Divergent Habitats Research Articles

No longer shipwrecked—Selkirkia (Boraginaceae) back on the mainland with generic rearrangements in South American “Omphalodes” based on molecular data

The genus Omphalodes (Boraginaceae) has recently been shown to be polyphyletic. Two distantly related lineages have already been segregated into the genera Memoremea (Central Europe) and Nihon (East Asia), respectively. We expanded the taxon sampling in the Omphalodeae and confirm that the genus is still paraphyletic to the two monotypic genera Selkirkia from the Juan Fernández Islands off the coast of Chile and Myosotidium from Chatham Island off the coast of New Zealand, plus two South American species currently assigned to Cynoglossum, and one species recently segregated from the latter genus as Mapuchea. Four clades are retrieved in a narrowly delimited Omphalodes group: 1) Iberodes, the annual southwestern European species of Omphalodes s.l. that have been recently segregated into this genus, 2) Omphalodes s.str., perennial western Eurasian species (including the type species of the genus), 3) the North American species of Omphalodes, and 4) the southern hemispheric Myosotidium as sister to a monophyletic group with Mapuchea plus the two other South American species of “Cynoglossum” and the island shrub Selkirkia berteroi. We argue that the taxa of this latter clade are best placed into an expanded genus Selkirkia. Selkirkia then represents a morphologically coherent entity with glochidiate nutlets. Its considerable difference in vegetative morphology to Myosotidium is easily explained by the highly divergent habitats the respective plants occupy. Lectotypifications, illustrations, and descriptions are provided for Myosotidium and the species of the expanded genus Selkirkia.

Divergent habitat filtering of root and soil fungal communities in temperate beech forests.

Distance decay, the general reduction in similarity of community composition with increasing geographical distance, is known as predictor of spatial variation and distribution patterns of organisms. However, changes in fungal communities along environmental gradients are little known. Here we show that distance decays of soil-inhabiting and root-associated fungal assemblages differ, and identify explanatory environmental variables. High-throughput sequencing analysis of fungal communities of beech-dominated forests at three study sites across Germany shows that root-associated fungi are recruited from the soil fungal community. However, distance decay is substantially weaker in the root-associated than in the soil community. Variance partitioning of factors contributing to the observed distance decay patterns support the hypothesis that host trees stabilize the composition of root-associated fungi communities, relative to soil communities. Thus, they not only have selective impacts on associated communities, but also buffer effects of changes in microclimatic and environmental variables that directly influence fungal community composition.

Responses and influencing factors of foliar photosynthetic characteristics of <italic>Larix gmelinii </italic>to changing environments

Investigating tree photosynthetic capacity is important for understanding the carbon cycles of terrestrial ecosystems and their responses and adaptation to climatic change. Dahurian Larch ( Larix gmelinii ) is one of the dominant tree species in Chinese boreal forests with a broad bio-geographic range under divergent habitats, and thus an ideal tree species for exploring tree adaptation to environment. In this study, we measured the foliar photosynthesis and associated physiological parameters of 30-year-old Dahurian larch trees from six provenances in a common garden at the Maoershan Forest Ecosystem Research Station in Northeast China for three years (2009–2011). The six provenances were located across the natural distribution range of the larch, spanning approximately 4° in latitude (48°–52°N), 5°C in mean annual temperature ( - 2.3–2.6°C), and 200 mm in mean annual precipitation (425–622 mm). To access the top canopy of the sampled trees, we constructed 15-m-high wooden scaffolds at the site. Three representative trees from each provenance were selected for the measurements per month from mid May to mid September. We measured three fully expanded sunlit fascicles on young short shoots at the top of the canopy of each tree in situ with an infrared gas analyzer. On non-rainy days, light and CO2 response curves were measured between 06:30 and 12:00 hours under optimal conditions. Our goal was to explore impacts of environmental changes on foliar photosynthetic characteristics of the larch and their driving factors. The main results were summarized as follows: (ⅰ) The leaf-area-based maximum net photosynthetic rate ( P max-a), dark respiratory rate ( R a), apparent quantum yield (AQY), maximum rate of carboxylation ( V max), maximum electron transport rate ( J max) and triose phosphate utilization rate (TPU) all increased significantly ( P T s) and aridity index (AI) of the seed-source original sites, while the light compensation point (LCP) and photorespiratory rate ( R p) showed an opposite trend. This suggests that the leaf photosynthetic characteristics genetically adapt to the original site conditions of the tree seed-sources, among which the temperature and precipitation are the major driving factors. (ⅱ) P max-a was positively correlated with AQY, V max, J max, TPU, and leaf nitrogen concentration, but negatively with LCP and R p ( P T s habitats had higher sensitivity of P max-a associated with other characteristics. (ⅲ) P max-a was significantly and positively correlated with 3-day mean temperature, mean monthly temperature, mean growing season temperature, 3-day mean relative humidity, and mean monthly precipitation of the common garden, while the R a showed opposite trends with the environmental factors except for the mean growing season temperature. This indicates that the leaf photosynthetic characteristics acclimate to the environmental conditions of the common garden. However, the trees from higher T s habitats had lower intercepts of the regression equations of P max-a associated with the environmental factors, and had the opposite trends for R a except for the mean growing season temperature. The results suggest that the relationships between foliar photosynthetic characteristics and environment are jointly controlled by both phenotypic acclimation to current site conditions and genotypic adaptation to the original environment of the seed-source. These findings provide insights on understanding the survival, reproduction and distribution of Dahurian larch to changing environments.

