1. Robbie got his 69th publication, and for some reason thought that was funny.
2. Candice returned from the US, jet-lagged and culture-shocked. We've missed her.
3. Billy's still ... somewhere?
4. Jaime's officially started her PhD, and taken up the last desk in the Fun Zone.
5. Another of Candice's PhD papers just got accepted for publication! This one's:
Bywater, C & Wilson RS. 2012. Is honesty the best policy? Testing signal reliability in fiddler crabs when receiver-dependent costs are high. Functional Ecology (in press Feb 2012)
6. Robbie decided it was time to get married. To me.
And that's February, 2012!
Monday, February 27, 2012
Monday, February 20, 2012
The Scent of a Predator (Well, Kind of)
The following article is adapted from a talk presented by Jaime Heiniger at SICB 2012, along with coauthors Billy Van Uitregt and Robbie Wilson. The original talk was called: "Fine tuning anti-predator responses: are the costs of inducible predator defences proportional to the magnitude of the responses?"
***
For amphibians, it's a mad, mad world. And - importantly - an unpredictable one. Natal pools might contain predators, or not; competitors, or not; food, or not; and conditions can change every day. As a result of all this unpredictability, many amphibians can alter their appearance and behaviour in ways that increase their likelihood of survival. But these defensive strategies usually come at a cost - slower growth, higher metabolic requirements, and smaller size at maturation are just a few common outcomes.
To maximise the benefits and minimise the costs associated with predator defense, it's predicted that the magnitude of the defensive response should reflect the magnitude of the threat. Thus, more threat = more phenotypic change; and less threat = less phenotypic change. This is known as the threat-sensitive predator avoidance hypothesis (TSPAH), and although it's known that prey can fine-tune their responses to the degree of predation risk, it's unclear if the magnitude of threat-sensitive defensive responses relate to their associated costs.
{Jaime} tested this idea by examining the effects of increases in perceived predation risk on the expression of defences and their associated costs in larvae of the toad, Bufo marinus. She reared tadpoles in varying concentrations of predation cue* and quantified their growth, morphology and development, as well as metamorphic size, locomotor performance and oxygen consumption.
*for those curious, predation cue is actually water from around deceased tadpoles. Tadpoles are sensitive to the smell of their dead mates. (Aren't we all?)
{Jaime} found that tadpoles responded to increases in perceived predation risk by gradually decreasing their activity.
As a consequence of their more-sedentary lifestyle, individuals metamorphosed later, smaller and with reduced endurance. Toads that emerged from the different treatments didn't vary in maximum jumping distance but those from 'high predation' treatments metamorphosed with longer relative hind limbs - meaning they could jump farther for their body size.
These are interesting results, because they show that
a) toads produce defenses that are proportional to the perceived threat
b) defensive behaviour is costly
c) the costs are in proportion to the amount of defense
d) but phenotypes produced in response to predation threat may aid the individual.
Cool stuff, Jaime!
***
For amphibians, it's a mad, mad world. And - importantly - an unpredictable one. Natal pools might contain predators, or not; competitors, or not; food, or not; and conditions can change every day. As a result of all this unpredictability, many amphibians can alter their appearance and behaviour in ways that increase their likelihood of survival. But these defensive strategies usually come at a cost - slower growth, higher metabolic requirements, and smaller size at maturation are just a few common outcomes.
 |
| toadlets in the lab |
To maximise the benefits and minimise the costs associated with predator defense, it's predicted that the magnitude of the defensive response should reflect the magnitude of the threat. Thus, more threat = more phenotypic change; and less threat = less phenotypic change. This is known as the threat-sensitive predator avoidance hypothesis (TSPAH), and although it's known that prey can fine-tune their responses to the degree of predation risk, it's unclear if the magnitude of threat-sensitive defensive responses relate to their associated costs.
