Avian Island Radiations Shed Light on the Dynamics of Adaptive and Nonadaptive Radiation.

Understanding the mechanisms underlying species formation and differentiation is a central goal of evolutionary biology and a formidable challenge. This understanding can provide valuable insights into the origins of the astonishing diversity of organisms living on our planet. Avian evolutionary radiations on islands have long fascinated biologists as they provide the ideal variation to study the ecological and evolutionary forces operating on the continuum between incipient lineages to complete speciation. In this review, we summarize the key insights gained from decades of research on adaptive and nonadaptive radiations of both extant and extinct insular bird species. We present a new comprehensive global list of potential avian radiations on oceanic islands, based on published island species checklists, taxonomic studies, and phylogenetic analyses. We demonstrate that our understanding of evolutionary processes is being greatly enhanced through the use of genomic tools. However, to advance the field, it is critical to complement this information with a solid understanding of the ecological and behavioral traits of both extinct and extant avian island species.

Genetic data from the extinct giant rat from Tenerife (Canary Islands) points to a recent divergence from mainland relatives.

Evolution of vertebrate endemics in oceanic islands follows a predictable pattern, known as the island rule, according to which gigantism arises in originally small-sized species and dwarfism in large ones. Species of extinct insular giant rodents are known from all over the world. In the Canary Islands, two examples of giant rats, †Canariomys bravoi and †Canariomys tamarani, endemic to Tenerife and Gran Canaria, respectively, disappeared soon after human settlement. The highly derived morphological features of these insular endemic rodents hamper the reconstruction of their evolutionary histories. We have retrieved partial nuclear and mitochondrial data from †C. bravoi and used this information to explore its evolutionary affinities. The resulting dated phylogeny confidently places †C. bravoi within the African grass rat clade (Arvicanthis niloticus). The estimated divergence time, 650 000 years ago (95% higher posterior densities: 373 000-944 000), points toward an island colonization during the Günz-Mindel interglacial stage. †Canariomys bravoi ancestors would have reached the island via passive rafting and then underwent a yearly increase of mean body mass calculated between 0.0015 g and 0.0023 g; this corresponds to fast evolutionary rates (in darwins (d), ranging from 7.09 d to 2.78 d) that are well above those observed for non-insular mammals.

Rallus nanus nomen novum: a replacement name for Rallus minutus Alcover et al. 2015.

In a recent paper, we described five new species of rails from the Macaronesian islands (Alcover et al., 2015). We proposed the name of Rallus minutus to designate the São Jorge rail. One day after its publication, Fred Ruhe (via e-mail) pointed out to us that the name was preoccupied, making Rallus minutus Alcover, Pieper, Pereira & Rando 2015 a primary homonym, which in turn makes it permanently invalid.

Five new extinct species of rails (Aves: Gruiformes: Rallidae) from the Macaronesian Islands (North Atlantic Ocean).

Five new species of recently extinct rails from two Macaronesian archipelagoes (Madeira and Azores) are described. All the species are smaller in size than their presumed ancestor, the European rail Rallus aquaticus. Two species inhabited the Madeira archipelago: (1) Rallus lowei n. sp., the stouter of the species described herein, was a flightless rail with a robust tarsometatarsus and reduced wings that lived on Madeira Island; (2) Rallus adolfocaesaris n. sp., a flightless and more gracile species than its Madeiran counterpart, inhabited Porto Santo. So far, six Azorean islands have been paleontologically explored, and the remains of fossil rails have been found on all of them. Here we formally describe the best-preserved remains from three islands (Pico, São Miguel and São Jorge): (1) Rallus montivagorum n. sp., a rail smaller than R. aquaticus with a somewhat reduced flying capability, inhabited Pico; (2) Rallus carvaoensis n. sp., a small flightless rail with short and stout legs and a bill apparently more curved than in R. aquaticus, was restricted to São Miguel; (3) Rallus minutus n. sp., a very small (approaching Atlantisia rogersi in size) flightless rail with a shortened robust tarsometatarsus, lived in São Jorge. We note also the presence of rail fossils on three other Azorean islands (Terceira, Graciosa and Santa Maria). In addition, we describe an extraordinarily complete fossil of an unnamed Rallus preserved in silica from the locality of Algar do Carvão on Terceira.

Radiocarbon evidence for the presence of mice on Madeira Island (North Atlantic) one millennium ago.

