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A consistent muscle activation strategy underlies crawling and swimming in Caenorhabditis elegans
(2014)
Although undulatory swimming is observed in many organisms, the neuromuscular basis for undulatory movement patterns is not well understood. To better understand the basis for the generation of these movement patterns, we studied muscle activity in the nematode Caenorhabditis elegans. Caenorhabditis elegans exhibits a range of locomotion patterns: in low viscosity fluids the undulation has a wavelength longer than the body and propagates rapidly, while in high viscosity fluids or on agar media the undulatory waves are shorter and slower. Theoretical treatment of observed behaviour has suggested a large change in force–posture relationships at different viscosities, but analysis of bend propagation suggests that short-range proprioceptive feedback is used to control and generate body bends. How muscles could be activated in a way consistent with both these results is unclear. We therefore combined automated worm tracking with calcium imaging to determine muscle activation strategy in a variety of external substrates. Remarkably, we observed that across locomotion patterns spanning a threefold change in wavelength, peak muscle activation occurs approximately 45° (1/8th of a cycle) ahead of peak midline curvature. Although the location of peak force is predicted to vary widely, the activation pattern is consistent with required force in a model incorporating putative length- and velocity-dependence of muscle strength. Furthermore, a linear combination of local curvature and velocity can match the pattern of activation. This suggests that proprioception can enable the worm to swim effectively while working within the limitations of muscle biomechanics and neural control.
Speolepta leptogaster (Winnertz, 1863) is frequently occurring in European subterranean environments. As for most cave animals, studies addressing non-anatomical aspects are sparse. Here we present the first molecular study on S. leptogaster. We investigated the demographic structure (i.e. COI locus) of 69 specimens from 36 underground populations in Hesse (Central German Uplands) to get first insights into the species’ dispersal ability.
In total, 14 haplotypes were revealed. Haplotype diversity was relatively high, whereas nucleotide diversity was low. Furthermore, a significant but low pattern of isolation-by-distance and (a) past population expansion event(s) were detected.
Our genetic results suggest a (good) active dispersal ability for Speolepta leptogaster. The occurrence of several surface records of adult specimens corroborates this hypothesis. We discuss the developmental stages of S. leptogaster in the context of the ecological classification system and regard the species as a eutroglophile. Evidence has been found to distinguish two larval types. A reconstructed life-cycle of the species is provided.
The Cueva del Azufre in Tabasco, Mexico, is a nutrient-rich cave and its inhabitants need to cope with high levels of dissolved hydrogen sulfide and extreme hypoxia. One of the successful colonizers of this cave is the poeciliid fish Poecilia mexicana, which has received considerable attention as a model organism to examine evolutionary adaptations to extreme environmental conditions. Nonetheless, basic ecological data on the endemic cave molly population are still missing; here we aim to provide data on population densities, size class compositions and use of different microhabitats. We found high overall densities in the cave and highest densities at the middle part of the cave with more than 200 individuals per square meter. These sites have lower H2S concentrations compared to the inner parts where most large sulfide sources are located, but they are annually exposed to a religious harvesting ceremony of local Zoque people called La Pesca. We found a marked shift in size/age compositions towards an overabundance of smaller, juvenile fish at those sites. We discuss these findings in relation to several environmental gradients within the cave (i.e., differences in toxicity and lighting conditions), but we also tentatively argue that the annual fish harvest during a religious ceremony (La Pesca) locally diminishes competition (and possibly, cannibalism by large adults), which is followed by a phase of overcompensation of fish densities.
Cryptochrome 1a, located in the UV/violet-sensitive cones in the avian retina, is discussed as receptor molecule for the magnetic compass of birds. Our previous immunohistochemical studies of chicken retinae with an antiserum that labelled only activated cryptochrome 1a had shown activation of cryptochrome 1a under 373 nm UV, 424 nm blue, 502 nm turquoise and 565 nm green light. Green light, however, does not allow the first step of photoreduction of oxidized cryptochromes to the semiquinone. As the chickens had been kept under ‘white’ light before, we suggested that there was a supply of the semiquinone present at the beginning of the exposure to green light, which could be further reduced and then re-oxidized. To test this hypothesis, we exposed chickens to various wavelengths (1) for 30 min after being kept in daylight, (2) for 30 min after a 30 min pre-exposure to total darkness, and (3) for 1 h after being kept in daylight. In the first case, we found activated cryptochrome 1a under UV, blue, turquoise and green light; in the second two cases we found activated cryptochrome 1a only under UV to turquoise light, where the complete redox cycle of cryptochrome can run, but not under green light. This observation is in agreement with the hypothesis that activated cryptochrome 1a is found as long as there is some of the semiquinone left, but not when the supply is depleted. It supports the idea that the crucial radical pair for magnetoreception is generated during re-oxidation.
