DOI: 10.5061/dryad.prr4xgz1m
title: Data from: Contemporary evolution of an at-risk stickleback population during a severe drought

description: Populations can be granted conservation status because they harbour a set
 of unique traits, evolutionary histories, or ecological roles. Such
 populations are often isolated and specialized and, as such, can be
 particularly vulnerable to environmental disturbances. Even if distinct
 populations survive and adapt to severe disturbances, they could show
 changes in the very traits that made them distinct in the first place.
 Here, we leverage a natural “experiment” involving an unarmoured
 population of threespine stickleback (Gasterosteus aculeatus) in Rouge
 Lake (Haida Gwaii, BC) – a population listed as Special Concern under the
 Canadian Species at Risk Act. In 2015, Rouge Lake nearly dried up during a
 severe drought event; yet the stickleback population appeared to have
 fully recovered its abundance in subsequent years. Using phenotypic
 measurements, we assessed the extent to which evolution in this population
 was impacted by the drought. We document important shifts in several
 phenotypic traits, with the largest occurring in precisely the trait that
 made the population distinct and prompted its original conservation
 designation. Specifically, fish with no lateral plates (i.e.,
 “unarmoured”) made up 51 % of the population before the drought, but only
 13 % after the drought. This shift held (13-16 % unarmoured) over the four
 years of our post-drought monitoring. Field observations support a strong
 demographic bottleneck, which we suggest might have been coupled with a
 shift in the selective regime. These findings underscore how populations
 of conservation concern are not only at risk of extinction; they are also
 at risk of losing the characteristics that make them unique. These
 dynamics highlight the need for policies to consider a population’s
 evolutionary potential and develop more flexible approaches than simply
 considering single-timepoint assessments of diversity.
description: # Contemporary evolution of an at-risk stickleback population during
 severe drought ## Description of the data and file structure This dataset
 contains phenotypic measurements and associated metadata for an unarmoured
 population of threespine stickleback (*Gasterosteus aculeatus*) from Rouge
 Lake, Haida Gwaii (BC, Canada). This unique population experienced a
 severe drought in 2015, which resulted in a major demographic bottleneck.
 By comparing fish sampled before and after the drought, the dataset
 documents a marked increase in lateral plate number—the trait that
 originally motivated the population’s conservation listing under COSEWIC.
 ### Files and variables #### File: rouge_morpho_data.csv **Description:**
 Note: "NA" means data unavailable ##### Variables * ID: Unique
 identifier assigned to an individual stickleback. * site: Lake or outlet.
 * year: Year of capture (2007, 2012, 2013, 2018, or 2022) * sl: The
 standard length (mm) of a given individual. * body_depth: The body depth
 (mm) of a given individual. * ap_length: The length of the ascending
 process (mm) of a given individual. * ap_width: The width of the ascending
 process (mm) of a given individual. * jaw_length: The length of the jaw
 (mm) of a given individual. * ppl: The length of the pelvic plate (mm) of
 a given individual. * ppw: The width of the pelvic plate (mm) of a given
 individual. * dorsal_1: The length of the first dorsal spine (mm) of a
 given individual. * dorsal_2: The length of the second dorsal spine (mm)
 of a given individual. * pelvic_spine: The length of the pelvic spine (mm)
 of a given individual. * sex: Male (M) or female (F). * lp_no: Total
 number of lateral plates on the left side of a given individual. *
 rp_no: Total number of lateral plates on the right side of a given
 individual.