Functional morphology of the tetra fish Astyanax lacustris differs between divergent habitats in the Pantanal wetlands.

This study investigated whether the body morphology of the tetra fish Astyanax lacustris (previously Astyanax asuncionensis) varied between populations inhabiting one lagoon (a lentic, shallow environment, with great habitat complexity created by aquatic macrophytes) and an adjacent river (a deeper, lotic environment where aquatic macrophytes are scarce) in a seasonally flooded wetland, despite population mixing during the wet season. Morphological differences matched a priori predictions of the theory relating functional body morphology and swimming performance in fishes between lagoon and river habitats. Observed morphological variation could have resulted from adaptive habitat choice by tetras, predation by piscivores and adaptive phenotypic plasticity during development.

Differences in rheotactic responses contribute to divergent habitat use between parapatric lake and stream threespine stickleback.

Migration among populations is widely thought to undermine adaptive divergence, assuming gene flow arises from random movement of individuals. If individuals instead differ in dispersal behavior, phenotype-dependent dispersal can reduce the effective rate of gene flow or even facilitate divergence. For example, parapatric populations of lake and stream stickleback tend to actively avoid dispersing into the adjoining habitat. However, the behavioral basis of this nonrandom dispersal was previously unknown. Here, we show that lake and stream stickleback exhibit divergent rheotactic responses (behavioral response to currents). During the breeding season, wild-caught inlet stream stickleback were better than lake fish at maintaining position in currents, faced upstream more, and spent more time in low-current areas. As a result, stream fish expended significantly less energy in currents than did lake fish. These divergent rheotactic responses likely contribute to divergent habitat use by lake and stream stickleback. Although rheotactic differences were absent in nonbreeding fish, divergent behavior of breeding-season fish may suffice for assortative mating by breeding location. The resulting reproductive isolation between lake and stream fish may explain the fine-scale evolutionary differentiation in parapatric stickleback populations.

Wetland suitability and connectivity for trans-Saharan migratory waterbirds.

