River Barriers Research Articles

Red River barrier and Pleistocene climatic fluctuations shaped the genetic structure of Microhyla fissipes complex (Anura: Microhylidae) in southern China and Indochina.

South China and Indochina host striking species diversity and endemism. Complex tectonic and climatic evolutions appear to be the main drivers of the biogeographic patterns. In this study, based on the geologic history of this region, we test 2 hypotheses using the evolutionary history of Microhyla fissipes species complex. Using DNA sequence data from both mitochondrial and nuclear genes, we first test the hypothesis that the Red River is a barrier to gene flow and dispersal. Second, we test the hypothesis that Pleistocene climatic cycling affected the genetic structure and population history of these frogs. We detect 2 major genetic splits that associate with the Red River. Time estimation suggests that late Miocene tectonic movement associated with the Red River drove their diversification. Species distribution modeling (SDM) resolves significant ecological differences between sides of the Red River. Thus, ecological divergence also probably promoted and maintained the diversification. Genogeography, historical demography, and SDM associate patterns in southern China with climate changes of the last glacial maximum (LGM), but not Indochina. Differences in geography and climate between the 2 areas best explain the discovery. Responses to the Pleistocene glacial–interglacial cycling vary among species and regions.

낙동강 하구역 진우도 남측 해역의 해저지형 변화

Bathymetric changes were studied in the southern sea off the Jinwoo-do Island, which is one of the deltaic barrier is- lands surrounding the Nakddong river estuary. In this study, 16 bathymetry data sets were obtained from June 2006 to April 2015. Two narrow channels, the one lying between Jinwoo-do and Shinja-do, and the other one lying between Nulcha-do and Jinwoo-do extended into the eastern and western parts of the study area, respectively. The eastern extension of the channel con- tained a passage of mixed estuarine waters of seawater and river water discharged from the Nakdong river barrier and the west Nakdong River. The western channel connected the Nakdong River estuary with the Busan New Port via a connecting pier. Total volumetric changes of sediments in study area and discharge flow of the Nakdong river barrier were analyzed. Bottom topographical changes occurred mainly in the eastern extension of the channel. These changes were initially characterized by gradual erosion or deposition followed by rapid restoration. The total volume of sediment gradually increased from June 2006 to March 2013, but experienced a sudden decrease in October 2013 because of typhoon Danas. Few fluctuations were observed from October 2013 to April 2015. Analysis of the cross-sectional bathymetry of the north-south direction showed that the deep- est point of the eastern channel moved 100-130 m westward and 200 m northward between June 2006 and April 2015.

Contrasting and congruent patterns of genetic structuring in two Microtus vole species using museum specimens

The common vole (Microtus arvalis) and the field vole (Microtus agrestis) are morphologically similar species but are ecological distinctive and differ in the details of their evolutionary history as revealed by mitochondrial DNA (mtDNA). The aim of this study is to describe patterns of genetic variability using microsatellite markers in populations of the common and field vole in Poland using museum specimens, to assess the degree of congruence with mtDNA variation and thereby determine the factors that influence current patterns of gene flow. We genotyped 190 individuals of the common vole at 11 loci and 190 individuals of the field vole at 13 loci. Overall differentiation based on F ST was higher for the common vole than in the field vole. We detected a significant isolation by distance pattern for both species. Bayesian analysis in STRUCTURE identified Eastern and Western geographic groups in Poland based on microsatellites for both species. The location of river barriers is likely to be the main factor in these partitions. The eastern-western subdivision with microsatellites does not coincide with the distribution of mtDNA lineages for either species. Unlike previous studies in the common and field vole elsewhere in Europe, we found no evidence of reproductive isolation between the mtDNA lineages of these species at their contact zones in Poland. This study highlights the different roles of evolutionary history and landscape in shaping contemporary genetic structure in voles in Poland.

