Colonization genetics of globally invasive marine bryozoa: does adaptation prior or post-introduction determine spread?
- Josh Mackie
San Jose State University
- Sean Craig
Humboldt State University
End Date: September 08, 2014
In part due to their location (out of sight, under water), the study of marine invasions has previously focused on identifying the exotic species discovered in a given bay or harbor, with fewer studies focused on the mechanisms by which these organisms invade a new site. Recent studies, for example, have catalogued the contents of ballast tanks in ships that have sailed from a distant port, taking on foreign water (and the propagules of exotic organisms) and emptying them into a new site (thus introducing non-native species in the process).
Our research centers on the geographic spread of bryozoans in the genus Watersipora. Global invasions by species in this genus have been frequent and widespread over the past 50 years, making it an important group for determining how ships, smaller vessels, and other modern impacts on coastlines (including copper anti-fouling paints) influence biological invasion.
Summary to DateIs vessel movement or water temperature the limiting factor in invasions? Two Watersipora species were grown under laboratory conditions to measure genetic influence on the ability to grow and reproduce successfully at a certain temperature. The motivating question was: can temperature-related fitness, as opposed to simply considering opportunities for dispersal, predict the pattern of invasion?
To test how sensitive invasions are to temperature, we centered studies on two “cryptic” species in the genus Watersipora, which in the past have only be distinguished by sequencing their mitochondrial Cytochrome Oxidase I (COI) gene because they are highly similar morphologically. Using genetic fingerprinting, via diploid microsatellite markers, combined with evidence of ancestry from the maternally inherited mitochondrial gene COI, we found no evidence of interbreeding of these two species.
These two species (in the Watersipora subtorquata complex) are found in different regions of the California coast. Watersipora ‘new sp.’ is found in the colder, northern waters of the California coast, whereas W. ‘subtorquata’ is found in bays and harbors along the extent of the Californian coast. We cultured multiple populations of the two species in a marine lab at either a lower temperature (11˚C) or a warmer temperature (18˚C). These common environment experiments showed that W. new sp. has poor survival in warm water, and is likely incapable of invading southern California waters, supporting the importance of genetic differences at the species-level in determining the invasion pattern.
Sampling and genetically typing colonies in the waters around San Francisco showed that fine-scale differences in temperature predicted the likelihood of finding either species. These observations demonstrate sea surface temperature, and differences of a few degrees, may predict non-native species dispersal patterns. The case study suggests also that climate change may rapidly alter range boundaries of such colonial organisms.
Field experiments measuring copper tolerance in marine organisms. Our field experiments confirm that these Watersipora species (and several other marine invertebrates), common to bays and harbors in California, have a high tolerance to the copper added into marine anti-fouling paints (used to keep ship hulls free from fouling). Interestingly, these results show that several marine organisms are no longer strongly deterred by these biocidal paints, emphasizing the need for new (hopefully environmentally friendly) marine paints/hull coatings to keep ships clean. New technologies are needed to reduce the continued introduction of copper-tolerant species around the world.
Ecological diversity of ‘cryptic’ species. Our genetic studies revealed the two Watersipora species examined are non-interbreeding species, although previously they were not recognized taxonomically as such because their physical appearances are so similar. The ecological differences highlighted in this study are large. Watersipora n. sp typically forms large colony aggregations in many areas of northern California. These structures (known sometimes as ‘bryoliths’) provide habitat for a highly diverse biomass of associated species. Larval dispersal behaviors of the two species also differ. The larvae recruiting to settlement panels in the field were found to be of the widely invasive form known as W. ‘subtorquata’. The larval dispersal pattern and timing of W. n. sp in the field is enigmatic, as larvae were not found on field-deployed settlement panels, even when panels were located in close proximity to large masses of adult colonies.
The use of genetics to explore differences among Watersipora species adds to interest in this group of bryozoans for studying a range of evolutionary and ecological phenomena. The project provided sequence data through Next Generation Illumina DNA sequencing, opening the door to further explorations of how traits such as colony growth form, reproductive timing and copper tolerance are controlled at the genomic level.
Related open access publication:
Mackie JA, Darling JA, Geller JB (2012) Ecology of cryptic invasions: latitudinal segregation among Watersipora (Bryozoa) species. Scientific Reports 2, 871, DOI: 810.1038/srep00871.
- Non-indigenous species