Meeting Abstract
Ernst Mayr (1961, Science 131: 1501–1506) suggested that understanding features of organisms involves the study of proximate and ultimate causes. Proximate causes occur during the life of the organism and ultimate causes occur prior to the life of the organism, as part of evolutionary history. Descriptive biology was viewed as fundamental for pursuing proximate and ultimate causes. Systematics encompasses these three components. Organisms, not taxa, are described, and proximate hypotheses (ontogenetic and functional) are inferred to explain some characters, whereas other characters are explained via ultimate causes in the form of intraspecific, specific, and phylogenetic hypotheses. Ultimate understanding is limited since hypothesis testing is rarely accomplished; descriptive- and proximate-level investigations offer better opportunities. Examples of interactions between descriptive, proximate, and ultimate understanding are presented from research on several features among Fabriciidae and Sabellidae polychaetes. Members of both taxa have two ‘peristomial’ rings, and distinct mid-ventral patches of cilia occur on the anterior peristomial ring among Fabriciidae and posterior ring among Sabellidae. Phylogenetic hypotheses suggest cilia patches are synapomorphies for the respective families. Since these hypotheses cannot be tested, it will be more productive to investigate whether or not cilia patches are homologous, which might be determined through ontogenetic and histological studies of proximate causes: are cilia derived from the larval prototroch or metatroch? Are anterior and posterior rings peristomial in origin? Pursuing proximate causes offers increased understanding in systematics not available via ultimate causes.
