Unfalsifiable Hypotheses

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Since March, I’ve been wandering around the Panamanian forest, watching birds and asking questions, hoping to come up with a few queries that are interesting and novel enough to be worthy of doctoral investigation.

The trouble with so many of my questions is that the hypotheses they generate are rather difficult to test. Wild animals–particularly volant vertebrates–come with certain observational and experimental limits. Additionally, due to a youth steeped in too much religion and literature, some of my hypotheses smack of just-so stories, ad hoc fallacies, and unfalsifiability.

Karl Popper. Photograph from Wikimedia Commons.

Sir Karl Popper. Photograph from Wikimedia Commons.

The philosopher Karl Popper is attributed with articulating and promulgating Science’s distaste for unfalsifiable hypotheses. In The Logic of Scientific Discovery, Karl Popper asserted that if a statement is to be scientific, it must be falsifiable: you must to be able to disprove it. If you can’t disprove it, than even most rational and coherent hypothesis can be considered a well-informed folkloric explanation.

In honor of all my reasonable, well-informed hypotheses that are tragically untestable–or at least, unreasonably difficult to test–I’d like to offer some unreasonable, ill-informed hypotheses as alternatives to standing theory.

1 – Lek Love

In many manakin species (Family: Pipridae), males form leks where they perform elaborate displays for passing females, with one or two males taking the vast majority of the mating success. Most studies on how these systems evolved and are maintained focus on males clustering around resources [1] or the more attractive males [2] to increase their access to females.

In my alternative hypothesis, male manakins do not form leks and dance for females. I believe that all male manakins are actually gay, and leks are their equivalents of dance clubs. They only copulate with the females to get them to leave.

Girl walks into a gay bar… clockwise from the top: Golden-crowned, Blue-capped, Lance-tailed, nondescript female, White-ruffed, and Red-capped Manakins

Straight girl walks into a gay bar… clockwise from the top: Golden-collared, Blue-crowned, Lance-tailed, nondescript female, White-ruffed, and Red-capped Manakins. Click on the links to see neat videos of each species’ courtship display.*

2 – Why Wag?

Motmots (Family: Motmotidae) are really nifty neotropical family of birds. When you approach a motmot, they’ll wag their pendulous tails from side-to-side like a feathered metronome, as in the video below. I find this behavior deeply charming, and I am tickled pink each time I catch a motmot tick-tocking its tail.

Current hypothesis holds that motmots wag their tails as a pursuit-deterrent against predators [3]. When a motmot twitches its tail, it is signaling its awareness to its hunter in an “I-see-you” of sorts. Its ambush foiled, the predator doesn’t waste its energy chasing the motmot, and the motmot wastes no energy being chased.

This explanation is grossly unsatisfying. I believe they wag their tails in an attempt to hypnotize unwary birdwatchers and implant suggestions for embarrassing social behaviors, triggered by alcohol. I’m certain this has happened to me twice since I arrived in Panamá, and is culpable for my untoward comportment at parties. Er-hem.

An inherently friendly Rufous Motmot (Baryphthengus martii).

An deceptively friendly Rufous Motmot (Baryphthengus martii), about to exert its mind control powers.

3 – The Cling of the Cocklebur

Cockleburs (Xanthium ssp.) are often cited as an example of animal-based (zoochorous) seed dispersal. Their tiny hooks grasp the fur and feathers to be taken way from their parent plants.

This is what the esteemed Justice Antonin Scalia** would call “a compendium of cockamamie“…or should we say cockle-mamie? Cockleburs do not hitch rides on your hiking shoes to disperse. Cockleburs are plagued by loneliness, and grab your socks just to feel close to someone.

Let them into your heart. Let them into your home. LET THEM IN.

Let them into your heart. Let them into your home.
LET THEM IN.

4 – Aposematism Á La Mode

Perhaps more than any other ecotype, the tropics are chock-a-block full of poisonous nasties. From snakes to frogs to caterpillars , there are countless things that produce toxins which–if they don’t kill you–will at least severely discomfort you.

Heliconius butterflies may look like candy, but carry toxins from plants they ate in their youth. Image from Wikimedia Commons

Heliconius butterflies, with their candy coloration, are a great example of aposematic Müllerian mimicry. Image from Wikimedia Commons

Biologists have long noted that there many of these toxic creatures use similar patterns of bright, noticeable colors. It is hypothesized that these Müllerian mimics have come to share common “don’t mess with me” signals through convergent evolution. Additionally, some non-toxic species are deceptively similar to poisonous ones, and are thought to co-opt the signal through Batesian mimicry.

However, I argue that there is no such thing as Müllerian nor Batesian mimicry. All of these blaring colors are just ancient fads started by toxic individuals, and perpetuated by weaker individuals–much like fashion in humans.

