Science - USA (2022-06-03)

INSIGHTS | PERSPECTIVES

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below acute toxicity. Sublethal effects are of-
ten compounded by synergistic interactions
with secondary stressors, including climate
change, reduced nutrition, disease, colony
state, and many others. Additionally, the ef-
fects of agrochemicals differ across species
and taxonomic groups, making it challenging
to predict their impacts across diverse polli-
nator communities.
Mounting evidence shows that agricul-
ture—and particularly high-intensity modern
agriculture—plays a role in declining insect
populations and may accelerate the effects
of other stressors such as climate change.
Large-scale, intensified agroecosystems are
associated with high rates of agrochemical
exposure, reduced floral diversity, and more
extreme temperatures. Potentially reflect-
ing the synergies between these stressors ,
the strongest negative impacts of climate on
insects occur in high-intensity agricultural
landscapes ( 13 ). It is necessary to support
insect biodiversity by reducing the effects of
agrochemicals. Two important avenues will
be reduced, more-targeted pesticide use and
improved regulation. Emerging technolo-
gies for high-throughput quantification of
sublethal impacts of agrochemicals on in-
sects (for example, on behavior, physiology,
or gene regulation) could improve our abil-
ity to screen effects across species. A better
understanding of stressor interactions will
also be critical for identifying environmental
contexts (e.g., seasonality, weather, etc.) when
pesticides pose the greatest risk to pollina-
tors. Postregistration monitoring could also
help identify unintended effects that were
not identified during screening. A potential
practical upside of the study of Weidenmüller
et al. is that food resources can mitigate the
effects of glyphosate, highlighting the poten-
tial value of incorporating pollinator plant-
ings and native habitat into working agricul-
tural landscapes. j

REFERE NCES AND NOTES

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    10.1126/science.abq5554

EVOLUTIONARY BIOLOGY

The clones are all right

I

n most animal species, only half of

the population—the females—invest

resources in producing offspring. But

some species consist entirely of females

that can produce offspring without

mating, a process known as parthe-

nogenesis. Parthenogenesis looks like the

more efficient system: A parthenogenetic

species seemingly ought to out-reproduce

and thus outcompete a similar species

that reproduces sexually. And yet the over-

whelming majority of species are sexual.

Why? This counterintuitive trend implies

that sexually produced offspring must

have some advantage over parthenoge-

netically produced ones, but what exactly

is this advantage? On page 1110 of this is-

sue, Kearney et al. ( 1 ) report an exhaustive

search for such an advantage in Australian

grasshoppers. Their negative result sug-

gests that the advantage may not be some-

thing discoverable by studying present-day

populations. It may play out on longer

time scales, in the patterns of origin and

extinction of whole lineages.

The parthenogenetic grasshopper spe-

cies Warramaba virgo (see the photo)

originated by hybridization between two

sexual species, Warramaba flavolineata

and Warramaba whitei. Kearney et al.

sampled populations from across the geo-

graphic ranges of all three species, bringing

the grasshoppers into the laboratory and

measuring 14 different fitness-related physi-

ological and life-history traits. The results

indicate that the fitness of the parthenoge-

netic grasshoppers is equal to that of the

sexual ones in every respect. One hypotheti-

cal route to such high fitness for partheno-

gens is by infusing genetic diversity from

sexual populations by means of multiple

hybrid origins or rare mating. The authors

tested for that by surveying DNA variation

across much of the grasshoppers’ genomes,

and the results rule out that possibility. The

parthenogens have little genetic diversity

compared with their sexual relatives and

are descendants of a hybrid ancestor that

lived more than 200,000 years ago.

Kearney et al. found in

the parthenogenetic

grasshopper Warramaba

virgo (shown here) that

asexually reproducing

species may thrive in the

short term even if they are

doomed in the long run.

Department of Biology, University of Massachusetts Amherst,

Amherst, MA, USA. Email: [email protected]

Parthenogenetic grasshoppers confound predictions

by showing no signs of decline

By Benjamin B. Normark

PHOTO: MICHAEL KEARNEY

1052 3 JUNE 2022 • VOL 376 ISSUE 6597