The colonisation of Madagascar by land-bound vertebrates

New twist to a fantastical distribution: Fiji-Tonga iguanas

Over-water 'rafting' accounts for much of the biota on the 'oceanic' islands. Arguably, the most spectacular example concerns the iguanas on Fiji and Tonga. Scarpetta et al. have recently provided compelling evidence for them originating in western North America, with their trans-oceanic dispersal occurring within the past 33 million years.

Biome conservatism prevailed in repeated long-distance colonization of Madagascar's mountains by Helichrysum (Compositae, Gnaphalieae)

Colonization and diversification processes are responsible for the distinctiveness of island biotas, with Madagascar standing out as abiodiversity hotspot exceptionally rich in species and endemism. Regardless of its significance, the evolutionary history and diversification drivers of Madagascar's flora remain understudied. Here we focus on Helichrysum (Compositae, Gnaphalieae) to investigate the evolutionary and biogeographic origins of the Malagasy flora. We inferred a highly resolved phylogeny based on target-enrichment data from 327 species (including 51 % of Malagasy endemics) and conducted ancestral range estimation analyses. Our results revealed at least six trans-oceanic dispersal events from different African regions to Madagascar during the Pliocene. In this process, biome conservatism prevailed, as evidenced by similarities between Malagasy lineages and their African relatives. The southern African grasslands, known to be the center of diversification and the main source of African Helichrysum lineages, played a key role in the colonization of Madagascar as the ancestral source area of at least three clades. The Tropical Afromontane region was revealed as the source of at least two montane Malagasy lineages that substantially radiated in-situ. Finally, a dispersal event from southwestern Africa led to a lineage represented by a single species adapted to the island's southwestern arid conditions. The main radiations of Helichrysum in Madagascar's mountains occurred within the last 2 My, coinciding with a transition towards cooler and drier conditions and the expansion of open habitats, likely driven by a combination of geographic and ecological speciation. Overall, our findings highlight the affinities between the montane floras of continental Africa and Madagascar.

Land Bridges and Rafting Theories to Explain Terrestrial-Vertebrate Biodiversity on Madagascar

Madagascar's celebrated land-vertebrate assemblage has long been studied and discussed. How the ancestors of the 30 different lineages arrived on the island, which has existed since 85 Mya and is separated from neighboring Africa by 430 km of water, is a deeply important question. Did the colonizations take place when the landmass formed part of Gondwana, or did they occur later and involve either now-drowned causeways or overwater dispersal (on vegetation rafts or by floating/swimming)? Following a historical review, we appraise the geological-geophysical evidence and the faunal-suite colonization record. Twenty-six of the clades are explained by temporally stochastic overwater dispersals, spanning 69-0 Mya, while two others are considered Gondwanan vicariant relicts. Due to a lack of information, the remaining two groups cannot be evaluated. The findings thus appear to resolve a debate that has rumbled along, with sporadic eruptions, since the mid-1800s.

Genomics, the diversification of mammals, and the evolution of placentation

When and why did variations in placental structure and function evolve? Such questions cannot be addressed without a reliable version of mammalian phylogeny. Twenty-five years ago, the mammalian tree was reshaped by molecular phylogenetics. Soon it was shown, in contrast to prevailing theories, that the common ancestor of placental mammals had invasive placentation. Subsequently, evolution of many other features of extraembryonic membranes was addressed. This endeavour stimulated research to fill gaps in our knowledge of placental morphology. Last year the mammalian tree was again revised based on a large set of genomic data. With that in mind, this review provides an update on placentation in the nineteen orders of placental mammals, incorporating much recent data. The principal features such as shape, interdigitation, the interhaemal barrier and the yolk sac are summarized in synoptic tables. The evolution of placental traits and its timing is then explored by reference to the revised mammalian tree. Examples are the early appearance of epitheliochorial placentation in the common ancestor of artiodactyls, perissodactyls, pangolins and carnivores (with reversion to invasive forms in the latter) and later refinements such as the binucleate trophoblast cells and placentomes of ruminants. In primates, the intervillous space gradually evolved from the more basic labyrinth whereas trophoblast invasion of the decidua was a late development in humans and great apes. Only seldom can we glimpse the "why" of placental evolution. The best examples concern placental hormones, including some striking examples of convergent evolution such as the chorionic gonadotropins of primates and equids. In concluding, I review current ideas about what drives placental evolution and identify significant gaps in our knowledge of placentation, including several relevant to the evolution of placentation in primates.