To complete their life cycle waterbirds rely on patchily distributed and often ephemeral wetlands along their migration route in a vast unsuitable matrix. However, further loss and degradation of remaining wetland habitats might lead to a configuration and size of stopovers that is no longer sufficient to ensure long-term survival of waterbird populations. By identifying optimal conservation targets to maintain overall habitat availability en route, we can accommodate an as yet absent functional connectivity component in larger management frameworks for migratory waterbirds, such as the Ramsar Convention and the EU Natura 2000 Network. Using a graph-based habitat availability metric (Equivalent Connected Area) we determine the functional connectivity of wetland networks for seven migratory waterbirds with divergent habitat requirements. Analyses are performed at two spatial extents both spanning the Mediterranean Sea and centered around Greece (Balkan-Cyrenaica and Greece-Cyrenaica). We create species-specific suitable habitat maps and account for human disturbance by species-specific disturbance buffers, based on expert estimates of Flight Initiation Distances. At both spatial extents we quantitatively determine the habitat networks’ overall functional connectivity and identify wetland sites that are crucial for maintaining a well-connected network. We show that the wetland networks for both spatial extents are relatively well connected and identify several wetland sites in Greece and Libya as important for maintaining connectivity. The application of disturbance buffers results in wetland site-specific reduction of suitable habitat area (0.90–7.36%) and an overall decrease of the network’s connectivity (0.65–6.82%). In addition, we show that the habitat networks of a limited set of species can be combined into a single network which accounts for their autoecological requirements. We conclude that targeted management in few but specific wetland complexes could benefit migratory waterbird populations. Deterioration of these vital wetland sites in Greece and Libya will have disproportionate consequences to the waterbird populations they support.

Divergent Impacts of Two Cattle Types on Vegetation in Coastal Meadows: Implications for Management

The proportion of beef cattle in relation to the total number of cattle has increased in Europe, which has led to a higher contribution of beef cattle in the management of semi-natural grasslands. Changes in vegetation caused by this change in grazers are virtually unexplored so far. In the present study, the impacts of beef and dairy cattle on vegetation structure and composition were compared on Bothnian Bay coastal meadows. Vegetation parameters were measured in seven beef cattle, six dairy heifer pastures, and in six unmanaged meadows. Compared to unmanaged meadows, vegetation in grazed meadows was significantly lower in height and more frequently colonized by low-growth species. As expected, vegetation grazed by beef cattle was more open than that on dairy heifer pastures where litter cover and proportion of bare ground were in the same level as in the unmanaged meadows. However, the observed differences may have in part arisen from the higher cattle densities in coastal meadows grazed by beef cattle than by dairy heifers. The frequencies of different species groups and the species richness values of vegetation did not differ between the coastal meadows grazed by the two cattle types. One reason for this may be the relatively short management history of the studied pastures. The potential differences in grazing impacts of the two cattle types on vegetation structure can be utilized in the management of coastal meadows for species with divergent habitat requirements.

Links between Genetic Groups, Indole Alkaloid Profiles and Ecology within the Grass-Parasitic Claviceps purpurea Species Complex.

The grass parasitic fungus Claviceps purpurea sensu lato produces sclerotia with toxic indole alkaloids. It constitutes several genetic groups with divergent habitat preferences that recently were delimited into separate proposed species. We aimed to 1) analyze genetic variation of C. purpurea sensu lato in Norway, 2) characterize the associated indole alkaloid profiles, and 3) explore relationships between genetics, alkaloid chemistry and ecology. Approximately 600 sclerotia from 14 different grass species were subjected to various analyses including DNA sequencing and HPLC-MS. Molecular results, supported by chemical and ecological data, revealed one new genetic group (G4) in addition to two of the three known; G1 (C. purpurea sensu stricto) and G2 (C. humidiphila). G3 (C. spartinae) was not found. G4, which was apparently con-specific with the recently described C. arundinis sp. nov, was predominantly found in very wet habitats on Molinia caerulea and infrequently in saline habitats on Leymus arenarius. Its indole-diterpene profile resembled G2, while its ergot alkaloid profile differed from G2 in high amounts of ergosedmam. In contrast to G1, indole-diterpenes were consistently present in G2 and G4. Our study supports and complements the newly proposed species delimitation of the C. purpurea complex, but challenges some species characteristics including host spectrum, habitat preferences and sclerotial floating ability.

Genetic consequences of cladogenetic vs. anagenetic speciation in endemic plants of oceanic islands.

