Experimental evidence of asymmetrical competition between two species of parasitic copepods.
(9/698)
Lepeophtheirus thompsoni and Lepeophtheirus europaensis are two parasitic copepods naturally isolated on their sympatric hosts, i.e. turbot (Psetta maxima L.) and brill (Scophthalmus rhombus L.), respectively They are able to meet, mate and hybridize on turbot experimentally but they are naturally prevented from doing so by a strong host preference when given a choice. Theory suggests that such a pattern is possible, but only under conditions of competition for the resource. In the present study the attachment rates of the two copepods were studied experimentally under various conditions of competition, infectious dose and number of available hosts. The results suggest a greater sensitivity to competition for the generalist species L. europaensis than for the specialist L. thompsoni, which is in agreement with theoretical predictions. (+info)
Polygyny, mate-guarding, and posthumous fertilization as alternative male mating strategies.
(10/698)
Alternative male mating strategies within populations are thought to be evolutionarily stable because different behaviors allow each male type to successfully gain access to females. Although alternative male strategies are widespread among animals, quantitative evidence for the success of discrete male strategies is available for only a few systems. We use nuclear microsatellites to estimate the paternity rates of three male lizard strategies previously modeled as a rock-paper-scissors game. Each strategy has strengths that allow it to outcompete one morph, and weaknesses that leave it vulnerable to the strategy of another. Blue-throated males mate-guard their females and avoid cuckoldry by yellow-throated "sneaker" males, but mate-guarding is ineffective against aggressive orange-throated neighbors. The ultradominant orange-throated males are highly polygynous and maintain large territories; they overpower blue-throated neighbors and cosire offspring with their females, but are often cuckolded by yellow-throated males. Finally, yellow-throated sneaker males sire offspring via secretive copulations and often share paternity of offspring within a female's clutch. Sneaker males sire more offspring posthumously, indicating that sperm competition may be an important component of their strategy. (+info)
Genomic imprinting, sibling solidairity and the logic of collective action.
(11/698)
Genomic imprinting has been proposed to evolve when a gene's expression has fitness consequences for individuals with different coefficients of matrilineal and patrilineal relatedness, especially in the context of competition between offspring for maternal resources. Previous models have focused on pre-emptive hierarchies, where conflict arises with respect to resource allocation between present and future offspring. Here we present a model in which imprinting arises from scramble competition within litters. The model predicts paternal-specific expression of a gene that increases an offspring's fractional share of resources but reduces the size of the resource pool, and maternal-specific expression of a gene with opposite effects. These predictions parallel the observation in economic models that individuals tend to underprovide public goods, and that the magnitude of this shortfall increases with the number of individuals in the group. Maternally derived alleles are more willing than their paternally derived counterparts to contribute to public goods because they have a smaller effective group size. (+info)
Problems with primate sex ratios.
(12/698)
Birth sex ratios of baboons in Gombe National Park, Tanzania, show an overall male bias of ca. 20%, but there is no obvious explanation for this trend. Individual females did not alter their sex ratios according to persistent levels of local resource competition. Sex ratios showed an unexpected relationship between age and rank: subordinate females had more sons when they were young; dominant females had more sons when they were old. The sex ratio of low-ranking females also varied with the severity of environmental conditions during pregnancy. Our findings suggest that mammalian sex ratios might be the product of more complex processes than is generally recognized or that sex-determining mechanisms impose sufficient constraints to prevent adaptive variation in all contexts. (+info)
Scramble in behaviour and ecology.
(13/698)
Nicholson's distinction between 'scramble' and 'contest' modes of competition has received widespread attention in ecology and in behaviour, though the emphasis has been different between the two disciplines. In ecology the focus has been on the effects on population; in behavioural ecology the focus has been on the consequences at the individual level. This paper reviews and develops a theory of scramble competition at the individual level, deriving a general evolutionarily stable strategy (ESS) for individual scramble expenditure in a patchy habitat in which individuals compete in local groups for available resources, and examines two population consequences. The critical parameter determining the relationship between individual scramble expenditure and the number of competitors in a patch is the expected resource per capita. If resource input, R, to a patch is constant and independent of the number of competitors, n, then as the number of competitors increases, the per-capita resources declines as R/n, and the ESS scramble level declines (in proportion to (n-1)/n2). However, if the resource input to a patch is positively related to the number of competitors in the patch, scramble expenditure may increase with the number of competitors. In the case where the per-capita resource input stays constant (i.e. R(n) = Rn), the scramble level increases with competitor number (in proportion to (n-1) /n). There are plausible ecological reasons why either of these extreme limits may be approached in nature, making it important to ascertain the relationship between R and n before predicting individual scramble expenditure. For example, resource input may be constant when groups of competitors are constrained to remain together in given patches, and constant per-capita resources may be approached when ideal-free foraging rules apply. However, in the latter case, scramble expenditure must be accounted for in determining the ideal-free distribution. An analysis shows that this leads to 'undermatching', i.e. the ratio of numbers of competitors for good/bad patches becomes progressively less than the ratio of input rates for good/bad patches as the difference between the good and bad patches increases. A second population consequence of the scramble ESS relates to the fact that scrambles may dramatically affect fitness. The per-capita gain in energy can be reduced by a factor of up to 1/n as a result of scramble expenditure, potentially reducing realized population size to as little as the square root of the maximum potential carrying capacity, though reasons are given why such large reductions are unlikely. (+info)
Male-male competition and parental care in collared flycatchers (Ficedula albicollis): an experiment controlling for differences in territory quality.
