Considering decoupled phenotypic diversification between ontogenetic phases in macroevolution: An example using Triggerfishes (Balistidae).

Across the Tree of Life, most studies of phenotypic disparity and diversification have been restricted to adult organisms. However, many lineages have distinct ontogenetic phases that differ from their adult forms in morphology and ecology. Focusing disproportionately on the evolution of adult forms unnecessarily hinders our understanding of the pressures shaping evolution over time. Non-adult disparity patterns are particularly important to consider for coastal ray-finned fishes, which often have juvenile phases with distinct phenotypes. These juvenile forms are often associated with sheltered nursery environments, with phenotypic shifts between adults and juvenile stages that are readily apparent in locomotor morphology. Whether this ontogenetic variation in locomotor morphology reflects a decoupling of diversification dynamics between life stages remains unknown. Here we investigate the evolutionary dynamics of locomotor morphology between adult and juvenile triggerfishes. We integrate a time-calibrated phylogenetic framework with geometric morphometric approaches and measurement data of fin aspect ratio and incidence, and reveal a mismatch between morphospace occupancy, the evolution of morphological disparity, and the tempo of trait evolution between life stages. Collectively, our results illuminate how the heterogeneity of morpho-functional adaptations can decouple the mode and tempo of morphological diversification between ontogenetic stages.

Diving into the diversity of colour patterns in reef fishes.

Colours and associated patterns are probably some of the most obvious phenotypic traits in animals and reef teleost fishes are often cited as a textbook example for illustrating this type of diversity. Even if it is well established that colour patterns play a central role in the ecology and evolution of reef fishes, we still lack the necessary toolkits to fully grasp the mechanisms driving the diversification of this obvious phenotypic trait. On the one hand, genotyping power seems now limitless thanks to current DNA sequencing technologies. Today, entire genomes of fishes can be easily produced for large sets of species. On the other hand, the description of colour patterns and the quantification of their variation across reef fishes might be highly challenging. In a cover manuscript in this issue of Molecular Ecology, Coulmance et al. (2023) introduced an innovative approach for extracting and quantifying the major colour pattern elements present in the hamlets (Hypoplectrus spp., Serranidae), a recent reef fish radiation from the Caribbean. Then, they intelligently used the quantified colour pattern variation as a phenotypic trait for a genome-wide association study (GWAS). Interestingly, using a method that required no a priori knowledge, they were able to recover well-established marks (e.g., vertical bars) and to highlight less expected colour pattern elements (e.g., dark to light gradient on ventral part as well as caudal and anal fins), which show strong association peaks on linkage group (LG) 12 and 04. Beyond the demonstration of the potential of their new quantitative analysis of colour pattern variation in reef fishes combined with GWAS, their findings offer new perspectives on our understanding of the intrinsic and extrinsic factors generating this outstanding diversity of the fish world.

Periodic Environmental Disturbance Drives Repeated Ecomorphological Diversification in an Adaptive Radiation of Antarctic Fishes.

AbstractThe ecological theory of adaptive radiation has profoundly shaped our conceptualization of the rules that govern diversification. However, while many radiations follow classic early-burst patterns of diversification as they fill ecological space, the longer-term fates of these radiations depend on many factors, such as climatic stability. In systems with periodic disturbances, species-rich clades can contain nested adaptive radiations of subclades with their own distinct diversification histories, and how adaptive radiation theory applies in these cases is less clear. Here, we investigated patterns of ecological and phenotypic diversification within two iterative adaptive radiations of cryonotothenioid fishes in Antarctica's Southern Ocean: crocodile icefishes and notoperches. For both clades, we observe evidence of repeated diversification into disparate regions of trait space between closely related taxa and into overlapping regions of trait space between distantly related taxa. We additionally find little evidence that patterns of ecological divergence are correlated with evolution of morphological disparity, suggesting that these axes of divergence may not be tightly linked. Finally, we reveal evidence of repeated convergence in sympatry that suggests niche complementarity. These findings reflect the dynamic history of Antarctic marine habitats and may guide hypotheses of diversification dynamics in environments characterized by periodic disturbance.

