Hormone‐mediated modulation of the electromotor CPG in pulse‐type weakly electric fish. Commonalities and differences across species

Like stomatogastric activity in crustaceans, vocalization in teleosts and frogs, and locomotion in mammals, the electric organ discharge (EOD) of weakly electric fish is a rhythmic and stereotyped electromotor pattern. The EOD, which functions in both perception and communication, is controlled by a two‐layered central pattern generator (CPG), the electromotor CPG, which modifies its basal output in response to environmental and social challenges. Despite major anatomo‐functional commonalities in the electromotor CPG across electric fish species, we show that Gymnotus omarorum and Brachyhypopomus gauderio have evolved divergent neural processes to transiently modify the CPG outputs through descending fast neurotransmitter inputs to generate communication signals. We also present two examples of electric behavioral displays in which it is possible to separately analyze the effects of neuropeptides (mid‐term modulation) and gonadal steroid hormones (long‐term modulation) upon the CPG. First, the nonbreeding territorial aggression of G. omarorum has been an advantageous model to analyze the status‐dependent modulation of the excitability of CPG neuronal components by vasotocin. Second, the seasonal and sexually dimorphic courtship signals of B. gauderio have been useful to understand the effects of sex steroids on the responses to glutamatergic inputs in the CPG. Overall, the electromotor CPG functions in a regime that safeguards the EOD waveform. However, prepacemaker influences and hormonal modulation enable an enormous versatility and allows the EOD to adapt its functional state in a species‐, sex‐, and social context‐specific manners.     

Habituation to a danger stimulus in two semiterrestrial crabs: ontogenic,ecological and opioid modulation correlates

Previous research on the habituation of the crab Chasmagnathus granulatus to an iterated visual danger stimulus disclosed two remarkable features of this mnemonic process: a) the ready acquisition and long-lasting nature of the habituated response, and b) the likely endogenous opioid modulation of the shortterm habituation, whose potential adaptive value was studied here. Both the habituation ability and the opioid modulation of such ability were analysed in Chasmagnathus granulatus and Pachygrapsus marmoratus, two closely related grapsid species that diverge widely in ecology. Results indicate that Chasmagnathus has a much greater capacity to habituate than Pachygrapsus, showing a more pronounced short-term habituation which seems to some extent mediated by an endogenous opioid mechanism, and a faster acquisition of a greater longterm habituation partially mediated by memorial representation of the contextual cues. A correlation between these differences and those related with the ecological pressure was discussed. The capacity of acquiring longterm habituation in crabs of the same species but different age was also assessed, showing that old animals clearly exhibit lower retention of the habituated response than young crabs. The possible correlation between this age-dependent change and an ontogenetic shift of habitat was discussed.     

Classification of insects by echolocating greater horseshoe bats

Summary Echolocating greater horseshoe bats (Rhinolophus ferrumequinum) detect insects by concentrating on the characteristic amplitude- and frequency modulation pattern fluttering insects impose on the returning echoes. This study shows that horseshoe bats can also further analyse insect echoes and thus recognize and categorize the kind of insect they are echolocating.Four greater horseshoe bats were trained in a twoalternative forced-choice procedure to choose the echo of one particular insect species turning its side towards the bat (Fig. 1). The bats were able to discriminate with over 90% correct choices between the reward-positive echo and the echoes of other insect species all fluttering with exactly the same wingbeat rate (Fig. 4).When the angular orientation of the reward-positive insect was changed (Fig. 2), the bats still preferred these unknown echoes over echoes from other insect species (Fig. 5) without any further training. Because the untrained bats did not show any prey preference, this indicates that the bats were able to perform an aspect-anglein-dependent classification of insects.Finally we tested what parameters in the echo were responsible for species recognition. It turned out that the bats especially used the small echo-modulations in between glints as a source of information (Fig. 7). Neither the amplitudenor the frequencymodulation of the echoes alone was sufficient for recognition of the insect species (Fig. 8). Bats performed a pattern recognition task based on complex computations of several acoustic parameters, an ability which might be termed cognitive.Abbreviations AM amplitude modulation - CF constant frequency - FM frequency modulation - S+ positive stimulus - S- negative stimulus     

