Drivers of Marine Biodiversity: Tiny, Freeloading Clams Find the Key to Evolutionary Success

ScienceDaily (Aug. 8, 2012) — What mechanisms control the generation and maintenance of biological diversity on the planet?

A small clam attached to its mud shrimp host. This species of clam, Neaeromya rugifera, is part of the Galeommatoidea superfamily. (Credit: Photo by Jingchun Li)

 

It’s a central question in evolutionary biology. For land-dwelling organisms such as insects and the flowers they pollinate, it’s clear that interactions between species are one of the main drivers of the evolutionary change that leads to biological diversity.

But the picture is much murkier for ocean dwellers, mainly because the scope of ecological interactions remains poorly characterized for most marine species. In one of the first efforts to examine how species interactions drive diversification of ocean-dwelling organisms, two University of Michigan researchers and an Australian colleague looked at the lifestyle choices within an exceptionally diverse superfamily of tiny clams, the Galeommatoidea.

They found that the fingernail-size-and-smaller clams’ propensity to shack up with much larger, burrowing creatures such as sea urchins, shrimp and worms was a key adaptation that led to the evolutionary success of the superfamily, as measured by its “megadiverse” status among marine bivalves. There are about 500 described species of galeommatoidean clams and many more undescribed species.

By becoming the uninvited house guests of their burrowing hosts, these freeloading, thin-shelled clams acquire a safe haven from predators prowling soft-bottomed sediments, where there’s nowhere else to hide. Gaining this deep refuge opened up a vast habitat type — soft-bottom marine sediments composed of sand, silt and clay — that would otherwise have remained unavailable to these clams.

Galeommatoidean clams are found worldwide in all the major ocean basins, in both rocky and soft-bottom habitats. Some of the clams live a solitary existence, while others form so-called commensal relationships with larger invertebrate hosts. A commensal relationship is one in which one organism benefits and the other is not harmed.

In a study scheduled for online publication Aug. 8 in the journal PLoS ONE, the U-M-led team performed a statistical analysis of the lifestyle and habitat preferences of 121 galeommatoidean species based on 90 source documents.

The researchers found that all but two of the 57 free-living species were restricted to hard-bottom habitats, typically hidden in rocky or coral-reef crevices. In contrast, 56 of the 60 commensal species were soft-sediment dwellers.

The results show that formation of commensal associations by galeommatoidean clams is robustly correlated with living in sediments. That finding is consistent with the hypothesis that evolution of these commensal relationships was primarily an adaptation to living in soft-bottom habitats.

“What was surprising was the overwhelming evidence that commensalism is associated with the soft-bottomed habitat. You seldom get such clear-cut data in an ecological study,” said Jingchun Li, a doctoral student in the U-M Department of Ecology and Evolutionary Biology and first author of the PLoS ONE paper.

Clams and other bivalves have evolved two general anti-predator strategies: armor (think oysters) and avoidance. Since galeommatoidean clams have fragile shells, they must go the avoidance route, and following a larger host into a burrow allows the clams to attain depths of up to 3 feet — hundreds of times their body lengths.

Galeommatoidean clams lack the siphons (often called necks) that other clams use to feed and breathe while remaining safely buried in the sand. Siphons consist of two tubes: Water enters the clam’s body through one siphon, flowing into gills that capture oxygen and trap food. The water then flows out of the clam through the other siphon.

The siphon-less galeommatoideans make up for that shortcoming by teaming up with hosts that constantly pump fresh seawater into, through, and then out of their burrows.

“This allows the clams to stay deep and safe, while still having access to water and oxygen and a food supply,” Li said. In this way, the hosts act as giant siphon substitutes for the tiny clams.

“Jingchun’s finding that the type of sea floor habitat strongly modulates the ecological importance of commensalism in these megadiverse clams gives us a novel insight into how ostensibly irrelevant background physical conditions may shape the evolution of species interactions in marine environments,” said study co-author Diarmaid O’Foighil, Li’s adviser and the director of the U-M Museum of Zoology.

The second phase of the clam study will test the relative importance of free-living and commensal lifestyles in driving galeommatoidean diversification. Using data from about 300 species, the researchers will construct a phylogenetic tree for the entire superfamily.

The third author of the PLoS ONE paper is Peter Middelfart of the Australian Museum.