This season's colors feature earth tones and neurotoxins

This season’s colors emphasize earth tones and neurotoxins

FOOTNOTES

*Not all manakin species form tight leks. Some display by singly, or in spread-out, “exploded” leks.

**I cannot tell you (1) how overjoyed I was at the Supreme Court’s ruling on gay marriage last month, nor (2) how baffling I found Justice Scalia’s rebuttal. I mean, sure, Justice Kennedy’s opinion was a little too florid for my tastes, but Justice Scalia’s rancor seemed out of all proportion and propriety. Oh, well.

CITATIONS

[1] TG Murphy. 2006. Predator-elicited visual signal: why the turquoise-browed motmot wag-displays its racketed tail. Behavioral Ecology 17(4): 547-553.

[2] R Durães, BA Loiselle, and JG Blake. 2007. Intersexual spatial relationships in a lekking species: blue-crowned manakins and female hot spots. Behavioral Ecology 18(6): 1029-1039.

[3] R Durães, BA Loiselle, and JG Blake. 2008. Spatial and temporal dynamics at manakin leks: reconciling lek traditionally with male turnover. Behavioral Ecology and Sociobiology 62(12): 1947-1957.

Dispersal

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Life is a motile phenomenon. Even those wee beasties that we usually observe being sessile–bivalves, corals, sponges–spend at least one stage of their life adrift, however briefly.* And most animals spend their entire lives in motion.

Seriously, have you ever seen an adult giant panda move?

Seriously, have you ever seen an adult giant panda move?

Many movements are the quotidian practicalities of staying alive: foraging and fleeing, courtship and copulation, and so on. Other movements follow seasonal rhythms: wildebeest chasing rains, the great migrations of birds, the disappearance of catadromous eels to their surreptitious spawning waters.

Of all the sundry (and sometimes arbitrary) classifications of movement, dispersal holds a strange fascination for me. So much so that I hope to pivot from the study of recruitment (central to my Master’s thesis) to investigating patterns of dispersal for my doctorate.

The definition of dispersal is forthright: it is the movement of an organism from its birthplace to wherever it ends up breeding.  The simplicity of this definition belies a complex and wondrous biological phenomenon, one that feeds into major concepts of population biology like gene flow, connectivity, distribution, colonization, and extinction.

But dispersal is perilous: an organism adrift can cross paths with harsh conditions, unexpected predators, and environs to which it is not adapted. There is no guarantee that the disperser will fall on fertile soil–it may wind up withering on rocks bereft of sustenance and opportunity.

Hortus_Deliciarum,_Das_Gleichnis_vom_Sämann

Das Gleichnis vom Sämann, by Herrad von Lansberg. Uploaded via Wikimedia Commons.

Why bother dispersing at all? If we are raised successfully in a given area, doesn’t it stand to reason that our niche is most likely found close to our birthplace? What are the rewards of leaving home? What are the costs of staying?

No matter what you think you're leaving behind…

No matter what you think you’re leaving behind, don’t look back.

Even more than most academics, ecologists are creatures of profound wanderlust. In late adolescence, something calls from beyond the familiar streets of our homes and quaint college towns.

Away we go, chasing research questions across unsuspecting horizons. We live in cramped quarters with strangers that become friends and sometimes lovers.** We unconsciously create these little tribes feel like family until the project ends, the degree is finished, or the grant money runs out. Then we disperse again, parting with confoundingly sweet sorrow.

The Field Cycle

You’d think we’d learn, but we never do.

The adventure always wins out over the heartbreak. Perhaps the it wouldn’t really be an adventure without a little heartbreak. But again, I ask: what would it cost us to stay?

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Baby plants on walkabout.

Plants provide some insight. They’ve devised countless strategies to send their offspring farther afield: sails of every shape and size to catch the wind, waterproof boats bobbing across wide waters, velcro cocklebur curls that hitchhike on fur and shoelace alike. So what happens to those apples that fail to fall far from the tree?

Turns out, the hazards of a seed landing too close to its parent are legion. The parent plant will be every seed predator’s favorite place to search for its next meal [1]. Even if a seed doesn’t get eaten, the newly sprouted seedling may have to compete with its parent for resources [2], and is subject to all the pathogens, parasites, and herbivores that rain down from above [3]. Clearly there is a strong selective benefit to dispersing under such conditions.

Zombie squirrels are the absolute worst.

Zombie squirrels are the absolute worst.

Perhaps our dispersals serve a similar end. Maybe we’re fleeing the hazards and vices that permeate our homes: the complacency that comes with comfort, personal stagnation in the absence of challenge, cozily toxic codependencies shared with family and friends.

Then again, we are not plants (even I can only stretch a metaphor so far). Perhaps I’d be better served seeking explanation within the same kingdom…

A great deal of research on dispersal in animals focuses on inbreeding avoidance, as the consequences of concentrating deleterious alleles over generations is–if not fatal–not very pretty [4]. Theory suggests that if an organism travels far enough, it will encounter mates genetically unrelated to it, with which it can produce suitably heterozygous offspring.

