resist_gd {wingen}

Create a moving window map of genetic diversity based on resistance

Description

Generate a continuous raster map of genetic diversity using resistance distances calculated with a conductivity surface

Usage

resist_gd(
  gen,
  coords,
  lyr,
  maxdist,
  distmat = NULL,
  stat = "pi",
  fact = 0,
  rarify = FALSE,
  rarify_n = 2,
  rarify_nit = 5,
  min_n = 2,
  fun = mean,
  L = "nvariants",
  rarify_alleles = TRUE,
  sig = 0.05,
  transitionFunction = mean,
  directions = 8,
  geoCorrection = TRUE
)

Arguments

gen

genetic data either as an object of type vcf or a path to a vcf file (note: order matters! The coordinate and genetic data should be in the same order; there are currently no checks for this)

coords

coordinates of samples as sf points, a two-column matrix, or a data.frame representing x and y coordinates (see Details for important information about projections)

lyr

conductivity layer (higher values should mean greater conductivity) to move window across. Can be either a SpatRaster or RasterLayer.

maxdist

maximum cost distance used to define neighborhood; any samples further than this cost distance will not be included (this can be thought of as the neighborhood radius, but in terms of cost distance). Can either be (1) a single numeric value or (2) a SpatRaster where each pixel is the maximum distance to be used for that cell on the landscape (must be the same spatial scale as lyr).

distmat

distance matrix output from get_resdist (optional; can be used to save time on distance calculations)

stat

genetic diversity statistic(s) to calculate (see Details, defaults to "pi"). Can be a single statistic or a vector of statistics

fact

aggregation factor to apply to lyr (defaults to 0; note: increasing this value reduces computational time)

rarify

if rarify = TRUE, rarefaction is performed (defaults to FALSE)

rarify_n

if rarify = TRUE, number of points to use for rarefaction (defaults to min_n)

rarify_nit

if rarify = TRUE, number of iterations to use for rarefaction (defaults to 5). Can also be set to "all" to use all possible combinations of samples of size rarify_n within the window.

min_n

minimum number of samples to use in calculations (any focal cell with a window containing less than this number of samples will be assigned a value of NA; defaults to 2)

fun

function to use to summarize rarefaction results (defaults to mean, must take na.rm = TRUE as an argument)

L

for calculating "pi", L argument in pi.dosage function. Return the average nucleotide diversity per nucleotide given the length L of the sequence. The wingen default is L = "nvariants", which sets L to the number of variants in the VCF. If L = NULL, returns the sum over SNPs of nucleotide diversity (note: L = NULL is the pi.dosage default which wingen does not use)

rarify_alleles

for calculating "biallelic_richness", whether to perform rarefaction of allele counts as in allelic.richness (defaults to TRUE)

sig

for calculating "hwe", significance threshold (i.e., alpha level) to use for hardy-weinberg equilibrium tests (defaults to 0.05)

transitionFunction

function to calculate transition values from grid values (defaults to mean)

directions

directions in which cells are connected (4, 8, 16, or other), see adjacent (defaults to 8)

geoCorrection

whether to apply correction to account for local distances (defaults to TRUE). Geographic correction is necessary for all objects of the class Transition that are either: (1) based on a grid in a geographic (lonlat) projection and covering a large area; (2) made with directions > 4 (see geoCorrection for more details).

Details

Coordinates and rasters should be in a Euclidean coordinate system (i.e., UTM coordinates) such that raster cell width and height are equal distances. As such, longitude-latitude systems should be transformed before using dist_gd. Transformation can be performed using st_set_crs for coordinates or project for rasters (see vignette for more details).

Coordinates and rasters should be in a projected (planar) coordinate system such that raster cells are of equal sizes. Therefore, spherical systems (including latitute-longitude coordinate systems) should be projected prior to use. Transformation can be performed using st_set_crs for coordinates or project for rasters (see vignette for more details).

Current genetic diversity metrics that can be specified with stat include:

• "pi" for nucleotide diversity (default) calculated using hierfstat pi.dosage. Use the L argument to set the sequence length (defaults to dividing by the number of variants).

• "Ho" for average observed heterozygosity across all sites

• "allelic_richness" for average number of alleles across all sites

• "biallelic_richness" for average allelic richness across all sites for a biallelic dataset (this option is faster than "allelic_richness")

• "hwe" for the proportion of sites that are not in Hardy–Weinberg equilibrium, calculated using pegas hw.test at the 0.05 level (other alpha levels can be specified by adding the sig argument; e.g., sig = 0.10).

• "basic_stats" for a series of statistics produced by hierfstat basic.stats including mean observed heterozygosity (same as Ho), mean gene diversities within population (Hs), Gene diversities overall (Ht), and Fis following Nei (1987). Population-based statistics (e.g., FST) normally reported by basic.stats are not included as they are not meaningful within the individual-based moving windows.

Value

SpatRaster that includes a raster layer of genetic diversity and a raster layer of the number of samples within the window for each cell

Examples

load_mini_ex()
rpi <- resist_gd(mini_vcf, mini_coords, mini_lyr, maxdist = 50)