Homoploid hybrid speciation in a rare endemic Castilleja from Idaho (Castilleja christii,Orobanchaceae)

• Premise of the study: Hybridization is an important evolutionary force in the history of angiosperms; however, there are few examples of stabilized species derived through homoploid hybrid speciation. Homoploid hybrid species are generally detected via the presence of genetic additivity of parental markers, novel ecological and spatial distinctions, and novel morphological traits, all of which may aid in the successful establishment of hybrid species from parental types. Speciation and diversification within the genus Castilleja (Orobanchaceae) has been attributed to high levels of hybridization and polyploidy, though currently there are no examples of homoploid hybrid speciation within the genus. We employed multiple lines of evidence to examine a putative hybrid origin in C. christii, a rare endemic, known only from 80 hectares at the summit of Mt. Harrison (Cassia Co., Idaho). • Methods: We used granule-bound starch synthase II (waxy) sequences and 26 morphological characters to address hybridization between C. christii and widespread congeners C. miniata and/or C. linariifolia in an area of sympatry. Chromosomes of C. christii were also counted for the first time. • Key results: All 230 direct-sequenced C. christii individuals had the additive genomes of both C. miniata and C. linariifolia. Castilleja christii shares traits with both parents but also has floral characters that are unique and transgressive. Cytological counts indicated that all three taxa are diploid. • Conclusions: We conclude that C. christii is a stabilized homoploid hybrid derivative of C. linariifolia and C. miniata and is likely following an independent evolutionary trajectory from its progenitors.     

Variation within and among the chloroplast genomes ofMelaleuca alternifolia andM. linariifolia (Myrtaceae)

Melaleuca alternifolia andM. linariifolia are commercially important Australian species harvested for their essential oils. Both species have relatively narrow and disjunct distributions on the central coast of eastern Australia. Variation in the chloroplast genome was assessed for eight individuals from each of twelve populations, representing the species' geographic range. Low nucleotide diversity withinM. alternifolia contrasted with high nucleotide diversity inM. linariifolia. CpDNA data are consistent with the southern population ofM. alternifolia being a hybrid population withM. linariifolia. The two species are sympatric in this region. Variation inM. linariifolia was geographically structured, with northern populations differing from southern populations by seven restriction site mutations, five length mutations and an inversion. There was no evidence of hybridisation of the cp genome of northernM. linariifolia with the partially sympatric speciesM. trichostachya. Intra- and interspecific variation in the chloroplast genomes ofM. alternifolia, M. linariifolia, andM. trichostachya indicate considerable potential for the use of intraspecific cpDNA studies in examining phylogenetic relationships in melaleucas.     

Dynamics of sahelian pastures in relation to drought and grazing

Summary The dynamics of the vegetation were studied in the transition zone from the savannah to the Sahel in order to distinguish between the influence of the recent drought and the influence of overgrazing on the natural rangelands. The drought affected especially the different plant species at the northern limit of their habitat. It is, however, not well possible to speak of a sahelisation of the savannah, since the species in regression were replaced by invaders, like Borreria spp, and not by true Sahelian species. An exception was Blepharis linariifolia, which moved to the south. Grazing affected good fodder grasses like Andropogon gayanus, which were replaced by a legume with a short growth cycle, Zornia glochidiata, and an unpalatable annual grass Elionurus elegans. The species much stimulated by the drought, Borreria spp. and Blepharis linariifolia, did not occur in the intensively grazed pastures.The work was carried out with the assistance of M.M.A. Djittye and A. Sow, Centre National de Recherche Zootechnique Sotuba, N. Diarra, Ecole Normale Supérieure, M. Togola, Station du Sahel, and M.I. Cissé, A. Diallo, L. Diarra, M. Sidibé, G. Traoré, Centre Pédagogique Supérieur     

Specialist pollinators deplete pollen in the spring ephemeral wildflower Claytonia virginica

