Characteristics of dispersal in sexually mature dragonflies

Abstract.

• 1 The population dynamics of a natural population of Sympetrum danae (Sulzer) were studied, by means of a mark—release—recapture method, to find indications of dispersal by mature adults. Additional information on orientation and the influence of phenotype (including age), density and weather was obtained by observations under natural conditions and in a large outdoor field cage.
• 2 80% of all mature adults caught around the natural pond were estimated to be immigrants. Considerable immigration was confirmed by the abdomen length of unmarked matures which did not accord with that expected from the locally emerged population. Total numbers captured and the minimum number known to be alive fell sharply at the time when most individuals were mature. At the same time, new matures continued to enter and disappear from the study area at an increasing rate.
• 3 Dispersive behaviour (escape flights) in the field enclosure was primarily age dependent in both sexes: it occurred from an age of 25–30 days onwards. This coincides with the time-lag between the emergence peak and increased dispersal in the field. Secondary effects on escape flights suggested that males tended to abandon low density areas.
• 4 Males flew relatively more southward than females.

     

Role of the Vegetal Body in the Regulation of Development in Bithynia tentaculata (Prosobranchia, Gastropoda)

In the first polar lobe of the egg of Bithyma tentaculata thereis a cup-shaped mass of small vesicles rich in RNA, called thevegetal body. It is passed to the CD blastomere with the polarlobe and then its contents are distributed to C and D. Whenthe polar lobe is removed, embryos form neither mesentoblastnor mesoderm bands. They fail to establish bilateral symmetryor to form eyes, foot, operculum and shell. AB half embryosdevelop only the structures found in lobeless embryos, whileCD halves develop lobe dependent adult structures such as eyes,foot and shell. AD- and BC-2/4-embryos develop similarly andboth have lobe dependent structures. Three quarter embryos developas in other molluscs except that ABD (–C) develops poorlyand ABC (–D) develops all lobe-dependent structures. Thus,all evidence available indicates that C receives cytoplasm usuallyrestricted to D in molluscs and therefore has the capacity toexert a similar morphogenetic influence on development.     

Trophic ecology of parabiotic ants: Do the partners have similar food niches?

Organisms associated with another species may experience both costs and benefits from their partner. One of these costs is competition, which is the more likely if the two species are ecologically similar. Parabioses are associations between two ant species that share a nest and often attend the same food sources. Albeit parabioses are probably mutualistic, parabiotic partners may compete for food. We therefore investigated feeding niches and dietary overlap of two parabiotically associated ants in Borneo using cafeteria experiments and stable isotope analyses. The two species strongly differed in their food choices. While Crematogaster modiglianii mostly foraged at carbohydrate‐rich baits, Camponotus rufifemur preferred urea‐rich sources. Both species also consumed animal protein. The ¹⁵N concentration in Ca. rufifemur workers was consistently lower than in Cr. modiglianii. Camponotus rufifemur but not Cr. modiglianii possesses microbial endosymbionts, which can metabolize urea and synthesize essential amino acids. Its lower ¹⁵N signature may result from a relatively higher intake of plant‐based or otherwise ¹⁵N‐depleted nitrogen. Isotopic signatures of the two partners in the same parabiosis showed strongly parallel variation across nests. As we did not find evidence for spatial autocorrelation, this correlation suggests an overlap of food sources between the two ant species. Based on model simulations, we estimated a diet overlap of 22–66% for nitrogen sources and 45–74% for carbon sources. The overlap may arise from either joint exploitation of the same food sources or trophallactic exchange of food. This suggests an intense trophic interaction and potential for competition between the parabiotic partners.     

Description and phylogeny of a new Neotropical genus of Acalyptini (Coleoptera: Curculionidae: Curculioninae) associated with the staminodes of Cyclanthaceae

