Johan Ahlgren

An electromyographic analysis of the temporalis function of normal occlusion

Electromyographic (EMG) activity was recorded from the anterior, middle, and posterior regions of the temporalis muscle in ten subjects with normal occlusion of the teeth and with the mandible at rest and during exertion of increased biting force, using bipolar intramuscular electrodes. Results show that the posterior part of the temporalis muscle maintains the mandibular posture. Although there is no statistically significant difference in EMG recordings between the three divisions of the temporalis muscle during intercuspal biting, individual variations in EMG pattern exist. During exertion of increased biting force the EMG activity increases proportionally in all parts of the muscle. During retruded biting force the posterior temporalis predominates. The EMG activity of the temporalis muscle is correlated to the form and position of the mandible.

Early and late electromyographic response to treatment with activators.

An EMG analysis of twenty Class II cases treated with activators shows that: 1. During daytime use of activators, the protractor muscles of the mandible are stimulated, while the retractors are inhibited. 2. During nightime use of activators, no functional stimulation can be recorded. The activator appears to be operated mainly by tissue stretching and the accompanying elastic rebound. 3. Before treatment, as well as after the treatment, Class II cases show a balanced EMG pattern during closure in the intercuspal position. 4. A narrow upper arch should be expanded before treatment in order to avoid occlusal interferences and to make it easier for the lower arch to adapt itself to a protruded position.

Mentalis and orbicularis oris activity in children with incompetent lips An electromyographic and cephalometric study

In order to study the function and the level of activity of the mentalis and the orbicularis oris superior muscles in subjects with different lip morphology, an electromyographic investigation was carried out on ten children with normal lip position (competent lips) and ten children with lip incompetence. The underlying skeletal and dento-alveolar morphology was studied by cephalometrics. All the children had malocclusions, but had received no orthodontic treatment. It was found that a relaxed lip position with no EMG activity could be taken up by all the children in both groups. Lip closure, mastication, and swallowing were performed with a significantly greater activity in subjects exhibiting lip incompetence than in those with normal lip position. The analysis of cephalometric values in relation to lip posture and perioral muscle activity showed that subjects with incompetent lips and increased perioral muscle activity had great lower anterior face height, high mandibular plane angle, postnormal skelet...

Costs of inducible defence along a resource gradient.

In addition to having constitutive defence traits, many organisms also respond to predation by phenotypic plasticity. In order for plasticity to be adaptive, induced defences should incur a benefit to the organism in, for example, decreased risk of predation. However, the production of defence traits may include costs in fitness components such as growth, time to reproduction, or fecundity. To test the hypothesis that the expression of phenotypic plasticity incurs costs, we performed a common garden experiment with a freshwater snail, Radix balthica, a species known to change morphology in the presence of molluscivorous fish. We measured a number of predator-induced morphological and behavioural defence traits in snails that we reared in the presence or absence of chemical cues from fish. Further, we quantified the costs of plasticity in fitness characters related to fecundity and growth. Since plastic responses may be inhibited under limited resource conditions, we reared snails in different densities and thereby levels of competition. Snails exposed to predator cues grew rounder and thicker shells, traits confirmed to be adaptive in environments with fish. Defence traits were consistently expressed independent of density, suggesting strong selection from predatory molluscivorous fish. However, the expression of defence traits resulted in reduced growth rate and fecundity, particularly with limited resources. Our results suggest full defence in predator related traits regardless of resource availability, and costs of defence consequently paid in traits related to fitness.

Camouflaged or tanned: plasticity in freshwater snail pigmentation

By having phenotypically plastic traits, many organisms optimize their fitness in response to fluctuating threats. Freshwater snails with translucent shells, e.g. snails from the Radix genus, differ considerably in their mantle pigmentation patterns, with snails from the same water body ranging from being completely dark pigmented to having only a few dark patterns. These pigmentation differences have previously been suggested to be genetically fixed, but we propose that this polymorphism is owing to phenotypic plasticity in response to a fluctuating environment. Hence, we here aimed to assess whether common stressors, including ultraviolet radiation (UVR) and predation, induce a plastic response in mantle pigmentation patterns of Radix balthica. We show, in contrast to previous studies, that snails are plastic in their expression of mantle pigmentation in response to changes in UVR and predator threats, i.e. differences among populations are not genetically fixed. When exposed to cues from visually hunting fish, R. balthica increased the proportion of their dark pigmentation, suggesting a crypsis strategy. Snails increased their pigmentation even further in response to UVR, but this also led to a reduction in pattern complexity. Furthermore, when exposed to UVR and fish simultaneously, snails responded in the same way as in the UVR treatment, suggesting a trade-off between photoprotection and crypsis.

Individual boldness is linked to protective shell shape in aquatic snails.