As an extra safeguard, patterns of dispersal are often sexually asymmetric (one sex demonstrating a propensity for hitting the road, while the other remains philopatric). Interestingly, the bias towards male or female dispersal varies greatly between and within taxonomic groups, and there has been plenty of hypothesizing as to how life history and social structure influence these patters [5, 6].

Examples of male and female sex-biased dispersal in 4 mammal orders. All images from Wikimedia Commons. (a) Spotted Hyena, (b) African Wild Dog, (c) Yellow Baboon, (d) Chimpanzee, (e) Common Shrew, (f) White-toothed Shrew, (g) Bechstein's Bat, (h) White-lined Bat

Examples of male and female sex-biased dispersal in 4 mammal orders. All images from Wikimedia Commons. (a) Spotted Hyena, (b) African Wild Dog, (c) Yellow Baboon, (d) Chimpanzee, (e) Common Shrew, (f) White-toothed Shrew, (g) Bechstein’s Bat, (h) White-lined Bat

It’s not clear whether or not humans have sex-biased dispersal; cultural practices of inheritance and nomadism strongly influence sex-specific patterns of movement. However, looking at the gender gap in post-secondary study-abroad programs, I’d hazard the guess that there might be some bias towards female dispersal in our species.***

That being said, I doubt that the average ecologist’s dispersal is merely a quest for outbreeding opportunities. Frequently, we leave behind partners in the pursuit of our science. Under the best of circumstances, our partings are amicable, tender, and affectionate. We allot ourselves a week to mope listening to sad music, and then carry on as though the loss weighs nothing.

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Of course, there are intellectual rewards for being willingly untethered. Would Wallace and Darwin have every puzzled out evolution had they not witnessed geographic patterns of adaptive radiation firsthand? Would MacArthur and Wilson have put together the Theory of Island Biogeography without the visiting dozens of archipelagos?

I suppose we never know what patterns and mysteries will catch interest when we wander into the unfamiliar. Alternatively, we never know what discoveries we miss when we don’t stay put.

My current ecological focus: the lek stylings of the Red-capped Manakin, Ceratopirpa mentalis

My current ecological focus: the lek stylings of the Red-capped Manakin, Ceratopirpa mentalis

Ultimately, I don’t know whether there’s one or hundred reasons why we disperse, or if the rewards of dispersal will ever pan out. All I know is that, even with the excitement another day in the tropics will bring tomorrow, its the panoply of a hundred unfamiliar birds, blossoms and beetles beyond counting…tonight, a piece of my heart is aches for a city on a river two thousand miles away. A city full of friends that feel like family, a city with a thousand memories of love.

Somewhere that, in the moments I forget myself, I call home.

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FOOTNOTES

*Maybe except for giant pandas. Those things are genuinely useless, and I’m pretty certain even the babies are lugged around by hovercraft conservationists.

**Great/terrible example of that here.

***Leastways, it’s a less obnoxious and condescending explanation than “Boys grow up slower than girls.” We do, but I don’t think that has anything to do with the pursuit of international study.

CITATIONS

1. DH Janzen. 1971. Seed predation by animals. Ann Rev Ec & Sys 2: 465-492.

2. R Nathan & HC Muller-Landau. 2000. Spatial patterns of seed dispersal, their determinants and consequences for recruitment. TREE 15(7): 278-285.

3. CK Augspurger & CK Kelly. 1984. Pathogen mortality of tropical tree seedlings: experimental studies of the effects of dispersal distance, seedling density, and light conditions. Oecologia 61: 211-217.

4. FC Ceballos & G Álvarez. 2013. Roayl dynasties as human inbreeding laboratories: the Habsburgs. Heredity 111: 114-121.

5. PJ Greenwood. 1980. Mating systems, philopatry and dispersal in birds and mammals. Animal Behaviour 28(4): 1140-1162.

6. KE Mabry, EL Shelley, KE Davis, DT Blumstein, & DH Van Vuren. 2013. Social mating system and sex-biased dispersal in mammals and birds: a phylogenetic analysis. PLoS ONE 8(3): e57980.

“Extinctify” Should be a Thing

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It was in Population and Community Ecology course that I first heard the word. My professor, Brent Smith, was lecturing on some aspect of Island Biogeography, when he said, “…and the smaller the island, the higher the probability of a species going extinct–or, as a former student would have stated, the more likely they’ll be extinctified.”

My fellow biologists, I have waited years for this term to catch on, and it hasn’t. I am disappointed that we have failed to force this marvelous, wonderful word into the English vernacular. It’s high time Extinctify became a thing.

Extinctify (ek-STEENK-tih-fī)

(1) verb, transitive: To drive to extinction, to extirpate globally, to cause the demise of a species.

