When scientists use a taxon name like Mammalia, it is important that they talk about the same thing. But, what does it mean to be the same thing in different phylogenetic hypotheses? And, how is taxonomic reference maintained across hypotheses? Here, we discuss the differences between real and hypothetical clades, and how such a distinction relates to the sameness problem. Since hypotheses influence how we perceive things and pursue science, we find it important to have a functioning nomenclatural system for clades as perceived in phylogenetic hypotheses. As a solution to the sameness problem for such clades, we argue that a taxon name does not primarily refer to a single clade that somehow mirror the reality of branches in the tree of life. Instead we suggest that a taxon name refers to a set, or natural kind, of counterfactual and reconstructed clades.
A study of a number of reproductive traits in two sympatric species of Pedicularis in northern Swedish Lapland, the subarctic-alpine P lapponica and the artic P hursuta, revealed that the life-history strategies of the two species differ profoundly High fruit set and low seed abortion rate, as m P hursuta, is common in arctic plants in late-thawing habitats and represents a case of extreme adversity selection rather than an indication of a ruderal life-history strategy Pedicularis lapponica, on the other hand, is a typical K-strategist (or stress-tolerator) requiring a longer period of growth for optimal reproduction Occuring at both low and high altitudes in the area, P lapponica tends to increase in self-compatibility with altitude, which is interpreted as an adaptation to lower pollinator visitation frequency in arctic environments The variation in length of the protruding part of the style in P lapponica is shown to be correlated with exposure to light Predispersal seed predation is severe m P lapponica at low altitudes, where the capsules are attacked by fly and moth larvae At high altitudes, a minor proportion of the capsules of P lapponica experience predation and only from flies, while P hursuta is completely unpredated
In this paper, we revisit the phylogeny of the eureptantic nemerteans. Three species (Kameginemertes parmiornatus, Drepanophoriella histriana, and Polyschista curacaoensis), not present in the original analyses by Härlin & Sundberg (1995), are included, and in the light of the new results we discuss the phylogenetic taxonomy as well as biogeography of the Eureptantia. The biogeography is assessed by dispersal-vicariance analysis (Ronquist 1997), and the new phylogenetic taxonomy is based on developments (Härlin 1998b, 1999b; Härlin & Sundberg 1998) of nomenclatural ideas originally presented by de Queiroz & Gauthier (1990, 1992).
Aposematism is one of the oldest phenomena in evolutionary biology and still a major puzzle to biologists. Despite its evolutionary nature, most attempts to understand aposematism are devoid of phylogenetic components. In addition, most studies that do take phylogeny into account need to bring the analysis even further. We argue that in order to fully understand aposematism we must have a clear picture of the evolutionary history behind present behaviours. In this paper we frame aposematism in a phylogenetic context and argue that most studies still are wanting in terms of demonstrating aposematism. Aposematism is not an end product but rather evolutionary scenarios including character transformations as well as prey-predator interactions. Finally, we suggest that, regardless how we restrict the concept of aposematism, knowing the directions of events facilitate all kinds of comparisons with a promise of uniting functional and evolutionary aspects into a historization of aposematism.
När Kristofer Helgen under ett besök på Field museum i Chicago drog ut en låda med vad han trodde var en samling kända tvättbjörnsarter blev han rejält överraskad.
– Jag tittade på pälsen, skallen, tänderna, hörselbenen. Inget i anatomin liknade något jag sett tidigare, säger Kristofer Helgen, som är zoolog vid Smithsonian museum i USA.
Det starkt rödfärgade skinnen han såg ledde till beskrivningen av en ny köttätande däggdjursart.
The origin and evolution of the eureptantic nemerteans is discussed from a biogeographic point of view. It is most likely that East Indian Ocean was part of the ancestral distribution of the Eureptantia. The area cladogram estimated by Brooks parsimony analysis (BPA) is to a high degree congruent with a vicariance explanation of the evolution of the Eureptantia and suggests an ancestral distribution concordant with the Tethys Sea. A general area cladogram based on a combined BPA analysis of eureptantic nemerteans and acanthuroid fishes is reconstructed and suggested as a hypothesis of the relationships between east Indian Ocean, west Indian Ocean, west Pacific Ocean, east Atlantic Ocean, west Atlantic Ocean, and the Mediterranean. This tree is compared with cladograms from the same areas based on other taxa.