{Jaime} tested this idea by examining the effects of increases in perceived predation risk on the expression of defences and their associated costs in larvae of the toad, Bufo marinus. She reared tadpoles in varying concentrations of predation cue* and quantified their growth, morphology and development, as well as metamorphic size, locomotor performance and oxygen consumption.
*for those curious, predation cue is actually water from around deceased tadpoles. Tadpoles are sensitive to the smell of their dead mates. (Aren't we all?)
 |
| taddies in the lab |
{Jaime} found that tadpoles responded to increases in perceived predation risk by gradually decreasing their activity.
As a consequence of their more-sedentary lifestyle, individuals metamorphosed later, smaller and with reduced endurance. Toads that emerged from the different treatments didn't vary in maximum jumping distance but those from 'high predation' treatments metamorphosed with longer relative hind limbs - meaning they could jump farther for their body size.
 |
| jaime's metamorph habitats |
These are interesting results, because they show that
a) toads produce defenses that are proportional to the perceived threat
b) defensive behaviour is costly
c) the costs are in proportion to the amount of defense
d) but phenotypes produced in response to predation threat may aid the individual.
Cool stuff, Jaime!
Wednesday, February 8, 2012
Why Be Fake? Because Honesty is Too Expensive ...
In earlier posts, we've talked about the life of a crab ... and about the predisposition for some crabs to fake how strong they are. At SICB in January, Candice presented a talk detailing why exactly it pays to be weak.
Here's my recap on Candice's talk ...
Crustaceans are violent types, posturing and fighting for territories, mating partners, and resources. Because claws are such excellent weapons, fights are often decided by the individuals merely checking each others' claws out. Bigger claws = dominance. This ameliorates the risks associated with claw-battle, while still deciding dominance.
But Candice has found that the size of the claw is not always indicative of its strength - namely, some individuals are fakers. You see, claw muscles - which are used to clamp and tear in a fight situation - are hidden inside the chitinous claw. So a big-clawed crustacean might just lack big muscles underneath, meaning it's more likely to lose if the interaction escalates into a fight.
So why wouldn't a crustacean just grow the muscle? This is what Candice wondered. She noticed that crabs with re-generated claws tended to have wimpy claws, relative to their claw size. So, she measured the energy needed to maintain claw muscles in fiddler crabs with strong, original claws as well as crabs with weak, regenerated claws.
Candice believes that dishonesty in fiddler crabs is related to metabolic costs - namely, how much energy is required to keep that muscle active. Crabs with strong, original claws spent ~22% of their metabolic energy budget on their claw muscle - pretty close to the amount of metabolic energy humans use to support our large glucose-hungry brains.
In contrast, crabs with weak, re-generated claws used only ~12% of their daily energy on claw muscle.
That constitutes a massive energetic savings for fakers, unless they get caught ...
 |
| image by Dan Hancox |
Crustaceans are violent types, posturing and fighting for territories, mating partners, and resources. Because claws are such excellent weapons, fights are often decided by the individuals merely checking each others' claws out. Bigger claws = dominance. This ameliorates the risks associated with claw-battle, while still deciding dominance.
But Candice has found that the size of the claw is not always indicative of its strength - namely, some individuals are fakers. You see, claw muscles - which are used to clamp and tear in a fight situation - are hidden inside the chitinous claw. So a big-clawed crustacean might just lack big muscles underneath, meaning it's more likely to lose if the interaction escalates into a fight.
So why wouldn't a crustacean just grow the muscle? This is what Candice wondered. She noticed that crabs with re-generated claws tended to have wimpy claws, relative to their claw size. So, she measured the energy needed to maintain claw muscles in fiddler crabs with strong, original claws as well as crabs with weak, regenerated claws.
Candice believes that dishonesty in fiddler crabs is related to metabolic costs - namely, how much energy is required to keep that muscle active. Crabs with strong, original claws spent ~22% of their metabolic energy budget on their claw muscle - pretty close to the amount of metabolic energy humans use to support our large glucose-hungry brains.