(2) verb, intransitive: To go extinct, for one’s entire species to disappear from the face of the earth.

Extinction is major biological phenomenon. It’s been happening at a background rate of 5 species per year for ages [1], and that rate is now accelerating beyond the mass-extinction threshold [2]. In spite of its prevalence and relevance, the idea of a species disappearing exists only as noun (extinction, the event) and adjective (extinct, the status). The concept wants for a verb–a verb that can imply causality, agency, or intent.*

Let’s take the elementary school example of mass extinction. At the tail end of the Cretaceous Period, an asteroid crashed into earth and eliminated 75% of the world’s multicellular eukaryotic species. You probably saw a sad diagram in your 1st grade Earth-Science textbook book that looked like this:

Public Domain image from Wikimedia Commons

Public Domain image from Wikimedia Commons

Ho-hum, the whole thing seems so blasé. The dinosaurs were like, “Well, I guess it’s time we went extinct,” and so they rolled over and died.

Unacceptable! The vocabulary fails to capture an insane and terrifying idea: a huge space rock burns giant reptiles off the face of the planet! With extinctify in play, the above figure would look more like this:

The term is actually K-Pg extinction now, but whatever.

The term is actually “K-Pg extinctify” now, but whatever.

That’s right: the asteroid extinctified the dinosaurs (along with the pterosaurs & mosasaurs & other beasties).

Extinctify can be applied to more recent events, particularly those in which humanity had a hand. While I recognize that plants, insects, and amphibians are likely suffering the worst of our destructive proclivities, bird art is more readily available for my illustrative pillaging:

moa

Public domain image from Wikimedia Commons

And you tell me–which headline has more pizzaz?

Original Audubon article here.

Original & excellent Audubon article by Barry Yeoman can be found here.

Extinctify isn’t just a word for bygone species, either. It should be a mainstay in the lexicon of conservation writers.

There is a place for poetry and elegance when we pen advocacy for the environment. Effective prose should enlighten the mind to the crisis of biodiversity loss while artfully strumming the heartstrings. However, sometimes it’s better to just cut to the chase. Take the following excerpt from Silent Spring [3] by Rachel Carson about pesticides:

Carson1 Beautiful? Yes. Compelling? Sure. But I think the message would be more efficiently conveyed had she laid it out like this:

Carson2 I think that’s as much argument as extinctify needs. So, my friends & fellow biologists, go forth into the world, say it loud and say it proud. EXTINCTIFY!

If you don’t, at least help me creating streaming software to catalogue, describe, 3-D print, and eventually resurrect paleobiota.

extinctifyGUI

Special thanks to L. Wyatt Carpenter for his patience and guidance with creating the Spotify parody logo in Illustrator, even though he didn’t think it was funny. I should probably thank him for always tolerating my bizarre sense of humor while I’m at it.

FOOTNOTES

*Yeah, that’s right, I just anthropomorphized extinction. Tee-hee.

CITATIONS

1. JH Lawton & R McCredie May. 1995. Extinction rates. Oxford University Press.

2. AD BarnoskyN MatzkeS TomiyaGOU WoganB SwartzTB QuentalC MarshallJL McGuireEmily L. LindseyKC MaguireB Mersey, & EA Ferrer. 2011. Has the Earth’s sixth mass extinction already arrived? Nature 471: 51-57.

3. R Carson. 1962. Silent Spring. Mariner Books.

U-Visibilia

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Conforming with stereotypes of urban white educated progressives (UWEP*), I listen to a lot of NPR. As such, I’ve recently subscribed to the Invisibilia podcast, created but the marvelous Lulu Miller and Alix Spiegel.

If you haven’t already given the show a listen, I definitely recommend it. Ms. Miller & Ms. Speigel do a wonderful job exploring that fuzzy intersection of science, psychology, philosophy, and humanism which they classify as Invisibilia: invisible, abstract forces that influence human behavior.

In honor/admiration/parody of their work, this post is about forces that shape animal behavior–forces that are invisible to us, but not to creatures that see ultraviolet radiation. I now christen a neologism to describe such phenomena: U-Visibilia.

Quick summary of electromagnetism: Homo sapiens primarily perceive wavelengths of light between 400nm-700nm. Wavelengths that are a tad longer than 700m are referred to as infrared (longer than visible red wavelengths). Those wavelengths that are shorter than 400nm are called ultraviolet, and are invisible to the human eye.**

The electromagnetic spectrum. Image from Wikimedia Commons, CC BY-SA 3.0.

The electromagnetic spectrum. Image from Wikimedia Commons, CC BY-SA 3.0.

Unlike humans, some animal species do perceive ultraviolet wavelengths, and signals in the ultraviolet can play an important role in their natural history. Let’s look at some examples of how animals use ultraviolet color in fighting, friending, and foraging.

