Sex is costly. You could die trying to find a mate. Your mate could kill you, or give you a disease. You could be unable to find a mate in the first place, in which case you’d be better off if you could reproduce asexually. Even without those risks, though, even in a simple genetic simulation, sexual reproduction means you only pass on half of your genes to your offspring.
So why do it? We know that it’s possible to reproduce without sex; lots of things do. It’s not just bacteria and protists, either: asexual reproduction occurs in some plants, insects, snails, amphibians, and reptiles, among many others. The logic of natural selection suggests that sex must confer some benefit that outweighs all the costs, at least in some situations. Essentially all of the proposed benefits of sex have to do with outcrossing, or mixing your genes with those of another, genetically distinct, individual.
Nevertheless, a lot of things that reproduce sexually do so without outcrossing. This is especially common in plants, where it’s called “self-pollination” or just “selfing.” Selfing is thought to provide short-term advantages relative to outcrossing–basically by avoiding the costs I’ve listed above. However, selfing also doesn’t provide most of the benefits associated with sex, so it’s thought to be a bad strategy in the long term. This leads to selfing being thought of as a “dead-end” strategy: the short-term advantages make it unlikely that a selfing species will return to outcrossing, and the reduced genetic variation produced by selfing make diversification less likely.
Erik Hanschen and colleagues have tested these predictions in the volvocine algae (I’m among the “colleagues,” as are John Wiens, Hisayoshi Nozaki, and Rick Michod): do selfing species ever return to outcrossing, and do they have a lower rate of diversification than outcrossing species? Both mating systems exist within the volvocine algae, and so they make a good test case. Roughly speaking, the term heterothallic refers to outcrossing species and homothallic to selfing species:
I listened to the first couple of episodes of the Big Biology podcast this weekend, and it’s quite good. Marty Martin from the University of South Florida and Art Woods from the University of Montana interview scientists about cool topics. In the first two episodes, they talk to Robert Dudley about why primates like alcohol and Denis Noble about the role(s) of stochasticity in biology.
One of the most remarkable things about multicellular organisms is the differentiation of genetically identical cells into functionally specialized cell types. It’s difficult to say exactly how many cell types a given species has, since we would first have to say how different two cells need to be to count as different types. Nevertheless, it’s clear that there’s a wide range among different multicellular groups. Within animals, for example, placozoa have around five cell types, mammals over a hundred.
Amazingly, all of these very different cell types share a genome: your liver cells are pretty much genetically identical to your brain cells (and your skin cells, your kidney cells, your muscle cells…). The dramatic differences in form and function among all these cell types are mainly a result of differences in gene expression.
Volvox has just two cell types: a dozen or so big cells that are responsible for reproduction and one or two thousand smaller cells that bear the flagella that colonies use to swim:
This was one of the main attractions for the researchers who developed Volvox as a model organism. With only two cell types, Volvox retains something close to its original form of cellular differentiation, making questions about how such differentiation evolved much more tractable.
“The president cannot obstruct justice because he is the chief law enforcement officer under (the Constitution’s Article II) and has every right to express his view of any case,” [President Trump’s personal lawyer John] Dowd told NBC News Monday.
Damn, that sounds familiar…oh yeah:
AbGradCon is an astrobiology conference for graduate students and other early-career researchers. It is intended to provide
a unique setting for astrobiologically-inclined graduate students and early career researchers to come together to share their research, collaborate, and network,
and it’s coming to Georgia Tech next year.
AbGradCon 2018 will be hosted by Georgia Institute of Technology in Atlanta, GA. The conference venue and attendee lodging will be at the Georgia Tech Hotel & Conference Center. The Technical Program for AbGradCon 2018 runs from June 4-8, while the Proposal Writing Retreat (PWR) will be held on June 1-4.
Brian Dunning’s done some sketchy shit, and he was sentenced to 15 months in prison for it. If you want to know more about that, Rebecca Watson’s scathing rebuke (and links within) is a good starting point. Nevertheless, I still listen to Skeptoid, and I think this new project sounds promising enough that I chipped in ten bucks: