ABSTRACT
When a parent's parentage differs across breeding attempts, established theory predicts that the parent should invest more in a brood when perceived parentage is high. We present a model of parental investment in which offspring unrelated to the parent have a competitive advantage over the parent's own offspring and take a larger share of investment. We show that this can weaken or, if the competitive advantage is great, reverse the predicted relationship between perceived parentage and parental investment. A moderate competitive advantage of extra-pair young over within-pair young could partly explain the lack of any clear relationship between paternal care and paternity in many studies, and could easily arise if females choose extra-pair partners for good genes. Our results are also relevant to interspecific avian brood parasitism. As parasites reared together with host offspring are often superior competitors, their hosts could benefit from increasing investment in response to suspected parasitism.
Subject(s)
Birds/physiology , Animals , Clutch Size , Female , Maternal Behavior , Models, Biological , Paternal Behavior , ReproductionABSTRACT
Social parasites may exploit their hosts by mimicking other organisms that the hosts normally benefit from investing in or responding to in some other way. Some parasites exaggerate key characters of the organisms they mimic, possibly in order to increase the response from the hosts. The huge gape and extreme begging intensity of the parasitic common cuckoo chick (Cuculus canorus) may be an example. In this paper, the evolutionary stability of manipulating hosts through exaggerated signals is analysed using game theory. Our model indicates that a parasite's signal intensity must be below a certain threshold in order to ensure acceptance and that this threshold depends directly on the rate of parasitism. The only evolutionarily stable strategy (ESS) combination is when hosts accept all signallers and parasites signal at their optimal signal intensity, which must be below the threshold. Supernormal manipulation by parasites is only evolutionarily stable under sufficiently low rates of parasitism. If the conditions for the ESS combination are not satisfied, rejector hosts can invade using signal intensity as a cue for identifying parasites. These qualitative predictions are discussed with respect to empirical evidence from parasitic mimicry systems that have been suggested to involve supernormal signalling, including evicting avian brood parasites and insect-mimicking Ophrys orchids.
Subject(s)
Parasites/physiology , Parasitic Diseases, Animal/parasitology , Adaptation, Physiological , Animals , Biological Evolution , Game Theory , Host-Parasite Interactions , Models, Biological , Parasitic Diseases, Animal/immunologyABSTRACT
Radiotherapy according to a "small volume/large absorbed dose"-concept was given to 31 patients with carcinoma of the oesophagus. Tumour control in the treated volume was obtained in 52%, but only 13% of the patients survived for 6 years. Metastases outside the treated volume were seen in 65% of the patients. The palliative results may be judged as not optimal.
Subject(s)
Esophageal Neoplasms/radiotherapy , Aged , Esophageal Neoplasms/mortality , Female , Humans , Male , Middle AgedABSTRACT
An electrode for transvenous permanent ventricular pacing equipped with a supermagnet was implanted in six dogs in the apex of the right ventricle for several weeks. As no signs of myocardial perforation occurred, the device which consists of the magnetic tip lead and an external supermagnet applied to the precordial region of the chest wall was implanted in 14 patients. The lead was introduced through the right cephalic vein in 12 patients and through the right external jugular vein in the remaining 2 patients. Threshold values were measured twice a day in 12 patients who received a Siemens-Elema Vario pacemaker 629. The average peak threshold was reached on the 11th day after implantation. No pacing failure or other signs of acute dislodgement of leads occurred during the first 30 days.
Subject(s)
Cardiac Pacing, Artificial/methods , Electrodes, Implanted , Magnetics , Animals , Cardiac Catheterization/instrumentation , Dogs , HumansSubject(s)
Arteriovenous Malformations/therapy , Embolization, Therapeutic/methods , Lung/blood supply , Adult , Angiography , Catheterization , Female , HumansABSTRACT
A patient with widespread acanthosis nigricans is described. No abdominal tumour was found. Explorative thoracotomy disclosed numerous enlarged lymph glands containing squamous cell carcinoma. The left lung was removed but meticulous search did not disclose any tumour. The glands were removed as radically as possible. After the operation the skin improved and the lesions have disappeared completely. The observation time is over three years.