Debate exists regarding the number of species of the moon jellyfish (genus Aurelia), a common member of the planktonic community of the coastal shelf seas around the world. Three Aurelia congeners (A. aurita, A. labiata and A. limbata) are currently considered to exist but recent genetic analyses suggested that this is an oversimplification. We analyzed the morphological characteristics of scyphistomae, morphological characteristics of ephyrae and differences in the time span of the strobilation process of Aurelia congeners from 17, 7 and 6 different source populations, respectively, of known species. Morphological characteristics of scyphistomae were similar among the 17 populations but those of ephyrae, such as the shape and form of lappets, were effective discriminators in the 6 cases examined. We recommend identifying species based on differences in 1) the morphological characteristics of scyphistomae and ephyrae (and not only medusae), 2) the genetics of individuals, and 3) the geographical occurrence of the population. This study adds to the growing body of knowledge on scyphozoan scyphistomae and ephyrae, stages of the metagenic life cycle of scyphozoans that have received relatively little study compared to medusae.
The present paper describes five new species of candonid ostracods in two genera: Pseudocandona agostinhoi sp. nov., P. cillisi sp. nov., P. claudinae sp. nov., Candobrasilopsis elongata sp. nov. and C. acutis sp. nov. The three species of Pseudocandona belong to the caribbeana-group in this genus. With the two new species of Candobrasilopsis, this genus now comprises four species.
Candobrasilopsis elongata sp. nov. is the most common of the five new species described here, while C. acutis sp. nov. and P. claudinae sp. nov. are known from one locality only, which is furthermore the same for both species: a small streamlet entering the Paraná River. With the description of the present five species, the number of species known from the Paraná River alluvial valley, including the Taquaruçu lakes, now amounts to 49.
A recent paper on the phylogenetic relationships of species within the cephalopod family Mastigoteuthidae meant great progress in stabilizing the classification of the family. The authors, however, left the generic placement of Mastigoteuthis pyrodes unresolved. This problem is corrected here by placing this species in a new monotypic genus, Mastigotragus, based on unique structures of the photophores and the funnel/mantle locking apparatus.
Two new species and one subspecies of Pharnaciini, belonging to two different genera, are described from Vietnam: one species and subspecies of Phryganistria Stål, 1875 and one species of Phobaeticus Brunner von Wattenwyl, 1907. Two species currently attributed to the genus Ramulus Saussure, 1862, Ramulus magnus (Brunner von Wattenwyl, 1907) and R. chinensis (Brunner von Wattenwyl, 1907), are transferred to Baculonistria Hennemann & Conle, 2008 comb. nov. Phobaeticus longicornis Bi & Wang, 1998 and Phobaeticus yuexiensis Chen & He, 1993 represent the male and female of Baculonistria magnus (Brunner von Wattenwyl, 1907) syn. nov. A lectotype is designated for Baculonistria chinensis (Brunner von Wattenwyl, 1907). The genus Baculonistria now contains three species. Nearchus bachmaensis Ta & Hoang, 2004 is transferred to Phryganistria and the new combination Phryganistria bachmaensis (Ta & Hoang, 2004) comb. nov. is proposed. The species is redescribed and the authors’ attribution corrected, the egg is described and figured for the first time.
Phryganistria tamdaoensis sp. nov. is described and figured from both sexes and the egg. Females of P. tamdaoensis sp. nov. are easily recognised by the conspicuously enlarged lanceolate cerci, a character previously unknown in this tribe. The distribution range of Phryganistria heusii heusii (Hennemann & Conle, 1997) is extended to Tam Dao National Park. A new subspecies Phryganistria heusii yentuensis subsp. nov. is described from Tay Yen Tu Nature Reserve from adult males and females and the eggs. Males can easily be distinguished from the nominal subspecies by their colouration. This huge subspecies represents the second longest insect recorded to date. A key to the species of the genus Phryganistria is provided. Phobaeticus trui sp. nov. is described from central Vietnam. It is the first species of Phobaeticus recorded from Vietnam. Adults of both sexes are illustrated.
