Abstract
Life history and sexual selection in mating evolution has continued to draw much interest from researchers. It is still not very clear whether sexual selection prevents or helps the mating behavior in order to adapt to modern environments. In a recent study by Wigby and Chapman (2006) behaviors such as the time it takes for mating, the probability of mating and duration for mating were the behaviors that were investigated in the same group of populations of seed beetles callosobruchus maculates. This study reviews some of the research done on this subject. In deed, there are many factors, which contribute to sexual selection. These in turn affect the life history of an organism. We shall try to know how these factors are interrelated, and how they affect the overall reproduction cycle of an organism.
In this research, the behavior was followed by the selection of life-history selection, which is young versus old reproduction that falls under sexual selection of monogamy and polygamy. In life history selection, the old females seemed to have slow rate of mating than the younger ones but sexual conflict under polygamy can slow down the adaptive life history evolution. It was found that life history selection resulted in changes in mating behavior but did not have any overall effect on sexual selection (Martin & Hosken 2003).
Populations that were treated for late reproduction also had equal reduced mating probability in early life despite of mating system. However, the life history selection in young life supported high mating probability in polygamy selection than monogamy selection (Chenoweth, Rundle & Blows 2008).
Even though the mating system played a great role in male and female evolution, the absence of sexual selection did not make any impact on the adaptation of evolution of mating behavior. The research also confirms that the relation between sexual selection and life history selection can either increase or decrease reproductive variance which is reliant on the ecological perspective (Martin et al 2003).
The evolution of mating behavior in replicate populations of C. maculates was investigated by giving the beetles chance to breed either young or old in their lifetime (young and old lines). Sexual selection and sexual conflict were stopped during the middle lines in each life history process. This was achieved by introducing monogamy where other lines were treated as polygamous where they could mate randomly for sexual selection. An experimental evolution was created which allowed in testing the contribution of sexual evolution of mating behavior under divergent life history selection. It is predicted that the beetles in young lines will have limited time for mating and laying eggs because of their rapid mating behavior as compared to the old lines. (Nick, Smiseth, and Kölliker 2012).
However, the old lines that have delayed mating and have delayed egg lying are predicted to be beneficial because the eggs that are produced early in life would be of no use to the next generation. Different selection models are predicted to have different results in relation to sexual selection (Wigby and Chapman 2006).
The mating of beetles that was selected from good gene model is predicted to have rapid evolution of mating behavior and oviposition in young polygamy lines. Likewise it has been predicted that sexual conflict from delayed mating will be stronger in old polygamy lines. The females will be chosen for delayed mating and oviposition and males will be selected for early mating and oviposition. As a result, the old polygamy lines might have strong sexual conflict, which can be shown in clear, shown in clear patterns in sympatric vs. allopatric crosses (Wigby et al 2006).
The test for divergence in reproductive traits was conducted by comparing allopatric mating trials within each of the mating system and life history selection. This helped to test whether the co evolution in both males and females proceeded in a similar manner in mating system (monogamous and polygamous population). The test also helped provide a detailed test of the ‘sexual conflict as engine of speciation’ hypothesis (Wigby et al 2006). The beetles in this experiment were taken from an Australian population in 2003. They were reared in laboratory from September 2006 for half a year with 500 beetles per generation and it was put at 30 degree C and 200 gram of organic dung beans (Fricke 2006).
The experiment was conducted to investigate the roles of life history and sexual selection in the adaptive evolution of mating behavior and how the male and female co evolution helps in reproductive isolation. A test was run and the result of sympatric mating trials had higher mating success in young lines and old lines. No effect on mating system was seen and there was no interaction between mating system and life history regime for mating success. No effects were seen of any of the fixed factors on latency to mating and copulation duration (Chenoweth et al 2008). The test was also conducted to see if the experiment supports the hypothesis that sexual conflict may be a powerful engine of speciation. The data shows that although the male and female co evolution in the experiment showed different mating patterns in sympatric and allopatric crosses, the response was more or less the opposite in old and young lines, where mating frequency is lower in allopatric and sympatric mating is followed under polygamy (Stephen and Wade 2003).Hence, the above results do not support the hypothesis.
The topic on why two species of seed beetles differed in their response to selection of age at reproduction was discussed and from the result the study shows that the basic difference on the fact that ‘old’ A. obtectus lines were selected without egg-laying substrate (beans) (Gavrilets 2000) whereas, the C. maculatus lines were selected in the presence of the egg-laying substrate in allopatric mating trials, young lines had higher mating success like in the sympatric trials.
However, there was not any effect in mating system on the mating success. There was an interaction between mating system and life history regime. No effects were seen of any of the fixed factors on latency to mating and copulation duration. However, there were some interactions on mating system and life history regime for copulation duration (Andersson 1994).
It was found that the population of beetles that were selected for the first reproduction had more frequent mating than that of the beetles that were selected for late reproduction. However, sexual selection had a little contribution even after the having an evidence that male and female co evolution acted in a different way in monogamous and polygamous populations. This can help to verify the variances in the result of earlier studies and is helpful for finding the path for future research. The study shows that mating behavior has a higher chance to be affected by sexual selection (Martin et al 2003).
The following results cannot be attributed to weak sexual selection for a few reasons that is due to high population density, were females are harassed by males most of the time. The sexual selection treatment had a significant effect on female ne fitness. This could verify that sexual conflict was present in the polygamy treatment but it was not present in the monogamy treatment (Gavrilets 2000). According to the design of allopatric mating, male and female co evolution acted differently in monogamy and polygamy treatments. It was also noted that mating behavior sand other traits had a rapid response to age selection at reproduction suggesting a genetic variation for such traits in the source population Chenoweth et al. 2008).
The study also shows that the interaction between sexual selection and life-history selection can result in either increased or decreased reproductive divergence depending on the ecological context. Although there is a huge dedication and interest in the subject of evolution of life history and sexual selection in the mating behavior and reproductive isolation, the field requires more experimental evidences that can manipulate both fields in separate ways to get a general idea for conclusion( Blows 2002, Chenoweth et al. 2008).However, according to the studies ,life histories selection can play more important role than sexual selection in the evolution of mating behavior at the early stage of adaptation.
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