Expanding the understanding of local community assembly in adaptive radiations.

COMMUNITIES ARE THOUGHT TO BE ASSEMBLED BY TWO TYPES OF FILTERS: by the environment relating to the fundamental niche and by biotic interactions relating to the realized niche. Both filters include parameters related to functional traits and their variation along environmental gradients. Here, we infer the general importance of environmental filtering of a functional trait determining local community assembly within insular adaptive radiations on the example of Caribbean Anolis lizards. We constructed maps for the probability of presence of Anolis ecomorphs (ecology-morphology-behavior specialists) on the Greater Antilles and overlaid these to estimate ecomorph community completeness (ECC) over the landscape. We then tested for differences in environmental parameter spaces among islands for real and cross-fitted ECC values to see whether the underlying assembly filters are deterministic (i.e., similar among islands). We then compared information-theoretic models of climatic and landscape parameters among Greater Antillean islands and inferred whether body mass as functional trait determines ECC. We found areas with high ECC to be strongly correlated with environmental filters, partly related to elevation. The environmental parameters influencing high ECC differed among islands. With the exception of the Jamaican twig ecomorph (which we suspect to be misclassified), smaller ecomorphs were more restricted to higher elevations than larger ones which might reflect filtering on the basis of differential physiological restrictions of ecomorphs. Our results in Anolis show that local community assembly within adaptive island radiations of animals can be determined by environmental filtering of functional traits, independently from species composition and realized environmental niche space.

Determinism in the diversification of Hispaniolan trunk-ground anoles (Anolis cybotes species complex).

The evolutionary processes that produce adaptive radiations are enigmatic. They can only be studied after the fact, once a radiation has occurred and been recognized, rather than while the processes are ongoing. One way to connect pattern to process is to study the processes driving divergence today among populations of species that belong to an adaptive radiation, and compare the results to patterns observed at a deeper, macroevolutionary level. We tested whether evolution is a deterministic process with similar outcomes during different stages of the adaptive radiation of Anolis lizards. Using a clade of terrestrial-scansorial lizards in the genus Anolis, we inferred the adaptive basis of spatial variation among contemporary populations and tested whether axes of phenotypic differentiation among them mirror known axes of diversification at deeper levels of the anole radiation. Nonparallel change associated with genetic divergence explains the vast majority of geographic variation. However, we found phenotypic variation to be adaptive as confirmed by convergence in populations occurring in similar habitats in different mountain ranges. Morphological diversification among populations recurs deterministically along two axes of diversification previously identified in the anole radiation, but the characters involved differ from those involved in adaptation at higher levels of anole phylogeny.

Molecular phylogeny and biogeography of Malagasy frogs of the genus Gephyromantis.

The genus Gephyromantis is a clade within the Malagasy-Comoroan family Mantellidae composed of rainforest frogs that live and breed to varying degrees independently from water. Based on DNA sequences of five mitochondrial and five nuclear genes we inferred the phylogeny of these frogs with full taxon coverage at the species level. Our preferred consensus tree from a partitioned Bayesian analysis of 5843 base pairs of 51 nominal and candidate species supports various major clades within the genus although the basal relationships among these remain unresolved. The data provide strong evidence for the monophyly of the subgenera Gephyromantis (after exclusion of Gephyromantis klemmeri), Laurentomantis, Vatomantis, and Phylacomantis. Species assigned to the subgenus Duboimantis belong to two strongly supported clades of uncertain relationships. G. klemmeri, previously in the subgenus Gephyromantis, was placed with high support sister to the Laurentomantis clade, and the Laurentomantis+G. klemmeri clade was sister to Vatomantis. A reconstruction of ancestral distribution areas indicates a diversification of several subgenera in the northern biogeographic regions of Madagascar and the dispersal out of northern Madagascar for several clades.

Speciation in little: the role of range and body size in the diversification of Malagasy mantellid frogs.

