|Feature Article - February 2011|
|by Do-While Jones|
Some scientists think the sex lives of bedbugs help explain evolution; but it just derails an otherwise useful study.
Bedbugs have been in the news lately because there has been a bedbug epidemic in recent months. One article caught our attention because it describes a study about the relationship between sex and aging in bedbugs. In particular, the scientists were attempting to discover if having lots of sex keeps bedbugs young and, if so, how. This has practical application because, if there is a correlation, one might be able to determine exactly why this is. This could lead to the discovery of an enjoyable way to keep people younger longer!
Unfortunately, this useful scientific study got derailed by evolution. The scientists became distracted by the evolutionary conflict they discovered. Here is the abstract describing the study.
Increased female reproductive rates usually result in accelerated senescence [aging]. This correlation provides a link between the evolutionary conflict of the sexes and aging when ejaculate components elevate female reproductive rates at the cost of future reproduction. It is not clear whether this female cost is manifest as shorter lifespan or an earlier onset or a steeper rate of reproductive senescence. It also is unclear whether beneficial ejaculates release females from reproductive trade-offs and, if so, which senescence parameters are affected. We examined these issues in the bedbug, Cimex lectularius, a long-lived insect that shows reduced female lifespan as well as female reproductive senescence at the male-determined mating frequency. We demonstrate experimentally that, independently of the mating frequency, females receiving more ejaculate show increased reproductive rates and enter reproductive senescence later than females receiving less ejaculate. The rate of reproductive senescence did not differ between treatments, and reproductive rates did not predict mortality. The ejaculate effects were consistent in inter- and intra-population crosses, suggesting they have not evolved recently and are not caused by inbreeding. Our results suggest that ejaculate components compensate for the costs of elevated female reproductive rates in bedbugs by delaying the onset of reproductive senescence. Ejaculate components that are beneficial to polyandrous females could have arisen because male traits that protect the ejaculate have positive pleiotropic effects and/or because female counteradaptations to antagonistic male traits exceed the neutralization of those traits. That males influence female reproductive senescence has important consequences for trade-offs between reproduction and longevity and for studies of somatic senescence. 1
The abstract is very confusing, and not just because of the terminology! The first sentence says that having lots of babies makes a female get old faster. So, having lots of sex would seem to be a bad thing. But then, in the middle of the abstract it says, “females receiving more ejaculate show increased reproductive rates and enter reproductive senescence later than females receiving less ejaculate.” This seems to imply that females who have better sex (quantitatively) have more babies for a longer period of time, entering menopause later in life. So, having a potent sex partner seems to be a good thing. You have to actually read the article to find out what they are really saying.
Sadly, the scientists don’t seem to care about discovering if having sex makes you old or keeps you young. Instead, their obsession with the evolutionary paradigm distracts scientists from figuring out how to learn anything practical from it.
Evolutionary scientists think in terms of “the cost of sex” because the evolution of sexual reproduction makes no logical sense. So, let’s look at a few key sentences and explain the paradox that inspires them.
In polyandrous species, the male optimum for an interacting phenotype is likely to be different from the female's, potentially resulting in an “evolutionary conflict between the individuals of the two sexes” (sexual conflict). 2
In other words, contrary to the old proverb, what’s good for the goose ISN’T good for the gander. In their words,
During reproduction many interacting phenotypes occur, and sexual conflict may arise from any of these interactions, e.g, the timing or duration of mating, the re-mating rate, the female egg-laying rate, and/or offspring performance. Whenever an interacting phenotype results in net mating costs to one sex, the conflict can be resolved by trade-offs in resource allocations; these trade-offs, in turn, will disturb the existing equilibrium formed by the correlations between other interacting phenotypes. Thus, even if there are no current mating costs to females, there still may be a mosaic of coexisting interacting phenotypes that are, when measured in isolation, costly, neutral, or beneficial to one sex. 3
This is just a complicated way of saying that males want females who will have sex with them every day, and don’t care if they sleep around. Females want males who won’t get them pregnant before they are ready, and will help them raise the child for a reasonable period of time before getting them pregnant again. If they have too many children, there is a good chance the mother will die in childbirth, or will die from malnutrition trying to suckle the young. If they have too many children, none of them will get enough food and all will die.
