Lack of morphological coevolution between male forelegs and female wings in Themira (Sepsidae: Diptera: Insecta)

The complex, species-specific foreleg armature in males of the genus Themira (Diptera: Sepsidae) provides an ideal system for testing competing hypotheses for the evolution of sexually dimorphic character divergence. In sepsid flies, the male holds onto the female by clasping her wing base with his modified forelegs. In the present study, we document the male leg and the female wing morphology using scanning electron microscopy and confocal microscopy. We use a phylogenetic tree for Themira to reconstruct male foreleg and female wing evolution and demonstrate that the male legs have evolved elaborate structures with little or no corresponding changes in wing morphology. This lack of interspecific variation in female wings is not in agreement with the hypothesis of a morphological 'evolutionary arms race' between males and females. However, there is also no evidence for sex-specific wing differences in sensory organs on the wing base that may explain how females could assess males according to Eberhard's 'cryptic female choice' hypothesis. Finally, our study reveals the function of several novel morphological clasping structures and documents that the male foreleg characters in Themira are highly homoplastic. Male forelegs in two clades evolve considerably faster than in other species or clades. These two clades include Themira superba and Themira leachi , species that have some of the most dramatically modified forelegs known in Diptera.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 227–238.     

Cladistic analysis of the Sepsidae (Cyclorrhapha: Diptera) based on a comparative scanning electron microscopic study of larvae

The result of a phylogenetic analysis of the Sepsidae based on larval characters is presented. It is shown that cyclorrhaphan larvae can be as rich a source of characters as Nematocera immatures when investigated using an SEM. The cladistic analysis comprised fifty-two species in sixteen genera of the Sepsidae and five outgroup species and used fifty-seven morphological characters. It found seven parsimonious trees which only differed with respect to the arrangement of some species within the genus Themira. The basal dichotomies of the phylogenetic trees are particularly well supported, indicating the conservative nature of larval characters. Orygma is confirmed as the sister group of all the remaining sepsids, the Sepsinae. There is good larval evidence that Ortalischema is the sister group of all remaining Sepsinae and that the Toxopodinae constitute an early radiation within the Sepsidae. According to larval data, some genera are paraphyletic ( Themira, Palaeosepsis ), but adult characters appear to contradict these findings. Among the traditionally recognized higher taxa within the Sepsidae, Hennig's Themira species-group and Steysbal's Sepsini have to be rejected as polyphyletic. However, Hennig's Sepsis species-group is confirmed as monophyletic and will probably constitute one major element of a future phylogenetic system of the Sepsidae. States of the strongly modified fore-legs of some adult sepsid males are mapped onto the phylogenetic tree, largely confirming Šulc's ideas about the evolution of these features. The origin and evolution of male sternites with brushes and a gland on the tibiae of the males ('osmeterium') are discussed. Whereas adult characters point to a sister-group relationship between the Sepsidae and the Ropalomeridae, larval characters appear to indicate a sister-group relationship between the Coelopidae and the Sepsidae. The evidence for both hypotheses is critically evaluated.     

Freshwater Euplotes Species with a 9 Type 1 Cirrus Pattern Depend upon Endosymbionts1,2

The hypothesis is advanced that all freshwater Euplotes species with a 9 type 1 fronto-ventral cirrus pattern (E. patella type) depend upon bacteria-like endosymbionts. Aposymbiotic cells of these species are unable to divide. The hypothesis is based on the investigation of 40 different freshwater Euplotes stocks collected in Germany, France, the USA, and Japan. No symbionts were found in E. crenosus and E. palustris, freshwater species with 10 fronto-ventral cirri, nor in E. muscicola, a representative of the freshwater Euplotes group with a 9 type 2 fronto-ventral cirrus pattern (E. affinis type). Characteristic for the essential endosymbionts are multiple nucleoids, a feature described earlier for omikron, an indispensable symbiont of E. aediculatus. Although the symbionts differ from omikron and among each other in size, shape, and their average number per host, they are believed to be related to omikron. In two stocks a different type of bacterium was found in which no defined nucleoids can be detected. Transfer of this symbiont into aposymbiotic cells, originally carrying omikron, revealed that it can restore the ability to multiply. Similarly, omikron was also able to restore the ability to divide in cells freed of this symbiont. It is assumed that this different type of symbiont is a secondary invader of Euplotes which displaced the original omikron-like endosymbiont. Some of the stocks were found to carry, in addition to omikron-like symbionts, other symbiotic bacteria; E. daidaleos carries in addition an alga. The findings suggest that the freshwater Euplotes species with a 9 type 1 cirrus pattern are closely related to each other and evolved from an ancestor (probably of cirrotype 10) which already was dependent upon endosymbionts of the omikron type. It supports the view that the two subgroups of freshwater Euplotes forms with a cirrotype of 9 have evolved independently from each other from species with 10 fronto-ventral cirri by losing a cirrus at different positions.     

Substitution of top predators: effects of pike invasion in a subarctic lake

1. Invasions of top predators may have strong cascading effects in ecosystems affecting both prey species abundance and lower trophic levels. A recently discussed factor that may enhance species invasion is climate change and in this context, we studied the effects of an invasion of northern pike into a subarctic lake ecosystem formerly inhabited by the native top predator Arctic char and its prey fish, ninespined stickleback. 2. Our study demonstrated a strong change in fish community composition from a system with Arctic char as top predator and high densities of sticklebacks to a system with northern pike as top predator and very low densities of sticklebacks. A combination of both predation and competition from pike is the likely cause of the extinction of char. 3. The change in top predator species also cascaded down to primary consumers as both zooplankton and predator‐sensitive macroinvertebrates increased in abundance. 4. Although the pike invasion coincided with increasing summer temperatures in the study area we have no conclusive evidence that the temperature increase is the causal mechanism behind the pike invasion. But still, our study provides possible effects of future pike invasions in mountain lakes related to climate change. We suggest that future pike invasions will have strong effects in lake ecosystems, both by replacing native top consumers and through cascading effects on lower trophic levels.     

