Navigation Links
Drivers of marine biodiversity: Tiny, freeloading clams find the key to evolutionary success
Date:8/8/2012

ANN ARBOR, Mich. What mechanisms control the generation and maintenance of biological diversity on the planet?

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.


'/>"/>
Contact: Jim Erickson
ericksn@umich.edu
734-647-1842
University of Michigan
Source:Eurekalert

Related biology news :

1. New milestone book documents changes in the south Florida marine ecosystem
2. First seabed sonar to measure marine energy effect on environment and wildlife
3. Paints and coatings containing bactericidal agent nanoparticles combat marine fouling
4. NOAA scholarship awarded to Jan Vicente to study the impact of ocean acidification on marine sponges
5. Stanford marine biologist Barbara Block wins Rolex Award for Enterprise
6. DNA evidence shows that marine reserves help to sustain fisheries
7. Deep sea animals stowaway on submarines and reach new territory
8. ORNL protein analysis investigates marine worm community
9. SeaSketch, the next generation of UCSBs MarineMap program, will aid marine spatial planning
10. NOAA discovers way to detect low-level exposure to seafood toxin in marine animals
11. Marine scientists urge government to reassess oil spill response
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:4/15/2016)... -- A new partnership announced today will help life ... a fraction of the time it takes today, ... insurance policies to consumers without requiring inconvenient and ... rapid testing (A1C, Cotinine and HIV) and higi,s ... pulse, BMI, and activity data) available at local ...
(Date:3/31/2016)...   LegacyXChange, Inc. ... LegacyXChange is excited to release its first ... be launched online site for trading 100% guaranteed authentic ... also provide potential shareholders a sense of the value ... industry that is notorious for fraud. The video is ...
(Date:3/22/2016)... India , March 22, 2016 /PRNewswire/ ... market research report "Electronic Sensors Market for Consumer ... Proximity, & Others), Application (Communication & IT, ... Geography - Global Forecast to 2022", published ... industry is expected to reach USD 26.76 ...
Breaking Biology News(10 mins):
(Date:6/27/2016)... 27, 2016  Global demand for enzymes is ... 2020 to $7.2 billion.  This market includes enzymes ... products, biofuel production, animal feed, and other markets) ... biocatalysts). Food and beverages will remain the largest ... consumption of products containing enzymes in developing regions.  ...
(Date:6/27/2016)... ... June 27, 2016 , ... Parallel 6 , ... announced today the Clinical Reach Virtual Patient Encounter CONSULT module which enables ... the physician and clinical trial team. , Using the CONSULT module, patients and physicians ...
(Date:6/27/2016)... 27, 2016   Ginkgo Bioworks , a leading ... was today awarded as one of the World ... world,s most innovative companies. Ginkgo Bioworks is engineering ... real world in the nutrition, health and consumer ... with customers including Fortune 500 companies to design ...
(Date:6/24/2016)... NC (PRWEB) , ... June 24, 2016 , ... Researchers ... the most commonly-identified miRNAs in people with peritoneal or pleural mesothelioma. Their findings are ... to read it now. , Diagnostic biomarkers are signposts in the blood, lung ...
Breaking Biology Technology: