on closely