Owing to the catastrophic extinction events that occurred following the Holocene arrival of alien species, extant oceanic island biotas are a mixture of recently incorporated alien fauna and remnants of the original fauna. Knowledge of the Late Quaternary pristine island faunas and a reliable chronology of the earliest presence of alien species on each archipelago are critical in understanding the magnitude and tempo of Quaternary island extinctions. Until now, two successive waves of human arrivals have been identified in the North Atlantic Macaronesian archipelagos (Azores, Madeira, Selvagens, Canary and Cape Verde Islands): 'aboriginal', which is limited to the Canary Islands around two millennia ago, and 'colonial', from the fourteenth century onwards. New surveys in Ponta de São Lourenço (Madeira Island) have allowed us to obtain and date ancient bones of mice. The date obtained (1033 ± 28 BP) documents the earliest evidence for the presence of mice on the island. This date extends the time frame in which the most significant ecological changes occurred on the island. It also suggests that humans could have reached Madeira before 1036 cal AD, around four centuries before Portugal officially took possession of the island.

Population connectivity buffers genetic diversity loss in a seabird.

BACKGROUND: Ancient DNA has revolutionized conservation genetic studies as it allows monitoring of the genetic variability of species through time and predicting the impact of ecosystems' threats on future population dynamics and viability. Meanwhile, the consequences of anthropogenic activities and climate change to island faunas, particularly seabirds, remain largely unknown. In this study, we examined temporal changes in the genetic diversity of a threatened seabird, the Cory's shearwater (Calonectris borealis). FINDINGS: We analysed the mitochondrial DNA control region of ancient bone samples from the late-Holocene retrieved from the Canary archipelago (NE Atlantic) together with modern DNA sequences representative of the entire breeding range of the species. Our results show high levels of ancient genetic diversity in the Canaries comparable to that of the extant population. The temporal haplotype network further revealed rare but recurrent long-distance dispersal between ocean basins. The Bayesian demographic analyses reveal both regional and local population size expansion events, and this is in spite of the demographic decline experienced by the species over the last millennia. CONCLUSIONS: Our findings suggest that population connectivity of the species has acted as a buffer of genetic losses and illustrate the use of ancient DNA to uncover such cryptic genetic events.

A new species of extinct scops owl (Aves: Strigiformes: Strigidae: Otus) from São Miguel Island (Azores Archipelago, North Atlantic Ocean).

The extinct São Miguel Scops Owl Otusfrutuosoi n. sp. is described from fossil bones found in Gruta de Água de Pau, a volcanic tube in São Miguel Island (Azores Archipelago, North Atlantic Ocean). It is the first extinct bird described from the Azores and, after the Madeiran Scops Owl (O. mauli Rando, Pieper, Alcover & Olson 2012a), the second extinct species of Strigiformes known in Macaronesia. The forelimb elements of the new taxon are shorter, the hindlimb elements are longer, and the pelvis is shorter and broader than in the Eurasian Scops Owl (O. scops Linnaeus). The new species differs from O. mauli in the smaller size of many of its bones, especially the ulna and tibiotarsus. Its measurements (estimated weight, wing area, and wing loading, and the ratio of humerus + ulna + carpometacarpus length/femur length) indicate weak powers of flight and ground-dwelling habits. The latest occurrence of the new species, as evidenced by a radiocarbon date of 1970 ± 40 BP from bone collagen, indicates a Late Holocene extinction event subsequent to 49 cal BC, and was probably linked to human arrival and subsequent habitat alterations.

Paleogenetic analyses reveal unsuspected phylogenetic affinities between mice and the extinct Malpaisomys insularis, an endemic rodent of the Canaries.

BACKGROUND: The lava mouse, Malpaisomys insularis, was endemic to the Eastern Canary islands and became extinct at the beginning of the 14(th) century when the Europeans reached the archipelago. Studies to determine Malpaisomys' phylogenetic affinities, based on morphological characters, remained inconclusive because morphological changes experienced by this insular rodent make phylogenetic investigations a real challenge. Over 20 years since its first description, Malpaisomys' phylogenetic position remains enigmatic. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we resolved this issue using molecular characters. Mitochondrial and nuclear markers were successfully amplified from subfossils of three lava mouse samples. Molecular phylogenetic reconstructions revealed, without any ambiguity, unsuspected relationships between Malpaisomys and extant mice (genus Mus, Murinae). Moreover, through molecular dating we estimated the origin of the Malpaisomys/mouse clade at 6.9 Ma, corresponding to the maximal age at which the archipelago was colonised by the Malpaisomys ancestor via natural rafting. CONCLUSION/SIGNIFICANCE: This study reconsiders the derived morphological characters of Malpaisomys in light of this unexpected molecular finding. To reconcile molecular and morphological data, we propose to consider Malpaisomys insularis as an insular lineage of mouse.

Diet of the extinct Lava mouse Malpaisomys insularis from the Canary Islands: insights from dental microwear.

