Historical factors that have shaped the evolution of tropical reef fishes: a review of phylogenies, biogeography, and remaining questions

A framework and review of evidence of the importance of coral reefs for marine birds in tropical ecosystems

As global heating and other anthropogenic influences alter tropical marine environments, it is unclear how marine bird populations will be impacted and whether their current roles in tropical marine ecosystems will change. Although marine birds roost and breed on tropical islands in large numbers, the direct trophic interactions between these birds and their prey across the tropics are poorly documented. We present a first framework for evaluating the dependence on and contributions of marine birds to tropical coral reef ecosystems and use it to examine the evidence for different kinds of interaction, focusing primarily on avian diets. We found 34 publications between 1967 and 2023 that presented a total of 111 data sets with enough detail for quantitative dietary analysis of tropical marine birds. Only two bird species out of 37 (5.4%) had diets of >50% coral reef fishes and only one, the Pacific Reef Egret, appeared to depend almost entirely on reef-based production. Marine birds are also prey for other marine organisms, but insufficient data are available for quantitative analysis. Evidence for indirect effects of birds in tropical marine environments is stronger than for direct dependence on coral reefs, particularly in relation to nutrient concentration and the fertilisation impacts of guano on corals. Dispersal of propagules (e.g. seeds, spores, invertebrate eggs) by bathing, drinking, resting or foraging birds is under-studied and poorly documented. Although the degradation of coral reefs appears unlikely to have a significant direct impact on food availability for most marine bird populations, indirect effects involving marine birds may be disrupted by global environmental change.

Genetic mechanism of body size variation in groupers: Insights from phylotranscriptomics

Animal body size variation is of particular interest in evolutionary biology, but the genetic basis remains largely unknown. Previous studies have shown the presence of two parallel evolutionary genetic clusters within the fish genus Epinephelus with evident divergence in body size, providing an excellent opportunity to investigate the genetic basis of body size variation in vertebrates. Herein, we performed phylotranscriptomic analysis and reconstructed the phylogeny of 13 epinephelids originating from the South China Sea. Two genetic clades with an estimated divergence time of approximately 15.4 million years ago were correlated with large and small body size, respectively. A total of 180 rapidly evolving genes and two positively selected genes were identified between the two groups. Functional enrichment analyses of these candidate genes revealed distinct enrichment categories between the two groups. These pathways and genes may play important roles in body size variation in groupers through complex regulatory networks. Based on our results, we speculate that the ancestors of the two divergent groups of groupers may have adapted to different environments through habitat selection, leading to genetic variations in metabolic patterns, organ development, and lifespan, resulting in body size divergence between the two locally adapted populations. These findings provide important insights into the genetic mechanisms underlying body size variation in groupers and species differentiation.

Blood meal identification reveals extremely broad host range and host-bias in a temporary ectoparasite of coral reef fishes

Appreciation for the role of cryptofauna in ecological systems has increased dramatically over the past decade. The impacts blood-feeding arthropods, such as ticks and mosquitos, have on terrestrial communities are the subject of hundreds of papers annually. However, blood-feeding arthropods have been largely ignored in marine environments. Gnathiid isopods, often referred to as "ticks of the sea", are temporary external parasites of fishes. They are found in all marine environments and have many consequential impacts on host fitness. Because they are highly mobile and only associated with their hosts while obtaining a blood meal, their broader trophic connections are difficult to discern. Conventional methods rely heavily on detecting gnathiids on wild-caught fishes. However, this approach typically yields few gnathiids and does not account for hosts that avoid capture. To overcome this limitation, we sequenced blood meals of free-living gnathiids collected in light traps to assess the host range and community-dependent exploitation of Caribbean gnathiid isopods. Using fish-specific COI (cox1) primers, sequencing individual blood meals from 1060 gnathiids resulted in the identification of 70 host fish species from 27 families. Comparisons of fish assemblages to blood meal identification frequencies at four collection sites indicated that fishes within the families Haemulidae (grunts) and Lutjanidae (snappers) were exploited more frequently than expected based on their biomass, and Labrid parrotfishes were exploited less frequently than expected. The broad host range along with the biased exploitation of diel-migratory species has important implications for the role gnathiid isopods play in Caribbean coral reef communities.

Widespread sympatry in a species-rich clade of marine fishes (Carangoidei)

A universal paradigm describing patterns of speciation across the tree of life has been debated for decades. In marine organisms, inferring patterns of speciation using contemporary and historical patterns of biogeography is challenging due to the deficiency of species-level phylogenies and information on species' distributions, as well as conflicting relationships between species' dispersal, range size and co-occurrence. Most research on global patterns of marine fish speciation and biogeography has focused on coral reef or pelagic species. Carangoidei is an ecologically important clade of marine fishes that use coral reef and pelagic environments. We used sequence capture of 1314 ultraconserved elements (UCEs) from 154 taxa to generate a time-calibrated phylogeny of Carangoidei and its parent clade, Carangiformes. Age-range correlation analyses of the geographical distributions and divergence times of sister species pairs reveal widespread sympatry, with 73% of sister species pairs exhibiting sympatric geographical distributions, regardless of node age. Most species pairs coexist across large portions of their ranges. We also observe greater disparity in body length and maximum depth between sympatric relative to allopatric sister species. These and other ecological or behavioural attributes probably facilitate sympatry among the most closely related carangoids.

Molecular phylogenetics reveals the evolutionary history of marine fishes (Actinopterygii) endemic to the subtropical islands of the Southwest Pacific

Remote oceanic islands of the Pacific host elevated levels of actinopterygian (ray-finned fishes) endemism. Characterizing the evolutionary histories of these endemics has provided insight into the generation and maintenance of marine biodiversity in many regions. The subtropical islands of Lord Howe, Norfolk, and Rangitāhua (Kermadec) in the Southwest Pacific are yet to be comprehensively studied. Here, we characterize the spatio-temporal diversification of marine fishes endemic to these Southwest Pacific islands by combining molecular phylogenies and the geographic distribution of species. We built Bayesian ultrametric trees based on open-access and newly generated sequences for five mitochondrial and ten nuclear loci, and using fossil data for time calibration. We present the most comprehensive phylogenies to date for marine ray-finned fish genera, comprising 34 species endemic to the islands, including the first phylogenetic placements for 11 endemics. Overall, our topologies confirm the species status of all endemics, including three undescribed taxa. Our phylogenies highlight the predominant affinity of these endemics with the Australian fish fauna (53%), followed by the East Pacific (15%), and individual cases where the closest sister taxon of our endemic is found in the Northwest Pacific and wider Indo-Pacific. Nonetheless, for a quarter of our focal endemics, their geographic affinity remains unresolved due to sampling gaps within their genera. Our divergence time estimates reveal that the majority of endemic lineages (67.6%) diverged after the emergence of Lord Howe (6.92 Ma), the oldest subtropical island in the Southwest Pacific, suggesting that these islands have promoted diversification. However, divergence ages of some endemics pre-date the emergence of the islands, suggesting they may have originated outside of these islands, or, in some cases, ages may be overestimated due to unsampled taxa. To fully understand the role of the Southwest Pacific subtropical islands as a 'cradle' for diversification, our study advocates for further regional surveys focused on tissue collection for DNA analysis.

Biogeography of the coastal fishes of the Socotra Archipelago: Challenging current ecoregional concepts

The Socotra Archipelago, located in the eastern Gulf of Aden, has a unique marine environment, which combines tropical and ‘pseudo-temperate’ elements. An updated species inventory recently considered its coastal fish diversity the highest among Arabian ecoregions, necessitating to re-assess the ichthyogeographic position of the island group. The main aim of this study is to describe the distributional biogeography of its coastal fish fauna in relation to contemporary ichthyogeographic and ecoregional concepts. Inferences are drawn with regard to the marine biogeographic arrangement and ecoregional partitioning of the Arabian region. The main datasets comprise eight and twenty selected families including 404 and 898 species, respectively, from Arabian ecoregions. The Socotra Archipelago has close affinities to a putative ecoregion in the eastern Gulf of Aden that extends to southern Oman. It is more closely related to the Arabian Sea coast of Oman than to ecoregions in the Red Sea and a putative ecoregion in the western Gulf of Aden. The Gulf of Aden does not represent a consistent ecoregion in ichthyogeographic terms, because its eastern and western parts are less closely related to one another than to other ecoregions. The Socotra Archipelago and the eastern Gulf of Aden should therefore not be assigned to a joined province with Red Sea ecoregions. The coastal fish faunas of the southern Red Sea have close affinities with those of the western Gulf of Aden. The Arabian/Persian Gulf is least related to the other Arabian ecoregions. The authors posit the Socotra Archipelago as a distinct ecoregion, either on its own or in combination with affiliated mainland areas. This best reflects the ichthyogeographic data and the exceptionally high levels of fish and overall marine diversity. Two alternative ecoregional delineations are proposed, serving as working hypotheses for onward research.

Diversification Rate is Associated with Rate of Molecular Evolution in Ray-Finned Fish (Actinopterygii)

Understanding the factors that drive diversification of taxa across the tree of life is a key focus of macroevolutionary research. While the effects of life history, ecology, climate and geography on diversity have been studied for many taxa, the relationship between molecular evolution and diversification has received less attention. However, correlations between rates of molecular evolution and diversification rate have been detected in a range of taxa, including reptiles, plants and birds. A correlation between rates of molecular evolution and diversification rate is a prediction of several evolutionary theories, including the evolutionary speed hypothesis which links variation in mutation rates to differences in speciation rates. If it is widespread, such correlations could also have significant practical impacts, if they are not adequately accounted for in phylogenetic inference of evolutionary rates and timescales. Ray-finned fish (Actinopterygii) offer a prime target to test for this relationship due to their extreme variation in clade size suggesting a wide range of diversification rates. We employ both a sister-pairs approach and a whole-tree approach to test for correlations between substitution rate and net diversification. We also collect life history and ecological trait data and account for potential confounding factors including body size, latitude, max depth and reef association. We find evidence to support a relationship between diversification and synonymous rates of nuclear evolution across two published backbone phylogenies, as well as weak evidence for a relationship between mitochondrial nonsynonymous rates and diversification at the genus level.

Historical biogeographical analysis of the Udoteaceae (Bryopsidales, Chlorophyta) elucidates origins of high species diversity in the Central Indo-Pacific, Western Indian Ocean and Greater Caribbean regions

There is a growing interest in elucidating the biogeographical processes underlying biodiversity patterns of seaweeds, with recent studies largely focusing on red and brown macroalgae. This study focuses on the siphonous green algal family Udoteaceae, which is diverse and globally distributed in tropical to warm-temperate seas, and includes species that form important components of tropical reefs. We explored the historical processes that have shaped current biodiversity patterns in the family by analyzing a comprehensive dataset of 568 specimens sampled across its geographical range, and including 45 species, corresponding to 59% of the known diversity. Historical biogeographical analysis was based on a three-locus time-calibrated phylogeny, and probabilistic modeling of geographical range evolution. Many species were found to have restricted ranges, indicative of low dispersal capacity. Our analysis points toward a Western Tethys origin and early diversification of the Udoteaceae in the Triassic period. Three centers of diversity were identified, which are, in order of highest species richness, the Central Indo-Pacific, the Western Indian Ocean, and the Greater Caribbean. Different drivers have likely played a role in shaping these diversity centres. Species richness in the Central Indo-Pacific likely resulted from speciation within the region, as well as recolonization from neighbouring regions, and overlap of some wider ranged species, corroborating the "biodiversity feedback" model. Species richness in the Western Indian Ocean can be explained by ancient and more recent diversification within the region, and dispersal from the Central Indo-Pacific. The Greater Caribbean region was colonized more recently, followed by diversification within the region.

Rapid embryonic development supports the early onset of gill functions in two coral reef damselfishes

The gill is one of the most important organs for growth and survival of fishes. Early life stages in coral reef fishes often exhibit extreme physiological and demographic characteristics that are linked to well-established respiratory and ionoregulatory processes. However, gill development and function in coral reef fishes is not well understood. Therefore, we investigated gill morphology, oxygen uptake and ionoregulatory systems throughout embryogenesis in two coral reef damselfishes, Acanthochromis polyacanthus and Amphiprion melanopus (Pomacentridae). In both species, we found key gill structures to develop rapidly early in the embryonic phase. Ionoregulatory cells appear on gill filaments 3-4 days post-fertilization and increase in density, whilst disappearing or shrinking in cutaneous locations. Primary respiratory tissue (lamellae) appears 5-7 days post-fertilization, coinciding with a peak in oxygen uptake rates of the developing embryos. Oxygen uptake was unaffected by phenylhydrazine across all ages (pre-hatching), indicating that haemoglobin is not yet required for oxygen uptake. This suggests that gills have limited contribution to respiratory functions during embryonic development, at least until hatching. Rapid gill development in damselfishes, when compared with that in most previously investigated fishes, may reflect preparations for a high-performance, challenging lifestyle on tropical reefs, but may also make reef fishes more vulnerable to anthropogenic stressors.

Coral reef fishes reveal strong divergence in the prevalence of traits along the global diversity gradient

Coral reefs are experiencing declines due to climate change and local human impacts. While at a local scale these impacts induce biodiversity loss and shifts in community structure, previous biogeographical analyses recorded consistent taxonomic structure of fish communities across global coral reefs. This suggests that regional communities represent a random subset of the global species and traits pool, whatever their species richness. Using distributional data on 3586 fish species and latest advances in species distribution models, we show marked gradients in the prevalence of size classes and diet categories across the biodiversity gradient. This divergence in trait structure is best explained by reef isolation during past unfavourable climatic conditions, with large and piscivore fishes better represented in isolated areas. These results suggest the risk of a global community re-organization if the ongoing climate-induced reef fragmentation is not halted.

Influence of historical changes in tropical reef habitat on the diversification of coral reef fishes

Past environmental changes are expected to have profoundly impacted diversity dynamics through time. While some previous studies showed an association between past climate changes or tectonic events and important shifts in lineage diversification, it is only recently that past environmental changes have been explicitly integrated in diversification models to test their influence on diversification rates. Here, we used a global reconstruction of tropical reef habitat dynamics during the Cenozoic and phylogenetic diversification models to test the influence of (i) major geological events, (ii) reef habitat fragmentation and (iii) reef area on the diversification of 9 major clades of tropical reef fish (Acanthuridae, Balistoidea, Carangoidea, Chaetodontidae, Haemulinae, Holocentridae, Labridae, Pomacentridae and Sparidae). The diversification models revealed a weak association between paleo-habitat changes and diversification dynamics. Specifically, the fragmentation of tropical reef habitats over the Cenozoic was found to be a driver of tropical reef fish diversification for 2 clades. However, overall, our approach did not allow the identification of striking associations between diversification dynamics and paleo-habitat fragmentation in contrast with theoretical model's predictions.

Congruent trophic pathways underpin global coral reef food webs

Ecological interactions uphold ecosystem structure and functioning. However, as species richness increases, the number of possible interactions rises exponentially. More than 6,000 species of coral reef fishes exist across the world's tropical oceans, resulting in an almost innumerable array of possible trophic interactions. Distilling general patterns in these interactions across different bioregions stands to improve our understanding of the processes that govern coral reef functioning. Here, we show that across bioregions, tropical coral reef food webs exhibit a remarkable congruence in their trophic interactions. Specifically, by compiling and investigating the structure of six coral reef food webs across distinct bioregions, we show that when accounting for consumer size and resource availability, these food webs share more trophic interactions than expected by chance. In addition, coral reef food webs are dominated by dietary specialists, which makes trophic pathways vulnerable to biodiversity loss. Prey partitioning among these specialists is geographically consistent, and this pattern intensifies when weak interactions are disregarded. Our results suggest that energy flows through coral reef communities along broadly comparable trophic pathways. Yet, these critical pathways are maintained by species with narrow, specialized diets, which threatens the existence of coral reef functioning in the face of biodiversity loss.

The largest known cowrie and the iterative evolution of giant cypraeid gastropods

Based on the fossil record, we explore the macroevolutionary relationship between species richness and gigantism in cowries (Cypraeidae), the best-studied family of gastropods, with a global diversity distribution that parallels that of tropical corals, mangroves and seagrasses. We introduce Vicetia bizzottoi sp. nov. based on a Priabonian fossil found in northeastern Italy, the largest documented cowrie found so far and the youngest of a lineage of Eocene Gisortiinae species. The Gisortiinae stratigraphic record in western Europe indicates that species selection favoured large size and armouring of the shell. Palaeoecology and per-stage species richness suggest that gigantism occurred in peripheral habitats with respect to diversity hotspots, where smaller species were favoured. The Eocene–Oligocene boundary was marked by a turnover and the Chattian global warming favoured small-sized species of derived clades. Species selection leading to gigantism is further documented in Miocene lineages of Zoila and Umbilia, in the southern hemisphere, two extant genera distributed at the periphery of modern diversity hotspots, suggesting that the negative relationship between size and diversity is a recurring pattern in the evolutionary history of cowries. This palaeontological evidence is projected onto the existing hypotheses that explain analogous biogeographic patterns in various other taxa. Likewise, body size-species richness negative relationship was possibly driven in cowries by physiological, ecological and life history constraints.

The Effects of Ecological Traits on the Rate of Molecular Evolution in Ray-Finned Fishes: A Multivariable Approach

Myriad environmental and biological traits have been investigated for their roles in influencing the rate of molecular evolution across various taxonomic groups. However, most studies have focused on a single trait, while controlling for additional factors in an informal way, generally by excluding taxa. This study utilized a dataset of cytochrome c oxidase subunit I (COI) barcode sequences from over 7000 ray-finned fish species to test the effects of 27 traits on molecular evolutionary rates. Environmental traits such as temperature were considered, as were traits associated with effective population size including body size and age at maturity. It was hypothesized that these traits would demonstrate significant correlations with substitution rate in a multivariable analysis due to their associations with mutation and fixation rates, respectively. A bioinformatics pipeline was developed to assemble and analyze sequence data retrieved from the Barcode of Life Data System (BOLD) and trait data obtained from FishBase. For use in phylogenetic regression analyses, a maximum likelihood tree was constructed from the COI sequence data using a multi-gene backbone constraint tree covering 71% of the species. A variable selection method that included both single- and multivariable analyses was used to identify traits that contribute to rate heterogeneity estimated from different codon positions. Our analyses revealed that molecular rates associated most significantly with latitude, body size, and habitat type. Overall, this study presents a novel and systematic approach for integrative data assembly and variable selection methodology in a phylogenetic framework.

Ice ages and butterflyfishes: Phylogenomics elucidates the ecological and evolutionary history of reef fishes in an endemism hotspot

For tropical marine species, hotspots of endemism occur in peripheral areas furthest from the center of diversity, but the evolutionary processes that lead to their origin remain elusive. We test several hypotheses related to the evolution of peripheral endemics by sequencing ultraconserved element (UCE) loci to produce a genome-scale phylogeny of 47 butterflyfish species (family Chaetodontidae) that includes all shallow water butterflyfish from the coastal waters of the Arabian Peninsula (i.e., Red Sea to Arabian Gulf) and their close relatives. Bayesian tree building methods produced a well-resolved phylogeny that elucidated the origins of butterflyfishes in this hotspots of endemism. We show that UCEs, often used to resolve deep evolutionary relationships, represent an important tool to assess the mechanisms underlying recently diverged taxa. Our analyses indicate that unique environmental conditions in the coastal waters of the Arabian Peninsula probably contributed to the formation of endemic butterflyfishes. Older endemic species are also associated with narrow versus broad depth ranges, suggesting that adaptation to deeper coral reefs in this region occurred only recently (<1.75 Ma). Even though deep reef environments were drastically reduced during the extreme low sea level stands of glacial ages, shallow reefs persisted, and as such there was no evidence supporting mass extirpation of fauna in this region.