In contrast, crabs with weak, re-generated claws used only ~12% of their daily energy on claw muscle.
That constitutes a massive energetic savings for fakers, unless they get caught ...
Monday, February 6, 2012
CB in DC
At this precise moment, Candice is working at the Natural History Museum in Washington, D.C. - measuring crustacean claws as part of a study for her PhD.
Or, she might be sleeping. (I can never get those time-differences right ... )
At any rate, this is her lovely little brownstone ...
She's even famous now, in a "The Lost Symbol
" kind of way, toiling away in the crustacean collections in Pod 5* at the Museum Support Centre (MSC), a high-security warehouse in the sketchy part of town.
*The same section of the warehouse featured in Dan Brown's book ... in case you haven't read it yet.
And how does Candice spend her days in DC? She's on the bus at 7:30, heading to the Natural History Museum in downtown DC, where she catches the shuttle to the warehouse facility where the crustacean collections are housed.
In to her little lab in the wet collections rooms by 8:30, she starts taking photos of crab claws and measuring the sizes of the shell and legs - for different specimens and different species. It sounds like quick work, but given she has to take 3 measurements of each crab leg (and each crab has 8 measurable legs), she may just be there ... all year.
Not really. But I'm sure that's how she feels sometimes. 10-15 minutes per crab x a warehouse full of crabs = significant porters needed at the end of the day.
Candice measures claws on her own, but has lunch with the other 10-15 researchers who work at the warehouse measuring, cataloging and sorting other types of invertebrates. They all chat and sometimes have science talks, so it's been a great way to meet everyone else.
Then it's back home again, to forget about claws for 12 hours or so.
And why is she doing all this? Candice is looking for tradeoffs between claw size and other morphology among different crustacean species - compensatory mechanisms (like we just learned about with geckoes). We'll talk more about the science after she gets back.
(all the pictures in this post were provided by Candice. Thanks!)
Or, she might be sleeping. (I can never get those time-differences right ... )
At any rate, this is her lovely little brownstone ...
She's even famous now, in a "The Lost Symbol
" kind of way, toiling away in the crustacean collections in Pod 5* at the Museum Support Centre (MSC), a high-security warehouse in the sketchy part of town.*The same section of the warehouse featured in Dan Brown's book ... in case you haven't read it yet.
And how does Candice spend her days in DC? She's on the bus at 7:30, heading to the Natural History Museum in downtown DC, where she catches the shuttle to the warehouse facility where the crustacean collections are housed.
In to her little lab in the wet collections rooms by 8:30, she starts taking photos of crab claws and measuring the sizes of the shell and legs - for different specimens and different species. It sounds like quick work, but given she has to take 3 measurements of each crab leg (and each crab has 8 measurable legs), she may just be there ... all year.
Candice measures claws on her own, but has lunch with the other 10-15 researchers who work at the warehouse measuring, cataloging and sorting other types of invertebrates. They all chat and sometimes have science talks, so it's been a great way to meet everyone else.
Then it's back home again, to forget about claws for 12 hours or so.
And why is she doing all this? Candice is looking for tradeoffs between claw size and other morphology among different crustacean species - compensatory mechanisms (like we just learned about with geckoes). We'll talk more about the science after she gets back.
(all the pictures in this post were provided by Candice. Thanks!)
Thursday, February 2, 2012
Trade-offs in Gecko Design
Sounds glam, right? Gecko design?
At the 2012 SICB in Charleston, Skye presented research that shows how traits that improve bite force in geckos have negative impacts on the gecko's sprint speed. Meaning that males who are better fighters might also be less adept at escaping predators ...
Costly design indeed.
Let's learn more by having a look at Skye's abstract, with {comments in brackets from me}.
The evolution of exaggerated ornaments and armaments is driven by the benefits accrued to reproductive success and by the costs imposed on viability. {This means that} when traits are required to perform multiple functions that are important to both reproduction and viability, trade-offs can result in a compromised phenotype.