Recent developments in biological nomenclature suggest advantages of phylogenetic alternatives to more traditional Linnaean approaches. My aim is to discuss some fundamental aspects underlying biological nomenclature in general and phylogenetic nomenclature in particular. A basic assumption, in both traditional and phylogenetic nomenclature, is that taxon names can and should be defined. From the ontological view of individuality I question this view and argue that taxon names only refer since no defining properties are involved for particular clades. Even if we accept the idea that a taxon is a natural kind with a historical essence, and thus has defining properties, I see problems of definitions from an epistemological and inferential point of view. Our conceptualization of phylogeny is dependent on our hypotheses. Therefore, definitions based on discarded hypotheses are problematic. Instead, each new and accepted hypothesis should form the basis of our conceptualization. Another theme in this paper is what should count as the same taxon under different hypotheses. Can a phylogenetic definition guarantee that a name always refers to the same taxon under different hypotheses? I argue that this is questionable. I conclude by suggesting that we need to rethink the role of definition, sameness, and stability in nomenclature. Rethinking these concepts, I believe, will shed some new light on biological nomenclature. My conclusions strongly favor a phylogenetic approach to nomenclature but also suggest that we, besides some practical problems, still have many interesting theoretical and philosophical aspects to take into account.
Forskare och forskning bedöms hela tiden. Det kan handla om huruvida en artikel ska bli publicerad i en viss tidskrift eller om en forskare ska tilldelas anslag eller inte. Ofta är det forskare som bedömer kollegor, så kallad peer-review. Forskning som nyligen publicerades i den nätbaserade vetenskapliga tidskriften PLOS Biology visar, dessvärre, att forskare är ganska dåliga på att bedöma vad som är betydelsefull forskning.
In this paper I draw attention to the concepts of content and ancestry in phylogenetic nomenclature. I argue that these concepts are tightly linked and that they cannot be separated as suggested by Bryant and Cantino [Biol. Rev. 77 (2002) 39] in their recent response to a critique of phylogenetic nomenclature. In addition, I argue that the basic assumption in phylogenetic nomenclature that a taxon-name always refers to the same ancestor or ancestry is questionable.
Phylogenetic approaches to biological nomenclature are becoming increasingly common. Here I compare the behaviour of two such approaches, the phylogenetic system of definition and the phylogenetic system of reference, when there is a shift in the preference of phylogenetic hypotheses. The comparison is based on a case study from nemertean systematics and is the first to compare two different phylogenetic approaches throughout three stages of change, including two stages of phylogenetic nomenclature. It is concluded that a phylogenetic system of reference in combination with uninomials is superior in conveying phylogenetic information.
Om relationen mellan biologin idag och Linnés klassificeringssystem
In the present paper I argue that the two systems of phylogenetic nomenclature hitherto proposed represent, in a generalized sense, two different philosophies for how science develops and progresses. The phylogenetic system of definition. initially proposed by de Queiroz and Gauthier [Syst. Zool. 39 (1990) 307], and later labeled PSD, is typically Popperian in the 'sense that science progresses toward truth by An accumulation of knowledge. Phylogenetic definitions of taxon names are assumed to adapt automatically to each new hypothesis of phylogeny, thereby reflecting better and better hypotheses. The phylogenetic system of reference proposed by Harlin [Zool. Scr. 27 (1998a) 381], on the other hand, is more Kuhnian, because it is built on the idea that successive hypotheses are incommensurable (and thus not cumulative) and that taxon names might be equalled with low-level paradigms.
This paper addresses the issue of philosophy of names within the context of biological taxonomy, more specifically how names refer. By contrasting two philosophies of names, one that is based on the idea that names can be defined and one that they cannot be defined, I point out some advantages of the latter within phylogenetic systematics. Due to the changing nature of phylogenetic hypotheses, the former approach tends to rob taxonomy from its unique communicative value since a name that is defined refers to whatever fits the definition. This is particularly troublesome should the hypothesis of phylogenetic relationship change. I argue that, should we decide to accept a new phylogenetic hypothesis, it is also likely that our view of what to name may change. A system where names only refer acknowledge this, and accordingly leaves it open whether to keep a name (and accept the way it refers in the new hypothesis) or discard a name and introduce new names for the parts of the tree that we find scientifically interesting. One of the main differences between a phylogenetic system of definition (PSD) and a phylogenetic system of reference (PSR) is that the former is governed by laws of language while the latter by communicative needs of taxonomists. Thus, a PSR tends to give primacy to phylogenetic trees rather than phylogenetic definitions of names should our views of which phylogenetic hypothesis to accept change.
