Please join us on Friday, October 2, for our weekly speaker seminar!
Seminar Pre- Reception: 3:00 PM in JHA 1214
Seminar: 3:30 PM in JHA 1216
Speaker: Dr. James Lamsdell
Hosted by: Dr. Curtis Congreve
Seminar Title: Learning from the Past: Horseshoe crabs as a case study in PaleoEcoEvoDevo
Abstract: The occupation of new environments by evolutionary lineages is frequently associated with morphological changes. This covariation of ecotype and phenotype is expected due to the process of natural selection, whereby environmental pressures lead to the proliferation of morphological variants that are a better fit for the prevailing abiotic conditions. One primary mechanism by which phenotypic variants are known to arise is through changes in the timing or duration of organismal development resulting in alterations to adult morphology, a process known as heterochrony. However, in order to explore these mechanisms in an appropriate context a historical perspective is required, combining evidence of organism ecology, evolutionary relationships, and developmental biology. One particularly interesting group in which such information is available is the Xiphosurida, or horseshoe crabs.
Horseshoe crabs have a fossil record stretching back hundreds of millions of years, and their apparent morphological stasis over this time has fed their reputation as ecological generalists that are able to survive any environmental change. The American Horseshoe Crab, Limulus polyphemus, is an important ecological component of the United States Atlantic coastline, particularly in areas such as Delaware Bay, where large numbers congregate on beaches to spawn. These spawning events are crucial sources of food for shorebirds including migrating Red Knots, which feed upon the eggs deposited within the sand. Horseshoe crabs are also exploited as a resource for the biomedical industry, conch and eel fisheries, and have historically been used as fertilizer. However, horseshoe crab numbers have declined steadily over the last few decades, raising questions as to the long-term welfare of the species. The fossil record shows that, despite their reputation for morphological and ecological conservatism, horseshoe crabs have undergone major marine to freshwater transitions at least two times in the past. The four extant horseshoe crab species (none of which have a fossil record) represent just a portion of the geographic and ecological diversity of a lineage which is not particularly immune to extinction. Exploring these historical changes in horseshoe crab ecology with reference to developmental patterns reveals repeated heterochronic trends associated with ecological shifts, elucidating on the operationality of evolutionary change influences both by historical, phylogenetic processes and external ecological pressures. A fuller understanding of horseshoe crab evolutionary history in turn provides opportunities to refine modern conservation efforts.