Latitudinal Diversity Patterns Research Articles

Correction to: Revisiting Alwyn H. Gentry’s forest transect data: latitudinal beta diversity patterns are revealed using a statistical sampling-model-based approach

Correction to: Revisiting Alwyn H. Gentry’s forest transect data: latitudinal beta diversity patterns are revealed using a statistical sampling-model-based approach

Latitudinal distributions of the species richness, phylogenetic diversity, and functional diversity of fleas and their small mammalian hosts in four geographic quadrants

We studied latitudinal patterns in the species richness (SR), the phylogenetic diversity (PD), and the functional diversity (FD) of fleas and their mammalian hosts. We asked whether these patterns in either fleas, hosts, or both 1) conform to a classical latitudinal gradient; 2) vary geographically; and 3) differ between fleas and hosts. We also asked whether the patterns of PD and FD follow those of SR. We collected data on the latitudinal distribution of 1022 flea and 900 mammal species from literature sources and calculated the SR, PD, and FD of both groups in 1° latitude bands. Then, we used broken‐stick regression models to analyse separately the latitudinal variation of 1) each diversity facet and 2) fleas and hosts in each geographic quadrant. The classical latitudinal gradient pattern was not found in either fleas or hosts across any facet of diversity or geographic quadrant, except for the PD of fleas in the southeastern quadrant and the FD of hosts in the southwestern quadrant. Latitudinal patterns of the SR, PD and FD of fleas and hosts differed substantially between geographic quadrants. Furthermore, the latitudinal distributions of flea and host SR were similar in three of four quadrants (except the northeastern quadrant), whereas the latitudinal distributions of flea and host PD were similar in the southwestern quadrant only. No similarity in flea versus host FD was revealed. The latitudinal patterns of flea and host PD and FD mostly did not follow those of their SR. We conclude that latitudinal gradients of species richness and phylogenetic and functional diversity appeared not to be universal phenomena. Instead, the latitudinal distributions of these diversity facets represent an interplay of ecological (current and past) and historical processes. For parasites, the processes acting on hosts add another layer of complexity underlying their latitudinal diversity patterns.

Revealing biogeographic patterns in genetic diversity of native and invasive plants and their association with soil community diversity in the Chinese coast

Within‐species genetic diversity is shaped by multiple evolutionary forces within the confines of geography, and has cascading effects on the biodiversity of other taxa and levels. Invasive species are often initially limited in genetic diversity but still respond rapidly to their new range, possibly through ‘pre‐adapted' genotypes or multiple sources of genetic diversity, but little is known about how their genetic structure differs from that of native species and how it alters the genetic‐species diversity relationship. Here, we selected a widespread native species Phragmites australis and its co‐occurring invasive competitor Spartina alterniflora as our model plant species. We investigated the genetic structure of P. australis using two chloroplast fragments and ten nuclear microsatellites in 13 populations along the Chinese coastal wetlands. We discovered a distinct geographical differentiation, showing that the northern and southern populations harbored unique genotypes. We also found a significant increase in genetic diversity (allelic richness and expected heterozygosity) from south to north. Combined with previous studies of S. alterniflora, the Mantel tests revealed a significant correlation of genetic distances between P. australis and S. alterniflora even when controlling for geographic distance, suggesting that the invasive species S. alterniflora might exhibit a phylogeographic pattern similar to that of the native species to some extent. Furthermore, our results suggest that the S. alterniflora invasion has altered the relationship between the genetic diversity of the dominant native plant and the associated species richness of soil nematodes. The reason for the alteration of genetic‐species diversity relationship might be that the biological invasion weakens the environmental impact on both levels of biodiversity. Our findings contribute to understanding the latitudinal patterns of intraspecific genetic diversity in widespread species. This work on the genetic diversity analysis of native species also provides significant implications for the invasion stage and ecological consequences of biological invasions.

The functional mechanism behind the latitudinal pattern of liana diversity: Freeze-thaw embolism reduces the ecological performance of liana species.