BACKGROUND: The rate and mode of lineage diversification might be shaped by clade-specific traits. In Madagascar, many groups of organisms are characterized by tiny distribution ranges and small body sizes, and this high degree of microendemism and miniaturization parallels a high species diversity in some of these groups. We here investigate the geographic patterns characterizing the radiation of the frog family Mantellidae that is virtually endemic to Madagascar. We integrate a newly reconstructed near-complete species-level timetree of the Mantellidae with georeferenced distribution records and maximum male body size data to infer the influence of these life-history traits on each other and on mantellid diversification. RESULTS: We reconstructed a molecular phylogeny based on nuclear and mitochondrial DNA for 257 species and candidate species of the mantellid frog radiation. Based on this phylogeny we identified 53 well-supported pairs of sister species that we used for phylogenetic comparative analyses, along with whole tree-based phylogenetic comparative methods. Sister species within the Mantellidae diverged at 0.2-14.4 million years ago and more recently diverged sister species had geographical range centroids more proximate to each other, independently of their current sympatric or allopatric occurrence. The largest number of sister species pairs had non-overlapping ranges, but several examples of young microendemic sister species occurring in full sympatry suggest the possibility of non-allopatric speciation. Range sizes of species included in the sister species comparisons increased with evolutionary age, as did range size differences between sister species, which rejects peripatric speciation. For the majority of mantellid sister species and the whole mantellid radiation, range and body sizes were associated with each other and small body sizes were linked to higher mitochondrial nucleotide substitution rates and higher clade diversity. In contrast, small range sizes were unexpectedly associated with a slow-down of mitochondrial substitution rates. CONCLUSIONS: Based on these results we define a testable hypothesis under which small body sizes result in limited dispersal capabilities and low physiological tolerances, causing smaller and more strongly fragmented ranges. This can be thought to facilitate reproductive isolation and thus favor speciation. Contrary to the expectation of the faster speciation of such microendemic phenotype species, we only found small body sizes of mantellid frogs to be linked to higher diversification and substitution rates, but not small range sizes. A joint analysis of various species-rich regional anuran radiations might provide enough species with all combinations of range and body sizes for a more conclusive test of this hypothesis.

Raising awareness of amphibian Chytridiomycosis will not alienate ecotourists visiting Madagascar.

Chytridiomycosis (Bd) is contributing to amphibian extinctions worldwide but has so far not been detected in Madagascar. The high likelihood for Bd to spread to the island and efface this amphibian diversity and endemism hotspot requires respective conservation policies to be developed. Bd could be introduced by the large number of tourists that visit protected areas; therefore, increasing awareness among tourists and encouraging them to participate in safety measures should be a priority conservation action. However, concerns have been raised that tourists would not be able to distinguish between an amphibian disease harmless to humans and emerging diseases that would imply a danger for human health, invoking a negative image of Madagascar as an ecotourism destination. We evaluated whether informing tourists about this infectious animal disease would cause health scare and diminish trip satisfaction. Based on 659 respondents we found that most ecotourists favored to be informed about Bd and were proactive about participating in prevention measures, refuting previous concerns.

Madagascar as a model region of species diversification.

Tropical biotas provide excellent settings in which to explore mechanisms of evolutionary diversification, yet these processes remain poorly understood. Pioneering work on biodiversity patterns and diversification processes in other tropical regions has recently been complemented by studies in Madagascar. Here we review diversity models and diversification mechanisms proposed for the fauna of this island and the perspectives for testing them. Madagascar has a diverse biota that has evolved in isolation, and is characterised by regionally pronounced and locally steep environmental gradients, common patterns of microendemism across taxa and numerous evolutionary radiations. These characteristics establish Madagascar as a promising system for the study of pattern and process in species diversification.

Vast underestimation of Madagascar's biodiversity evidenced by an integrative amphibian inventory.

Amphibians are in decline worldwide. However, their patterns of diversity, especially in the tropics, are not well understood, mainly because of incomplete information on taxonomy and distribution. We assess morphological, bioacoustic, and genetic variation of Madagascar's amphibians, one of the first near-complete taxon samplings from a biodiversity hotspot. Based on DNA sequences of 2,850 specimens sampled from over 170 localities, our analyses reveal an extreme proportion of amphibian diversity, projecting an almost 2-fold increase in species numbers from the currently described 244 species to a minimum of 373 and up to 465. This diversity is widespread geographically and across most major phylogenetic lineages except in a few previously well-studied genera, and is not restricted to morphologically cryptic clades. We classify the genealogical lineages in confirmed and unconfirmed candidate species or deeply divergent conspecific lineages based on concordance of genetic divergences with other characters. This integrative approach may be widely applicable to improve estimates of organismal diversity. Our results suggest that in Madagascar the spatial pattern of amphibian richness and endemism must be revisited, and current habitat destruction may be affecting more species than previously thought, in amphibians as well as in other animal groups. This case study suggests that worldwide tropical amphibian diversity is probably underestimated at an unprecedented level and stresses the need for integrated taxonomic surveys as a basis for prioritizing conservation efforts within biodiversity hotspots.