Six new species of Platypalpus Macquart, 1827 are described from tropical forest at Yangambi (Democratic Republic of the Congo): Platypalpus bolikoi sp. nov., P. ikoso sp. nov., P. lokonda sp. nov., P. manjano sp. nov., P. saffradi sp. nov. and P. yangambensis sp. nov. All species are photographed and, except for P. saffradi sp. nov. known only from females, male terminalia are illustrated for all. A key is provided for the six species of DR Congo. COI barcodes are available for all species at GenBank.
The Malagasy genus Belbina Stål, 1863 (Hemiptera: Fulgoridae) is revised, transferred from the Enchophorinae Haupt, 1829 to the Aphaeninae Blanchard, 1847, and two new species, B. bourgoini sp. nov. and B. laetitiae sp. nov., are described. The genus Cornelia Stål, 1866 is proposed as a junior synonym of Belbina. The following new combinations are proposed: Belbina bergrothi (Schmidt, 1911) comb. nov. and B. nympha (Stål, 1866) comb. nov. The combination Belbina foliacea Lallemand, 1950 is restored. Aphana madagascariensis Westwood, 1851 is redescribed, transferred to Belbina and the new combination B. madagascariensis (Westwood, 1851) is proposed. Belbina vicina Lallemand, 1959 is proposed as a junior synonym of B. falleni Stål, 1863 and Cornelia atomaria (Brancsik, 1893) as a junior synonym of Belbina nympha (Stål, 1866). Neotypes are designated for B. madagascariensis (Westwood, 1851) comb. nov. and B. servillei (Spinola, 1839). The genus now comprises 12 species from Madagascar. A list of diagnostic characters, an identification key, illustrations of the male genitalia and distribution maps are provided. The falleni+ species group is defined based on characters of the male genitalia and contains the following 5 species: B. bloetei Lallemand, 1959, B. falleni Stål, 1863, B. laetitiae sp. nov., B. lambertoni Lallemand, 1922 and B. pionneaui Lallemand, 1922.
The osteology of “Coccodus” lindstroemi is studied in detail and it is demonstrated that this species does not belong to the genus Coccodus, but is a rather primitive member of the pycnodontiform family Gladiopycnodontidae. Indeed, the snout of “Coccodus” lindstroemi is elongated in a rostrum formed by the prefrontal and the premaxilla. This rostrum extends beyond the lower jaw level. The toothless premaxilla is sutured by its upper margin to the lower margin of the long and broad prefrontal.
The pectoral fin is lost and replaced by a pectoral spine which articulates on the cleithrum. A long nuchal spine resting on the dermosupraoccipital is present. The body is entirely covered by scales that are flakelike in the abdominal region and scute-like in the caudal region. Joinvillichthys gen. nov. is thus erected
with “Coccodus” lindstroemi as the type species. It is also shown that specimens with dumpier head and body, usually ranged in “Coccodus” lindstroemi, represent another species of the same genus for which the taxon Joinvillichthys kriweti gen. et sp. nov. is created. Specimens sometimes considered as possible juveniles of “Coccodus” lindstroemi form a distinctive new genus and species of gladiopycnodontid fish, Pankowskichthys libanicus gen. et sp. nov. Pankowskichthys differs from Joinvillichthys by many
osteological structures.
Twenty new species of the millipede genus Chaleponcus Attems, 1914, are described from the Udzungwa Mountains: C. netus sp. nov., C. quasimodo sp. nov., C. malleolus sp. nov., C. scopus sp. nov., C. nikolajscharffi sp. nov., C. mwanihanensis sp. nov., C. basiliscus sp. nov., C. krai sp. nov., C. nectarinia sp. nov., C. circumvallatus sp. nov., C. ibis sp. nov., C. vandenspiegeli sp. nov., C. vilici sp. nov., C. teres sp. nov., C. hamerae sp. nov., C. termini sp. nov., C. gracilior sp. nov., C. mwabvui sp. nov., C. howelli sp. nov. and C. tintin sp. nov. Together with C. dabagaensis Kraus, 1958, they constitute the Chaleponcus dabagaensis-group, well characterized by apparently apomorphic gonopodal characters, presumably monophyletic, and the first example of a major radiation within the Udzungwas. All species are restricted to altitudes >1390 m, all but one were found in only one, rarely two forest reserves, and the vast majority of specimens were collected in montane forest. Chaleponcus gracilior sp. nov. was collected in four forest reserves, often in secondary habitats where other species were only exceptionally found. Co-occurrence of multiple species, inter-specific differences in body size and unusual tarsal setation of a few species tentatively suggest adaptive radiation.
