Stochastic Mapping Research Articles

Historical biogeography of Pomaderris (Rhamnaceae): Continental vicariance in Australia and repeated independent dispersals to New Zealand

AimGondwanan biogeographic patterns include a combination of old vicariance events following the breakup of the supercontinent, and more recent long-distance dispersals across the southern landmasses. Floristic relationships between Australia and New Zealand have mostly been attributed to recent dispersal events rather than vicariance. We assessed the biogeographic history of Pomaderris (Rhamnaceae), which occurs in both Australia and New Zealand, by constructing a time-calibrated molecular phylogeny to infer (1) phylogenetic relationships and (2) the relative contributions of vicariance and dispersal events in the biogeographic history of the genus. LocationAustralia and New Zealand. MethodsUsing hybrid capture and high throughput sequencing, we generated nuclear and plastid data sets to estimate phylogenetic relationships and fossil calibrated divergence time estimates for Pomaderris. BioGeoBEARS and biogeographical stochastic mapping (BSM) were used to assess the ancestral area of the genus and the relative contributions of vicariance vs dispersal, and the directionality of dispersal events. ResultsOur analyses indicate that Pomaderris originated in the Oligocene and had a widespread Australian distribution. Vicariance of western and eastern Australian clades coincides with the uplift of the Nullarbor Plain c. 14 Ma, followed by subsequent in-situ and within-biome diversification with little exchange across regions. A rapid radiation of southeastern Australian taxa beginning c. 10 Ma was the source for at least six independent long-distance dispersal events to New Zealand during the Pliocene–Pleistocene. Main conclusionsOur study demonstrates the importance of dispersal in explaining not only the current cross-Tasman distributions of Pomaderris, but for the New Zealand flora more broadly. The pattern of multiple independent long-distance dispersal events for Pomaderris, without significant radiation within New Zealand, is congruent with other lowland plant groups, suggesting that this biome has a different evolutionary history compared with the younger alpine flora of New Zealand, which exhibits extensive radiations often following single long distance dispersal events.

Laticifers in Sapindaceae: Structure, Evolution and Phylogenetic Importance.

Laticifer occurrence and structure are poorly known in Sapindaceae. Occurrence is likely underestimated owing to the low production of latex in most species. We investigated 67 species from 23 genera of Sapindaceae to verify laticifer occurrence and their structural, developmental and chemical features, as well as their evolutionary history in the family. Shoots were collected from herbarium and fresh specimens for histological analyses. Three characters derived from laticifer features were coded and their ancestral states reconstructed through Bayesian stochastic mapping and maximum likelihood estimation. Only articulated non-anastomosing laticifers were found in Sapindaceae. Laticifers differentiate early during shoot development and are found in the cortex, phloem, and pith. Latex is mostly composed of lipids. Callose and suberin were detected in laticifer cell walls in some genera. Reconstruction of laticifer ancestral states showed that laticifers are present in most clades of Sapindaceae with some reversals. Callose in the laticifer cell wall was found exclusively in Serjania and Paullinia (tribe Paullinieae), a character regarded as independently derived. Occurrence of laticifers in Sapindaceae is broader than previously reported. Articulated non-anastomosing laticifers had five independent origins in Sapindaceae with some secondary losses, occurring in five out of six genera of Paullinieae and 10 other genera outside Paullinieae. Particularly, callose in the laticifer cell wall evolved independently twice in the family, and its occurrence may be interpreted as a key-innovation that promoted the diversification of Paullinia and Serjania. Our study suggests that laticifer characters may be useful in understanding the generic relationships within the family.

