Inter- and intra-season stability of vocal individual signatures in a social seabird, the crested auklet

Vocal plasticity due to changes of social context is well documented in passerine birds. In other bird species, the impact of social environment changes on the whole vocal structure and on individual specific signatures remains largely unexplored. Here, we assessed inter- and intra-season stability of specific features of individual signatures in advertising calls of crested auklet (Aethia cristatella) males and tested the effects of pair mate and territory changes on the stability of the calls. The crested auklet is a highly social seabird of the North Pacific that breeds in dense colonies, and its individuals switch pair mates and territories with probability of 25–54%. During summer 2008–2010, we recorded 464 trumpet calls from 21 individually marked males and determined their pair mates and positions of their displaying places on a breeding colony of Talan Island, Sea of Okhotsk. We found that strong individual specific features of crested auklet trumpet calls stay stable not only during one season but also from year to year. However, we failed to find any effects of pair mate or territory changes on individual signatures of crested auklet trumpet calls. Our results suggest that crested auklets can potentially use their individually specific trumpet calls to form long-term social bonds both between pair mates and between neighbors; however, future experimental studies should test whether this is indeed the case.     

Experimental evidence for a semi-flexible conformation for arabinoxylans

Purified water-soluble arabinoxylans from wheat flour were deferuloylated and fractionated into six fractions by graded ethanol precipitation. Further fractionation by HPSEC on Sephacryl S500 resulted in 48 subfractions with low polydispersity index. Conformational characteristics (persistence length q, hydrodynamic parameter v and Mark-Houwink exponent a) were similar among all subfractions and fitted with a semi-flexible conformation, whatever their structural characteristics. Substitution degree of the xylan backbone by arabinose residues has no influence on the conformation of arabinoxylans.     

Experimental evidence for multistability in a photobiochemical system

The kinetic behavior of a typical Hill reaction catalyzed by thylakoids and using the oxidized form of 2,6-dichloroindophenol (DCPIPox) as the artificial electron acceptor, is considered. Here, the light absorption process and the reduction of DCPIPox are autocatalytically coupled, leading to the occurrence of multiple steady states with respect to either the acceptor concentration or the incident light intensity. Experimental evidence is presented for both cases and the emergence of autocatalysis is discussed. The effect of the spatial arrangement on the global behavior of the system described is emphasized.     

Male parasitism and intrasexual competition in a burrowing barnacle

Summary In sexually dimorphic animals, large male body size is often associated with direct interference competition among males for access to females or resources used in reproduction. In constrast, small male body size may be associated with indirect scramble competition among males for temporal or spatial access to females. Minute, “parasitic” males of the acrothoracican barnacleTrypetesa lampas (Hancock) appear to compete with one another for permanent attachment sites on the external body of the female. Several spatial patterns suggest indirect male-male competition: 1) males were consistently aggregated on the anterior surface of the female ovarian disc; 2) the average distance from attached males to the site of insemination correlated positively with local male density; 3) average male body size on a female decreased as a function of male density; 4) the distribution of males on the left and right hand sides of the female ovarian disc was more even than expected, suggesting that males avoided crowded settlement sites. The number of males attached to a female increased with female body size and matched a null model in which males colonized female “targets” of differing areas. These results suggest that competition between males primarily affected settlement sites and male body sizes within, rather than among, females. Male parasitism may have evolved through both sexual selection for efficient access to females (Ghiselin 1974) and natural selection for reduced burrow density in a space-limited habitat (Turner and Yakovlev 1983).     

Experimental evidence for physical cues involved in oviposition site selection of lotic hydrobiosid caddis flies

Cues involved in determining the distribution of invertebrate propagules within a stream landscape contribute greatly to our knowledge of the supply and arrangement of new recruits and thus an improved understanding of factors that might ultimately affect population parameters. Previous observations indicated that both current velocity and rock size were important determinants of the egg mass distribution of certain hydrobiosid caddis flies that lay their eggs in single masses beneath emergent rocks. These observations were tested experimentally in a temperate, upland Australian stream. Manipulations of current speed confirmed that females of Ulmerochorema sp. and the Taschorema complex deposited more eggs on rocks in elevated current speeds (>0.40 ms(-1)) whereas Apsilochorema sp. deposited more eggs on rocks in slow currents (<0.30 ms(-1)). This latter result did not coincide with previous observational data. The anomaly between observational and experimental data, however, was reconciled by the outcome of a further experiment that tested the influence of the emergent or 'landing pad' size of rocks as the abundance of Apsilochorema egg masses increased with landing pad size independent of the prevailing flow conditions. Landing pad size did not influence the abundance of egg masses of Taschorema or Ulmerochorema. Patterns of female visits to rocks indicated that taxa might distinguish between favoured egg-laying sites prior to landing on rocks. Large aggregations of adult male and female Ulmerochorema collected from rocks favoured for oviposition provide indirect evidence for mating induced swarming behaviour associated with oviposition site selection. This study provides a framework for more sophisticated questions relating to the influence of oviposition site selection on structuring populations of lotic macroinvertebrates.     