Parasitoid wasps new to Britain (Hymenoptera: Platygastridae,
Eurytomidae, Braconidae & Bethylidae)
(2014)
One genus and five species are recorded as new to Britain: Fidiobia, Fidiobia hispanica, Macroteleia bicolora (Platygastridae); Sycophila binotata (Eurytomidae); Schizoprymnus collaris (Braconidae); and Laelius pedatus (Bethylidae). Keys to British Macroteleia and Laelius are provided.
Provisional synonymy is proposed between Macroteleia minor and M. brevigaster, and synonymy is proposed between Laelius femoralis, L. microneurus and L. nigricrus. The possible mode of introduction of Sycophila binotata is discussed. A lectotype is designated for Schizoprymnus collaris.
Halirages helgae sp. nov. is recorded from the shelf slopes of the Norwegian Sea at depths of 1000 to 2600 m in the Arctic cold water masses. A total of 50 specimens were found at five stations. The
species differs from other known species in the genus Halirages Boeck, 1871 by the bilobed posterior margin of pereonite 7. A synoptic table to the northeast Atlantic species of Halirages is provided.
The endophallic structure of the genus Laius is studied and discussed based on the examination of 19 species from Asia to the Indian Ocean. The structure contains two primary sclerites (named gonoporal piece and ligula), a secondary sclerite on the basal part of the gonoporal piece (named additional sclerite) in some species, and a membranous basal area closely covered with many spines (named spinous area). Five species groups are recognized based on the morphology of the endophallic sclerites. The sympatric species have different body sizes and quite distinguishable endophallic sclerites (= different species group), while the allopatric species have overlapping body sizes and similar endophallic sclerites (= same species group). Three new species are described and six previously known species are redescribed with endophallic sclerites, and the descriptions of endophallic sclerites of the remaining ten species are added. The larva of Laius rodriguesensis sp. nov. is also described. The genus
Nossibeus Evers, 1994 is synonymised with Laius Guérin-Méneville, 1830.
The taxonomy of the family Desmodoridae (Nematoda: Desmodorida) is partially revised based on morphology. The diagnoses of the Desmodoridae and the subfamilies Desmodorinae and Spiriniinae are emended to accommodate re-analyzed morphological features. Eight known species are redescribed and the implication of the new findings for the taxonomy of the group is discussed. Amphispira and Metadesmodora are confirmed as genera inquirendae. Alaimonema and Sigmophoranema, and their corresponding type species, are proposed as inquirendae due to poor descriptions of the type material. The other three species of Sigmophoranema are transferred to the genus Onyx because they bear the diagnostic features of this group: spear-like dorsal tooth and s-shape precloacal supplements. Echinodesmodora, Paradesmodora and Stygodesmodora are transferred to the Spiriniinae based on the absence of a head capsule and on the amphidial fovea being surrounded by cuticle striation. Paradesmodora toreutes is transferred to the genus Acanthopharyngoides as A. toreutes comb. nov. The genus Onepunema does not fit in the family Desmodoridae because of diorchic males; thus, it is regarded as taxon incertae sedis.
Lists of valid genera for the two subfamilies are provided. A dichotomic key for the identification of the 14 genera within the Spiriinae is provided.
The South African endemic bees of the "euryglossiform" species of the genus Scrapter Lepeletier & Serville, 1828 are revised and illustrated. The species-group is defined for the first time and comprises 20 species, 16 of which are described here as new: Scrapter exiguus sp. nov. ♀, ♂, S. gessorum sp. nov. ♀, S. inexpectatus sp. nov. ♀, S. luteistigma sp. nov. ♀, ♂, S. minutissimus sp. nov. ♂, S. minutuloides sp. nov. ♀, S. minutus sp. nov. ♀, S. nanus sp. nov. ♀, ♂, S. nigerrimus sp. nov. ♀, S. nigritarsis sp. nov. ♀, S. papkuilsi sp. nov. ♀, ♂, S. punctatus sp. nov. ♀, ♂, S. pygmaeus sp. nov. ♀, S. roggeveldi sp. nov. ♀, ♂, S. spinipes sp. nov. ♀, ♂ and S. ulrikae sp. nov. ♀, ♂. For S. acanthophorus Davies, 2005 and S. sittybon Davies, 2005 the female is here described for the first time. A key to all species is provided.