IMPORTANCE OF MACRO‐ VERSUS MICROSTRUCTURE IN MODULATING LIGHT LEVELS INSIDE CORAL COLONIES1

Adjusting the light exposure and capture of their symbiotic photosynthetic dinoflagellates (genus Symbiodinium Freud.) is central to the success of reef‐building corals (order Scleractinia) across high spatio‐temporal variation in the light environment of coral reefs. We tested the hypothesis that optical properties of tissues in some coral species can provide light management at the tissue scale comparable to light modulation by colony architecture in other species. We compared within‐tissue scalar irradiance in two coral species from the same light habitat but with contrasting colony growth forms: branching Stylophora pistillata and massive Lobophyllia corymbosa. Scalar irradiance at the level of the symbionts (2 mm into the coral tissues) were <10% of ambient irradiance and nearly identical for the two species, despite substantially different light environments at the tissue surface. In S. pistillata, light attenuation (90% relative to ambient) was observed predominantly at the colony level as a result of branch‐to‐branch self‐shading, while in L. corymbosa, near‐complete light attenuation (97% relative to ambient) was occurring due to tissue optical properties. The latter could be explained partly by differences in photosynthetic pigment content in the symbiont cells and pigmentation in the coral host tissue. Our results demonstrate that different strategies of light modulation at colony, polyp, and cellular levels by contrasting morphologies are equally effective in achieving favorable irradiances at the level of coral photosymbionts.     

Comparison of Substrate-Borne Vibrational Signals of Two Congeneric Stink Bug Species, Thyanta pallidovirens and T. custator accerra (Heteroptera: Pentatomidae)

Vibrational signals (songs) were recorded and compared for two stink bug species, Thyanta pallidovirens and T. custator accerra. Females of both species produced two songs. Male T. pallidovirens also produced two songs, whereas male T. c. accerra produced four. Songs emitted by females of both species were comparable in structure and function, as was one of the male-produced songs. During the courtship phase of mating behavior, males of both species emitted a song with similar function but different temporal and spectral properties. Basic properties of songs, such as the dominant frequencies, were similar to those of songs of other pentatomid species, but the extensive use of frequency modulation and overlapping duets were novel. Differences in songs, combined with differences in male-produced pheromones, may play a role in the reproductive isolation of these congeners.     

Seed dormancy and control of germination in Sisymbrella dentata (L.) O.E. Schulz (Brassicaceae)

• Seed germination responsiveness to environmental cues is crucial for plant species living in changeable habitats and can vary among populations within the same species as a result of adaptation or modulation to local climates. Here, we investigate the germination response to environmental cues of Sisymbrella dentata (L.) O.E. Schulz, an annual endemic to Sicily living in Mediterranean Temporary Ponds (MTP), a vulnerable ecosystem.
• Germination of the only two known populations, Gurrida and Pantano, was assessed over a broad range of conditions to understand the role of temperatures, nitrate, hormones (abscisic acid – ABA and gibberellins – GA) and after‐ripening in dormancy release in this species.
• Seed germination responsiveness varied between the two populations, with seeds from Gurrida germinating under a narrower range of conditions. Overall, this process in S. dentata consisted of testa and endosperm rupture as two sequential events, influenced by ABA and GA biosynthesis. Nitrate addition caused an earlier testa rupture, after‐ripening broadened the thermal conditions that allow germination, and alternating temperatures significantly promoted germination of non‐after‐ripened seeds.
• Primary dormancy in S. dentata seeds likely allows this plant to form a persistent seed bank that is responsive to specific environmental cues characteristic of MTP habitats.

     

Discrimination of wingbeat motion by bats,correlated with echolocation sound pattern

Summary Bats of the species Rhinolophus rouxi, Hipposideros lankadiva and Eptesicus fuscus were trained to discriminate between two simultaneously presented artificial insect wingbeat targets moving at different wingbeat rates. During the discrimination trials, R. rouxi, H. lankadiva and E. fuscus emitted long-CF/FM, short-CF/FM and FM echolocation sounds respectively. R. rouxi, H. lankadiva and E. fuscus were able to discriminate a difference in wingbeat rate of 2.7 Hz, 9.2 Hz and 15.8 Hz, respectively, between two simultaneously presented targets at an absolute wingbeat rate of 60 Hz, using a criterion of 75% correct responses.The performance of the different bat species is correlated with the echolocation signal design used by each species, particularly with the presence and relative duration of a narrowband component preceding a broadband FM component. These results provide behavioral evidence supporting the hypothesis that bats that use CF/FM echolocation sounds have adaptations for the perception of insect wingbeat motion and that long-CF/FM species are more specialized for this task than short-CF/FM species.Abbreviations CF constant frequency - FM frequency modulation     

BOOK REVIEW

Echolocation calls of four species of insectivorous bats of central Chile were recorded and characterized to determine vocal signatures that allow their identification in the field. Pulses of Tadarida brasiliensis were characterized by the highest duration and the lowest values for all frequencies, which do not overlap those of the remaining species. Tadarida emits narrowband, shallow frequency-modulated search calls. All three vespertilionid species studied (Histiotus montanus, Lasiurus varius and Myotis chiloensis) showed similar echolocation design to one another, consisting of a downward frequency modulation at the beginning of the signal followed by a narrowband quasi-constant frequency component; however, their calls differ by their spectral characteristics. Discriminant function analysis of six acoustic parameters (duration, initial frequency, slope frequency modulation, peak frequency, minimal and maximal frequencies) gave an overall classification of 87.4%, suggesting species could be correctly classified based on echolocation calls. Call duration and minimal frequency were the variables most important for species identification.     

INTER- AND INTRASPECIFIC GENETIC VARIATION IN TWELVE PRYMAESIUM (HAPTOPHYCEAE) CLONES1

The haptophytes Prymnesium parvum Carter and Prymnesium patelliferum Green, Hibberd, and Pienaar are two closely related species, which can only be distinguished by minor differences in the morphology of their organic body scales. The two Prymnesium species are reported to coexist at several locations, including the Sands-fjord system in southwestern Norway. Comparisons of physiology and toxicity within the two species have failed to reveal differences that can add to the small morphological distinctions used to separate them. To investigate the genetic relationship between the two species, we compared the sequence of the first internal transcribed spacer region (ITS1)and length variation in one intron separating calmodulin genes for four P. parvum strains and eight P. patelliferum strains. Both the ITS1 sequence and the banding patterns obtained by PCR amplification of one intron in the calmodulin genes indicated that the Prymnesium isolates are related by their geographic origin instead of 4 their species affiliation. The results indicate that P. parvum and P. patelliferum are so closely related that they could be considered one species. Alternatively, we discuss the possibility that the two species might be joined in a heteromorphic haploid-diploid life cycle, as is now widely reported for other haptophycean algae.     

Cryptic species in the Pyropia yezoensis complex (Bangiales,Rhodophyta): Sympatric occurrence of two cryptic species even on same rocks

In a previous study on wild populations of Pyropia, the occurrence of two possible new species (Pyropia sp. 2 and Pyropia sp. 3) which are closely related to the two commercially important Pyropia species, P. yezoensis and P. tenera, was confirmed as the result of molecular phylogenetic analyses. To characterize the morphological features of the two wild Pyropia species, we collected Pyropia blades in a natural population in which Pyropia sp. 3 was known to occur, and carried out molecular identification before detailed morphological observations. Through the molecular identification we found, unexpectedly, that Pyropia sp. 2 blades grew sympatrically in the same site. Therefore, after molecular identification, we examined in detail the external morphology and anatomy of the two wild Pyropia species using more than 10 blades each. As a result, it is concluded that all of the blades of the two species are morphologically identical to P. yezoensis, but distinct from P. tenera. It is therefore considered that both of the two wild Pyropia species are cryptic species within the P. yezoensis complex. Furthermore, this study revealed that the two cryptic species grew sympatrically, even on the same rocks within the natural habitat.     

Ectomycorrhizal fungal communities of native and non-native Pinus and Quercus species in a common garden of 35-year-old trees

Non-native tree species have been widely planted or have become naturalized in most forested landscapes. It is not clear if native trees species collectively differ in ectomycorrhizal fungal (EMF) diversity and communities from that of non-native tree species. Alternatively, EMF species community similarity may be more determined by host plant phylogeny than by whether the plant is native or non-native. We examined these unknowns by comparing two genera, native and non-native Quercus robur and Quercus rubra and native and non-native Pinus sylvestris and Pinus nigra in a 35-year-old common garden in Poland. Using molecular and morphological approaches, we identified EMF species from ectomycorrhizal root tips and sporocarps collected in the monoculture tree plots. A total of 69 EMF species were found, with 38 species collected only as sporocarps, 18 only as ectomycorrhizas, and 13 both as ectomycorrhizas and sporocarps. The EMF species observed were all native and commonly associated with a Holarctic range in distribution. We found that native Q. robur had ca. 120% higher total EMF species richness than the non-native Q. rubra, while native P. sylvestris had ca. 25% lower total EMF species richness than non-native P. nigra. Thus, across genera, there was no evidence that native species have higher EMF species diversity than exotic species. In addition, we found a higher similarity in EMF communities between the two Pinus species than between the two Quercus species. These results support the naturalization of non-native trees by means of mutualistic associations with cosmopolitan and novel fungi.     

中甸灯台报春与鹅黄灯台报春的系统演化

中甸灯台报春和鹅黄灯台报春在形态上较为相似,通常被认为是亲缘关系较近的物种。该研究选取核基因ITS序列和叶绿体trn L-F为分子标记,利用贝叶斯的方法构建系统树,在用两种分子标记构建的系统树中,两种报春均以0.81的支持率聚成一个分支,明确了两种报春的姐妹种关系。首先,通过选取两个物种的五个形态学性状,进行主成分分析,聚类结果中两种报春各自的个体分别聚在两块区域,表明两种报春的形态学性状产生了明显的分化,且中甸灯台报春的花部各性状值明显大于鹅黄灯台报春,表明花部综合征和繁育系统间的相关联系。然后,通过用8对SSR分子标记对两种报春进行STRUCTURE聚类分析,结果检测K的最适值为2,此时中甸灯台报春和鹅黄灯台报春的个体各自以不同颜色聚成界限清晰的两块区域,揭示了两种报春在分子水平上也产生了显著而稳定的分化,通过Ima2软件,依据叶绿体联合序列,计算了两种报春的分化时间大约是在更新世,推测这两个姐妹种的物种分化受更新世气候动荡和一些地质历史事件的影响。最后,运用maxent软件分析两个物种的生态位差异,结果表明最干季节降水量、年均降水量和季节性降水量对中甸灯台报春的分布有重要影响,最冷季节平均温度、最干月降水量、年均降水量和季节性降水量对鹅黄灯台报春的分布有重要影响,两个物种间的生态位产生了分化。由此推测,这种生态位的差异是物种分化的结果,同时也是物种间系统演化的重要驱动力。     

Mating System and Clonal Architecture: A Comparative Study in Two Marine Angiosperms

In the present study, we compared the clonal architecture between two seagrass species, the dioecious Cymodocea nodosa and the hermaphroditic, self-compatible Zostera noltii, in order to verify the hypothesis that clonal growth strategies and resulting genet architecture are associated with mating system in clonal plants. It is expected that self-incompatible species should be associated to a guerrilla growth form, because of pollen limitation due to obligate outbreeding, while the ecologically advantageous phalanx strategy can be adopted in self-compatible species. Genotypic diversity and heterozygosity were also assessed in the two species. Sampling has been conducted in mixed stands, collecting shoots of the two species at the same points of the sampling grid, in order to even out any effects of environmental heterogeneity. Species-specific microsatellite loci have been used as molecular markers to identify clones and assess their spatial distribution in both species. As expected, we found an intermingled configuration of genets in the dioecious C. nodosa while Z. noltii was characterized by a clumped, `phalanx-type' distribution of clones. C. nodosa was characterized by higher genotypic diversity with regard to Z. noltii, while heterozygosity levels were comparable in the two species. Coordinating Editor: Dr J. Tuomi     

Spatial distribution of epiphytes on Populus tremula in relation to dispersal mode

