intrasexual selection

It basically states that mate preferences in one sex establish domains of mate competition in the opposite sex, with the end-goal being to increase one’s own mate value while decreasing that of a competitor. A significant amount of this variation was explained by rainfall and lunar phase, suggesting that the sexual activity of both sexes is synchronized by these climatic variables. Under these conditions, there was no relationship evident between male body mass and amplectant position. Some species have therefore developed methods to prevent this.

At high male density, fights were generally instigated when males roaming the chorus inadvertently contacted, or attempted to amplex, other roaming males. After each recording, male density was determined within the area monitored by randomly placing a 1-m2 quadrat in the aggregation and counting the number of males within it. Male density and water temperature independently explained a significant proportion of the variation in the frequencyof agonistic interactions between males (multiple regression: r 2 = 0.36, F2,139 = 38.1, p <.001). Male density had a significant negative effect upon duration males spent calling relative to duration spent silent (coeff = −6.20 ± 2.32, t = 2.68, p =.01), whereas body mass had a significant positive effect upon duration males spent calling relative to duration spent silent (coeff = 11.85 ± 3.63, t = 3.26, p =.002). In many of these taxa, competition between males for mates is intense, and group spawning has been interpreted as a strategy used by males to secure fertilizations without having attracted a female through advertisement (D'Orgeix and Turner, 1995; Fukuyama, 1991; Jennions et al., 1992; Jennions and Passmore, 1993; Kusano et al., 1991; Pyburn, 1970; Roberts, 1994). The number of females detected in a chorus was also significantly influenced by climatic conditions (multiple-regression analysis: r2 =.26, F3,43 = 4.85, p <.01). Find out more about the author, hover over the picture above for more information and links. The investigation was conducted in a natural breeding population near Kangaroo Gully 30 km southeast of Perth, Western Australia. the male against male competition for females. Consequently, when competition becomes too intense, males often abandon calling for alternative noncalling mating tactics.

15 no. Since men looking for a long-term partner value fidelity, women also try to decrease the mate value of another woman by calling her “promiscuous” or mentioning that “she’s had many partners in the past” and therefore will not make a good long-term mate. After interaction, males were collected and weighed (to the nearest 0.1 g) by using a digital balance. It has also been observed that fights between males are common and that a proportion of males within a chorus do not call but either remain motionless in close association with a caller or roam the breeding area (Byrne, 2002b). To test the hypothesis that group spawnings are the outcome of noncalling (satellite or searching) males joining mating pairs, females were detected by randomly traversing the study site.

For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Because the number of frogs present around a mating could change with the movement of females and males through the chorus, it was necessary to make counts quickly. With increasing male density, males allocated less time to calling and more time to satellite behavior or roaming (searching) the chorus. However, these call stations are usually only defended for a few nights because they either become flooded after heavy rainfall or they dry out between rain events (Byrne, 2002b).

Since men primarily value physical beauty, women compete with each other to appear more beautiful. These predictions are based on the assumption that variation in OSR and male density are correlated with variation in the intensity of intrasexual selection. But there’s also another way to better one’s own chances of reproductive success i.e. In this way the estimate of OSR and male density was made close to the time when spawning commenced. Once a male has mated with a female, it is still possible for the sperm of another male to fertilise the female.

Your comments are welcomed! However, the proportion of group spawnings arising from female choice versus male interception at low versus high male density was significantly different (low male density: choice = 13/18, high male density; choice = 6/19, Fisher's Exact test: n = 37 group spawnings, p =.02). Individual females are attracted to the vocalizations of a specific male (Smith and Roberts, 2003a) and typically initiate amplexus (sexual embrace of a female by a male) by moving under a caller between the arms or along the side between the arms and legs (Byrne, 2002b). For both pair and group spawnings, Fisher's Exact tests were used to determine whether (1) there were significant differences in the proportions of calling versus noncalling males involved in spawns that occurred at low and high male density (defined above), and (2) whether there were significant differences in whether spawns resulted from choice or were forced at low and high male density. Click here to ensure you're always up to date an receive regular articles and updates via email!

The eggs are large and generally deposited in discrete clumps at the site where a male advertises (Byrne, 2002b; Seymour and Roberts, 1995). the male against male competition for females. We also observed the events that led to 47 physical contests between males. Estimates of nightly temperature were made by averaging seven recordings taken at 2-hour intervals between 1800 and 0600 h. For analyses, average nightly male density, total number of females encountered per night, and average nightly OSR were the dependent variables and mean nightly temperature (in Celcius), days since rain (more than 3 mm), and days since full moon were the independent variables. = 0.58, t = 8.3, p = <.001; water temperature: partial corr. The proportion of spawnings arising from female choice versus male interception at low versus high male density was also significantly different (low male density: choice = 13/17; high male density: choice = 1/5, Fisher's Exact test: n = 22 pair spawnings, p =.03). Matings were scored as occurring at low or high male density (defined above). Since men primarily value physical beauty, women compete with each other to appear more beautiful. When breeding is prolonged, females have more time to choose a mate, but males can usually mate many times over a season so there are increased opportunities for mate monopolization (Sullivan et al., 1995). As the distance between competing individuals decreases, often owing to clumped distribution of resources, the encounter rate, and hence frequency of agonistic interactions, between males is likely to rise (de Boer, 1981). It is done to gain the opportunity to mate with the nearby females. In the Australian frog Crinia georgiana, matings frequently involve a single female and multiple males (group spawning). Research was supported by a Gene Rodgerson Scholarship and the Australian Research Council. However, in these species males that join pairs do not differ phenotypically from paired males, suggesting that all males use this tactic opportunistically (Halliday, 1998).


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