There is a strong decrease in liana diversity along latitudinal and altitudinal gradients at a global scale, and there is a marked difference in liana diversity between tropical and temperate ecosystems. From these observations, it has been proposed that cold temperatures would restrict the ecological patterns of liana because of their vascular system's vulnerability to freeze-thaw embolism. Our objective was to establish the functional mechanism that drives the loss of liana diversity along a latitudinal temperature gradient. We evaluate the ecological performance of liana in 10 different species based on the apical growth rate, as well as functional traits associated with efficiency (maximum hydraulic conductivity and percentage conductivity lost) and safety of water transport (vessel diameter, vessel density, wood density, and root pressure). We found that at the colder (more southern) site within the latitudinal gradient, liana species showed lower performance, with a fivefold decrease in their apical growth rate as compared to the warmer (more northern) sites. We postulate that this lower performance results from a much lower water transport efficiency (26.1-fold decrease as compared to liana species that inhabit warmer sites) that results from higher freeze-thaw (37.5% of PLC) and reduction of vessel diameter (3 times narrower). These results are unmistakable evidence that cold temperature restricts liana performance: in a cold environment, liana species exhibit a strong decrease in performance, low efficiency, and higher safety of water transport. Conversely, at warmer sites, we found that liana species exhibit functional strategies associated with higher performance, higher efficiency, and lower safety of water transport capacity. This trade-off between efficiency and safety of water transport and their effects on performance could explain the latitudinal pattern of liana diversity.

Revisiting Alwyn H. Gentry’s forest transect data: latitudinal beta diversity patterns are revealed using a statistical sampling-model-based approach

Gentry’s forest transect data have been frequently used to assess global patterns of plant diversity and plant species compositional changes along environmental and geographical gradients. Based on the worldwide woody plant abundance records from Gentry’s 197 localities/plots (each consisting of ten 2 m × 50 m subplots/transects), we apply a recently developed sampling-model-based standardization method (iNEXT.beta3D standardization) to examine how beta diversity among subplots varies with latitude. Beta diversity quantifies the extent of among-subplot differentiation which represents the interacting effect of species abundance distribution and spatial aggregation. Here beta diversity is obtained by a multiplicative decomposition scheme based on the framework of Hill numbers of any order q ≥ 0. Under statistical sampling models, data in nearly all of the 197 localities were incomplete, i.e., there were species present in the assemblage but undetected in the data. For Gentry’s data collected along narrow transects, the dependence among sampled individuals due to spatial aggregation is generally weak. The observed beta diversity depends on the among-subplot differentiation and sampling effort/completeness, which in turn induce dependence of the observed beta diversity on alpha and gamma diversity. To control for sampling effort/completeness, the iNEXT.beta3D method standardizes both alpha and gamma diversity at the same level of sample coverage to formulate coverage-based beta diversity. The resulting standardized beta diversity provides a statistical solution to remove the dependence of beta diversity on both alpha and gamma diversities, and thus reflects the pure among-subplot differentiation. The coverage-based standardization reveals latitudinal beta diversity patterns/trends not only for richness-based, but also for abundance-sensitive beta diversity.

Interhemispheric biodiversity peaks of living brachiopods coinciding with warm-temperate zones and correlated to a multitude of biotic, abiotic and evolutionary factors

Applying Locally Weighted Scatter-plot Smoother (LOESS) regression, we analysed the global latitudinal diversity patterns of 394 living brachiopod species. We found a consistent bimodal pattern dominated by two mid-latitude peaks located respectively at 35–40°S and 30–35°N (~warm-temperate zones, WTZs). The bimodality was found to be largely persistent and consistent irrespective of taxonomic, bathymetric and spatial scales. We tested the strength of seven ecological hypotheses thought to potentially explain the classic unimodal latitudinal diversity gradient. The Rapoport's rule was found to be the strongest model fitting the bimodal pattern, followed by the Species-Energy hypothesis. The mechanisms through which the mean latitudinal ranges and thermal niches of living brachiopods may have combined to produce the bimodality are further linked to two other factors: 1) most living brachiopods seem to have a strong adaptation to the mesothermal conditions of the WTZs, and 2) for living brachiopods, the WTZs appear to represent both a source of speciation indicated by a relatively higher per-genus diversification rate and a ‘sink’ of biodiversity due to biogeographic mixing and a concentration of species range-end points.

Micro- to Macro-Scale Foraminiferal Distributions: The Contributions of Martin A. Buzas*

Abstract The research that Martin A. Buzas has published over the past more than 40 years has influenced us greatly. That research has many strands that cannot be dealt with in this short review. However, the theme of micro- to macroscale foraminiferal distributions is interwoven throughout Buzas's research career. Distributions are something that Buzas is very fond of. He was trained in statistics as well as foraminifera and so it was inevitable that he would combine his knowledge of statistical distributions with foraminiferal distributions at several different scales. He has studied the distribution of foraminifera at microscales, horizontally within a 10 cm2 area of the sea floor or vertically, cm by cm within a 20 cm core. He has also worked at the mesoscale, quantifying, through the pioneering use of the General Linear Model, the relationship of foraminiferal distributions and environmental variables in space and time. This research led to the hypothesis of pulsating patches. He has worked at the macroscale with S. J. Culver, defining the distribution of benthic foraminiferal provinces, showing that all foraminiferal distributions, particularly around the coasts of North and Central America, belong to the same statistical distribution. Their work has documented the assembly and disassembly of communities and the latitudinal patterns of deep-sea benthic foraminiferal diversity in the Atlantic basin. Most recently, with his coauthor, mathematical statistician L. C. Hayek, Buzas has delved deep into the intricacies of species diversity and solved a 50 year-old supposedly intractable problem of mathematically relating species richness with species evenness. This work led to the introduction of new approaches to understanding community structure and recognizing boundaries between adjacent communities (SHE analysis). Many of us work long hours and publish many papers over our careers but few of us truly influence the fundamentals of our science. Marty Buzas is one micropaleontologist whose work will be of lasting significance.

Global patterns and drivers of genetic diversity among marine habitat‐forming species

AbstractAimIntraspecific genetic diversity is one of the pillars of biodiversity, supporting the resilience and evolutionary potential of populations. Yet, our knowledge regarding the patterns of genetic diversity at macroecological scales, so‐called macrogenetic patterns, remains scarce, particularly in marine species. Marine habitat‐forming (MHF) species are key species in some of the most diverse but also most impacted marine ecosystems, such as coral reefs and marine forests. We characterize the patterns and drivers of genetic diversity in MHF species and provide a macrogenetic baseline, which can be used for conservation planning and for future genetic monitoring programmes.LocationGlobal.Time periodContemporary.Major taxa studiedBryozoans, hexacorals, hydrozoans, octocorals, seagrasses, seaweeds, sponges.MethodsWe analysed a database including genetic diversity estimates based on microsatellites in more than 9,000 georeferenced populations from 140 species, which belong to seven animal and plant taxa. Focusing on expected heterozygosity, we used generalized additive models to test the effect of latitude, taxon, and conservation status. We tested the correlation between the species richness and the genetic diversity.ResultsWe reveal a significant but complex biogeographic pattern characterized by a bimodal latitudinal trend influenced by taxonomy. We also report a positive species genetic diversity correlation at the scale of the ecoregions. The difference in genetic diversity between protected and unprotected areas was not significant.Main conclusionsThe contrasting results between MHF animals and plants suggest that the latitudinal genetic diversity patterns observed in MHF species are idiosyncratic, as reported in terrestrial species. Our results support the existence of shared drivers between genetic and species diversities, which remain to be formally identified. Concerning, these macrogenetic patterns are not aligned from the existing network of marine protected areas. Providing the first macrogenetic baseline in MHF species, this study echoes the call regarding the need to consider genetic diversity in biodiversity assessments and management.

Range restricted old and young lineages show the southern Western Ghats to be both a museum and a cradle of diversity for woody plants.

