Strong character incongruence and character choice in phylogeny of sea stars of the Asterinidae

Abstract

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 mapped onto the phylogeny inferred from the alternative 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.Additional key words: total evidence, modes of development, life history, mtDNA, AsteroideaThe choice of characters for use in phylogenetic analyses is an important and contentious issue in animal phylogenetics. Since Haeckel (1866), phenotypic characters from the earliest parts of the life cycle (such as the morphological forms of planktonic larvae) have been viewed as a potentially rich source of phylogenetic information. However, even in the early 20 th century, there was growing skepticism of the utility of early life history characters for tracing evolutionary relationships (e.g., Conklin 1928; Gould 1977). The subsequent growth of larval ecology as a research discipline led to renewed interest in the phylogenetic history of embryological and larval diversity, with a sharp focus on the study of early life history characters expressed during sexual reproduction or during larval development before metamorphosis to the adult form (McHugh & Rouse 1998). Molecular phylogenetic studies of taxa that include species with diverse early a Author for correspondence. E-mail: michael.hart@dal.ca b Present address: Department of Biological Sciences, SimonFraser University, Burnaby, British Columbia V5A 1S6, Canada life histories have suggested the evolution of convergent similarities in early life history characters such as egg size, type of parental care, offspring dispersal ability, larval morphology, and fertilization ecology (Hart 2000). Many of these characters reflect functional adaptations of a complex life cycle in which individuals sequentially inhabit planktonic and benthic habitats: the similarities in character states could represent shared ancestral states as a result ...

Adaptations to Benthic Development: Functional Morphology of the Attachment Complex of the Brachiolaria Larva in the Sea StarAsterina gibbosa

“…Successive evolutionary transitions would then have occurred to give rise to various types of nonfeeding larval development by (a) loss of larval feeding structures such as ciliated bands and functional gut, and gain of large, yolky eggs, followed by (b) loss of planktonic dispersal, and then (c) gain of parental brood protection. Recently, however, molecular phylogenetic studies conducted on the family Asterinidae (Hart et al, 1997(Hart et al, , 2004 showed that ordered transformations between the four modes of development comprising brachiolariae (i.e., planktotrophic-pelagic, leci-thotrophic-pelagic, lecithotrophic-benthic, and lecithotrophic-intragonadal) could not be easily reconstructed, and that many parallel changes in larval form, habitat, and dispersal potential occurred. For example, in this family, benthic lecithotrophy evolved three times independently, in Parvulastra (Patiriella) exigua, in Aquilonastra (Asterina) minor and in the two sister species, Asterina gibbosa and Asterina phylactica (Hart et al, 2004;Byrne, 2006).…”

“…Recently, however, molecular phylogenetic studies conducted on the family Asterinidae (Hart et al, 1997(Hart et al, , 2004 showed that ordered transformations between the four modes of development comprising brachiolariae (i.e., planktotrophic-pelagic, leci-thotrophic-pelagic, lecithotrophic-benthic, and lecithotrophic-intragonadal) could not be easily reconstructed, and that many parallel changes in larval form, habitat, and dispersal potential occurred. For example, in this family, benthic lecithotrophy evolved three times independently, in Parvulastra (Patiriella) exigua, in Aquilonastra (Asterina) minor and in the two sister species, Asterina gibbosa and Asterina phylactica (Hart et al, 2004;Byrne, 2006). In these species, brachiolariae all possess a hypertrophied attachment complex (Ludwig, 1882;MacBride, 1896;Komatsu et al, 1979;Marthy, 1980;Byrne, 1995Byrne, , 2006.…”

Viviparity in the Sea StarCryptasterina hystera(Asterinidae)—Conserved and Modified Features in Reproduction and Development

“…Within the Echinodermata, the Asterinidae, a major family of sea stars, is particularly noted for its diverse life histories (Byrne and Cerra, 1996;Hart et al, 1997Hart et al, , 2003Hart et al, , 2004Byrne et al, 1999a). Species in the asterinid genera Patiriella and Cryptasterina exhibit a range of developmental modes, including a most derived method of propagation-incubation of progeny in the gonads and birth of juveniles (Byrne, 1996;Byrne and Cerra, 1996;Byrne et al, 2003a).…”

Phylogenetic analyses of marine sponges within the order Verongida: a comparison of morphological and molecular data

“…Predicting which morphological characters accurately reflect evolutionary relatedness (i.e., those exhibiting variation based on genetic factors) and which characters do not has proven difficult in sponge taxonomy. The use of molecular data in conjunction with traditional morphological analyses may provide a means of elucidating which morphological characters are homologous and diagnostic and which are homoplasic and uninformative (Alvarez et al 2000;Hart et al 2004).…”