Barriers to salmon migration impact body condition, offspring size, and life history variation in an avian consumer

The impacts of barriers, such as dams, and associated stream effects on the migration of salmon have been well documented, but there is much less information on consequences for terrestrial vertebrates in these freshwater systems. Salmon themselves provide food resources to higher trophic levels and deposit rich marine‐derived nutrients (MDN) that benefit the base of freshwater food webs. We studied a higher‐order terrestrial consumer of aquatic prey, the American dipper Cinclus mexicanus, in a riparian food web, to test the hypothesis that barriers to salmon migration negatively impact body condition, and ultimately life history. We predicted that, compared to dippers breeding above barriers, those in areas with salmon would receive MDN and thus be in better condition, have greater breeding effort (frequency of multiple brood attempts), produce larger offspring in better condition, be more likely to maintain year‐round territories, and have higher annual survival. Using stable isotopes as signatures of MDN, we found that 13C and 15N were more enriched in dippers below barriers, confirming access to MDN. Female dippers below barriers had greater mass corrected for body size, were more likely to attempt multiple broods within a season and produced larger female offspring. Furthermore, dippers below barriers were more likely to maintain year‐round territories and had higher annual survival. Our results demonstrate how river barriers such as dams influence vital rates and life histories of higher‐order consumers.

Property flood resilience database: an innovative response for the insurance market

The property flood resilience database (PFR-d) has been created through a research feasibility study undertaken by the Building Research Establishment, AXA Insurance and Lexis Nexis Risk Solutions in the UK. The project was funded by Innovate-UK and was undertaken over the period of May 2014 to August 2015. There has been a growing realisation that flood management has to move from a position where flood defence (e.g. major river barriers and drainage infrastructure) is the only solution to flood risk to one of flood resilience. This shift requires an increase in responsibility for a variety of stakeholders, including property owners. The PFR-d was conceived as a product that code fit within the existing insurance frameworks and systems. The PFR-d is a ‘missing piece of data’ for insurers that could assist in providing more appropriate insurance pricing in high flood risk areas, or where properties have suffered repeat flooding events.

Illumina based whole mitochondrial genome of Junonia iphita reveals minor intraspecific variation.

In the present study, the near complete mitochondrial genome (mitogenome) of Junonia iphita (Lepidoptera: Nymphalidae: Nymphalinae) was determined to be 14,892 bp. The gene order and orientation are identical to those in other butterfly species. The phylogenetic tree constructed from the whole mitogenomes using the 13 protein coding genes (PCGs) defines the genetic relatedness of the two J. iphita species collected from two different regions. All the Junonia species clustered together, and were further subdivided into clade one consisting of J. almana and J. orithya and clade two comprising of the two J. iphita which were collected from Indo and Indochinese subregions separated by river barrier. Comparison between the two J. iphita sequences revealed minor variations and Single Nucleotide Polymorphisms were identified at 51 sites amounting to 0.4% of the entire mitochondrial genome.

Groundwater Thermal Monitoring to Characterize Streambed Water Fluxes of the Brenta River (Northern Italy)

The work proposed deals with the characterization of temporal and spatial variability of water exchange fluxes from/to the Brenta river streambed (Veneto, Italy), critically important to regional water resources management. The aquifer system evolves from a large undifferentiated aquifer close to the adjacent mountain ranges, later developing into a well-structured multi-layer system made up of six well-defined confined aquifers constituting the noteworthy subsurface reservoirs of the area. A three-dimensional groundwater flow model of the multi-aquifer system of the Central Veneto, within a 3300 km2 area, integrating a large amount of data, has been developed to analyze the behaviour of this large, complex and well-monitored sedimentary system. The temporal and spatial variability of the water exchange flux is investigated using heat as a tracer in conjunction with water-level measurements (in the river and in piezometers close to the river): an effective method for estimating groundwater/surface water exchanges. In the study area, 5 groundwater monitoring wells (4 on the right bank, 1 on the left bank) were drilled along the river banks near a pilot transversal ramp (permeable river barrier) built in order to reduce the downstream flooding risk and to increase the river dispersion. A hydrothermal model of the river and of the underlying aquifer was implemented to improve the estimation of the water exchange between the Brenta river and the aquifer system. The contribution of exchange between the river and the underlying aquifer is quantified by comparing simulations of water flow and heat transport to observed temperature and levels in river and in groundwater.

Reshaping the Riparian: Human Mobility and Fixed Infrastructure

New Orleans, Louisiana USA is on the banks of the massive Mississippi River and its history is inextricably linked to this water that serves as a vital transportation corridor and also presents an ever-present flood hazard. This text examines the use of levees to offset the risk of flooding and how that fixed infrastructure has contributed to population dynamics in the lower river valley. Early efforts to fend off floods focused on the threat of the river, and colonial and later federal efforts led to the erection of massive earthen embankments. By the 20th century, the threat of hurricane driven storm surge prompted investments in additional levees designed to complement the river barriers and keep the sea out of the city. Levees offered a false sense of security, and failures of this protection system have contributed to population losses after major hurricanes in 1965 and 2005. These episodic demographic shifts are a harbinger of population dynamics that will accompany sea level rise in other coastal areas.

Poison frogs rely on experience to find the way home in the rainforest.

Among vertebrates, comparable spatial learning abilities have been found in birds, mammals, turtles and fishes, but virtually nothing is known about such abilities in amphibians. Overall, amphibians are the most sedentary vertebrates, but poison frogs (Dendrobatidae) routinely shuttle tadpoles from terrestrial territories to dispersed aquatic deposition sites. We hypothesize that dendrobatid frogs rely on learning for flexible navigation. We tested the role of experience with the local cues for poison frog way-finding by (i) experimentally displacing territorial males of Allobates femoralis over several hundred metres, (ii) using a harmonic direction finder with miniature transponders to track these small frogs, and (iii) using a natural river barrier to separate the translocated frogs from any familiar landmarks. We found that homeward orientation was disrupted by the translocation to the unfamiliar area but frogs translocated over similar distances in their local area showed significant homeward orientation and returned to their territories via a direct path. We suggest that poison frogs rely on spatial learning for way-finding in their local area.

Historical changes in the functional connectivity of rivers based on spatial network analysis and the past occurrences of diadromous species in Portugal

The disruption of longitudinal connectivity caused by artificial barriers in rivers is considered to be a major threat to freshwater fish communities at the global scale. In Portugal, the construction of several big dams all through the 20th century was a major cause of disappearance or decline of long distance migratory fish species from various rivers. In this study we analysed the historical changes of functional connectivity for diadromous fish at the Tagus basin river network (Portugal), using a spatial graph approach that integrates both structural connectivity and habitat suitability. Due to the presence of many artificial barriers, the current distribution of species does not reflect natural environmental conditions. Therefore, historical data on the occurrence of species is paramount to assess the potential habitat suitability. The compilation of historical data on the distribution of diadromous species [Sea Lamprey—Petromyzon marinus (Linnaeus 1758) and Allis shad—Alosa alosa (Linnaeus 1758)] was based on geographical dictionaries and geo-referenced information for Portugal dated between 1700 and 1900. Habitat suitability was expressed as the probabilities of occurrence of empirical predictive models based on the historical records and a set of regionalized environmental data. The loss of connectivity caused by big dam construction between 1928 and 2004 was then analysed using a spatial graph approach. The output of this analysis will aid decision-makers to optimize targets of connectivity restoration actions aiming at enhancing the functional connectivity of the river network for diadromous species, using the historical situation as a benchmark.

Late Pliocene rodents from the Irrawaddy sediments of central Myanmar and their palaeogeographical significance

The Upper Pliocene Irrawaddy sediments in the Gwebin area of central Myanmar recently yielded a rodent assemblage that contains nine species belonging to four families: four species of Muridae, three of Hystricidae, one of Spalacidae, and one of Sciuridae. The murids consist of Hapalomys cf. longicaudatus, Maxomys pliosurifer sp. nov., Rattus jaegeri and cf. Rattus sp. indet., which include both extinct and extant forms. Maxomys pliosurifer is relatively similar to Maxomys surifer that lives in South-East Asia in terms of tooth morphology but retains plesiomorphic features shared with the ancestral rat, Karnimata, and possible sister genera of Maxomys, such as Ratchaburimys and Millardia. The three hystricids belong to the genus Hystrix and consist of two extinct brachydont species (Hystrix paukensis and Hystrix sp. indet.) and one hypsodont species similar to living form (Hystrix cf. brachyura). This finding indicates that primitive brachydont species and derived hypsodont species of Hystrix had likely coexisted in the locality, but the brachydont species are significantly more common amongst specimens collected from the Gwebin area. The spalacid species is Cannomys cf. badius and the sciurid species is Menetes sp. indet. These two rodents are similar to living species in continental South-East Asia although they show minor differences in tooth characteristics compared to the living forms. Some species and genera of the fossil rodent assemblage from the Gwebin area also occur in Upper Pliocene localities of Thailand, suggesting chronological correlation between these two faunas. Moreover, these fossil rodent assemblages are composed primarily of the species distributed endemically in continental South-East Asia. Late Pliocene rodents of continental South-East Asia were affected by river barriers that formed during the Mio-Pliocene, and they were probably not able to disperse from South-East Asia into South and East Asia.http://zoobank.org/urn:lsid:zoobank.org:pub: 0171B3BE-02D4-433C-A5CE-4729C537FAF8

