Week 07: Does transgenderism exist in nature? Some examples in birds and insects

Being transgender myself, I have often wondered if there are similar manifestations of gender expression in other species. This discussion seemed like the perfect place to explore this topic. There were quite a few papers to choose from. I picked two papers about birds, and one about insects because I felt that they provided the clearest cut examples of transgenderism in nature and were both super interesting!

In the beginning of the quarter, we talked about gender being how an organism uses morphology and/or behavior to carry out a sexual role. So it makes sense then that if we can find examples of animals adopting behaviors typical of the opposite gender, or an individual developing morphology that mimics a gender different from their own, we can examine these cases as potential examples of transgenderism in nature. Remember that we also talked about the categories of sex being based upon the gametes produced by an individual. Males produce small gametes or sperm and females produce large gametes or eggs. These definitions can help us to remember the important difference between sex and gender so that we can resist the temptation to use these terms interchangeably. That really doesn’t work well when we are describing the multiple scenarios of gender expression that we see in nature.

First, let’s talk about the hooded warbler paper. This study was done by Daniel K. Niven, in 1993. He examined a male hooded warbler, Wilsonia citrina, that acted like a female bird for 2 years in a row. I suppose you could say that this bird was transgender at least in terms of behavior, but it’s all semantics, right? This was a cool paper because it was presenting the observations from a very factual standpoint, and the researcher let us draw our own conclusions. He basically observed this bird that he called Y participating in typically female hooded warbler activities such as nest building and sitting on the nest. There was another male bird (X) whose territory the nest was in, that apparently accepted Y as a mate, feeding him and the nestlings. Now you may ask, where did the nestlings come from if Y was in fact male, He can’t lay eggs, right? Turns out hooded warbler females often lay eggs in other birds’ nests, or the eggs may have come from a brown headed cowbird female laying her egg in a hooded warbler nest.

warbler

A brown headed cowbird nestling (right) being raised by a warbler adult (left) [Source]

Therefore, Y had no shortage of surrogate nestlings! Unfortunately, however, the nest was depredated, and Y took off for the rest of the year. He then did the same thing again the next year with another male bird (Z) who also accepted him as a mate. So here are two separate male birds in different territories that have accepted Y as a mate even though it was shown at the end of the study that Y had fully developed male gonads with no evidence of any ovarian tissue. The interesting thing, and of course the thing that we don’t know, is why Y acted this way. This was obviously a clear example of transgender behavior in this bird, and it seems that if there is one bird adopting these behaviors there are probably more. I bet there are a bunch of ecology research projects going on right now to study this very phenomenon!

Next, let’s talk about damselflies. We discussed a paper that describes two different female morphs of the damselfly species Ischnura ramburi. One female morph, the andromorph, mimics the coloration and to some extent the behavior of the male damselfly. The other female morph, the heteromorph, looks like the female which is more cryptically colored. Hugh M. Robertson, the author of the paper wanted to know why the andormorph (which we could think of as a transgender morph) existed. In other words, what advantage might the andromorph have? Damselflies have very short lifespans, and as he found out in this study, copulate for long periods of time. Robertson though there might be an advantage gained by avoiding this time and resource consuming activity. To explore what he called the andromorph advantage, he marked and monitored the behavior of damselflies during one season around a pond in Lake Placid, Florida, collecting data on the types of interactions between males and females, both andromorph and heteromorph. He found that the average length of copulation was 3 hours, and that the heteromorphs copulated 2 times as often as the andromorphs. He then theorized that if the andromorphs were not spending all this time copulating, they would have more time to grow and care for eggs, be less subject to predation, and have more mate choice, all seem like advantages, right? There was some debate in our group as to whether he actually proved that there was an advantage gained by being an andromorph. For example, couldn’t being brightly colored actually make you more susceptible to predation? In any event, the paper did get us thinking about the possibilities of variation in gender expression in nature, and what could be the possible drivers behind that variation.

andromorphfemale

Brightly colored female andromorph of Ischnura ramburii (Source)

heteromorph female

More cryptically colored female heteromorph of Ischnura ramburii (Source)

The final paper was written by Robert Bleiweiss and was about asymmetry in expression of transsexual phenotypes in hummingbirds. This paper examined the numbers of male hummingbirds that looked like female hummingbirds and compared them to the numbers of female hummingbirds that looked like male hummingbirds. Are you confused yet? I liked this paper for a few reasons, but it was confusing. The main take home point for me was that the author was able to show that there is in fact asymmetry in these two types of hummingbirds. The feminine male birds were much less common than the masculine females. This seemed like a good argument for a spectrum of gender expression rather than strict adherence to the idea of the binary, that a bird needed to be either female or male in phenotype. I think that the very fact that there is asymmetry and not equal expression of phenotypes for each sex implies that gender expression is not binary, and that we should consider a spectrum of phenotypic expression across all species. We talked about how confusing it was that the author chose to use the term transsexual rather than transgender. We agreed that if we thought about this paper in terms of the definitions of sex and gender that we came up with in week one, it made much more sense.

hummingbirdfemale

A female Heliangelus viola hummingbird exhibiting female like female coloration (Source)

hummingbird male

A male Heliangelus viola hummingbird exhibiting male like male coloration (Source)

These papers were great examples of what transgenderism might look like in nature. In examining both birds and insects we found simple examples that got us thinking about what some of the potential drivers of the expression of transgenderism in nature could be. We also got an idea of the tremendous diversity of different expressions of gender related behaviors, and we were inspired to start thinking beyond the binary even in nature.

Outreach Idea:

In order to get folks to start thinking about gender expression as a continuum instead of binary, present them with different examples of species such as the hummingbirds or damselflies above that have different variations or morphs of male and female. There will be some species with morphs that have female gametes but act or look more male, and some species that have morphs that have male gametes but look and act more female, and there will be some species that have both! Divide up into groups and have each group pick a species, then have them list all the possible advantaged and disadvantages to having these different morphs. This will get folks not only to start thinking about a non-binary system of gender expression, but what some of the drivers of this continuum could be. Have fun with it, and draw pictures!

-Dane

Resources

Niven, D. K. (1993). Male-male nesting behavior in Hooded Warblers. The Wilson Bulletin, 105(1), 190-193. PDF

Robertson, H. M. (1985). Female dimorphism and mating behaviour in a damselfly, Ischnura ramburi: females mimicking males. Animal Behaviour, 33, 805-809. PDF

Bleiweiss, R. (2001). Asymmetrical expression of transsexual phenotypes in hummingbirds. Proceedings of the Royal Society of London B, 268, 639-646. PDF

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