水坝拆除对黑水河鱼类群落结构和空间分布的影响

水坝拆除引起河流连通性、水动力、河流地貌等一系列变化,直接影响了鱼类群落结构和空间分布。黑水河为金沙江左岸一级支流,其上共建四级电站,出于支流生境恢复需求,第四级水坝老木河水坝于2018年12月实行拆除。为探明低水头坝拆除对鱼类群落的影响,结合2018年6月和2019年6月黑水河下游60.4km河段10个点位的渔获物调查,对拆坝前后鱼类群落结构和生态类型变化、优势物种与单位捕捞努力量以及不同河段间的群落相似性进行了分析。结果表明,水坝拆除半年后优势物种仍以鲤科和鳅科为主,但物种数和丰度整体上增加;生态类型上以杂食、喜急流和产微粘性卵鱼为主;拆坝后鱼类群落空间分布变化明显,靠近河口的自然河段鱼类上溯洄游到原坝址的上下游,部分长江上游特有鱼类在原坝址附近发生定殖行为,且拆坝后各河段的鱼类组成结构有同质化趋势。总体上,老木河水坝的拆除对黑水河下游的鱼类群落结构和空间分布产生了积极的影响。     

Factors affecting the distribution and abundance of Cloeon and Caenis (Ephemeroptera) larvae in a tropical impounded river, Nigeria

Impoundment of rivers affects the mayfly (Ephemeroptera) fauna inhabiting such water bodies, especially with respect to their distribution and abundance. A two‐year study of the mayfly fauna and some of the physicochemical parameters of the Opa stream–reservoir revealed that there are two mayfly genera inhabiting it, Cloeon and Caenis. The number of Cloeon larvae collected was 10,930 while the number of Caenis larvae was 450. It was observed that although both genera occurred at all the sampling stations, their numbers were reduced in the stream below the dam due to increased water current velocity. There were significant differences in the abundance of Cloeon among the stations, but none for Caenis. Submerged aquatic plants and water current velocity were found to be the major factors responsible for the significant differences. There were significant correlations between the number of Cloeon larvae and pH as well as between dissolved oxygen concentration and Caenis. These findings are discussed with reference to inter‐specific differences in patterns of response to environmental parameters. A species‐specific approach is suggested for studies on the strategies that enable mayfly species maintain their populations in stressed and unstable aquatic ecosystems.     

Development of 10 polymorphic microsatellite loci isolated from the mountain beaver, Aplodontia rufa rufa (Rafinesque)

We developed 10 microsatellite markers for the mountain beaver, Aplodontia rufa rufa. In three populations of A. r. rufa, the number of alleles for these loci ranged from monomorphic to nine. Average observed heterozygosities in these populations ranged from 0.29 to 0.60. We also tested previously published markers from the endangered subspecies A. r. nigra in A. r. rufa populations.     

Deconstructing a controversial local range expansion: conservation biogeography of the painted reed frog (Hyperolius marmoratus) in South Africa

Local range expansions might either be the response of populations to climate or landscape change, or be caused directly by human intervention. In the latter case the expansion would be considered the first in the steps leading to a biological invasion. In species typically not the subject of human commerce, distinguishing the causes of local range expansions is problematic. Range dynamic theory provides a basis for doing so, and, when used to assess phylogeographical information, can be a powerful conservation biogeographical approach. Here we adopt this approach to resolve the controversial case of the recent range expansion of the painted reed frog (Hyperolius marmoratus) in southern South Africa. Within the last decade, H. marmoratus has spread westward approximately 500 km from its historical range. This local range expansion could either represent human‐mediated jump dispersal, or a response to landscape or climate change. To date, the latter has been assumed, although not universally. Using a phylogeographic approach to investigate these competing hypotheses, a portion of the mitochondrial COI gene was sequenced for individuals from within the historical range (n = 178), and four putatively introduced populations in dams (n = 121). There was substantial geographical population structure within the historical range, and these populations were significantly different from the dam populations (Φ_ST = 0.817, P < 0.001). The presence of one or a few dissimilar haplotypes in the dams suggests that introductions are from a number of different sources. This, in conjunction with new survey data, supports the hypothesis that recent establishment of these populations is the result of human‐mediated jump dispersal. The impact of this range expansion on ecosystem functioning is unknown, but given the rapid spread of this species and its potential influence on ecosystems, safeguards should be put in place to control further introductions and to restrict the currently invasive populations.     