Marine dispersal and barriers drive Atlantic seahorse diversification

AbstractAimTo investigate how marine barriers shaped the demographic history of Atlantic seahorses (Syngnathidae: Hippocampus).LocationAtlantic Ocean.MethodsRange‐wide sampling (n = 390) at mitochondrial and up to five nuclear DNA loci was carried out across the Hippocampus erectus species complex (H. erectus from the Caribbean/North America, H. patagonicus from South America and H. hippocampus from Europe and West Africa). Multi‐species coalescent and approximate Bayesian computation (ABC) frameworks were used to estimate support of competing biogeographical hypotheses and demographic parameters, including lineage divergence times, effective population sizes and magnitudes of population size change.ResultsWe identified four distinct lineages within the H. erectus complex. A posterior probability of 0.626 and corresponding Bayes factors ranging from 3.68 to 11.38 gave moderate to strong support for a basal divergence between South American populations of H. patagonicus and Caribbean/North American populations of H. erectus coincident with the inter‐regional freshwater outflow of the Amazon River Barrier (ARB). Estimates of historical effective population sizes and divergence times indicate that European and West African populations of H. hippocampus expanded after colonization from a more demographically stable Caribbean/North American H. erectus.Main conclusionsOur findings of trans‐Atlantic colonization followed by isolation across a deep oceanic divide, and isolation across a freshwater barrier, may demonstrate a contrast in marine divide permeability for this group of rafters. Demographic inference supports the establishment of an ancestral population of the H. erectus complex in the Americas, followed by the ARB splitting it into Caribbean/North and South American lineages at a time of increased sedimentation and outflow. Our estimates suggest that following this split, colonization occurred across the Atlantic via the Gulf Stream currents with subsequent trans‐Atlantic isolation. These results illustrate that rafting can be a means of range expansion over large distances, but may be insufficient for sustaining genetic connectivity across major barriers, thereby resulting in lineage divergence.

Do rivers and human-induced habitat fragmentation affect genetic diversity and population structure of the European ground squirrel at the edge of its Pannonian range?

The European ground squirrel (EGS) (Spermophilus citellus) populations of Vojvodina (Serbia) represent the southernmost part of its distribution in the Pannonian lowland. For species with low dispersal abilities a presence of even weak barriers can have significant influence on genetic structure among adjacent populations. We examined here the effects of habitat fragmentation and river barriers on the genetic structure of the EGS based on 12 microsatellite loci. Bayesian clustering methods were used as additions to classical population genetic approaches. We found that EGS populations in Vojvodina are highly fragmented, but their genetic variation is still higher than in peripheral populations in Central Europe. Populations in Vojvodina consistently grouped into three genetic clusters. The Danube, but not the Tisza River, represents an important barrier to gene flow. EGS populations in the studied area did not show the signs of recent genetic bottlenecks, as would be expected from observations of recent population declines. Conservation strategy should be focused on maintenance of remained suitable habitats and optimal population sizes.

River barriers and cryptic biodiversity in an evolutionary museum.

The Riverine Barriers Hypothesis (RBH) posits that tropical rivers can be effective barriers to gene flow, based on observations that range boundaries often coincide with river barriers. Over the last 160 years, the RBH has received attention from various perspectives, with a particular focus on vertebrates in the Amazon Basin. To our knowledge, no molecular assessment of the RBH has been conducted on birds in the Afrotropics, despite its rich avifauna and many Afrotropical bird species being widely distributed across numerous watersheds and basins. Here, we provide the first genetic evidence that an Afrotropical river has served as a barrier for birds and for their lice, based on four understory bird species collected from sites north and south of the Congo River. Our results indicate near-contemporaneous, Pleistocene lineage diversification across the Congo River in these species. Our results further indicate differing levels of genetic variation in bird lice; the extent of this variation appears linked to the life-history of both the host and the louse. Extensive cryptic diversity likely is being harbored in Afrotropical forests, in both understory birds and their lice. Therefore, these forests may not be “museums” of old lineages. Rather, substantial evolutionary diversification may have occurred in Afrotropical forests throughout the Pleistocene, supporting the Pleistocene Forest Refuge Hypothesis. Strong genetic variation in birds and their lice within a small part of the Congo Basin forest indicates that we may have grossly underestimated diversity in the Afrotropics, making these forests home of substantial biodiversity in need of conservation.