Photopic adaptations to a changing environment in two Lake Victoria cichlids

During the past 30 years, Lake Victoria cichlid fishes have encountered severe environmental and ecological changes including an introduced predator and new prey types. Furthermore, increased eutrophication has led to reduced water transparency and shifted the spectral composition of underwater light to longer wavelengths. In the present study, collections of two cichlid species, Haplochromis pyrrhocephalus and Haplochromis tanaos, from before and after the environmental changes, were compared with respect to their photopic resolution and sensitivity. Eyes of both species were dissected and retinal features were measured from tangential sections. In both species, the eyes became smaller, independently of body size. This decrease possibly occurred to make space for other structures that increased in size. In H. pyrrhocephalus, a significantly lower resolution was found. However, the size, and thus photon‐catching ability of the double cones, remained unchanged, despite the smaller eyes. In the modern populations of H. tanaos, the double cone size increased in relation to eye size, so that the photon‐catching ability of the smaller fish remained the same. However, no significant decrease in resolution was found. Shortwave sensitivity was found to be lower in both modern populations because of a reduction or the complete absence of single cones. The results obtained in the present study imply that these resurgent zooplanktivores are capable of adapting their eye morphology to the changed environmental conditions without losing crucial aspects used for survival and reproduction. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 328–341.     

Taxonomy of the African giant pouched rats (Nesomyidae: Cricetomys): molecular and craniometric evidence support an unexpected high species diversity

Our study combined a mitochondrial cytochrome b phylogeny with cranial measurements from giant pouched rats collected across sub‐Saharan Africa. The mitochondrial phylogeny resolves two West African clades and a clade with east and central Africa representatives. This last clade can be further divided into four subclades. Altogether they represent six species (Cricetomys gambianus, Cricetomys ansorgei, Cricetomys emini, and three undescribed taxa) that can be distinguished on the basis of their mitochondrial DNA sequences and craniometry. In the absence of adequate craniometric data the existence of Cricetomys kivuensis cannot be confirmed by our data. Our combined molecular and craniometric data allowed us to broadly delineate the distribution ranges of the detected species. Cricetomys gambianus occurs in the savannah and forest clearings of West Africa. Cricetomys ansorgei is distributed in the savannah of East and southern Africa. Cricetomys emini, as currently recognized across the Guineo‐Congolian forest of Africa, is shown to be diphyletic. Cricetomys sp. 1, a separate operational taxonomic unit closely resembling C. emini, occurs in the forest zone of West Africa. An undescribed sister‐species of C. ansorgei, Cricetomys sp. 2, occurs in the forest of Central Africa along the left bank of the Congo River. Cricetomys sp. 3 occurs on the right bank of the Congo River from Cameroon to the Republic of Congo, whereas the true C. emini also occurs on the right bank of the Congo River but appears to be restricted to the Democratic Republic of Congo. Cranial phenotype within the genus tends to conform to ecological zonation (either forest or savannah) rather than to phylogenetic affiliation of the species concerned, suggesting that diversifying selection across environmental gradients could be responsible for biological diversification within the genus.     

Role of Rostellum Desiccation in Emasculation-Induced Phenomena in Orchid Flowers

The effects of relative humidity (RH) and of treatment of therostellum with aminoethoxyvinylglycine (AVG), 1-aminocyclopropane-1-carboxylicacid (ACC) and water-insoluble vacuum grease on emasculation-inducedphenomena in Cymbidium and Phalaenopsis flowers were investigated.Under conditions of high RH and after treatment of the rostellumwith water-insoluble grease, the normal response to emasculation(i.e. increased ethylene production, lip coloration and wilting)was absent. However, under conditions of high RH this responsecould be restored by the addition of 2.0 nmol ACC on to therostellar surface. Under conditions of low RH the response wasinhibited by AVG; this inhibition was partially reversed byaddition of 2.0 nmol ACC. The data provide evidence that desiccation of the rostellumis responsible for post-emasculation phenomena in orchid flowers. Key words: Emasculation, ethylene, orchids, senescence     

A family of serine proteases of Clavibacter michiganensis subsp. michiganensis: chpC plays a role in colonization of the host plant tomato

Genes for seven putative serine proteases (ChpA–ChpG) belonging to the trypsin subfamily and homologous to the virulence factor pat-1 were identified on the chromosome of Clavibacter michiganensis subsp. michiganensis ( Cmm ) NCPPB382. All proteases have signal peptides indicating export of these proteins. Their putative function is suggested by two motifs and an aspartate residue typical for serine proteases. Furthermore, six cysteine residues are located at conserved positions. The genes are clustered in a chromosomal region of about 50 kb with a significantly lower G + C content than common for Cmm . The genes chpA , chpB and chpD are pseudogenes as they contain frame shifts and/or in-frame stop codons. The genes chpC and chpG were inactivated by the insertion of an antibiotic resistance cassette. The chpG mutant was not impaired in virulence. However, in planta the titre of the chpC mutant was drastically reduced and only weak disease symptoms were observed. Complementation of the chpC mutant by the wild-type allele restored full virulence. ChpC is the first chromosomal gene of Cmm identified so far that affects the interaction of the pathogen with the host plant.