Describing novel mitochondrial genomes of Antarctic amphipods.

To date, only one mitogenome from an Antarctic amphipod has been published. Here, novel complete mitochondrial genomes (mitogenomes) of two morphospecies are assembled, namely, Charcotia amundseni and Eusirus giganteus. For the latter species, we have assembled two mitogenomes from different genetic clades of this species. The lengths of Eusirus and Charcotia mitogenomes range from 15,534 to 15,619 base pairs and their mitogenomes are composed of 13 protein coding genes, 22 transfer RNAs, 2 ribosomal RNAs, and 1 putative control region CR. Some tRNAs display aberrant structures suggesting that minimalization is also ongoing in amphipod mitogenomes. The novel mitogenomes of the two Antarctic species have features distinguishing them from other amphipod mitogenomes such as a lower AT-richness in the whole mitogenomes and a negative GC- skew in both strands of protein coding genes. The genetically most variable mitochondrial regions of amphipods are nad6 and atp8, while cox1 shows low nucleotide diversity among closely and more distantly related species. In comparison to the pancrustacean mitochondrial ground pattern, E. giganteus shows a translocation of the nad1 gene, while cytb and nad6 genes are translocated in C. amundseni. Phylogenetic analysis based on mitogenomes illustrates that Eusirus and Charcotia cluster together with other species belonging to the same amphipod superfamilies. In the absence of reference nuclear genomes, mitogenomes can be useful to develop markers for studying population genetics or evolutionary relationships at higher taxonomic levels.

Unprecedented Biting Performance in Herbivorous Fish: How the Complex Biting System of Pomacentridae Circumvents Performance Trade-Offs.

AbstractIt is well accepted that the complexity of functional systems may mitigate performance trade-offs. However, data supporting this theory are hard to find because they need to be based on a functional system with different complexity levels in closely related species. The Pomacentridae (damselfishes) provide an excellent opportunity to test this hypothesis because most of the species have two mouth-closing systems: the first using the adductor mandibulae, as in all teleost fishes, and the second relying on the ceratomandibular (cmd) ligament, a synapomorphic trait of the family. Interestingly, some pomacentrids have secondarily lost the cmd ligament during evolution and therefore have a less complex mouth-closing system. Using dissection, kinematic analysis, and mathematical modeling, we demonstrated that the possession of two mouth-closing systems enabled grazing damselfishes to have a forceful and extremely fast bite. This combination challenges a major functional trade-off in fish jaw dynamics, as systems better suited for force transmission are usually less suited for speed transmission, and vice versa. The combination of grazing behavior, small and robust lower jaws (conferring high biting force), and an ultrafast bite is unusual within actinopterygians. These attributes and their associated performance seem to be required conditions to colonize the ecological niche of farming, that is, the maintenance of small filamentous algae crops serving as both food and storage.

Divergent evolutionary morphology of the axial skeleton as a potential key innovation in modern cetaceans.

Cetaceans represent the most diverse clade of extant marine tetrapods. Although the restructuring of oceans could have contributed to their diversity, other factors might also be involved. Similar to ichthyosaurs and sharks, variation of morphological traits could have promoted the colonization of new ecological niches and supported their diversification. By combining morphological data describing the axial skeleton of 73 cetacean species with phylogenetic comparative methods, we demonstrate that the vertebral morphology of cetaceans is associated with their habitat. All riverine and coastal species possess a small body size, lengthened vertebrae and a low vertebral count compared with open ocean species. Extant cetaceans have followed two distinct evolutionary pathways relative to their ecology. Whereas most offshore species such as baleen whales evolved towards an increased body size while retaining a low vertebral count, small oceanic dolphins underwent deep modifications of their axial skeleton with an extremely high number of short vertebrae. Our comparative analyses provide evidence these vertebral modifications have potentially operated as key innovations. These novelties contributed to their explosive radiation, resulting in an efficient swimming style that provides energetic advantages to small-sized species.

Staging and normal table of postembryonic development of the clownfish (Amphiprion ocellaris).

