Female Barn Swallows Gain Indirect but not Direct Benefits through Social Mate Choice

Female mate choice is responsible for the evolution of male secondary sexual ornaments. If male ornamental traits reflect indirect, genetic benefits and/or direct, material benefits to females, choosy females may benefit from their choice, indirectly and/or directly. We examined a breeding population of Japanese barn swallows Hirundo rustica gutturalis to determine whether male tail streamer length reflected indirect and/or direct benefits to females. There was no significant positive relationship between male streamer length and the number of extra-pair young (EPY) sired, suggesting that male tail streamers are not a signal of indirect benefits (i.e. good genes theory). In addition, we found no evidence that males with longer streamers fed their offspring more frequently or sired more within-pair young (WPY). The result indicates that male streamer length probably does not act as a signal of direct benefits. Our finding that the length of tail streamers in Japanese barn swallows plays no role in sexual selection is not consistent with studies on European subspecies, but is consistent with studies on North American subspecies where sexual selection on tail streamer is weak. The present study supports the recent suggestion that the pattern of sexual selection on tail streamer length in barn swallows varies geographically. Instead of tail length, males in better condition sired more EPY and WPY. Males in better condition, however, did not feed their nestling more frequently. These results indicate that females gain indirect benefits but not direct benefits, in terms of feeding of young, on choosing social mates.     

Experimental tail elongation in male Barn Swallows Hirundo rustica reduces provisioning of young, but only in second broods

At the beginning of the breeding season, the outermost tail feathers of 31 male Barn Swallows Hirundo rustica were either shortened by 20 mm, elongated by 20 mm or left unmanipulated. In first broods, the number of feeding bouts (per nestling per hour) by males and females did not differ significantly among experimental groups. However, in second broods, males with elongated tails fed their nestlings less often than males with shortened or unmanipulated tails. Male tail elongation may have been detrimental to flight, making capture of insects more difficult. Females paired to long-tailed males did not compensate for this reduction in feeding by males and their nestlings received less food. Neither feeding rates nor brood size differed significantly between first and second broods. Variation in abundance of large insects at different times of the day (high around noon and low in the morning and afternoon) matched variation in feeding rates, supporting the importance of large insects in the Barn Swallow diet. Different feeding rate patterns in first and second broods by males with elongated tails could have at least three explanations: (1) such males were able to adjust their parental effort to some extent, temporarily compensating for an imposed handicap; (2) they were more sensitive than males in the other experimental groups to late season food shortage (a decrease in numbers of large insects, the main Barn Swallow prey, was observed as the season progressed); and (3) they were more sensitive than males in the other experimental groups to the deterioration in their physical condition after first broods.     

Recapture Heterogeneity in Cliff Swallows: Increased Exposure to Mist Nets Leads to Net Avoidance

Ecologists often use mark-recapture to estimate demographic variables such as abundance, growth rate, or survival for samples of wild animal populations. A common assumption underlying mark-recapture is that all animals have an equal probability of detection, and failure to meet or correct for this assumption–as when certain members of the population are either easier or more difficult to capture than other animals–can lead to biased and inaccurate demographic estimates. We built within-year and among-years Cormack-Jolly-Seber recaptures-only models to identify causes of capture heterogeneity for a population of colonially nesting cliff swallows (Petrochelidon pyrrhonota) caught using mist-netting as a part of a 20-year mark-recapture study in southwestern Nebraska, U.S.A. Daily detection of cliff swallows caught in stationary mist nets at their colony sites declined as the birds got older and as the frequency of netting at a site within a season increased. Experienced birds’ avoidance of the net could be countered by sudden disturbances that startled them into a net, such as when we dropped a net over the side of a bridge or flushed nesting cliff swallows into a stationary net positioned at a colony entrance. Our results support the widely held, but seldom tested, belief that birds learn to avoid stationary mist nets over time, but also show that modifications of traditional field methods can reduce this source of recapture heterogeneity.     

