DOI: 10.5061/dryad.z08kprrpm
title: Prickly postglacial pioneers: freshwater plankton community composition influences fatty acid desaturase (FADS2) copy number in Southern Greenland threespine sticklebacks

description: The adaptation of marine fish to freshwater environments includes
 prodigious examples of rapid evolution. Given the scarcity of ω-3
 long-chain polyunsaturated fatty acids (LC-PUFA) in freshwater, we expect
 selection to be strong on fish transitioning to freshwater habitats and
 yet the underlying ecological causes of genomic and phenotypic
 differentiation are poorly understood for traits associated with lipid
 content and composition. Threespine stickleback (Gasterosteus aculeatus)
 have repeatedly colonized, and adapted to, freshwater habitats across the
 northern hemisphere. These freshwater populations often show elevated copy
 number of the fatty acid desaturase 2 gene (FADS2), which increases the
 biosynthetic capacity of LC-PUFA. The starkly lower content of LC-PUFA in
 freshwater compared to marine prey, especially docosahexaenoic acid (DHA),
 likely imposes strong positive selection on freshwater fish for either
 increased biosynthesis or greater dietary acquisition of LC-PUFA. The
 recently colonized and relatively undisturbed threespine stickleback
 populations in postglacial coastal lakes of Southern Greenland offer an
 exceptional opportunity to study how variation in the copy number of FADS2
 is related to abiotic and biotic conditions of lakes and their
 morphometry. As expected, given its position on the stickleback X
 chromosome, we found strong sexual dimorphism in FADS2 copy number in all
 populations (19 freshwater, 1 marine, and 1 brackish), and an increased
 dimorphism in some freshwater populations. We also found that FADS2 copy
 number was negatively correlated, for both males and females, with the
 abundance of copepods, which are a DHA-rich food source in the zooplankton
 community. Overall, our results suggest that the prey community context of
 lakes might influence the process of metabolic adaptation of marine fish
 colonizing freshwater ecosystems.
description: Readme File for "Prickly postglacial pioneers: adaptation of
 threespine stickleback to freshwater influences fatty acid desaturase
 (FADS2) copy number in Southern Greenland" Datasets Dataset 1 -
 FADS_Data This dataset contains information on threespine stickleback
 fatty acid desaturase 2 gene copy number (FADS2) from populations sampled
 in southern Greenland as they relate to environmental characteristics of
 freshwater lakes. We collected information on the plankton community
 composition of freshwater lakes by sampling water bodies with plankton
 nets, and sampled threespine stickleback tissue to determine gene copy
 number with qPCR (after DNA extraction) These data were then used to
 investigate whether variation in FADS2 gene copy number among populations
 was related to differences in environmental conditions. Fishec: Unique
 individual ID numbers for collected specimens Sex: Sex identification for
 each specimen (categorical, M or F) Site: Name of collection site Site2:
 Collection site with marine populations pooled Site3: Sites split into
 freshwater or marine categories ASIN_Plank_Comp: Arcsin transformed column
 of plankton composition Plank_Comp: Proportion of copepods in the plankton
 community (1 = entirely copepods, 0 = no copepods) Total_BM: The total
 zooplankton biomass (BM) in ug/L for a given lake (sum of Copepod_BM and
 Cladocera_BM) Log_Total_BM: Log transformation of Total_BM Copepod_BM: Sum
 of Calanoid_BM and Cyclopoid_BM (ug/L) Calanoid_BM: Total biomass calanoid
 copepods in our sample (ug/L) Cyclopoid_BM: Total biomass cayclopoid
 copepods in our sample (ug/L) Cladocera_BM: Total biomass of cladocera in
 our sample (ug/L) Region: Q, A, and T represent the three regions
 Qassiarsuk, Akia, and Tuttutoq sampled in this study Salty: Sites scored
 as saltwater or freshwater Salty2: Same as Salty, but with saltwater split
 into Marine and Coastal brackish populations Areaha: Lake area in hectares
 Log_Areaha: Log transformed lake area Elevation: Lake elevation in meters
 Log_Elevation: Log transformed lake elevation FADS2: Relative FADS2 copy
 number from our gqPCR - This is our estimate of the number of gene copies
 that are present in the genome of a particular fish Dataset 2 - Env_Data
 This dataset contains information on the phyiscal properties of freshwater
 lakes in Greenland (e.g. lake area and elevation) along with the biomass
 of plankton and proportion of copepods captured from field sampling of
 zooplankton. Lake: Name of sampling site Prop_Copepods: Proportion of
 copepods found in the zooplankton sample from 0-1 (1 = entirely copepods,
 0 = no copepods) Lake_Area: Lake area measured in hectares Lake_Elevation:
 Lake elevation measured in meters Total_Zoop_BM: Total zooplankton biomass
 measured in ug/L Dataset 3 - summary_FADS This is a summarized version of
 the first dataset (FADS_Data.csv), showing the mean and maximum FADS2 copy
 number for males and females from each lake with standard error, standard
 deviation, and number of individuals per site. Estimates of FADS2 gene
 copy number are derived from qPCR Site: Name of collection site Type: A
 categorical variable describing whether fish were sourced from freshwater,
 brackish, or saltwater populations N_fem: Number of female fish collected
 at this site mean_fem: The mean FADS2 gene copy number for females for a
 given site max_fem: The maximum FADS2 gene copy number found in female
 fish from a given site sd_fem: Standard deviation around the FADS2 mean
 for females se_fem: Standard error for FADS2 mean for females N_male:
 Number of male fish collected at this site mean_male: The mean FADS2 gene
 copy number for males for a given site max_male: The maximum FADS2 gene
 copy number found in male fish from a given site sd_male: Standard
 deviation around the FADS2 mean for males se_male: Standard error for
 FADS2 mean for males