The study is supported by a Rackham International Student Fellowship from the University of Michigan, a Molluscan Research Grant from the Malacological Society of Australasia, and a grant from the National Science Foundation.

 

Story Source:

The above story is reprinted from materials provided byUniversity of Michigan.


Journal Reference:

  1. Jingchun Li, Diarmaid Ó Foighil, Peter Middelfart. The Evolutionary Ecology of Biotic Association in a Megadiverse Bivalve Superfamily: Sponsorship Required for Permanent Residency in SedimentPLoS ONE, 2012; 7 (8): e42121 DOI:10.1371/journal.pone.0042121
Citation:

University of Michigan (2012, August 8). Drivers of marine biodiversity: Tiny, freeloading clams find the key to evolutionary success.ScienceDaily. Retrieved August 11, 2012, from http://www.sciencedaily.com/releases/2012/08/120809090308.htm

Ecology and Phylogenetics Together Offer New Views of Earth’s Biodiversity

ScienceDaily (Aug. 6, 2012) — Patterns in nature are in everything from ocean currents to a flower’s petal. Scientists are taking a new look at Earth patterns, studying the biodiversity of yard plants in the U.S. and that of desert mammals in Israel, studying where flowers and bees live on the Tibetan plateau and how willow trees in America’s Midwest make use of water.

Caterpillars feed in a forest in Peru: do insects have an effect on where plants live? (Credit: G. Lamarre)


They’re finding that ecology, the study of relationships between living organisms and their environment, and phylogenetics, research on evolutionary relationships among groups of organisms, are inextricably intertwined.

Results of this tale of two fields are highlighted in a special, August 2012 issue of the journal Ecology, published by the Ecological Society of America (ESA). Most of the results reported are funded by the National Science Foundation (NSF).

The issue will be released at the annual ESA meeting, held this year from August 5-10 in Portland, Ore.

Melding information from ecology and phylogenetics allows scientists to understand why plants and animals are distributed in certain patterns across landscapes, how these species adapt to changing environments across evolutionary time–and where their populations may be faltering.

“To understand the here and now, ecologists need more knowledge of the past,” says Saran Twombly, program director in NSF’s Division of Environmental Biology. “Incorporating evolutionary history and phylogenies into studies of community ecology is revealing complex feedbacks between ecological and evolutionary processes.”

Maureen Kearney, also a program director in NSF’s Division of Environmental Biology adds, “Recent studies have demonstrated that species’ evolutionary histories can have profound effects on the contemporary structure and composition of ecological communities.”

In the face of rapid changes in Earth’s biota, understanding the evolutionary processes that drive patterns of species diversity and coexistence in ecosystems has never been more pressing, write co-editors Jeannine Cavender-Bares of the University of Minnesota, David Ackerly of the University of California at Berkeley and Kenneth Kozak of the University of Minnesota.

“As human domination of our planet accelerates,” says Cavender-Bares, “our best hope for restoring and sustaining the ‘environmental services’ of the biological world is to understand how organisms assemble, persist and coexist in ecosystems across the globe.”

Papers in the volume address subjects such as the vanishingly rare oak savanna ecosystem of U.S. northern tier states, revealing an ancient footprint of history on the savanna as well as how it has fared in a 40-year fire experiment.

Other results cover the influence of ecological and evolutionary factors on hummingbird populations; habitat specialization in willow tree communities; growth strategies in tropical tree lineages and their implications for biodiversity in the Amazon region; and the characteristics of common urban plants.

“The studies in this issue show that knowledge of how organisms evolve reveals new insights into the ecology and persistence of species,” says Cavender-Bares.

Plants in urban yards, for example, are more closely related to each other–and live shorter lives–than do plants in rural areas, found Cavender-Bares and colleagues.

Their study compared plant diversity in private urban yards in the U.S. Midwest with that in the rural NSF Cedar Creek Long-Term Ecological Research site in Minnesota.

Cities are growing faster and faster, with unexpected effects, says Sonja Knapp of the Hemholtz Center for Environmental Research in Germany, lead author of the paper reporting the results.

“Understanding how urban gardening affects biodiversity is increasingly important,” says Cavender-Bares. “Urbanites should consider maintaining yards with a higher number of species.”