SMap: Evolution of independent, dependent and conditioned discrete characters in a Bayesian framework

Abstract Trait evolution analyses enable the comparison of characters amongst different species—a useful technique when inferring ancestral phenotypes based on a phylogeny of living taxa. The evolution of discrete characters can be mapped on the branches of a phylogenetic tree using stochastic mapping. Here we present sMap, a new program to perform stochastic mapping analyses. Key features characterising sMap are: a wide variety of models and prior distributions; the ability to use a posterior distribution of trees and to compute marginal likelihoods to perform model selection analyses; and the implementation of three kinds of characters: ‘independent’ characters, which do not interact with each other; ‘dependent’ characters, which co‐evolve at the same time; and ‘conditioned’ characters, whose state is determined by the state of other characters. Here we present two examples that show how sMap can be used to perform stochastic mapping analyses, produce robust results and answer new kinds of questions. sMap is freely available and distributed under a GPL licence, in a command‐line and Graphical User Interface version; a detailed user manual with examples and tutorials is also provided. The wide variety of algorithms implemented in sMap enables accurate analyses of the evolution of discrete characters. Conditioned characters can be used to study the interaction of simple traits to produce complex phenotypes. As a multiplatform and open‐source project, sMap can be used on a variety of systems and situations, such as academic research and teaching.

Adaptive Fuzzy Output-Constrained Control for Nonlinear Stochastic Systems With Input Delay and Unknown Control Coefficients.

This article considers an adaptive fuzzy control problem for nonstrict-feedback nonlinear stochastic systems, which contain input delay, output constraints, and unknown control coefficients, simultaneously. First, an original stochastic nonlinear mapping and the Pade approximation transformation techniques are developed to solve the symmetric output constraints and input delay. Then, an adaptive fuzzy controller is designed for the unknown nonlinear systems, in which the Nussbaum function is employed to deal with the unknown time-varying control coefficients. Tracking errors are ensured to converge to a small neighborhood around the origin, and the system output does not violate the predefined constrained conditions. All the signals of the closed-loop systems have proven to remain bounded in probability. Moreover, the asymmetric output-constrained control is also studied. Two simulation examples are provided to show the effectiveness of the developed method.

Evolution of habitat preference in 243 species of Bent-toed geckos (Genus Cyrtodactylus Gray, 1827) with a discussion of karst habitat conservation.

Understanding the processes that underpin adaptive evolutionary shifts within major taxonomic groups has long been a research directive among many evolutionary biologists. Such phenomena are best studied in large monophyletic groups that occupy a broad range of habitats where repeated exposure to novel ecological opportunities has happened independently over time in different lineages. The gekkonid genus Cyrtodactylus is just such a lineage with approximately 300 species that range from South Asia to Melanesia and occupy a vast array of habitats. Ancestral state reconstructions using a stochastic character mapping analysis of nine different habitat preferences were employed across a phylogeny composed of 76% of the known species of Cyrtodactylus. This was done in order to ascertain which habitat preference is the ancestral condition and from that condition, the transition frequency to more derived habitat preferences. The results indicate that a general habitat preference is the ancestral condition for Cyrtodactylus and the frequency of transitioning from a general habitat preference to anything more specialized occurs approximately four times more often than the reverse. Species showing extreme morphological and/or ecological specializations generally do not give rise to species bearing other habitat preferences. The evolution of different habitat preferences is generally restricted to clades that tend to occur in specific geographic regions. The largest radiations in the genus occur in rocky habitats (granite and karst), indicating that the transition from a general habitat preference to a granite or karst‐dwelling life style may be ecologically uncomplicated. Two large, unrelated clades of karst‐associated species are centered in northern Indochina and the largest clade of granite‐associated species occurs on the Thai‐Malay Peninsula. Smaller, independent radiations of clades bearing other habitat preferences occur throughout the tree and across the broad distribution of the genus. With the exception of a general habitat preference, the data show that karst‐associated species far out‐number all others (29.6% vs. 0.4%–10.2%, respectively) and the common reference to karstic regions as “imperiled arcs of biodiversity” is not only misleading but potentially dangerous. Karstic regions are not simply refugia harboring the remnants of local biodiversity but are foci of speciation that continue to generate the most speciose, independent, radiations across the genus. Unfortunately, karstic landscapes are some of the most imperiled and least protected habitats on the planet and these data continue to underscore the urgent need for their conservation.