Fighting

Our study begins with the Florida Scrub-jay (Aphelocoma coerulescens). Endemic to patchy oak scrub in Florida, Scrub-jays are sassy, violent, and handsome animals. Adult plumage is sexually monomorphic in the visible spectrum, as seen below.***

Aphelocoma coerulescens, perching on my hand. We were both so young then.

Adult Aphelocoma coerulescens, perching on my hand. We were both so young.

These jays are cooperative breeders; young birds often hang around the nest for several years after fledging and help raise their siblings. This family set-up elicits dominance structure among breeders and helpers [1].

Some of this hierarchy is vetted in the first year of life, before jays develop the blue hood of their parents. Young “brown-heads” will squabble over resources, with some individuals consistently winning out, while others hastily yield.

fsj1

This is my sad attempt to draw begging behavior from the juvenile on the right, which turned out especially poorly. A video of that with congeners here.

How do these birds determine who’s stronger than whom? Is it body size? Parental favoritism? Some invisible power? Or is it…U-Visibilia?

Turns out that while we see their heads as brown and wings as light blue, both have reflectance in the UV, which the jays definitely can see. My brilliant friend Angela Tringali tested whether the strength of reflectance in UV-Blue spectra predicted the outcomes of dominance interactions [2]. To do this, she measured UV-blue reflectance in hatch-year siblings, and assessed dominance by quantifying who “won” or “lost” in fights over a feeder of peanuts. fsj2 Unsurprisingly, individuals with brighter UV-blue colors ranked higher than their duller siblings. Angela took this exploration a step further by altering the plumage of more dominant jays with two different treatments. The first treatment group got their feathers colored with a Sharpie© marker, which heavily depressed their UV-blue reflectance. The second group received a sham treatment–a marker that mussed up feathers without diminishing UV reflectance.

After altering their plumage, the Sharpie-d bird’s odds of winning interactions diminished, while control and sham-treamtent birds retained their dominance in feeder trials.*** So there you go. U-Visibilia.

Friending

We now turn to damselfish. Ambon and lemon damselfish (Pomacentrus amboinensis and P. moluccensis) are two similar species that are moderately difficult to distinguish with untrained human eyes.

dam1

Pomacentrus amboinensis and P. moluccensis. They look the same because I flipped the image. Gasp!

However, males actively chase members of their own species (conspecifics) off territories, while they are more tolerant of males of the sister species (heterospecifics). This makes sense, as conspecifics pose a greater competitive threat to resources and mates than do heterospecifics.

How do males quickly and successfully identify friend from foe?§ Is it scent? Is it secret fish finshakes? Or is it…U-Visibilia?

damsel2

Siebeck et al. think that species recognition has more to do with the shape of the pattern than the colors within the pattern.

Siebeck et al. [3] demonstrated that both species of damselfish come equipped with the ability to see UV light, and that males have strong UV reflective patterns on their faces. The shape of these blotches is specific to species, with Ambon damselfish showing heavier blotches and stripes than the lemon damselfish.

So if the visiting fish’s face is a different the resident’s fish’s face, they can be fish-friends! Maybe they’ll fish-friend each other of Fish-facebook. Fishbook? Fishbookfriendface? Ugh. Okay, they’ll just not be antagonists.

Foraging

Lastly, we investigate predatory stylings of Thomisus spectabilis, an Australian crab spider that specializes in snatching honey bees (Apis mellifera) when they visit daisy flowers.

Snatch!

Snatch!

To the human eye, these spiders blend in pretty well with the flower petals, so you may expect this camouflage aides them in hunting bees.

However, Heiling et al. [4] demonstrated that bees are more likely to visit flowers with spiders than flowers without spiders. This suggests that bees do perceive the spiders, often to mortal consequence.

How do they these crab spiders attract bees? With inter-species pheromones? Mind powers? Tractor beams? Or is it…U-Visibila?

Go towards the [ultraviolet] light!

Go towards the [ultraviolet] light!

Surprise! T. spectabilis is strongly reflective in the UV spectrum. Many flowers have UV ornaments to help attract and guide pollinators [5]. Our spiders “boost” this UV signal with their own colors, increasing the attractiveness of the flower to passing pollinators. The summary of this research gets Heiling et al. a page in Nature. Happy ending for the scientists, if not the bees.

Well, that’s all for now. I won’t be posting for another two weeks–I’ve gotta finish some logistic stuff for Panama, and get Program MARK to cooperate with our new analyses. But check back on February 16, when I’ll write and doodle about heartbreak and break-ups in the animal world in the wake of Valentine’s Day.

FOOTNOTES

*Don’t confuse UWEPs with Yuppies. Yuppies were upwardly-mobile professionals. We’re professionally stagnant .