Adaptive radiation is a common mode of speciation among plants endemic to oceanic islands. This pattern is one of cladogenesis, or splitting of the founder population, into diverse lineages in divergent habitats. In contrast, endemic species have also evolved primarily by simple transformations from progenitors in source regions. This is anagenesis, whereby the founding population changes genetically and morphologically over time primarily through mutation and recombination. Gene flow among populations is maintained in a homogeneous environment with no splitting events. Genetic consequences of these modes of speciation have been examined in the Juan Fernández Archipelago, which contains two principal islands of differing geological ages. This article summarizes population genetic results (nearly 4000 analyses) from examination of 15 endemic species, involving 1716 and 1870 individuals in 162 and 163 populations (with amplified fragment length polymorphisms and simple sequence repeats, respectively) in the following genera: Drimys (Winteraceae), Myrceugenia (Myrtaceae), Rhaphithamnus (Verbenaceae), Robinsonia (Asteraceae, Senecioneae) and Erigeron (Asteraceae, Astereae). The results indicate that species originating anagenetically show high levels of genetic variation within the island population and no geographic genetic partitioning. This contrasts with cladogenetic species that show less genetic diversity within and among populations. Species that have been derived anagenetically on the younger island (1-2 Ma) contain less genetic variation than those that have anagenetically speciated on the older island (4 Ma). Genetic distinctness among cladogenetically derived species on the older island is greater than among similarly derived species on the younger island. An important point is that the total genetic variation within each genus analysed is comparable, regardless of whether adaptive divergence occurs.

Getting in shape: habitat-based morphological divergence for two sympatric fishes

Freshwater fishes often show large amounts of body shape variation across divergent habitats and, in most cases, the observed differences have been attributed to the environmental pressures of living in lentic or lotic habitats. Previous studies have suggested a distinct set characters and morphological features for species occupying each habitat under the steady–unsteady swimming performance model. We tested this model and assessed body shape variation using geometric morphometrics for two widespread fishes, Goodea atripinnis (Goodeidae) and Chirostoma jordani (Atherinopsidae), inhabiting lentic and lotic habitats across the Mesa Central of Mexico. These species were previously shown to display little genetic variation across their respective ranges. Our body shape analyses reveal morphometric differentiation along the same axes for both species in each habitat. Both possess a deeper body shape in lentic habitats and a more streamlined body in lotic habitats, although the degree of divergence between habitats was less for C. jordani. Differences in the position of the mouth differed between habitats as well, with both species possessing a more superior mouth in lentic habitats. These recovered patterns are generally consistent with the steady–unsteady swimming model and highlight the significance of environmental forces in driving parallel body shape differences of organisms in divergent habitats. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114, 152–162.

Variation in Melanism and Female Preference in Proximate but Ecologically Distinct Environments

AbstractVariation in pigmentation traits is an effective window to evolutionary processes due to their importance for survival and reproduction. In particular, one of the leading hypotheses for the maintenance of conspicuous pigmentation in natural populations is its signaling function in mate choice. Here, we demonstrate the occurrence of melanism in poeciliid fishes of the genus Poecilia that inhabits toxic, hydrogen sulfide springs in southern Mexico and the absence of melanism from closely related populations in reference habitats lacking hydrogen sulfide. Assays of female mate preference in both habitat types were used to examine whether divergence in female preference for melanism contributes to its maintenance in hydrogen sulfide springs. We found significant variation in female preferences for melanistic males. Specifically, melanistic females from the toxic spring exhibited a significant preference for melanistic males, while non‐melanistic females from the same population exhibited no preference. Females from the non‐sulfidic reference population discriminated strongly against melanistic males. Preferences of melanistic females appear to be a significant force in the maintenance of melanism in sulfidic habitats and suggest a change in preference as the divergence from non‐sulfidic ancestors. Potential polymorphism in preference within the hydrogen sulfide spring indicates that preference for melanistic males may not be environmentally controlled. Thus, a change in preference following divergence can promote the maintenance of variation in pigmentation within populations and between divergent habitats.

Niche divergence promotes rapid diversification of East African sky island white-eyes (Aves: Zosteropidae).

