Major Ecological Shifts Research Articles

The role of geography, ecology, and hybridisation in the evolutionary history of Canary Island Descurainia.

Oceanic islands offer the opportunity to understand evolutionary processes underlying rapid diversification. Along with geographic isolation and ecological shifts, a growing body of genomic evidence has suggested that hybridisation can play an important role in island evolution. Here we use genotyping-by-sequencing (GBS) to understand the roles of hybridisation, ecology, and geographic isolation in the radiation of Canary Island Descurainia (Brassicaceae). We carried out GBS for multiple individuals of all Canary Island species and two outgroups. Phylogenetic analyses of the GBS data were performed using both super-matrix and gene tree approaches and hybridisation events were examined using D-statistics and Approximate Bayesian Computation (ABC). Climatic data were analysed to examine the relationship between ecology and diversification. Analysis of the supermatrix dataset resulted in a fully resolved phylogeny. Species networks suggest a hybridisation event has occurred for D. gilva, with these results being supported by ABC analysis. Strong phylogenetic signals for temperature and precipitation indicate one major ecological shift within Canary Island Descurainia. Inter-island dispersal played a significant role in the diversification of Descurainia, with evidence of only one major shift in climate preferences. Despite weak reproductive barriers and the occurrence of hybrids, hybridisation appears to have played only a limited role in the diversification of the group, with a single instance detected. The results highlight the need to use phylogenetic network approaches that can simultaneously accommodate ILS and gene flow when studying groups prone to hybridisation; patterns that might otherwise be obscured in species trees. This article is protected by copyright. All rights reserved.

Eco-morphological evolution of the Bolivar Peninsula (Texas, U.S.A.) during the last 2,000 years: A multi-proxy record of coastal environmental changes

In the face of rapidly changing climate and increasing natural and anthropogenic disturbances, the long-term dynamics of coastal ecosystems in relation to hurricanes and human activities has become a focus of research for ecologists and geomorphologists across the Gulf of Mexico. This study integrates diatom, remote sensing, geochemical, and hydrodynamic analyses to document the ecological and morphological development of the barrier-island and estuary-wetland complex bordering Galveston Bay, Texas, from the late Holocene to the Anthropocene. The multi-proxy dataset revealed two major ecological shifts between 1320 and 840 cal yr BP and between 230 cal yr BP and 2008 AD in Galveston Bay. The first shift was driven by the landfall of a backdoor hurricane at ∼1000 cal yr BP in combination with the aperiodic and intense long-shore current that caused the barrier complex to retreat over fluvial deposits while the Bolivar Peninsula was growing toward the west. These morphological changes resulted in a narrower inlet, hence, restricting the marine influence from entering the bay and converting Galveston Bay to a wave-dominated estuary that was shallower and fresher. The second shift was caused by increasing modification to the waterway and infrastructures since 1800 AD. As a result, rapid sediment accretion was induced near the North Jetty, forming the current Bolivar Flats and setting the stage for mangrove colonization. The warming climate and hurricanes in recent decades acted as catalysts that accelerated mangrove expansion on the Bolivar Peninsula. Our results imply that the proposed coastal barrier system will likely increase the sediment deficit, alter the biogeochemical environment, and impact the primary productivity in the bay. However, on a regional scale, more and more mangrove stands are expected to appear around estuaries and lagoons, and along man-made jetties and barriers along the Gulf.

Divergent vertebral formulae shape the evolution of axial complexity in mammals

Complexity, defined as the number of parts and their degree of differentiation, is a poorly explored aspect of macroevolutionary dynamics. The maximum anatomical complexity of organisms has undoubtedly increased through evolutionary time. However, it is unclear whether this increase is a purely diffusive process or whether it is at least partly driven, occurring in parallel in most or many lineages and with increases in the minima as well as the means. Highly differentiated and serially repeated structures, such as vertebrae, are useful systems with which to investigate these patterns. We focus on the serial differentiation of the vertebral column in 1,136 extant mammal species, using two indices that quantify complexity as the numerical richness and proportional distribution of vertebrae across presacral regions and a third expressing the ratio between thoracic and lumbar vertebrae. We address three questions. First, we ask whether the distribution of complexity values in major mammal groups is similar or whether clades have specific signatures associated with their ecology. Second, we ask whether changes in complexity throughout the phylogeny are biased towards increases and whether there is evidence of driven trends. Third, we ask whether evolutionary shifts in complexity depart from a uniform Brownian motion model. Vertebral counts, but not complexity indices, differ significantly between major groups and exhibit greater within-group variation than recognized hitherto. We find strong evidence of a trend towards increasing complexity, where higher values propagate further increases in descendant lineages. Several increases are inferred to have coincided with major ecological or environmental shifts. We find support for multiple-rate models of evolution for all complexity metrics, suggesting that increases in complexity occurred in stepwise shifts, with evidence for widespread episodes of recent rapid divergence. Different subclades evolve more complex vertebral columns in different configurations and probably under different selective pressures and constraints, with widespread convergence on the same formulae. Further work should therefore focus on the ecological relevance of differences in complexity and a more detailed understanding of historical patterns.

Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition

The Ediacara Biota-the oldest communities of complex, macroscopic fossils-consists ofthree temporally distinct assemblages: the Avalon (ca. 575-560 Ma), White Sea (ca.560-550 Ma), and Nama (ca. 550-539 Ma). Generic diversity varies among assemblages, with a notable decline at the transition from White Sea to Nama. Preservation and sampling biases, biotic replacement, and environmental perturbation have been proposed as potential mechanisms for this drop in diversity. Here, we compile a global database of the Ediacara Biota, specifically targeting taphonomic and paleoecological characters, to test these hypotheses. Major ecological shifts in feeding mode, life habit, and tiering level accompany an increase in genericrichness between the Avalon and White Sea assemblages. We find that ∼80% of White Sea taxa are absent from the Nama interval, comparable to loss during Phanerozoic mass extinctions. The paleolatitudes, depositional environments, and preservational modes that characterize the White Sea assemblage are well represented in the Nama, indicating that this decline is not the result of sampling bias. Counter to expectations of the biotic replacement model, there are minimalecological differences between these two assemblages. However, taxa that disappear exhibit a variety of morphological and behavioral characters consistent with an environmentally driven extinction event. The preferential survival of taxa with high surface area relative to volume may suggest that this was related to reduced global oceanic oxygen availability. Thus, our data support a link between Ediacaran biotic turnover and environmental change, similar to other major mass extinctions in the geologic record.

Ecosystem transformation following the mid-nineteenth century cessation of Aboriginal fire management in Cape Pillar, Tasmania

Ongoing European suppression of Aboriginal cultural land management since early-nineteenth century colonisation is widely thought to have caused major transformations across all Australian landscapes, including vegetation thickening, severe fires and biodiversity declines. However, these effects are often confounded in the densely settled southern Australia due to European land transformation. Landscapes currently under conservation and national park management in Tasmania are generally less disturbed, providing an opportunity to track ecosystem changes caused by the removal of Aboriginal peoples following colonisation in southern Australia. We use a multi-proxy palaeoecological technique and the analysis of historical aerial photography to investigate these changes in Cape Pillar, southeast Tasmania. Results reveal a major ecological shift following European colonisation, with the replacement of stable, open wet heathland characterised by minor fires (active cultural land use) with dense dry scrub characterised by major fires (cessation of cultural land use). We also discuss potential background role of regional climatic shifts in the observed ecological changes. Management programmes designed to restore open heathland pre-colonial cultural ecosystem would help reduce the risk of large fires in Cape Pillar.

Directionally biased habitat shifts and biogeographically informative cytonuclear discordance in the Hawaiian silversword alliance (Compositae).

Expanded phylogenetic analyses of the Hawaiian silversword alliance (Argyroxiphium, Dubautia, Wilkesia; Compositae) were undertaken to assess evolutionary and biogeographic informativeness of cytonuclear discordance and any biases in evolutionary directionality of ecological transitions within this prominent example of adaptive radiation. Samples spanning the geographic and ecological distributions of all recognized taxa were included in phylogenetic and biogeographic analyses of nuclear ribosomal DNA (nrDNA) and cpDNA sequences. Bayesian model testing approaches were used to model ecological evolution and the evolution of nuclear chromosomal arrangements while accounting for phylogenetic uncertainty. Cytonuclear discordance detected previously appears to reflect chloroplast capture, at least in part, with nrDNA trees being largely congruent with nuclear chromosomal structural data and fine-scale taxonomy. Comparison of biogeographic histories estimated from the posterior distributions of nrDNA and cpDNA trees, including inferred chloroplast-capture events, provides additional resolution of dispersal history, including a back-dispersal to Maui Nui from Hawai'i. A newly resolved major nrDNA clade of endemic Kaua'i taxa that mostly were described as new-to-science since the 1980s strengthens the earlier hypothesis that diversification on Kaua'i has not waned since the island began to decline in area through subsidence and erosion. Bias in habitat shifts was estimated, with transitions from dry-to-mesic or -wet and from wet-to-mesic or -bog habitats dominating diversification of the silversword alliance from a dry-adapted tarweed ancestor. The habitat-transition biases estimated here may indicate more limited pathways of ecological evolution than proposed previously for an adaptive radiation involving such major ecological shifts.

Extreme Precipitation and Flooding Contribute to Sudden Vegetation Dieback in a Coastal Salt Marsh.

Climate extremes are becoming more frequent with global climate change and have the potential to cause major ecological regime shifts. Along the northern Gulf of Mexico, a coastal wetland in Texas suffered sudden vegetation dieback following an extreme precipitation and flooding event associated with Hurricane Harvey in 2017. Historical salt marsh dieback events have been linked to climate extremes, such as extreme drought. However, to our knowledge, this is the first example of extreme precipitation and flooding leading to mass mortality of the salt marsh foundation species, Spartina alterniflora. Here, we investigated the relationships between baseline climate conditions, extreme climate conditions, and large-scale plant mortality to provide an indicator of ecosystem vulnerability to extreme precipitation events. We identified plant zonal boundaries along an elevation gradient with plant species tolerant of hypersaline conditions, including succulents and graminoids, at higher elevations, and flood-tolerant species, including S. alterniflora, at lower elevations. We quantified a flooding threshold for wetland collapse under baseline conditions characterized by incremental increases in flooding (i.e., sea level rise). We proposed that the sudden widespread dieback of S. alterniflora following Hurricane Harvey was the result of extreme precipitation and flooding that exceeded this threshold for S. alterniflora survival. Indeed, S. alterniflora dieback occurred at elevations above the wetland collapse threshold, illustrating a heightened vulnerability to flooding that could not be predicted from baseline climate conditions. Moreover, the spatial pattern of vegetation dieback indicated that underlying stressors may have also increased susceptibility to dieback in some S. alterniflora marshes.Collectively, our results highlight a new mechanism of sudden vegetation dieback in S. alterniflora marshes that is triggered by extreme precipitation and flooding. Furthermore, this work emphasizes the importance of considering interactions between multiple abiotic and biotic stressors that can lead to shifts in tolerance thresholds and incorporating climate extremes into climate vulnerability assessments to accurately characterize future climate threats.

Deep Lake Explorer: A web application for crowdsourcing the classification of benthic underwater video from the Laurentian Great Lakes

Underwater video is increasingly used to study aspects of the Great Lakes benthos including the abundance of round goby and dreissenid mussels. The introduction of these species has resulted in major ecological shifts in the Great Lakes, but the abundance and impacts of these species have heretofore been underassessed due to limitations of monitoring methods. Underwater video (UVID) can “sample” hard bottom sites where grab samplers cannot. Efficient use of UVID data requires affordable and accurate classification and analysis tools. Deep Lake Explorer (DLE) is a web application developed to support crowdsourced classification of UVID collected in the Great Lakes. Volunteers (i.e., the crowd) used DLE to classify 199 videos collected in the Niagara River, Lake Huron, and Lake Ontario for the presence of round gobies, dreissenid mussels, or aquatic vegetation, and for dominant substrate type. We compared DLE classification results to expert classification of the same videos to evaluate accuracy. DLE had the lowest agreement with expert classification for hard substrate (77%), and highest agreement for vegetation presence (90%), with intermediate agreement for round goby and mussel presence (89% and 79%, respectively). Video quality in the application, video processing, abundance of species of interest, volunteer experience, and task complexity may have affected accuracy. We provide recommendations for future crowdsourcing projects like DLE, which can increase timeliness and decrease costs for classification but may come with tradeoffs in accuracy and completeness.

Sedimentary diatom and pigment-inferred recent anthropogenic accelerated eutrophication of a Mediterranean lake (Lake Dojran, Republic of North Macedonia / Greece)

Lake eutrophication is recognised as a serious global challenge, and many regional legislative programmes are being made to attempt to relieve nutrient pollution and restore deteriorated lake ecological state. However, it is of primary importance to understand the degradation processes and reference conditions. The palaeolimnological approach allows us to use ecological evidences preserved in lake sediments to track the changes of lake trophic status under human impact. Diatoms, a proxy for ecological and limnological change, and pigments, a proxy for algal production and composition, were analysed on a short sediment sequence from Lake Dojran (Republic of North Macedonia and Greece), and their preservation qualities were evaluated before environmental interpretation. Good diatom preservation is inferred mainly from the consistent co-occurrence of robust, highly-silicified taxa and small taxa throughout the sequence. Pigment evaluation of the comparison between wet sediment samples in dark and cold storage and their corresponding dry sediment samples lyophilized immediately after the recovery reveals that sediment restoration conditions are critical for the accuracy of analysis. We show that the increased chlorophyll and xanthophyll pigment concentrations, particularly the siliceous-algae pigment fucoxanthin and diatoxanthin, together with the distinct increase in diatom concentration, indicate accelerated lake eutrophication and a major ecological shift linked to intensified water abstraction practice and agricultural expansion in the late 18th to early 19th century. Evidence of diatom assemblage composition is muted probably by the dominance of widely-tolerant small fragilaroid species in diatom composition and the better competitive ability of cyanobacteria and chlorophytes than diatoms for low light under eutrophic and turbid conditions. This study improves our understanding of recent human-induced environmental change and current ecological restoration target in this lake.

Poleward shift in large‐river fish communities detected with a novel meta‐analysis framework

Abstract Ongoing global changes are causing major ecological shifts worldwide. Biological trends need to be assessed over long periods of time to better understand past and current community responses. The present study developed a methodological framework for meta‐analyses to be conducted that account for the temporal and spatial autocorrelation of observational data. We provided the R code for processing this framework, which enables temporal trends to be tested through the analysis of long‐term, spatially structured datasets. Taking both types of autocorrelation into account resulted in more conservative but arguably more reliable statistical outcomes. This meta‐analysis framework was then applied to investigate long‐term trends in environmental and fish‐community time series in multiple stations in large French rivers over the past 4 decades. General significant upward and downward trends were highlighted in water temperature and flow discharge, respectively, over the study period. Concomitantly, the density of numerous species increased, resulting in large increases in both species richness (about + 50%) and total fish abundance (approximately four‐fold), but with no significant trend in species evenness. Strong changes in species composition were observed during the study period, with an overall upward trend in the relative abundance of newcomers (i.e. species not sampled during the first years of the survey), while the trend in relative abundance of non‐native species was non‐significant. Moreover, the strongest signal underlying community changes was replacement of northern by southern species. This study showed major changes in fish density and community structure in large rivers over the past 40 years and represents, to our knowledge, one of the first large‐scale actual demonstrations (i.e. based on observations rather than predictions) of an overall poleward shift of freshwater fish communities in response to ongoing global changes.

Adult Antarctic krill proves resilient in a simulated high CO2 ocean

Antarctic krill (Euphausia superba) have a keystone role in the Southern Ocean, as the primary prey of Antarctic predators. Decreases in krill abundance could result in a major ecological regime shift, but there is limited information on how climate change may affect krill. Increasing anthropogenic carbon dioxide (CO2) emissions are causing ocean acidification, as absorption of atmospheric CO2 in seawater alters ocean chemistry. Ocean acidification increases mortality and negatively affects physiological functioning in some marine invertebrates, and is predicted to occur most rapidly at high latitudes. Here we show that, in the laboratory, adult krill are able to survive, grow, store fat, mature, and maintain respiration rates when exposed to near-future ocean acidification (1000–2000 μatm pCO2) for one year. Despite differences in seawater pCO2 incubation conditions, adult krill are able to actively maintain the acid-base balance of their body fluids in near-future pCO2, which enhances their resilience to ocean acidification.