The Western Ghats (WG) mountain chain is a global biodiversity hotspot with high diversity and endemicity of woody plants. The latitudinal breadth of the WG offers an opportunity to determine the evolutionary drivers of latitudinal diversity patterns. We examined the spatial patterns of evolutionary diversity using complementary phylogenetic diversity and endemism measures. To examine if different regions of the WG serve as a museum or cradle of evolutionary diversity, we examined the distribution of 470 species based on distribution modelling and occurrence locations across the entire region. In accordance with the expectation, we found that the southern WG is both a museum and cradle of woody plant evolutionary diversity, as a higher proportion of both old and young evolutionary lineages are restricted to the southern WG. The diversity gradient is likely driven by high geo-climatic stability in the south and phylogenetic niche conservatism for moist and aseasonal sites. This is corroborated by persistent lineage nestedness at almost all evolutionary depths (10-135 million years), and a strong correlation of evolutionary diversity with drought seasonality, precipitation and topographic heterogeneity. Our results highlight the global value of the WG, demonstrating, in particular, the importance of protecting the southern WG-an engine of plant diversification and persistence.

The latitudinal gradient of functional diversity of Miocene marine mollusks from Chile

Understanding latitudinal variations in biodiversity is central for biogeography. Along the coasts of the Southeast Pacific, several taxa show inverse latitudinal patterns of biodiversity, i.e. increasing species numbers from lower to higher latitudes. A plausible explanation for these patterns is that fjords, formed during the Pleistocene glaciations, increased the diversity of available biotopes that allowed for higher diversity in high latitudes. Assessing this hypothesis requires us to analyze latitudinal patterns of functional diversity (which is intimately related to niche use) in the absence of fjords, i.e. earlier than their formation. Here we test if the fossil record before the generation of fjords shows higher functional diversity at lower than at higher latitudes (a ‘regular' functional diversity gradient).We analyzed four components of functional diversity (functional richness, functional divergence, functional dispersion and functional evenness) for a fossil marine mollusk fauna from the lower Miocene (~18 million years ago) across four regions spanning more than 10 latitudinal degrees of the Chilean coast (between ~34°S and 45°S).The functional richness of gastropods and bivalves decreased non‐linearly from low to high latitudes. Contrarily, the functional evenness of gastropods remained relatively constant across the region and that of bivalves peaked at 45°S. The functional divergence and functional dispersion of taxonomic groups did not exhibit clear patterns of latitudinal variation. The multivariate analysis uncovered non‐linear latitudinal patterns in the abundance of functional groups (gastropods and bivalves), with the largest abundance towards lower latitudes.These results suggest that the niche breadth of mollusk assemblages might have decreased with latitude in the lower Miocene. This work can shed light on the mechanisms underlying the latitudinal variation of diversity observed today, offering a better understanding of how these patterns changed over time.

Diversity and ecological footprint of Global Ocean RNA viruses.

DNA viruses are increasingly recognized as influencing marine microbes and microbe-mediated biogeochemical cycling. However, little is known about global marine RNA virus diversity, ecology, and ecosystem roles. In this study, we uncover patterns and predictors of marine RNA virus community- and "species"-level diversity and contextualize their ecological impacts from pole to pole. Our analyses revealed four ecological zones, latitudinal and depth diversity patterns, and environmental correlates for RNA viruses. Our findings only partially parallel those of cosampled plankton and show unexpectedly high polar ecological interactions. The influence of RNA viruses on ecosystems appears to be large, as predicted hosts are ecologically important. Moreover, the occurrence of auxiliary metabolic genes indicates that RNA viruses cause reprogramming of diverse host metabolisms, including photosynthesis and carbon cycling, and that RNA virus abundances predict ocean carbon export.