Rhaptothyreus is arguably the most enigmatic nematode taxon due to a combination of unusual morphological features (e.g., large feather-like amphids, vestigial mouth, trophosome, single spicule), unclear phylogenetic relationships (possible affinities with the Enoplida, Mermithida and Benthimermithida) and a distribution restricted to the deep sea. Here I provide the first record of the genus in the Western Pacific Ocean and describe new morphological features of a moulting juvenile. This specimen is characterised by features that differ markedly from those of the adults, the most prominent being the absence of cephalic sensillae and amphids and the presence of a stylet-like structure in the buccal cavity. Similar contrasts in morphology are found between adults and juveniles of the order Benthimermithida, which is characterised by free-living adults and parasitic juveniles.
Other morphological (large body size, presence of trophosome) and distributional characteristics (predominantly deep-sea distribution, juveniles rare / absent in sediments) are also common to both groups. Published records show that Rhaptothyreus is commonly found in oligotrophic environments (e.g., abyssal plain) where organisms bearing symbiotic bacteria are not typically found, which makes the presence of endosymbiotic bacteria inside the trophosome unlikely. These observations are consistent with the existence of a parasitic juvenile life stage in Rhaptothyreus.
Three new species of Pachygnatha, P. bispiralis sp. nov., P. intermedia sp. nov. and P. ventricosa sp. nov., are described from forest areas in western Burundi. The presence of P. procincta Bosmans & Bosselaers, 1994 in Burundi confirms its very wide distribution spanning most of Africa.
Pachygnatha appears to be an important element of the afromontane spider fauna.
Datua brevirostris Lallemand, 1959 is transferred to the genus Egregia Chew Kea Foo, Porion & Audibert, 2011 in the Aphaeninae and the new combination Egregia brevirostris (Lallemand, 1959)
comb. nov. is proposed. Egregia marpessa Chew Kea Foo, Porion & Audibert, 2011, the type-species of the genus Egregia, is synonymized with Egregia brevirostris (Lallemand, 1959). A second species, Egregia laprincesse sp. nov. is described from Sumatra, extending the distribution of the genus hitherto recorded only from Borneo. Distribution maps and an identification key are provided. The male genitalia of E. brevirostris are illustrated and described. The genus Datua Schmidt, 1911 now contains a single species, D. bisinuata Schmidt, 1911.
The Afrotropical Rhyssinae are reviewed. A total of 12 species are reported from the region, including five new species: Epirhyssa brianfisheri sp. nov., E. gavinbroadi sp. nov., E. shaka sp. nov., E. villemantae sp. nov. and E. tombeaodiba sp. nov. The generic status of E. brianfisheri sp. nov. is discussed since this species could also be considered to be an extra-limital Triancyra species, emphasizing the putative paraphyletic status of Epirhyssa. Epirhyssa ghesquierei Seyrig, 1937, E. overlaeti Seyrig, 1937 and E. uelensis Benoit, 1951 are newly reported from Cameroon. We provide illustrated diagnoses and identification notes. Finally, we discuss the apparent scarcity of African rhyssines compared to other regions.
This study presents a taxonomic update of the Tetramorium weitzeckeri species group.
Tetramorium mpala sp. nov. is described from Laikipia, Kenya, and placed in the T. weitzeckeri species complex. In addition, we also provide an illustrated identification key to the three species complexes of the T. weitzeckeri species group, and an updated illustrated identification key to the species of the T. weitzeckeri species complex.
Jirds (genus Meriones) are a diverse group of rodents, with a wide distribution range in Iran. Sundevall’s jird (Meriones crassus Sundevall, 1842) is one such species that shows a disjunct distribution, found on the Iranian Plateau and Western Zagros Mountains. Morphological differences observed between these two populations, however, lack quantitative support. Morphological differences between geographical populations of Meriones crassus were analysed and compared with those of the sympatric M. libycus. Similarities in the cranial morphology of these species were found, e.g. in a relatively large and inflated bulla. A two-dimensional geometric morphometric analysis was done on the skull of 275 M. crassus and 220 M. libycus from more than 70 different localities in their distribution range. Results confirm cranial differences between specimens of M. crassus from the Western Zagros and those from Africa and Arabia, mainly at the level of the relative size of the tympanic bulla, that were significantly correlated with the annual rainfall and elevation. Moreover, the study supports the hypothesis that the Western Zagros specimens are both a geographically and phenotypically distinct group compared to the other Iranian M. crassus specimens, suggesting that the former might be a distinct species.
