Abstract
BackgroundCentral American crater lake cichlid fish of the Midas species complex (Amphilophus spp.) are a model system for sympatric speciation and fast ecological diversification and specialization. Midas cichlids have been intensively analyzed from an ecological and morphological perspective. Genomic resources such as transcriptomic and genomic data sets, and a high-quality draft genome are available now. Many ecologically relevant species-specific traits and differences such as pigmentation and cranial morphology arise during development. Detailed descriptions of the early development of the Midas cichlid in particular, will help to investigate the ontogeny of species differences and adaptations.ResultsWe describe the embryonic and larval development of the crater lake cichlid, Amphilophus xiloaensis, until seven days after fertilization. Similar to previous studies on teleost development, we describe six periods of embryogenesis - the zygote, cleavage, blastula, gastrula, segmentation, and post-hatching period. Furthermore, we define homologous stages to well-described teleost models such as medaka and zebrafish, as well as other cichlid species such as the Nile tilapia and the South American cichlid Cichlasoma dimerus. Key morphological differences between the embryos of Midas cichlids and other teleosts are highlighted and discussed, including the presence of adhesive glands and different early chromatophore patterns, as well as variation in developmental timing.ConclusionsThe developmental staging of the Midas cichlid will aid researchers in the comparative investigation of teleost ontogenies. It will facilitate comparative developmental biological studies of Neotropical and African cichlid fish in particular. In the past, the species flocks of the African Great Lakes have received the most attention from researchers, but some lineages of the 300–400 species of Central American lakes are fascinating model systems for adaptive radiation and rapid phenotypic evolution. The availability of genetic resources, their status as a model system for evolutionary research, and the possibility to perform functional experiments including transgenesis makes the Midas cichlid complex a very attractive model for evolutionary-developmental research.
Highlights
Central American crater lake cichlid fish of the Midas species complex (Amphilophus spp.) are a model system for sympatric speciation and fast ecological diversification and specialization
The present study aims to be a foundation for future studies examining the genetic and developmental factors that lead to phenotypic diversification among an extremely young species of a species-rich lineage of cichlid fish
Description of the early development of the Midas cichlid We document in detail the early development of the Midas cichlid, Amphilophus xiloaensis, during the first seven days following fertilization at 28°C
Summary
Central American crater lake cichlid fish of the Midas species complex (Amphilophus spp.) are a model system for sympatric speciation and fast ecological diversification and specialization. The cichlid radiations in Nicaraguan crater lakes (Figure 1, Table 1) provide a promising opportunity to study the early stages of speciation and diversification. This is because members of the Midas cichlid species complex (Amphilophus spp. or Amphilophus citrinellus spp.) have diverged repeatedly in several crater lakes, both sympatrically and allopatrically, often within a few thousand years [2,5,6,7]. The Midas cichlid complex underwent a rapid diversification within very short time spans (between 2000 and 25,000 years) and, interestingly, repeatedly evolved several adaptive traits (hypertrophied lips, elongated body shapes, dental innovations) in parallel in multiple crater lakes (Figure 1, Table 1). Midas cichlids are an excellent model system for the comparative study of the phenotype-genotype relationship
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