Pollinators that collect pollen – and specifically, pollen‐specialist bees – are often considered to be the best pollinators of a (host) plant. Although pollen collectors and pollen specialists often benefit host plants, especially in the pollen that they deliver (their pollination “effectiveness”), they can also exact substantial costs because they are motivated to collect as much pollen as possible, reducing the proportion of pollen removed that is subsequently delivered to stigmas (their pollination “efficiency”). From the plant perspective, pollen grains that do not pollinate conspecific stigmas are “wasted”, and potentially costly. We measured costs and benefits of nectar‐collecting, pollen‐collecting, and pollen‐specialist pollinator visitation to the spring ephemeral Claytonia virginica. Visits by the pollen‐specialist bee Andrena erigeniae depleted pollen quickly and thoroughly. Although all pollinators delivered roughly the same number of grains, the pollen specialist contributed most to C. virginica pollen delivery because of high visitation rates. However, the pollen specialist also removed a large number of grains; this removal may be especially costly because it resulted in the depletion of pollen grains in C. virginica populations. While C. virginica appears to rely on pollen transfer by the pollen specialist in these populations, nectar‐collecting visitors could provide the same benefit at a lower cost if their visitation rates increased. Pollen depletion affects a pollinator's value to plants, but is frequently overlooked. If they lower the effectiveness of future floral visitors, visits by A. erigeniae females to C. virginica may be more detrimental than beneficial compared to other pollinators and may, in some circumstances, reduce plant fitness rather than increase it. Therefore, A. erigeniae and C. virginica may vary in their degree of mutualism depending on the ecological context.     

Reproductive traits explain contrasting ecological features in sponges: the sympatric poecilosclerids Hemimycale columella and Crella elegans as examples

Our study focused on the Mediterranean species Hemimycale columella and Crella elegans, which have overlapping ecological distributions but contrasting population densities and resilience. We formulated the hypothesis that differential reproductive traits were the main cause underlying these ecological differences in the study area. The issues addressed were whether recruits compete for the substrate, either because their respective reproductive cycles overlap or/and larval performance differs between species, and whether a contrasting investment in reproduction contributed to explain their diverse densities. Both species were simultaneous hermaphrodites and incubated their larvae. The reproductive period was notably shorter in C. elegans than in H. columella, while investment in reproductive tissue was higher in individuals of H. columella than in C. elegans. In contrast, C. elegans larvae harbored larger amounts of lipids and yolk inclusions than H. columella larvae. Moreover, the former contained amazing collagen masses densely packed among their inner cells. H. columella is likely to produce a higher number of poorer equipped larvae while C. elegans seems to produce a lower number of more resistant, better fitted with energy reserves, and thus potentially more successful larvae. These reproductive patterns agree with a higher and stable density of C. elegans in the study site compared with a more variable abundance of H. columella.     

Multimodal mimicry of hosts in a radiation of parasitic finches*

Brood parasites use the parental care of others to raise their young and sometimes employ mimicry to dupe their hosts. The brood-parasitic finches of the genus Vidua are a textbook example of the role of imprinting in sympatric speciation. Sympatric speciation is thought to occur in Vidua because their mating traits and host preferences are strongly influenced by their early host environment. However, this alone may not be sufficient to isolate parasite lineages, and divergent ecological adaptations may also be required to prevent hybridization collapsing incipient species. Using pattern recognition software and classification models, we provide quantitative evidence that Vidua exhibit specialist mimicry of their grassfinch hosts, matching the patterns, colors and sounds of their respective host's nestlings. We also provide qualitative evidence of mimicry in postural components of Vidua begging. Quantitative comparisons reveal small discrepancies between parasite and host phenotypes, with parasites sometimes exaggerating their host's traits. Our results support the hypothesis that behavioral imprinting on hosts has not only enabled the origin of new Vidua species, but also set the stage for the evolution of host-specific, ecological adaptations.     