Ant assemblages in the taiga biome: testing the role of territorial wood ants

Summary Ants were collected with sets of pitfall traps in four coniferous-forest habitats in southern Finland. A three-level competition hierarchy concept was used to generate predictions on ant community structure. The levels of the hierarchy, and the respective predictions, from top to bottom were: (1) The dominant territorial wood ants (Formica rufa-group species), expected to exclude each other. (2) The other aggressive species, likely to be excluded by the F. rufa-group. (3) The submissive species, non-aggressive and defending only their nest, and thus likely to coexist with the dominants but in reduced numbers. As expected, the species of the F. rufa-group excluded each other, and the species number of the other aggressive ants was significantly cut down in the presence of the F. rufa-group. The aggressive species F. sanguinea and Camponotus herculeanus showed complementary occurrences with the F. rufa-group, and Lasius niger reduced occurrences. The number of the submissive species was not significantly affected by the F. rufa-group. However, pairwise correlation coefficients were significantly more often negative than positive between presence of the F. rufa-group and average proportion of pitfalls per set with a submissive species, each analyzed in turn. The result indicates that the F. rufa-group also reduced the colony densities of the submissive species. We conclude that in the taiga biome territorial wood ants are, after adjusting for physical vicissitudes of the environment, the major structuring force of ant species assemblages.     

Patterns of range-wide genetic variation in six North American bumble bee (Apidae: Bombus) species

The increasing evidence for population declines in bumble bee (Bombus) species worldwide has accelerated research efforts to explain losses in these important pollinators. In North America, a number of once widespread Bombus species have suffered serious reductions in range and abundance, although other species remain healthy. To examine whether declining and stable species exhibit different levels of genetic diversity or population fragmentation, we used microsatellite markers to genotype populations sampled across the geographic distributions of two declining (Bombus occidentalis and Bombus pensylvanicus) and four stable (Bombus bifarius; Bombus vosnesenskii; Bombus impatiens and Bombus bimaculatus) Bombus species. Populations of declining species generally have reduced levels of genetic diversity throughout their range compared to codistributed stable species. Genetic diversity can be affected by overall range size and degree of isolation of local populations, potentially confounding comparisons among species in some cases. We find no evidence for consistent differences in gene flow among stable and declining species, with all species exhibiting weak genetic differentiation over large distances (e.g. >1000 km). Populations on islands and at high elevations experience relatively strong genetic drift, suggesting that some conditions lead to genetic isolation in otherwise weakly differentiated species. B. occidentalis and B. bifarius exhibit stronger genetic differentiation than the other species, indicating greater phylogeographic structure consistent with their broader geographic distributions across topographically complex regions of western North America. Screening genetic diversity in North American Bombus should prove useful for identifying species that warrant monitoring, and developing management strategies that promote high levels of gene flow will be a key component in efforts to maintain healthy populations.     

Local depletion of two larger Duikers in the Oban Hills Region,Nigeria

Across West and Central Africa, duikers are important for trade and consumption; their populations are expected to become depleted. Reliable data on their status are scanty in Nigeria. We assessed duiker populations in the Oban Sector of Cross River National Park through diurnal and nocturnal surveys along 32 transects of 2 km each. After 508‐km survey effort, only Ogilby's duiker (Cephalophus ogilbyi) and blue duiker (Philantomba monticola) were recorded. Using habitat as a covariate in modelling detection probability in DISTANCE 6.0, we estimated densities for the blue duiker ranging from 15.5 (95% CI: 7.8–30.9) in the core, 5.8 (CI: 2.6–12.9) in the buffer and 0.9 (CI: 0.09–10.1) km² in farm fallow to no duikers in the plantation. For Ogilby's duiker, densities ranged from 1.6 (95% CI: 0.7–3.7) km² in the core, 2.0 (CI: 0.8–5.1) in buffer to no duikers in farm fallow and plantation. The apparent absence of yellow‐backed and Bay duikers may indicate local depletion. We call on all stakeholders to rise up to the challenge of rescuing this biological hotspot in Nigeria from further degradation and species loss through improved funding for well‐equipped field staff and institutionalized community wildlife management.     

