Carleton Newsroom covers my research

A pastry caterpillar attacked by bird during my field experiment in 2010

Carleton Newsroom just posted a story about my research. The full article can be found on the Carleton University website here: Grad Student Aims to Discover Secret of Caterpillar Eyespots

Details about this research can be found in the earlier post What I did and how I did it: an experiment with pastry caterpillars or you can find the full article here.

Related:

• Introduction to my research
• Modelling dough caterpillars provide camouflage clue (BBC Nature article)
• Fake caterpillars help scientists to trick birds (CBBC Newsround version of the BBC Nature article) 
• Life is stranger than fiction (The Pokémon post mentioned in the Carleton article)

Papilio canadensis eggs and 1st instar

Eggs and Hatchlings!

One of the female butterflies that I had sleeved over a branch of Trembling Aspen laid 2 eggs on June 14 2012. Females are very picky when it comes to the leaves they choose for egg laying, and Papilio canadensis butterflies typically lay just one egg on a given leaf. This strategy is common among butterflies, especially ones whose caterpillars are palatable prey items.

Here are some photos of the progression from just-laid to hatching:

Papilio canadensis egg on day of laying - June 14 2012

Papilio canadensis egg 3 days old - June 17 2012

Papilio canadensis egg on day of hatching - June 20 2012

1st instar Papilio canadensis caterpillar hours after hatching - June 20 2012.
Note that the egg shell has already been eaten.

1st instar Papilio canadensis caterpillar hours after hatching - June 20 2012.
If disturbed the caterpillar will weakly thrash, but is mostly inactive.  

Last year I reared these caterpillars too, so check out earlier posts to find more photos and information about these little guys!

Earlier posts:

• Papilio canandensis caterpillars (1st instar) 
• 2nd cohort of caterpillars hatched
• Field and Lab Notes
• 4 new eggs

Effects of eyespots and body colour on caterpillar survival

What I did and how I did it: an experiment with pastry caterpillars

Me (Tom Hossie) examining a late 5th instar Papilio canadensis caterpillar that I reared last summer (2011)

Today the BBC Nature website posed a short piece on my research - see the write-up here. This write-up talks about the work I did in the summer of 2010 for the first chapter of my PhD thesis. This work was recently recently published in a journal called Animal Behaviour. You can see a copy of the article here via ScienceDirect. Note also that the photos from the BBC Nature piece are ones that I took during my research over the last two years.

A 5th instar Papilio canadensis caterpillar reared last summer (2011)

In this project I wanted to examine the relative protection aforded to caterpillars by eyespots, countershading, and any synergistic protective effects of these traits. This design was partly motivated by the question of whether eyespots could protect prey better than simply increasing their crypsis (e.g., via countershading), but also after seeing several examples of caterpillars with eyespots I had noticed that many of them were in fact countershaded as well. 

Aside: I should say that countershading is an animal colour pattern where the pigments on the dorsal surfaces (i.e., the animal's back) are darker than the ventral pigments. Most, but not all, of the hypothesized functions of countershading suggest a camouflage function. For example, the self-shadow concealment hypothesis proposes that having dark pigments where the body is naturally illuminated by the sun and lighter pigments in those areas that are naturally shaded may increase background matching, or weaken 3D cues used by predators to detect their prey.

My experiment had 4 treatments: solid-no eyespots, solid-eyespots, countershaded-no eyespots, and countershaded-eyespots. So, I made artificial caterpillars using flour and lard, dyed using with food-colouring (to add eyespots I used non-toxic paint). Once made, the "caterpillars" were pinned to tree branches (yes, caterpillars spend a non-trivial amount of time on tree branches) and monitored continuously over 90h. Specifically we were looking for peck marks left by birds or "caterpillars" that went missing altogether. Many other researchers have used a similar design to examine other questions, I just modified it to test the effect of eyespots on caterpillar-like prey.

The 4 prey types I used in this project

Field experiments are inherently ‘noisy’ meaning that because of a number of factors out of your control it can sometimes be difficult to detect significant patterns. Other researchers had shown previously that bigger eyespots resulted in greater protection of moth-like targets, and as this was the first time anyone had examined the protective effect of eyespots on caterpillars in this way we used relatively large eyespots to increase our chance of detecting an effect. Eyespot size and the specific eyespot pattern employed both could have influenced our results, but future work is needed to address these questions. Perhaps a more interesting point is the possible effect of morphological changes made by the caterpillar to change when it feels threatened. Many caterpillars with eyespots inflate their anterior body segments to change the shape of the “head” possibly to look more imposing or to increase their resemblance of a snake. We are investigating this question currently.

Update: We have now conducted this research examining the role of the "head" shape during the rest and defensive postures. We found that both inflated anterior body segments and eyespots can deter bird attacks. This work was published in the journal Animal Behaviour. See the full article here.

One of my field sites for this work. Kemptville, ON.