DNA SEQUENCE VARIATION IN THE RIBOSOMAL INTERNAL TRANSCRIBED SPACER REGION OF FRESHWATER CLADOPHORA SPECIES (CHLOROPHYTA)1

Freshwater species of Cladophora (Chlorophyta) are globally distributed and occupy an unusually wide range of ecological habitats. Delineating species is difficult because most easily observed morphological traits are highly variable and because sexual reproduction has not been clearly documented. Synthesizing ecological data on freshwater Cladophora species is problematic because it is unclear whether freshwater Cladophora species comprise many genetically distinct species or a few ecologically and morphologically variable and/or plastic species. We determined nucleotide sequences of the internal transcribed spacer (ITS) region of the nuclear ribosomal cistron of freshwater Cladophora species from a wide range of habitats and geographic locations. We compared these sequences to those derived from culture collections of C. fracta and C. glomerata, the two most commonly reported freshwater Cladophora species. Cladophora fracta and C. glomerata had very similar ITS sequences (95.3%). All other sequences were identical to those from the C. fracta or C. glomerata culture collections with the exception of one California sample that was similar to both C. fracta (95.6%) and C. glomerata (92.4%). ITS genotypes did not correlate with morphology or geography. This analysis shows that common freshwater Cladophora species comprise very few (possibly one) ecologically and morphologically variable species.     

Les problèmes de systématique dans les recherches écologiques sur les insectes entomophages

Summary The first step in ecological studies of entomophagous insects is the collection of the different species associated to a given host in a given biotope. Many species are frequently encountered and their identification is often impossible or limited to the name of the genus, because detailed publications on systematics are not available and there are not enough specialised taxonomists. The needs for a precise identification increase when the study of the role of natural enemies is undertaken; the maximum complexity being reached when biological control methods are to be developped. It is then necessary to establish differences between biological races, sibling species etc. A striking example of these kind of difficulties is given by the biological control of California red scale. Progress in the field of systematics of entomophagous insects is only possible if we have a better knowledge of their biological and ecological requirements. Some examples are given of recent results obtained by different study groups of the C.I.L.B.: O. concolor bred fromC. capitata and fromD. oleae have been recognized as a single species, the adaptability of which is now studied-stress has been put on characteristics and efficiency of different strains ofP. perniciosi. Specificity and geographical distribution of egg parasites of genusOoencyrtus are reviewed in the mediterranan area... A close cooperation is to be maintained between workers in the fields of systematics and ecology, the contribution of C.I.L.B. will be of a great value.      

Elevated mtDNA diversity in introduced populations of Cynotilapia afra (Günther 1894) in Lake Malawi National Park is evidence for multiple source populations and hybridization

Genetic variation in many invasive species shows little or no signs of a founder event, suggesting that high genetic diversity may facilitate establishment success. The rocky‐shore, plankton‐feeding cichlid fish Cynotilapia afra is endemic to Lake Malawi, but naturally absent from many suitable sites. In the 1960s, this species was introduced to the southern areas of the lake, presumably as a result of the aquarium fish trade. It has now become established on a number of rocky areas within the Lake Malawi National Park. Here, we analysed DNA sequence variation in the mitochondrial control region of six native and four introduced populations of C. afra, and three populations of the closely‐related and hybridizing Pseudotropheus zebra. In contrast to previous studies of Lake Malawi rock dwelling cichlids, network analyses suggested that native populations of C. afra showed high levels of lineage sorting in mtDNA. Introduced populations showed higher sequence and haplotype diversity than their native counterparts. Our analyses suggested that the elevated gene diversity was largely attributed to the fact that the introduced C. afra populations were derived from several genetically distinct and geographically separate populations, and to a lesser extent because of introgressive hybridization with native P. zebra. The establishment and spread of C. afra may be partly because of its ability to occupy a vacant ecological niche, but it may also have been facilitated by its enhanced genetic diversity.     

