Invertebrate bioturbation can reduce the clogging of sediment: an experimental study using infiltration sediment columns

1. Invertebrate bioturbation can strongly affect water‐sediment exchanges in aquatic ecosystems. The objective of this study was to quantify the influence of invertebrates on the physical characteristics of an infiltration system clogged with fine sediment. 2. Two taxa (chironomids and tubificids) with different bioturbation activities were studied in experimental slow infiltration columns filled with sand and gravel and clogged with a 2 cm layer of fine sediment at the surface. We measured the effects of each taxon separately and combined on hydraulic head, water mobility and sediment reworking. 3. The results showed that invertebrates could reduce sediment clogging and this effect was linked to the functional mode of bioturbation of each group. Tubificid worms dug networks of galleries in the fine sediment, creating pathways for water flow, which reduced the clogging of sediment. In contrast, the U‐shaped tubes of chironomids were restricted to the superficial layer of fine sediments and did not modify the hydraulic conductivity of experimental columns. The combination of invertebrates did not show any interactive effects between tubificids and chironomids. The occurrence of 80 tubificids in the combination was enough to maintain the same hydraulic conductivity that 160 worms did in monospecific treatment. 4. The invertebrates like tubificid worms can have a great benefit on functioning of clogged interfaces by maintaining high hydraulic conductivity, which contributes to increased water‐sediment exchanges and stimulates biogeochemical and microbial processes occurring in river sediments.     

Cicada ear geometry: species and sex effects

Many insect species rely on their sense of audition to find a mate, to localize prey or to escape from a predator. Cicadas are particularly known for their loud call and the conspicuous tympanal hearing system located in their abdomen. The vibration pattern of the tympanal membrane (TM) has been investigated recently revealing mechanical properties specific to species and sex. Although TM size and shape is likely to affect these patterns, the geometry of the cicada ear has never been examined per se. Focusing on three Mediterranean cicada species, namely Cicadatra atra, Cicada orni and Lyristes plebejus, we investigated the structure of TM shape variation at two levels, within and across species. Applying an elliptic Fourier analysis to the outlines of both male and female TMs, we estimated sexual dimorphism and species effects. Cicadatra atra showed a large TM compared with its small size, probably as a result of selective constraints related to the role of the TM in sound production. Sexual dimorphism seemed to be greater than interspecific variation, indicating that constraints operating on sex might be more selective than those acting on species identification. In addition, C. orni appeared to be significantly different from the two other species. This morphological peculiarity could be related to the unique vibrational pattern of its membrane. This would establish for the first time a direct link between the shape and mechanism of a hearing organ. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 922–934.     

Ecophysiological aspects of bruchid reproduction. I. The influence of pod maturity and seeds of Phaseolus vulgaris and the influence of insemination on the reproductive activity ofZabrotes subfasciatus

ABSTRACT.

• 1 Economically important bruchid beetles like Zabrotes sub-fasciatus (Boh.) are able to reproduce both in the field before the legume crop harvest – whilst the seeds are still enclosed within pods – and on seeds in storage sites.
• 2 To take into account this reproductive feature, the influence of pods at different stages of maturity and seeds of Phaseolus vulgaris (Lin.) together with the influence of insemination on the reproductive activity of Zabrotes subfasciatus were examined.
• 3 Female fecundity, insemination and ovarian production were studied under laboratory conditions approximating as closely as possible to the thermal and photoperiodic regimes of the Costa Rican region from which the experimental strain originated.
• 4 The three stages of pod maturity used in experiments (fresh green, fresh yellow and dry yellow pods, all non-dehiscent) induced copulations and significantly stimulated oogenesis. Fecundities of females in the presence of pods were low and did not differ from controls.
• 5 The influence of bean seeds on female reproductive activity was more pronounced than that of pods. Contact with seeds led to a marked increase in the number of sexual meetings, ovarian production and egg-laying activity. Under these conditions, eggs are laid directly on the larvae's food.
• 6 Insemination alone stimulated oogenesis but did not induce egg-laying.
• 7 Possible additive or synergistic interactions between host plant information perceived by females, the effects of egg-laying and insemination are suggested to explain the observed results.
• 8 The adaptive value of this form of reproductive regulation by host plant seeds and pods is discussed in terms of the natural history and oviposition behaviour of Zabrotes subfasciatus.

     

Discordance in body size, colour pattern, and advertisement call across genetically distinct populations in a Neotropical anuran (Dendropsophus ebraccatus)

Patterns of intraspecific geographic variation in morphology and behaviour, when examined in a phylogenetic context, can provide insight into the microevolutionary processes driving population divergence and ultimately speciation. In the present study, we quantified behavioural and phenotypic variation among populations from genetically divergent regions in the Central American treefrog, Dendropsophus ebraccatus . Our fine-scale population comparisons demonstrated regional divergence in body size, colour pattern frequencies, and male advertisement call. None of the characters covaried with phylogenetic history or geographic proximity among sampled populations, indicating the importance of highly localized selection pressures and genetic drift in shaping character divergence among isolated regions. The study underscores how multiple phenotypic characters can evolve independently across relatively small spatial scales.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 298–313.     

A Comparative Study of 14 Strains of Naegleria australiensis Demonstrates the Existence of a Highly Virulent Subspecies: N. australiensis italica n. spp.1

Fourteen strains of Naegleria australiensis, including the type strain, were compared for virulence for mice, maximum growth temperature, lectin agglutination, isoenzyme pattern, and total protein banding pattern. Their relation to other species of Naegleria also was compared by immunoelectrophoretic analysis. Strains with high virulence, comparable to that of N. fowleri, were found to be different in concanavalin A agglutination as well as with regard to zymograms and total protein patterns. Although serologically different from N. fowleri and reacting with N. australiensis antiserum in the fluorescent antibody test, these high-virulence strains differed in number of immunoelectrophoretic precipitin bands. Because of these results, the high-virulence strains are considered to be a subspecies of N. australiensis. The low-virulence strains showed minor differences from the type strain. Thus, N. australiensis does not appear to be as homogenous a species as N. fowleri. Pathogenic N. australiensis also seems to be more widespread than previously thought.