Evolution in changing seas: The loss of plasticity under predator invasion and warming oceans
Data files
Feb 05, 2025 version files 163.02 KB
Abstract
The impact of invasive predators during the early stages of invasion is often variable in space and time. Such variation is expected to initially favor plasticity in prey defenses but fixed defenses as invaders become established. Coincident with the range expansion of an invasive predatory crab in the Gulf of Maine we document rapid changes in shell thickness – a key defense against shell crushing predators – of an intertidal snail. Field experiments, conducted 20 years apart, revealed that temporal shifts in shell thickness were driven by the evolution of increased trait means and erosion of thickness plasticity. The virtual elimination of the trade-off in tissue mass that often accompanies thicker shells is consistent with the evolution of fixed defenses under increasingly certain predation risk.
README: Evolution in changing seas: The loss of plasticity under predator invasion and warming oceans
https://doi.org/10.5061/dryad.d51c5b0c1
Description of the data and file structure
The dataset contains three Excel spreadsheets which encompass all of the data used in statistical analyses for this manuscript. The data include (1) the density of green crabs (Carcinus maenas) at multiple sites in the Gulf of Maine for 1973, 2003, 2017-2018, and 2021, (2) morphological measurements (shell length and thickness, shell and tissue mass) of snails (Littorina obtusata) that were reciprocally transplanted between a northern and southern site in the Gulf of Maine and raised in the presence and absence of green crab risk cues, and (3) morphological measurements (shell thickness and tissue mass) for multiple snail populations across the Gulf of Maine 1995-1997 and 2017-2018. All data are presented in tabular form. Spreadsheet descriptions and column definitions are provided below.
Files and variables
File: Trussell.Corbett.Updated.ReciprocalTransplantExperiment.xlsx
Description: Contains the data used in analyses of initial and final shell thickness (mm), shell length (mm), shell mass (mg) and tissue mass (mg) of snails (Littorina obtusata) that were reciprocally transplanted between a northern and southern site in the Gulf of Maine and raised in the presence and absence of green crab risk cues.
Variables
- Year – Denotes the year in which the experiment was conducted.
- Population – Denotes the source population (North, South) of the snails used in the reciprocal transplant experiment.
- Location – Denotes the site (North, South) at which snails were raised as part of the reciprocal transplant experiment.
- Risk Treatment – Denotes whether snails were raised in the presence (Crab) or absence (No Crab) of green crab risk cues during the reciprocal transplant experiment.
- Replicate - Denotes the specific unit that snails were raised in as part of the reciprocal transplant experiment.
- Initial Shell Thickness – Represents the shell thickness (mm) of snails at the beginning of reciprocal transplant experiment.
- Initial Shell Length – Represents the initial shell length (mm) of snails at the beginning of reciprocal transplant experiment.
- Initial Shell Mass – Represents the initial shell mass (mg) of snails at the beginning of reciprocal transplant experiment.
- Initial Tissue Mass – Represents the initial tissue mass (mg) of snails at the beginning of reciprocal transplant experiment.
- Final Shell Thickness – Represents the shell thickness (mm) of snails at the end of reciprocal transplant experiment.
- Final Shell Length – Represents the initial shell length (mm) of snails at the end of reciprocal transplant experiment.
- Final Shell Mass – Represents the initial shell mass (mg) of snails at the end of reciprocal transplant experiment.
- Final Tissue Mass – Represents the initial tissue mass (mg) of snails at the end of reciprocal transplant experiment.
File: Trussell.Corbett.Updated.GreenCrabDensity.csv
Description: Contains the data used in analyses of green crab (Carcinus maenas) density across multiple years and sites in the Gulf of Maine.
Variables
- Site Location Year – Denotes the site name of the collection site and the year data were collected.
- Latitude Year – Indicates the latitude of each sampling site.
- Green Crab Density Year – Indicates the number of green crabs found at each site and year.
File: Trussell.Corbett.Updated.ShellThickness.TissueMass.Cline.xlsx
Description: Contains the data used in analyses of shell thickness (mm) and tissue mass (mg) for multiple snail (Littorina obtusata) populations in the Gulf of Maine for the years spanning 1995-1997 and 2017-2018. *Note that the cell for tissue mass in row 850 is empty because that sample was lost.
Variables
- Year – Denotes the years in which the snail populations were sampled.
- Site Name – Denotes the name of each sampling site.
- Latitude – Indicates the latitude of each sampling site.
- Shell Length – Indicates the shell length (mm) of each snail.
- Shell Thickness – Indicates the shell thickness (mm) of each snail.
- Tissue Mass – Indicates the tissue mass (mg) of each snail.
- Shell Mass – Indicates the shell mass (mg) of each snail.
Access information
Data was derived from the following sources:
- All data were collected by J.C. Corbett and G.C. Trussell. Green crab density data for 1973 (Welch et al. 1973) and 2003 (Edgell & Rochette 2008) were obtained from previously published work.
Methods
Crab Surveys
Crab surveys were conducted at eight wave-protected sites to characterize regional variation of green crab abundance in the Gulf of Maine. Four sites were in the northern Gulf (Quoddy Region of Maine) while the remaining four were in the southern Gulf (Nahant to Cape Ann, Massachusetts). Surveys lasted for one hour, began and concluded within two hours of low tide, and were conducted monthly from July to October in 2017-2018 and 2021. Historical crab density data for 1973 and 2003 were obtained from previously published surveys.
Clinal Variation in L. obtusata Shell Thickness and Tissue Mass
Between 1995 and 1997, our previous work (29) collected samples of Littorina obtusata from 25 populations spanning GOM rocky intertidal habitats. Between 2017 and 2018, we collected samples from 22 of the same populations (snails were not present at 3 of the sites sampled in 1995-1997) to examine how phenotypic clines may have changed following increased ocean temperatures and increased green crab density in the northern GOM. For each population, snails (n = 50 per population) were haphazardly collected while attempting to maximize size range and returned to the laboratory for measurement of shell length and shell thickness with digital calipers. Mean shell thickness (hereafter, shell thickness) was calculated by taking the mean of whorl thickness and opposite whorl thickness. We then used a C-clamp to crack the shell of each snail and shell fragments were separated from soft tissue. Shell fragments and soft tissue were placed in separate aluminum trays and dried at 60°C for 48h before weighing on an analytical balance.
Reciprocal Transplant Experiment in the Field
To examine how shell thickness and its plasticity have changed after 20 years (1998-2018), in 2018 we repeated the reciprocal transplant experiment that was conducted in 1998. To allow a robust comparison of the two experiments, we carefully replicated all aspects of the 1998 experiment including using the same experimental chambers that were deployed into the field 20 years earlier. In early May 2018, we collected juvenile L. obtusata (5-6 mm in shell length) from a northern (Quoddy Head, Lubec, ME) and southern (Lobster Cove, Manchester, MA) site in the Gulf. All snails were individually tagged with a color-coded dot of permanent ink that was then sealed with cyanoacrylate glue. We measured initial shell length and shell thickness with digital calipers (± 0.01 mm) and shell mass and tissue mass (± 0.001 g) were estimated using a non-destructive weighing technique.
After completing initial measurements, we transported snails from both populations to the northern or southern site in mid-May. At each site, we placed six snails (hereafter, response snails) from a single population and approximately 60 g of brown algae (Ascophyllum nodosum) as food into 24 separate, replicate cylindrical containers (5-cm height x 10-cm diameter) that had mesh windows (mesh size = 3mm) to allow water flow. Hence, at each site 12 replicate containers housed snails from either the northern or southern population and 6 replicates for each population exposed snails to either the presence (Crab) or absence (No Crab) of predation risk. To create these risk treatments, each container stocked with response snails was secured beneath a similar container that was perforated on all sides and housed either (a) a mature male green crab (Crab) and 30 conspecific snails (hereafter, stimulus snails) or (b) just 30 stimulus snails (No Crab) to serve as a control. Each pair of stimulus-response containers was placed inside a large, replicate cylindrical chamber (11-cm height x 28-cm diameter) that had mesh windows (mesh size = 3mm) to permit water flow. These large chambers were anchored haphazardly in the mid-intertidal zone (~1.5 m MLW). Ocean temperature was monitored at 5-minute intervals during the experiment with dataloggers (Tidbits, model UTBI-001, Onset Computer Corp.) that were placed inside 3 replicate chambers at each site. Every 14 days we replaced stimulus snails in both the Crab and No Crab containers. For appropriate replicates, we also confirmed that crabs were alive; any dead crabs were replaced immediately. Overall, we had to replace 7 crabs at the northern site and 7 crabs at the southern site. At day 45, we replaced the Ascophyllum that served as food for response snails in all replicates. After 90 days in the field, all response snails were returned to the Northeastern University Marine Science Center (Nahant, Massachusetts) for measurement of final snail shell length, shell thickness, and tissue mass.