Messager, M. and J.D. Olden. 2019. Phenotypic variability of rusty crayfish (Faxonius rusticus) at the leading edge of its riverine invasion. Freshwater Biology 64: 1196-1209.

Scripts, data, and directory structure used to sssess phenotypic changes in rusty crayfish Faxonius rusticus (previously Orconectes rusticus) across their invasion gradient in the John Day River (JDR, Oregon, U.SA.), a major tributary of the Columbia River.
Updated code, data, and documentation at: https://github.com/messamat/InvasionEdge_rustycrayfish

Abstract: 1.
Species
around the globe are undergoing phenotypic shifts at ecologically relevant
timescales as they invade new ecosystems and respond to changing environments.
Disentangling
the contribution of environmental gradients from the process of range expansion
in shaping these changes, and identifying the specific traits undergoing
selection, are both critical to anticipate the secondary spread and impact of
invasive species.

2.
Here,
we investigate phenotypic changes in rusty crayfish (Faxonius rusticus), a nuisance invasive
species, through an extensive survey of their invasion gradient in multiple
tributaries of the John Day River (JDR, Oregon, U.SA.), a major tributary of
the Columbia River.

3.
Rusty
crayfish in the JDR have developed better physiological condition (intrinsic
growth and/or reproductive potential measured as RNA/DNA ratio) but less
competitive morphology (lighter body and smaller claws) as they spread upstream
and downstream from their location of initial introduction. In addition, rusty
crayfish in invasion front populations are at a lower trophic level than
conspecifics closer to core areas.

4.
By
accounting for variations in temperature, primary productivity, and prey
(macroinvertebrates) biomass throughout the invasion extent of rusty crayfish,
our findings suggest that low conspecific densities at the invasion edge and
spatial sorting primarily drive these phenotypic changes. The trends observed here
are thus likely to intensify over time as rusty crayfish continues to rapidly
spread throughout the JDR and reach the mainstem Columbia River.

5.
Our study shows that
phenotypic shifts can manifest rapidly over environmental gradients experienced
during the range expansion of aquatic invasive species. Patterns in both
morphological and functional traits documented in the JDR demonstrate the
importance of both environmental factors and dispersal
processes in shaping these responses in riverine networks.