Science - USA (2022-06-03)

SCIENCE science.org

MEMBRANES

Refining

petroleum with

membranes

Polymeric membranes

may lower the energy

requirement for oil

refineries

By Hyeokjun Seo and Dong-Yeun Koh

T

he utility of membrane technology

in a wide range of industries is be-

ing driven by the integration of ad-

vanced materials into process-ready

devices, rising energy prices, and

the need for decarbonization. The

groundbreaking invention of an asymmet-

ric cellulose acetate membrane in the early

1960s popularized the concept of pressure-

driven separation. The desalination and gas

purification fields, in particular, embraced

this technology and have since developed

more energy-efficient systems for various

applications. This paradigm shift is now be-

ing further accelerated in membrane-based

petroleum refining with the development of

membrane materials such as those from the

spirobifluorene aryl diamine (SBAD) fami-

lies ( 1 ). On page 1105 of this issue, Chisca et

al. ( 2 ) offer a concept for membrane-based

crude oil fractionation that combines sim-

ple pore tuning of polymeric membranes

with traditional membrane fabrication

methods, which may allow for fast sorting

of complex hydrocarbons.

Crude oil separation—the process of

separating crude oil into different petro-

leum products—is a crucial process of the

product supply chains for fuels and com-

modities. The US Energy Information

Administration (EIA) forecasts the current

global production of petroleum and liquid

fuels, at about 100 million barrels per day,

to keep increasing until 2050 ( 3 ). In the ab-

sence of a competitive alternative for fuel

and various petroleum products, the hydro-

carbon industry must aggressively reduce

the carbon footprint of its operation ( 4 ).

This is where advanced membrane separa-

tion strategies come into play, as membrane

Department of Chemical and Biomolecular Engineering

(BK21 Four), Korea Advanced Institute of Science and

Technology, Daejeon 34141, South Korea.

Email: [email protected]

Clonal Warramaba grasshoppers are thus
in robust health after about a quarter of a
million years without sex. This corroborates
what some biologists have long suspected—
many parthenogenetic species are thriving.
For instance, some parthenogenetic insects
are abundant pests ( 2 , 3 ), and recent ge-
nomic studies of parthenogenetic animals
have found little evidence of any deleterious
consequences ( 4 , 5 ). So, if parthenogenetic
populations have a huge reproductive ad-
vantage over sexual ones, with no ill effects,
why are most species sexual?
Kearney et al. attribute the rarity of par-
thenogenetic lineages to the rarity of their
origins, but origins are likely only part of
the story, with extinctions being the other
part. Parthenogenetic lineages have a fa-
mously “twiggy” distribution, with most of
them having originated relatively recently
in geological terms, thus constituting mere
“twigs” on the tree of life rather than major
branches. This pattern implies that parthe-
nogenetic lineages have a strong tendency
to go extinct ( 6 , 7 ).
Many scientists have assumed that the
process that drives parthenogenetic lin-
eages to extinction must operate on short
time scales and must also give an advantage
to sexual individuals in competition with
parthenogenetic ones ( 8 – 10 ). But the news
about Warramaba grasshoppers casts doubt
on this assumption and supports an alterna-
tive view, that the short-term and long-term
fates of parthenogens are decoupled. In the
short term, parthenogens very often thrive,
but in the long term, they are almost always
doomed ( 7 ). Or, to put it another way, even if
parthenogenesis doesn’t confer costs, it ap-
pears to confer substantial risks.
What, then, are the long-term risks of par-
thenogenesis? In theory, sexual reproduc-
tion—specifically the genetic recombina-
tion that it entails—breaks up associations
between beneficial and harmful genetic
variants, allowing natural selection to pro-
mote the spread of beneficial variants and
the loss of harmful ones ( 9 ). Consequently,
adaptive evolution is expected to be more
efficient in sexual populations than par-
thenogenetic ones. This may make sexual
populations more evolutionarily resilient to
severe challenges, such as new pathogens,
predators, or competitors or other changes
in the environment.
The news about the healthy grasshoppers
may prompt researchers who are assessing
parthenogenesis to look less at its costs and
more at its risks. Unfortunately, risk is more
difficult to measure than cost—just ask any
investor. Although measuring risk is more
difficult, it is not impossible. One needs to
proceed as an actuary does, by compiling sta-
tistics about large numbers of similar cases.

Here, the relevant cases are species. To mea-

sure how risky parthenogenesis is, and on

what time scale, there needs to be something

like a census of all the members of a large

group of related species, assessing which are

parthenogenetic and which are sexual.

Such a comprehensive approach, includ-

ing every species in a large group, has the

advantage of avoiding selection biases re-

garding which parthenogenetic lineages to

study. Kearney et al. refer to W. virgo as a

“classic case” of parthenogenesis because it

has been studied for decades with increas-

ingly sophisticated methods. Perhaps these

grasshoppers attracted the attention of gen-

erations of researchers because they are

unusually successful and abundant. A more

comprehensive study may turn up cases

of rarer parthenogenetic lineages, some of

which may be paying higher costs ( 4 ).

A comprehensive phylogenetic study will

enable the analysis of differences between

the extinction rates of sexual and partheno-

genetic lineages ( 11 , 12 ), the investigation of

time scales on which these occur, and com-

parative analyses to zero in on potential

causes. A call for such a study on a large group

of parthenogenesis-prone organisms is a tall

order. Such comprehensive phylogenetic

trees have been assembled for a few groups

of vertebrates, but to study parthenogenesis,

the crucial groups to look at are invertebrates

such as insects, mites, and nematodes. These

lineages are much lesser known, with a large

proportion of species that do not yet even

have scientific names or descriptions ( 13 ). For

instance, of the four species of Warramaba

mentioned by Kearney et al., three were un-

named until 2018 ( 14 ). The better we can un-

derstand these neglected branches of the tree

of life, the better we will be able to investigate

both the risks of being parthenogenetic and

their counterpart—the long-term rewards of

being sexual. j

REFERENCES AND NOTES

1. M. R. Kearney et al., Science 376 , 1110 (2022).


2. A. A. Hoffmann, K. T. Reynolds, M. A. Nash, A. R. Weeks,
   Proc. R. Soc. London Ser. B 275 , 2473 (2008).


3. L. Ross, N. B. Hardy, A. Okusu, B. B. Normark, Evolution
   67 , 196 (2013).


4. K. S. Jaron et al., J. Hered. 112 , 19 (2021).


5. J. Kočí et al., Mol. Ecol. 29 , 3038 (2020).


6. I. Schön, D. K. Lamatsch, K. Martens in Recombination
   and Meiosis: Models, Means, and Evolution, R. Egel, D.-H.
   Lankenau, Eds. (Springer, 2008), pp. 341–376.


7. G. C. Williams, Natural Selection: Domains, Levels, and
   Challenges (Oxford Univ. Press, 1992).


8. G. C. Williams, Sex and Evolution (Princeton Univ. Press,
   1975).


9. S. P. Otto, J. Hered. 112 , 9 (2021).


10. M. Neiman, P. G. Meirmans, T. Schwander, S. Meirmans,
    Evolution 72 , 1194 (2018).


11. W. P. Maddison, P. E. Midford, S. P. Otto, Syst. Biol. 56 , 701
    (2007).


12. D. S. Caetano, B. C. O’Meara, J. M. Beaulieu, Evolution 72 ,
    2308 (2018).


13. N. E. Stork, Annu. Rev. Entomol. 63 , 31 (2018).


14. M. R. Kearney, Zootaxa 4482 , 201 (2018).

10.1126/science.abq3024

3 JUNE 2022 • VOL 376 ISSUE 6597 1053