The weevil genus Azotoctla gen. nov. (Coleoptera: Curculionidae: Curculioninae: Acalyptini Thomson), is described to accommodate the following 15 new Neotropical species: Azotoctla aecuatorialis sp. nov. (Ecuador), Azotoctla anerunca sp. nov. (Ecuador), Azotoctla angustacra sp. nov. (Ecuador), Azotoctla curvirostra sp. nov. (Peru), Azotoctla dasygastra sp. nov. (Costa Rica and Honduras), Azotoctla femorata sp. nov. (Colombia, Costa Rica, Ecuador and Panama), Azotoctla gomezi sp. nov. (Colombia, Costa Rica and Panama), Azotoctla gottsbergeri sp. nov. (Brazil), Azotoctla clemmyssa sp. nov. (Colombia), Azotoctla melolauta sp. nov. (Colombia), Azotoctla migueli sp. nov. (Colombia), Azotoctla nana sp. nov. (Panama), Azotoctla punctata sp. nov. (Costa Rica), Azotoctla tibiatra sp. nov. (Belize), and Azotoctla tuberquiai sp. nov. (Colombia). Azotoctla is placed in the tribe Acalyptini, subtribe Staminodeina Franz, thus representing the sister taxon of Staminodeus Franz. The monophyly of Azotoctla is supported by the following inferred traits: a noncarinate rostrum that is tumescent above the antennal insertion in males; equilaterally subtriangular hemisternites of the male sternum 8; paired, longitudinal, laterally positioned sclerites of the aedeagus; and a bifurcate lamina of the female sternum 8, which bears explanate, diverging furcal arms. A key to the species of Azotoctla is provided; and the salient features of each species are illustrated and presented along with distributional and natural history data. A morphological cladistic analysis of 23 terminal species (eight outgroup, 15 ingroup) and 33 characters yielded a single most parsimonious cladogram (length = 75 steps, consistency index = 52, retention index = 77), with the ingroup topology ((A. aecuatorialis, (A. anerunca, A. gottsbergeri)), (A. punctata, ((A. angustacra, A. nana), (A. tibiatra, (A. clemmyssa, (A. curvirostra, A. femorata)), (A. melolauta, ((A. gomezi, A. migueli), (A. dasygastra, A. tuberquiai))))))). Species of Azotoctla are reproductively associated with the ephemeral staminodes of different members of the Neotropical monocot family Cyclanthaceae; most commonly with the widespread genus Carludovica Ruiz & Pavón. The interspecific homogeneity in external morphology, coupled with marked differences in genital traits and an apparent absence of narrow geographical ranges mediated by either host plants and/or biogeographical factors, jointly suggest that the diversification of Azotoctla is a relatively recent phenomenon and driven strongly by sexual selection. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 559–623.     

Behavioural and chemical mechanisms behind a Mediterranean ant–ant association

1. Interspecific competition among ants is common, and so is competitive exclusion among dominant ant species. In contrast, specific associations between non‐parasitic ant species are rare, especially in the temperate zones. As an exception, the subordinate ant Camponotus lateralis frequently co‐occurs with the dominant Crematogaster scutellaris but rarely with other dominant ants. 2. This association is one of various associations between Camponotus and Crematogaster species across the world. However, the mechanisms behind these co‐occurences are largely unknown. 3. In the present study, we therefore investigated the association of Ca. lateralis and Cr. scutellaris. We studied the spatial association of the nests, interspecific aggression, both species' cuticular hydrocarbon profiles, and their propensity to follow the other species' pheromone trails. 4. Crematogaster scutellaris usually attacked and displaced the generally submissive Ca. lateralis, but was significantly less aggressive at jointly used trails. Camponotus nests were always in close proximity to Crematogaster nests. 5. The cuticular hydrocarbons of both species consisted of alkanes with chain lengths between C21 and C35. The two species had 25 hydrocarbons in common, including mono‐, di‐, and tetramethyl alkanes. Despite this qualitative similarity, however, the quantitative hydrocarbon composition differed between the two species. 6. Camponotus lateralis followed artificial trails containing trail pheromones of Cr. scutellaris, but the latter did not follow Ca. lateralis trail pheromones. Interspecific trail‐following by Camponotus, but not vice versa, has been observed in another Camponotus–Crematogaster association and may be a more general mechanism that facilitates associations between the two ant genera.     

Characterization of microsatellite markers for the invasive ant species Anoplolepis gracilipes

We present primer sequences for eight polymorphic microsatellite loci for the formicine ant Anoplolepis gracilipes, a serious pest species in South‐East Asia and Pacific islands and still spreading on all continents. Microsatellite loci were isolated with a highly efficient method of enrichment. The number of alleles ranged from two to 19 with an observed heterozygosity ranging from 0.842 to 1.0. The markers were designed for a sociogenetic study as well as for population genetics.     