Oviposition preference and larval performance of North American monarch butterflies on four Asclepias species

Monarch butterflies, Danaus plexippus L. (Lepidoptera: Nymphalidae), occur world‐wide and are specialist herbivores of plants in the milkweed family (Asclepiadaceae). In North America, two monarch populations breed east and west of the continental divide in areas populated by different host plant species. To examine the population variation in monarch responses to different Asclepias species, we measured oviposition preference and larval performance among captive progeny reared from adult butterflies collected in eastern and western North America. Host plant use was evaluated using two milkweed species widely distributed in eastern North America (A. incarnata and A. syriaca), and two species common to western North America (A. fascicularis and A. speciosa). We predicted that exposure to different host plant species in their respective breeding ranges could select for divergent host use traits, so that monarchs should preferentially lay more eggs on, and larvae should perform better on, milkweed species common to their native habitats. Results showed that across all adult female butterflies, oviposition preferences were highest for A. incarnata and lowest for A. fascicularis, but mean preferences did not differ significantly between eastern and western monarch populations. Larvae from both populations experienced the highest survival and growth rates on A. incarnata and A. fascicularis, and we again found no significant interactions between monarch source population and milkweed species. Moreover, the average rank order of larval performance did not correspond directly to mean female oviposition preferences, suggesting that additional factors beyond larval performance influence monarch oviposition behavior. Finally, significant family level variation was observed for both preference and performance responses within populations, suggesting an underlying genetic variation or maternal effects governing these traits.     

Genetic variation of blood proteins within and between local populations of grivet monkey (Cercopithecus aethiops aethiops) in central Ethiopia

A population genetic study by blood protein electrophoresis revealed that populations of wild grivet monkeys in central Ethiopia show a comparatively low level of variability and less differentiation among local populations over broad geographical areas. This is evaluated by comparison with other wild primate studies using the same electrophoretic technique. A total of 196 blood samples, collected from 10 local populations comprising 11 troops distributed along approximately 600 km of the Awash River, were examined for 33 genetic loci. The low level of variability was indicated by the proportion of polymorphic loci (P_poly), which was on average 11% with an average heterozygosity (H) of 3%. A tendency for lower genetic differentiation among local populations was shown by theG _ST value of 0.09, an averageF _ST of 0.08, andNei's genetic distance; ranging from 0.002 to 0.023. Considering paleoclimatological studies of the area and ecological traits of this species, these findings can be explained as a consequence of a comparatively recent and repeated series of rapid habitat expansions following severe climatic conditions.     

Is there genetic connectivity among the critically endangered White‐winged Flufftail (Sarothrura ayresi) populations from South Africa and Ethiopia?

The White‐winged Flufftail (Sarothrura ayresi) is known to occur in the highland marshes of Ethiopia, as well as almost 4000 km in South Africa. The White‐winged Flufftail is listed globally as Critically Endangered. In South Africa the population is estimated to be <50 birds. These birds are severely threatened by habitat destruction. Thus far, no genetic studies have been conducted on S. ayresi to confirm genetic connectivity between the South African and Ethiopian populations. In this study, analysis of mitochondrial and nuclear markers was conducted for White‐winged Flufftail samples from South African and Ethiopian birds, as well as Red‐chested Flufftail (Sarothrura rufa) for species comparison. Analyses of the DNA regions identified three variations between the two populations, supporting the hypothesis that these two populations are not different species or subspecies but are rather one migrating population with different seasonal occupied ranges. However, these results do not exclude the possibility of additional breeding and nonbreeding sites. Low genetic diversity in the populations of White‐winged Flufftails was observed, which needs to be further elucidated with fast evolving co‐dominant markers such as microsatellites, as this low diversity may ultimately contribute to the extinction of the species.     

