Reversed sexual dimorphism

Reversed Sexual Dimorphism (RSD) feels like such an interesting puzzle (and something I learned more about in class yesterday regarding fish.  Look up Angler fish and what happens to those poor little males!). 

There seem to be a couple different questions around this phenomenon.  Part of this is pointed out in the paper I talked about yesterday by Plumpton & Lutz (1996), in which the females were heavier, but the males were larger on every measure of body size. The authors suggested that it could have been sampling error because of the breeding season, but maybe it's something else. 

Swaddle and colleagues (2000) list a bunch of different birds who display RSD (e.g., hawks and vultures (Accipitridae), falcons (Falconidae), sandpipers and snipe (Scolopacidae), phalaropes (Charadriidae), jacanas (Jacanidae), skuas (Stercorariidae), boobies (Sulidae), frigate birds (Fregatidae), owls (Strigiformes), cuckoos (Cuculidae), hummingbirds (Trochilidae), manakins (Pipridae), and some ratites (Struthioniformes)).  These birds show (what I'm going to naively call) complete RSD.  That is, the females are larger than the males on all traits.  

Swaddle and colleagues look at the fairy wren, where the story is far less clear.  

Some species of Fairy wren (Maluridae) demonstrate complete RSD, whereas others demonstrate independence between body parts.  That is, the males might have longer tarsus length whereas the females have longer tails. This suggests independence of features for RSD (and maybe sexual dimorphism in general?). 

Most theories of sexual dimorphism (in primates, at least) suggest that males are larger in order to protect access to mates, and by extension access to resources.  What might it mean for a species to have sexual selection working independently on different traits?  Swaddle and colleagues (2000) state that such a generalist theory won't work with the (elegant) evidence they found. They found that RSD occurs in tail length during the breeding season, suggesting that the shorter tails of the males might be selected for by females (and are used extensively in the males' mating displays).  

What might this mean if we look at RSD (or SD generally) and the traits as independently selected for, rather than generally selected for. Instead of all over size differences = sexual dimorphism for mate/territory defence or attraction, perhaps different traits are selected for for different reasons. In some species this happens consistently that one sex is larger, in other species, maybe it happens independently? 

Of course, I'm now going to see what folks say about burrowing owls and RSD..... 

And you really should read this paper -- they do a beautiful job incorporating behavioural evidence, morphology, and phylogenetic modelling. 

Swaddle, J.P., Karubian, J., & Pruett-Jones, S. (2000). A novel evolutionary pattern of reversed sexual dimorphism in fairy wrens: implications for sexual selection. Behavioural Ecology, 11(3), 345-349. 

More on Burrowing Owls

I spent Friday night reading about Burrowing Owls (Athene cunicularia).  If you haven't seen one in real life, you should. Most engaging birds ever (not my pictures, below is from Canadian photography life).

After spending a couple weeks in New Mexico (and the lead up to the trip) these birds became a bit of an obsession.  There are power point slides to demonstrate just the level I took this obsession that will remain secret until I die and are housed with my partner who will protect them with his life as well.

Being a comparative psychologist, it just made sense that I would dive into the literature and find out what was out there.  I was surprised by how little there was.

Martin (1973) studied two locations of owls outside of Albuquerque (15 breeding pairs).  It's a really nice overview if you haven't ever read a bird paper and don't know anything about owls, burrowing in particular.

Here's what I'm finding most interesting about these animals -- and I suspect a lot of it has to do with the fact that I study primates and sometimes canines.  In these species, we see sexual dimorphism.  The males are typically larger (in some cases much larger) than the females.  We posit that this is because of mate defense.  Sterck and colleagues (1997) post that given that resources are the limiting factor for female reproduction, females tend to map onto food patches.  Given that females are the limiting factor for male reproduction, males tend to map onto females.  Different sorts of social groups arise from this given the type of food, the distribution of the food, and how much of each (food and mates) can be guarded by one or more animals.

Martin (1973) found that the males were heavier that the females by a mean of 7.9 g. (These are little birds). However, strigiformes (aka owls) exhibit something called reversed sex dimorphism (RSD).  In these birds, and in falconiformes, the female is larger than the male. Plumpton and Lutz (1994) found that female burrowing owls were smaller than males on all measures rectrix length (tail feathers, I think), wing chord (wing length for us lay folks), tarsometatarsus length (body length, I think).  The females were, however, heavier than the males.  The authors acknowledge that this was during nesting time and the female mass might be larger due to reproductive events (eggs, nesting).

So here's what I'm thinking about.  What are the selection pressures that select for RSD in other owls?  I need to also look this up and find some research on what that looks like.  And then, what are the different selection pressures that do not select for RSD in burrowing owls?  Plumpton and Lutz (1994) make an interesting argument at the end of their paper that the lack of RSD in burrowing owls might help to inform why we see RSD in raptors like falconiformes and strigiformes (are owls raptors?).

Next question is about burrowing owls hissing like rattlesnakes!!!

I include references in case you're interested in reading about burrowing owls!

Botelho, Eugene S., Patricia C. Arrowood, and D. M. Bird. “Nesting Success of Western Burrowing Owls in Natural and Human-Altered Environments.” Raptors in Human Landscapes. Academic Press, New York, 1996, 61–68.