The impact of river fragmentation on the population persistence of native and alien mink: an ecological trap for the endangered European mink

The genetic diversity of feral and ranch American mink was studied in order to detect gene flux among rivers, investigate the processes of invasion, and determine the possible effects of river barriers. Tissue samples of 78 feral American mink from 5 different river catchments and 18 ranch mink, collected between 2007 and 2011 in Biscay, northern Spain, were genotyped at 21 microsatellite loci. Lack of genetic differentiation of feral mink among the sites and high differentiation between feral and ranch mink was suggested. These results confirm that the mink population established on Butron River at the beginning of the 1990s may be the origin of almost all the feral mink population within the study area. Additionally, the occurrence of American and European mink was used to analyse the effect of fragmentation on the population viability. The size and composition of the home range of male European mink was considered to model minimum viable units for presence/absence. Forty-two minimum viable units were randomly distributed among rivers in order to analyse the effect of fragmentation on mink occurrence. Barriers were mapped and classified as slight, moderate or absolute, depending on the effect on mink movement, and were introduced into the models. The presence of European and American mink depended on the non-fragmented main river stretches and the number of tributaries free from barriers. Results showed that fragmented rivers can be temporarily occupied but the likelihood of death means that these areas are only sink patches for mink.

Identifying biases at different spatial and temporal scales of diversification: a case study in the Neotropical parrotlet genus Forpus

The temporal origins of the extraordinary biodiversity of the Neotropical region are highly debated. Recent empirical work has found support for alternative models on the tempo of speciation in Neotropical species further fuelling the debate. However, relationships within many Neotropical lineages are poorly understood, and it is unclear how this uncertainty impacts inferences on the evolution of taxa in the region. We examined the robustness of diversification patterns in the avian genus Forpus by testing whether the use of different units of biodiversity (i.e. biological species and statistically inferred species) impacted diversification rates and inferences regarding important biogeographic breaks in the genus. We found that the best-fit model of diversification for the biological species data set was a declining rate of diversification; whereas a model of constant diversification was the best-fit model for statistically inferred species or subspecies. Moreover, the relative importance of different landscape features in delimiting genetic structure across the landscape varied across data sets with differing units of biodiversity. Patterns based on divergence times among biological species indicated old speciation events across major geographic and river barriers. In contrast, data sets more inclusive of the diversity in Forpus illustrate the role of both old divergence across major landscape features and more recent divergences that are possibly attributed to Pleistocene climatic changes. Overall, these results indicate that conflicting models on the temporal origins of Neotropical birds may be attributable to sampling biases.

Beyond the river: underlying determinants of population acoustic signal variability in Amazonian direct-developing Allobates (Anura: Dendrobatoidea)

The multidimensional nature of animal signals makes acoustic traits potentially subject to different determinants. The Amazonian frogs Allobates nidicola and Allobates masniger have an allopatric distribution, occurring along the left and right sides of the Madeira River, respectively. These are two sister, phenotypically similar species whose eggs are deposited and develop entirely in a terrestrial nest. In this study, we analyzed 2,000 advertisement calls recorded from ten localities across Central Amazonia, in order to understand the role of determinants of acoustic signal variability at the population and species levels. We assessed, through nested analyses of variance, the differentiation of six characters of this sexual signal among populations and between interfluves. Moreover, we measured the degree of variability and the extent of temperature- and body size-induced plasticity in call traits. We also tested for isolation-by-distance effects in phenotypic differentiation through Mantel tests. Coefficients of variation were higher among than within populations for all call measurements. Spectral call properties were more distinctive than temporal traits among populations and species. Advertisement call traits showed strong temperature-induced plasticity (e.g., 45 % of the variation in note duration). In contrast, the effects of body size were restricted to frequency-related characters. The river barrier effect was significant among all the acoustic variables analyzed even after controlling for male body size. Geography (sampling locality) and body size also jointly affected call variability. No correlation between geographical and acoustic distances among populations was observed, suggesting that local stabilizing selective pressures have an important role in the evolution of call differentiation.