Incongruent latitudinal patterns of taxonomic, phylogenetic and functional diversity reveal different drivers of caddisfly community assembly across spatial scales

AbstractAimCommunity assembly processes are difficult to observe in nature but can be inferred from species diversity patterns. However, taxonomic patterns may be consistent with multiple explanations, such as habitat filtering or biogeographical processes, which can also act differently across spatial scales. Here, we assessed multiple facets of diversity to determine the relative contributions of local versus regional processes and historical versus contemporary factors in establishing macroecological patterns.LocationFrom the Mediterranean peninsulas to northern Scandinavia.Time periodSpecies occurrence data gathered since c. 1980.Major organism group studiedTrichoptera (Insecta).MethodsBased on an extensive functional space and a phylogenetic tree including 197 and 509 species, respectively, and the composition of 180 communities, we assessed the distribution of taxonomic, functional and phylogenetic diversity within 18 ecoregions (local α‐ and β‐diversity) and among those ecoregions (regional γ‐ and β‐diversity).ResultsLocal estimates of taxonomic, functional and phylogenetic α‐ and β‐diversity were similar across Europe, which reveals that all streams have similar carrying capacity even though the local abiotic factors involved are likely different among ecoregions. In contrast, regional taxonomic and phylogenetic diversities decreased as latitude increased, whereas functional richness and functional dispersion displayed unimodal relationships. The position of species on the functional space was not conserved, while northern species pools were found to be phylogenetically clustered and southern ones overdispersed. The nestedness component mainly contributed to the taxonomic and phylogenetic β‐diversity among northern communities, whereas in southern latitudes the turnover was dominant.Main conclusionsDecoupled latitudinal patterns of taxonomic, phylogenetic and functional diversity reveal the importance of regional environmental filtering over local factors in limiting species range and shaping the regional species pool. The biogeographical signature is still present; the northern recolonizations following the Pleistocene glaciations originated exclusively from central regions, instead of Mediterranean refugia, as was previously accepted.

Biogeographic patterns of soil microbe communities in the deserts of the Hexi Corridor, northern China

Recent studies show that different microorganisms, especially bacteria and fungi, exhibit contrasting latitudinal, longitudinal, and altitudinal diversity patterns at a global scale, but little is known about biogeographic patterns in desert ecosystems. In this study, we chose a narrow geographic channel, namely the deserts of northern China’s Hexi Corridor as the study area. Based on field survey and next-generation sequencing (Illumina MiSeq PE300 Platform), to map soil microbial geographic diversity patterns in this area and further determine the main driving factors responsible for shaping the soil microbial community. The results show that bacteria and eukaryotic diversity increased linearly with increasing longitude and altitude, but decreased with increasing latitude in the Hexi Corridor deserts, whereas archaeal diversity showed little change along these geographic gradients. Some individual phyla within the bacterial, archaeal, and eukaryota communities were not always consistent with collective trends, e.g., for the α-diversity of the ten most dominant bacterial phyla, only six phyla showed a statistically significant increase with altitude. The soil microbial community composition was jointly shaped by geographic distance and environmental variables (regional climatic factors and local edaphic variables). The effect of geographic distance on the soil microbial community composition was slightly stronger than that of the environmental variables. Intra-domain links were stronger than inter-domain links in the soil microbial network of the Hexi Corridor deserts, and these links were mostly positive. Although bacteria formed more connections than both archaea and eukaryotes, removing the archaea resulted in a lower natural connectivity, suggesting that the archaea were the core group for building this desert region’s soil microbial co-occurrence network. Taken together, these findings deepen our understanding of regional-scale soil microbial diversity patterns in this desert ecosystem.

