DOI: 10.5061/dryad.79cnp5j3c
title: Immigration delays but does not prevent adaptation following environmental change: experimental evidence

description: In today’s rapidly changing world, it is critical to examine how animal
 populations will respond to severe environmental change. Following events
 such as pollution or deforestation that cause populations to decline,
 extinction will occur unless populations can adapt in response to natural
 selection, a process called evolutionary rescue. Theory predicts that
 immigration can delay extinction and provide novel genetic material that
 can prevent inbreeding depression and facilitate adaptation. However, when
 potential source populations have not experienced the new environment
 before (i.e., are naive), immigration can counteract selection and
 constrain adaptation. This study evaluated the effects of immigration of
 naive individuals on evolutionary rescue using the red flour beetle,
 Tribolium castaneum, as a model system. Small populations were exposed to
 a challenging environment, and three immigration rates (zero, one, or five
 migrants per generation) were implemented with migrants from a benign
 environment. Following an initial decline in population size across all
 treatments, populations receiving no immigration gained a higher growth
 rate one generation earlier than those with immigration, illustrating the
 constraining effects of immigration on adaptation. After seven
 generations, a reciprocal transplant experiment found evidence for
 adaptation regardless of immigration rate. Thus, while the immigration of
 naive individuals briefly delayed adaptation, it did not increase
 extinction risk or prevent adaptation following environmental change.
description: # Immigration delays but does not prevent adaptation following
 environmental change: experimental evidence Corresponding authors: Lily F.
 Durkee, [l.durkee@colostate.edu]();
 Ruth A. Hufbauer,
 [ruth.hufbauer@colostate.edu](mailto:ruth.hufbauer@colostate.edu) Data
 collected and code written by: L. F. Durkee ## Raw data file descriptions
 Among all files, "NA" is used to represent null values. ### 1)
 all_blocks-rescue-1-7-update-apr23.csv **Description:** census data from
 the rescue experiment for every generation (`gen`) * `gen`: whole numbers
 represent numerical generations; `gen` of 1.01, 2.01, etc. represents the
 timing of the immigration event (1 or 5 migrants each gen) * `block`:
 temporal block, 3 total (A, B, and C) * `array`: the set of populations
 using the same source population, labeled 1-8 in blocks A & B, 1-9 in
 block C (25 total) * `unique_array`: unique array name for every array *
 `group_rt`, `boxID_rt`: different group numbers for populations included
 in the reciprocal transplant experiment; ID used during the reciprocal
 transplant experiment * `type`: "sink" refers to experimental
 populations exposed to the challenging environment; "source"
 refers to source populations. * `trt`: 0, 1, or 5 migrants every
 generation (0/gen, 1/gen, 5/gen, respectively); all "1 event"
 patches were removed from the experiment * `MO`: "migrant
 origin" refers to the dispersal array - dispersing migrants are
 indicated by "box 4" and 0-migrant populations are indicated by
 "none". All populations receiving "box 1" migrants
 were removed from the experiment. * `init_N`: the number of parents that
 started the generation * `census_N`: the number of adults produced after
 35 days * `mig_N`: the number of migrants added * `new_N`: the population
 size after immigration * `pupae`, `larvae`, `dead`: the number of pupae,
 larvae, and dead adults counted during census; not included in the
 analysis * `trt_key_new`, `trt_order_new`, `trt_key_old`, `trt_order_old`,
 `trt_key_new1`, `boxID`: Combinations of variables used to create a unique
 ID for each population (`boxID`) * `changed_to_ctrl`,
 `changed_to_control`: both used to indicate if "1 event" patches
 were changed to 0-migrant populations after receiving no migrants
 throughout the experiment; these were removed from the analysis *
 `extinct`, `pathogen`: 1/0 indicators if the populations went extinct or
 naturally went extinct due to pathogen infection ### 2) rescue-apr23.csv
 **Description:** Census data formatted for the growth rate analysis;
 variable names are the same as above, with a few additional ones described
 below. * `rescue3`, `rescue2`, `rescue1`: three definitions of rescue *
 `rescue3`: previous three generations had growth rate &gt; 1 * `rescue2`:
 previous two generations had growth rate &gt; 1 * `rescue1`: the
 complement of extinct * `lambda`: growth rate for that generation,
 calculated as `census_N` (t) / `init_N` (t-1) ### 3)
 reciprocal-transplant-update-apr23.csv **Description:** data from the
 reciprocal transplant experiment (gen 9). Several of the variables are
 repeated from the two described datasets. New variables are described
 below. * `pop_num`: new unique ID given to each population during the
 reciprocal transplant experiment * `patch_type`: same as `type` above *
 `rescue_trt`: the immigration rate used throughout the rescue experiment;
 "total" refers to source populations * `treatment`:
 "migration" (1 or 5 migrants), "no migration" (0
 migrants), or "source" * `init_date`, `census_date`: the date
 the populations were initiated and censused, respectively * `double`:
 refers to whether a "double set up" (populations initiated over
 2 days with the same parents, done only for small populations) was used
 during the common environment generation * `environment`: the
 concentration of deltamethrin used in the reciprocal transplant experiment
 * `init_N`: 40 parents initiated every population this generation;
 `init_N` &lt; 40 were removed from the analysis * `census_N`: the number
 of adults produced after 35 days * `pup`, `lar`: pupae and larvae produced
 after 35 days (not included in the analysis) ### 4)
 maternal_effects_gen.csv **Description:** data from the common environment
 generation (gen 8) * `age`: age of parents; numbers of 34 and 35 for the
 same pop_num indicate a double setup was performed * `treatment`:
 immigration rate used during rescue experiment * `treatment`: population
 treatment during the rescue experiment (0, 1, or 5 migrants, 1 event
 [removed from analysis], or source) * `rep`: replicate number ### 5)
 pop_numbers.csv **Description:** the unique population numbers for every
 replicate; in the script, this file is merged with the above files to
 assign unique integers (`pop_num`) to every population. Repeated variable
 names are defined above. * `pop_num`: unique integer assigned to every
 experimental and source population * `trt_key`: the combination of `type`,
 `trt`, and `MO` (all defined above) * `boxID`: unique code assigned to
 each population ### 6) Deltamethrin_Dosage_BIG.csv **Description:** Data
 from the preliminary experiment used to determine the dose of deltamethrin
 to use during the rescue experiment * `Strain`: "All Red Mix"
 refers to the original stock population of beetles used to initiate this
 experiment * `ppm`: refers to concentration in ppm in the test environment
 * `Box`: replicate number for each patch * `Init_N`: 50 parents were used
 to initiate each population * `Census_N`: the number of adults produced by
 day 35 * `Age`: refers to the age of the parents; "old" refers
 to 35-day-old parents, "young" refers to 28-day-old parents ###
 7) order-experiment-gen1.csv **Description:** Data from the order
 experiment, which tested whether the order of set-up affected growth rate.
 We present the results from the first generation. The protocol for this
 experiment closely mimicked the rescue experiment, except the treatments
 were simply the order of the patches (1-7). After this experiment, we
 removed the first three patches (the populations receiving "box
 1" migrants) due to significant differences in growth rate due to the
 order of setup. We saw no difference in growth rate for patches 4-7, the
 treatments included in the final analysis. * `Array`: unique integers for
 each population grouping of 7 patches (to mimic the rescue experiment) *
 `Trt`: the order of the patch in the array, ranges from 1-7