Heterospecific mating preferences for a feather ornament in least auklets

Auklets (Alddae, Aethiini) include five species of small, sociallymonogamous, sexually monomorphic seabirds that display a varietyof feather and bare-part ornaments during the breeding season.Previous experimental work on two auklet species has demonstratedthat some ornaments are likely to be favored by sexual selectionbecause mutual male and female mating preferences benefit individualswith the most elaborate expression of these traits. In thisstudy we experimentally investigated whether naturally crestlessleast auklets Aethia pusilla have a maring preference for foreheadcrests similar to the most prominent ornament of two other species,crested A. cristatella and whiskered auklets A. pygmaea. Ourobjective was to investigate the function of this ornament asa species-recognition mechanism or as a product of one or moreof three proposed sexual selection models that address the originof elaborate traits and preferences. During the experiment,least auklets reacted to realistic models equipped with artificialforehead crests with approximately an order of magnitude morefrequent sexual displays and greater interest, consistent withthe idea that they have a mating preference for crests, eventhough they do not naturally express this ornament This heterospecificpreference also favored large crest size. These results refutethe possibility that least auklet forehead ornamentation alonedetermines species recognition at present Among models of sexualselection considered, the results are consistent with the sensoryexploitation model, although this could not be established unequivocallybecause a viability indicator or Fisherian mechanism could havebeen involved if least auklets had an ancestor with a foreheadcrest.     

Individuality in trumpet calls of the crested auklet (<Emphasis Type="Italic">Aethia cristatella</Emphasis>), a highly social species

Crested auklet is a unique representative of the family Alcidae with a complex social behavior nesting in dense colonies with a size of up to one million individuals. Here we study specific individual features in their trumpet calls, loud vocalizations used by auklets as an advertising display. In 2008 and 2009, we recorded 231 calls of 24 individually marked male crested auklets from the Talan Island (Sea of Okhotsk). According to a stepwise discriminant function analysis based on seven variables in the call introduction, the rate of correct call assignment to an individual was 84.8% and that in the case of seven variables of the main part of the call was 82.3%, which considerably exceeds a random classification. Thus, a single introduction or a single main part of the call is sufficient for a reliable individual identification of a calling bird. We assume that such redundancy of information for individual recognition can enhance identification of calls of a large number of auklet conspecifics in dense colonies with a nesting density of several tens of pairs per 1 m².     

Experimental evidence that selection favors character displacement in the ivyleaf morning glory

While there is abundant evidence to suggest that pollinators influence the evolution of plant floral traits, there is little direct evidence that interactions between plant species shape the evolution of such characteristics. The purpose of this study was to determine whether the presence of the morning glory Ipomoea purpurea alters patterns of selection on floral traits of its congener, Ipomoea hederacea. We show that while selection on I. hederacea floral traits is effectively neutral when I. purpurea flowers are absent, selection acts to increase clustering of anthers about the stigma when I. purpurea flowers are present. Our results provide direct experimental evidence that the presence of flowers of a co-occurring congener can influence patterns of natural selection on floral traits that influence the mating system and contribute to prezygotic isolation. To the extent that this result is general, it also lends support to the claim that distributional patterns interpreted as ecological and reproductive character displacement in other plant species have been caused by natural selection generated by interactions among plant species.     

Experimental evidence for a persistent spore bank in Sphagnum

Spore capsules of four Sphagnum species were buried at different depths in peat on a bog. Spore viability was determined after 0, 1, 2 and 3 yr. Viability generally declined with time, but viable spores were still found at all depths after 3 yr. The light-coloured spores of S. balticum and S. tenellum retained their viability better than the darker spores of S. fuscum and S. lindbergii . Survival was highest under wet but aerobic conditions, but was also high under humid or periodically desiccated conditions. By contrast, most spores stored under wet, anaerobic conditions died within 2–3 yr. These results, and predictions from them, are not consistent with earlier results for spores of long-lived and dominant bryophytes, or for seeds of phanerogams of undisturbed wetlands and forests. There was no correlation between spore size and longevity across species, but the small spores from small capsules of S. balticum and S. tenellum generally showed higher viability than those from the medium-sized and large capsules of the same species. This suggests a positive intraspecific relationship between longevity and dispersal distance. There was an indication of conditional dormancy, controlled by weather, in Sphagnum spores. The experiments indicate that Sphagnum spores can form a long-term persistent spore bank under suitable conditions, with a half-life of between 1 and 20 yr (mean across species of 2.6 and 5.0 yr at two depths studied), and with potential values in individual spore capsules of several decades, or even of centuries. Sphagnum spores kept refrigerated showed 15–35% viable spores after 13 yr. The capacity to form a persistent spore bank that can be activated whenever favourable conditions occur might help explain the wide geographical distribution of many Sphagnum species in the boreal and temperate zones, where they have managed to colonize almost every suitable patch of acidic, nutrient-poor wetland.     