Abstract. We examined if the spatial distribution of epiphytes in a forest stand differs between two sexually and three asexually dispersed species. As study species we have chosen two sexually dispersed species, the lichen Collema curtisporum and the bryophyte Orthotrichum speciosum, and three asexually dispersed species, the lichens C. furfuraceum and Leptogium saturninum and the bryophyte O. obtusifolium. All of these species grow on Populus tremula. In P. tremula stands, individual trees may be regarded as distinct patches for the studied species, while the stand represents a “landscape” of discrete patches. The study was performed in two relatively homogeneous forest stands. The study revealed that the asexually dispersed species were more common than the sexually dispersed. It was also shown that the sexually dispersed species were more aggregated than P. tremula in both stands. In contrast, the distribution of the asexually dispersed species mirrors, more or less, the distribution of their host, i.e. the spatial pattern shown by P. tremula. It is unlikely that the measured environmental variables strongly influenced the observed spatial distribution. Thus, we suggest that the different dispersal and establishment strategies were important in shaping the local distribution of the species.     

Multilocus species delimitation in Mesoamerican Scaptotrigona stingless bees (Apidae: Meliponini) supports the existence of cryptic species

Accelerating taxonomic knowledge and making accurate species identifications are critically important given the current biodiversity crisis, particularly in biodiversity hotspots such as Mesoamerica. Objective species delimitation that reduces investigator‐driven bias is fundamental to the establishment of appropriate conservation strategies, above all in managed species. Previous morphological and molecular studies on three managed stingless bee species of the genus Scaptotrigona distributed in Mexico (S. mexicana, S. pectoralis and S. hellwegeri) suggested that both S. mexicana and S. hellwegeri are cryptic species complexes. Herein we tested species delimitation by analysing sequence information of five markers (two mitochondrial: cox1 and 16S, and three nuclear: ITS1, EF1‐α, ArgK) within a Bayesian coalescent framework to test the putative species. We obtained two different hypotheses using a Generalized Mixed Yule Coalescent (GMYC) model: four (cox1) and six (16S) species. After the species validation step with the Bayesian species‐delimitation analysis (BPP), we suggest that only S. mexicana is a complex of two species with different distribution (along the Pacific and the Atlantic coasts, respectively). We highly recommend avoiding colony exchange between geographical regions in order to conserve the genetic integrity of both taxa.     

Comparative phenology and growth in different species of the Mediterranean maquis of central Italy

A phenomorphological survey was carried out in central Italy to study the effects of increasing water stress on some characteristic species of the Mediterranean maquis. Nutrient content and leaf water potential were examined. The results show that three different groups exist which diverge in the modulation of growth activity. 1) Evergreen sclerophyllous species (e.g. Pistacia lentiscus, Phillyrea media, Arbutus unedo, Ruscus aculeatus), which were supposed to be drought-tolerant, in fact limited their growth activity to a brief period before aridity increased. A similar growth pattern was exhibited by those species (e.g. Quercus ilex, Erica arborea, Smilax aspera) that stopped producing new leaves and branches during the driest season and that recovered after the first rain; i.e., their growth period lasted longer. 2) Drought-deciduous species (e.g. Calicotome villosa) that adopted the drought-avoidance strategy had two vegetative periods interrupted by a phase during which they completely shed their leaves. 3) Semideciduous species (Cistus monspeliensis) with mesophitic leaves adopted an intermediate response. These grew even in the dry and cold season.     

Biochemical properties and evaluation of washing performance in commercial detergent compatibility of two collagenolytic serine peptidases secreted by Aspergillus fischeri and Penicillium citrinum

Filamentous fungi secrete diverse peptidases with different biochemical properties, which is of considerable importance for application in various commercial sectors. In this study, we describe the isolation of two fungal species collected from the soil of decayed organic matter: Aspergillus fischeri and Penicillium citrinum. In a submerged bioprocess, we observed better peptidase production with the fungus P. citrinum, which reached a peak production at 168?h with 760?U/mL, in comparison with the fungus A. fischeri, which reached a peak production at 72?h with 460?U/mL. In both situations, the fermentative medium contained 0.5% crushed feathers as a source of nitrogen. On performing biochemical characterization, we detected two alkaline serine peptidases: The one secreted by P. citrinum had optimal activity at pH 7.0 and at 45°C, while the one secreted by A. fischeri had optimal activity in pH 6.5–8 and at 55–60°C. Metallic ions were effective in modulating these peptidases; in particular, Cu²⁺ promoted negative modulation of both peptidases. The peptidases were stable and functional under conditions of nonionic surfactants, temperatures up to 45°C for 1?h, and incubation over a wide pH range. In addition, it was observed that both peptidases had the capacity to hydrolyze collagen and performed well in removing an egg protein stain when supplemented into a commercial powder detergent; this was especially true for the peptidase from P. citrinum.     