BACKGROUND: The clownfish Amphiprion ocellaris is one of the rare coral reef fish species that can be reared in aquaria. With relatively short embryonic and larval development, it could be used as a model species to study the impact of global changes such as temperature rise or anthropogenic threats (eg, pollution) on the postembryonic development at molecular and endocrinological levels. Establishing a developmental table allows us to standardize sampling for the scientific community willing to conduct experiments on this species on different areas: ecology, evolution, and developmental biology. RESULTS: Here, we describe the postembryonic developmental stages for the clownfish A. ocellaris from hatching to juvenile stages (30 days posthatching). We quantitatively followed the postembryonic growth and described qualitative traits: head, paired and unpaired fins, notochord flexion, and pigmentation changes. The occurrence of these changes over time allowed us to define seven stages, for which we provide precise descriptions. CONCLUSIONS: Our work gives an easy system to determine A. ocellaris postembryonic stages allowing, thus, to develop this species as a model species for coral reef fishes. In light of global warming, the access to the full postembryonic development stages of coral reef fish is important to determine stressors that can affect such processes.

Magic Traits in Magic Fish: Understanding Color Pattern Evolution Using Reef Fish.

Color patterns provide easy access to phenotypic diversity and allow the questioning of the adaptive value of traits or the constraints acting on phenotypic evolution. Reef fish offer a unique opportunity to address such questions because they are ecologically and phylogenetically diverse and have the largest variety of pigment cell types known in vertebrates. In addition to recent development of their genetic resources, reef fish also constitute experimental models that allow the discrimination of ecological, developmental, and evolutionary processes at work. Here, we emphasize how the study of color patterns in reef fish can be integrated in an Eco/Evo/Devo (ecological evolutionary developmental) perspective and we illustrate that such an approach can bring new insights on the evolution of complex phenotypes.

Diversification and functional evolution of reef fish feeding guilds.

A core eco-evolutionary aim is to better understand the factors driving the diversification of functions in ecosystems. Using phylogenetic, trophic, and functional information, we tested whether trophic habits (i.e. feeding guilds) affect lineage and functional diversification in two major radiations of reef fishes. Our results from wrasses (Labridae) and damselfishes (Pomacentridae) do not fully support the 'dead-end' hypothesis that specialisation leads to reduce speciation rates because the tempo of lineage diversification did not substantially vary among guilds in both fish families. Our findings also demonstrate a tight relationship between trophic habits and functional roles held by fish in reef ecosystems, which is not associated with a variation in the tempo of functional diversification among guilds. By illustrating the pivotal importance of the generalist feeding strategy during the evolutionary history of reef fishes, our study emphasises the role of this feeding guild as a reservoir for future diversity.

Genetic diversity mirrors trophic ecology in coral reef fish feeding guilds.

Genetic diversity is essential for species persistence because it provides the raw material for evolution. For marine organisms, short pelagic larval duration (PLD) and small population size are characteristics generally assumed to associate with low genetic diversity. The ecological diversity of organisms may also affect genetic diversity with an expected corollary that more restricted habitat and dietary requirements could lead to a reduced genetic diversity because of pronounced genetic structuring. Here, we tested whether groups of species with narrower trophic niches displayed lower genetic diversity than those with broader niches. In order to test those predictions, we used different trophic guilds (i.e., groups of species having similar trophic habits) of coral reef damselfishes in Moorea (French Polynesia) for which we determined their genetic diversity using restriction site-associated DNA sequencing (RADseq) and their trophic ecology with stomach contents and stable isotope data. We found that pelagic feeders- the guild picking zooplankton in the water column- exhibited the lowest genetic diversity despite having the longest PLD and the largest population size. This guild had also the lowest variation in habitat characteristics and dietary composition compared to benthic feeders (i.e., those mainly grazing on algae) and the intermediate group (i.e., those feeding on zooplankton, filamentous algae and small benthic invertebrates). Our findings highlight the association between trophic ecology and genetic diversity that should be more commonly investigated in population genetics.

Ontogenetic and phylogenetic simplification during white stripe evolution in clownfishes.