Sometimes my caterpillars were attacked by ants...

...and other times they were attacked by slugs (usually after a light rain)

A number of the pastry caterpillars were attacked by unwanted enemies of pastry. Ants were a big one, slugs were another. Both leave distinctive damage markings. Because we used a statistical technique called Cox-proportional hazards (a type of survival analysis) we were able to stop these unwated attacks from having an effect on our results by “censoring” them at the time when the unwanted attack occurred. Slugs were especially problematic after light rain. Along with the distinctive damage they leave on the pastry caterpillars you can tell the slugs were feeding on them because you can see the green food-coloured pastry in their stomachs! 

In this experiment, eyespots alone were not sufficient to protect caterpillars. In real caterpillars however other factors are also at play which likely increase the protective effect of eyespots. For example, in our pastry caterpillar experiment we weren't able to include the effect of behaviours expressed by caterpillars upon attack. We think that in caterpillars the protective effect of eyespots is enhanced by behaviours expressed upon attack that either startle off the attacker or resemble the movements of a threatening object like a snake. Also, eyespots may afford greater protection from insect-eating birds in the tropical ecosystems where a bird’s innate and/or learned wariness of eye-like features is heightened because of the greater diversity and abundance of dangerous things like snakes.

Interestingly, the countershaded-eyespots treatment - which were most like our local eyespot caterpillars (Papilio canadensis) - survived the best. This was an important finding because almost no empirical work had been done to examine the protective effect of caterpillar eyespots. Other work has shown that eyespots can increase survival of butterflies and moth-like targets, yet although eyespots are perhaps even more common in caterpillars only a handful of studies have ever attempted to examine the strength of their protective effect in this life stage. The most interesting result of this work is the synergistic effect of eyespots and body-colour. In isolation neither countershading nor eyespots significantly reduced predation on our pastry caterpillars, but together predation dropped significantly. To me, this suggests that seemingly independent defences are working together in ways that we don’t fully appreciate. Now that we have shown that eyespots can protect caterpillars we are looking to understand why some species evolve eyespots and not others.

Here is the full citation for this research:

Hossie, T. J., Sherratt, T. N., (2012) Eyespots interact with body colour to protect caterpillar-like prey from avian predators. Animal Behaviour 84(1): 167-173, doi:10.1016/j.anbehav.2012.04.027


Minor updates July 17 2013

Sleeving June 2012

So the sapling Populus tremuloides that I used to sleeve females over last year has almost no foliage on it this year, presumably because it is in a very shady spot. This means that I don't think sleeving the female Papilio canadensis butterflies over it is likely to result in egg laying. If I can find some nice saplings that I can transplant I might try that later, but in the meantime I have sleeved the females that I caught onto branches of trees out at another location. Here is what it looks like:

 
Unfortunately, with this set up I can't set up the heal lamp overhead which may have helped induce egg laying last year. This is why I tried to select spots where there is at least partial sun. The butterflies have to be hand fed if you keep them like this or else they will dehydrate, so far I have been feeding them a nectar solution once a day via  a soaked cotton ball. The females may or may not have mated, and I didn't have success attempting to hand-pair females last year. Depending on how thins go I might try it again this year.

Field Season 2012

This summer I am replicating a few things that I have done over previous summers. First, I am running another field experiment with pastry caterpillars similar to the work I did in the summer of 2010. That work resulted in a nice paper and was recently published in Animal Behaviour (see manuscript here). In addition to this, I will be rearing Papilio canadensis caterpillars from eggs laid by wild-caught females to repeat what I did last summer (2011).

As I explained in an earlier post, you need special authorization to collect Papilio butterflies in Ontario. I have approval to collect 20 Papilio canadensis butterflies. I haven't had much success trying to hand-pair wild-caught Swallowtails, but I did have some success inducing wild-caught females to lay eggs in captivity last summer. So, this season I'm only focusing on females. Males and females not only look different (see earlier post on sexing), but they behave differently. Males are usually seen patrolling for females along flyways lined with their host plant (Trembling aspen, Populus tremuloides), or sometimes "puddling" in a group of other males. Females on the other hand don't puddle, and are really only encountered around nectar sources. Basically, if you see a swallowtail flying quickly along a tree line or puddling its probably a male, if you see one fluttering slowly around a flower its probably a female. The flight season for Papilio canadensis typically ends mid-to-late June so I have to move quickly if I am going catch gravid females.

I have been out a lot this past week, and I had only seen males. All the prime nectar sources from last year either weren't flowering or had been cut back. Today after patrolling my usual sites and coming out empty-handed again I decided to explore new areas. Well, it worked, and I can tell you that I was pretty relieved.

Papilio canadensis female - first female of 2012!

The first 2 came in rapid succession, I caught the first feeding on the flower below and after I tucked her away safely another came to visit a flower just feet away from where I caught the first. The is the flower that they were feeding on:

I'll try to remember to look up the name of the flower, or if you know just post it below in the comments! After doing some more exploring I found an even bigger patch of these flowers and I caught a third female.

