WHAT MOLECULAR PHYLOGENIES TELL US ABOUT THE EVOLUTION OF LARVAL FORMS

Citation
Rr. Strathmann et Dj. Eernisse, WHAT MOLECULAR PHYLOGENIES TELL US ABOUT THE EVOLUTION OF LARVAL FORMS, American zoologist, 34(4), 1994, pp. 502-512
Citations number
65
Categorie Soggetti
Zoology
Journal title
ISSN journal
00031569
Volume
34
Issue
4
Year of publication
1994
Pages
502 - 512
Database
ISI
SICI code
0003-1569(1994)34:4<502:WMPTUA>2.0.ZU;2-B
Abstract
There is interest in assembling a robust hypothesis of animal relation ships based on molecular and other character-based evidence, but even if a high degree of phylogenetic resolution is available, there remain challenging problems for postulating ancestral larval traits. This di stinction between hypotheses of genealogies and our knowledge of speci fic traits is illustrated with specific examples of the portion of var iable larval traits that are homoplastic (i.e., they require convergen ces, parallelisms, or character reversals) with respect to specific mo lecular-based genealogical hypotheses. Corresponding molecular studies suggest (1) maximal incongruity in larval form and metamorphosis for extant echinoderm classes, (2) convergences in larval size and form as sociated with coloniality in ascidians, (3) multiple losses of the loc omotory larval tail in molgulid ascidians, (4) multiple losses of larv al feeding and gain of apomictic parthenogenesis within a genus of biv alves, (5) multiple losses of larval feeding in echinoids, (6) alterna tive explanations of the distribution of feeding and non-feeding larva e among gastropods, and (7) recent modifications in embryonic and larv al development of echinoids following prolonged stasis. These examples show that inferences from phylogenetic studies will ultimately be lim ited by the extent to which homoplasy and polarity can be unambiguousl y assessed for larval traits. These limitations are illustrated by alt ernative hypotheses for larval trait synapomorphies among phyla, evolu tion of feeding with opposed prototrochal and metatrochal ciliary band s, and the retention or reacquisition of the locomotory nauplius of th e Euphausiacea and Dendrobranchiata. inferences on the evolution of la rval traits require other sorts of evidence, perhaps including informa tion on the evolution of genes that play important roles in morphogene sis and their sites of expression.