Effects of an Immune Challenge on Multiple Components of Song Display in Barn Swallows Hirundo rustica: Implications for Sexual Selection

Bird song is believed to honestly reveal male quality including the ability of singers to face parasitism. In a natural population of barn swallows Hirundo rustica, we experimentally imposed a cost on song production by an immune challenge. We therefore vaccinated a group of reproducing males with an antigen (Newcastle disease virus), and injected phosphate‐buffered saline to a control group. Immune challenge significantly reduced one song feature, rattle duration. This decrease was related to male quality, as measured by tail length, because males with short tails reduced the duration of their rattle significantly more than males with long tails. In addition, another song feature, strophe duration, decreased in the control group, while it remained constant in the challenged group. Duration of the rattle has previously been found to be positively related to testosterone level, and it may hence reflect male competitive ability. Thus, male barn swallows may not have the potential to produce long rattles when their immune system is challenged. By maintaining their strophe duration after an immune challenge, males may compensate for the decrease in rattle duration. Our results suggest that different song features may convey different types of information, and that barn swallow song, in particular their rattle, may reliably reveal information about activation of the immune system.     

A gp41 MPER-specific Llama VHH Requires a Hydrophobic CDR3 for Neutralization but not for Antigen Recognition

The membrane proximal external region (MPER) of the HIV-1 glycoprotein gp41 is targeted by the broadly neutralizing antibodies 2F5 and 4E10. To date, no immunization regimen in animals or humans has produced HIV-1 neutralizing MPER-specific antibodies. We immunized llamas with gp41-MPER proteoliposomes and selected a MPER-specific single chain antibody (VHH), 2H10, whose epitope overlaps with that of mAb 2F5. Bi-2H10, a bivalent form of 2H10, which displayed an approximately 20-fold increased affinity compared to the monovalent 2H10, neutralized various sensitive and resistant HIV-1 strains, as well as SHIV strains in TZM-bl cells. X-ray and NMR analyses combined with mutagenesis and modeling revealed that 2H10 recognizes its gp41 epitope in a helical conformation. Notably, tryptophan 100 at the tip of the long CDR3 is not required for gp41 interaction but essential for neutralization. Thus bi-2H10 is an anti-MPER antibody generated by immunization that requires hydrophobic CDR3 determinants in addition to epitope recognition for neutralization similar to the mode of neutralization employed by mAbs 2F5 and 4E10.     

Similarity but not equivalence: Ecological niche comparison between sandflies from the Pleistocene and future scenarios in Central and South America

Sandfly species (Diptera: Psychodidae) are suspected or proven vectors of Leishmania spp. in the American region. Understanding niche conservatism (NC) in insect vectors allows an understanding of constraints on adaptive responses, and thus implications for disease ecology. Therefore, in this study, the authors evaluated NC in three vector species of leishmaniasis (Lutzomyia gomezi, Psathyromyia shannoni and Pintomyia ovallesi) in Central and South America. For this, the authors performed niche identity and similarity testing through paired comparisons in ENMTools and niche overlap in Niche Analyst. The authors found that species niches were more similar to each other than if the points had been randomly extracted, and they also found extensive similarity between Pa. shannoni and Lu. gomezi niches and in Pa. shannoni niches over different timescales. The authors suggest Pa. shannoni as a priority species due to fundamental niche similarity with phylogenetically related species and also its extensive evolutionary history and ecological plasticity that could affect the emergence and resurgence of leishmaniasis in areas endemic by this vector.     

Call Transmission Efficiency in Native and Invasive Anurans: Competing Hypotheses of Divergence in Acoustic Signals

Invasive species are a leading cause of the current biodiversity decline, and hence examining the major traits favouring invasion is a key and long-standing goal of invasion biology. Despite the prominent role of the advertisement calls in sexual selection and reproduction, very little attention has been paid to the features of acoustic communication of invasive species in nonindigenous habitats and their potential impacts on native species. Here we compare for the first time the transmission efficiency of the advertisement calls of native and invasive species, searching for competitive advantages for acoustic communication and reproduction of introduced taxa, and providing insights into competing hypotheses in evolutionary divergence of acoustic signals: acoustic adaptation vs. morphological constraints. Using sound propagation experiments, we measured the attenuation rates of pure tones (0.2–5 kHz) and playback calls (Lithobates catesbeianus and Pelophylax perezi) across four distances (1, 2, 4, and 8 m) and over two substrates (water and soil) in seven Iberian localities. All factors considered (signal type, distance, substrate, and locality) affected transmission efficiency of acoustic signals, which was maximized with lower frequency sounds, shorter distances, and over water surface. Despite being broadcast in nonindigenous habitats, the advertisement calls of invasive L. catesbeianus were propagated more efficiently than those of the native species, in both aquatic and terrestrial substrates, and in most of the study sites. This implies absence of optimal relationship between native environments and propagation of acoustic signals in anurans, in contrast to what predicted by the acoustic adaptation hypothesis, and it might render these vertebrates particularly vulnerable to intrusion of invasive species producing low frequency signals, such as L. catesbeianus. Our findings suggest that mechanisms optimizing sound transmission in native habitat can play a less significant role than other selective forces or biological constraints in evolutionary design of anuran acoustic signals.     