The Eastern Afromontane biodiversity hotspot composed of highly fragmented forested highlands (sky islands) harbours exceptional diversity and endemicity, particularly within birds. To explain their elevated diversity within this region, models founded on niche conservatism have been offered, although detailed phylogeographic studies are limited to a few avian lineages. Here, we focus on the recent songbird genus Zosterops, represented by montane and lowland members, to test the roles of niche conservatism versus niche divergence in the diversification and colonization of East Africa's sky islands. The species-rich white-eyes are a typically homogeneous family with an exceptional colonizing ability, but in contrast to their diversity on oceanic islands, continental diversity is considered depauperate and has been largely neglected. Molecular phylogenetic analysis of ∼140 taxa reveals extensive polyphyly among different montane populations of Z. poliogastrus. These larger endemic birds are shown to be more closely related to taxa with divergent habitat types, altitudinal distributions and dispersal abilities than they are to populations of restricted endemics that occur in neighbouring montane forest fragments. This repeated transition between lowland and highland habitats over time demonstrate that diversification of the focal group is explained by niche divergence. Our results also highlight an underestimation of diversity compared to morphological studies that has implications for their taxonomy and conservation. Molecular dating suggests that the spatially extensive African radiation arose exceptionally rapidly (1–2.5 Ma) during the fluctuating Plio-Pleistocene climate, which may have provided the primary driver for lineage diversification.

A tight association in two genetically unlinked dispersal related traits in sympatric and allopatric salt marsh beetle populations

Local adaptation likely involves selection on multiple, genetically unlinked traits to increase fitness in divergent habitats. Conversely, recombination is expected to counteract local adaptation under gene flow by breaking down adaptive gene combinations. Western European populations of the salt marsh beetle Pogonus chalceus are characterized by large interpopulation variation at various geographical ranges in two traits related to dispersal ability, i.e. wing size and different allozymes of the mitochondrial NADP(+)-dependent isocitrate dehydrogenase (mtIdh) gene. In this study, we tested whether variation in wing length was as strongly genetically determined in locally adapted populations in a sympatric mosaic compared to allopatric populations, and if variation in mtIDH and wing size was genetically unlinked. We demonstrate that the genetic determination of wing size is very high (h (2) = 0.90) in sympatry and of comparable magnitude as geographically separated populations. Second, we show that, although frequencies of mtIDH allozymes are tightly associated with mean population wing size across Western European populations, the correlation is strongly reduced within some of the populations. These findings demonstrate that the divergence involves at least two traits under independent genetic control and that the genetically distinct ecotypes are retained at geographical distances with ample opportunity for gene flow.

Association between integration structure and functional evolution in the opercular four-bar apparatus of the threespine stickleback,Gasterosteus aculeatus(Pisces: Gasterosteidae)

Phenotypes may evolve to become integrated in response to functional demands. Once evolved, integrated phenotypes, often modular, can also influence the trajectory of subsequent responses to selection. Clearly, connecting modularity and functionally adaptive evolution has been challenging. The teleost skull and jaw structures are useful for understanding this connection because of the key roles that these structures play in feeding in novel environments with different prey resources. In the present study, we examined such a structure in the threespine stickleback: the opercular four-bar lever that functions in jaw opening. Comparing oceanic and two fresh-water populations, we find marked phenotypic divergence in the skull opercular region, and the major axes of morphological and functional variation of the lever are found to be highly correlated. All three populations share the same global skull integration structure, and a conserved, strongly-supported modular organization is evident in the region encompassing the lever. Importantly, a boundary between two modules that subdivides the lever apparatus corresponds to the region of most prominent morphological evolution. The matched modular phenotypic and functional architecture of head and jaw structures of stickleback therefore may be important for facilitating their rapid adaptive transitions between highly divergent habitats. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 375–390.