Population genomics of local adaptation versus speciation in coral reef fishes (Hypoplectrus spp,Serranidae)

Are the population genomic patterns underlying local adaptation and the early stages of speciation similar? Addressing this question requires a system in which (i) local adaptation and the early stages of speciation can be clearly identified and distinguished, (ii) the amount of genetic divergence driven by the two processes is similar, and (iii) comparisons can be repeated both taxonomically (for local adaptation) and geographically (for speciation). Here, we report just such a situation in the hamlets (Hypoplectrus spp), brightly colored reef fishes from the wider Caribbean. Close to 100,000 SNPs genotyped in 126 individuals from three sympatric species sampled in three repeated populations provide genome‐wide levels of divergence that are comparable among allopatric populations (F_st estimate = 0.0042) and sympatric species (F_st estimate = 0.0038). Population genetic, clustering, and phylogenetic analyses reveal very similar patterns for local adaptation and speciation, with a large fraction of the genome undifferentiated (F_st estimate ≈ 0), a very small proportion of F_st outlier loci (0.05–0.07%), and remarkably few repeated outliers (1–3). Nevertheless, different loci appear to be involved in the two processes in Hypoplectrus, with only 7% of the most differentiated SNPs and outliers shared between populations and species comparisons. In particular, a tropomyosin (Tpm4) and a previously identified hox (HoxCa) locus emerge as candidate loci (repeated outliers) for local adaptation and speciation, respectively. We conclude that marine populations may be locally adapted notwithstanding shallow levels of genetic divergence, and that from a population genomic perspective, this process does not appear to differ fundamentally from the early stages of speciation.     

Habitat characterization of the morphologically similar mayfly larvae,Caenis and Tricorythodes (Ephemeroptera)

The larvae of Caenis (Caenidae) and Tricorythodes (Tricorythidae), once considered to be confamilial, have notable morphological and behavioural similarities. Univariate and multivariate (discriminant analysis) techniques were used to determine which environmental variables best characterized the larval habitats of Caenis and Tricorythodes at 40 sample sites on 29 rivers within the Interior Plains of Alberta, Canada. River width, depth and substrate type distinguished riverine habitats of the two genera. Larvae of Tricorythodes occurred in wide rivers of varying depths that possessed coarse substrates. Although larvae of Caenis occurred in a variety of habitats, they were found more frequently on stable substrates in narrow, deep rivers.     

Population genetic structure of annual and perennial populations of Zostera marina L. along the Pacific coast of Baja California and the Gulf of California

The Baja California peninsula represents a biogeographical boundary contributing to regional differentiation among populations of marine animals. We investigated the genetic characteristics of perennial and annual populations of the marine angiosperm, Zostera marina, along the Pacific coast of Baja California and in the Gulf of California, respectively. Populations of Z. marina from five coastal lagoons along the Pacific coast and four sites in the Gulf of California were studied using nine microsatellite loci. Analyses of variance revealed significant interregional differentiation, but no subregional differentiation. Significant spatial differentiation, assessed using θ_ST values, was observed among all populations within the two regions. Z. marina populations along the Pacific coast are separated by more than 220 km and had the greatest θ_ST (0.13–0.28) values, suggesting restricted gene flow. In contrast, lower but still significant genetic differentiation was observed among populations within the Gulf of California (θ_ST = 0.04–0.18), even though populations are separated by more than 250 km. This suggests higher levels of gene flow among Gulf of California populations relative to Pacific coast populations. Direction of gene flow was predominantly southward among Pacific coast populations, whereas no dominant polarity in the Gulf of California populations was observed. The test for isolation by distance (IBD) showed a significant correlation between genetic and geographical distances in Gulf of California populations, but not in Pacific coast populations, perhaps because of shifts in currents during El Niño Southern Oscillation (ENSO) events along the Pacific coast.     

Local adaptation in populations of a Brachionus group plicatilis cryptic species inhabiting three deep crater lakes in Central Mexico