BACKGROUND: Biologists have long been fascinated by the striking diversity of complex color patterns in tropical reef fishes. However, the origins and evolution of this diversity are still poorly understood. Disentangling the evolution of simple color patterns offers the opportunity to dissect both ultimate and proximate causes underlying color diversity. RESULTS: Here, we study clownfishes, a tribe of 30 species within the Pomacentridae that displays a relatively simple color pattern made of zero to three vertical white stripes on a dark body background. Mapping the number of white stripes on the evolutionary tree of clownfishes reveals that their color pattern diversification results from successive caudal to rostral losses of stripes. Moreover, we demonstrate that stripes always appear with a rostral to caudal stereotyped sequence during larval to juvenile transition. Drug treatments (TAE 684) during this period leads to a dose-dependent loss of stripes, demonstrating that white stripes are made of iridophores and that these cells initiate the stripe formation. Surprisingly, juveniles of several species (e.g., Amphiprion frenatus) have supplementary stripes when compared to their respective adults. These stripes disappear caudo-rostrally during the juvenile phase leading to the definitive color pattern. Remarkably, the reduction of stripe number over ontogeny matches the sequences of stripe losses during evolution, showing that color pattern diversification among clownfish lineages results from changes in developmental processes. Finally, we reveal that the diversity of striped patterns plays a key role for species recognition. CONCLUSIONS: Overall, our findings illustrate how developmental, ecological, and social processes have shaped the diversification of color patterns during the radiation of an emblematic coral reef fish lineage.

Buccal venom gland associates with increased of diversification rate in the fang blenny fish Meiacanthus (Blenniidae; Teleostei).

At the macroevolutionary level, many mechanisms have been proposed to explain explosive species diversification. Among them morphological and/or physiological novelty is considered to have a great impact on the tempo and the mode of diversification. Meiacanthus is a genus of Blenniidae possessing a unique buccal venom gland at the base of an elongated canine tooth. This unusual trait has been hypothesized to aid escape from predation and thus potentially play an important role in their pattern of diversification. Here, we produce the first time-calibrated phylogeny of Blenniidae and we test the impact of two morphological novelties on their diversification, i.e. the presence of swim bladder and buccal venom gland, using various comparative methods. We found an increase in the tempo of lineage diversification at the root of the Meiacanthus clade, associated with the evolution of the buccal venom gland, but not the swim bladder. Neither morphological novelty was associated with the pattern of size disparification in blennies. Our results support the hypothesis that the buccal venom gland has contributed to the explosive diversification of Meiacanthus, but further analyses are needed to fully understand the factors sustaining this burst of speciation.

Body shape convergence driven by small size optimum in marine angelfishes.

Convergent evolution of small body size occurs across many vertebrate clades and may reflect an evolutionary response to shared selective pressures. However it remains unclear if other aspects of phenotype undergo convergent evolution in miniaturized lineages. Here we present a comparative analysis of body size and shape evolution in marine angelfishes (Pomacanthidae), a reef fish family characterized by repeated transitions to small body size. We ask if lineages that evolve small sizes show convergent evolution in body shape. Our results reveal that angelfish lineages evolved three different stable size optima with one corresponding to the group of pygmy angelfishes (Centropyge). Then, we test if the observed shifts in body size are associated with changes to new adaptive peaks in shape. Our data suggest that independent evolution to small size optima have induced repeated convergence upon deeper body and steeper head profile in Centropyge These traits may favour manoeuvrability and visual awareness in these cryptic species living among corals, illustrating that functional demands on small size may be related to habitat specialization and predator avoidance. The absence of shape convergence in large marine angelfishes also suggests that more severe requirements exist for small than for large size optima.

Size and shape variations of the bony components of sperm whale cochleae.