Reproductive isolation is mediated by pollen incompatibility in sympatric populations of two Arnebia species

To explore uncertain aspects of the processes that maintain species boundaries, we evaluated contributions of pre‐ and postpollination reproductive isolation mechanisms in sympatric populations of Arnebia guttata and A. szechenyi. For this, we investigated their phylogenetic relationships, traits, microenvironments, pollinator visits, action of natural selection on floral traits, and the outcome of hand pollination between the two species. Phylogenetic analysis indicates that A. szechenyi is a derived species that could be closely related to A. guttata, and both could be diploid species. Arnebia guttata flowers have larger parts than A. szechenyi flowers, but smaller nectar guides. Soil supporting A. szechenyi had higher water contents than soil supporting neighboring populations of A. guttata (in accordance with their geographical distributions). The pollinators shared by the two species preferred A. szechenyi flowers, but interspecific visitations were frequent. We found evidence of conflicting selection pressures on floral tube length, flower diameter and nectar guide size mediated via male fitness, and on flower diameter and floral tube diameter via female fitness. Hand‐pollination experiments indicate complete pollen incompatibility between the two species. Our results suggest that postpollination prezygotic mechanisms are largely responsible for reproductive isolation of sympatric populations of the two Arnebia species.     

Two sites for GTP binding in cathodic haemoglobins from Anguilliformes

Cathodic haemoglobins of four species of anguilliform fish were characterized from a functional point of view, with special regard to the interaction with their physiological effectors. A series of oxygen-binding experiments at increasing GTP concentrations was carried out in order to compare GTP-binding activities in the absence and presence of saturating amounts of chloride. The results indicated that the cathodic haemoglobin of three species (Anguilla anguilla, Conger conger and Muraena helena) do have two sites for GTP-binding. In the absence of chloride, the two sites cannot be discriminated, whereas in the presence of chloride, a competition between the two anions occurred for the second GTP-binding site. The cathodic haemoglobin of Gymnothorax unicolor, which showed lower GTP sensitivity than the other haemoglobins examined, displayed only one GTP-binding site. The presence of an additional phosphate-binding site is not exceptional, although the way haemoglobin interacts with the two organic phosphate molecules may differ among species. This property may provide an auxiliary means of haemoglobin modulation for species that inhabit environments where oxygen availability is highly variable and haemoglobin-oxygen affinity needs to be modulated to different extents in order to satisfy physiological oxygen requirements.     

Ecological divergence in the presence of gene flow in two closely related Oryza species (Oryza rufipogon and O. nivara)

Ecological divergence plays a prominent role in the process of speciation, but how divergence occurs in the face of gene flow is still less clear, and remains controversial among evolutionists. Here we investigated the nucleotide diversity, divergence and gene flow between Oryza nivara and O. rufipogon using sequences of seven chloroplast and nuclear loci. By analysing samples from 26 wild populations across the geographic ranges of the two species, we showed that both species were highly structured and O. rufipogon maintained a higher level of species‐wide diversity than O. nivara. Notably, phylogenetic, amova and F_ST analyses were unable to detect significant nucleotide differentiation between the two species. We estimated that the two species began to diverge at c. 0.16 million years ago. Our coalescent‐based simulations strongly rejected the simple isolation model of zero migration between species, but rather provided unambiguous evidence of bidirectional gene flow between species, particularly from O. rufipogon to O. nivara. Our simulations also indicated that gene flow was recurrent during the divergence process rather than arising from secondary contact after allopatric divergence. In conjunction with different morphological and life‐history traits and habitat preference in the two species, this study supports the hypothesis that these Oryza species are better treated as ecotypes that diverged quite recently and are still under the process of divergence. Importantly, we demonstrate the ecological divergence between O. rufipogon and O. nivara in the presence of significant gene flow, implying that natural selection plays a primary role in driving the divergence of the two Oryza species.