1. Salinity is a strong selective force for many aquatic organisms, affecting both ecological and evolutionary processes. Most of our knowledge on the effects of salinity on rotifers in the Brachionus plicatilis species complex is based mainly on populations from waterbodies that experience broad environmental changes both seasonally and annually. We tested the hypothesis that, despite the supposedly high potential for gene flow among rotifers inhabiting neighbouring environments, constant salinity has promoted local adaptation, genetic population divergence and even cryptic speciation in B. plicatilis complex populations from three deep maar lakes of distinct salinities [1.1, 6.5 and 9.0 g L^?1 total dissolved solids (TDS)] in Central Mexico. 2. To look for local adaptation, we performed common garden experiments to test the effect of different salinities on population density and intrinsic growth rate (r). Then, we evaluated the genetic divergence by sequencing the cytochrome c oxidase subunit I (COI) gene and performed reproductive trials to assess the potential gene flow among the three populations and with other closely related B. plicatilis complex species. 3. We confirmed that the rotifer populations have phenotypic plasticity in tolerance of salinity, but only rotifers from the least saline lake are adapted to low salinity. Among the populations, sequence divergence at COI was very low (just a single haplotype was found), suggesting a persistent founder effect from a relatively recent single colonisation event and a subsequent dispersal from one lake to the others, and a very restricted immigration rate. In the phylogenetic analysis, rotifers from this area of Mexico clustered in the same clade with the middle‐sized species Brachionus ibericus and B. sp. ‘Almenara’. Mexican rotifers showed successful recognition, copulation and formation of hybrids among them, but interpopulation breeding with the Spanish B. ibericus and B. sp. ‘Almenara’ was unsuccessful. 4. We conclude that the B. plicatilis complex populations from these three lakes belong to a new biological species not yet described (presently named B. sp. ‘Mexico’). To our knowledge, this is the first report of local adaptation of a natural B. plicatilis complex population living in freshwater conditions (1.1 g L^?1 TDS).     

Commensal ecology, urban landscapes, and their influence on the genetic characteristics of city-dwelling Norway rats (Rattus norvegicus)

Movement of individuals promotes colonization of new areas, gene flow among local populations, and has implications for the spread of infectious agents and the control of pest species. Wild Norway rats ( Rattus norvegicus ) are common in highly urbanized areas but surprisingly little is known of their population structure. We sampled individuals from 11 locations within Baltimore, Maryland, to characterize the genetic structure and extent of gene flow between areas within the city. Clustering methods and a neighbour-joining tree based on pairwise genetic distances supported an east–west division in the inner city, and a third cluster comprised of historically more recent sites. Most individuals (~95%) were assigned to their area of capture, indicating strong site fidelity. Moreover, the axial dispersal distance of rats (62 m) fell within typical alley length. Several rats were assigned to areas 2–11.5 km away, indicating some, albeit infrequent, long-distance movement within the city. Although individual movement appears to be limited (30–150 m), locations up to 1.7 km are comprised of relatives. Moderate F _ST, differentiation between identified clusters, and high allelic diversity indicate that regular gene flow, either via recruitment or migration, has prevented isolation. Therefore, ecology of commensal rodents in urban areas and life-history characteristics of Norway rats likely counteract many expected effects of isolation or founder events. An understanding of levels of connectivity of rat populations inhabiting urban areas provides information about the spatial scale at which populations of rats may spread disease, invade new areas, or be eradicated from an existing area without reinvasion.     

Climatic and geographic effects on the spatial genetic pattern of a landbird species (Alectoris rufa) on the Iberian Peninsula

Understanding the spatial pattern of genetic diversity may be pivotal to adaptive conservation management of a given taxon. The red-legged partridge (Alectorisrufa, Linnaeus 1758) is naturally widely distributed from the Mediterranean to humid temperate zones. According to a recent study, the genetic structure of this species comprises five clusters, three of which are in the Iberian Peninsula (glacial refugia). Partridge demographic expansion events and climatic shifts during Pleistocene glaciations have been used to test the hypotheses concerning Iberian red-legged partridge distribution. We tested the existence of climatic and geographic relationships on genetic diversity/distances. We employed markers from two different genetic systems, such as part of the mitochondrial DNA control region (n = 113) and 20 species-specific microsatellite DNA loci (n = 377), including climatic and geographic factors from the 14 Iberian localities where A. rufa populations were sampled. Our results showed a mitochondrial genetic diversity pattern associated with a thermic gradient, and a decrease of genetic diversity in peripheral populations that concurred with the ‘abundant centre’ hypothesis. Overall, current climatic variables reliably described genetic variation and differentiation in the red-legged partridge, which may be a result of local species adaptation.     

Trophic interactions and benthic animal community structure in the Colorado River, Arizona, U.S.A.