Several mass strandings of sperm whales occurred in the North Sea during January and February 2016. Twelve animals were necropsied and sampled around 48 h after their discovery on German coasts of Schleswig Holstein. The present study aims to explore the morphological variation of the primary sensory organ of sperm whales, the left and right auditory system, using high-resolution computerised tomography imaging. We performed a quantitative analysis of size and shape of cochleae using landmark-based geometric morphometrics to reveal inter-individual anatomical variations. A hierarchical cluster analysis based on thirty-one external morphometric characters classified these 12 individuals in two stranding clusters. A relative amount of shape variation could be attributable to geographical differences among stranding locations and clusters. Our geometric data allowed the discrimination of distinct bachelor schools among sperm whales that stranded on German coasts. We argue that the cochleae are individually shaped, varying greatly in dimensions and that the intra-specific variation observed in the morphology of the cochleae may partially reflect their affiliation to their bachelor school. There are increasing concerns about the impact of noise on cetaceans and describing the auditory periphery of odontocetes is a key conservation issue to further assess the effect of noise pollution.

Comparative Feeding Ecology of Cardinalfishes (Apogonidae) at Toliara Reef, Madagascar.

Bruno Frédérich, Loïc N. Michel, Esther Zaeytydt, Roger Lingofo Bolaya, Thierry Lavitra, Eric Parmentier, and Gilles Lepoint (2017) Despite their importance in coral reef ecosystem function and trophodynamics, the trophic ecology of nocturnal shes (e.g. Apogonidae, Holocentridae, Pempheridae) is by far less studied than diurnal ones. The Apogonidae (cardinal shes) include mostly carnivorous species and evidence of trophic niche partitioning among sympatric cardinal shes is still limited. The present study combines stomach contents and stable isotope analyses to investigate the feeding ecology of an assemblage of eight cardinal shes from the Great Reef of Toliara (SW Madagascar). δ13C and δ15N of shes ranged between -17.49‰ and -10.03‰ and between 6.28‰ and 10.74‰, respectively. Both stomach contents and stable isotopes showed that they feed on planktonic and benthic animal prey in various proportions. Previous studies were able to group apogonids in di erent trophic categories but such a discrimination is not obvious here. Large intra-speci c variation in the stomach contents and temporal variation in the relative contribution of prey to diet support that all apogonids should be considered as generalist, carnivorous shes. However the exploration of the isotopic space revealed a clear segregation of isotopic niches among species, suggesting a high level of resource partitioning within the assemblage. According to low inter-speci c variation in stomach content compositions, we argue that the di erences in isotopic niches could be driven by variation in foraging locations (i.e. microhabitat segregation) and physiology among species. Our temporal datasets demonstrate that the trophic niche partitioning among cardinal shes and the breadth of their isotopic niches are dynamic and change across time. Factors driving this temporal variation need to be investigated in further studies.

Triclosan exposure results in alterations of thyroid hormone status and retarded early development and metamorphosis in Cyprinodon variegatus.

Thyroid hormones are critically involved in somatic growth, development and metamorphosis of vertebrates. The structural similarity between thyroid hormones and triclosan, an antimicrobial compound widely employed in consumer personal care products, suggests triclosan can have adverse effects on the thyroid system. The sheepshead minnow, Cyprinodon variegatus, is now used in ecotoxicological studies that have recently begun to focus on potential disruption of the thyroid axis by endocrine disrupting compounds. Here, we investigate the in vivo effects of exposure to triclosan (20, 50, and 100µgL-1) on the thyroid system and the embryonic and larval development of C. variegatus. Triclosan exposure did not affect hatching success, but delayed hatching time by 6-13h compared to control embryos. Triclosan exposure affected the ontogenetic variations of whole body thyroid hormone concentrations during the larval phase. The T3 peak around 12-15 dph, described to be indicative for the metamorphosis climax in C. variegatus, was absent in triclosan-exposed larvae. Triclosan exposure did not produce any deformity or allometric repatterning, but a delayed development of 18-32h was observed. We conclude that the triclosan-induced disruption of the thyroid system delays in vivo the start of metamorphosis in our experimental model. We observed a global developmental delay of 24-45h, equivalent to 4-7% prolongation of the developmental time in C. variegatus. The costs of delayed metamorphosis can lead to reduction of juvenile fitness and could be a determining factor in the outcome of competitive interactions.

Non-reef environments impact the diversification of extant jacks, remoras and allies (Carangoidei, Percomorpha).