**Human’s photorecepting cones do respond to ultraviolet wavelengths, particularly blue cones. However, the lenses of our eyes filter out these wavelengths; people who have received artificial lenses through surgery perceive UV as blue-white or violet-white.

***Angela’s experiment is more detailed than my summary makes it out to be; there’s good stuff regarding inter-sexual conflict, too. Go read it.

§Okay, so maybe “friend from foe” isn’t as accurate as “not-a-big-competitor from definitely-a-competitor“, but whatever.

CITATIONS

1. GE Woolfenden & JW Fitzpatrick. 1977. Dominance in the Florida Scrub-jay. The Condor 79(1): 1-12.

2. A Tringali & Reed RJ Bowman. 2012. Plumage reflectance signals dominance in Florida Scrub-jay, Aphelocoma corulescens, juveniles. Animal Behaviour 84(6): 1517-1522.

3. UE Siebeck, AN Parker, D Sprenger, LM Mäther, & G Wallis. 2010. A species of reef fish that uses ultraviolet patterns for covert face recognition. Current Biology 20(5): 407-410.

4. AM Heiling, ME Herberstein, & Lars Cittka. 2003. Pollinator attraction: crab-spiders manipulate flower signals. Nature 421: 334.

5. CE Jones, SL Buchmann. 1974. Ultraviolet floral patterns as functional orientation cues in hymenopterous pollination systems. Animal Behavior 22(2): 481-485.

Attraction and Selection 3: Display & Epilogue

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Charles Darwin got there first.

Yes, Alfred Russell Wallace was hot on his heels. Yes, Erasmus Darwin had offered a comparable hypothesis (albeit lacking mechanism). Yes, Lynn Margulis championed theories that added lightyears of insight to the story of life…but Charles Darwin got there first.

All us evolutionary wannabes are scrambling to catch up. Every word I’ve written and logical chain I’ve argued in this trilo-blog follows a well-trodden groove that began with The Origin of Species and The Descent of Man, a groove worn smooth by the likes of Julian Huxley, Ronald Fisher, Ernst Mayr, E.O. Wilson, and many others. All that neurotic chatter about muscle mass, male contests, and fancy adornment? It inevitably leads here.

With that in mind, I’ll let Chucky D open this final chapter for me:

The Descent of Man, Chapter 8. Emphasis and pigeons added by me.

The Descent of Man, Chapter 8 [1]. Emphasis and pigeons added by me.

That’s right. Once you’re ornamented and rocking your bling, you need a way to show it off. This last installment on attraction and selection will focus on those marvelous “antics”, or commonly referred to as courtship displays.

Much like adornments, some displays can be practical. If you have ever owned a male Betta fish (Betta splendens), you probably observed it blowing masses of bubbles. Those frothy structures are nests for eggs, and are an important criteria for females searching for a mate [2].

If the sheer number of nests wrens build doesn't unnerve you, the interiors of the nests will. They could make a series called Stick Horders about it.

Marsh Wren, doing the splits. As them Marsh Wrens do.

Nest building is a common courtship component in fish and bird species, and it can get a little out of hand. I once foolishly attempted to monitor a pair of House Wrens (Troglodytes aedon) breeding in my yard, only to discover that the male was building bags of nests, and the female only laid in the ones I didn’t find. This is a trope in the wren family (Troglodytidae). Male Marsh Wrens (Cistothorus palustris) will build as many as 12 nests, only a few of which will receive any use by females. There has been some debate as to whether this overzealous home-building is an advertisement of male quality [3], a function of polygyny [4], or just a way to screw with predators/ornithologists [5]. Whatever the explanation, the building of at least one nest is a signal of a male’s capacity as a parent.

Another example of practical courtship is nuptial feeding. In many insect [6], arachnid [7], and bird species [8], males will woo females with a romantic meals. Male shrikes (Laniidae, one of the gnarliest passerine families out there) maintain “larders” of impaled mice and lizards. Female shrikes prefer males with the most macabre displays, and lay more eggs when males bring the bloody mess right to them [9].

Two perspectives on nuptial feeding.

Two perspectives on nuptial feeding.

Likewise, males of some insect species deliver salts and other sustenance to aid females in egg production. These nuptial gifts can be captured prey, but often take the form of a spermatophore–a nutritional matrix filled with ejaculate that females eat after absorbing the sperm [10]. It’s like a gift with edible wrapping paper, only much grosser.

In arachnids, the role of nuptial feedings is more complicated. While a prey offering may help enrich the eggs the female lays, it’s also conceivable that the male is hoping to just sate the female enough to live and mate another day [11].

The parallels between nest building/nuptial feeding and human behavior are easy to draw. A whole slew of studies have addressed the relationship between male wealth and reproductive success. The selection gradient diminishes somewhat with industrialization [12], but on the whole the wealthiest blokes take the lion’s share of mating opportunities [13, 14, 15]. Alas, my paltry checking account and moldering 403(b) are unlikely to win me any suitors.

