DiceCT for fishes: recommendations for pairing iodine contrast agents with µCT to visualize soft tissues in fishes.

Computed tomography (CT) scanning and other high-throughput three-dimensional (3D) visualization tools are transforming the ways we study morphology, ecology and evolutionary biology research beyond generating vast digital repositories of anatomical data. Contrast-enhanced chemical staining methods, which render soft tissues radio-opaque when coupled with CT scanning, encompass several approaches that are growing in popularity and versatility. Of these, the various diceCT techniques that use an iodine-based solution like Lugol's have provided access to an array of morphological data sets spanning extant vertebrate lineages. This contribution outlines straightforward means for applying diceCT techniques to preserved museum specimens of cartilaginous and bony fishes, collectively representing half of vertebrate species diversity. This study contrasts the benefits of using either aqueous or ethylic Lugol's solutions and reports few differences between these methods with respect to the time required to achieve optimal tissue contrast. It also explores differences in minimum stain duration required for different body sizes and shapes and provides recommendations for staining specimens individually or in small batches. As reported by earlier studies, the authors note a decrease in pH during staining with either aqueous or ethylic Lugol's. Nonetheless, they could not replicate the drastic declines in pH reported elsewhere. They provide recommendations for researchers and collections staff on how to incorporate diceCT into existing curatorial practices, while offsetting risk to specimens. Finally, they outline how diceCT with Lugol's can aid ichthyologists of all kinds in visualizing anatomical structures of interest: from brains and gizzards to gas bladders and pharyngeal jaw muscles.

The ecological and genomic basis of explosive adaptive radiation.

Speciation rates vary considerably among lineages, and our understanding of what drives the rapid succession of speciation events within young adaptive radiations remains incomplete1-11. The cichlid fish family provides a notable example of such variation, with many slowly speciating lineages as well as several exceptionally large and rapid radiations12. Here, by reconstructing a large phylogeny of all currently described cichlid species, we show that explosive speciation is solely concentrated in species flocks of several large young lakes. Increases in the speciation rate are associated with the absence of top predators; however, this does not sufficiently explain explosive speciation. Across lake radiations, we observe a positive relationship between the speciation rate and enrichment of large insertion or deletion polymorphisms. Assembly of 100 cichlid genomes within the most rapidly speciating cichlid radiation, which is found in Lake Victoria, reveals exceptional 'genomic potential'-hundreds of ancient haplotypes bear insertion or deletion polymorphisms, many of which are associated with specific ecologies and shared with ecologically similar species from other older radiations elsewhere in Africa. Network analysis reveals fundamentally non-treelike evolution through recombining old haplotypes, and the origins of ecological guilds are concentrated early in the radiation. Our results suggest that the combination of ecological opportunity, sexual selection and exceptional genomic potential is the key to understanding explosive adaptive radiation.

Reef fish functional traits evolve fastest at trophic extremes.

Trophic ecology is thought to exert a profound influence on biodiversity, but the specifics of the process are rarely examined at large spatial and evolutionary scales. We investigate how trophic position and diet breadth influence functional trait evolution in one of the most species-rich and complex vertebrate assemblages, coral reef fishes, within a large-scale phylogenetic framework. We show that, in contrast with established theory, functional traits evolve fastest in trophic specialists with narrow diet breadths at both very low and high trophic positions. Top trophic level specialists exhibit the most functional diversity, while omnivorous taxa with intermediate trophic positions and wide diet breadth have the least functional diversity. Our results reveal the importance of trophic position in shaping evolutionary dynamics while simultaneously highlighting the incredible trophic and functional diversity present in coral reef fish assemblages.

AnnotationBustR: an R package to extract subsequences from GenBank annotations.

BACKGROUND: DNA sequences are pivotal for a wide array of research in biology. Large sequence databases, like GenBank, provide an amazing resource to utilize DNA sequences for large scale analyses. However, many sequence records on GenBank contain more than one gene or are portions of genomes. Inconsistencies in the way genes are annotated and the numerous synonyms a single gene may be listed under provide major challenges for extracting large numbers of subsequences for comparative analysis across taxa. At present, there is no easy way to extract portions from many GenBank accessions based on annotations where gene names may vary extensively. RESULTS: The R package AnnotationBustR allows users to extract sequences based on GenBank annotations through the ACNUC retrieval system given search terms of gene synonyms and accession numbers. AnnotationBustR extracts subsequences of interest and then writes them to a FASTA file for users to employ in their research endeavors. CONCLUSION: FASTA files of extracted subsequences and accession tables generated by AnnotationBustR allow users to quickly find and extract subsequences from GenBank accessions. These sequences can then be incorporated in various analyses, like the construction of phylogenies to test a wide range of ecological and evolutionary hypotheses.

Feeding ecology underlies the evolution of cichlid jaw mobility.

The fish feeding apparatus is among the most diverse functional systems in vertebrates. While morphological and mechanical variations of feeding systems are well studied, we know far less about the diversity of the motions that they produce. We explored patterns of feeding movements in African cichlids from Lakes Malawi and Tanganyika, asking whether the degree of kinesis is associated with dietary habits of species. We used geometric morphometrics to measure feeding kinesis as trajectories of shape change, based on 326 high-speed videos in 56 species. Cranial morphology was significantly related to feeding movements, both of which were distributed along a dietary axis associated with prey evasiveness. Small-mouthed cichlids that feed by scraping algae and detritus from rocks had low kinesis strikes, while large-mouthed species that eat large, evasive prey (fishes and shrimps) generated the greatest kinesis. Despite having higher overall kinesis, comparisons of trajectory shape (linearity) revealed that cichlids that eat mobile prey also displayed more kinematically conserved, or efficient, feeding motions. Our work indicates that prey evasiveness is strongly related to the evolution of cichlid jaw mobility, suggesting that this same relationship may explain the origins and diversity of highly kinetic jaws that characterize the super-radiation of spiny-rayed fishes.

Replicated divergence in cichlid radiations mirrors a major vertebrate innovation.

Decoupling of the upper jaw bones--jaw kinesis--is a distinctive feature of the ray-finned fishes, but it is not clear how the innovation is related to the extraordinary diversity of feeding behaviours and feeding ecology in this group. We address this issue in a lineage of ray-finned fishes that is well known for its ecological and functional diversity--African rift lake cichlids. We sequenced ultraconserved elements to generate a phylogenomic tree of the Lake Tanganyika and Lake Malawi cichlid radiations. We filmed a diverse array of over 50 cichlid species capturing live prey and quantified the extent of jaw kinesis in the premaxillary and maxillary bones. Our combination of phylogenomic and kinematic data reveals a strong association between biting modes of feeding and reduced jaw kinesis, suggesting that the contrasting demands of biting and suction feeding have strongly influenced cranial evolution in both cichlid radiations.

A pharyngeal jaw evolutionary innovation facilitated extinction in Lake Victoria cichlids.

Evolutionary innovations, traits that give species access to previously unoccupied niches, may promote speciation and adaptive radiation. Here, we show that such innovations can also result in competitive inferiority and extinction. We present evidence that the modified pharyngeal jaws of cichlid fishes and several marine fish lineages, a classic example of evolutionary innovation, are not universally beneficial. A large-scale analysis of dietary evolution across marine fish lineages reveals that the innovation compromises access to energy-rich predator niches. We show that this competitive inferiority shaped the adaptive radiation of cichlids in Lake Tanganyika and played a pivotal and previously unrecognized role in the mass extinction of cichlid fishes in Lake Victoria after Nile perch invasion.