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Study challenges theory that sexual conflict is a driver of speciation


Male diving beetle Graphoderus zonatus/
© Niels Sloth/Biopix (Eurekalert)

From ScienceDaily:

In nature, males eager attempts to mate with females can be so extreme that they will harm females. Such negative impact of mating interactions has been suggested to promote the emergence of new species under some circumstances. Surprisingly, one type of diving beetle species now show that this conflict between the sexes can instead lead to an evolutionary standstill in which mating enhancing traits in males and counter-adaptations in females prevent the formation of new species…

In many diving beetles, males are equipped with crafted suction cups on their front legs used to attach on the back of females during mating. This grasping ability has become so effective that females can be harmed under high mating pressure, lasting up to many hours for each mating attempt. As a consequence, some females have developed a more rough back that becomes more difficult for the male to attach to.

“Sometimes nature creates designs that goes beyond our imagination” says Kaj Sand-Jensen, a professor at the University of Copenhagen’s Freshwater Biology Section. “It is truly fascinating how the constant quest for mating success has shaped the front legs of these beetles into flawless suction cups.” …

The outcome is a situation with no consistent long-term advantage for any single female type. Instead, populations move towards a state where both smooth and granulated females are equally abundant and thereby minimizing the mating pressure on a specific female type. Hence, the diving beetles are kept in an evolutionary limbo and the two type of females are maintained by the ongoing and intense mating harassment from the males.

Well, nature is a clever old bird then. But how do we know that the beetles haven’t had this distribution of female types for a long time?

“This study will be an important baseline for developing a better understanding of the evolutionary outcome of sexual conflict in natural populations” says Erik Svensson, a professor at Lund University, who has studied the evolutionary consequences of such female variation for more than 20 years.” Paper.(open access) – Lars Lønsmann Iversen, Erik I. Svensson, Søren Thromsholdt Christensen, Johannes Bergsten, Kaj Sand-Jensen. Sexual conflict and intrasexual polymorphism promote assortative mating and halt population differentiation. Proceedings of the Royal Society B: Biological Sciences, 2019; 286 (1899): 20190251 DOI: 10.1098/rspb.2019.0251 More.

It has been thought that females’ efforts to escape males “could initiate the evolution of new species”:

“Here, we document an alternative outcome: that sexual conflict instead prevents populations from diverging from each other and becoming new species.” …

“The story is more complicated than we previously thought. We now know that sexual conflict can prevent population divergence and halt speciation.”Nick Carne, “Water beetles mate themselves to an evolutionary standstill” at Cosmos Magazine

Sexual conflict, and sexual selection in general could conceivably turn out to be so “complicated” that, while it usually makes a difference when it occurs, it does not point in any particular direction for evolution.

That just adds to the problems with the concept of speciation.

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See also: Microbes can make evolution work faster for their hosts Okay, but then aren’t the microorganisms the unit of selection rather than the host’s genes? This might work for some adaptations to habitats (they describe one), but it won’t be Darwinism.

Can sex explain evolution?


A physicist looks at biology’s problem of “speciation” in humans


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