Malpaisomys insularis is a mouse-like rodent endemic to the eastern Canary Islands. It became extinct during the fourteenth century. It was a remarkable species living under hyperarid conditions. A dental microwear analysis was performed in order to determine its former diet. The elevated number of fine scratches found in Malpaisomys molars suggests that it consumed a significant part of Poaceae, grass consumption leaving the most distinctive features on dental wear facets. A graminivorous diet with a high amount of abrasive items is in agreement with the broad teeth of Malpaisomys, considered as adapted to grass consumption. However, in the absence of potential competitors over its native range, it is likely that Malpaisomys also foraged on dicots to meet higher nutrient and energetic requirements. The ecology of Malpaisomys is discussed from these results in the context of the desertic climatic conditions of the eastern Canary Islands and with a special concern on its small body size in contrast to other large-sized island murine species such as the giant rats of the central Canary Islands.

Disentangling ancient interactions: a new extinct passerine provides insights on character displacement among extinct and extant island finches.

BACKGROUND: Evolutionary studies of insular biotas are based mainly on extant taxa, although such biotas represent artificial subsets of original faunas because of human-caused extinctions of indigenous species augmented by introduced exotic taxa. This makes it difficult to obtain a full understanding of the history of ecological interactions between extant sympatric species. Morphological bill variation of Fringilla coelebs and F. teydea (common and blue chaffinches) has been previously studied in the North Atlantic Macaronesian archipelagos. Character displacement between both species has been argued to explain bill sizes in sympatry. However, this explanation is incomplete, as similar patterns of bill size have been recorded in F. coelebs populations from islands with and without F. teydea. METHODOLOGY/PRINCIPAL FINDINGS: The discovery of a new extinct species in Tenerife (Canary Islands), here named Carduelis aurelioi n. sp. (slender-billed greenfinch), provides the opportunity to study ancient ecological interactions among Macaronesian finches. To help understand the evolutionary histories of forest granivores in space and time, we have performed a multidisciplinary study combining: (1) morphological analyses and radiocarbon dating (11,460±60 yr BP) of the new taxon and, (2) molecular divergence among the extant finch species and populations in order to infer colonization times (1.99 and 1.09 My for F. teydea and F. coelebs respectively). CONCLUSION/SIGNIFICANCE: C. aurelioi, F. coelebs and F. teydea co-habited in Tenerife for at least one million years. The unique anatomical trends of the new species, namely chaffinch-like beak and modified hind and forelimbs, reveal that there was a process of divergence of resource competition traits among the three sympatric finches. The results of our study, combined with the presence of more extinct greenfinches in other Macaronesian islands with significant variation in their beak sizes, suggests that the character displacement has influenced patterns of divergence in bill size and shape on other Macaronesian islands as well.

Ancient DNA of the extinct lava shearwater (Puffinus olsoni) from the Canary Islands reveals incipient differentiation within the P. puffinus complex.

BACKGROUND: The loss of species during the Holocene was, dramatically more important on islands than on continents. Seabirds from islands are very vulnerable to human-induced alterations such as habitat destruction, hunting and exotic predators. For example, in the genus Puffinus (family Procellariidae) the extinction of at least five species has been recorded during the Holocene, two of them coming from the Canary Islands. METHODOLOGY/PRINCIPAL FINDINGS: We used bones of the two extinct Canary shearwaters (P. olsoni and P. holeae) to obtain genetic data, for use in providing insights into the differentiation process within the genus Puffinus. Although mitochondrial DNA (mtDNA) cytochrome b sequences were successfully retrieved from four Holocene specimens of the extinct Lava shearwater (P. olsoni) from Fuerteventura (Canary Islands), the P. holeae specimens yielded no DNA. Only one haplotype was detected in P. olsoni, suggesting a low genetic diversity within this species. CONCLUSIONS: The phylogenetic analyses based on the DNA data reveal that: (i) the "Puffinus puffinus complex", an assemblage of species defined using osteological characteristics (P. puffinus, P. olsoni, P. mauretanicus, P. yelkouan and probably P. holeae), shows unresolved phylogenetic relationships; (ii) despite the differences in body size and proportions, P. olsoni and the extant P. puffinus are sister species. Several hypotheses can be considered to explain the incipient differentiation between P. olsoni and P. puffinus.

Ancient mtDNA analysis and the origin of the Guanches.

The prehistoric colonisation of the Canary Islands by the Guanches (native Canarians) woke up great expectation about their origin, since the Europeans conquest of the Archipelago. Here, we report mitochondrial DNA analysis (HVRI sequences and RFLPs) of aborigine remains around 1000 years old. The sequences retrieved show that the Guanches possessed U6b1 lineages that are in the present day Canarian population, but not in Africans. In turn, U6b, the phylogenetically closest ancestor found in Africa, is not present in the Canary Islands. Comparisons with other populations relate the Guanches with the actual inhabitants of the Archipelago and with Moroccan Berbers. This shows that, despite the continuous changes suffered by the population (Spanish colonisation, slave trade), aboriginal mtDNA lineages constitute a considerable proportion of the Canarian gene pool. Although the Berbers are the most probable ancestors of the Guanches, it is deduced that important human movements have reshaped Northwest Africa after the migratory wave to the Canary Islands.