NOR-Chromosome morphology and evidence for rDNA selection in phylactolaemates

Silver-stained chromosome spreads from the phylactolaemate ectoprocts Fredericella indica, Fredericella browni, Plumatella repens, Pectinatella magnifica and Asajirella gelatinosa show that each of these species has a single pair of NORs. In the first four species each NOR is immediately adjacent to the centromere of a large metacentric chromosome. Giemsa-stained preparations from Cristatella mucedo show centromeric gapping in a similar large metacentric, indicating the same type of NOR-chromosome. In Asajirella gelatinosa the two NORs are on a pair of smaller chromosomes, and are not immediately adjacent to a centromere. A close NOR-centromere association would inhibit meiotic crossing over in the NOR region. Since in phylactolaemates reproduction is primarily asexual, often by formation of statoblasts, there is potential intraclonal selection for favorable ribosomal DNA (rDNA) mutations, including from simultaneous germination of otherwise genetically identical statoblasts within a limited area and competition between cell lines within statoblasts. Inhibition of meiotic crossing over within the NOR would maintain its integrity during periods when intraclonal selection would not be occurring. This suggests that a more rapid rate of rDNA evolution is possible in phylactolaemates than in most other organisms, and is consistent with a derivation of this group from the morphologically similar phoronids, despite phylogenetic interpretations of rDNA sequence data that suggest the two groups are not closely related.     

Strong evidence for selection for larger brood size in a great tit population

We measured the selection pressure on brood size in a recentlyestablished population of great tits (Parus major L.) in thenorthern Netherlands by manipulating brood size in three years(1995: n = 51, 1997: n = 66, 1998: n = 51), and we estimatedfitness consequences in terms of local survival of both offspringand parents. Enlarged broods had highest fitness; the offspringfitness component was positively affected by manipulation andthe parental fitness component was unaffected. Parental survivaland the probability that parents produced a second clutch werenot affected by the treatment. However, parents that had raisedenlarged broods produced their second clutch later in the season.Clutch size, brood size, and laying date of birds recapturedin the next breeding season were largely independent of thetreatment. We conclude that there is strong evidence for selectionfor larger brood size and reject the individual optimizationhypothesis for this population because the number of young inthe nest predicts fitness independently of the manipulationhistory.     

Experimental evidence for kin-biased helping in a cooperatively breeding vertebrate

The widespread belief that kin selection is necessary for the evolution of cooperative breeding in vertebrates has recently been questioned. These doubts have primarily arisen because of the paucity of unequivocal evidence for kin preferences in cooperative behaviour. Using the cooperative breeding system of long-tailed tits (Aegithalos caudatus) in which kin and non-kin breed within each social unit and helpers are failed breeders, we investigated whether helpers preferentially direct their care towards kin following breeding failure. First, using observational data, we show that not all failed breeders actually become helpers, but that those that do help usually do so at the nest of a close relative. Second, we confirm the importance of kinship for helping in this species by conducting a choice experiment. We show that potential helpers do not become helpers in the absence of close kin and, when given a choice between helping equidistant broods belonging to kin and non-kin within the same social unit, virtually all helped at the nest of kin. This study provides strong evidence that kinship plays an essential role in the maintenance of cooperative breeding in this species.     

Experimental evidence for edge-related predation in a fragmented agricultural landscape

Abstract This study tested the hypothesis that increased predation of experimental nests occurs close to a forest edge in a fragmented agricultural landscape. Artificial nests and eggs of willie wagtails Rhipidura leucophrys and superb fairy-wrens Malurus cyaneus were used in experiments to assess the extent and nature of predation occurring throughout the known breeding seasons of these species. Predators were identified by the imprints they left in plasticine eggs, and by remote photography. Surveys of avian predators were undertaken to investigate the relationship between predation intensity and predator distribution and abundance. Avian predators accounted for almost all predation for which a predator could be identified (96%). Five of seven predator species photographed attacking wagtail nests were corvids or artamids. Fairy-wren nests suffered relatively low rates of predation (29%) compared to wagtail nests (87%). Increased predation at the habitat edge was recorded for wagtail nests only; predation was correlated with the distribution and abundance of predatory avian species. The different extent and pattern of predation on fairy-wren nests could be explained by problems in detecting predation by mammals, and by possible failure of avian predators to locate the cryptic nests.