Fortunately, many displays don’t require material goods to be found attractive. You could trawl the internet for weeks without running out of videos of exaggerated animal courtship performances (for real). Some displays are simple, like the push-up performance by Sceloporus lizards that show off male’s upper body strength and flashy sides:

So strong. So manly.

Other displays are more complicated, like the tremendous dancing of peacock spiders (Maratus sp.), who have risen to internet fame thanks to Jurgen Otto high-resolution videography.

Other displays seem to be just plain annoying. Male red-eared sliders (Trachemys scripta) will use their long finger claws to repeatedly tap and brush females’ faces. It’s as weird as it sounds. If someone did that to me for 20 minutes, I’d probably mate with them just to get them to lay off.

Shtaaaaaaaaaahp

With such a preponderance of courtship displays, we have to ask: are they a signal of male quality, or merely an invitation to mate? After all, complex displays can function to prevent inter-species mating, allowing both sexes to avoid issues of gametic incompatibility [16, 17]. To ensure that courtship is a sexually selected signal of quality and not just a pre-zygotic barrier to hybridization, we need to determine whether variation in display within species reflects male quality, and in turn translates into female preference.

For our starting example, let’s look at a species familiar to us North Americans: the Song Sparrow (Melospiza melodia). This streaky little creature breeds cross the northern US and Southern Canada, and down California into Baja (range map here).

If you spend time this spring in open fields, you’ll notice that individual sparrows have uniquely variable songs; some males sing several complex songs, while others seem stuck with a few dull melodies.

Zounds! A variable display! So does variation reflect female preference?

song Indeed, captive female Song Sparrows solicit copulations more frequently when exposed to more diverse repertoires of recorded songs in lab settings [18]. Additionally, more diverse song repertoires are predictive of higher reproductive success in wild male Song Sparrows [19], suggesting that repertoire diversity is an honest signal of male quality.

The relationship between male song quality and female preference is well established in many songbird species [2021, 22] and some insects [23, 24]. But what makes song an honest signal of male quality? Much like fluctuating asymmetry, song may reflect a bird’s past. A low-quality bird that couldn’t obtain the calories to grow the neural circuitry, and thus have a smaller song repertoire [25].

The costs of courtship don’t stop at learning displays. Often, the display itself is injurious to the performing. Take wolf spiders: males court females by sending vibrations through the substrate and waving about their heavily tufted forelegs. Female wolf spiders show preference for larger tufts and better vibrations, as demonstrated by simulated males in the Uetz lab in the video below. When researchers induced increased drumming frequency by presenting males with a line-up of females, males rapidly lost weight…and sometimes just plain died of exhaustion [26].

Other examples of display-hard/die-young can be here and here, but perhaps my absolute favorite cost-of-display example is with the Cock-of-the-Rock (Rupicola sp).

An Andean Cock-of-the-Rock (Rupicola peruvianus). Photo by Joel Lisenby, shared under CC BY-SA 3.0

An Andean Cock-of-the-Rock (Rupicola peruvianus). Photo by Joel Lisenby, shared under CC BY-SA 3.0 via Wikimedia

There are two species (give or take) of these South American cotingas: Guianan and Andean. The males are bizarre creatures, searing red or orange with crests that cover their beaks and alien-bright irises; the females are a subdued rust-brown. The species is highly dimorphic in its behavior as well; females raise offspring entirely on their own, and only interact with males when mate-searching. When females are searching, males certainly put on a show.

Cock-of-the-Rocks (or Cocks-of-the-Rock? Cocks-of-the-Rocks?…let’s call ’em COTRs) engage in lek mating: males gather in geographically fixed locations to compete and display for soliciting females. Freed from the demands of parenting, males spend their days preening, strutting, and make a ruckus whenever a single lady shows up.* I really mean ruckus–this is what a lek sounds like when a female kicks it into high gear:

Now, imagine you are a predator wandering the rainforest understory. It’s dark and quiet; most prey items are small and quick, cautiously flitting through shadows. Suddenly, you come upon a lek of screaming, blaze-bright birds entirely focused on showing off.

Turns out this a real consequence for COTR leks. A paper by Pepper W. Trail in 1987 [27] described how frequently male leks would flip out over incoming predators…or flip out because of false alarms. 90% of the times the males fled crashing into the vegetation, it was for false alarms.

Lekkk

Variation in lek size in the Andean Cock-of-the-Rock.*

As if waiting around to holler for a quickie while predators snatch at you from the shadows, mating success in lek species is incredibly skewed: usually one or a few males win most of the paternity in a given breeding season. Seriously, can you image participating in this silly dance for months on end and never getting laid?

Blue Manakin (Chiroxiphia caudata) Lek. Only one guy is gonna be invited to partake in some nookie.