Populations of Stegelleta are described from California, New Zealand and Senegal. An amphimictic population from California is identified as belonging to S. incisa and compared with type specimens from Utah and an amphimictic population from Italy. One population from New Zealand is close to S. incisa but considered to represent a new species, Stegelleta laterocornuta sp. nov. It is particularly characterised by a 379–512 μm long body in females and 365–476 μm in males; cuticle divided into 16 rows of blocks at midbody (excluding lateral field); lateral field with four incisures; three pairs of asymmetrical lips, U-shaped primary axils without guarding processes, each lip asymmetrically rectangular with a smooth margin, only lateral lips have slender acute tines; three labial probolae, bifurcated at half of their length; vulva without flap; spermatheca 17–31 μm long; postuterine sac 7–24 μm long; spicules 21.5–23.5 μm long. Other specimens from New Zealand are identified as belonging to S. tuarua. A parthenogenetic population from Senegal is identified as belonging to S. ophioglossa and compared with type specimens from Mongolia and records of several other populations of S. ophioglossa. The generic diagnosis is emended and a key to the species of Stegelleta is provided.
Characterized by small body size, apically rounded/lobed anterior gonopod telopodites, long slender posterior gonopod telopodites, and torsion in the cyphopod receptacles, Floridobolus fl oydi, n. sp., is described from the southern sector of the Brooksville Ridge in northwestern peninsular Florida. It inhabits sandy “Big Scrub” environments like F. penneri Causey, 1957, and F. orini Shelley, 2014, and is documented from the sector’s center and northern periphery, in Hernando and Citrus Counties, respectively, with a sight record from the eastern periphery. Its discovery supports the thesis that each sand ridge in peninsular Florida may harbor a unique species of this endemic genus.
Background: The invasive eel parasite Anguillicoloides crassus (syn. Anguillicola crassus) is considered one of the major causes for the decline of the European eel (Anguilla anguilla) panmictic population. It impairs the swim bladder function and reduces swimming performance of its host. The life cycle of this parasite involves different intermediate and paratenic hosts. Despite an efficient immune system of the paratenic fish hosts acting against infections with A. crassus, levels of parasitized eels remain high in European river systems. Recently, the round goby Neogobius melanostomus (Gobiidae) has become dominant in many rivers in Europe and is still spreading at a rapid pace. This highly invasive species might potentially act as an important, so far neglected paratenic fish host for A. crassus.
Methods: Based on own observations and earlier single sightings of A. crassus in N. melanostomus, 60 fresh individuals of N. melanostomus were caught in the Rhine River and examined to assess the infection levels with metazoan parasites, especially A. crassus. Glycerin preparations were used for parasite identification.
Results: The parasite most frequently found in N. melanostomus was the acanthocephalan Pomphorhynchus sp. (subadult stage) which occurred mainly encysted in the mesenteries and liver. Every third gobiid (P = 31.7%) was infected by A. crassus larvae (L3) which exclusively occurred inside the acanthocephalan cysts. No intact or degenerated larvae of A. crassus were detected elsewhere in the goby, neither in the body cavity and mesenteries nor in other organs. Affected cysts contained the acanthocephalan larvae and 1-12 (mI =3) living A. crassus larvae. Additionally, encysted larvae of the nematode Raphidascaris acus were detected in the gobies, but only in the body cavity and not inside the acanthocephalan cysts.
Conclusions: Based on our observations, we suggest that A. crassus might actively bypass the immune response of N. melanostomus by invading the cysts of acanthocephalan parasites of the genus Pomphorhynchus using them as "Trojan horses". Providing that eels prey on the highly abundant round goby and that the latter transfers viable infective larvae of A. crassus, the new paratenic host might have a strong impact on the epidemiology of A. crassus.
Evolutionary genetics of bears and red foxes over phylogenetic and phylogeographic time scales
(2014)
Climatic fluctuations during the Pleistocene (2.6-0.01 million years) have played an important role during evolution of many species. Cyclic range contractions and expansions had demographic consequences within species, provided environmental conditions for population divergence and speciation and enabled secondary contact and interspecific hybridization. These and other evolutionary processes have left genetic signatures in the genomes of affected organisms. Comprehensive and unbiased estimates of evolutionary processes can be obtained using genetic markers from different parts of the genome and by integrating population genetic and phylogenetic concepts.