Various factors may impact the processes of diversification of a clade. In the marine realm, it has been shown that coral reef environments have promoted diversification in various fish groups. With the exception of requiem sharks, all the groups showing a higher level of diversity in reefs than in non-reef habitats have diets based predominantly on plankton, algae or benthic invertebrates. Here we explore the pattern of diversification of carangoid fishes, a clade that includes numerous piscivorous species (e.g. trevallies, jacks and dolphinfishes), using time-calibrated phylogenies as well as ecological and morphological data from both extant and fossil species. The study of carangoid morphospace suggests that reef environments played a role in their early radiation during the Eocene. However, contrary to the hypothesis of a reef-association-promoting effect, we show that habitat shifts to non-reef environments have increased the rates of morphological diversification (i.e. size and body shape) in extant carangoids. Piscivory did not have a major impact on the tempo of diversification of this group. Through the ecological radiation of carangoid fishes, we demonstrate that non-reef environments may sustain and promote processes of diversification of different marine fish groups, at least those including a large proportion of piscivorous species.

Modular diversification of the locomotor system in damselfishes (Pomacentridae).

As fish move and interact with their aquatic environment by swimming, small morphological variations of the locomotor system can have profound implications on fitness. Damselfishes (Pomacentridae) have inhabited coral reef ecosystems for more than 50 million years. As such, habitat preferences and behavior could significantly constrain the morphology and evolvability of the locomotor system. To test this hypothesis, we used phylogenetic comparative methods on morphometric, ecological and behavioral data. While body elongation represented the primary source of variation in the locomotor system of damselfishes, results also showed a diverse suite of morphological combinations between extreme morphologies. Results show clear associations between behavior, habitat preferences, and morphology, suggesting ecological constraints on shape diversification of the locomotor system. In addition, results indicate that the three modules of the locomotor system are weakly correlated, resulting in versatile and independent characters. These results suggest that Pomacentridae is shape may result from the interaction between (1) integrated parts of morphological variation that maintain overall swimming ability and (2) relatively independent parts of the morphology that facilitate adaptation and diversification.

Chemical spying in coral reef fish larvae at recruitment.

When fish larvae recruit back to a reef, chemical cues are often used to find suitable habitat or to find juvenile or adult conspecifics. We tested if the chemical information used by larvae was intentionally produced by juvenile and adult conspecifics already on the reef (communication process) or whether the cues used result from normal biochemical processes with no active involvement by conspecifics ("spying" behavior by larvae). Conspecific chemical cues attracted the majority of larvae (four out of the seven species tested); although while some species were equally attracted to cues from adults and juveniles (Chromis viridis, Apogon novemfasciatus), two exhibited greater sensitivity to adult cues (Pomacentrus pavo, Dascyllus aruanus). Our results indicate also that spying cues are those most commonly used by settling fishes (C. viridis, P. pavo, A. novemfasciatus). Only one species (D. aruanus) preferred the odour of conspecifics that had had visual contact with larvae (communication).

A morphological novelty for feeding and sound production in the yellowtail clownfish.

The yellowtail clownfish Amphiprion clarkii is able to close its mouth very quickly by means of the cerato-mandibular (c-md) ligament, a synapomorphic trait of Pomacentridae joining the hyoid bar to the medial part of the lower jaw. This fast closure induces tooth collision, thus producing sounds that the clownfish uses during agonistic behaviors. To investigate whether this rapid jaw movement is also used during feeding, we analyzed the kinematics of sound production and feeding. Sound production, feeding on live planktonic prey, and feeding on food attached to tweezers was filmed with a high-speed camera. Three kinds of kinematic patterns were detected and were associated with the two different types of food presented: one performed to catch planktonic prey (PP), and two (called B-1 and B-2) to bite attached food items. The kinematic pattern of B-2 is similar to that observed during sound production (SP) and the transection of the c-md ligament highlights that sound production and biting-2 motions are dependent on this morphological trait. Our data show that the c-md ligament in addition to its role in sound production allows duplication of the mouth-closing mechanism during feeding. This highlights the key role played by the c-md ligament in sound production and feeding on attached prey. J. Exp. Zool. 323A: 227-238, 2015. © 2015 Wiley Periodicals, Inc.