Hello and welcome to your Daily Fun Fact From Flora ,

Today is your favourite day of the week — it’s Wednesday’s What Was the World Doing Ages and Ages Ago

So let’s have a recap of what we"ve seen so far this calendar year.

We saw life begin on the 25th February. Photosynthesis started on the 28th March. Multicellular organisms appeared on the 16th August.

NOW we have the evolution of sexual reproduction on the 17th September.

Phwoar this year is just flying by.

We"ve already discussed the evolutionary confusion surrounding sexual reproduction and why it might have evolved (I jumped the gun a bit there oops) so I"m going to take you on a slightly different exploration of sexual reproduction. And that — is the role of sexual selection.

Now sexual selection is a fundamental component of sexual reproduction.

If you’re gonna mingle ya genes — you gotta make sure they’re a good “un.

This is often seen in the form of exaggerated displays and courtship behaviours in males. But these are bit odd, because they seem to be totally inconsistent

with

COME DANCE WITH ME DEBORAH ** Why would you want all these traits that are actually very costly and difficult to maintain. I mean think of the peacock — lugging all those feathers around is going to make it difficult to find food and run away from predators.

In a slightly more niche example, male tungara frogs attract their lovely lady friends using “chuck” calls. These calls are actually heard by fringe-eared bats which use them to find males that they can then eat. Hmmm. Sexy — yes. But not so good when trying not to get eaten.

Plus they look real funny.

I know you’re now dying to know what this “chuck” sounds like now but I"m afraid this is the most accurate representation I have:

So why do males have these really costly traits? Well — sexual selection operates on the variation in individual reproductive success. The more variation there is, the more intense the selection is on the traits that can be used to measure that reproductive success.

This leads to the evolution of traits that signal some sort of competitive advantage in reproduction — even if they have these big costs.

Now I know what you’re thinking. Flora — a shouting frog isn’t going to tell you how “good” a mate it is.

Except that it kind of is.

There’s an argument called the “good genes” hypothesis that basically says — because these traits are so costly to produce, only the good males will be able to live with them without dying or being eaten.

Because, in any environment, there is a limited number of resources there is a trade-off in males between their investment in these snazzy, sexy traits and important things like movingand eatingand breathing.

We can see this is stalk-eyed flies. Their eyes are found at the end of elongated lobes and females just love a male with a wider eye span. They start with normal looking eyes and when they reach maturity the males will inflate their lobes — forcing their eyes outward kind of like this:

I KNOW ISN"T THAT NUTS.

In experiments, when you feed males a poor diet their eye-spans are much less than males that are fed nutrient-rich diets. Therefore, in a poor-quality environment females can use the eye-span as a proxy for how good the male is at surviving and finding food in the habitat. The males that are really strongly affected by that harsh environment can be easily identified and ignored.

Now these will only work if they are honest signals. A stalk-eyed fly cannot control its eye-span — only it’s nutritional intake can.

If we go back to the example of the frogs, only larger males can make the deep “chucks” that the females love so much. That’s how they know a male is a good “un. If males could make those deep “chucks” without being larger the system would break down. Females would catch on that the call was no longer a good indicator of male fitness and would stop listening.

Sometimes these traits aren’t about nutrition but are about immuno-competence instead. Testosterone determines the expression of male sexual traits in a lot of species, butalso handicaps their immune systems. Therefore, the ones that express the condition most strongly need to be in tip top shape (genetically speaking) to allow for that.

Sometimes these traits are even preferred when they are artificially made more extreme. We can see this in long-tailed widow birds. These bad boys are a strongly sexually dimorphic species — meaning that the males and females look REALLY different. Males have a really elongated tail that they display to females during courtship.

Mmmmm dat tail is LONG.

So what some researchers did is they investigated whether females like males with longer tails. To test this they used four different treatments:

Tail is clippedTail is elongated Control 1 (males had tails clipped and put back at the same length) Control 2 (males were handled without altering the tail)

They then measured female preference by seeing how many nests females built in the territories of these different males. Long story short — females went NUTS for the males with super-extra-long tails.

Pretty nuts. So basically evolution is likely to keep pushing those tails longer and longer because the females thing it’s sexy.

Hope you enjoyed this little foray into some more sexy topics.

Lots of love,

Flora