Cephlapodcast has announced the Second Annual Unofficial International Cephalopod Appreciation and Awareness Day. I wonder what Adolf Naef would have said?
Naef said a lot about cephalopods and their relationships. As a respected world authority on octopuses and their relatives, Naef has produced several texts that have until now only interested David and I in parts (mostly the systematic theory and methodology). Our only foray into the fascinating world of calamari occurred recently when were contacted by Jan Strugnell - a cephalopodist from the University of Cambridge and admirer of Naef's work. Jan had an interesting question - why did Naef's phylogeny and classification of Argonautoidea differ?
The Argonautoidea Lamarck, 1809 (paper nautiluses and their relatives) are divided into two subfamilies: Tremoctopodinae and Argonautinae. The former includes Alloposidae and Tremoctopodidae and, the latter Argonautidae and Ocythoidae. Naef produced the following diagram (Figure 1a) with the following accompanying text:
"The typical relationship between the 4 genera which form the family are shown in the following graph: i.e., the genera developed by secondary specialization from forms I-IV in a direct series.These two conflicting statements (one pictorial and one as text) pose an interesting problem. What does the diagram represent and what was Naef thinking?
The ideal or hypothetical form I corresponds to the type of the family; form II corresponds to the type of the 3 genera, form II to the type of the 2 highest genera. Form IV is the ancestral form of Argonauta. The forms derived from II and III are clearly natural groups which can be defined, despite the specialization of their recent representatives. The important morphological relationships, however, call for a division into 2 subfamiles by drawing a line between II and II, i.e. a distinction between lower (I) and a higher (II) stage of variation. This is, of course, arbitrary ... and is only intended to introduce order for practical purposes by stressing the essential and omit characters of less importance. This division stresses the distance between forms II and III and creates the two natural subfamiles: Tremoctopodinae and Argonautinae (Naef 1972: 732).
Naef believed both subfamilies to be monophyletic (natural groups). What Naef did diagrammatically shows a transition from the Haeckelian tree-thinking to modern systematics.
In order to understand what Naef did we go to the introduction of his work on the Fauna and Flora of the Bay of Naples. Firstly the graph is a phylogenetic tree as we understand it today. Back in Naef's day (prior to molecular systematics) the graph was termed a 'genealogical' tree. Phylogenetic trees were considered to be true depictions of ancestor-descendant relationships, an idea rarely entertained today. In Naef's phylogenetic tree, we see that forms are placed at the nodes. Naef's forms are types, namely "an abstract but naturally possible form from which a multitude of actually existing forms may have developed ..." (Naef, 1972: 15). Forms are not ancestor-descendant relationships but rather abstract transitional series between basic and specialized forms based on the concept of metamorphosis. Incorporate theses points together and you have a tree depicting the transition of forms that relate directly to the relationships of the taxa on the branches.
Naef is depicting a back-to-front cladogram. In Naef's diagram the forms are being shown to be transitional within a dichotomous framework (Figure 1b); very much like showing a character tree within a consensus tree at the same time. A modern representation of Naef's tree would place the forms at the nodes (Figure 1c). What at first appears to be a rooted phylogentic tree, turns out to be a poorly drawn cladogram that places too much emphasis on transitional forms than it does on taxic relationships.
Naef's tree represents a transitional period between Haeckel and Hennig. Naef attempted to save us from the Haeckel's 'oak' trees that later inspired the neoDarwinian Modern Synthesis by emphasizing the importance of natural (monophyletic) groups. Naef's methodological and theoretical work should also be celebrated on Cephalopod Awareness Day.
Naef, A. (1972). Cephalopoda (systematics). Fauna and Flora of the Bay of Naples (Fauna e Flora del Golfo di Napoli), Monograph 35, Part I, [Vol. I], Fascicle II. Washington, Smithsonian Institute Libraries.