The aim of the present paper is to explore the role of the character in phylogenetic systematics. I argue that too much emphasis is put on particular characters rather than congruence both in the choice of phylogenetic hypotheses and in taxonomic decisions. This means that the logical priority of the tree over the characters is neglected. To a large extent, this is a result of not paying enough attention to the individuality thesis which states that clades are historical individuals and hence contingent in nature.
I review how some influential nemertean systematistshave perceived and illustrated phylogenetic trees andargue that the nineteenth century nemerteantaxonomists still influence many contemporarynemertean taxonomists to a high degree. By showing hownineteenth century systematics differs from moremodern views on trees, I hope to convey the advantagesof a cladistic approach to tree-thinking and nemerteansystematics. Furthermore I propose a systematizationof the Eureptantia that illustrates the cladisticapproach to tree-thinking but, more importantly, isalso a better representation of eureptantic phylogenythan previous classifications.
Although naming biological clades is a major activity in taxonomy, little attention has been paid to what these names actually refer to. In philosophy, definite descriptions have long been considered equivalent to the meaning of names and biological taxonomy is a scientific application of these ideas. One problem with definite descriptions as the meanings of names is that the name will refer to whatever fits the description rather than the intended individual (clade). Recent proposals for explicit phylogenetic definitions of clade names suffer from similar problems and we argue that clade names cannot be defined since they lack intension. Furthermore we stress the importance of "tree-thinking" for phylogenetic reference to work properly.
A phylogeny for the 34 species we consider well enough described in the suborder Eureptantia (phylum Nemertea) is inferred by cladistic analysis based on 38 morphological characters. The phylogenetic reconstruction indicates that many previously recognised genera and families are paraphyletic. These findings are discussed and compared with earlier classifications. We also present an identification key to the species based on the cladistic analysis.
We question recent claims that cladistic analysis is inapplicable in nemerteans (phylum Nemertea) due to a supposedly high degree of convergence. We further argue that terms like convergence and parallelism are historical sayings and only make sense in a phylogenetic context. Therefore, an approach aiming to produce phylogenetic hypotheses cannot be rejected on the grounds of a high degree of convergence before the actual hypothesis. Convergence is not an empirical observation, but a conclusion made after an analysis. We also discuss the view that knowledge of a character's function is a prerequisite for phylogenetic analysis and conclude that this is an invalid approach. Function, like any other way of sharpening our observations, helps in formulating non-phylogenetic hypotheses of homology, but the crucial test is congruence with other characters on a phylogeny.
Nemerteans (phylum Nemertea) have been viewed by mostzoologists as descended from, or closely related to,the flatworms. This view is based mainly on theirsupposedly acoelomate body. Their ancestry, however,is a point of controversy and there is evidence for acoelomate, protostomous origin. Notwithstanding thesedifferent views, most zoologists consider nemerteansto be phylogenetically distant from the chordates.Four authors (Hubrecht, Macfarlane, Jensen, Willmer),however, have postulated that nemerteans instead areclosely related to the chordates and that they sharea most recent common ancestor with the vertebrates. We argue that this view is based on a flawed view ofhomology and of seeing evolution as a series ofprogressions, which has no support in modernevolutionary thinking. Since there are nomorphological synapomorphies supporting aChordata-Nemertea clade, these authors instead guesswhat characteristics in extant nemerteans gave rise tocharacters observed in recent chordates. For example,they propose that the nemertean proboscis sheath hasevolved into the notochord. This is mere speculation,lacking testable propositions and is hence void ofinformation, and thus becomes futile in our view. However, the idea of a nemertean-vertebrate sisterrelationship as such is a testable hypotheses, and wetest it by applying the parsimony criterion to a setof morphological characters, and a set of molecular(the 18S rRNA gene) characters. Both tests reject thehypothesis.
Previous studies on the palaeonemertean Tubulanus annulatus have hinted on possible geographic variation, or even a species complex. This study describes the variation in morphology, focusing on the characters that have been supposed to vary geographically. Specimens from the Swedish west coast (Tjärnö and Kristineberg), Scottish west coast (Millport), and the Mediterranean (Naples and Split) were included in the study. It is concluded that the pattern of variation in the studied characters do not correspond to geography and most of the character states previously thought to vary geographically are in fact found within one and the same population.