Putrescine biosynthesis in mammalial cells: Essential for DNA synthesis but not for mitosis

The object of this study was to examine the role of putrescine in the regulation of DNA synthesis and mitosis in synchronized Chinese hamster ovary cells using 1,3-diaminopropane (DAP) which is a potent inhibitor of ornithine decarboxylase (EC 4.1.17). Inhibition of putrescine biosynthesis significantly reduced the incorporation of [${}^3\text{H}$]-TdR into DNA but had no effect on the progression of cells from G1 to S phase. However, inhibition of putrescine synthesis in synchronized S phase cells did not affect their progression to mitosis. In these experiments, the DAP treatment had little or no effect on the levels of spermidine and spermine. These results indicate that putrescine biosynthesis is essential for the completion of DNA synthesis but not required for mitosis and cell division.     

Strong divergence in trait means but not in plasticity across hatchery and wild populations of sea-run brown trout Salmo trutta

There is ample evidence that organisms adapt to their native environment when gene flow is restricted. However, evolution of plastic responses across discrete environments is less well examined. We studied divergence in means and plasticity across wild and hatchery populations of sea-run brown trout (Salmo trutta) in a common garden experiment with two rearing environments (hatchery and a nearly natural experimental stream). Since natural and hatchery environments differ, this arrangement provides an experiment in contemporary adaptation across the two environments. A Q(ST) - F(ST) approach was used to investigate local adaptation in survival and growth over the first summer. We found evidence for divergent selection in survival in 1 year and in body length in both years and rearing environments. In general, the hatchery populations had higher survival and larger body size in both environments. Q(ST) in body size did not differ between the rearing environments, and constitutive divergence in the means was in all cases stronger than divergence in the plastic responses. These results suggest that in this system, constitutive changes in mean trait values are more important for local adaptation than increased plasticity. In addition, ex situ rearing conditions induce changes in trait means that are adaptive in the hatchery, but potentially harmful in the wild, suggesting that hatchery rearing is likely to be a suboptimal management strategy for trout populations facing selection in the stream environment.     

Strong signature of selection in seeder populations but not in resprouters of the fynbos heath Erica coccinea (Ericaceae)

A higher frequency of natural selection is expected in populations of organisms with shorter generation times. In fire‐prone ecosystems, populations of seeder plants behave as functionally semelparous populations, with short generation times compared to populations of resprouter plants, which are truly iteroparous. Therefore, a stronger signature of natural selection should be detected in seeder populations, favoured by their shorter generation times and higher rates of population turnover. Here we test this idea in Erica coccinea from the Cape Floristic Region, which is dimorphic for post‐fire regeneration mode. We measured three floral traits supposedly subject to natural selection in seeder and resprouter populations. We then compared phenotypic trait variation with neutral genetic variation in each group of populations using P_ST–F_ST comparisons to detect signatures of natural selection in seeders and resprouters. We found a strong signature of selection in seeder populations, but not in resprouters. Furthermore, anthers of seeders were more exserted (and larger) than those of resprouters. These differences were maintained at sites where seeders and resprouters co‐occurred, suggesting that phenotypic plasticity or adaptation to different growth environments are unlikely explanations for trait variation. These results provide empirical support for the hypothesis that the genetic signature of natural selection is certainly more intense in seeder than in resprouter populations, favoured by their comparatively faster generation turnovers. Increased frequency of natural selection would increase differentiation among populations, thus promoting speciation in pyrophytic seeder lineages of the Cape flora.     

