Astronomical orientation and learning in the earwig Labidura riparia

Astronomical orientation experiments have been carried out on adults and young of the earwig Labidura riparia. In the water, the earwigs

1.

(1) assumed a correct landward orientation, concordant with their home shore;     

The evaluation of the European earwig (Forficula auricularia) as a predator of the damson-hop aphid (Phorodon humuli). II. Choice of prey

Experiments on the European earwig (Forficula auricularia L.) were made determine the efficiency of prey capture and defence reactions of the damson-hop aphid (Phorodon humuli (Schrank)).The older the earwig the more efficient was its search for aphids. Adult aphids waxed early earwig instars successfully. Young earwigs did not choose but encountered and captured young aphids more successfully than older ones, allowing older aphids to reproduce successfully.     

Testosterone increases repertoire size in an open-ended learner: An experimental study using adult male European starlings (Sturnus vulgaris)

Song in songbirds is a learned secondary sexual behavior, first acquired during a sensitive phase of juvenile development, which is affected by hormones such as testosterone (T). While the latter has received much attention, the potential involvement of T in the adult repertoire changes observed in a number of species is much less understood. Yet, this may prove essential to understand the role of song as a sexually selected trait. We therefore performed a T-implantation experiment during the non-breeding season (when T is basal), using adult male European starlings (Sturnus vulgaris), a songbird species in which song repertoire size (and composition) changes seasonally and increases with age. Repertoire size increased rapidly in T-males, but not in control males, indicating a role for T in repertoire size changes. This increase resulted from a lower proportion of dropped song types in T-males than in control males, while the proportion of added song types did not differ between both groups. Interestingly, the observed repertoire turnover (adding and removing song types from the repertoire) in both groups, suggests that elevated plasma T levels were not essential for changes in repertoire composition (contrary to repertoire size). Finally, T-males (but not control males) significantly increased their song rate, while neither group showed a significant change in their song bout length and phrase repetition rate. Taken together, our results suggest a role for T in adult song learning and provide new insights into the information content of repertoire size and song bout length as sexually selected traits.     

The composition of the haemolymph of the New Zealand earwig, Anisolabis littorea

The haemolymph of the maritime earwig, Anisolabis littorea, has been analysed for inorganic and organic components. The inorganic fraction has a high sodium ion concentration and osmotic pressure but a relatively lower chloride ion concentration. The organic fraction has a high amino acid content—the principal ones being proline, alanine, glutamic acid, and glutamine, and tyrosine. In contrast to the high aminoacidemia there is a very low carbohydrate content and no detectable trehalose in the haemolymph. The evolution of the composition of insect blood is discussed.     

The C. elegans adult male germline: Stem cells and sexual dimorphism

The hermaphrodite Caenorhabditis elegans germline has become a classic model for stem cell regulation, but the male C. elegans germline has been largely neglected. This work provides a cellular analysis of the adult C. elegans male germline, focusing on its predicted stem cell region in the distal gonad. The goals of this study were two-fold: to establish the C. elegans male germline as a stem cell model and to identify sex-specific traits of potential relevance to the sperm/oocyte decision. Our results support two major conclusions. First, adult males do indeed possess a population of germline stem cells (GSCs) with properties similar to those of hermaphrodite GSCs (lack of cell cycle quiescence and lack of reproducibly oriented divisions). Second, germ cells in the mitotic region, including those most distal within the niche, exhibit sex-specific behaviors (e.g. cell cycle length) and therefore have acquired sexual identity. Previous studies demonstrated that some germ cells are not committed to a sperm or oocyte cell fate, even in adults. We propose that germ cells can acquire sexual identity without being committed to a sperm or oocyte cell fate.     

Multiple paternity and mating group size in the European earwig,Forficula auricularia

1. The patterns of multiple paternity among the progeny of females are key properties of genetic mating systems. Female multiple mating should evolve due to direct or indirect benefits, but it may also partly be driven by the encounter rate with different potential mates. 2. In this study this hypothesis was experimentally tested in the European earwig (Forficula auricularia L.) by establishing experimental mating groups that differed in the number of males and females (i.e. density). The number of sires and mean sibling relatedness in each clutch were estimated using microsatellite‐based paternity analysis. 3. As predicted, the mean number of sires per clutch was significantly increased, and sibling relatedness decreased, in the higher density treatment where more potential male mates were available. This change was less than proportional to the number of males in the mating groups, indicating that mechanisms limiting multiple paternity in large mating groups were involved. There were no significant relationships between female reproductive success or male siring success with morphology (body size, weight, and forceps size). 4. The present results show that multiple paternity in F. auricularia clutches is partly determined by the availability of male mates and suggest that this effect is modulated by mechanisms in males and/or females that limit multiple paternity.     