Do host‐associated microbes show a contrarian latitudinal diversity gradient? Insights from Mytilus californianus, an intertidal foundation host

AbstractAimThe latitudinal diversity gradient (LDG) is one of the most pervasive large‐scale trends in biodiversity. However, whether microbial taxa also conform to this pattern remains poorly known. This study uses the gill and shell‐surface microbiomes of the marine bivalve Mytilus californianus to test whether the diversity of host‐associated microbial communities declines with increasing latitude, as predicted by the LDG.LocationNortheastern Pacific coast, ranging from Sitka, AK to La Jolla, CA, USA (spanning 24.12 degrees of latitude).TaxonBacteria and Archaea associated with M. californianus gills and shell‐surfaces.MethodsWe amplified and sequenced the 16S rRNA gene from M. californianus gill and shell‐surface samples. We used linear and quadratic regressions, accounting for spatial autocorrelation when needed, of average alpha and gamma diversities of the whole microbiome, as well as individual microbial clades, to determine whether these taxa conformed to the traditional LDG. We also used permutational multivariate analysis of variance to determine the level of compositional differentiation among sampling sites.ResultsGill and shell‐surface microbiota show differing latitudinal diversity patterns, with both micro‐environments exhibiting high levels of compositional differentiation along latitude. Individual microbial clades within each micro‐environment also show different latitudinal trends, most likely due to differing ecologies and life histories.Main conclusionsMytilus californianus‐associated microbial taxa show a flat, hump‐shaped or contrarian LDG, suggesting that a steep decline in diversity with increasing latitude may not be a universal pattern across different domains of life.

An approach for estimating haplotype diversity from sequences with unequal lengths

Abstract Genetic diversity is an essential component of biodiversity. Developing robust quantification methods is critically important in depicting the genetic diversity underlying the geographical distributions of species, especially for the sequence data with unequal lengths. Traditional calculation of genetic diversity depends on sequences of equal length. However, many homologous sequences downloaded from online repositories vary in length, posing a significant challenge to quantify the genetic diversity, especially haplotype diversity. We developed a new approach independent of sequence length by applying the same parameters used in calculating nucleotide diversity to estimate haplotype diversity. We compared this novel approach with the calculations by the program DNAsp, and we used simulation data from terrestrial vertebrates (birds, mammals and amphibians) and Homo sapiens to validate the method's performance. We further applied this approach to explore the global latitudinal gradients of haplotype diversity in amphibians, mammals and birds, and compared the results by traditional methods. The haplotype diversity calculated by our novel approach is consistent with the results from DNAsp. The simulations showed that our approach is robust and has a good estimating performance for sequence data with unequal lengths. For the datasets of terrestrial vertebrates and H. sapiens, our approach is capable of estimating haplotype diversity with unequal intraspecific sequence lengths. In contrast to patterns based on traditional methods, we observed different latitudinal patterns of haplotype diversity between the northern and southern hemispheres for terrestrial vertebrates, which is consistent with the updated pattern of nucleotide diversity for mammals. The present work contributes to the development of more precise quantification methods, which may be broadly applied to assessing biogeographical patterns of genetic diversity.

Multi‐scale biodiversity analyses identify the importance of continental watersheds in shaping lake zooplankton biogeography

AbstractAimWe examined variation in crustacean zooplankton composition and diversity across Canada, the most lake‐rich country in the world. In addition to α‐diversity patterns, we explore mechanisms behind β‐diversity spatial variation, using taxonomic and functional metrics. Our goal was to explore geographical gradients and related mechanisms shaping zooplankton distribution across different spatial scales.LocationCanada.TaxonCrustacean zooplankton.MethodsPelagic zooplankton was sampled in and characterized for 624 lakes across Canada, spanning 12 ecozones (defined by climatic, vegetation and geological differences) or 6 continental drainage basins as part of the NSERC Canadian Lake Pulse Network project. We compared taxon and trait distributions, as well as spatial (longitudinal and latitudinal) patterns of community composition and diversity. We computed taxonomic and functional spatial β‐diversity indices, decomposing these into taxon replacement and richness differences. Finally, species (or traits) and lake uniqueness (contributions) to β‐diversity (SCBD and LCBD) were estimated by ecozone and continental basin.ResultsIn all, 90 crustacean zooplankton species were identified across the country. Differences in zooplankton taxonomic and functional composition were more distinct when considered by continental basin than by ecozone. α‐diversity varied greatly across space, with greatest diversity in eastern Canada. β‐diversity was greatest when based on taxonomy and was driven by richness differences across all spatial and biodiversity dimensions.Main conclusionsStructuring factors influencing zooplankton taxon and trait assemblages vary across spatial scales, being more important at the broadest scale considering continental hydrodynamics. Our results point to the combined effects of physical barriers to longitudinal dispersal and climate change in shaping zooplankton taxonomic and functional biogeography across Canadian lakes.