In the special issue, researchers also look at topics such as what determines the number of coexisting species in local and regional communities of salamanders. Kenneth Kozak of the University of Minnesota and John Wiens of Stony Brook University report that variation in the amount of time salamanders occupy different climate zones is the primary factor.

Evolution of an herbaceous flower called goldfields, and how that led to the plant’s affinity for certain habitats, is the subject of a paper by David Ackerly, Nancy Emery of Purdue University and colleagues. Emery is the paper’s lead author.

In all, 17 papers combine ecology and phylogenetics to offer new answers to long-standing questions about the patterns and processes of biodiversity on Planet Earth.

 

Link:

http://www.nsf.gov/news/news_summ.jsp?cntn_id=125048&org=NSF&from=news

Citation:

National Science Foundation (2012, August 6). Ecology and phylogenetics together offer new views of Earth’s biodiversity. ScienceDaily. Retrieved August 9, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120806130852.htm

What We Know and Don’t Know About Earth’s Missing Biodiversity

ScienceDaily (July 17, 2012) — Most of the world’s species are still unknown to science although many researchers grappled to address the question of how many species there are on Earth over the recent decades. Estimates of non-microbial diversity on Earth provided by researchers range from 2 million to over 50 million species, with great uncertainties in numbers of insects, fungi, nematodes, and deep-sea organisms.


Some groups of species, such as plants and birds, are well-known, with scientists discovering relatively few new ones each year. For insects and fungi, however, it is almost impossible to guess how many unknown species there are.

These findings were revealed in a first-ever study by researchers from the National University of Singapore (NUS), James Cook University in Australia, Microsoft Research in the United Kingdom and Duke University in the United States, and was first published in Trends in Ecology & Evolution on 10 July 2012.

The researchers emphasise the importance of technology such as DNA barcoding, new databases and crowd-sourcing, that could greatly accelerate the rate of species discovery.

Unknown Biodiversity: Estimates

In their study, Scheffers and his colleagues collated information from numerous studies that attempt to estimate numbers and characteristics of unknown biodiversity. What may seem like straight forward questions about Earth’s biodiversity are “deceptively complex,” warned the researchers.

“What we do know,” said lead researcher Brett R. Scheffers, who is from the Department of Biological Sciences at NUS, “is that these unknown species are likely living in places where they are in danger of extinction, and that we could lose many before we realise how valuable they are.”

“The problem is how one protects an animal that has never been seen,” he added. “What we want to know is how many species there are, what they look like and where do they live.”

The report suggests that many of these species are important for medicine, water purification and provide numerous other services for humanity. For instance, a group of marine snails — the cone snail — is important for drug development ranging from pain killers to treatment of neurological diseases. Many species of these snails are newly discovered, and there is likely many more still waiting to be discovered.

“We simply cannot afford to lose these species because of neglect and short-sided economic gains,” explained co-author Professor William Laurance of James Cook University in Cairns, Australia.

Major Challenges

The researchers pointed out major challenges that complicate biodiversity inventory. These include accidentally assigning two different species the same name, and animals that look nearly identical and can therefore only be identified by genetic analyses.

Co-author Dr. Lucas Joppa from Microsoft Research in Cambridge, United Kingdom said, “Missing species will likely be hard to find, such as deep-sea organisms, high mountain species or those species that live beneath the ground. Missing biodiversity will be small — both in body size and the amount of area that they live in. This is a concern as both of these factors relate to a species vulnerability to environmental disturbances.”

Advances in Technology

Although these challenges present real struggles for future records, Scheffers and his colleagues stress that progress is being made. Novel techniques, such as DNA barcoding, new databases and crowd-sourcing, could greatly accelerate the rate of species discovery.

“New technologies such as environmental DNA analyses now exist and can detect a species’ presence from mere water samples without ever visually observing it,” said Scheffers. “Data sharing technologies over the Internet about species locations and discoveries are also expediting and expanding the catalogue of life.”

 

Journal Reference:

  1. Brett R. Scheffers, Lucas N. Joppa, Stuart L. Pimm, William F. Laurance. What we know and don’t know about Earth’s missing biodiversity. Trends in Ecology & Evolution, 2012; DOI: 10.1016/j.tree.2012.05.008

 

National University of Singapore (2012, July 17). What we know and don’t know about Earth’s missing biodiversity. ScienceDaily. Retrieved July 18, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120717084802.htm