Multiple origins of the Juan Fernández kelpfish fauna and evidence for frequent and unidirectional dispersal of cirrhitoid fishes across the South Pacific

The challenging biogeography of the Juan Fernández Islands and Coast Range of central Chile explained by new models of East Pacific tectonics

Biogeographers have often been puzzled by several unusual features in the Juan Fernández Islands (JFI) biota. These include the very high endemism density, multiple endemics that are older than the current islands, close biogeographic affinities with the central and West Pacific, and affinities with the diverse Coast Range of central Chile. We review aspects of biogeography in the JFI and the Coast Range in light of recent geological studies. These have examined the mantle below the East Pacific and South America, and have produced radical, new ideas on tectonic history. A long-lived, intraoceanic archipelago ~9000 km long is now thought to have existed in the East Pacific (passing between the JFI hotspot and mainland Chile) until the mid-Cretaceous. At this time, South America, which was moving westward with the opening of the Atlantic, collided with the archipelago. The assumption that the JFI biota is no older than its current islands is questionable, as taxa would have survived on prior islands produced at the JFI hotspot. We propose a new interpretation of evolution in the region based on tectonics rather than on island age and incorporating the following factors: the newly described East Pacific Archipelago; a long history for the JFI hotspot; metapopulation dynamics, including metapopulation vicariance; and formation of the Humboldt Current in the Cretaceous. The model accounts for many distinctive features of the JFI and Coast Range biota.

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.

Reef Fish Diversity Across the Temperate South Pacific Ocean

Patterns of species richness and their structuring forces at multiple scales provide a critical context for research efforts focusing on ecology, evolution, and conservation. Diversity gradients have been demonstrated in tropical reef fish, but corresponding patterns and mechanisms remain poorly understood in temperate regions. We conducted hierarchical (spatially nested) sampling of temperate reef fish faunas across > 140 degrees of longitude in the eastern and western South Pacific Ocean. Our sampling efforts spanned five distinct provinces: the Southeast Australian Shelf (SAS), Northern and Southern New Zealand (N-SNZ), Juan Fernandez and Desventuradas Islands (JFD), and the Warm Temperate Southeastern Pacific (WTPA). We evaluated (i) spatial variation in patterns of species richness and abundance (using Chao 1 index), and distribution of functional diversity (using several functional attributes: max body size, trophic groups, feeding guilds, trophic level, habitat use, gregariousness, and activity patterns) and (ii) scale-dependencies in these patterns. Species richness declined from west to east across the temperate South Pacific, but this pattern was detectable only across larger spatial scales. A functional redundancy index was significantly higher in the western South Australian Shelf at multiple scales, revealing that species contribute in equivalent ways to an ecosystem function such that one species may substitute for another. We also detected that patterns of variation in functional diversity differed from patterns of variation in species richness, and were also dependent on the spatial scale of analysis. Lastly, we identified that species’ traits are not equally distributed among reef fish assemblages, where some provinces are characterized by a distinct functional component within their reef fish assemblages. Planktivorous and schooling species, for instance, dominated the assemblages in the eastern Pacific, which is characterized by higher primary productivity and steep bathymetric slopes favoring these traits. Demersal and pairing behavior traits dominated the reef fish assemblages in western Pacific provinces (SAS, SNZ). We conclude that combining the identifies and species’ traits allow us to disentangle historical, biogeographic and environmental factors that structure reef fish fauna.

DNA reconciles morphology and colouration in the drunk blenny genus Scartichthys (Teleostei: Blenniidae) and provides insights into their evolutionary history

The blenniids of the genus Scartichthys are one of the most common fishes of Central and South American Pacific coastal reefs. This being said, Scartichthys spp. remain difficult to identify in the field, and identification is particularly challenging across the c. 6000 km where three of the four currently accepted species are known to occur in sympatry. A reason for this is that the main taxonomic characters from traditional taxonomy are indeed elusive. In addition, at the same time, species can display multiple colour patterns in the field, depending on their ontogenetic stage, habitat association and reproductive behaviour. Overall, molecular characterization is warranted to help address these issues. In this study, the authors have used a novel approach to revise the genus by combining colouration, morphological and molecular data of representative specimens of the four currently valid species and seven described colour patterns. From this, the authors show that only three of the four species should be considered as valid; Scartichthys gigas (Steindachner, 1876), Scartichthys variolatus (Valenciennes, 1836) and Scartichthys viridis (Valenciennes, 1836), whereas Scartichthys crapulatus (Williams, 1990) should be synonymized with S. viridis. In the same way, the analyses in this study show that one of the colour patterns attributed so far only to S. gigas is characteristic of the juvenile stages of S. viridis. The time-calibrated phylogeny of this study shows that this genus is relatively young and that the estimated time of divergence between S. gigas and S. viridis is c. 1.71 Ma. In comparison, the Desventuradas and Juan Fernandez Islands endemic S. variolatus diverged c. 1.95 Ma. The results of this study help to clarify the taxonomy of Scartichthys.

Biogeography in Cellana (Patellogastropoda, Nacellidae) with Special Emphasis on the Relationships of Southern Hemisphere Oceanic Island Species

Oceanic islands lacking connections to other land are extremely isolated from sources of potential colonists and have acquired their biota mainly through dispersal from geographically distant areas. Hence, isolated island biota constitutes interesting models to infer biogeographical mechanisms of dispersal, colonization, differentiation, and speciation. Limpets of the genus Cellana (Nacellidae: Patellogastropoda) show limited dispersal capacity but are broadly distributed across the Indo-Pacific including many endemic species in isolated oceanic islands. Here, we examined main distributional patterns and geographic boundaries among Cellana lineages with special emphasis in the relationships of Southern Hemisphere oceanic islands species. Phylogenetic reconstructions based on mtDNA (COI) recognized three main clades in Cellana including taxa from different provinces of the Indo-Pacific. Clear genetic discontinuities characterize the biogeography of Cellana and several lineages are associated to particular areas of the Indo-Pacific supporting the low dispersal capacity of the genus across recognized biogeographical barriers in the region. However, evolutionary relationships within Cellana suggest that long-distance dispersal processes have been common in the history of the genus and probably associated to the origin of the species in Hawaii and Juan Fernández Archipelago. Therefore, the presence of Cellana species in geographically distant Southern Hemisphere oceanic islands, such as the Juan Fernández Archipelago, suggests that long-distance dispersal mediated by rafting may have played an important role in the biogeography of the genus.

Multiple colonizations lead to cryptic biodiversity in an island ecosystem: comparative phylogeography of anchialine shrimp species in the Ryukyu Archipelago, Japan

Archipelagos of the Indo-West Pacific are considered to be among the richest in the world in biodiversity, and phylogeographic studies generally support either the center of origin or the center of accumulation hypothesis to explain this pattern. To differentiate between these competing hypotheses for organisms from the Indo-West Pacific anchialine ecosystem, defined as coastal bodies of mixohaline water fluctuating with the tides but having no direct oceanic connections, we investigated the genetic variation, population structure, and evolutionary history of three caridean shrimp species (Antecaridina lauensis, Halocaridinides trigonophthalma, and Metabetaeus minutus) in the Ryukyu Archipelago, Japan. We used two mitochondrial genes--cytochrome c oxidase subunit I (COI) and large ribosomal subunit (16S-rDNA)--complemented with genetic examination of available specimens from the same or closely related species from the Indian and Pacific Oceans. In the Ryukyus, each species encompassed 2-3 divergent (9.52%-19.2% COI p-distance) lineages, each having significant population structure and varying geographic distributions. Phylogenetically, the A. lauensis and M. minutus lineages in the Ryukyus were more closely related to ones from outside the archipelago than to one another. These results, when interpreted in the context of Pacific oceanographic currents and geologic history of the Ryukyus, imply multiple colonizations of the archipelago by the three species, consistent with the center of accumulation hypothesis. While this study contributes toward understanding the biodiversity, ecology, and evolution of organisms in the Ryukyus and the Indo-West Pacific, it also has potential utility in establishing conservation strategies for anchialine fauna of the Pacific Basin in general.

