After 3,000 years of dormancy, the seeds of this extinct date palm species were still viable!
I spent much of the first half of last week collecting information about the origin of sex. This topic had lots of good literature (if old, much of it was from the 80s), but it was very much about meiosis, and I doubted that I could handle writing about meiosis for a whole semester. So I’ve changed my topic. I want to examine the coevolution of pollinator-plant relationships.
Though some angiosperms are wind-pollinated, most require an animal pollinator like an insect or a bird to move pollen grains between male and female flower parts. Flowers use many different strategies to trick their pollinators and get this job done. As the preferences of the pollinators change, they create sexually selective pressures on plants. Over time, this can lead to speciation. Perhaps this is a main reason for the massive diversity of angiosperms? Potential thesis, eh?
Plants employ all kinds of crazy deceptive strategies to try to entice pollinators. Overall, these can be separated into two broad categories: food-deceptive and sex-deceptive. There is some evidence that sex-deceptive strategies are more efficient, i.e. more fit. Additionally, I found a paper that showed hummingbird pollination to be more efficient that insect pollination. This seems to indicate a kind of fitness hierarchy of pollinator-plant relationships.
Finally, pollinator-plant systems are often presented as mutualistic, but is this really the case? From what I’ve read so far, it seems like the plants are duping the poor pollinators. The plants are the only ones benefiting from/relying upon the system (usually), and the plants are evolving in response to the pollinators, not the other way around. It’s really not co-evolution, as often presented. It’s a one-way thing.
So, there are some of the directions I’m thinking about. Stay tuned for a more refined thesis!
The question of why sex is so important is integral to the whole concept behind the book that we’ll be putting together. So why has sexual reproduction flourished? Why is it better than asexual reproduction? Why not be able to do both? Dr. Tatiana mentions that there are as many as 20 viable hypotheses, so that would be plenty to make a chapter. There’s the Red Queen, the idea that sex provides important genetic recombinations in order to aim at evolution’s ever-moving target. The ratchet and the hatchet hold that sex is good because it shuffles genes to help species prevent the accumulation of deleterious mutations.
According to a nice review I read, most models in favor of sex talk about how sex: 1) increases genetic variation, 2) reduces mutations and repairs damage by recombination, 3) provides benefits to the individual. I uncovered a few others as well that have to do with everything from spontaneous bubble formation and population-level fitness benefits to capitalizing on novel genetic information and environmental pressures.
Becks, Lutz, and Aneil F. Agrawal. “Higher Rates Of Sex Evolve In Spatially Heterogeneous Environments.” Nature 468.7320 (2010): 89-92. Academic Search Premier. Web.
Hadany, Lilach, and Tuvik Beker. “Sexual Selection And The Evolution Of Obligatory Sex.” BMC Evolutionary Biology 7.(2007): 245-251. Academic Search Premier. Web. 22 Sept. 2013.
Kondrashov, A. S., 1988. Deleterious mutations and the evolution of sexual reproduction. Nature 336: 435-40.
Kondrashov, A. S. Classification of hypotheses on the evolution of amphimixis. Journal of Heredity 84: 372-87.
Lin, Robert J., and Lin Feng. “Coerced Group Collaborative Evolution As An Explanation For Sexual Reproduction’s Prevalence.” Natural Science 2.11 (2010): 1253-1263. Academic Search Premier. Web.
Lodé, Thierry. “What’s Sex Really All About?.” New Scientist 212.2837 (2011): 30-31.Academic Search Premier. Web.
Maynard Smith, J., 1978. The Evolution of Sex. Cambridge University Press. 1986. Contemplating Life Without Sex. Nature 324: 300-301.
Owen, John B. “Evolutionary Consequences Of Sexual Reproduction. (Cover Story).”Biologist 55.3 (2008): 164-168. Academic Search Premier. Web.
Sex is all about power. Contraceptives harness that power. In nature, males and females use various contraceptive-like strategies to try to control their reproductive outcomes, and Judson tells us about many of them. Females seem to use “contraception” to reinforce their choosiness (pre-fertilization sperm receptacles, hostile vaginal shape/chemistry). On the other hand, males seem only resort to contraception-like techniques when faced with intrasexual selection: sperm of competing males. Guys might peck at a mate’s cloaca before sex, release spermicidal chemicals, or have a complicated penis that acts as a plunger or a bristly scouring brush. Males also create a variety of “chastity belts” (detachable penises, huge bulky sperm, and cement-like seals) to guard against subsequent sperm competitors–rather the opposite of contraception, but still related and quite costly for males.