Explaining the ocean's richest biodiversity hotspot and global patterns of fish diversity

For most marine organisms, species richness peaks in the Central Indo-Pacific region and declines longitudinally, a striking pattern that remains poorly understood. Here, we used phylogenetic approaches to address the causes of richness patterns among global marine regions, comparing the relative importance of colonization time, number of colonization events, and diversification rates (speciation minus extinction). We estimated regional richness using distributional data for almost all percomorph fishes (17 435 species total, including approximately 72% of all marine fishes and approximately 33% of all freshwater fishes). The high diversity of the Central Indo-Pacific was explained by its colonization by many lineages 5.3-34 million years ago. These relatively old colonizations allowed more time for richness to build up through in situ diversification compared to other warm-marine regions. Surprisingly, diversification rates were decoupled from marine richness patterns, with clades in low-richness cold-marine habitats having the highest rates. Unlike marine richness, freshwater diversity was largely derived from a few ancient colonizations, coupled with high diversification rates. Our results are congruent with the geological history of the marine tropics, and thus may apply to many other organisms. Beyond marine biogeography, we add to the growing number of cases where colonization and time-for-speciation explain large-scale richness patterns instead of diversification rates.

Geography and island geomorphology shape fish assemblage structure on isolated coral reef systems

We quantify the relative importance of multi-scale drivers of reef fish assemblage structure on isolated coral reefs at the intersection of the Indian and Indo-Pacific biogeographical provinces. Large (>30 cm), functionally-important and commonly targeted species of fish, were surveyed on the outer reef crest/front at 38 coral reef sites spread across three oceanic coral reef systems (i.e. Christmas Island, Cocos (Keeling) Islands and the Rowley Shoals), in the tropical Indian Ocean (c. 1.126 x 106 km2). The effects of coral cover, exposure, fishing pressure, lagoon size and geographical context, on observed patterns of fish assemblage structure were modelled using Multivariate Regression Trees. Reef fish assemblages were clearly separated in space with geographical location explaining ~53 % of the observed variation. Lagoon size, within each isolated reef system was an equally effective proxy for explaining fish assemblage structure. Among local-scale variables, 'distance from port', a proxy for the influence of fishing, explained 5.2% of total variation and separated the four most isolated reefs from Cocos (Keeling) Island, from reefs with closer boating access. Other factors were not significant. Major divisions in assemblage structure were driven by sister taxa that displayed little geographical overlap between reef systems and low abundances of several species on Christmas Island corresponding to small lagoon habitats. Exclusion of geographical context from the analysis resulted in local processes explaining 47.3% of the variation, highlighting the importance of controlling for spatial correlation to understand the drivers of fish assemblage structure. Our results suggest reef fish assemblage structure on remote coral reef systems in the tropical eastern Indian Ocean reflects a biogeographical legacy of isolation between Indian and Pacific fish faunas and geomorphological variation within the region, more than local fishing pressure or reef condition. Our findings re-emphasise the importance that historical processes play in structuring contemporary biotic communities.

Variation in social systems within Chaetodon butterflyfishes, with special reference to pair bonding

For many animals, affiliative relationships such as pair bonds form the foundation of society and are highly adaptive. Animal systems amenable for comparatively studying pair bonding are important for identifying underlying biological mechanisms, but mostly exist in mammals. Better establishing fish systems will enable comparison of pair bonding mechanisms across taxonomically distant lineages that may reveal general underlying mechanistic principles. We examined the utility of wild butterflyfishes (f: Chaetodontidae; g: Chaetodon) for comparatively studying pair bonding. Using stochastic character mapping, we provide the first analysis of the evolutionary history of butterflyfish sociality, revealing that pairing is ancestral, with at least seven independent transitions to gregarious grouping and solitary behavior since the late Miocene. We then formally verified social systems in six sympatric and wide-spread species representing a clade with one ancestrally reconstructed transition from paired to solitary grouping at Lizard Island, Australia. In situ observations of the size, selective affiliation and aggression, fidelity, and sex composition of social groups confirmed that Chaetodon baronessa, C. lunulatus, and C. vagabundus are predominantly pair bonding, whereas C. rainfordi, C. plebeius, and C. trifascialis are predominantly solitary. Even in the predominantly pair bonding species, C. lunulatus, a proportion of adults (15%) are solitary. Importantly, inter- and intra-specific differences in social systems do not co-vary with other previously established attributes, including parental care. Hence, the proposed butterflyfish populations are promising for inter- and intra-species comparative analyses of pair bonding and its mechanistic underpinnings. Avenues for further developing the system are proposed, including determining whether the aforementioned utility of these species applies across their geographic disruptions.