Suitable for studies on evolutionary processes and patterns over different evolutionary time scales are bears (Ursidae) and foxes (Vulpes), which occupy a wide range of habitats and evolved during the past few millions of years. In my thesis, I therefore used bears and red foxes as study species to investigate the genetic variation within and between species and to obtain estimates of evolutionary relationships and divergence times of populations and species that I interpreted in a climatic context. Further, I investigated population genetic processes during the evolution of bears. My thesis includes three publications and one submitted manuscript, spanning different evolutionary time scales - from evolutionary relationships and processes among species (phylogenetic time scales, Publications I & II), among populations and closely related species in a geographical context (phylogeographic time scales, Publications II & III), to ongoing processes within species (population genetic time scales, Publication IV).
In Publication I (Kutschera et al. 2014, Mol Biol Evol 31(8):2004-2017), I studied bears at several nuclear markers from several individuals per species, complemented with markers from the Y chromosome. Using approaches based on a population genetic concept (coalescent theory) I obtained a species tree with divergence time estimates. Further, I studied two evolutionary processes in bears, interspecific gene flow and incomplete lineage sorting (ILS). This study contributed to the growing evidence that population genetic processes can be relevant on time scales up to several millions of years.
In Publication II (Hailer, Kutschera et al. 2012, Science 336(6079):344-347), we complemented previous mitochondrial (mt) DNA-based inference of the evolutionary history of polar and brown bears with nuclear DNA. Coalescence-based species tree analyses of multiple nuclear markers from several individuals per species placed polar bears as sister lineage to brown bears and their divergence time to about 600 thousand years ago (ka). This contrasted previous mtDNA-based inference. We explained this discrepancy between mtDNA and nuclear DNA with interspecific gene flow between polar and brown bears.
In Publication III (Kutschera et al. 2013, BMC Evol Biol 13:114), I studied range-wide phylogeographic events and their timing in red foxes. A synthesis of newly generated and published mtDNA sequences was analyzed using a coalescence-based approach with multiple fossil calibration points. Thereby, I validated the identity and geographic distribution of several red fox lineages and showed that red foxes colonized North America and Japan several times independently during the late Pleistocene (126-11 ka) and around the last glacial maximum (26.5-19 ka). In a comparison of my results from red foxes to brown bears and grey wolves, I identified similar phylogeographic patterns.
In Publication IV (Kutschera et al., submitted to Biol Conserv), I found similar levels of genetic variability in vagrant polar bears that had reached Iceland compared to established subpopulations from across the range. Based on climate projections reported by the Intergovernmental Panel on Climate Change in 2014, polar bear habitat will markedly decline and become increasingly fragmented within the next decades. Dispersal will play an important role by connecting isolated subpopulations, thereby maintaining genetic diversity levels. My results indicate that vagrants could stabilize genetic variability when immigrating into established subpopulations.
In conclusion, my thesis provided a deeper understanding of evolutionary genetic processes and patterns and their timing in bears and red foxes in a climatic context, which can have conservation implications. Further, I showed that processes like ILS and interspecific gene flow can be relevant over different time scales and are important aspects of evolutionary history. Thereby, my thesis contributed to the knowledge on the evolutionary history of several carnivore species and on evolutionary processes acting within and between closely related species.
Tympanal hearing organs of insects emit distortion-product otoacoustic emissions (DPOAEs) which are indicative of nonlinear mechanical sound processing. General characteristics of insect DPOAEs are comparable to those measured in vertebrates, despite distinct differences in ear anatomy. DPOAEs appear during simultaneous stimulation with two pure tones (f1<f2) as additional spectral peaks at frequencies of nf1-(n-1)f2 and nf2-(n-1)f1, with the 2f1-f2 emission being the most prominent one. Insect DPOAEs are highly vulnerable to manipulations that interfere with the animal's physiological state and disappear after death. First evidence from locusts suggested that scolopidial mechanoreceptors might play a role in frequency-specific DPOAE generation (Möckel et al. 2007). The overall aim of this thesis was to determine the source of sensitive, nonlinear hearing at high frequencies and of DPOAE generation in tympanal organs of insects.
