SEXUAL SELECTION AND SURVIVAL SELECTION ON WING COLORATION AND BODY SIZE IN THE RUBYSPOT DAMSELFLY HETAERINA AMERICANA

I review methodological problems that can lead to false evidence for selection on secondary sexual characters and present a study of selection in rubyspot damselflies (Hetaerina americana) that avoids these pitfalls. Male rubyspots have a large red spot on each wing that grows to a terminal size after sexual maturity. Selection gradient analyses revealed evidence for positive sexual and survival selection on both terminal wing spot size and body size. Phenotype manipulations confirmed that wing spot size was subject to direct sexual selection, but showed that the positive slope of survival on wing spot size was an indirect effect of selection on unmeasured traits. This study provides the strongest evidence yet for sexual selection on coloration in Odonata, but also provides clear examples of why phenotypic selection statistics must be calculated and interpreted cautiously.     

LOCAL ADAPTATION AND AGENTS OF SELECTION IN A MOBILE INSECT

The deme-formation hypothesis states that selection can produce adaptive genetic variation within and among phytophagous insect populations. We conducted three field experiments and tested this prediction by transferring eggs and measuring performance of a mobile leafmining insect, Stilbosis quadricustatella. In Experiment 1, we compared the rate of mine initiation of leafminers transferred to natal and novel sites. In Experiment 2, we compared mine-initiation rate of leafminers transferred to natal and novel host-plant species. In Experiment 3, we compared the mine-initiation rate, mine-completion rate, and sources of mortality of miners transferred to neighboring natal and novel Quercus geminata trees. In the first, second, and third experiments, leafminer larvae initiated significantly more mines at the natal site, on the natal plant species, and on the natal Q. geminata tree, evidence for adaptive differentiation. Furthermore, plant-mediated mortality was significantly lower among miners transferred to natal Q. geminata trees. This result supports a key assumption of the deme-formation hypothesis: insects adapt to the defensive phenotypes of individual trees. However, natural-enemy mortality was significantly higher among miners transferred to natal trees, essentially reversing the plant effect. Therefore, rates of successful mine completion were similar on natal (19%) and novel (17%) trees. This experiment suggests that host plants and natural enemies may represent opposing forces of selection. Leafminers adapted to individual trees may realize a selective advantage only when natural-enemy densities are low.     

REMARKABLE SELECTIVE CONSTRAINTS ON EXONIC DINUCLEOTIDE REPEATS

Long dinucleotide repeats found in exons present a substantial mutational hazard: mutations at these loci occur often and generate frameshifts. Here, we provide clear and compelling evidence that exonic dinucleotides experience strong selective constraint. In humans, only 18 exonic dinucleotides have repeat lengths greater than six, which contrasts sharply with the genome‐wide distribution of dinucleotides. We genotyped each of these dinucleotides in 200 humans from eight 1000 Genomes Project populations and found a near‐absence of polymorphism. More remarkably, divergence data demonstrate that repeat lengths have been conserved across the primate phylogeny in spite of what is likely considerable mutational pressure. Coalescent simulations show that even a very low mutation rate at these loci fails to explain the anomalous patterns of polymorphism and divergence. Our data support two related selective constraints on the evolution of exonic dinucleotides: a short‐term intolerance for any change to repeat length and a long‐term prevention of increases to repeat length. In general, our results implicate purifying selection as the force that eliminates new, deleterious mutants at exonic dinucleotides. We briefly discuss the evolution of the longest exonic dinucleotide in the human genome—a 10 x CA repeat in fibroblast growth factor receptor‐like 1 (FGFRL1)—that should possess a considerably greater mutation rate than any other exonic dinucleotide and therefore generate a large number of deleterious variants.     

Observations on the role of simuliids and culicids in the transmission of avian and anuran trypanosomes

Although Trypanosoma rotatorium undergoes transformation and prolific multiplication in the mid and hindgut of Culex territans, several attempts to experimentally infect laboratory-reared, Rana pipiens by different routes were unsuccessful. Trypanosoma avium undergoes a similar pattern of development in the gut of Simulium rugglesi. Experimental infections of T. avium in ducklings indicates that S. rugglesi serves as an intermediate host and probably as an active and passive vector of the parasite in nature.     