The landscape genetics of syntopic topminnows (Fundulus notatusandF. olivaceus) in a riverine contact zone

The metapopulation dynamics of a species are influenced by the spatial arrangement of preferred habitats across a landscape. Increasing habitat patchiness can result in greater population subdivision, leading to more pronounced population genetic structure. Therefore, even subtle differences in habitat preferences among species could lead to substantial differences in genetic structure. Members of the Fundulus notatus species complex of topminnows include a headwater specialist and a large river specialist with broadly overlapping geographical distributions. Both species are often found in the same drainage systems, but partially isolated by divergent habitat preferences. The purpose of this research was to determine whether distribution along a stream continuum in a contact zone influences population genetic patterns in two species of topminnow (Fundulus olivaceus and Fundulus notatus). Fish were collected in the summers of 2010–2012, and habitat data were collected in summer 2012, within all major tributaries of the Saline River in southern Illinois. In total, 523 fish were genotyped using seven microsatellite loci to assess genetic variation. Species distributions in F. notatus and F. olivaceus were associated with habitat factors that covaried with cumulative drainage area. Populations of F. olivaceus showed a greater level of genetic structure reflected in a significant pattern of isolation by distance, while populations of F. notatus showed no such pattern. Spatial autocorrelation analysis revealed that at an individual level, both species became increasingly divergent with waterway distance. Overall, clear interspecific differences in habitat preferences were translated into measurable but relatively subtle differences in population genetic structure.

Ongoing Speciation in the Tibetan Plateau Gymnocypris Species Complex

Local adaptation towards divergent ecological conditions often results in genetic differentiation and adaptive phenotypic divergence. To illuminate the ecological distinctiveness of the schizothoracine fish, we studied a Gymnocypris species complex consisting of three morphs distributed across four bodies of water (the Yellow River, Lake Qinghai, the Ganzi River and Lake Keluke) in the Northeast Tibetan Plateau. We used a combination of mitochondrial (16S rRNA and Cyt b) and nuclear (RAG-2) genetic sequences to investigate the phylogeography of these morphs based on a sample of 277 specimens. Analysis of gill rakers allowed for mapping of phenotypic trajectories along the phylogeny. The phylogenetic and morphological analyses showed that the three sparsely rakered morphs were present at two extremes of the phylogenetic tree: the Yellow River morphs were located at the basal phylogenetic split, and the Lake Keluke and Ganzi River morphs at the peak, with the densely rakered Lake Qinghai morphs located between these two extremes. Age estimation further indicated that the sparsely rakered morphs constituted the oldest and youngest lineages, whereas the densely rakered morph was assigned to an intermediate-age lineage. These results are most compatible with the process of evolutionary convergence or reversal. Disruptive natural selection due to divergent habitats and dietary preferences is likely the driving force behind the formation of new morphs, and the similarities between their phenotypes may be attributable to the similarities between their forms of niche tracking associated with food acquisition. This study provides the first genetic evidence for the occurrence of convergence or reversal in the schizothoracine fish of the Tibetan Plateau at small temporal scales.

Contrasting Population and Life History Responses of a Young Morph-Pair of European Whitefish to the Invasion of a Specialised Coregonid Competitor, Vendace

Invasions of non-native species represent a global problem of great scientific interest. Here we study in detail the response in population and life history characteristics of closely related native species, with divergent habitat preferences, that are impacted by an invading species over a sufficient time period to allow a new stable state to become established. A time series of 20 years starting at the first occurrence of the invader (vendace Coregonus albula (L.)) allows exploration of the long term population and life history response of two ecologically, morphologically, and genetically different native sympatric morphs (DR- and SR-) of congeneric whitefish C. lavaretus (L.). The whitefish morphs are taxonomically equally related to the invading vendace, but only the planktivorous DR-whitefish share its pelagic niche. We would expect that the ecological differences between the whitefish morphs may be used as a predictor of competitive effects. Vendace exhibited an initial boom-and-bust development, and has continued to fluctuate in density. The responses of the pelagic DR-whitefish were: i) an immediate habitat shift, ii) a subsequent population decline caused by increased annual mortality, and iii) a new stable state at a lower density and apparently relaxed competition. The ecologically more distant benthivorous SR-whitefish also showed significant, but a much more limited response during this process, indicating damped indirect interactions through the food-web. This long-term case-study found that in two native eco-species equally related to the invader, only one of the eco-species was highly affected. Direct competition for resources is obviously important for species interactions, whereas the taxonomic relatedness per se seems to offer little predictive power for invasion effects.

