Andolalao Rakotoarison

Host Ecology Rather Than Host Phylogeny Drives Amphibian Skin Microbial Community Structure in the Biodiversity Hotspot of Madagascar

Host-associated microbiotas of vertebrates are diverse and complex communities that contribute to host health. In particular, for amphibians, cutaneous microbial communities likely play a significant role in pathogen defense; however, our ecological understanding of these communities is still in its infancy. Here, we take advantage of the fully endemic and locally species-rich amphibian fauna of Madagascar to investigate the factors structuring amphibian skin microbiota on a large scale. Using amplicon-based sequencing, we evaluate how multiple host species traits and site factors affect host bacterial diversity and community structure. Madagascar is home to over 400 native frog species, all of which are endemic to the island; more than 100 different species are known to occur in sympatry within multiple rainforest sites. We intensively sampled frog skin bacterial communities, from over 800 amphibians from 89 species across 30 sites in Madagascar during three field visits, and found that skin bacterial communities differed strongly from those of the surrounding environment. Richness of bacterial operational taxonomic units (OTUs) and phylogenetic diversity differed among host ecomorphs, with arboreal frogs exhibiting lower richness and diversity than terrestrial and aquatic frogs. Host ecomorphology was the strongest factor influencing microbial community structure, with host phylogeny and site parameters (latitude and elevation) explaining less but significant portions of the observed variation. Correlation analysis and topological congruency analyses revealed little to no phylosymbiosis for amphibian skin microbiota. Despite the observed geographic variation and low phylosymbiosis, we found particular OTUs that were differentially abundant between particular ecomorphs. For example, the genus Pigmentiphaga (Alcaligenaceae) was significantly enriched on arboreal frogs, Methylotenera (Methylophilaceae) was enriched on aquatic frogs, and Agrobacterium (Rhizobiaceae) was enriched on terrestrial frogs. The presence of shared bacterial OTUs across geographic regions for selected host genera suggests the presence of core microbial communities which in Madagascar, might be driven more strongly by a species’ preference for specific microhabitats than by the physical, physiological or biochemical properties of their skin. These results corroborate that both host and environmental factors are driving community assembly of amphibian cutaneous microbial communities, and provide an improved foundation for elucidating their role in disease resistance.

Distinct Patterns of Desynchronized Limb Regression in Malagasy Scincine Lizards (Squamata, Scincidae)

Scincine lizards in Madagascar form an endemic clade of about 60 species exhibiting a variety of ecomorphological adaptations. Several subclades have adapted to burrowing and convergently regressed their limbs and eyes, resulting in a variety of partial and completely limbless morphologies among extant taxa. However, patterns of limb regression in these taxa have not been studied in detail. Here we fill this gap in knowledge by providing a phylogenetic analysis of DNA sequences of three mitochondrial and four nuclear gene fragments in an extended sampling of Malagasy skinks, and microtomographic analyses of osteology of various burrowing taxa adapted to sand substrate. Based on our data we propose to (i) consider Sirenoscincus Sakata & Hikida, 2003, as junior synonym of Voeltzkowia Boettger, 1893; (ii) resurrect the genus name Grandidierina Mocquard, 1894, for four species previously included in Voeltzkowia; and (iii) consider Androngo Brygoo, 1982, as junior synonym of Pygomeles Grandidier, 1867. By supporting the clade consisting of the limbless Voeltzkowia mira and the forelimb-only taxa V. mobydick and V. yamagishii, our data indicate that full regression of limbs and eyes occurred in parallel twice in the genus Voeltzkowia (as hitherto defined) that we consider as a sand-swimming ecomorph: in the Voeltzkowia clade sensu stricto the regression first affected the hindlimbs and subsequently the forelimbs, whereas the Grandidierina clade first regressed the forelimbs and subsequently the hindlimbs following the pattern prevalent in squamates. Timetree reconstructions for the Malagasy Scincidae contain a substantial amount of uncertainty due to the absence of suitable primary fossil calibrations. However, our preliminary reconstructions suggest rapid limb regression in Malagasy scincids with an estimated maximal duration of 6 MYr for a complete regression in Paracontias, and 4 and 8 MYr respectively for complete regression of forelimbs in Grandidierina and hindlimbs in Voeltzkowia.

Reconciling molecular phylogeny, morphological divergence and classification of Madagascan narrow-mouthed frogs (Amphibia: Microhylidae)

A recent study clarified several aspects of microhylid phylogeny by combining DNA sequences from Sanger sequencing and anchored phylogenomics, although numerous aspects of tree topology proved highly susceptible to data partition and chosen model. Although the phylogenetic results of the study were in conflict with previous publications, the authors made several changes to the taxonomy of Madagascars cophyline microhylids. We re-analyzed part of their data together with our own molecular and morphological data. Based on a supermatrix of 11 loci, we propose a new phylogeny of the Cophylinae, and discuss it in the context of a newly generated osteological dataset. We found several sample misidentifications, partially explaining their deviant results, and propose to resurrect the genera Platypelis and Stumpffia from the synonymy of Cophyla and Rhombophryne, respectively. We provide support for the previous genus-level taxonomy of this subfamily, and erect a new genus, Anilany gen. nov., in order to eliminate paraphyly of Stumpffia and to account for the osteological differences observed among these groups. Deep nodes in our phylogeny remain poorly supported, and future works will certainly refine our classification, but we are confident that these will not produce large-scale rearrangements.