{Imagine, for example, a species of bird in which females are more likely to mate with males that have larger tails; but males with larger tails are more likely to be captured by predators. Both reproductive potential and survival are important to the male - so evolutionarily, the bird may end up compromising on tail length to make sure he both reproduces and survives.}
{Intuitively, we expect that exaggerated male traits (like super-long tails) would decrease locomotor capacity, resulting in lower survival rates due to predation.} Despite only mixed empirical support for such locomotor costs, recent studies suggest these costs may be masked as a result of the evolution of compensatory mechanisms that offset any detrimental effects.
{What are compensatory mechanisms? Imagine if that bird with the long tail-feathers developed longer wings, that enhanced its flying abilities. It might offset some of the survival costs of the long tail.}
In this study, {Skye} provides a comprehensive assessment of the importance of potential locomotor costs that are associated with improved male-male competitive ability by simultaneously testing for locomotor trade-offs and compensatory mechanisms. For males of the Asian house gecko (Hemidactylus frenatus), both fighting capacity and escape performance are likely to place conflicting demands on an individual’s phenotype.
Males that are highly territorial and aggressive are more likely to require greater investment in jaw size/strength in order to compete with rival males; {Skye} found that males with larger heads had stronger bites and showed greater prey-capture and fighting capacity. This performance trade-off was amplified for male geckoes with larger heads when {they were} sprinting up inclines.
{So, what does this mean? Geckoes with large heads are better at fighting and better at capturing prey, but may be worse at evading predators themselves. A compensatory mechanism would be something - like longer legs - that would enhance their ability to avoid predation.} {However, Skye} found little evidence for compensatory mechanisms that off-set the functional trade-off between bite force and sprint speed.
Ongoing work in this area includes testing the survival of male geckoes with different sized heads in controlled-but-natural conditions.
At the 2012 SICB in Charleston, Skye presented research that shows how traits that improve bite force in geckos have negative impacts on the gecko's sprint speed. Meaning that males who are better fighters might also be less adept at escaping predators ...
Costly design indeed.
Let's learn more by having a look at Skye's abstract, with {comments in brackets from me}.
Trade-offs and compensatory traits: bite force and sprint speed pose conflicting demands on the design of male geckos (Hemidactylus frenatus)
by Skye Cameron, Melissa Wynn and Robbie Wilson
The evolution of exaggerated ornaments and armaments is driven by the benefits accrued to reproductive success and by the costs imposed on viability. {This means that} when traits are required to perform multiple functions that are important to both reproduction and viability, trade-offs can result in a compromised phenotype.
{Imagine, for example, a species of bird in which females are more likely to mate with males that have larger tails; but males with larger tails are more likely to be captured by predators. Both reproductive potential and survival are important to the male - so evolutionarily, the bird may end up compromising on tail length to make sure he both reproduces and survives.}
 |
| image |
{Intuitively, we expect that exaggerated male traits (like super-long tails) would decrease locomotor capacity, resulting in lower survival rates due to predation.} Despite only mixed empirical support for such locomotor costs, recent studies suggest these costs may be masked as a result of the evolution of compensatory mechanisms that offset any detrimental effects.
{What are compensatory mechanisms? Imagine if that bird with the long tail-feathers developed longer wings, that enhanced its flying abilities. It might offset some of the survival costs of the long tail.}
In this study, {Skye} provides a comprehensive assessment of the importance of potential locomotor costs that are associated with improved male-male competitive ability by simultaneously testing for locomotor trade-offs and compensatory mechanisms. For males of the Asian house gecko (Hemidactylus frenatus), both fighting capacity and escape performance are likely to place conflicting demands on an individual’s phenotype.
 |
| image |
 |
| image |
Ongoing work in this area includes testing the survival of male geckoes with different sized heads in controlled-but-natural conditions.
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