The first project of the present thesis involved general characteristics of DPOAE generation in the bushcricket Mecopoda elongata and the selective exclusion of the scolopidial mechanoreceptors using the neuroactive insectizide pymetrozine (Möckel et al. 2011). Pymetrozin appears to act highly effective and selectively on chordotonal organs, without affecting other sensory organs that lack scolopidial receptors. Pymetrozine solutions were applied as closely as possible to the scolopidia via a cuticle opening in the tibia, distally to the organ. Applications at concentrations between 10-3 and 10-7 M led to a pronounced and irreversible decrease of DPOAE amplitudes. Both this study on bushcrickets (Möckel et al. 2011) and an earlier one on locusts (Möckel et al. 2007) hence indicate the involvement of scolopidia in DPOAE generation in insects, by using complementary methods (pharmacological versus mechanical manipulation) and different animal models.
The second project of the present thesis investigated the temperature-dependence of DPOAEs in the locust Locusta migratoria (Möckel et al. 2012). The suggested biological origin of acoustic two-tone distortions in insects should involve metabolic processes, whose temperature-dependence would directly affect the DPOAE generation. Body temperature shifts resulted in reversible, level- and frequency-dependent effects on the 2f1–f2 emission. Using low f2 frequencies of up to 10 kHz, a body temperature increase (median +8–9°C) led to an upward shift of DPOAE amplitudes of approximately +10 dB, whereas a temperature decrease (median –7°C) was followed by a reduction of DPOAE amplitudes by 3 to 5 dB. Both effects were only present in the range of the low-level component of DPOAE growth functions below f2 stimulus levels of approximately 30-40 dB SPL. Emissions induced by higher stimulus levels and frequencies (e.g. 12 and 18 kHz) remained unaffected by any temperature shifts. The Arrhenius activation energy of the underlying cellular component amounted to 34 and 41 kJmol-1 (for growth functions measured with 8 and 10 kHz as f2, respectively). Such activation energy values provide a hint that an intact dynein-tubulin system within the scolopidial receptors could play an essential part in the DPOAE generation in tympanal organs.
The third project of this thesis demonstrated mechanical DPOAE analogs in the tympanum's vibration pattern during two-tone stimulation in the locust Schistocerca gregaria, using laser Doppler vibrometry (Möckel et al. 2014). DPOAE generation crucially relies on the integrity of the scolopidial mechanoreceptors (Möckel et al. 2007, 2011), which in locusts, directly attach to the tympanal membrane. During two-tone stimulation, DPOAEs were shown to mechanically emerge at the tympanum region where the auditory mechanoreceptors are attached. Those emission-coupled vibrations differed remarkably from tympanum waves evoked by external pure tones of the same frequency, in terms of wave propagation, energy distribution, and location of amplitude maxima. In contrast to traveling wave-like characteristics of externally evoked vibrations, intrinsically generated waves were locally restricted to the region around the high frequency receptors’ attachment position. The mechanical gradient of the tympanal membrane that leads to direction-dependent properties probably avoids the spreading of these locally evoked waves, which are then reflected and occur only in restricted areas as standing waves. Selective inactivation of mechanoreceptors by mechanical lesions did not affect the tympanum's response to external pure tones, but abolished the emission's displacement amplitude peak. These findings provide evidence that tympanal auditory receptors, comparable to the situation in mammals, comprise the required nonlinear response characteristics, which during two-tone stimulation lead to additional, highly localized deflections of the tympanum.
We have isolated a cDNA coding for a putative invertebrate-type dopamine receptor (Peadop2) from P. americana brain by using a PCR-based strategy. The mRNA is present in samples from brain and salivary glands. We analyzed the distribution of the PeaDOP2 receptor protein with specific affinity-purified polyclonal antibodies. On Western blots, PeaDOP2 was detected in protein samples from brain, subesophageal ganglion, thoracic ganglia, and salivary glands. In immunocytochemical experiments, we detected PeaDOP2 in neurons with their somata being located at the anterior edge of the medulla bilaterally innervating the optic lobes and projecting to the ventro-lateral protocerebrum. In order to determine the functional and pharmacological properties of the cloned receptor, we generated a cell line constitutively expressing PeaDOP2. Activation of PeaDOP2-expressing cells with dopamine induced an increase in intracellular cAMP. In contrast, a C-terminally truncated splice variant of this receptor did not exhibit any functional property by itself. The molecular and pharmacological characterization of the first dopamine receptor from P. americana provides the basis for forthcoming studies focusing on the significance of the dopaminergic system in cockroach behavior and physiology.
Arachnides N°73 (2014)
(2014)