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More than one way to invade: lessons from genetic studies of Carcinus shore crabs
Citation:
DARLING, J. More than one way to invade: lessons from genetic studies of Carcinus shore crabs. Chapter 6, B. Galil and P. Clark (ed.), In the Wrong Place: Alien Marine Crustaceans - Distributions, Biology and Impacts. Springer-Verlag, Berlin, Germany, 6:661-685, (2011).
Impact/Purpose:
Non-indigenous aquatic species (NIAS) are widely recognized as a major environmental threat to ecosystems and economies across the United States (US). Continued introduction and spread of NIAS ranks second only to habitat loss in terms of effects on native biodiversity, effects on existing food webs and resulting economic costs. NIAS introductions have been increasing at unprecedented rates over past decades, largely due to modernization and growth of global transport infrastructure and economic trade. Understanding the role played by principle vectors and conditions favoring NIAS spread must become a critical element of any comprehensive plan for environmental protection that ensures the sustainability of endemic ecosystems and the beneficial resources they provide. EERD has initiated a research effort to develop tools to detect morphologically cryptic NIAS, understand transport pathways and secondary spread of invasive species, and assess patterns and environmental influences on hybridization between native and invading taxa. A primary objective of this research is to evaluate the relative contributions of coastal versus long-distance ballast mediated introductions, and to differentiate secondary introductions via ballast transport from post-introduction range expansion.The study includes targeted screening of ballast (from international and coastal traffic) and population genetic surveys for species of concern to determine whether San Francisco Bay is acting as a local source pool for secondary spread (via ship and/or current transport) to other west coast estuaries. Target organisms include Spartina alterniflora,which has disrupted Pacific Coast ecosystem processes and threatens endemic cordgrass species due to competition and hybridization, as well as globally significant invaders such as European green crab (Carcinus maenas) and the Chinese mitten crab (Eriocheir sinensis). In a related study, EERD researchers are assessing the use of DNA identification tools for early detection and monitoring of invasive species in high risk ports across the Great Lakes. Freshwater fish invasions of rivers in the Southeastern U.S. also provide unique opportunities for understanding ecological and genetic consequences of NIAS introductions. EERD has begun a collaborative and interdisciplinary study to evaluate the spread of red shiner (Cyprinella lutrensis) across Southeastern drainages relative to competition and hybridization with endemic blacktail shiners (C. venusta), land use patterns, and stream remediation scenarios. The research is aimed at determining whether spread and introgresive hybridization by C. lutrensisis facilitated by land use impacts on water quality (ie. urbanization and turbidity). Corresponding genetic studies on the longitudinal distribution of C. lutrensis x C. venusta hybridization will further indicate whether land use impacts on water quality correspond to genetic pathways of invasion. Additional laboratory studies on C. lutrensis and C. venusta mate recognition and hybrid fitness are being conducted to experimentally test whether increased turbidity eliminates or weakens interspecific reproductive barriers and increase rates of hybridization. The information gained from these studies will ultimately feed into spatially explicit population models to evaluate how remediation strategies might limit ecological competition and hybridization to maintain drainage specific evolutionary lineages of C. venusta and other native congeners. This research also represents an application of an integrative approach EERD is developing for assessing the condition of aquatic habitats based on landscape, community, and genetic analyses.
Description:
The European green crab Carcinus maenas is one of the world's most widely recognized marine invaders. The success of this species has provided opportunities to explore genetic patterns associated with establishment and population expansion following independent introduction events to widely different recipient ecosystems. Recent studies have revealed an extraordinary diversity of such patterns. Globally, genetic reconstruction of invasion histories suggests complicated scenarios comprising multiple introductions to some regions as well as secondary introductions deriving from previously established invasive populations. In addition, detailed genetic analyses of several introduced populations indicate that successful invasion may involve rapid expansion from single low diversity founder populations, multiple introductions from genetically distinct sources with subsequent intraspecific admixture, or even interspecific hybridization between C. maenas and its sibling species C. aestuarii. The complexity of this global picture highlights the contingent nature of individual biological invasion events. Nevertheless, genetic study of non-native Carcinus populations provides crucial insights into invasion dynamics relevant to green crab management and control, and offers an unusually rich system within which to explore the genetic consequences of colonizations and range expansions in coastal marine ecosystems.