Asymmetric dispersal of southern bull-kelp (Durvillaea antarctica) adults in coastal New Zealand: testing an oceanographic hypothesis

Coastal populations are often connected by unidirectional current systems, but the biological effects of such asymmetric oceanographic connectivity remain relatively unstudied. We used mtDNA analysis to determine the phylogeographic origins of beach-cast bull-kelp (Durvillaea antarctica) adults in the Canterbury Bight, a 180 km coastal region devoid of rocky-reef habitat in southern New Zealand. A multi-year, quantitative analysis supports the oceanographically derived hypothesis of asymmetric dispersal mediated by the north-flowing Southland Current. Specifically, 92% of beach-cast specimens examined had originated south of the Bight, many drifting north for hundreds of kilometres, and some traversing at least 500 km of ocean from subantarctic sources. In contrast, only 8% of specimens had dispersed south against the prevailing current, and these counter-current dispersers likely travelled relatively small distances (tens of kilometres). These data show that oceanographic connectivity models can provide robust estimates of passive biological dispersal, even for highly buoyant taxa. The results also indicate that there are no oceanographic barriers to kelp dispersal across the Canterbury Bight, indicating that other ecological factors explain the phylogeographic disjunction across this kelp-free zone. The large number of long-distance dispersal events detected suggests drifting macroalgae have potential to facilitate ongoing connectivity between otherwise isolated benthic populations.

Contemporary habitat discontinuity and historic glacial ice drive genetic divergence in Chilean kelp

BACKGROUND

South America's western coastline, extending in a near-straight line across some 35 latitudinal degrees, presents an elegant setting for assessing both contemporary and historic influences on cladogenesis in the marine environment. Southern bull-kelp (Durvillaea antarctica) has a broad distribution along much of the Chilean coast. This species represents an ideal model taxon for studies of coastal marine connectivity and of palaeoclimatic effects, as it grows only on exposed rocky coasts and is absent from beaches and ice-affected shores. We expected that, along the central Chilean coast, D. antarctica would show considerable phylogeographic structure as a consequence of the isolating effects of distance and habitat discontinuities. In contrast, we hypothesised that further south--throughout the region affected by the Patagonian Ice Sheet at the Last Glacial Maximum (LGM)--D. antarctica would show relatively little genetic structure, reflecting postglacial recolonisation.

RESULTS

Mitochondrial (COI) and chloroplast (rbcL) DNA analyses of D. antarctica from 24 Chilean localities (164 individuals) revealed two deeply divergent (4.5 - 6.1% for COI, 1.4% for rbcL) clades from the centre and south of the country, with contrasting levels and patterns of genetic structure. Among populations from central Chile (32 degrees-44 degrees S), substantial phylogeographic structure was evident across small spatial scales, and a significant isolation-by-distance effect was observed. Genetic disjunctions in this region appear to correspond to the presence of long beaches. In contrast to the genetic structure found among central Chilean populations, samples from the southern Chilean Patagonian region (49 degrees-56 degrees S) were genetically homogeneous and identical to a haplotype recently found throughout the subantarctic region.

CONCLUSIONS

Southern (Patagonian) Chile has been recolonised by D. antarctica relatively recently, probably since the LGM. The inferred trans-oceanic ancestry of these Patagonian populations supports the notion that D. antarctica is capable of long-distance dispersal via rafting. In contrast, further north in central Chile, the correspondence of genetic disjunctions in D. antarctica with long beaches indicates that habitat discontinuity drives genetic isolation among established kelp populations. We conclude that rafting facilitates colonisation of unoccupied shores, but has limited potential to enhance gene-flow among established populations. Broadly, this study demonstrates that some taxa may be considered to have either high or low dispersal potential across different temporal and geographic scales.