Speciation in ninespine stickleback: reproductive isolation and phenotypic divergence among cryptic species of Japanese ninespine stickleback

Although similar patterns of phenotypic diversification are often observed in phylogenetically independent lineages, differences in the magnitude and direction of phenotypic divergence have been also observed among independent lineages, even when exposed to the same ecological gradients. The stickleback family is a good model with which to explore the ecological and genetic basis of parallel and nonparallel patterns of phenotypic evolution, because there are a variety of populations and species that are locally adapted to divergent environments. Although the patterns of phenotypic divergence as well as the genetic and ecological mechanisms have been well characterized in threespine sticklebacks, Gasterosteus aculeatus, we know little about the patterns of phenotypic diversification in other stickleback lineages. In eastern Hokkaido, Japan, there are three species of ninespine sticklebacks, Pungitius tymensis and the freshwater type and the brackish-water type of the P. pungitius-P. sinensis species complex. They utilize divergent habitats along coast-stream gradients of rivers. Here, we investigated genetic, ecological and phenotypic divergence among three species of Japanese ninespine sticklebacks. Divergence in trophic morphology and salinity tolerance occurred in the direction predicted by the patterns observed in threespine sticklebacks. However, the patterns of divergence in armour plate were different from those previously found in threespine sticklebacks. Furthermore, the genetic basis of plate variation may differ from that in threespine sticklebacks. Because threespine sticklebacks are well-established model for evolutionary research, the sympatric trio of ninespine sticklebacks will be an invaluable resource for ecological and genetic studies on both common and lineage-specific patterns of phenotypic diversification.

Cyanobacterial diversity in the hot spring, pelagic and benthic habitats of a tropical soda lake

Hot springs and saline-alkaline lakes of East Africa are extreme habitats regarding temperature, or salinity and pH, respectively. This study examines whether divergent habitats of Lake Bogoria, Kenya, impacts cyanobacterial community structure. Samples from the hot springs, pelagic zone and sediment were analysed by light microscopy, multilocus 454-amplicons sequencing and metagenomics to compare the cyanobacterial diversity. Most of the phylogenetic lineages of Cyanobacteria occurred exclusively in the Bogoria hot springs suggesting a high degree of endemism. The prevalent phylotypes were mainly members of the Oscillatoriales (Leptolyngbya, Spirulina, Oscillatoria-like and Planktothricoides). The Chroococcales were represented by different clades of Synechococcus but not a single phylotype clustered with any of the lineages described earlier from different continents. In contrast, we found that the pelagic zone and the sediments were inhabited by only a few taxa, dominated by Arthrospira and Anabaenopsis. Arthrospira, the main food base of Lesser Flamingo, was detected in all three habitats by amplicons pyrosequencing, indicating its resilience and key role as a primary producer. Despite the close connection between the three habitats studied, the cyanobacterial communities in the hot springs and lake differed considerably, suggesting that they are unable to adapt to the extreme conditions of the neighbouring habitat.

Niche partitioning between close relatives suggests trade-offs between adaptation to local environments and competition.

Niche partitioning among close relatives may reflect trade-offs underlying species divergence and coexistence (e.g., between stress tolerance and competitive ability). We quantified the effects of habitat and congeneric species interactions on fitness for two closely related herbaceous plant species, Mimulus guttatus and Mimulus laciniatus, in three common habitat types within their sympatric range. Drought stress strongly reduced survival of M. guttatus in fast-drying seeps occupied by M. laciniatus, suggesting that divergent habitat adaptation maintains this niche boundary. However, neither seedling performance nor congeneric competition explained the absence of M. laciniatus from shady streams where M. guttatus thrives. M. laciniatus may be excluded from this habitat by competition with other species in the community or mature M. guttatus. Species performance and competitive ability were similar in sympatric meadows where plant community stature and the growing season length are intermediate between seeps and streams. Stochastic effects (e.g., dispersal among habitats or temporal variation) may contribute to coexistence in this habitat. Habitat adaptation, species interactions, and stochastic mechanisms influence sympatric distributions for these recently diverged species.