African bushpigs exhibit porous species boundaries and appeared in Madagascar concurrently with human arrival

Several African mammals exhibit a phylogeographic pattern where closely related taxa are split between West/Central and East/Southern Africa, but their evolutionary relationships and histories remain controversial. Bushpigs (Potamochoerus larvatus) and red river hogs (P. porcus) are recognised as separate species due to morphological distinctions, a perceived lack of interbreeding at contact, and putatively old divergence times, but historically, they were considered conspecific. Moreover, the presence of Malagasy bushpigs as the sole large terrestrial mammal shared with the African mainland raises intriguing questions about its origin and arrival in Madagascar. Analyses of 67 whole genomes revealed a genetic continuum between the two species, with putative signatures of historical gene flow, variable FST values, and a recent divergence time (<500,000 years). Thus, our study challenges key arguments for splitting Potamochoerus into two species and suggests their speciation might be incomplete. Our findings also indicate that Malagasy bushpigs diverged from southern African populations and underwent a limited bottleneck 1000-5000 years ago, concurrent with human arrival in Madagascar. These results shed light on the evolutionary history of an iconic and widespread African mammal and provide insight into the longstanding biogeographic puzzle surrounding the bushpig's presence in Madagascar.

Another step through the crux: a new microendemic rock-dwelling Paroedura (Squamata, Gekkonidae) from south-central Madagascar

Using an integrative taxonomic approach including genetic and morphological data, we formally describe a new microendemic gecko species belonging to the Paroedurabastardi clade, previously referred to as P.bastardi D. We name this taxon currently known from Anja Reserve and Tsaranoro Valley Forest (south-central Madagascar), as P.manongavatosp. nov. The new species differs from other species of the P.bastardi clade by ≥ 12.4% uncorrected p-distance at the mitochondrial 16S rRNA gene and it forms a monophyletic group in the COI mtDNA phylogenetic tree. It lacks haplotype sharing at the nuclear KIAA1239 and CMOS genes with the other species of the same complex, including the syntopic P.rennerae. Given its limited extent of occurrence and high levels of habitat fragmentation linked to forest clearances and fires, we propose the IUCN Red List Category of Critically Endangered, based on the B1ab(iii) criterion. The conservation value of Anja Reserve and Tsaranoro Valley Forest is remarkable. Preserving the remaining deciduous forest habitat is of paramount importance to protect these narrow-range reptile species.

Ancestral African Bats Brought Their Cargo of Pathogenic Leptospira to Madagascar under Cover of Colonization Events

Madagascar is home to an extraordinary diversity of endemic mammals hosting several zoonotic pathogens. Although the African origin of Malagasy mammals has been addressed for a number of volant and terrestrial taxa, the origin of their hosted zoonotic pathogens is currently unknown. Using bats and Leptospira infections as a model system, we tested whether Malagasy mammal hosts acquired these infections on the island following colonization events, or alternatively brought these bacteria from continental Africa. We first described the genetic diversity of pathogenic Leptospira infecting bats from Mozambique and then tested through analyses of molecular variance (AMOVA) whether the genetic diversity of Leptospira hosted by bats from Mozambique, Madagascar and Comoros is structured by geography or by their host phylogeny. This study reveals a wide diversity of Leptospira lineages shed by bats from Mozambique. AMOVA strongly supports that the diversity of Leptospira sequences obtained from bats sampled in Mozambique, Madagascar, and Comoros is structured according to bat phylogeny. Presented data show that a number of Leptospira lineages detected in bat congeners from continental Africa and Madagascar are imbedded within monophyletic clades, strongly suggesting that bat colonists have indeed originally crossed the Mozambique Channel while infected with pathogenic Leptospira.