Invertebrate Tidbits

Ronald L. Shimek, Ph. D.

Hart, M. W., S. L. Johnson, J. A. Addison, and M. Byrne. 2004. Strong character incongruence and character choice in phylogeny of sea stars of the Asterinidae.
Invertebrate Biology. l23(4): 343-356.

Abstract:

Historically, characters from early animal development have been a potentially rich source of phylogenetic information, but many traits associated with the gametes and larval stages of animals with complex life cycles are widely suspected to have evolved frequent convergent similarities. Such convergences will confound true phylogenetic relationships. We compared phylogenetic inferences based on early life history traits with those from mitochondrial DNA sequences for sea stars in the genera Asterina, Cryptasterina, and Patiriella (Valvatida: Asterinidae). Analysis of these two character sets produced phylogenies that shared few clades. We quantified the degree of homoplasy in each character set when rnapped onto the phylogeny inferred from the alterative characters. The incongruence between early life history and nucleotide characters implies more homoplasy in the life history character set. We suggest that the early life history traits in this case are most likely to be misleading as phylogenetic characters because simple adaptive models predict convergence in early life histories, We show that adding early life history characters may slightly improve a phylogeny based on nucleotide sequences, but adding nucleotide characters may be critically important to improving inferences from phylogenies based on early life history characters.

Comments:

Many aquarists are familiar with the small sea stars in the family Asterinidae that are common in reef aquaria. Although often placed in the genus Asterina, they actually have not been identified by any reputable taxonomist. The authors of this paper examined 17 similar and related sea star species and tried to determine the relationships between them. Because of the complexities of their development and structures, they were unable to unambiguously determine the relationships. This paper is interesting in that its authors looked at several sea stars that were roughly the same size and morphology as the ones found in aquaria. Several of these stars were similar in appearance to the stars found in aquaria; however, none of the stars investigated in the study reproduced by fission, which is the aquarium species’ method of reproduction. Given the data presented in this paper, it is unlikely that the relationships between small asterinid species of sea stars found in aquaria will soon be conclusively identified. It appears that much of the critical information about the species is available only from an analysis of the species’ DNA, and that those data will have to be added to the various traditional morphological data to determine the relationships within this large group of small sea stars species.