Insights into the evolutionary history of Indo-Pacific bloodfeeding terrestrial leeches (Hirudinida:Arhynchobdellida:Haemadipisdae)

Haemadipsidae is a clade of notorious bloodfeeding annelids adapted to tropical and sub-tropical rainforests found throughout the Indo-Pacific. This family traditionally includes duognathous (two-jawed) endemics, each placed in their own genus, from continental and volcanic islands including: Australia, Indonesia, Madagascar, Papua New Guinea, Philippines, Seychelles, and South Pacific islands, while trignathous (three-jawed) Tritetrabdella species and the speciose Haemadipsa are exclusive to the Indian subcontinent ranging into east and south-east Asia. One of the more compelling aspects of haemadipsids is their distribution on post-Gondwanan landmasses. In this study, the phylogenetic relationships, taxonomy and biogeographic patterns of Haemadipsidae were examined. Over 5 kb of sequence data from three genes (nuclear 18S rDNA and 28S rDNA and mitochondrial COI) for 37 haemadipsid exemplars, representing 12 of the 15 recognised genera, were analysed under the criteria of maximum parsimony and Bayesian inference. The results show that widespread duognathous species form a monophyletic group derived from trignathous ancestry and are sister to a new trignathous clade for Haemadipsidae. This phylogenetic hypothesis rejected Gondwanan vicariance as an explanation for the diversification of haemadipsids. Haemadipsidae is accepted as the formal name for these Indo-Pacific leeches. Whereas the subdivisions Haemadipsinae and Domanibdellinae are clarified, there is a need to establish a new subfamily, Tritetrabdellinae, for the newly identified trignathous clade that is sister to Domanibdellinae. This study provides a basis for continued elucidation of the evolutionary relationships and classification of these terrestrial annelids.

Signatures of seaway closures and founder dispersal in the phylogeny of a circumglobally distributed seahorse lineage

BACKGROUND

The importance of vicariance events on the establishment of phylogeographic patterns in the marine environment is well documented, and generally accepted as an important cause of cladogenesis. Founder dispersal (i.e. long-distance dispersal followed by founder effect speciation) is also frequently invoked as a cause of genetic divergence among lineages, but its role has long been challenged by vicariance biogeographers. Founder dispersal is likely to be common in species that colonize remote habitats by means of rafting (e.g. seahorses), as long-distance dispersal events are likely to be rare and subsequent additional recruitment from the source habitat is unlikely. In the present study, the relative importance of vicariance and founder dispersal as causes of cladogenesis in a circumglobally distributed seahorse lineage was investigated using molecular dating. A phylogeny was reconstructed using sequence data from mitochondrial and nuclear markers, and the well-documented closure of the Central American seaway was used as a primary calibration point to test whether other bifurcations in the phylogeny could also have been the result of vicariance events. The feasibility of three other vicariance events was explored: a) the closure of the Indonesian Seaway, resulting in sister lineages associated with the Indian Ocean and West Pacific, respectively; b) the closure of the Tethyan Seaway, resulting in sister lineages associated with the Indo-Pacific and Atlantic Ocean, respectively, and c) continental break-up during the Mesozoic followed by spreading of the Atlantic Ocean, resulting in pairs of lineages with amphi-Atlantic distribution patterns.

RESULTS

Comparisons of pairwise genetic distances among the seahorse species hypothesized to have diverged as a result of the closure of the Central American Seaway with those of published teleost sequences having the same distribution patterns show that the seahorses were among the last to diverge. This suggests that their cladogenesis was associated with the final closure of this seaway. Although two other divergence events in the phylogeny could potentially have arisen as a result of the closures of the Indonesian and Tethyan seaways, respectively, the timing of the majority of bifurcations in the phylogeny differed significantly from the dates of vicariance events suggested in the literature. Moreover, several divergence events that resulted in the same distribution patterns of lineages at different positions in the phylogeny did not occur contemporaneously. For that reason, they cannot be the result of the same vicariance events, a result that is independent of molecular dating.

CONCLUSION

Interpretations of the cladogenetic events in the seahorse phylogeny based purely on vicariance biogeographic hypotheses are problematic. We conclude that the evolution of the circumglobally distributed seahorse lineage was strongly influenced by founder dispersal, and suggest that this mode of speciation may be particularly important in marine organisms that lack a pelagic dispersal phase and instead disperse by means of rafting.