Tropical reef fishes are widely regarded as being perhaps the most morphologically diverse vertebrate assemblage on earth, yet much remains to be discovered about the scope and patterns of this ...diversity. We created a morphospace of 2,939 species spanning 56 families of tropical Indo-Pacific reef fishes and established the primary axes of body shape variation, the phylogenetic consistency of these patterns, and whether dominant patterns of shape change can be accomplished by diverse underlying changes. Principal component analysis showed a major axis of shape variation that contrasts deep-bodied species with slender, elongate forms. Furthermore, using custom methods to compare the elongation vector (axis that maximizes elongation deformation) and the main vector of shape variation (first principal component) for each family in the morphospace, we showed that two thirds of the families diversify along an axis of body elongation. Finally, a comparative analysis using a principal coordinate analysis based on the angles among first principal component vectors of each family shape showed that families accomplish changes in elongation with a wide range of underlying modifications. Some groups such as Pomacentridae and Lethrinidae undergo decreases in body depth with proportional increases in all body regions, while other families show disproportionate changes in the length of the head (e.g., Labridae), the trunk or caudal region in all combinations (e.g., Pempheridae and Pinguipedidae). In conclusion, we found that evolutionary changes in body shape along an axis of elongation dominates diversification in reef fishes. Changes in shape on this axis are thought to have immediate implications for swimming performance, defense from gape limited predators, suction feeding performance and access to some highly specialized habitats. The morphological modifications that underlie changes in elongation are highly diverse, suggesting a role for a range of developmental processes and functional consequences.
Anglerfish are creatures of the deep ocean, featuring glowing lures, huge, toothy mouths and parasitic males physically attached to females. A new study finds that genomic degradation of the immune ...system facilitated the origin of parasitic males as anglerfishes invaded the deep zone where they experienced an adaptive radiation.
Anglerfish are creatures of the deep ocean, featuring glowing lures, huge, toothy mouths and parasitic males physically attached to females. A new study finds that genomic degradation of the immune system facilitated the origin of parasitic males as anglerfishes invaded the deep zone where they experienced an adaptive radiation.
Studies of the evolution of phenotypic diversity have gained momentum among neontologists interested in the uneven distribution of diversity across the tree of life. Potential morphological diversity ...in a lineage is a function of the number of independent parameters required to describe the form, and innovations such as structural duplication and functional decoupling can enhance the potential for diversity in a given clade. The functional properties of organisms are determined by underlying parts, but any property that is determined by three or more parts expresses many-to-one mapping of form to function, in which many morphologies will have the same functional property. This ubiquitous feature of organismal design results in surfaces of morphological variation that are neutral with respect to the functional property, and enhances the potential for simultaneously optimizing two or more functions of the system.
Ambient light levels are often considered to drive the evolution of eye form and function. Diel activity pattern is the main mechanism controlling the visual environment of teleost reef fish, with ...day-active (diurnal) fish active in well-illuminated conditions, whereas night-active (nocturnal) fish cope with dim light. Physiological optics predicts several specific evolutionary responses to dim-light vision that should be reflected in visual performance features of the eye.
We analyzed a large comparative dataset on morphological traits of the eyes in 265 species of teleost reef fish in 43 different families. The eye morphology of nocturnal reef teleosts is characterized by a syndrome that indicates better light sensitivity, including large relative eye size, high optical ratio and large, rounded pupils. Improved dim-light image formation comes at the cost of reduced depth of focus and reduction of potential accommodative lens movement. Diurnal teleost reef fish, released from the stringent functional requirements of dim-light vision have much higher morphological and optical diversity than nocturnal species, with large ranges of optical ratio, depth of focus, and lens accommodation.
Physical characteristics of the environment are an important factor in the evolution and diversification of the vertebrate eye. Both teleost reef fish and terrestrial amniotes meet the functional requirements of dim-light vision with a similar evolutionary response of morphological and optical modifications. The trade-off between improved dim-light vision and reduced optical diversity may be a key factor in explaining the lower trophic diversity of nocturnal reef teleosts.
The relationship between phenotype and fitness can be visualized as a rugged landscape. Multiple fitness peaks on this landscape are predicted to drive early bursts of niche diversification during ...adaptive radiation. We measured the adaptive landscape in a nascent adaptive radiation of Cyprinodon pupfishes endemic to San Salvador Island, Bahamas, and found multiple coexisting high-fitness regions driven by increased competition at high densities, supporting the early burst model. Hybrids resembling the generalist phenotype were isolated on a local fitness peak separated by a valley from a higher-fitness region corresponding to trophic specialization. This complex landscape could explain both the rarity of specialists across many similar environments due to stabilizing selection on generalists and the rapid morphological diversification rate of specialists due to their higher fitness.
The world’s oceans are home to many fantastic creatures, including about 16,000 species of actinopterygian, or ray-finned, fishes. Notably, 85% of marine fish species come from a single ...actinopterygian subgroup, the acanthomorph or spiny-rayed fishes. Here, we review eight functional innovations found in marine acanthomorphs that have been instrumental in the adaptive radiation of this group in the marine realm. Jaw protrusion substantially enhances the suction feeding mechanism found in all fish. Fin spines serve as a major deterrent to predators and enhance the locomotor function of fins. Pharyngognathy, a specialization of the second pair of jaws in the pharynx, enhances the ability of fishes to process hard and tough prey. Endothermy allows fishes to function at high levels of physiological performance in cold waters and facilitates frequent movement across strong thermal gradients found in the open ocean. Intramandibular joints enhance feeding for fishes that bite and scrape prey attached to hard surfaces. Antifreeze proteins prevent ice crystal growth in extracellular fluids, allowing fish to function in cold waters that would otherwise freeze them. Air-breathing allowed fishes at the water’s edge to exploit terrestrial habitats. Finally, bioluminescence functions in communication, attracting prey and in hiding from predators, particularly for fishes of the deep ocean. All of these innovations have evolved multiple times in fishes. The frequent occurrence of convergent evolution of these complex functional novelties speaks to the persistence and potency of the selective forces in marine environments that challenge fishes and stimulate innovation.