The theory of evolution is based on the notion that individuals who produce a large number of offspring who are better suited for survival will predominate. So, there is an evolutionary conflict between males who want frequent sex and females who want sex only when they are ready to have more children. All species should have evolved to the point where they have the optimum amount of sex, producing the maximum number of offspring that they can raise; but they haven’t. Evolutionists are searching for the answer to why natural selection didn’t work out that way.
Here is another example of how the theory of evolution distracts scientists.
… several studies have found ejaculate components to be beneficial in several aspects of female reproduction, but it is not known whether such benefits evolved via sexual conflict (e.g., 4, 6, 22) or by traditional female choice. For example, females may have evolved the ability to metabolize manipulative ejaculate substances, or they may choose males that provide the largest direct benefits (e.g., nuptial gifts). In the former case, the metabolism of manipulative substances may be costly initially and so result in trade-offs in females; in the latter case, one would not necessarily expect trade-offs. 4
Let’s translate that into plain English. During sex, more than just sperm cells are transferred from the male to the female. The sperm cells are carried in a liquid that contains other chemicals (antioxidants, antibiotics, amino acids, etc.) as well. Several studies have found that these chemicals are beneficial to females.
… the ejaculates of C. lectularius have been found to contain antioxidant and antibacterial activity as well as essential amino acids. These substances all have potential fitness benefits for females. 5
Candidate traits for the reduction of somatic damage and/or trade-off release are immune effectors, antioxidants, stress-defense substances, and micronutrients in the seminal fluid. Representatives of all 4 types of compound have been found among the >100 components in the semen of bedbugs. 6
But rather than focusing on why these chemicals are beneficial, the scientists are distracted trying to figure out how the benefits evolved. Did they evolve through sexual conflict, or female choice (where that choice might be based on which males give them the best presents)? They even speculate that, by chance, some females might have been lucky enough to have a mutation that can metabolize [use] those chemicals to their advantage.
We did not find the trade-offs predicted by life-history theory and evolutionary models of aging, because increased reproductive rates early in life did not result in earlier reproductive senescence. It is possible that ejaculate components either directly reduce aging damage in the female or release females from trade-offs. 7
So, what is their conclusion?
In conclusion, our data show an important male effect on female fitness and aging patterns and demonstrate that beneficial male postcopulatory traits can evolve alongside harmful male traits. 8
Despite the fact that males evolved the harmful desire to have too much sex, some beneficial traits must also have evolved to cancel out their selfish lust. Here is their fanciful explanation:
That male traits evolve which are beneficial to females may seem surprising in a species that has a high mating frequency that is controlled by males and has last-male sperm precedence: Any newly evolving beneficial ejaculate substance favors competing males that mate subsequently. We envisage 2 possible routes by which such beneficial male effects may have arisen. First, ejaculate traits originally may have had a negative effect on females, as is currently observed for some Drosophila proteins. Consequently, female traits, such as the ability to metabolize ejaculate substances, may be selected for in females. Although the evolution of such female counteradaptations currently is believed merely to neutralize male harm, it may have progressed in bedbugs to benefit females. Alternatively, it is possible that male–male competition does not always have negative side effects on females (pleiotropic sexual antagonism). Instead it may result in male traits that evolved to protect the ejaculate (ejaculate defense traits) having a positive pleiotropic effect on the female such as the antioxidant and the antibacterial activity found in bedbug ejaculates. 9
They can’t explain how this could have evolved because it didn’t evolve. They are just trying to guess ways it could have evolved. To admit that it could not have evolved opens the door to the possibility that there is some design.
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Reinhardt, et al., PNAS, December 22, 2009, “Ejaculate components delay reproductive senescence while elevating female reproductive rate in an insect”, pages 21743-7, https://www.pnas.org/content/106/51/21743