Global biogeography and diversification of a group of brown seaweeds (Phaeophyceae) driven by clade‐specific evolutionary processes

AbstractAimHistorical processes that shaped current diversity patterns of seaweeds remain poorly understood. Using Dictyotales, a globally distributed order of brown seaweeds as a model, we test if historical biogeographical and diversification patterns are comparable across clades. Dictyotales contain some 22 genera, three of which, Dictyota, Lobophora and Padina, are exceptionally diverse. Specifically, we test whether the evolutionary processes that shaped the latitudinal diversity patterns in these clades are in line with the tropical conservatism, out‐of‐the‐tropics or diversification rate hypotheses.LocationGlobal coastal benthic marine environments.TaxonDictyotales (Phaeophyceae).MethodsSpecies diversity was inferred using DNA‐based species delineation, addressing cryptic diversity and circumventing taxonomic problems. A six‐gene time‐calibrated phylogeny, distribution data of 3,755 specimens and probabilistic modelling of geographical range evolution were used to infer historical biogeographical patterns. The phylogeny was tested against different trait‐dependent models to compare diversification rates for different geographical units as well as different thermal affinities.ResultsOur results indicate that Dictyotales originated in the Middle Jurassic and reach a current peak of species diversity in the Central Indo‐Pacific. Ancestral range estimation points to a southern hemisphere origin of Dictyotales corresponding to the tropical southern Tethys Sea. Our results demonstrate that diversification rates were generally higher in tropical regions, but increased diversification rates in different clades are driven by different processes. Our results suggest that three major clades underwent a major diversification burst in the early Cenozoic, with Dictyota and Padina expanding their distribution into temperate regions while Lobophora retained a predominantly tropical niche.Main conclusionsOur results are consistent with both the tropical conservatism hypothesis, in which clades originate and remain in the tropics (Lobophora), and the out‐of‐the‐tropics scenario, where taxa originate and expand towards the temperate regions while preserving their presence in the tropics (Dictyota, Padina).

The multiple origins of sexual size dimorphism in global amphibians

AbstractAimBody size explains most of the variation in fitness within animal populations and is therefore under constant selection from ecological and reproductive pressures, which often promote its evolution in sex‐specific directions, leading to sexual size dimorphism (SSD). Several hypotheses have been proposed to explain the vast diversity of SSD across species. These hypotheses emphasize: (a) the mate competition benefits to larger male size (sexual selection); (b) the benefits of larger female size for fecundity (fecundity selection); (c) the simultaneous benefits of niche divergence for males and females to reduce intersexual competition for ecological resources (natural selection); and (d) the underlying impact of geographical variation in climatic pressures expected to shape large‐scale patterns of SSD in synergy with the above selection pressures (e.g., intensification of fecundity selection as breeding seasons shorten). Based on a new, global‐scale amphibian dataset, we address the shortage of large‐scale, integrative tests of these four hypotheses.LocationGlobal.Time periodExtant.Major taxa studiedClass Amphibia.MethodsUsing a > 3,500 species dataset spanning body size, ecological, life‐history, geographical and climatic data, we performed phylogenetic linear models to address the sexual, fecundity, ecological and climatic hypotheses of SSD.ResultsEvolution of SSD is discordant between anurans and salamanders. Anuran SSD is shaped by climate (male‐biased SSD increases with temperature seasonality) and by nesting site. In salamanders, SSD converges across species that occupy the same types of microhabitats (“ecodimorphs”), whereas reproductive or climatic pressures have no effects on their SSD. These contrasts are associated with latitudinal gradients of SSD in anurans, but not in salamanders.Main conclusionsAmphibian SSD is driven by ecological and climatic pressures, whereas no roles for sexual or fecundity selection were detected. We show that macroevolutionary processes determined by different forms of selection lead to latitudinal patterns of trait diversity, and the lack of them.