Growth rates of selected Australian tropical rainforest tree species under controlled conditions

Controlled environment treatments were applied to assess the effects of temperature on the seedling mortality and growth rates of Toona australis and Flindersia brayleyana, two tropical rainforest tree species from northeast Queensland, Australia. Past workers have assigned these two species to the same ecological niche in terms of their response to canopy disturbance and gap-phase regeneration; however, their geographic ranges are very different. The hypothesis was that the species confined to the warm tropics (F. brayleyana) would have higher seedling mortality and a slower growth rate at lower temperatures than the species that occurs over a wide latitudinal range from the warm tropics to cooler temperate environments (T. australis). Significant differences were found in the growth rates of these two species in the warm (29/22° C) and cool (22/10°C), but not the intermediate (24/16° C), day/night temperature regimes. Their growth rates both decreased with decreasing temperature, but the decrease was significantly less for F. brayleyana which had the faster growth rate and lower seedling mortality in the cool regime. These results led to the rejection of the hypothesis and a test of the assignment of these two species to the same ecological niche. The test involved monitoring their growth to sapling-size in the intermediate temperature regime together with four other co-occurring tropical rainforest tree species belonging to different ecological niches. The growth rates and proportions of above-ground biomass allocated to woody tissue distinguished T. australis and a fast-growing pioneer species from F. brayleyana and three primary forest species. The stem heights and aboveground biomass of T. australis and the pioneer species exceeded the other four species by factors ranging from two to five. It is concluded that T. australis does not belong to the same ecological niche as F. brayleyana, and it is recommended that more research be conducted on the ecotypic temperature responses of the taxon T. australis.     

Population dynamics of Caprella dilatata and Caprella equilibra (Peracarida: Amphipoda) in a Southwestern Atlantic harbour

We studied the population dynamics and reproductive biology of Caprella dilatata and Caprella equilibra in order to provide the basis for understanding the ecological role of both species in Mar del Plata Harbour. Caprellids and organisms from the fouling community were obtained by sampling in the harbour, monthly from April 2014 to March 2015. Mean density of C. dilatata was homogeneous during most of the study period (ca. 50–200 ind/100?g) and reached their maximum in May (ca. 650 ind/100?g), while C. equilibra did not show any differences during the sampling period (ca. 30 ind/100?g). Juveniles of C. dilatata reached their highest densities in May, while ovigerous females were at their maximum values in late spring, summer and early autumn, and no correlation was found between seawater temperature and monthly density. On the other hand, C. equilibra reached its maximum juvenile and ovigerous female densities in summer, and showed a positive correlation with seawater temperature. Sex-ratio was female biased in C. dilatata, but in C. equilibra it was equal between sexes. The number of eggs carried by females was positively correlated to the size in both species. The present study suggests that the population dynamics of C. equilibra are intimately related to seawater temperature, while for C. dilatata no relationship was found. Future studies of ecology and behaviour traits in caprellid species are needed in order to determine the ecological role and the environmental factors that could affect both species.     

Ecological niche conservation and differentiation in the wood-feeding cockroaches, Cryptocercus, in the United States

The distribution of a species is determined by a set of ecological correlates (biotic and abiotic factors) and historical phenomena that define and constrain its ecological niche. By examining the geographical projection of the ecological niche, it is possible to identify areas that are suitable for the species ecologically but that are not actually inhabited. Previous studies have used such discords to anticipate the existence of undescribed species; the absence of species may also result from historical barriers that have prevented colonization of the area. Thus, discords between potential and realized niches of a species may result from aspects of the species’s biology (e.g. lack of dispersal ability, specific habitat requirements) or from barriers to dispersal. In this study, we developed ecological niche models of the five Nearctic species of wood‐feeding cockroaches in the genus Cryptocercus. One species, C. clevelandi, occurs in the western USA and four (C. darwini, C. garciai, C. punctulatus, C. wrighti) are distributed in the Appalachian Mountains in the eastern USA. In general, modelled niches for all species showed ecological restriction relative to the total range of available conditions. Niche models for the eastern USA species predicted the geographical distributions of the other eastern USA species, with the exception of C. garciai, suggesting general overall conservatism in ecological characteristics. Some interspecific differences in modelled niches were also apparent. In general, C. clevelandi was predicted to occupy cooler and drier areas relative to the eastern USA species; among the eastern USA species, C. darwini and C. garciai were predicted to inhabit warmer areas relative to C. punctulatus and C. wrighti. Interspecific differences and similarities were consistent with the phylogenetic relationships among Cryptocercus species previously reported. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 457–466.     