The existence of consistent individual differences in behaviour (‘animal personality’) has been well documented in recent years. However, how such individual variation in behaviour is maintained over evolutionary time is an ongoing conundrum. A well-studied axis of animal personality is individual variation along a bold–shy continuum, where individuals differ consistently in their propensity to take risks. A predation-risk cost to boldness is often assumed, but also that the reproductive benefits associated with boldness lead to equivalent fitness outcomes between bold and shy individuals over a lifetime. However, an alternative or complementary explanation may be that bold individuals phenotypically compensate for their risky lifestyle to reduce predation costs, for instance by investing in more pronounced morphological defences. Here, we investigate the ‘phenotypic compensation’ hypothesis, i.e. that bold individuals exhibit more pronounced anti-predator defences than shy individuals, by relating shell shape in the aquatic snail Radix balthica to an index of individual boldness. Our analyses find a strong relationship between risk-taking propensity and shell shape in this species, with bolder individuals exhibiting a more defended shell shape than shy individuals. We suggest that this supports the ‘phenotypic compensation’ hypothesis and sheds light on a previously poorly studied mechanism to promote the maintenance of personality variation among animals.

The influence of predator regime on the behaviour and mortality of a freshwater amphipod, Gammarus pulex

In species with restricted dispersal, traits may become genetically fixed leading to local adaptations. Therefore, predator avoidance in a prey species may differ between populations experiencing different predator regimes, but also between sexes within a population due to different vulnerability to predators. In this study we used male and female Gammarus pulex from two different predator regimes: fishless ponds, where invertebrates are the dominant predators and ponds with predatory fish. In the laboratory we examined refuge use, mortality, leaf decomposition rate and pair-formation in G. pulex when exposed to predator cues from either invertebrate predators or fish. Individuals from fish ponds spent more time in refuge and had a higher mortality than those from fishless ponds independent of predator cues. There was no effect of pond predator regime or predator cues on leaf decomposition rates. Further, fewer individuals formed pairs in G. pulex from fish ponds than from fishless ponds. Male G. pulex had a higher mortality and a higher decomposition rate than females independent of predator cues. However, there was no difference in refuge use between sexes. Our study shows that there are general differences in behaviour traits, both between predator regimes and sexes in G. pulex.

Metallic implants as growth markers in infants with craniofacial anomalies.

The purpose of the study was to test the retention of metallic implants in bone tissue for evaluation of early facial growth patterns in patients with craniofacial malformations. Implants were inserted in 51 patients (age range: 1-17 months) with different diagnoses, the majority of them with various types of cleft lip and/or palate. Seven positions in the maxilla and four in the mandible were employed. Roentgencephalometric follow-up examinations were carried out at various stages up to the age of about three years. The results indicated that the frequency of implants firmly retained within the bone decreased with time depending on the craniofacial deformity and the implant sites. Stability seemed most critical in positions close to the alveolar processes where more than one-half of the implants inserted were dislocated or lost at the three-year follow-up. For the maxillary implants the patients with bilateral cleft lip and palate displayed the highest failure rate. This investigation did not support continuation of the implant method in infants as used in the present study.

Experimental evidence for a mismatch between insect emergence and waterfowl hatching under increased spring temperatures

By combining a large-scale experimental assessment on timing of insect emergence with longtermmonitoring of waterfowl hatching date, we here show that insect emergence is mainly driven bytemperatur ...

Behaviour of freshwater snails (Radix balthica) exposed to the pharmaceutical sertraline under simulated predation risk

Due to their potential for affecting the modulation of behaviour, effects of selective serotonin reuptake inhibitors (SSRIs) in the environment are particularly interesting regarding interspecies interactions and non-consumptive effects (NCEs) induced by predator cues in prey organisms. We evaluated the effects of sertraline (0.4, 40 ng/L, 40 µg/L) over 8 days on activity and habitat choice in the freshwater snail Radix balthica, on snails’ boldness in response to mechanical stimulation (simulating predator attack), and their activity/habitat choice in response to chemical cues from predatory fish. We hypothesised that sertraline exposure would detrimentally impact NCEs elicited by predator cues, increasing predation risk. Although there were no effects of sertraline on NCEs, there were observed effects of chemical cue from predatory fish on snail behaviour independent of sertraline exposure. Snails reduced their activity in which the percentage of active snails decreased by almost 50% after exposure to fish cue. Additionally, snails changed their habitat use by moving away from open (exposed) areas. The general lack of effects of sertraline on snails’ activity and other behaviours in this study is interesting considering that other SSRIs have been shown to induce changes in gastropod behaviour. This raises questions on the modes of action of various SSRIs in gastropods, as well as the potential for a trophic “mismatch” of effects between fish predators and snail prey in aquatic systems.