Characterization of B and H blood-group active glycosphingolipids from human B erythrocyte membranes

Two blood group B active glycosphingolipids (B-I and B-II) previously isolated and highly purified from human B erythrocytes [21] were analysed first by degradation with α-D-galactosidase from coffee beans, α-L-fucosidase from bovine kidney and with 0,1 N trichloracetic acid; the native B-glycolipids as well as their degradation products were then investigated by methylation analysis with combined gas chromatography-mass spectrometry, by thin layer chromatography, twodimensional immunodiffusion and by the hemagglutination inhibition technique. Together with the results obtained by mass spectrometry of permethylated glycolipids [26] the following structures were elucidated: α-D-galactopyranosyl-(1 → 3)-[α-L-fucopyranosyl-(1 → 2)]-D-galactopyranosyl-(1 → 4)-N-acetyl-D-glucosaminosyl-(1 → 3)-D-galactopyranosyl-(1 → 4)-D-glucopyranosyl-(1 → 1)-ceramide for the B-I glycosphingolipid and α-D-galactopyranosyl-(1 → 3)-[α-L-fucopyranosyl-(1 → 2)]-D-galactopyranosyl-(1 → 4)-N-acetyl-D-glucosaminosyl-(1 → 3)-D-galactopyranosyl-(1 → 4)-N-acetyl-D-glucosaminosyl-(1 → 3)-D-galactopyranosyl-(1 → 4)-D-glucopyranosyl-(1 → 1)-ceramide for the B-II glycosphingolipid. A H active glycolipid fraction from B erythrocytes further purified by thin layer chromatography was also investigated by methylation analysis. The pattern of its partially methylated alditol acetates was essentially the same as that of the α-galactosidase treated and permethylated B-I glycolipid. It also exhibited strongly precipitating and hemagglutination inhibiting H properties as well as the two α-galactosidase treated B-I and B-II glycosphingolipids. Based upon these data the following tentative structure was proposed: α-L-fucopyranosyl-(1 → 2)-D-galactopyranosyl-(1 → 4)-N-acetyl-D-glucosaminosyl-(1 → 3)-D-galactopyranosyl-(1 → 4)-D-glucopyranosyl-(1 → 1)-ceramide. Gas chromatographic analysis revealed sphingosine and lignoceric, nervonic and behenic acids to be the main components of the ceramide residues of the three glycosphingolipids. From the data presented the H active substance very probably can be regarded as the immediate precursor of the B-I glycosphingolipid from human B erythrocyte membranes.     

Bottom‐up Conservation

Conservation initiatives that have worked well in temperate and developed regions have often been applied in the tropics but with only limited success. Part of this failure is due to top–down conservation planning that has been conducted without taking local socio‐economic considerations into adequate account. Here, we argue that conservation approaches would benefit from a deeper understanding of human–nature interactions.     

Abdominal movements, heartbeats and gas exchange in pupae of the Colorado potato beetle, Leptinotarsa decemlineata

The rhythms of abdominal movements, heartbeats and gas exchange in the pupae of Leptiontarsa decemlineata (Say) were recorded simultaneously using an electrolytic respirometer and infrared gas analyser, both combined with contact thermography. Abdominal pulsations and heartbeat occurred periodically with little variance among individuals. The abdominal pulsations and heartbeat pauses varied individually within large limits, with the frequency of abdominal pulsations being six to seven times lower than that of the heart pulses. A proportion of the pupae (20%) showed discontinuous gas exchange with large, actively ventilated CO₂ bursts, whereas others (≈ 25%) exhibited continuous regular microcycles (flutter) with abrupt intake of air into the tracheae before discrete microbursts of carbon dioxide. The abdominal pulsations exerted only a minor influence on ventilation during the microcycles. More than 90% of the bursts of abdominal movement coincided with a series of forward directed heartbeats, but interspersed between the bouts of abdominal movement commonly two to three heartbeat pulses were observed that were not associated with abdominal movements. A period of abdominal movement associated with a heartbeat pulse was commonly initiated by one or two vigorous strokes of abdominal rotation.     

Modus Darwin

Modus Darwin is a principle of inference that licenses the conclusion that two species have a common ancestor, based on the observation that they are similar. The present paper investigates the principle's probabilistic foundations.