Here at SDSMT, along with our colleagues at the University of Tennessee and Clemson University, faculty and students are conducting research to better understand the nature of chemosymbiosis in lucinid bivalves. Lucinids (family Lucinidae) are important members of coastal biomes, particularly seagrass beds, as they harbor bacteria that oxidize reduced sulfur compounds released from the seagrass, thereby keeping harmful levels of sulfur under control. Because of the utility that lucinids have in maintaining important coastal biomes, our aim is to study the genetic, taxonomic, and functional diversity of lucinids in order to understand their evolutionary history and role in the preservation of these coastal biomes that have so much ecological and economic importance.
In the summers of 2015 and 2016, our research has taken us to San Salvador Island in the Bahamas to sample lucinids from shallow-marine coastal biomes. In 2016, our research supported the field course "GEOL 412/490/512: Field Studies in Coastal Biomes" to educate SDSMT and UT students on the nature of coastal biomes and to get them involved with the research. |
Student Projects
"My research focuses on comparing populations of the lucinid species Ctena orbiculata from open ocean habitats from those that inhabit inland marine lakes. C. orbiculata is a small lucinid found throughout the Caribbean and Gulf regions. It is also the only lucinid species we found inhabiting two small inland marine lakes on San Salvador. Because these inland populations have been isolated from the open ocean for so long, I am investigating possible evolutionary changes that may make these populations unique. These inland lakes can be thought of as "islands" in which evolution can play out many different ways depending on the unique environmental context of each lake.
Currently I have performed morphometric analyses based on shell dimensions on our C. orbiculata specimens. Results show that lake specimens tended to be larger than those in coastal habitats, indicating a clear difference in size range depending on locality. Specimens from Crescent Pond (see map) were largest, followed by those from Moon Rock Pond, with specimens from the open ocean surrounding the island being the smallest in size. While an environmental explanation has not been ruled out, I also found that no specimens from either lake experienced predation, whereas over 50% of our specimens from the open ocean were clearly killed by drilling predators (see shell pictures). Therefore, these two inland lakes may not support predators of C. orbiculata, allowing individuals to grow larger on average than their open water relatives. Continuing studies from these inland marine lake biomes is important for fully understanding the evolutionary history of lucinids as they provide us with natural laboratories for observing evolution under many different conditions. To study these populations of C. orbiculata further, I plan to employ geometric morphometrics to investigate possible differences between these populations based on shell geometry rather than size. As there are many more marine lakes on San Salvador, there is a great deal that we still do not know, but also many opportunities to learn more about lucinid evolution in action." |
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"My project this summer consisted of looking at several lucinid species from Pigeon Creek and seeing if there were any changes in size, abundance or presence/absence from 2015 to 2016. The species I looked at in particular consisted of Codakia orbicularis, Ctena orbiculata, Lucina pensylvanica, Divalinga quadrisulcata and Radiolucina amianta. Localities were split between year and location, so I ended up with three sites which included the north end of Pigeon Creek 2015, the mouth of Pigeon Creek 2015, and the mouth of Pigeon Creek 2016. Each specimen was categorized by locality, year and if it was a live or dead collected. Afterwards, height and length measurements were taken for analysis of size. The number of taxa found at a site was also recorded for abundance and presence/absence data. I used PAST, a Paleontological Statistics program, to help run my analysis for morphometric data and diversity data.
My results came back that the live specimens (Mouth 2015 and 2016) had no significant difference in size between sites. The dead morphometrics showed that Codakia and Ctena were larger at the North End of Pigeon Creek than either year at the Mouth. The dead Lucina and Divalinga specimens showed no significant differences in size between their compared sites. The diversity data showed that live and dead sites tended to group close to each other, such as the dead 2015 and 2016 specimens from the Mouth, the live 2015 and 2016 specimens from the Mouth, and the dead 2015 specimens from the North End. Within those groups Codakia and Lucina grouped closely with the live specimens, since they were the only taxa (besides one Divalinga specimen) present in the live assemblages. The dead mouth 2015 and 2016 localities stayed centered in the graph since it contained the largest diversity of taxa. The North End was its own separate group and was grouped near Ctena, which was its most abundant taxa present in the sample." |
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