Finite-time adaptive neural control for nonstrict-feedback stochastic nonlinear systems with input delay and output constraints

This paper addresses a novel finite-time adaptive neural control (FTANC) problem for nonstrict-feedback stochastic nonlinear systems (NSFSNS), in which the input delay and output constrained problems are considered simultaneously. First, the Pade approximation technique is adopted to transform the delay input system into a delay-free one. Second, the stochastic nonlinear mapping technique is developed to solve the symmetric and asymmetric output constraints in the system. Then, the adaptive neural controller is designed based on backstepping technique, such that the closed-loop systems are semi-globally practical finite-time stable (SGPFTS) in probability, and the tracking error converges to a small neighborhood of the origin after a finite period of time. Two simulation examples show the effectiveness of the proposed approach.

Paleotemperatures and recurrent habitat shifts drive diversification of treefrogs across distinct biodiversity hotspots in sub‐Amazonian South America

AbstractAimWe investigate the biogeographical history and diversification in a treefrog lineage distributed in contrasting (open and forested) ecoregions of South America, including three biodiversity hotspots. We evaluate the role of dispersal and whether other factors such as diversity‐dependence or paleotemperatures could explain the diversification pattern for this group. Especially focusing on the savanna endemics, we illuminate the processes governing the species assembly and evolution of the Cerrado savanna.LocationSouth American ecoregions south of the Amazon (i.e. Atlantic Forest, Cerrado, Araucaria Forest, Pampas, Central and Southern Andes).TaxonBoana pulchella group.MethodsWe built the most complete time‐calibrated phylogeny for the group to date. We then reconstructed ancestral ranges using the dispersal‐extinction‐cladogenesis (DEC) model comparing different dispersal scenarios considering distance, adjacency and ecological similarity among regions. Centre‐of‐origin hypotheses in forest and open ecoregions were also tested. Using biogeographical stochastic mapping, we additionally estimated the contribution of range shifts across different biomes. Lastly, we evaluated several diversification models, including the effect of time, diversity‐dependence and temperature‐dependence on speciation and extinction rates.ResultsThe Boana pulchella group originated during the Early Miocene (~17.5 MYA) and underwent high speciation rates during the Middle Miocene Climatic Optimum, with a decreasing trend following the Miocene Climatic Transition. We found no support for a single ecoregion acting as a centre of origin and diversification; instead, we inferred recurrent range shifts with dispersal among dissimilar adjacent ecoregions. Speciation linearly dependent on paleotemperatures, with either no or very low constant extinction rates, best explained the slowdown diversification pattern.Main conclusionsOur results support a species assembly of Cerrado savanna in South America during the Miocene with intermittent interchange with rain forest habitats. Past climate changes impacted the rate new species originated with apparently no impact on extinction. Finally, the repeated habitat shifts among open/dry and forested/humid ecoregions, rather than long‐term in‐situ diversification in single areas, highlights the very dynamic historical interchange between contrasting habitats in South America, possibly contributing to its high species diversity.

Origin, diversity, and conservation of karst-associated Bent-toed Geckos (Genus Cyrtodactylus) in Myanmar (Burma)

Fifty-eight percent of the 43 known species of the Bent-toed Geckos (Cyrtodactylus) from Myanmar are found only in karstic habitats in the Shan Plateau and Salween and Ayeyarwady basins. A stochastic character mapping analysis indicated that the occupation of karstic habitats evolved at least four times independently in Burmese lineages with both Sundaic and Indian origins. Karstic habitats not only serve as foci for speciation but are refugia for species extirpated from the surrounding forested habitats due to agricultural development. Despite the high levels of biodiversity and site-specific endemism in karstic habitats in Myanmar, they are some of the least protected ecosystems. The immense financial returns from unsustainable resource extraction (cement manufacturing) makes the challenge of legal karst conservation extremely difficult. Sadly, their continued exploitation for limestone shows no signs of abating. Until karst habitats in Myanmar are thoroughly investigated, a significant portion of this country’s herpetological diversity will remain underestimated and unprotected.

Geographical isolation, habitat shifts and hybridisation in the diversification of the Macaronesian endemic genus Argyranthemum (Asteraceae).

Inferring the processes responsible for the rich endemic diversity of oceanic island floras is important for our understanding of plant evolution and setting practical conservation priorities. This requires an accurate knowledge of phylogenetic relationships, which have often been difficult to resolve due to a lack of genetic variation. We employed genotyping-by-sequencing (GBS) to investigate how geographical isolation, habitat shifts, and hybridisation have contributed to the evolution of diversity observed in Argyranthemum Webb (Asteraceae), the largest genus of flowering plants endemic to the Macaronesian archipelagos. Species relationships were resolved, and biogeographical stochastic mapping identified intra-island speciation as the most frequent biogeographic process underlying diversification, contrary to the prevailing view in Argyranthemum and the Canary Islands. D-statistics revealed significant evidence of hybridisation between lineages co-occurring on the same island, however there was little support for the hypothesis that hybridisation may be responsible for the occurrence of nonmonophyletic multi-island endemic (MIE) species. Geographic isolation, habitat shifts and hybridisation have all contributed to the diversification of Argyranthemum, with intra-island speciation found to be more frequent than previously thought. Morphological convergence is also proposed to explain the occurrence of nonmonophyletic MIE species. This study reveals greater complexity in the evolutionary processes generating Macaronesian endemic diversity.

A phylogenetic approach to understand the evolution of reproduction in coleoid cephalopods

A central question in the evolution of life-histories is whether organisms reproduce once or repeatedly. For cephalopods, the main differences between semelparous and iteroparous are based on ovulation pattern and spawning type. The different reproductive strategies in coleoid cephalopods could be related to the habitat in which the species dwell (coastal vs. oceanic) and/or to environmental forces, thus, both aspects should be quantitatively evaluated under an evolutionary perspective to reconstruct: (a) the ancestral ovulation type of coleoid cephalopods, and (b) the potential of correlated evolution between ovulation type versus habitat and environment. Ancestral states of ovulation type were estimated using stochastic mapping based on literature data (i.e. synchronous or asynchronous), and this information was combined with a new molecular phylogeny including 165 species. The evolutionary correlation between ovulation type, habitat, and environment was estimated by means of the Markov model comparing the rates of gain and loss. The estimates of ancestral states of ovulation type for coleoid cephalopods resulted in a high probability that Octopodiformes evolved from synchronous ovulation type, and Decapodiformes from asynchronous ovulation type. The three traits evaluated presented phylogenetic signal, although no correlation was found between habitat and ovulation type. Overall, species in stable environments showed a tendency towards synchronous ovulation type, while the asynchronous ovulation pattern was found more frequently in species that live in unstable environments, being this last trait also responsible for triggering the change of ovulation type in some species throughout evolution.

Phylogeny and biogeography of South American marsh pitcher plant genus Heliamphora (Sarraceniaceae) endemic to the Guiana Highlands

Heliamphora is a genus of carnivorous pitcher plants endemic to the Guiana Highlands with fragmented distributions. We present a well resolved, time-calibrated, and comprehensive Heliamphora phylogeny estimated using Bayesian inference and maximum likelihood based on nuclear genes (26S, ITS, and PHYC) and secondary calibration. We used stochastic mapping to infer ancestral states of morphological characters and ecological traits. Our ancestral state estimations revealed that the pitcher drainage structures characteristic of the genus transformed from a hole to a slit in single clade, while other features (scape pubescence and hammock-like growth) have been gained and lost multiple times. Habitat was similarly labile in Heliamphora, with multiple transitions from the ancestral highland habitats into the lowlands. Using a Mantel test, we found closely related species tend to be geographically closely distributed. Placing our phylogeny in a historical context, major clades likely emerged through both vicariance and dispersal during the Miocene with more recent diversification driven by vertical displacement during the Pleistocene glacial-interglacial thermal oscillations. Despite the dynamic climatic history experienced by Heliamphora, the temperature changes brought by global warming pose a significant threat, particularly for those species at the highest elevations.