A review of the taxonomy and osteology of the Rhombophryne serratopalpebrosa species group (Anura: Microhylidae) from Madagascar, with comments on the value of volume rendering of micro-CT data to taxonomists

Over the last three years, three new species of saw-browed diamond frogs (Rhombophryne serratopalpebrosa species group)-a clade of cophyline microhylid frogs native to northern and eastern Madagascar-have been described. We here review the taxonomy of these frogs based on a new multi-gene phylogeny of the group, which confirms its monophyly but is insufficiently resolved to clarify most intra-group relationships. We confirm Rhombophryne guentherpetersi (Guibé, 1974) to be a member of this group, and we re-describe it based on its type series and newly collected material; the species is characterised by small superciliary spines (overlooked in its original description), as well as large tibial glands and an unusually laterally compressed pectoral girdle. We go on to describe two new species of this group from northern Madagascar: both R. diadema sp. nov. from the Sorata Massif and R. regalis sp. nov. from several sites in the northeast of the island possess three superciliary spines, but they are characterised by several subtle morphological and osteological differences. The new species are separated from all known congeners by an uncorrected pairwise distance of at least 5.1% in a ca. 550 bp fragment of the 16S rRNA gene. In order to highlight the significance of the skeleton in the taxonomy of this group, we provide a detailed description of its generalized osteology based on volume-rendered micro-CT scans of all described members, revisiting already-described skeletons of some species, and describing the skeletons of R. guentherpetersi, R. coronata, and the new taxa for the first time. Use of volume rendering, instead of surface rendering of micro-CT data, resulted in some discrepancies due to the properties of each method. We discuss these inconsistencies and their bearing on the relative value of surface and volume rendering in the taxonomists toolkit. We argue that, while surface models are more practical for the reader, volumes are generally a more objective representation of the data. Thus, taxonomic description work should be based on volume rendering when possible, with surface models presented as an aid to the reader.

Widespread vulnerability of Malagasy predators to the toxins of an introduced toad

Invasive species are a key factor contributing to the global decline of biodiversity, and understanding the underlying mechanisms is crucial to mitigate detrimental effects [1]. One such mechanism is the introduction of invasive species with defensive strategies, such as novel toxins, that can disrupt native predator communities [2]. Disruption of such communities can produce trophic cascades, impacting a diverse array of taxa [2]. Madagascar, a globally significant biodiversity hotspot, has recently experienced the introduction of a toxic bufonid amphibian, the Asian common toad (Duttaphrynus melanostictus) [3]. Since its invasion, the toad population has expanded rapidly, making control efforts problematic and eradication extremely difficult [4]. Previous cases of bufonid introductions, such as the ongoing spread of the cane toad (Rhinella marina) in Australia, have resulted in the decimation of many indigenous species [2], prompting fears that Madagascar may be similarly impacted [4]. Here we show that these fears are warranted: we demonstrate that many Malagasy vertebrates are likely to be susceptible to the toxins of this invasive toad.

Yet another small brown frog from high altitude on the Marojejy Massif, northeastern Madagascar (Anura: Mantellidae)

Madagascar hosts a high diversity of small brown frogs. In this paper, we add another one by describing Gephyromantis (Duboimantis) tohatra sp. nov. The new species is a small brown mantellid frog discovered on a recent expedition to Marojejy National Park in northeastern Madagascar. It is characterised, among other things, by its small size (snout-vent length ~33 mm), an orange to yellowish belly, two dorsolateral ridges, and a distinctive call composed of 7-10 pulsed notes. The new species occurs sympatrically with other members of the subgenus Duboimantis at high altitude (~1700 m above sea level), including its sister species G. schilfi from which it radically differs by advertisement call and by a substantial genetic divergence of 4.3% uncorrected pairwise distance in the mitochondrial 16S rRNA gene. It thus joins the diverse assemblage of Gephyromantis species known from high altitudes on the mountain massifs of northern Madagascar.

Stumbling upon a New Frog Species of Guibemantis (Anura: Mantellidae) on Top of the Marojejy Massif in Northern Madagascar

We describe a new frog species of the genus Guibemantis, subgenus Pandanusicola, from Marojejy National Park in northeastern Madagascar. Guibemantis milingilingy, the new species, exhibits high genetic divergence from all other described species of Guibemantis based on DNA sequences of a fragment of the mitochondrial 16S rRNA gene. This new species inhabits Pandanus plants like the majority of other members of this subgenus, but is found at much higher elevations (2026 m a.s.l.). It differs from its closest relative, G. punctatus, by the lack of speckled or spotted dorsal patterns and by the presence of a distinctly dark tympanum. As a high-elevation species, it is likely to be a species sensitive to climate change, similar to other montane endemics in Madagascar.