Aminoacyl-tRNA synthesis in archaea: different but not unique

Accurate aminoacyl-tRNA synthesis is essential for correct translation of the genetic code in all organisms. Whereas many aspects of this process are conserved, others display a surprisingly high level of divergence from the canonical Escherichia coli model system. These differences are most pronounced in archaea where novel mechanisms have recently been described for aminoacylating tRNAs with asparagine, cysteine, glutamine and lysine. Whereas these mechanisms were initially assumed to be uniquely archaeal, both the alternative asparagine and lysine pathways have subsequently been demonstrated in numerous bacteria. Similarly, studies of the means by which archaea insert the rare amino acid selenocysteine in response to UGA stop codons have helped provide a better understanding of both archaeal and eukaryal selenoprotein synthesis. Most recently a new co-translationally inserted amino acid, pyrrolysine, has been found in archaea although again there is some suggestion that it may also be present in bacteria. Thus, whereas archaea contain a preponderance of non-canonical aminoacyl-tRNA synthesis systems most are also found elsewhere albeit less frequently.     

Call Variation in the Bufo microscaphus Complex: Implications for Species Boundaries and the Evolution of Mate Recognition

Since the Modern Synthesis, many species concepts have considered characters mediating mate recognition essential to both the identification and definition of species. To explore divergence in mate recognition systems, calls were recorded and toads measured from all three species of the monophyletic Bufo microscaphus species complex including five populations of Bufo californicus, three populations of B. microscaphus, and one population of B. mexicanus. Call duration, dominant frequency, and pulse rate were significantly related to temperature, but not snout-vent length. When adjusted for temperature, calls of B. californicus had a significantly longer call duration, higher dominant frequency, and slower pulse rate than B. mexicanus and B. microscaphus, which did not differ from one another. However, the magnitude of variation among populations of B. californicus was similar to that between species. Discriminant analysis using call variables provided some separation of B. californicus and B. mexicanus from B. microscaphus, and cross-validation analysis correctly classified approximately 75% of B. californicus and B. mexicanus. Given only slight divergence in mate recognition systems between B. californicus and the other two taxa, the biological significance of this difference remains ambiguous. Comparisons among B. americanus group members indicate that hybridizing taxa may or may not exhibit divergence in advertisement calls. Maintenance of independently evolving lineages may be driven by other evolutionary mechanisms. These results support the notion that species recognition is best viewed as an effect of mate recognition.     

Almost but not quite a subspecies: a case of genetic but not morphological diagnosability in Nicrophorus (Coleoptera: Silphidae)

Allopatric populations that show genetic differentiation but lack phenotypic diagnosability are difficult to classify. In 1946, Arnett described a new species of burying beetle (Silphidae: Nicrophorus) from Luzon Island, Philippines, Nicrophorus benguetensis. In 2002, Sikes et al., finding the species to be inconsistently diagnosable, synonymized N. benguetensis under Nicrophorus nepalensis Hope 1831. We rigorously and quantitatively test the validity of N. benguetensis using several different species delimitation criteria. We employed discrete and quantitative character‐based methods to test similarity criteria using linear morphometrics in a discriminant analysis framework, and percentage sequence divergences based on sequences from four mitochondrial DNA (mtDNA) genes (COI, COII, ND4 and ND5) and two nuclear genes [28S (D2 region) and CAD]. We also employed tree‐based methods to test phylogenetic criteria using mtDNA sequences and morphology with parsimony, Bayesian inference and maximum likelihood. The analysis of discrete phenotypic characters did not reliably diagnose N. benguetensis. The results of the discriminant analysis provided moderate support for the validity of N. benguetensis (71.4% of the specimens were properly classified). There is adequate genetic distance between N. benguetensis and its nearest neighbour for DNA barcoding to identify an unknown sequence, although this may be an artefact of the small sample size. Phylogenetic analyses of the morphological data, with and without the morphometric data, yielded unresolved trees. Molecular phylogenetic results found N. benguetensis to be monophyletic, but neither clearly rejected nor supported its validity. Two of our approaches using molecular data diagnosed N. benguetensis, but those that used phenotypic data did not exceed a 75% success rate. We conclude, therefore, that N. benguetensis, despite being a weakly distinct allopatric population, and deserving of additional study, should remain synonymized until further analysis suggests otherwise. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 311–333.