Latitudinal patterns of species diversity on South American rocky shores: Local processes lead to contrasting trends in regional and local species diversity

AbstractAimWe evaluated whether patterns of species diversity (α, β and γ) of rocky shore assemblages followed latitudinal gradients (i.e. LDGs) along the South American coasts, and tested hypotheses related to potential processes sustaining or disrupting the expected LDG pattern at various spatial scales.LocationCoasts of South America.TaxonMacroalgae and sessile/slow‐moving macrofauna on intertidal rocky shores.MethodsWe evaluated changes in species composition across 143 sites. The degree of replacement and loss of species at different spatial scales (i.e. coasts, regions and sites) were estimated to help distinguish among ecological, historical and evolutionary hypotheses for explaining LDGs. Furthermore, components of diversity and taxonomic distinctness were measured, and variability in these measures was decomposed using analysis of covariance. Finally, we examined relationships between diversity and a suite of environmental and anthropogenic variables to identify potential mechanisms that may be responsible for the reported spatial relationships.ResultsSpecies composition varied with latitude, and this variability was relatively consistent on both coasts. At all spatial scales, replacement of species was the dominant phenomenon (>95%), rather than loss in the total number of species (<5%). LDGs were strongly dependent on the diversity component and the spatial scale: generally, positive for regional β‐diversity, negative for α‐diversity and site β‐diversity. Sea surface temperature (SST) was the variable that best explained patterns of diversity along both coasts (14%–22%), but other regional and local environmental variables associated with river discharges, upwelling, confluence of currents, tides and anthropogenic pressures also accounted for an important portion of variation (5%–14% each).Main conclusionsSpecies diversity of South American rocky shores followed, with interruptions, LDGs. The trend of those LDGs, however, depended on the scale and metric used to describe diversity. It is proposed that patterns of LDGs at various scales are not the result of a single overarching process but are strongly influenced by local and regional processes. Although the most evident environmental gradient was the decrease in SST towards the south, it was demonstrated that regional and local environmental variables were also important for understanding the increase in regional β‐diversity towards the tropics.

Latitudinal distribution of polyplacophorans along the South-eastern Pacific coast: unravelling biases in geographical diversity patterns

Latitudinal diversity patterns in marine species are commonly estimated from literature records, which at times are incomplete and/or biased. Advances in molecular phylogenetics have contributed to avoid this bias, clarifying the identity of the species, improving our knowledge of species diversity and distribution. With the aim to identify biogeographic biases, we compiled and compared range distribution data of polyplacophorans along the South-eastern Pacific (SEP) coast (0°–56° S) generated from: (i) literature review (LIT dataset) and (ii) Operational Taxonomic Units (OTUs dataset), based on the analysis of 8949 individuals obtained from field sampling and biological collections. Cytochrome oxidase I (COI) and 16S rRNA of 104 specimens were used for genetic identification of conflictive morphospecies. Multivariate analysis (nMDS, PERMANOVA) were applied to test differences between datasets (LIT, OTUs) and also between biogeographic ecoregions. Just like prior studies based on literature reviews, the richness of LIT species showed an increase with latitude. Contrastingly, OTUs’ richness peaked at intermediate latitudes showing a bell-shaped distribution, indicating that the LIT dataset was flawed by inaccuracies in the identification and location of polyplacophoran species on the South-eastern Pacific, causing an overestimation of their geographic ranges. Our results contrast with the previous richness patterns described for the SEP polyplacophorans, where species richness was reported to increase with latitude. Both an overestimation of geographic ranges and inaccuracies in the identification of species cause these differences. Biogeographical studies should be conducted on the basis of a comprehensive review of specimens with verifiable occurrences, and incorporate as far as possible genetic analysis to define the identity of conflicting morphospecies, in order to improve the estimation of species richness and the understanding of marine biodiversity.