Major ecological shifts within the dominant nonstarter lactic acid bacteria in mature Greek Graviera cheese as affected by the starter culture type

Traditional Greek Graviera cheese is often produced from thermized milk to control undesirable bacterial contaminants. Since thermization also reduces the desirable lactic acid bacteria (LAB) microbiota of raw milk, natural undefined or commercially defined starters are used. This study evaluated effects of the type of starter added to bulk thermized milk on the microbiology of mature (day-90) Graviera cheese. Cheeses produced with a natural starter culture (NSC) in non-concentrated yogurt-like form or a commercial starter culture (CSC) containing Streptococcus thermophilus and various Lactococcus lactis strains in concentrated freeze-dried form, were analyzed microbiologically, and 200 LAB isolates (100 from each type of cheese) were identified. The LAB microbiota of the mature CSC-cheeses was dominated by nonstarter strains of Lactobacillus paracasei and Lb. plantarum whereas indigenous Enterococcus faecium and E. durans strains of high phenotypic and genotypic diversity predominated in the respective NSC-cheeses. Populations of enterococci in CSC-cheeses were subdominant by 10 to 100-fold compared with those in NSC-cheeses; E. faecium was the most frequently isolated Enterococcus species from the mature CSC-cheeses. Sporadic or no isolates of other LAB species, including the commercial S. thermophilus and Lc. lactis starter strains in the CSC-cheeses and the natural S. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus starter strains plus indigenous Lactococcus, Leuconostoc and E. faecalis in the NSC-cheeses, were detected. In conclusion, the replacement of the NSC with the CSC controlled growth of dairy enterococci in favor of mesophilic nonstarter lactobacilli during ripening. While safety concerns associated with the inefficiency of NSCs to prevent outgrowth of indigenous enterococci suggest that CSCs should be preferred by traditional Greek Graviera cheese processors, panel sensory evaluations showed that the NSC-ripened cheeses were of slightly lower appearance but of occasionally higher flavor scores than the CSC-ripened cheeses.

Burrowers from the Past: Mitochondrial Signatures of Ordovician Bivalve Infaunalization

Bivalves and gastropods are the two largest classes of extant molluscs. Despite sharing a huge number of features, they do not share a key ecological one: gastropods are essentially epibenthic, although most bivalves are infaunal. However, this is not the ancestral bivalve condition; Cambrian forms were surface crawlers and only during the Ordovician a fundamental infaunalization process took place, leading to bivalves as we currently know them. This major ecological shift is linked to the exposure to a different redox environoments (hypoxic or anoxic) and with the Lower Devonian oxygenation event. We investigated selective signatures on bivalve and gastropod mitochondrial genomes with respect to a time calibrated mitochondrial phylogeny by means of dN/dS ratios. We were able to detect 1) a major signal of directional selection between the Ordovician and the Lower Devonian for bivalve mitochondrial Complex I, and 2) an overall higher directional selective pressure on bivalve Complex V with respect to gastropods. These and other minor dN/dS patterns and timings are discussed, showing that the Ordovician infaunalization event left heavy traces in bivalve mitochondrial genomes.

Fishers’ knowledge indicates short-term temporal changes in the amount and composition of catches in the southwestern Atlantic

The scarcity of data on fish catches difficult management of small-scale fisheries in developing countries. This study applies fishers’ knowledge to investigate temporal changes in the amount (biomass) and composition (major ecological categories) of fishing resources exploited by small-scale coastal fisheries in the southeastern Brazilian coast. Four hypotheses were investigated: (1) The amount of fish caught reported by fishers would decrease over time. (2) Older fishers would report higher fish catches than younger fishers. (3) Recent interviews would mention large-sized predators less often. (4) Recent interviews would mention less high valued fishing resources. Interviews with 421 fishers in 36 communities in the southeastern Brazilian coast were analyzed, covering a time span of 14 years, from 1995 to 2009. The hypothesis 1 was confirmed, 3 was partially confirmed, while 2 and 4 were not confirmed. Fishers’ age was unrelated to all variables. The results from fishers’ interviews indicated the temporal trends of: (1) a decrease in the biomass of fish caught; (2) an increase in the occurrence of smaller fish and invertebrates in the catch; (3) an increase of high value fishing resources; and (4) maintenance of large predators. The first two indicators suggest excessive fishing, but the later indicators (3 and 4) suggest that the socioecological system of the southeastern Brazilian coast had not yet undergone major ecological shifts.

Long-term changes in pigmentation of arctic Daphnia provide potential for reconstructing aquatic UV exposure

Despite the biologically damaging impacts of solar ultraviolet radiation (UV) in nature, little is known about its natural variability, forcing mechanisms, and long-term effects on ecosystems and organisms. Arctic zooplankton, for example the aquatic keystone genus Daphnia (Crustacea, Cladocera) responds to biologically damaging UV by utilizing photoprotective strategies, including pigmentation. We examined the preservation and content of UV-screening pigments in fossil Daphnia remains (ephippia) in two arctic lake sediment cores from Cornwallis Island (Lake R1), Canada, and Spitsbergen (Lake Fugledammen), Svalbard. The aims were to document changes in the degree of UV-protective pigmentation throughout the past centuries, elucidate the adaptive responses of zooplankton to long-term variations in UV exposure, and estimate the potential of fossil zooplankton pigments in reconstructing aquatic UV regimes. The spectroscopic absorbance measurements of fossil Daphnia ephippia under UV (280–400 nm) and visible light (400–700 nm) spectral ranges indicated that melanin (absorbance maxima at UV wavebands 280–350 nm) and carotenoids (absorbance maxima at 400–450 nm) pigments were preserved in the ephippia in both sediment cores. Downcore measurements of the most important UV-protective pigment melanin (absorbance measured at 305 and 340 nm) showed marked long-term variations in the degree of melanisation. These variations likely represented long-term trends in aquatic UV exposure and were positively related with solar radiation intensity. The corresponding trends in melanisation and solar activity were disrupted at the turn of the 20th century in R1, but remained as strong in Fugledammen. The reversed trends in the R1 core were simultaneous with a significant aquatic community reorganization taking place in the lake, suggesting that recent environmental changes, likely related to climate warming had a local effect on pigmentation strategies. This time horizon is also concurrent with previously recorded major ecological shifts in circumpolar lakes when human induced changes in ecological processes of sensitive arctic ecosystems started to occur. The current centennial record of UV-induced melanisation of sedimentary Daphnia ephippia presents unique reference material for assessing UV impacts in arctic aquatic ecosystems before human influence and during the 20th century climate change and provides potential for assessing past aquatic UV regimes.

Variable impact of late-Quaternary megafaunal extinction in causing ecological state shifts in North and South America

Loss of megafauna, an aspect of defaunation, can precipitate many ecological changes over short time scales. We examine whether megafauna loss can also explain features of lasting ecological state shifts that occurred as the Pleistocene gave way to the Holocene. We compare ecological impacts of late-Quaternary megafauna extinction in five American regions: southwestern Patagonia, the Pampas, northeastern United States, northwestern United States, and Beringia. We find that major ecological state shifts were consistent with expectations of defaunation in North American sites but not in South American ones. The differential responses highlight two factors necessary for defaunation to trigger lasting ecological state shifts discernable in the fossil record: (i) lost megafauna need to have been effective ecosystem engineers, like proboscideans; and (ii) historical contingencies must have provided the ecosystem with plant species likely to respond to megafaunal loss. These findings help in identifying modern ecosystems that are most at risk for disappearing should current pressures on the ecosystems' large animals continue and highlight the critical role of both individual species ecologies and ecosystem context in predicting the lasting impacts of defaunation currently underway.

No deep diving: evidence of predation on epipelagic fish for a stem beaked whale from the Late Miocene of Peru

Although modern beaked whales (Ziphiidae) are known to be highly specialized toothed whales that predominantly feed at great depths upon benthic and benthopelagic prey, only limited palaeontological data document this major ecological shift. We report on a ziphiid-fish assemblage from the Late Miocene of Peru that we interpret as the first direct evidence of a predator-prey relationship between a ziphiid and epipelagic fish. Preserved in a dolomite concretion, a skeleton of the stem ziphiid Messapicetus gregarius was discovered together with numerous skeletons of a clupeiform fish closely related to the epipelagic extant Pacific sardine (Sardinops sagax). Based on the position of fish individuals along the head and chest regions of the ziphiid, the lack of digestion marks on fish remains and the homogeneous size of individuals, we propose that this assemblage results from the death of the whale (possibly via toxin poisoning) shortly after the capture of prey from a single school. Together with morphological data and the frequent discovery of fossil crown ziphiids in deep-sea deposits, this exceptional record supports the hypothesis that only more derived ziphiids were regular deep divers and that the extinction of epipelagic forms may coincide with the radiation of true dolphins.

Divergence at the edges: peripatric isolation in the montane spiny throated reed frog complex.