(14/698)
Females are known to benefit from mate choice in several different ways but the relationship between these benefits has received little attention. The quality of resources provided by males, such as nest sites, and paternal care are often assumed to covary positively However, because the location of the nest affects the cost of parental care, these two benefits from mate choice can easily be confounded. To investigate the provisioning ability of successful competitors while controlling for differences in territory quality we removed early-settled pairs of collared flycatchers (Ficedula albicollis) and allowed replacement by later-arriving males or floaters (i.e.'poor competitors'). A control group of early-settled males (i.e. 'good competitors') had their females removed. Females paired to good competitors enjoyed a significantly higher reproductive success and tended to receive more parental assistance from their mates compared with females mated to poor competitors. Thus, some males seem able not only to compete successfully over resources but also to feed their offspring at a relatively higher rate. An alternative explanation, that poor competitors invested less in offspring quality in response to a lower share of paternity, could be rejected. The rate of extra-pair paternity did not differ between the two treatment groups. Our results suggest that male- male competition can sometimes facilitate female choice of superior care-givers. Thus, a female's benefit from choosing a competitive male may not be restricted to the quality of the resource he defends but can also include superior paternal care. (+info)
Body composition changes in female bodybuilders during preparation for competition.
(15/698)
OBJECTIVE: To determine anthropometric and body composition changes in female bodybuilders during preparation for competition. DESIGN: There was an attempt to match subjects in the control and experimental groups for height and percentage body fat (%BF) for the initial test of this longitudinal study. SUBJECTS: Five competitive bodybuilders (-X +/- s.d.: 35.3 +/- 5.7 y; 167.3 +/- 3.7 cm; 66.38 +/- 6.30 kg; 18.3 +/- 3.5 %BF) and five athletic females (-X +/- s.d.: 30.9 +/- 13.0 y; 166.9 +/- 3.9 cm; 55.94 +/- 3.59 kg; 19.1 +/- 3.3 %BF) were recruited from advertisements in a bodybuilding newsletter and placed on sports centre noticeboards. INTERVENTIONS: The following measurements were conducted 12 weeks, 6 weeks and 3-5 d before the bodybuilders' competitions: anthropometric profile, body density by underwater weighing, total body water via deuterium dilution and bone mineral mass from a dual-energy X-ray absorptiometry scan. A combination of the last three measurements enabled the %BF to the determined by a four compartment model. RESULTS: A significant (P < or = 0.001) 5.80 kg body mass loss by the bodybuilders as they prepared for competition was primarily due to a reduction in fat mass (FM; -4.42 kg; 76.2%) as opposed to fat-free mass (FFM; -1.38 kg; 23.8%). The decreases in body mass and FM over the final 6 weeks were greater than those over the first 6 weeks. Their %BF decreased (P < 0.001) from 18.3 to 12.7, whereas the values for the control group remained essentially unchanged at 19.1-19.6 %BF. These body composition changes by the bodybuilders were accompanied by a significant decline (P < 0.001) of 25.5 mm (76.3-50.8 mm) in the sum of eight skinfold thicknesses (triceps + subscapular + biceps + iliac crest + supraspinale + abdominal + front thigh + medial calf). CONCLUSIONS: Although the bodybuilders presented with low %BFs at the start of the experiment, they still significantly decreased their body mass during the 12 week preparation for competition and most of this loss was due to a reduction in FM as opposed to FFM. (+info)
The evolution of bourgeois, parasitic, and cooperative reproductive behaviors in fishes.
(16/698)
Among vertebrate classes, fishes exhibit by far the greatest variability in competitive and cooperative behaviors in male reproduction. Scramble competition between reproductive males is one possibility. Another possibility occurs when resources, mates, or locations can be monopolized, in which case males may invest in primary access to fertilizations by adopting a "bourgeois" strategy, or they may employ alternative mating tactics to evade the reproductive monopoly of other males. Adaptations in morphology, physiology, and behavior to bourgeois and alternative phenotypes are highly divergent. Here I review the functional characteristics that differ between bourgeois and parasitic phenotypes, and discuss the variability of alternative reproductive tactics at the levels of plasticity, determination, and selection. Examples will illustrate the importance of ecology, and will suggest that variation in reproductive tactics is largely adaptive. Behavioral solutions to competition for mates and fertilizations often involve agonistic behavior and conflict, but also cooperation among competitors (e.g., when subordinate males pay a price to bourgeois males for gaining access to fertilizable eggs). Application of molecular genetic tools has helped to uncover intricate sexual and social relationships in various fish species, including species that display some of the most complex reproductive and social patterns known among the vertebrates. (+info)