Ecological role of control agent,and not just host‐specificity,determine risks of biological control

Biological control agents used to manage alien vegetation are generally viewed as providing an ecosystem service, owing to reduced ecological and economic costs of invasion following their release. In particular, gall‐formers are popular as biological control agents because they are host‐specific and therefore considered low risk. However, galls can also be considered to be ecological engineers, because they provide nutritional resources for native invertebrates. We tested whether native invertebrates had formed associations with the gall‐forming fungus Uromycladium tepperianum, introduced into South Africa to control the Australian invasive alien tree Acacia saligna, by collecting U. tepperianum galls and monitoring emergence. We found that a number of invertebrates had formed associations with the biological control agent, among which was the important citrus pest, Thaumatotibia leucotreta (false codling moth). We used pheromone‐baited traps to ascertain if this supplementary source of T. leucotreta increased their abundance in orchards close to patches of gall host, but did not find this to be the case. We did find, however, that control measures used by farmers explained T. leucotreta abundances in traps, which may have obscured detection of any effects of a nearby host for the pest. Nevertheless, this study illustrates the first case of a host‐specific classical biological control agent providing resources for an economically significant crop pest. We conclude that although biological control agents are strictly vetted to ensure host‐specificity, introduced biological control agents that become abundant and can act as ecological engineers pose risks when native biota form associations with them, resulting in a number of possible cascading ecosystem effects. In addition, there could be economic consequences when these associated species include agricultural pests. We conclude that not just host specificity, but potential ecological effects of biological control agents, should be considered in their selection.     

Non‐native fishes and climate change: predicting species responses to warming temperatures in a temperate region

1. Temperate regions with fish communities dominated by cold‐water species (physiological optima <20 °C) are vulnerable to the effects of warming temperatures caused by climate change, including displacement by non‐native cool‐water (physiological optima 20–28 °C) and warm‐water fishes (physiological optima >28 °C) that are able to establish and invade as the thermal constraints on the expression of their life history traits diminish. 2. England and Wales is a temperate region into which at least 38 freshwater fishes have been introduced, although 14 of these are no longer present. Of the remaining 24 species, some have persisted but failed to establish, some have established populations without becoming invasive and some have become invasive. The aim of the study was to predict the responses of these 24 non‐native fishes to the warming temperatures of England and Wales predicted under climate change in 2050. 3. The predictive use of climate‐matching models and an air and water temperature regression model suggested that there are six non‐native fishes currently persistent but not established in England and Wales whose establishment and subsequent invasion would benefit substantially from the predicted warming temperatures. These included the common carp Cyprinus carpio and European catfish Silurus glanis, fishes that also exert a relatively high propagule pressure through stocking to support angling and whose spatial distribution is currently increasing significantly, including in open systems. 4. The potential ecological impacts of the combined effects of warming temperatures, current spatial distribution and propagule pressure on the establishment and invasion of C. carpio and S. glanis were assessed. The ecological consequences of C. carpio invasion were assessed as potentially severe in England and Wales, with impacts likely to relate to habitat destruction, macrophyte loss and increased water turbidity. However, evidence of ecological impacts of S. glanis elsewhere in their introduced range was less clear and so their potential impacts in England and Wales remain uncertain.     

Coexistence of two Cyclotella diatom species in the plankton of Lake Baikal

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Succession and growth rates of encrusting crustose coralline algae (Rhodophyta,Cryptonemiales) in the upper fore-reef environment off Ishigaki Island,Ryukyu Islands

Observations were made on the succession and growth rates of crustose coralline algae growing in situ on artificial substrata in a shallow fore-reef environment on Ishigaki Island, Ryukyu Islands. Succession in well-illuminated environments manifests itself as a gradual replacement of species having very thin thalli by those having larger and thicker thalli. The species Porolithon onkodes, Paragoniolithon conicum and Lithophyllum insipidum achieved dominance by competitive interactions of overgrowing margins. The thicker species recruit quickly (within the first few months), but because of their slow growth rate do not displace the pioneer species that have very thin thalli until after the latter begin to die. Regardless of seasonal temperature fluctuations, which exceed 10 °C, the coralline algal succession is the same for each season. The maximum lateral growth rates of the major species range between 2.9 and 3.9 mm/month. Vertical growth rates of Porolithon onkodes, the thickest species, are the most rapid (more than 2 mm/year at maximum) relative to those of other species. Accretion rates of entire coralline algal cover on ungrazed substrata range from 1.0 to 1.2 mm/year (not allowing any lag time for recruitment), whereas those of grazed substrata are lower. These results are consistent with species which are ecological equivalents and live in similar environments on Caribbean reefs.     

Detecting two-dimensional spatial structure in biological data

Summary Cliff and Ord (1973) made versatile methods available for the direct utilization of location data in the analysis of dispersion patterns, but their monograph has as yet seen little use in the ecological literature. Application of their weighted forms of Geary's c and Moran's I indices of spatial autocorrelation to some marine benthos data demonstrates a diversity of population structure not anticipated on the basis of more common measures of pattern. These indices provide objective means to evaluate numerous recent spatial models and hypotheses in geographical ecology and genetics. The procedures are particularly attractive because (1) they efficiently utilize data which are often wasted (i.e., sample coordinates), (2) their application puts few constraints on sampling designs which would otherwise be employed, and (3) they reveal and quantify pattern differences which are not obvious to the untrained eye.Contribution #949 from the Department of Oceanography, University of Washington     

Interspecific interference competition alters habitat use patterns in two species of land snails

Focus has been placed on the relative importance of environmental heterogeneity and biological interactions on community structure. For land snails, abiotic factors have commonly been assumed to be the most important factors for shaping communities because resources for land snails are commonly not limiting, and because interspecific resource competition would not be strong enough to promote ecological divergence. However, clear divergence in habitat use is often observed among sympatric land snail species. Such an ecological divergence would be promoted not by resource competition but by other interactions such as aggression. To test this hypothesis, laboratory experiments were designed to explore aggressive behaviour in the land snails Euhadra quaesita and E. peliomphala and field surveys were conducted to examine their habitat use. In the laboratory experiments, we examined how the presence of one species affects the growth of the other species by supplying sufficient amounts of food and calcium for both species. Experimental trials showed that adult E. quaesita decreased the growth of E. peliomphala under constant diet conditions. In contrast, E. peliomphala did not affect the growth of E. quaesita. Because E. peliomphala was often attacked by E. quaesita and its shell was often eroded by E. quaesita gnawing, aggression by E. quaesita appears to be the primary factor reducing the growth of E. peliomphala. When the two species coexist in nature, adults and juveniles of E. quaesita are terrestrial, while those of E. peliomphala are arboreal. When these species occurred alone, E. quaesita were still terrestrial, but E. peliomphala were more terrestrial than when they were in sympatry. Our results suggest that habitat use of these species in the natural communities is affected by interspecific interference. These findings further suggest that the divergence of habitat use between the species can occur by aggression even in environments with unlimited resources.