BackgroundPeripatric speciation and peripheral isolation have uncertain importance in species accumulation, and are largely overshadowed by assumed dominance of allopatric modes of speciation. Understanding the role of different speciation mechanisms within biodiversity hotspots is central to understanding the generation of biological diversity. Here, we use a phylogeographic analysis of the spiny-throated reed frogs and examine sister pairings with unbalanced current distributional ranges for characteristics of peripatric speciation. We further investigate whether forest/grassland mosaic adapted species are more likely created through peripatric speciation due to instability of this habitat type.ResultsWe reconstructed a multi-locus molecular phylogeny of spiny-throated reed frogs which we then combined with comparative morphologic data to delimit species and analyze historical demographic change; identifying three new species. Three potential peripatric speciation events were identified along with one case of allopatric speciation. Peripatric speciation is supported through uneven potential and realized distributions and uneven population size estimates based on field collections. An associated climate shift was observed in most potentially peripatric splits. Morphological variation was highest in sexually dimorphic traits such as body size and gular shape, but this variation was not limited to peripatric species pairs as hypothesized. The potentially allopatric species pair showed no niche shifts and equivalent effective population sizes, ruling out peripatry in that speciation event. Two major ecological niche shifts were recovered within this radiation, possibly as adaptations to occupy areas of grassland that became more prevalent in the last 5 million years. Restricted and fluctuating grassland mosaics within forests might promote peripatric speciation in the Eastern Arc Biodiversity Hotspot (EABH).ConclusionsIn our case study, peripatric speciation appears to be an important driver of diversity within the EABH biodiversity hotspot, implying it could be a significant speciation mechanism in highly fragmented ecosystems. Extensive peripatric speciation in this montane archipelago may explain the abundance of discrete lineages within the limited area of the EABH, as inferred in remote island archipelagos. Future phylogenetic studies incorporating demographic and spatial analyses will clarify the role of peripatric speciation in creating biodiversity hotspots.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0384-3) contains supplementary material, which is available to authorized users.

Herbivore diversity improves benthic community resilience to ocean acidification

Ocean acidification is expected to alter a wide range of marine systems, but there is great uncertainty about the outcome because indirect effects are often crucial in ecology. Work at volcanic seeps has shown that major ecological shifts occur due to chronic exposure to acidified seawater. Changes in herbivore densities are often seen and this may interact with direct CO2 effects to determine benthic community structure. Here, an exclusion experiment was used to test effects of herbivory in benthic communities along a pCO2 gradient off Methana (Greece). A manipulative experiment was used to examine how large herbivores affected sublittoral algal communities as seawater carbon dioxide levels increased. Sea urchins and herbivorous fish dramatically reduced macroalgal biomass at background carbon dioxide levels; this effect was not hampered by increased pCO2 despite lower sea urchin densities near the seeps, since herbivorous fish abundances increased concurrently. We found that carbon dioxide levels up to about 2000μatm are unlikely to reduce the role of herbivory in structuring benthic communities if tolerant species are able to replace those that are vulnerable. A shift from sea urchins to fish as main grazers highlights that ocean acidification may cause unexpected responses at the community level, and that maintaining high functional redundancy in marine ecosystems is key to improving their resilience.

Phylogenetic signal and major ecological shifts in the ecomorphological structure of stream fish in two river basins in Brazil

We tested the contribution of the phylogenetic and specific components to the ecomorphological structure of stream fish from the upper Paraguai River and upper São Francisco River basins, and identified nodes in the phylogenetic tree at which major ecological shifts occurred. Fish were sampled between June and October of 2008 in 12 streams (six in each basin). In total, 22 species from the upper Paraguai River basin and 12 from the upper São Francisco River were analyzed. The ecomorphological patterns exhibited phylogenetic signal, indicating that the ecomorphological similarity among species is associated with the degree of relatedness. A strong habitat template is most likely to be the primary cause for a high phylogenetic signal. A significant contribution from the specific component was also detected, supporting the idea that the phylogenetic signal occurs in some clades for some traits, but not in others. The major ecological shifts were observed in the basal nodes, suggesting that ecological niche differences appear to accumulate early in the evolutionary history of major clades. This finding reinforces the role of key traits in the diversification of Neotropical fishes. Ecological shifts in recent groups could be related to morphological modifications associated with habitat use.