In humans, contraceptives aren’t directly used to maximize reproductive success. Instead, they substantially decrease the number of offspring females produce over their lifetimes. This is counterintuitive; humans are weird. Why use the BC? Humans are reaching a carrying capacity, so maybe this is our way of decreasing overpopulation. On an individual level, contraceptives function to enhance choosiness, just as they appear to work for female animals (though it is rather Bateman-y to assume all responsibility rests in the hands of our females).
However, artificial contraceptives are also being employed to control populations (of both humans and animals who are considered pesky). There is A LOT of literature out there about the practical and ethical applications of such management strategies, which ones are best, potential negative behavioral/long term effects of contraceptives, opposition from hunting and wildlife advocacy groups, etc. I found some articles on the issue:
Fan, Timothy M. “Are Intact Dogs Less Likely To Get Cancer?.” Veterinary Medicine108.6 (2013): 298-299. Academic Search Premier. Web.
Gorman, James. “Putting Nature on the Pill.” New York Times 31 Aug. 2004: F1+.Academic Search Premier. Web.
Kirkpatrick, Jay F., Robin O. Lyda, and Kimberly M. Frank. “Contraceptive Vaccines For Wildlife: A Review.” American Journal Of Reproductive Immunology 66.1 (2011): 40-50. Academic Search Premier. Web.
Li. Daiquin, et al. “Animal Behaviour: Castration Boosts Spider Stamina.” Nature 486.7403 (2012): 296. Academic Search Premier. Web.
Yoder, Christi A., et al. “Review Of Issues Concerning The Use Of Reproductive Inhibitors, With Particular Emphasis On Resolving Human-Wildlife Conflicts In North America.” Integrative Zoology 5.1 (2010): 15-30. Academic Search Premier. Web.
Also, credit for the above picture: http://weknowmemes.com/2012/08/birth-control-effectiveness/
I have several ideas for topics and, shockingly, most of them have to do with plants, a Kingdom whose sex is underrated by Dr. Tatiana and many others. (Sex advice for all creation, huh?) For example, did you know that some plants’ seeds are regularly polyembryonic? It’s like plant twins, but not really, because instead of it being a matter of chance, it’s an actual strategy that certain plants employ. But why?
Also, just like there are differences in sperm morphology between and within animal species, pollen size and shape can vary dramatically. Think about it: the wind can carry lots of grains of all kinds of different pollen, but how does a plant discriminate which pollen belongs to it? The same problem faces other sessile organisms, like sea squirts and anemones and all those other sea critters, who must rely on external sources of pollination.
The one time (so far) that Dr. Tatiana mentions plants, she’s only talking about them in context of sex in another insect species (she discusses orchids that trick horny pollinators into thinking they can mate with the plant’s flower). Speaking of the orchids, what are flowers for? Flowers are reproductive adaptations that have allowed angiosperms to be really successful. I could do a review of some of the different strategies encompassed by flowers. There’s the “eat me” strategy, the “have sex with me” strategy, and what else?
Some plants can reproduce without pollinators and other external sources of transportation, though. Some plants self-pollinate. Another potential topic might compare and contrast self-pollinating and cross-pollinating.
Finally, outside Plantae, I’m rather interested in the various groups that males or females form for social and sexual reasons. (I would call this chapter of our book “Gang Bangs.”) First of all, groups are protective, a feature both sexes can benefit from. Females can be grouped into harems, but how do they benefit from this since it limits their promiscuity? In males, we talked a lot about leks, which exist in cases where females are choosy and males are showy. Males might also band together for more sinister purposes of violence, if they are too young or too unfit to mate otherwise.
In these cases, though, Dr. Tatiana mentions that females are much less likely to conceive. This I found controversial as well–in addition to duration of copulation, are there other internal or post-copulatory mechanisms that raped females can employ to avoid rape? It would make sense that any trait that can allow the female to influence reproductive outcomes may arise and persist as a counter-adaptive measure in species where rape is prevalent. Checking that out might be a viable research option as well.
Check our the subjects of my most recent blog post doing their thing.