Analysis of the -CSA-ES with Repair by Projection Applied to a Conically Constrained Problem.

Theoretical analyses of evolution strategies are indispensable for gaining a deep understanding of their inner workings. For constrained problems, rather simple problems are of interest in the current research. This work presents a theoretical analysis of a multi-recombinative evolution strategy with cumulative step size adaptation applied to a conically constrained linear optimization problem. The state of the strategy is modeled by random variables and a stochastic iterative mapping is introduced. For the analytical treatment, fluctuations are neglected and the mean value iterative system is considered. Nonlinear difference equations are derived based on one-generation progress rates. Based on that, expressions for the steady state of the mean value iterative system are derived. By comparison with real algorithm runs, it is shown that for the considered assumptions, the theoretical derivations are able to predict the dynamics and the steady state values of the real runs.

Stochastic semidiscretization method: Second moment stability analysis of linear stochastic periodic dynamical systems with delays

In this paper, an efficient numerical approach is presented, which allows the analysis of the moment dynamics, stability, and stationary behavior of linear periodic stochastic delay differential equations. The method leads to a high dimensional stochastic mapping with periodic statistical properties, from which the periodic first and second moment mappings are derived. The application of the method is demonstrated first through the analysis of the stochastic delay Mathieu equation. Then a practical case study, where the effect of spindle speed variation on the stability and the resulting surface quality of turning operations is investigated.

Structure and evolution of polysporangiate anthers in Melastomataceae

Polysporangiate anthers, i.e., anthers bearing more than four sporangia, are an unusual condition that has been reported in several angiosperm families, including Melastomataceae. The structure of anthers in Melastomataceae and taxa from its sister lineage was investigated in 302 species, which were categorized as polysporangiate or non-polysporangiate based on original and literature data. Additionally, the evolutionary history of the anther type in the family was assessed by stochastic character mapping. The polysporangiate anthers of Melastomataceae exhibit two corrugated thecae with transverse septa of parenchymatous tissue partitioning the four pollen sacs into several small locules, this being the most common type of sporangia multiplication among angiosperms. Despite the fact that non-polysporangiate anthers are the most common character-state observed and have been reconstructed in most ancestral nodes of the phylogeny, a relatively large number of transitions to polysporangiate anthers were estimated in our analyses. One event was detected in Meriania, four events were detected in Miconia, and two (with a reversal) or three independent transitions in Microlicia. Most species with polysporangiate anthers occur in Microlicia, representing about 41 % of the species in the genus. Even though tetrasporangiate anthers are the most common condition among angiosperms, dithecal polysporangiate anthers occur in at least 74 taxa of Melastomataceae, in a unique association with poricidal dehiscence.

Estimating dispersal and evolutionary dynamics in diploporan blastozoans (Echinodermata) across the great Ordovician biodiversification event

AbstractEchinoderms make up a substantial component of Ordovician marine invertebrates, yet their speciation and dispersal history as inferred within a rigorous phylogenetic and statistical framework is lacking. We use biogeographic stochastic mapping (BSM; implemented in the R package BioGeoBEARS) to infer ancestral area relationships and the number and type of dispersal events through the Ordovician for diploporan blastozoans and related species. The BSM analysis was divided into three time slices to analyze how dispersal paths changed before and during the great Ordovician biodiversification event (GOBE) and within the Late Ordovician mass extinction intervals. The best-fit biogeographic model incorporated jump dispersal, indicating this was an important speciation strategy. Reconstructed areas within the phylogeny indicate the first diploporan blastozoans likely originated within Baltica or Gondwana. Dispersal, jump dispersal, and sympatry dominated the BSM inference through the Ordovician, while dispersal paths varied in time. Long-distance dispersal events in the Early Ordovician indicate distance was not a significant predictor of dispersal, whereas increased dispersal events between Baltica and Laurentia are apparent during the GOBE, indicating these areas were important to blastozoan speciation. During the Late Ordovician, there is an increase in dispersal events among all paleocontinents. The drivers of dispersal are attributed to oceanic and epicontinental currents. Speciation events plotted against geochemical data indicate that blastozoans may not have responded to climate cooling events and other geochemical perturbations, but additional data will continue to shed light on the drivers of early Paleozoic blastozoan speciation and dispersal patterns.