Building a bridge, transport infrastructure and population characteristics: Explaining active travel into Glasgow

BackgroundIt is widely agreed that walking and cycling are good for individual and public health. There is a lack of evidence about what works to promote active travel. This paper aimed to explain the variation in active travel into Glasgow, a post industrial city in the West of Scotland. MethodsCensus travel data from 2001 and data from a cordon count performed over 2 day in 2007, 2008, 2009 and 2010 were used to estimate the number of pedestrians and cyclists entering and leaving the City centre from four City sectors. ResultsIn 2001, pedestrian commuters (12.6%) were more common than cycling commuters (1.3%). There was no clear pattern in cycling or pedestrian commuting by deprivation. The number of cyclists crossing the cordon increased between 2007 and 2010 but interpretation of this is difficult because of variation in seasons and weather. The highest level of cycle commuting was from the sector with the best cycling infrastructure and the highest pedestrian commuting was in the sector without significant road or river barriers. The construction of a new bridge over the river Clyde was associated with an increase in the number of pedestrians and cyclists entering and leaving the cordon from that sector, even after accounting for displacement. ConclusionActive travel in Glasgow is relatively uncommon but is facilitated in areas with fewer physical barriers and better infrastructure. Cordon counts can provide useful localised data on levels of active commuting into City centres.

Sexual signals of the Amazonian frog Allobates paleovarzensis: geographic variation and stereotypy of acoustic traits

AbstractBecause of its close relationship with the process of evolutionary differentiation, it is expected that geographic variability in acoustic sexual traits should be greater among than within populations. This is particularly expected in organisms with typically high population genetic structure and low dispersal abilities, such as anuran amphibians. We studied the acoustic traits of the advertisement call in the small-sized dendrobatoid frogAllobates paleovarzensisthrough its range in Central Amazonia. We accessed the variability of call traits from the within-male to the among-population levels, and evaluated the degree of stereotypy of the call characteristics. Call variability had comparable magnitudes within and among populations, and was independent of the degree of stereotypy of call measurements. Therefore, none of the call traits stood out as a potential cue for discrimination between populations. Spectral call measurements were static and strongly related with body size, which explained between 30 and 35% of the variation of these acoustic traits. Temporal characters of the notes were dynamic and influenced by environmental temperature (e.g., 27% of note rate variation), whilst temporal measurements of the entire calls were not related to the co-factors analysed. Both spectral and temporal call traits varied among populations and between sides of the Amazon River. Our results also indicate that body size and sampling site jointly affected the variability of the call traits. However, geographic distances among populations and the river barrier had no significant effect on the overall acoustic variation, indicating that local stabilising selective forces may be important in the process of call differentiation.

A quantitative assessment of fish passage efficiency

AbstractIn an attempt to restore the connectivity of fragmented river habitats, a variety of passage facilities have been installed at river barriers. Despite the cost of building these structures, there has been no quantitative evaluation of their overall success at restoring fish passage. We reviewed articles from 1960 to 2011, extracted data from 65 papers on fish passage efficiency, size and species of fish, and fishway characteristics to determine the best predictors of fishway efficiency. Because data were scarce for fishes other than salmonids (order Salmoniformes), we combined data for all non‐salmonids for our analysis. On average, downstream passage efficiency was 68.5%, slightly higher than upstream passage efficiency of 41.7%, and neither differed across the geographical regions of study. Salmonids were more successful than non‐salmonids in passing upstream (61.7 vs. 21.1%) and downstream (74.6 vs. 39.6%) through fish passage facilities. Passage efficiency differed significantly between types of fishways; pool and weir, pool and slot and natural fishways had the highest efficiencies, whereas Denil and fish locks/elevators had the lowest. Upstream passage efficiency decreased significantly with fishway slope, but increased with fishway length, and water velocity. An information‐theoretic analysis indicated that the best predictors of fish passage efficiency were order of fish (i.e. salmonids > non‐salmonids), type of fishway and length of fishway. Overall, the low efficiency of passage facilities indicated that most need to be improved to sufficiently mitigate habitat fragmentation for the complete fish community across a range of environmental conditions.