Patterns of endemism and species richness in Malagasy cophyline frogs support a key role of mountainous areas for speciation.

Cophyline narrow-mouthed frogs (Anura: Microhylidae) are a diverse endemic radiation of Madagascar. Cophylines contain a high proportion of range restricted species and constitute a good model system to understand patterns of evolutionary diversification in tropical ecosystems. We combine spatial and phylogenetic analyses for a near-complete taxon sample to test competing explanations for patterns of species richness (SR) and endemism. Our reconstruction of the phylogeny of cophylines indicates the presence of 22 new species and several instances of nonmonophyly. We found a strong historical signal in current cophyline ranges indicating a high degree of spatial niche conservatism in clade diversification, with clades occurring in the North of Madagascar constituting the most derived in the phylogeny. We identified six positively correlated centers of SR and endemism that can neither be explained by stochastic models such as elevational or latitudinal mid-domain effect, nor by low-elevation river catchments. Instead, the locations of these centers in areas spanning a high altitudinal range in combination with specific climatic parameters support a key role of mountainous areas for speciation of these anurans, although we cannot exclude an influence of habitat loss due to human impact. High conservation priority is ascribed to these areas.

Molecular phylogeny of Malagasy reed frogs, Heterixalus, and the relative performance of bioacoustics and color-patterns for resolving their systematics.

The members of the genus Heterixalus constitute one of the endemic frog radiations in Madagascar. Here we present a complete species-level phylogeny based on DNA sequences (4876 base pairs) of three nuclear and four mitochondrial markers to clarify the phylogenetic relationships among and within all known species of this genus, as well as the phylogenetic position of the monospecific Seychellean Tachycnemis seychellensis. Although the performance to resolve supported clades of Heterixalus species differed among the investigated gene fragments when analyzed separately, we could identify five well-supported species groups within Heterixalus in the combined analysis of all gene fragments. Our data strongly support a Heterixalus-Tachycnemis clade, and indicate the probable monophyly of Heterixalus placed sister to Tachycnemis. However, the diversification of these lineages may have happened in a short interval of time, leading to an unstable placement of Tachycnemis in the single-gene fragment phylogenies. Referring to the hitherto existing classification of Heterixalus, which is predominantly based on chromatic and bioacoustic characters, we examined the relative performance of these data sets relative to our molecular phylogeny. A Bayesian tree reconstructed with a bioacoustic data set yielded a higher resemblance to the molecular phylogeny than a tree constructed using a chromatic data set, which supports the importance of bioacoustic characters for systematic analyses of these anurans.

Pharmacological properties of motion vision in goldfish measured with the optomotor response.

In goldfish, the retinal pathways involved in motion coding have been demonstrated to have an L-cone dominated action spectrum (S. Schaerer, C. Neumeyer, Motion detection in goldfish investigated with the optomotor response is "color blind", Vision Res. 36 (1996) 4025-4034). The neurotransmitters involved in retinal motion coding mechanisms, and the relevance of these retinal motion coding mechanisms for motion perception, are little investigated in fish. In this study, the optomotor response was used to investigate the effect of antagonists on different receptor types for acetylcholine (ACh), GABA, for the dopamine D2-receptor (D2-R) - which is known to modulate the action spectrum in motion coding (C. Mora-Ferrer, K. Behrend, Dopaminergic modulation of photopic temporal transfer properties in goldfish retina investigated with the ERG, Vision Res. 44 (2004) 2067-2081) - and of an agonist for against the mGluR6-receptor (mGluR6) on goldfish motion vision in the photopic range. Blockade of nicotinic ACh-R, GABAa-R and both GABAa- and GABAc-R eliminated the optomotor response completely. Neither a muscarinic ACH-R antagonist, a D2-R antagonist or a mGluR6-agonist affected goldfish motion vision. The pharmacological profile of the goldfish optomotor response resembles the pharmacological profile of direction-selective ganglion cells (DS-GC) described for vertebrate retinas in electrophysiological experiments, e.g. (S. Weng, W. Sun, S. He, Identification of ON-OFF direction-selective ganglion cells in the mouse retina, J. Physiol. 562 (2005) 915-923). This indicates that cells with direction-selective receptive field properties exist in the goldfish retina. It is proposed that these cells provide the input for the full field motion perception in goldfish.