Phylogenomics Resolves the Relationships within Antennaria (Asteraceae, Gnaphalieae) and Yields New Insights into its Morphological Character Evolution and Biogeography

There is an erratum for this article at: https://doi.org/10.1600/036364420X15959578652451 Abstract—Antennaria are dioecious perennial herbs distributed mainly in the Holarctic Region, with their major center of diversity in the Rocky Mountains of Western North America. The genus comprises 33 known sexual diploid/tetraploid species and at least five polyploid agamic complexes which mostly reproduce by forming asexual seeds. We performed a phylogenetic reconstruction of the 31 sexually-reproducing Antennaria species using a novel target enrichment method that employs custom capture probes designed to work across Asteraceae. Both concatenated and coalescent-based analyses of DNA sequence data from hundreds of nuclear loci recovered Antennaria as a monophyletic group except for the long-disputed species, Antennaria linearifolia, which was recovered outside of the genus. Antennaria was further resolved into three distinct, major lineages. Analysis of ancestral state reconstruction of 12 taxonomically important morphological characters elucidated patterns of character evolution throughout the genus. Estimations of ancestral geographic ranges and molecular dating analyses demonstrated the Rocky Mountain region, including the Vancouverian Province, as the center of origin for the genus Antennaria, around 5.8 MYA. Subsequent dispersals of Antennaria into the Arctic and Appalachian provinces, Canadian provinces, and Eurasia took place roughly 3.2 MYA, 2.4 MYA, and 1.6 MYA, respectively. Biogeographical stochastic mapping indicated that 51.4% of biogeographical events were based on within-area speciation. The remaining 48.6% of the events were divided into two types of dispersals: 1) range expansion dispersals (anagenic, 37%), and 2) founder/jump dispersals (cladogenic, 11.6%). Our results provide a framework for future evolutionary studies of Antennaria, including speciation, origin(s) of polyploidy, and agamospermy in the genus.

Denoising Stochastic Progressive Photon Mapping Renderings Using a Multi-Residual Network

Stochastic progressive photon mapping (SPPM) is one of the important global illumination methods in computer graphics. It can simulate caustics and specular-diffuse-specular lighting effects efficiently. However, as a biased method, it always suffers from both bias and variance with limited iterations, and the bias and the variance bring multi-scale noises into SPPM renderings. Recent learning-based methods have shown great advantages on denoising unbiased Monte Carlo (MC) methods, but have not been leveraged for biased ones. In this paper, we present the first learning-based method specially designed for denoising-biased SPPM renderings. Firstly, to avoid conflicting denoising constraints, the radiance of final images is decomposed into two components: caustic and global. These two components are then denoised separately via a two-network framework. In each network, we employ a novel multi-residual block with two sizes of filters, which significantly improves the model’s capabilities, and makes it more suitable for multi-scale noises on both low-frequency and high-frequency areas. We also present a series of photon-related auxiliary features, to better handle noises while preserving illumination details, especially caustics. Compared with other state-of-the-art learning-based denoising methods that we apply to this problem, our method shows a higher denoising quality, which could efficiently denoise multi-scale noises while keeping sharp illuminations.

Multiple Photon Sampling Technique Based on Stochastic Progressive Photon Mapping

This paper introduces a multiple photon sampling technique based on stochastic progressive photon mapping. We use the image space concept to divide the scene into continuous sub-blocks and then we calculate our proposed distance function and photon number function in each of the sub-blocks. The distance function is used to calculate the distance error of the hit point and to determine whether each sub-block is located at a boundary between different objects. The photon number function is used to calculate the photon number error and to determine whether the photon distribution in each sub-block is uniform. Based on the values of the distance error and the photon number error, the multiple photon sampling technique is used to acquire multiple samples of the hit point in each sub-block. Instead of using a single radius for the radiance estimate, we use three different radii and compute the final radiance estimate as a weighted average of the three values. When compared with the existing stochastic progressive photon mapping method, our method provides a better solution to the photon distribution problem and can also reduce bias and noise, especially in the scene with drastic changes in light and dark.