The origin and evolution of coral species richness in a marine biodiversity hotspot

The Coral Triangle (CT) region of the Indo-Pacific realm harbors an extraordinary number of species, with richness decreasing away from this biodiversity hotspot. Despite multiple competing hypotheses, the dynamics underlying this regional diversity pattern remain poorly understood. Here, we use a time-calibrated evolutionary tree of living reef coral species, their current geographic ranges, and model-based estimates of regional rates of speciation, extinction, and geographic range shifts to show that origination rates within the CT are lower than in surrounding regions, a result inconsistent with the long-standing center of origin hypothesis. Furthermore, endemism of coral species in the CT is low, and the CT endemics are older than relatives found outside this region. Overall, our model results suggest that the high diversity of reef corals in the CT is largely due to range expansions into this region of species that evolved elsewhere. These findings strongly support the notion that geographic range shifts play a critical role in generating species diversity gradients. They also show that preserving the processes that gave rise to the striking diversity of corals in the CT requires protecting not just reefs within the hotspot, but also those in the surrounding areas.

†Sorbinicharax verraesi: An unexpected case of a benthic fish outside Acanthomorpha in the Upper Cretaceous of the Tethyan Sea

†Sorbinicharax verraesi is a marine teleostean fish from the Upper Cretaceous of Nardò (Italy). It was first attributed to the otophysan order Characiformes, which represents potential evidence for the controversial marine origin of the clade. Through a review of all the available material, we demonstrate that this species is not an otophysan since it lacks key structures that would allow for its inclusion in this group. †Sorbinicharax has a body shape that recalls ground fishes classically assigned to Acanthomorpha. However, no unambiguous feature allows us to relate it to this clade. In fact, the presence of cellular bony tissue supports its exclusion from Eurypterygii. Since no feature permits the definitive attribution of †Sorbinicharax to any teleost group, it remains as Teleostei incertae sedis. We infer that the morphology of †Sorbinicharax indicates a benthic ecology. It displays: an anteriorly wide body with enlarged ribs; large pectoral fins, while anal and dorsal fins are reduced; a large head measuring ¼ of the total body length; and a mouth opening dorsally in a high position. Such morphology was so far undescribed in Nardo. It is surprisingly displayed by a non-eurypterygian teleost fish which means by a fish which does not belong to the clades that diversify since the upper Cretaceous and include the extant families that show ground ecomorphologies.

Phylogenetic perspectives on reef fish functional traits

Functional traits have been fundamental to the evolution and diversification of entire fish lineages on coral reefs. Yet their relationship with the processes promoting speciation, extinction and the filtering of local species pools remains unclear. We review the current literature exploring the evolution of diet, body size, water column use and geographic range size in reef-associated fishes. Using published and new data, we mapped functional traits on to published phylogenetic trees to uncover evolutionary patterns that have led to the current functional diversity of fishes on coral reefs. When examining reconstructed patterns for diet and feeding mode, we found examples of independent transitions to planktivory across different reef fish families. Such transitions and associated morphological alterations may represent cases in which ecological opportunity for the exploitation of different resources drives speciation and adaptation. In terms of body size, reconstructions showed that both large and small sizes appear multiple times within clades of mid-sized fishes and that extreme body sizes have arisen mostly in the last 10 million years (Myr). The reconstruction of range size revealed many cases of disparate range sizes among sister species. Such range size disparity highlights potential vicariant processes through isolation in peripheral locations. When accounting for peripheral speciation processes in sister pairs, we found a significant relationship between labrid range size and lineage age. The diversity and evolution of traits within lineages is influenced by trait-environment interactions as well as by species and trait-trait interactions, where the presence of a given trait may trigger the development of related traits or behaviours. Our effort to assess the evolution of functional diversity across reef fish clades adds to the burgeoning research focusing on the evolutionary and ecological roles of functional traits. We argue that the combination of a phylogenetic and a functional approach will improve the understanding of the mechanisms of species assembly in extraordinarily rich coral reef communities.