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Saturday, March 8, 2008

Why do Female Mates Multiply?

After the greatest act of life(SEX), He questions his She...

He asks-"Darling why do u need another mate when am there?"

She says-"Honey for better "TRADE_OFF"...I get better partners... better genes... better kids.. !!"

Thats the story in the animal kingdom. The monopoly of feminines, the Art of Polygamy... the search for more life...!!

Something drags me to this topic of sex in ecology. Infact sex forms the basis of life. Had their been no sex, there would have been no life with diversity and what one could have been seeing would have been perhaps the "CLONES".

The Darwinian principle of Natural Selection forms a vital and prime-facial aspect of Origin of life and Selection by Nature, Fitness and blah blah. Talk to any ecologist or evloutionary biologist, one will hear these profound terminologies. I am sure about that words at least though am not an evolutionary ecologist nor a hard core ecologist. But I am an ecologist who thinks of it very often and so this write up goes.

Literature and works of many papers fascinated me to this field infact and not to forget one man "Eric Charnov"... recently I attended a talk in CES, IISc about the evolution of intelligence and creativity in human" by Geoffery Miller... the writer of two books " he Mating Mind and "The Mating Intelligence".

I suppose that forms an essential part of Behavioural Ecologia also. Infact why should it not be, when u get ur better genes to be passed on to your generations and so u can proudly say" Thats my gene..."

Mate choice by males has been recognized at least since Darwin's time, but its phylogenetic distribution and effect on the evolution of female phenotypes remain poorly known. Moreover, the relative importance of factors thought to underlie the evolution of male mate choice (especially parental investment and mate quality variance) is still unresolved. Here I synthesize the empirical evidence and theory pertaining to the evolution of male mate choice and sex role reversal in insects, and examine the potential for male mating preferences to generate sexual selection on female phenotypes. Although male mate choice has received relatively little empirical study, the available evidence suggests that it is widespread among insects (and other animals). In addition to 'precopulatory' male mate choice, some insects exhibit 'cryptic' male mate choice, varying the amount of resources allocated to mating on the basis of female mate quality.

As predicted by theory, the most commonly observed male mating preferences are those that tend to maximize a male's expected fertilization success from each mating. Such preferences tend to favour female phenotypes associated with high fecundity or reduced sperm competition intensity. Among insect species there is wide variation in mechanisms used by males to assess female mate quality, some of which (e.g. probing, antennating or repeatedly mounting the female) may be difficult to distinguish from copulatory courtship. According to theory, selection for male choosiness is an increasing function of mate quality variance and those reproductive costs that reduce, with each mating, the number of subsequent matings that a male can perform ('mating investment') Conversely, choosiness is constrained by the costs of mate search and assessment, in combination with the accuracy of assessment of potential mates and of the distribution of mate qualities. Stronger selection for male choosiness may also be expected in systems where female fitness increases with each copulation than in systems where female fitness peaks at a small number of matings. This theoretical framework is consistent with most of the empirical evidence. Furthermore, a variety of observed male mating preferences have the potential to exert sexual selection on female phenotypes. However, because male insects typically choose females based on phenotypic indicators of fecundity such as body size, and these are usually amenable to direct visual or tactile assessment, male mate choice often tends to reinforce stronger vectors of fecundity or viability selection, and seldom results in the evolution of female display traits. Research on orthopterans has shown that complete sex role reversal (i.e. males choosy, females competitive) can occur when male parental investment limits female fecundity and reduces the potential rate of reproduction of males sufficiently to produce a female-biased operational sex ratio. By contrast, many systems exhibiting partial sex role reversal (i.e. males choosy and competitive) are not associated with elevated levels of male parental investment, reduced male reproductive rates, or reduced male bias in the operational sex ratio. Instead, large female mate quality variance resulting from factors such as strong last-male sperm precedence or large variance in female fecundity may select for both male choosiness and competitiveness in such systems. Thus, partial and complete sex role reversal do not merely represent different points along a continuum of increasing male parental investment, but may evolve via different evolutionary pathways.

After reading a chapter in the Molecular Ecology book by Bevee, I felt the reality inanimal's world for having more mates. It's nevertheless due to the potential benefits that females may gain from mating more than once in a single reproductive cycle. The relationship between non-genetic and genetic benefits is briefly explored. May be multiple mating aids for purely non-genetic benefits which is unlikely as it invariably leads to the possibility of genetic benefits as well. There are identifying cases where females use pre-copulatory cues to identify mates prior to remating. In the simplest case, females remate because they identify a superior mate and 'trade up' genetically.

The main evidence for this process comes from extra-pair copulation in birds. Second, we note other cases where pre-copulatory cues may be less reliable and females mate with several males to promote post-copulatory mechanisms that bias paternity. Although a distinction is drawn between sperm competition and cryptic female choice, but the genetic benefits to polyandry in terms of producing more viable or sexually attractive offspring do not depend on the exact mechanism that leads to biased paternity. Post-copulatory mechanisms of paternity biasing may: (1) reduce genetic incompatibility between male and female genetic contributions to offspring; (2) increase offspring viability if there is a positive correlation between traits favoured post-copulation and those that improve performance under natural selection; (3) increase the ability of sons to gain paternity when they mate with polyandrous females. A third possibility is that genetic diversity among offspring is directly favoured. This can be due to bet-hedging (due to mate assessment errors or temporal fluctuations in the environment), beneficial interactions between less related siblings or the opportunity to preferentially fertilise eggs with sperm of a specific genotype drawn from a range of stored sperm depending on prevailing environmental conditions. Examples are more profound in social insects which form the concrete basis for the role of genetic diversity among progeny in elevating fitness. We can conclude that post-copulatory mechanisms provide a more reliable way of selecting a genetically compatible mate than pre-copulatory mate choice. Some of the best evidence for cryptic female choice by sperm selection is due to selection of more compatible sperm. One can thus eventualize the fact that multiple mating increases offspring fitness via genetic gains. Not the least the role of multiple mating in promoting assortative fertilization and increasing reproductive isolation between populations may help us to understand sympatric speciation.


Reena said...

what an article.. feel like watching geographic channel

Jojo said...

interesting article, please keep posting.

Amrita Tripathy said...

thanx reena n jojo... keep surfing..

chaitra said...

your highness lady tripathy(adressing requested by her highness) , the best "photos telling stories" that i have seen!! ...:)

anupam said...

This was smtn straight out of a genious ecologist's mind. A thorough package!! Hats off!! Kp us enlighted in future as well!!

anupam said...

This was smtn straight out of an ecologist's mind. A thorough n well packaged piece. Hats off!! Pls keep us enlightened in future as well!! Warm wishes!