Butts, K. O., and J. C. Lewis. “The Importance of Prairie Dog Towns to Burrowing Owls in Oklahoma.” In Proceedings of the Oklahoma Academy of Science, 62:46–52, 1982. http://digital.library.okstate.edu/oas/oas_pdf/v62/p46_52.pdf.

Catlin, D. H., D. K. Rosenberg, and K. L. Haley. “The Effects of Nesting Success and Mate Fidelity on Breeding Dispersal in Burrowing Owls.” Canadian Journal of Zoology 83, no. 12 (2005): 1574–80.

Conway, Courtney J., Victoria Garcia, Matthew D. Smith, and Katie Hughes. “Factors Affecting Detection of Burrowing Owl Nests during Standardized Surveys.” The Journal of Wildlife Management 72, no. 3 (2008): 688–96.

Conway, Courtney J., and John C. Simon. “Comparison of Detection Probability Associated with Burrowing Owl Survey Methods.” The Journal of Wildlife Management, 2003, 501–11.

Desmond, Martha J., and Julie A. Savidge. “Factors Influencing Burrowing Owl (Speotyto Cunicularia) Nest Densities and Numbers in Western Nebraska.” American Midland Naturalist, 1996, 143–48.

Haug, Elizabeth A., and Andrew B. Didiuk. “Use of Recorded Calls to Detect Burrowing Owls (Uso de Llamados Grabados Para Detectar La Presencia de Athene Cunicularia).” Journal of Field Ornithology, 1993, 188–94.

Haug, Elizabeth A., and Lynn W. Oliphant. “Movements, Activity Patterns, and Habitat Use of Burrowing Owls in Saskatchewan.” The Journal of Wildlife Management, 1990, 27–35.

Levey, Douglas J., R. Scot Duncan, and Carrie F. Levins. “Animal Behaviour: Use of Dung as a Tool by Burrowing Owls.” Nature 431, no. 7004 (2004): 39–39.

Machicote, Marcela, Lyn C. Branch, and Diego Villarreal. “Burrowing Owls and Burrowing Mammals: Are Ecosystem Engineers Interchangeable as Facilitators?” Oikos 106, no. 3 (2004): 527–35.

Martin, Dennis J. “Selected Aspects of Burrowing Owl Ecology and Behavior.” Condor, 1973, 446–56.

Owings, Donald H., Matthew P. Rowe, and Aaron S. Rundus. “The Rattling Sound of Rattlesnakes (Crotalus Viridis) as a Communicative Resource for Ground Squirrels (Spermophilus Beecheyi) and Burrowing Owls (Athene Cunicularia).” Journal of Comparative Psychology 116, no. 2 (2002): 197.

Restani, MARCO, L. R. Rau, and D. L. Flath. “Nesting Ecology of Burrowing Owls Occupying Black-Tailed Prairie Dog Towns in Southeastern Montana.” Journal of Raptor Research 35, no. 4 (2001): 296–303.

Rowe, Matthew P., Richard G. Coss, and Donald H. Owings. “Rattlesnake Rattles and Burrowing Owl Hisses: A Case of Acoustic Batesian Mimicry.” Ethology 72, no. 1 (1986): 53–71.

The internet doesn't make you smarter!

My favourite psychologist -- Frank Keil -- is an author on a study looking at how when folks do internet searches they believe they know what they're just glancing over -- or not even finding! -- on the internet.  Here's a Summary of the study. 

This is a really interesting thing to think about in education.  I know that if I google something, I'll shortly forget the answer. Sometimes, I won't even remember that I've googled it until I do it again and recognize the answer. It isn't really knowledge in the same way that the vast volume of material I learned to do my comprehensive exams for my PhD is knowledge -- I can still pull that out, with dates and citations.  But what is it then, and is it useful for those of us standing in front of a classroom?

I've seen it done both ways.  I fall into the "No Googling" camp.  If you think about something, you likely can figure it out.  Although, this applies largely to the sorts of process based, problem solving, experiential education that I do in my classrooms.  I don't want students fact checking as we're trying to figure out why males and females have different mating strategies.  

My question here is geared more specifically towards how we can do this with facts.  There seems to be a tension between process and content.  I'm pretty sure that this tension is not a real tension, but rather arises from a generation of professors who were educated on facts, but then are asked to teach the process of fact-acquisition (e.g., critical thinking, logical argumentation, resilience, self-reflection, etc.).  We think that because we can tell you when Wilhelm Wundt's laboratory was started in Leipzig (ummm 1879), we "know more". 

Given Google, I wonder if we (the university educators) have set up the results in Keil's study perfectly.  We profess to know more than our students; therefore, when they get a new fact, it adds to their "what I know" counter.  Even if it isn't retained, it's there long enough to count as something they know. 

I think there's another way to do this, and I'd like to see what happens if Keil's study is twisted a bit to move into the larger context of education.  Namely, what happens if we ask them to figure something out?  They can use the internet, or not.  I'd be willing to wager that the students who have to figure something out without using the internet will be more confident in their knowledge, and their retention of that knowledge, that those who look up "how do I do X" on google. 

Sounds like a follow up study........