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Biomedical subjects

T Székely

Publications and source records attributed to T Székely.

17 recordsLinked to original sources
PubMed2003

Directional changes in sexual size dimorphism in shorebirds, gulls and alcids.

The Charadrii (shorebirds, gulls and alcids) are one of the most diverse avian groups from the point of view of sexual size dimorphism, exhibiting extremes in both male-biased and female-biased dimorphism, as well as monomorphism. In this study we use phylogenetic comparative analyses to investigate how size dimorphism has changed over evolutionary time, distinguishing between changes that have occurred in females and in males. Independent contrasts analyses show that both body mass and wing length have been more variable in males than in females. Directional analyses show that male-biased dimorphism has increased after inferred transitions towards more polygynous mating systems. There have been analogous increases in female-biased dimorphism after transitions towards more socially polyandrous mating systems. Changes in dimorphism in both directions are attributable to male body size changing more than female body size. We suggest that this might be because females are under stronger natural selection constraints related to fecundity. Taken together, our results suggest that the observed variation in dimorphism of Charadrii can be best explained by male body size responding more sensitively to variable sexual selection than female body size.

Animals↗
PubMed2000

Trade-off between mating opportunities and parental care: brood desertion by female Kentish plovers.

Why do some parents care for their young whereas others divorce from their mate and abandon their offspring? This decision is governed by the trade-off between the value of the current breeding event and future breeding prospects. In the precocial Kentish plover Charadrius alexandrinus females frequently, but not always, abandon their broods to be cared for by their mate, and seek new breeding partners within the same season. We have shown previously that females' remating opportunities decline with date in the season, so brood desertion should be particularly favourable for early breeding females. However, the benefits are tempered by the fact that single-parent families have lower survival expectancies than those where the female remains to help the male care for the young. We therefore tested the prediction that increasing the value of the current brood (by brood-size manipulation) should increase the duration of female care early in the season, but that in late breeders, with reduced remating opportunities, desertion and thus the duration of female care should be independent of current brood size. These predictions were fulfilled, indicating that seasonally modulated trade-offs between current brood value and remating opportunities can be important in the desertion decisions of species with flexible patterns of parental care.

Animals↗
PubMed2000

A dynamic game-theoretic model of parental care.

We present a model in which members of a mated pair decide whether to care for their offspring or desert them. There is a breeding season of finite length during which it is possible to produce and raise several batches of offspring. On deserting its offspring, an individual can search for a new mate. The probability of finding a mate depends on the number of individuals of each sex that are searching, which in turn depends upon the previous care and desertion decisions of all population members. We find the evolutionarily stable pattern of care over the breeding season. The feedback between behaviour and mating opportunity can result in a pattern of stable oscillations between different forms of care over the breeding season. Oscillations can also arise because the best thing for an individual to do at a particular time in the season depends on future behaviour of all population members. In the baseline model, a pair splits up after a breeding attempt, even if they both care for the offspring. In a version of the model in which a pair stays together if they both care, the feedback between behaviour and mating opportunity can lead to more than one evolutionarily stable form of care.

Animals↗
PubMed2000

Sexual size dimorphism in shorebirds, gulls, and alcids: the influence of sexual and natural selection.

Charadrii (shorebirds, gulls, and alcids) have an unusual diversity in their sexual size dimorphism, ranging from monomorphism to either male-biased or female-biased dimorphism. We use comparative analyses to investigate whether this variation relates to sexual selection through competition for mates or natural selection through different use of resources by males and females. As predicted by sexual selection theory, we found that in taxa with socially polygynous mating systems, males were relatively larger than females compared with less polygynous species. Furthermore, evolution toward socially polyandrous mating systems was correlated with decreases in relative male size. These patterns depend on the kinds of courtship displays performed by males. In taxa with acrobatic flight displays, males are relatively smaller than in taxa in which courtship involves simple flights or displays from the ground. This result remains significant when the relationship with mating system is controlled statistically, thereby explaining the enigma of why males are often smaller than females in socially monogamous species. We did not find evidence that evolutionary changes in sexual dimorphism relate to niche division on the breeding grounds. In particular, biparental species did not have greater dimorphism in bill lengths than uniparental species, contrary to the hypothesis that selection for ecological divergence on the breeding grounds has been important as a general explanation for patterns of bill dimorphism. Taken together, these results strongly suggest that sexual selection has had a major influence on sexual size dimorphism in Charadrii, whereas divergence in the use of feeding resources while breeding was not supported by our analyses.

Animals↗
PubMed1997

A general technique for computing evolutionarily stable strategies based on errors in decision-making.

Realistic models of contests between animals will often involve a series of state-dependent decisions by the contestants. Computation of evolutionarily stable strategies for such state-dependent dynamic games are usually based on damped iterations of the best response map. Typically this map is discontinuous so that iterations may not converge and even if they do converge it may not be clear if the limiting strategy is a Nash equilibrium. We present a general computational technique based on errors in decision making that removes these computational difficulties. We show that the computational technique works for a simple example (the Hawk-Dove game) where an analytic solution is known, and prove general results about the technique for more complex games. It is also argued that there is biological justification for inclusion of the types of errors we have introduced.

Animals↗
PubMed1987

Separation, quantitation and isolation of cannabinoids from Cannabis sativa L. by overpressured layer chromatography.

Two overpressured layer chromatography (OPLC) methods have been developed for the separation of neutral and acidic cannabinoids. The first is an adaptation of Korte's well known method to the OPLC system, which improves its reproducibility. The second one is a new technique based on the phenomenon of chromatographic solvent demixing. The eluent itself is also divided into zones. In the alpha-zone the neutral cannabinoids and in the beta-zone the acidic ones are separated. As a result of the good and reproducible separation, there is a possibility to quantitate cannabinoids by densitometry. The on-line version of OPLC proved suitable for the isolation of hemp constituents.

Adsorption↗
PubMed1984

[Surgery of glomus tumors].

The diagnostic and therapeutic possibilities for glomus tumors around the bulb of the jugular vein or in the tympanic cavity are discussed. The author believes that such a case should be treated surgically. The results of 15 patients suffering from glomus tumor treated during the last 19 years are presented. Those which had individual cerebral nerve paralysis or who had to have extensive operation on account of the size of the tumor are dealt with in detail.

Adult↗
PubMedDate not supplied

Long-term follow-up of the effect of tympanic neurectomy on sialadenosis and recurrent parotitis.

We examined the effect of tympanic neurectomy on the clinical symptoms and secretory function of the parotids in 13 patients with chronic parotitis or sialadenosis for 3 years. Each patient had significantly fewer complaints immediately after the surgery. In quite a few patients the improvement was transient only. Three years after neurectomy 3 of the 10 examined patients were free from complaints and 4 further patients had less severe complaints than before the surgery. Neurectomy was followed by a significant decrease in parotid flow rate and an increase in the sodium concentration of parotid saliva, while potassium concentration showed a slight decrease. Three years after the surgery the flow rate and the sodium concentration were moderately higher than before that. There was a significant, long-lasting change in the amylase activity of parotid saliva; 3 years after neurectomy it attained one-third of the preoperative value. A pharmacological test, carried out 3 years after neurectomy in 2 patients, suggested parasympathetic reinnervation of the parotid.

Atropine↗