Fossil Patagonian Plants Show High Insect Feeding diversity 52
Million Years Ago
South America has the most biodiversity of any major
region today and according to an international team of researchers,
that biodiversity began at least 52 million years ago.
Fossil leaf in the laurel family with over 30
examples of probable fairy moth feeding, from Laguna del Hunco
in Patagonia, Argentina (52 Myr). Note leaf cases at centers
of damaged areas. Scale intervals 1 cm. (Image courtesy of
Penn State)
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"What defines terrestrial ecology is plant insect interactions,"
says Dr. Peter Wilf, assistant professor of geosciences and the John
T. Ryan Jr. Faculty Fellow. "But there is very little information
about the history of insects eating plants in South America, despite
the tremendous number of plant and animal species there today. This
study provides the first window to the past on the South American
continent's ancient diversity and abundance of insects on plants 52
million years ago. This ancient biodiversity is a legacy that will
help us understand today's South American diversity."
Wilf, working with Conrad C. Labandeira, National Museum of
Natural History, the Smithsonian Institution; Kirk R. Johnson,
Denver Museum of Nature & Science, and N. Ruben Cuneo, Museo
Paleontologico Egidio Feruglio (MEF), Trelew, Argentina, looked at
plant diversity and insect feeding richness on fossil plants and
compared fossil leaves collected at Laguna del Hunco, Patagonia,
Argentina, that date to the globally warm Eocene, with fossil leaves
collected at three Eocene sites in North America -- Republic,
Washington; Green River, Utah; and Sourdough, Wyoming. The
researchers looked at the types and amounts of insect consumption on
the fossilized leaves at all four locations.
"All four floras are very rich in fossil plant species and the
Laguna del Hunco flora is the most diverse of the group," Wilf says.
They report in today's (June 20) online version of the Proceedings
of the National Academy of Sciences that by 52 million years ago,
plants and insects in Patagonia were more diverse and abundant than
those at that time in North America.
"We still do not know when Patagonia became that diverse," says
Wilf. "We have to go back in time some more to find the beginning of
increased diversity."
The researchers were very careful in the field to ensure they
achieved an unbiased sample. They also used computerized resampling
methods to eliminate any possible bias from unequal sample
sizes.
"We used identical collection methods for all the fossil leaf
collections," says Wilf. "For example, Kirk Johnson and his crews
collected the fossils at both Green River and Republic and he also
was on our Patagonia expeditions, so we can easily compare the
samples. In collecting, we count every leaf that we find and we
collect every identifiable leaf that has insect damage. Conrad
Labandeira and I scored all of the thousands of leaves from the four
fossil floras for insect damage using the same proceedures." The
researchers took the 3599 specimens collected in Patagonia from 25
quarries. The fossils are housed at the MEF in Trelew which Ruben
Cuneo directs. These fossil leaves grew during the Eocene global
climatic optimum, the warmest time period in the last 70 million
years. During this time, there were no polar ice caps and alligators
were found above the Arctic circle.
The researchers classified damage by feeding group and damage
type. The four feeding groups are those insects that feed on the
external leaf, chewing holes, edges and other leaf parts; those
insects that mine tissues inside the leaf; those that produce
bulbous galls and those that pierce and suck the leaves. Because
different insects chew, mine, gall and pierce in different ways, the
researchers recognized 52 discrete damage types from the four
feeding groups. They applied these categories to both bulk samples
from single quarries and to individual leaf species.
The insect damage on the 3599 fossil leaves from Patagonia was
compared to the 1019 fossil leaves from Republic, 894 leaves from
Green River and 792 leaves from Sourdough.
The Republic site is the most similar to the Laguna del Hunco
site in terms of volcanic setting, age, environment and distance
from the coast. After adjusting for sample size, the Republic site
also is the most diverse in plant species of the North American
sites and has diverse feeding damage.
The researchers found that the number of damage types at each of
the four major Patagonian quarries significantly exceeds each of the
three North American samples. The number of functional feeding
groups is also greater than all North American samples for three of
the four major quarries. The diversity of damage types and feeding
groups at the Patagonian sites for individual plant species hosts is
also highest.
"Insect damage on leaves, the remains of insect meals, is
uniquely valuable data," says Wilf. "While actual insect fossils can
give us taxonomic information, leaf damage provides unique
ecological data about which and how many kinds of insects were
eating and interacting with ancient plant species in the deep past.
Also, insect damage on fossil plants, which can be very abundant,
can give us a great deal of information about insects at times and
places with very few insect fossils."
Finding insect fossils is rarely easy. Fewer than 100 fossil
insect species have been described from South America for the past
65 million years, including a handful from Laguna del Hunco. The
recent Laguna del Hunco survey recorded about 100 new insect
fossils, which are now under study to determine which and how many
species they represent.
This scarcity of insect information can be mitigated by looking
at the fossilized remains of what the insects had for dinner. The
current evidence from South America suggests that there were a large
number of different insect lineages feeding on a large number of
plant species.
"There was tremendous diversity and abundance of insects and
plants in the Eocene," says Wilf. "Insects depend on plants to
survive. If you have diverse plants, you get diverse animals. We
know that plant and insect diversity are linked today and our study
shows that plant and insect diversity were linked in the past as in
today's South America."
###
The National Geographic Society and the National Science
Foundation funded this work.
This story has been adapted from a news release issued by
Penn State.
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