Intra‐floral resource partitioning between endemic and invasive flower visitors: consequences for pollinator effectiveness

1. Sympatric flower visitor species often partition nectar and pollen and thus affect each other's foraging pattern. Consequently, their pollination service may also be influenced by the presence of other flower visiting species. Ants are solely interested in nectar and frequent flower visitors of some plant species but usually provide no pollination service. Obligate flower visitors such as bees depend on both nectar and pollen and are often more effective pollinators. 2. In Hawaii, we studied the complex interactions between flowers of the endemic tree Metrosideros polymorpha (Myrtaceae) and both, endemic and introduced flower‐visiting insects. The former main‐pollinators of M. polymorpha were birds, which, however, became rare. We evaluated the pollinator effectiveness of endemic and invasive bees and whether it is affected by the type of resource collected and the presence of ants on flowers. 3. Ants were dominant nectar‐consumers that mostly depleted the nectar of visited inflorescences. Accordingly, the visitation frequency, duration, and consequently the pollinator effectiveness of nectar‐foraging honeybees (Apis mellifera) strongly decreased on ant‐visited flowers, whereas pollen‐collecting bees remained largely unaffected by ants. Overall, endemic bees (Hylaeus spp.) were ineffective pollinators. 4. The average net effect of ants on pollination of M. polymorpha was neutral, corresponding to a similar fruit set of ant‐visited and ant‐free inflorescences. 5. Our results suggest that invasive social hymenopterans that often have negative impacts on the Hawaiian flora and fauna may occasionally provide neutral (ants) or even beneficial net effects (honeybees), especially in the absence of native birds.     

Do simultaneous hermaphrodites choose their mates? Effects of body size in a planarian flatworm

1. We tested whether or not the simultaneous hermaphrodite Dugesia polychroa mates randomly with respect to partner size, a strong indicator of female fecundity.
2. The number and duration of copulations were recorded in forty-eight pairs over 5 days. To minimize effects of individual differences in copulatory activity, all animals were each tested twice: once with an equally large partner ( n = 24 equal-sized pairs) and once with a partner of different size (smaller or larger, respectively, ratio 1 : 1.5,
n = 24 unequal-sized pairs).
3. The animals copulated frequently. No significant differences were observed between treatments in the number of pairs that copulated. Mating behaviour of equal-sized and unequal-sized pairs was compared in a pair-wise analysis. Latency to the first copulation and the average number of copulations did not differ when mating with an equal- or unequal-sized partner. Average copulation duration increased with increasing size in equal-sized pairs, but not in unequal-sized pairs.
4. In an additional experiment, where three large and three small animals were combined (three replicates) and observed for 1–3 days, the mating pattern did not differ from random mating by size.
5. Our data indicate that in D. polychroa the decision to mate is essentially random with respect to size. We argue that this is not caused by, for example, high costs of mate searching, but that simultaneous hermaphrodites with reciprocal insemination mate indiscriminately when (i) matings are easy to obtain and (ii) the cost of mating is low or compensated for by sperm digestion.     

Analysing the history of the derelomine flower weevil–Carludovica association (Coleoptera: Curculionidae; Cyclanthaceae)

The evolutionary history of the interaction among species of derelomine flower weevils (Coleoptera: Curculionidae: Derelomini) and the Panama-hat palm Carludovica (Cyclanthaceae) is analysed with emphasis on the congruence of (1) topologies and (2) character state transformations in each of the Neotropical clades. For this purpose cladistic analyses are complemented with host plant records, natural history information and selected morphological studies of the associated taxa. The interaction is specialized, involving pollination, oviposition into the inflorescences and the predation of seeds (particularly within Systenotelus ). As results from a range of standard coevolutionary methods of analysis indicate, however, events of colonization, extinction and independent (non-reciprocal) speciation have been abundant throughout the history of the association. At the same time it is possible to specify the homology and succession of characters among species of derelomines and Carludovica and interpret them as reciprocal adaptations to attack and protect the seeds, respectively. It is argued that – in light of the limited evolutionary stability of many insect–plant interactions – the question of coevolution is most effectively addressed by combining information from the character- and topology-based approaches.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 483–517.     

Some Aspects of Melanin Formation of Melanocytes Cultured on Collagen-Coated Microcarrier Beads

Melanocytes cultured on collagen-coated Cytodex 3 microcarrier Sephadex beads caused remarkable pigmentation of the beads during the period of culture when optimal density was reached. Electron microscopy of melanocytes on the microcarriers revealed that the cells and their dendrites invaginate into the microcarrier surface layer. Removal of the cells by trypsinization showed that some pigment granules were left on the carrier surface and within the cavities present on the microcarrier surface. In order to investigate whether the pigmentation of the microcarriers could be a result of indole intermediates of melanogenesis present in the culture medium, extracts were studied by gas chromatography/mass spectrometry for the presence of these compounds. Two compounds (5,6-dihydroxyindole-2-carboxylic acid and 6-hydroxy-5-methoxyindole-2-carboxylic acid) so far have been identified in the medium extracts. Results indicate that microcarrier culture of melanocytes can serve as an interesting model for electron microscopy studies of melanocytes with regard to pigmentation and cell attachment.