Transitions between biomes are common and directional in Bombacoideae (Malvaceae)

AbstractAimTo quantify evolutionary transitions between tropical evergreen rain forest and seasonally dry biomes, to test whether biome transitions affect lineage diversification and to examine the robustness of these results to methodological choices.LocationThe tropics.Time periodThe Cenozoic.Major taxa studiedThe plant subfamily Bombacoideae (Malvaceae).MethodsWe inferred ancestral biomes based on a fossil‐dated molecular phylogeny of 103 species (59% of the clade) and recorded the number of transitions among biomes using biogeographical stochastic mapping based on the dispersal‐extinction‐cladogenesis model. We then estimated diversification rates using state‐specific speciation and extinction rate (SSE) methods. Furthermore, we tested the sensitivity of the results to model choice, phylogenetic uncertainty, measurement error and biome definition.ResultsWe found numerous transitions from evergreen rain forest to seasonally dry biomes, and fewer in the opposite direction. These results were robust to methodological choices. Biome type did not influence diversification rates, although this result was subject to uncertainty, especially related to model choice and biome definition.Main conclusionsOur results contradict the idea of evolutionary biome conservatism in Bombacoideae, and support previous findings that evergreen rain forests serve as a source for the flora of seasonally dry biomes. The impact of biome classification and biome definition on the results suggest caution when using a biome concept for biogeographical reconstruction and diversification rate analysis.

Global Diversification Dynamics Since the Jurassic: Low Dispersal and Habitat-Dependent Evolution Explain Hotspots of Diversity and Shell Disparity in River Snails (Viviparidae).

The Viviparidae, commonly known as River Snails, is a dominant group of freshwater snails with a nearly worldwide distribution that reaches its highest taxonomic and morphological diversity in Southeast Asia. The rich fossil record is indicative of a probable Middle Jurassic origin on the Laurasian supercontinent where the group started to diversify during the Cretaceous. However, it remains uncertain when and how the biodiversity hotspot in Southeast Asia was formed. Here, we used a comprehensive genetic data set containing both mitochondrial and nuclear markers and comprising species representing 24 out of 28 genera from throughout the range of the family. To reconstruct the spatiotemporal evolution of viviparids on a global scale, we reconstructed a fossil-calibrated phylogeny. We further assessed the roles of cladogenetic and anagenetic events in range evolution. Finally, we reconstructed the evolution of shell features by estimating ancestral character states to assess whether the appearance of sculptured shell morphologies was driven by major habitat shifts. The molecular phylogeny supports the monophyly of the three subfamilies, the Bellamyinae, Lioplacinae, and Viviparinae, but challenges the currently accepted genus-level classification in several cases. The almost global distribution of River Snails has been influenced both by comparatively ancient vicariance and more recent founder events. In Southeast Asia, Miocene dispersal was a main factor in shaping the modern species distributions. A recurrent theme across different viviparid taxa is that many species living in lentic waters exhibit sculptured shells, whereas only one strongly sculptured species is known from lotic environments. We show that such shell sculpture is habitat-dependent and indeed evolved several times independently in lentic River Snails. Considerably high transition rates between shell types in lentic habitats probably caused the co-occurrence of morphologically distinct shell types in several lakes. In contrast, directional evolution toward smooth shells in lotic habitats, as identified in the present analyses, explains why sculptured shells are rarely found in these habitats. However, the specific factors that promoted changes in shell morphology require further work. [biogeographical analyses; fossil-calibrated phylogeny; fossil-constrained analyses; Southeast Asia; stochastic character mapping.].