Mating strategy shifts in male green treefrogs (Hyla cinerea): An experimental study

Four field experiments were designed to study calling and satellite mating strategies in the green treefrog, Hyla cinerea. (1) The calling male was removed from 19 satellite associations and 11 of the 19 satellite males began calling. (2) After the calling male was removed from 10 satellite associations, a speaker broadcast synthetic mating calls. All of the satellite males oriented to the speaker. (3) Synthetic mating calls were played back to 14 calling males. Eleven males stopped calling and oriented to the speaker during at least one trial. (4) Sequences of synthetic mating calls and synthetic encounter calls were broadcast to 12 calling males. Nine males became satellites when the speaker emitted mating calls; none did so when encounter calls were presented.     

An insight into the genetic polymorphism among European populations of Lactuca serriola assessed by AFLP

Prickly lettuce (Lactuca serriola) is world-wide distributed and very variable species generally considered as a progenitor of the cultivated lettuce (Lactuca sativa). Altogether, 50 populations of L. serriola were characterized by means of amplified fragment length polymorphism (AFLP) and by isozyme analysis. Relationships among individuals and populations were examined by applying the unweighted pair-group method with the arithmetic averages (UPGMA) clustering algorithm, principal coordinate analysis (PCA) and the Nei's gene diversity index. The studied set of populations split into three main groups based on the AFLP polymorphism analysis. The first group contained L. sativa (control). The second group comprised two L. serriola accessions; one of them was identified as L. serriola f. integrifolia and the other as a mixture of two L. serriola forms. The largest and the most diverse third group contained the remaining L. serriola accessions. The population clustering corresponded approximately to their geographical distribution in Europe. At least five distinct geographic groups were recognised: 1) Northern European; 2) Slovenian; 3) very heterogeneous Central and Western European (mostly north of the Alps); 4) Mediterranean; 5) prevalence of L. serriola f. integrifolia, mostly comprising accessions from the United Kingdom and the Netherlands. This study showed that accessions originating in various eco-geographical conditions of Europe differ significantly in their genetic and protein polymorphism, as well as in morphology. Some European L. serriola populations (e.g. from Scandinavia and United Kingdom/British Isles/) seems to be isolated and homogeneous; in contrast, populations occurring in Central Europe are very diverse and genetically overlapping.     

An experimental investigation of the development of Porocephalus crotali (Pentastomida : Porocephalida) in the western diamondback rattlesnake (Crotalus atrox)

The development of Porocephalus crotali in the rattlesnake definitive host (Crotalus atrox) is described. Infective nymphs excyst, penetrate the body cavity by boring through the stomach mucosa, and, in as little as 12 days, enter the lung where they grow to maturity. Copulation, which was observed at 75 and 86 days post-infection, is followed by prolonged sperm storage in spermathecae. This heralds a long prepatent period. Egg production, commencing 230–250 days after infection, is massive and continuous over a lifetime of several years. Hook data indicates that at least three moults separate the infective nymph and the adult female making a minimum of nine for the complete development from the primary larva. There was little evidence of pathological symptoms.     

Sexual dimorphism in responses to unfamiliar intruders in the tamarin, Saguinus oedipus

Aspects of social structure in group-living species can be inferred by observing the responses of individuals to unfamiliar animals. This study examined the responses of mated pairs of cotton-top tamarins (Saguinus oedipus oedipus) to presentation of either unfamiliar conspecifics or members of a related tamarin species, the saddle-back tamarin (Saguinus fuscicollis fuscicollis). Male and female responses to intruders differed: resident males threatened, displayed piloerection, approached, and attacked intruders, especially males, while resident females showed increases in suprapubic scentmarking in the presence of intruders. Both males and females discriminated between the species of intruders, exhibiting more threats, scent-marking, piloerection, and approaches in the presence of conspecific intruders. There are pronounced sex differences in the signals and behaviour patterns that are elicited in an aggressive or territorial encounter with unfamiliar conspecifics in this monogamous primate.     

An experimental investigation into the effect of crevice availability on abundance and size-structure in a population of Littorina rudis (Maton): Gastropoda: Prosobranchia

Littorina rudis (Maton) is a common species on a wide variety of rocky shores. At Newhaven L. rudis is generally abundant on boulders, juveniles being reliant upon empty barnacle shells for shelter. The experimental addition of crevices resulted in greatly increased population densities, suggesting that crevice availability is normally a limiting factor on this shore. A relationship is demonstrated between the size of artificially provided crevices and the mean shell lengths of the populations of L. rudis they support. The relevance of crevice availability and quality, including empty barnacle shells, to the abundance and size distribution of L. rudis and other littorines is discussed.     

An investigation of sibling recognition in Rana cascadae tadpoles

Sibling recognition was studied experimentally in tadpoles of the Cascades frog, Rana cascadae. Sibships were divided into two groups at an early developmental stage. One group was reared with siblings and the second with a mixture of siblings and non-siblings. Whe given a choice of associating with a sibling or non-sibling group, individuals reared with siblings preferred siblings. One mixed-reared group spent more time associating with unfamiliar siblings than unfamiliar nonsiblings. Tadpoles of another mixed-reared group preferred to associate with pure siblings over a mixture of siblings and non-siblings with which they were reared. When the stimulus animals were taken exclusively from the mixed-rearing tank, two mixed-reared groups showed no sibling preferences. Our results suggest that early association with non-siblings does not affect sibling recognition in this species.     

An investigation of the photodynamic pigments in extracts of Lachnanthes tinctoria

Extracts of various parts of Lachnanthes tinctoria have been examined for photodynamic activity. One active compound from the seed pods has been identified as lachnanthocarpone.     

Nosema pyrausta infection in Macrocentrus grandii, a braconid parasite of the European corn borer, Ostrinia nubilalis

Macrocentrus grandii which develop within Nosema pyrausta-infected larvae of the European corn borer, Ostrinia nubilalis, develop direct systemic infections from the ingestion of spores at the time of larval emergence from the host. Infections adversely affect pupal development and adult longevity. Infected females are unable to transmit the microsporidian to additional corn borer hosts. Pathogen development in the parasite host appears identical to its development in the corn borer host and mature spores show no morphological differences in size or shape when observed at the ultrastructural level. The prevalence of infection in natural parasite populations is 53.8% and closely parallels the 56.7% prevalence of infection in corn borer populations. Results suggest N. pyrausta may play a significant role in limiting M. grandii populations when levels of N. pyrausta in corn borers are high.     

Annual oscillation of preferred temperature in the freshwater snail Lymnaea auricularia: effect of light and temperature

The thermal preference of the freshwater snail Lymnaea auriculria (Gastropoda: Pulmonata), measured 49 times over 3 years, oscillated around a mean of 19·3°C, with an amplitude of 13·4°C. This oscillation was significantly phase-linked to both the natural photoperiod and natural ambient temperature. Lymnaea hatched and maintained in constant conditions of temperature (21°C) and photoperiod (12 h) over 2 years showed a constant thermal preference of 19·8±1·4°C. The preference was maintained between 19·5 and 20·4°C when the snails were kept at 5, 15, 20 and 27°C and in photoperiods of 8 and 16 h. In a changing artificial photoperiod which followed an annual cycle, the preference fluctuated about a mean of 19·3°C with an amplitude of 3·9°C. When the photoperiod was constant but the temperature oscillated the preference remained constant. Thus the circannual cycle seems to be an exogenous oscillation entrained by the photoperiod.     

Status-appropriate singing behavior,testosterone and androgen receptor immunolabeling in male European starlings (Sturnus vulgaris)

Vocalizations convey information about an individual's motivational, internal, and social status. As circumstances change, individuals respond by adjusting vocal behavior accordingly. In European starlings, a male that acquires a nest site socially dominates other males and dramatically increases courtship song. Although circulating testosterone is associated with social status and vocal production it is possible that steroid receptors fine-tune status-appropriate changes in behavior. Here we explored a possible role for androgen receptors. Male starlings that acquired nest sites produced high rates of courtship song. For a subset of males this occurred even in the absence of elevated circulating testosterone. Immunolabeling for androgen receptors (ARir) was highest in the medial preoptic nucleus (POM) in males with both a nest site and elevated testosterone. For HVC, ARir was higher in dominant males with high testosterone (males that sang longer songs) than dominant males with low testosterone (males that sang shorter songs). ARir in the dorsal medial portion of the nucleus intercollicularis (DM) was elevated in males with high testosterone irrespective of dominance status. Song bout length related positively to ARir in POM, HVC and DM, and testosterone concentrations related positively to ARir in POM and DM. Results suggest that the role of testosterone in vocal behavior differs across brain regions and support the hypothesis that testosterone in POM underlies motivation, testosterone in HVC relates to song quality, and testosterone in DM stimulates vocalizations. Our data also suggest that singing may influence AR independent of testosterone and that alternative androgen-independent pathways regulate status-appropriate singing behavior.