Hybrids between the Florida amphioxus (Branchiostoma floridae) and the Bahamas lancelet (Asymmetron lucayanum): Developmental morphology and chromosome counts

TitleHybrids between the Florida amphioxus (Branchiostoma floridae) and the Bahamas lancelet (Asymmetron lucayanum): Developmental morphology and chromosome counts
Publication TypeJournal Article
Year of Publication2015
AuthorsHolland N.D, Holland LZ, Heimberg A.
JournalBiological Bulletin
Volume228
Pagination13-24
Date Published2015/02
Type of ArticleArticle
ISBN Number0006-3185
Accession NumberWOS:000350750000002
Keywordsbasal chordate amphioxus; different modes; embryos; evolution; gene-expression; mitochondrial genome; Nerve cord; retinoic acid; sea-urchin; strongylocentrotus-purpuratus
Abstract

The cephalochordate genera Branchiostoma and Asymmetron diverged during the Mesozoic Era. In spite of the long separation of the parental clades, eggs of the Florida amphioxus, B. floridae, when fertilized with sperm of the Bahamas lancelet, A. lucayanum (and vice versa), develop through embryonic and larval stages. The larvae reach the chordate phylotypic stage (i.e., the pharyngula), characterized by a dorsal nerve cord, notochord, perforate pharynx, and segmented trunk musculature. After about 2 weeks of larval development, the hybrids die, as do the A. lucayanum purebreds, although all were eating the same algal diet that sustains B. floridae purebreds through adulthood in the laboratory; it is thus unclear whether death of the hybrids results from incompatible parental genomes or an inadequate diet. The diploid chromosome count in A. lucayanum and B. floridae purebreds is, respectively, 34 and 38, whereas it is 36 in hybrids in either direction. The hybrid larvae exhibit several morphological characters intermediate between those of the parents, including the size of the preoral ciliated pit and the angles of deflection of the gill slits and anus from the ventral midline. Based on the time since the two parent clades diverged (120 or 160 million years, respectively, by nuclear and mitochondrial gene analysis), the cross between Branchiostoma and Asymmetron is the most extreme example of hybridization that has ever been unequivocally demonstrated among multicellular animals.

Short TitleBiol. Bull.
Student Publication: 
No