An embryonic staging series up to hatching for Cyprinodon variegatus: An emerging fish model for developmental, evolutionary, and ecological research

Abstract

Using multiple taxa to research development is necessary for making general conclusions about developmental patterns and mechanisms. We present a staging series for Cyprinodon variegatus as a basis for further study of the developmental biology of fishes in the genus Cyprinodon and for comparative work on teleost fishes beyond the standard models. Cyprinodon are small, euryhaline fishes, widely distributed in fresh, brackish, and hypersaline waters of southern and eastern North America. Cyprinodontids are closely related to fundulids, providing a comparative reference point to the embryological model, Fundulus heteroclitus. Ecologists and evolutionary biologists commonly study Cyprinodon, and we have been using Cyprinodon to study skull variation and its genetic basis among closely related species. We divided embryonic development of C. variegatus into 34 morphologically identifiable stages. We reference our staging series to that already defined for a related model species, Oryzias latipes (medaka) that is studied by a large community of researchers. We provide a description of the early chondrogenesis and ossification of skull and caudal fin bones during the latter stages of embryonic development. We show that Cyprinodon are tractable for studying development. Eggs can be obtained easily from breeding pairs and our study provides a staging system to facilitate future developmental studies.

Ecological divergence in sympatry causes gene misexpression in hybrids

“…This is consistent with a model of gene expression evolution governed largely by stabilizing selection and drift (Whitehead & Crawford, 2006). However, at eight days postfertilization (8 dpf), when craniofacial structures of the skull begin to ossify (Lencer & McCune, 2018), geographic distance was no longer associated with differential expression (Figure 1c; PGLS; p = .18), which was higher between sympatric trophic specialist species on San Salvador Island than between generalist populations spanning 1,000 km across the Caribbean. Thus, differential gene expression at 8 dpf was much higher than expected due to isolation by distance, suggesting that strong directional selection on gene expression was important during ecological divergence in sympatry.…”

Thalamic neurons drive distinct forms of motor asymmetry that are conserved in teleost and dependent on visual evolution

“…To determine if light-search and motor asymmetry are conserved properties of larval teleost fish and how these behavioral features are modulated in evolution, we assessed the response to changes in illumination in five related fish species. We assessed 4-5 dpf old Danionella cerebrum [32][33][34] , 6-7 dpf old fathead minnow (Pimephales promelas) [35][36][37] , 5-6 dpf Mexican tetras (Astyanax mexicanus) 38,39 , 12-14 dpf medaka (Oryzias latipes) 40,41 , and 6-7 dpf Sheepshead pupfish (Cyprinodon variegatus) 42,43 to compare responses with Zebrafish (Danio rerio, TL strain). Across all species the timepoints used for testing corresponded with free-swimming larval stages.…”