Birds aren’t the only group whose antics draw in the hungry nasties [28, 29]. Male túngara frogs (Physalaemus pustulosus) risk getting snatched by fringed-lipped bats (Trachops cirrhosis) each time they join the chorus [sick imagery of that here and here]. To make matters worse, the complicated calls that females túngara frogs prefer are also preferred by bats.; the better a male sings for ladies, the easier it is for bats to find him [30].

Darwin and most of his successors have seen parallels between the song and dance of the animal kingdom and those of our own species. There are legitimate arguments that our artistic traditions are as much about social bonding as they are about mate selection, and I suspect there’s a lot of truth to that hypothesis [31]. However, the sexually dimorphic registers of human voices [32], females’ increased preference for lower pitches when fertile [33], and the seemingly supernatural allure of guitarists suggest that musical and dancing facility may be yet another signal used in human mate selection.

Also, remember that discussion of fluctuating asymmetry in Part 1? It turns out that there’s a strong relationship between a man’s symmetry and his dancing abilities: more symmetrical dudes have better moves than us Lopsided Larry’s [34]. Moreover, dancing highlights existing asymmetries, such that the attractive power of a man’s shimmy diminishes with increasing physical asymmetry.

If you’ve stuck with me to this point, you know what’s coming next: this is the part where I point out how the cited research indicates my paucity of attractive quality.

Truth be told, I’m not horrible with music; I can carry a tune if need be. But I am an abysmal dancer…think along the lines of Allie Brosh‘s experiences recreating Beyoncé. I spend most of my time in clubs awkwardly shuffling by my lonesome while my boyfriend and friends cut every rug in the joint.

So what’s the point of all this? I’ve burned some 6,000 words highlighting all the ways I cannot be considered attractive from a biological or sexual selection-perspective. Can I say anything to redeem this self-pity party? Isn’t there supposed to be some moral that me and all the fugly uggos can use to lift our spirits?

Of course there is. Next time you’re sitting around, anxious about whether you’re hot enough to make par, or glowering at everyone fitter than you at the gym, take a moment to imagine yourself as you’d like to be. Really indulge yourself. Picture your body, its every angle and curve ideal. Visualize your shape as buxom or lanky, gracile or virile, your every blemish erased–whatever your fantasy is, hold it fully in your mind and really see it.

idealz

Now, without forgetting what that person looked like, summon an image of the people you admire most. Picture all those people–living or dead–you think really matter, people whose approval you strive to obtain, people who you could point to and declare: “This person, they are worthy of emulation!”

right

If you’re even a half-developed human, you didn’t choose your heroes on the basis of sex appeal. Some might as homely as the rest of us mere mortals.

If your idols are handsome, I bet that quality pales in comparison to their other distinctions: brilliance, devotion, compassion, diligence, equanimity, patience, and a hundred other noble elements that contribute to greatness.

Don’t sully these concepts by claiming morality is hot, or that altruism is lush. I know you want to, but don’t. Kindness, perseverance, courage, forgiveness, honesty don’t need to be sexy. They are traits with intrinsic merit.

I guess the moral of the story is this…whether you think of attraction is selected for, or culturally determined, or in the eye of the beholder, the hard truth remains the same: we may never be as attractive as we want to be–no matter what a Dove Commercial says.

All we can do is try our best to not give a fuck because there are much higher aspirations than physical perfection. The unrelenting pursuit of justice, determination to unveil the mysteries of the universe, commitment to serving the least of our brothers–such attributes are the making of true champions.

Dr. Jonas E. Salk, creator of the polio vaccine. Rather than get rich with this creation, Dr. Salk did not patent the vaccine. The lowered cost of production ensured has saved millions of lives. Public Domain Image

Dr. Jonas E. Salk, creator of the polio vaccine. Rather than get rich with this creation, Dr. Salk did not patent the vaccine. The lowered cost of production ensured has saved millions of lives. Public Domain Image.

Among my resolutions for this year is demote being attractive to the lowest of my ambitions. If I could reach into my past to exchange every second of body anxiety for a moment that I took to be kind, or to enrich my mind, or to be creative…heavens, my life would look different today.

So here’s to making life look different. Here’s to tossing aside body dysmorphia and leaving the mad game of sexual selection to creatures who can’t aspire to higher ideals, creatures who have no need of justice or virtue or science.

Besides, they look better displaying than any of us.

Footnote

*If you ever have a chance to visit any kind of lek, I highly recommend it; they are among the most hilarious and transfixing phenomenon in nature. If you’re a North American, you can probably check out a Prairie Chicken lek. However, please be careful and respectful to the lek when you do visit–flushing the displaying males could be energetically costly and lower the quality of the lek site.

**This illustration is a little misleading. The advantage of having a noisier, more vigilant lek are discussed in Pepper paper. But I really wanted to draw a derpy COTR being attacked by a snake, so I did.

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