Nectar patch a great collecting spot for female P. canadensis

Similar nectaring patch to the one above, just a few meters away from it.

I sleeved these three females over live saplings of Trembling Aspen and I will feed them tomorrow.

Caterpillar of the day: Papilio cresphontes

The Giant Swallowtail - Papilio cresphontes (Papilionidae)

Papilio cresphontes caterpillar resting on a lemon leaf. Photo: Wikipedia.org

The Ottawa Citizen reported today that the range of the Giant Swallowtail (Papilio cresphontes) butterfly has now reached Ottawa (click here to see the full article). Interestingly, I observed a butterfly earlier this May near Kilmarnock Lock that I had suspected was a P. cresphontes, but I thought that I must have been mistaken because - to my knowledge - the species didn't occur this far north.

A year ago macroecologist Jeremy Kerr, who studies range shifts in butterflies, had apparently predicted that P. cresphontes would reach Ottawa in three years. Kerr is a macroecologist, meaning that he studies large-scale ecological processes such as species range shifts of changes in species richness over large spacial scales. Butterflies are one of the main systems used in his research partly because reasonably accurate species richness and abundance data is concurrently available over both a long time scale and wide geographic range.

This beautiful butterfly has a wingspan approaching 15cm (range: 8.5-14cm). The fore wing (FW) length ranges from 55-62 mm with an average of 58.5 mm. Yes, this butterfly is quite large!

Papilio cresphontes adult. Photo: Wikipedia.org

Papilio cresphontes adult. Photo: Wikipedia.org

The caterpillar life stage starts out like other Papilio species, masquerading as a bird-dropping. Yet, unlike many Papilio caterpillars it does not change into a green caterpillar with eyespots (e.g. P. glaucus, P. troilus), or a caterpillar with repeating rings of different colours (e.g., Papilio polyxenes) in its later and larger instars. The caterpillar feeds on Rutaceae species, such as Citrus, Zanthoxylum americanum, Ptelea trifoliata, Ruta graveolens. Other Papilio species that similarly remain as bird droppings are all closely related and include: Papilio anchisiades, Papilio astyalus, Papilio erostratus, Papilio hectorides, Papilio thaos, and Papilio torquatus. The caterpillar gets to about 5.5 cm.

Papilio cresphontes caterpillar extending it's osmeterium. Photo: Wikipedia.org

If you see one of these butterflies, or any species for that matter, be sure to report you sighting at eButterfly.ca

**UPDATE: See a video about the recent northward migration of Papilio cresphontes here! **

Life is stranger than fiction

Eyespot caterpillar the inspiration for a Pokémon character

Papilio troilus looks like the work of a cartoon animator, but instead this species was actually the inspiration  for a character called Caterpie from the cartoon Pokémon. Apparently, insects were used heavily as inspiration for Pokémon species.

Pokémon characters inspired by swallowtail butterflies. Left to right: Caterpie, Butterfree, and Metapod.

Late instar Papilio troilus in a leaf shelter [Photo: Wikipedia.org] 

Caterpie has several features similar to Papilio caterpillars including large eyespots, and a Y-shaped osmeterium - a defensive organ charateristic feature of the Papilio genus. It also has a green dorsal body and a yellow ventral side, and therefore most closely resembles larval Papilio troilus and the closely related Papilio palamedes. Either of these species could have been the inspiration for Caterpie.

Yet, various websites [wrongly] cite other Swallowtail species as the inspiration. For example, the current Wikipedia page lists Papilio cresphontes as the species on which Caterpie is based, but P. cresphontes isn't green during any of it's larval stages and doesn't even have eyespots (#TaxonomyFail)! Papilio glaucus is cited as the model here, which is a closer guess (at least this species is green with eyespots), but this is also wrong because P. glaucus lacks the yellow underbelly (instead it is a lighter green than the dorsal side).

Final instar Papilio thaos caterpillar which looks nearly identical to Papilio cresphontes which has been wrongly cited as the inspiration for Caterpie.

Final instar Papilio canadensis caterpillar with the osemeterium (a defensive organ) extended.  P. canadensis was considered a sub-species of P. glaucus until recently and both have very similar-looking caterpillars.

I have always thought the little downward-slanting markings within the eyespots of some Papilio caterpillars  (including Papilio canadensis pictured above) looked like the classic cartoon "eyebrows" used to indicate a character's anger (e.g. the Angry Birds logo). In fact, a similar technique has been used with Caterpie when the character is launching it's "String Shot" attack.

Caterpie launching the String Shot attack. Note the angry eyebrows. [Image from Bulbapedia.net]   

Just like real caterpillars, Caterpie eventually pupates into Metapod (which does resemble the chrysalis of Papilio species), and finally into Butterfree which does not look like any Swallowtail butterfly I have seen...