Wainwright and Longo review eight biological innovations that enabled acanthomorphs to become the dominant group of fish in the modern ocean.
Ray-finned fishes make up half of all living vertebrate species. Nearly all ray-finned fishes are teleosts, which include most commercially important fish species, several model organisms for ...genomics and developmental biology, and the dominant component of marine and freshwater vertebrate faunas. Despite the economic and scientific importance of ray-finned fishes, the lack of a single comprehensive phylogeny with corresponding divergence-time estimates has limited our understanding of the evolution and diversification of this radiation. Our analyses, which use multiple nuclear gene sequences in conjunction with 36 fossil age constraints, result in a well-supported phylogeny of all major rayfinned fish lineages and molecular age estimates that are generally consistent with the fossil record. This phylogeny informs three longstanding problems: specifically identifying elopomorphs (eels and tarpons) as the sister lineage of all other teleosts, providing a unique hypothesis on the radiation of early euteleosts, and offering a promising strategy for resolution of the "bush at the top of the tree" that includes percomorphs and other spiny-finned teleosts. Contrasting our divergence time estimates with studies using a single nuclear gene or whole mitochondrial genomes, we find that the former underestimates ages of the oldest ray-finned fish divergences, but the latter dramatically overestimates ages for derived teleost lineages. Our time-calibrated phylogeny reveals that much of the diversification leading to extant groups of teleosts occurred between the late Mesozoic and early Cenozoic, identifying this period as the "Second Age of Fishes."
Functional decoupling of oral and pharyngeal jaws is widely considered to have expanded the ecological repertoire of cichlid fishes. But, the degree to which the evolution of these jaw systems is ...decoupled and whether decoupling has impacted trophic diversification remains unknown. Focusing on the large Neotropical radiation of cichlids, we ask whether oral and pharyngeal jaw evolution is correlated and how their evolutionary rates respond to feeding ecology. In support of decoupling, we find relaxed evolutionary integration between the two jaw systems, resulting in novel trait combinations that potentially facilitate feeding mode diversification. These outcomes are made possible by escaping the mechanical trade-off between force transmission and mobility, which characterizes a single jaw system that functions in isolation. In spite of the structural independence of the two jaw systems, results using a Bayesian, state-dependent, relaxed-clock model of multivariate Brownian motion indicate strongly aligned evolutionary responses to feeding ecology. So, although decoupling of prey capture and processing functions released constraints on jaw evolution and promoted trophic diversity in cichlids, the natural diversity of consumed prey has also induced a moderate degree of evolutionary integration between the jaw systems, reminiscent of the original mechanical trade-off between force and mobility.
Spiny-rayed fishes, or acanthomorphs, comprise nearly one-third of all living vertebrates. Despite their dominant role in aquatic ecosystems, the evolutionary history and tempo of acanthomorph ...diversification is poorly understood. We investigate the pattern of lineage diversification in acanthomorphs by using a well-resolved time-calibrated phylogeny inferred from a nuclear gene supermatrix that includes 520 acanthomorph species and 37 fossil age constraints. This phylogeny provides resolution for what has been classically referred to as the “bush at the top” of the teleost tree, and indicates acanthomorphs originated in the Early Cretaceous. Paleontological evidence suggests acanthomorphs exhibit a pulse of morphological diversification following the end Cretaceous mass extinction; however, the role of this event on the accumulation of living acanthomorph diversity remains unclear. Lineage diversification rates through time exhibit no shifts associated with the end Cretaceous mass extinction, but there is a global decrease in lineage diversification rates 50 Ma that occurs during a period when morphological disparity among fossil acanthomorphs increases sharply. Analysis of clade-specific shifts in diversification rates reveal that the hyperdiversity of living acanthomorphs is highlighted by several rapidly radiating lineages including tunas, gobies, blennies, snailfishes, and Afro-American cichlids. These lineages with high diversification rates are not associated with a single habitat type, such as coral reefs, indicating there is no single explanation for the success of acanthomorphs, as exceptional bouts of diversification have occurred across a wide array of marine and freshwater habitats.
Adaptive radiations are known for rapid morphological and species diversification in response to ecological opportunity, but it remains unclear if distinct mechanisms drive this pattern. Here, we ...show that rapid rates of morphological diversification are linked to the evolution of novel ecological niches in two independent Cyprinodon radiations nested within a wide-ranging group repeatedly isolated in extreme environments. We constructed a molecular phylogeny for the Cyprinodontidae, measured 16 functional traits across this group, and compared the likelihoods of single or multiple rates of morphological diversification. We found that rates of morphological diversification within two sympatric Cyprinodon clades containing unique trophic specialists are not part of an adaptive continuum with other clades, but are instead extreme outliers with rates up to 131 times faster than other Cyprinodontidae. High rates were not explained by clade age, but were instead linked to unique trophic niches within Cyprinodon, including scale-eating, zooplanktivory, and piscivory. Furthermore, although both radiations occur in similar environments and have similar sister species, they each evolved unique trophic specialists and high rates of morphological diversification in different sets of traits. We propose that the invasion of novel ecological niches may be a key mechanism driving many classic examples of adaptive radiation.
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