1. Cladophora glomerata is the dominant filamentous green alga in the tailwaters of the Colorado River, U.S.A., below Glen Canyon Dam, but becomes co-dominant with filamentous cyanobacteria, Oscillatoria spp., below the confluence of the Paria River (26km below the dam) where suspended sediments are elevated. 2. Benthic algal assemblages played an important role in the distribution of the amphipod, Gammarus lacustris, in the dam-controlled Colorado River through Grand Canyon National Park, Arizona. Cladophara and G. lacustris showed a weak positive relationship at ten cobble-riffle habitats in the Colorado River from Lees Ferry (25km below the dam) to Diamond Creek (362km downstream), while no relationship was found between Oscillatoria and G. lacustris. 3. The relationship between algal substrata and G. lacustris was tested by a series of in situ habitat choice experiments. G. lacustris showed a significant preference for Cladophora (with epiphytes) over Oscillatoria spp., detritus and gravel in treatment pans at Lees Ferry. 4. Epiphytic diatoms (i.e. food) were the overriding determinant of subtratum choice by G. lacustris in laboratory experiments. Gammarus chose the Cladophora/epiphytic diatom community over sonicated Cladophora with few diatoms. The amphipods also chose string soaked in diatom extract over string without diatom extract. 5. Importance of mutualistic interactions in aquatic benthic community structure is discussed.     

A new breeding population of Mediterranean Gulls Larus melanocephalus in the species' main wintering area maintains independent spatial dynamics

We studied a newly established breeding population of the range‐expanding Mediterranean Gull Larus melanocephalus in eastern Spain, situated in close proximity to the species' main wintering area. By investigating the origin, population composition and wintering area of the new breeders, we found that recruitment from locally wintering birds was unlikely and that the emerging colonies were probably attracting birds from populations wintering 700–1200 km away in Portugal and southern Spain. Our findings reveal that expanding populations may follow their own dynamics, independently of other populations of the same species, and may consist of different individuals altogether.     

Comparative population genetic structure in a plant-pollinator/seed predator system

Comparative analyses of spatial genetic structure of populations of plants and the insects they interact with provide an indication of how gene flow, natural selection and genetic drift may jointly influence the distribution of genetic variation and potential for local co‐adaptation for interacting species. Here, we analysed the spatial scale of genetic structure within and among nine populations of an interacting species pair, the white campion Silene latifolia and the moth Hadena bicruris, along a latitudinal gradient across Northern/Central Europe. This dioecious, short‐lived perennial plant inhabits patchy, often disturbed environments. The moth H. bicruris acts both as its pollinator and specialist seed predator that reproduces by laying eggs in S. latifolia flowers. We used nine microsatellite markers for S. latifolia and eight newly developed markers for H. bicruris. We found high levels of inbreeding in most populations of both plant and pollinator/seed predator. Among populations, significant genetic structure was observed for S. latifolia but not for its pollinator/seed predator, suggesting that despite migration among populations of H. bicruris, pollen is not, or only rarely, carried over between populations, thus maintaining genetic structure among plant populations. There was a weak positive correlation between genetic distances of S. latifolia and H. bicruris. These results indicate that while significant structure of S. latifolia populations creates the potential for differentiation at traits relevant for the interaction with the pollinator/seed predator, substantial gene flow in H. bicruris may counteract this process in at least some populations.     

Zooplankton Communities of a Dammed Estuary in the Bay of Fundy,Canada

The upper estuary of the macrotidal Petitcodiac River, New Brunswick, Canada, was converted to a freshwater impoundment by construction of a causeway in 1968. Thirty years later, zooplankton community structure in the impoundment was characteristic of a disturbed ecosystem. The depauperate zooplankton consisted of a mixture of freshwater and marine/brackish taxa, but was not typical of regional estuaries or lakes. The causeway dam was an obstacle to fish migration, and several anadromous species that would formerly have been represented in the ichthyoplankton were absent. The invertebrate plankton community was dominated by rotifers, likely as a result of frequent water level fluctuations, and highly suspended sediment levels in the water column. Estuarine/marine calanoids (Eurytemora affinis, Temora longicornis, Centropages typicus, Tortanus discaudatus), the mysid Neomysis americana, and Cancer crab zoeae were collected in fresh water up to 14 km upstream of the causeway.